JP2006033213A - Method and system for optical transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmission method and an optical transmission system capable of shortening fault time in a system by the minimum control of polarization entering to an optical fiber, reducing the risk of deterioration in transmission quality by the erroneous control of polarization, and relieving the request to reliability in an optical device. <P>SOLUTION: A light signal outputted from an optical transmitter is allowed to pass through a polarization control means, and then is transmitted to the optical fiber to monitor the error rate or PMD (polarization mode dispersion) of a reception signal at a reception side. Only when the deterioration in transmission quality by the PMD becomes large, and the error rate or PMD exceeds a threshold, the polarization entering to the optical fiber is polarized at a transmission side for suppressing deterioration in the waveform by PMD. And both the error rate and PMD are simultaneously used for determining control start. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for reducing or suppressing a system failure time due to polarization mode dispersion of an optical transmission line such as an optical fiber or an optical amplifying repeater through which an optical signal propagates.

  In ultra-high-speed optical transmission and long-distance optical transmission, degradation of transmission quality due to polarization mode dispersion (PMD), in which the group speed of optical signals in the optical transmission line differs depending on two orthogonal polarization main axes, is a major problem. It becomes.

The size of the primary PMD is expressed as a group delay time difference (DGD: Differential Group
Delay). PMD characteristics depend on optical fiber manufacturing processes and installation conditions, and show changes over time due to changes in stress and environmental temperature applied to the optical fiber. When the DGD increases, the received waveform is distorted depending on the polarization state of the optical signal incident on the optical fiber, and the transmission quality deteriorates.

  Conventionally, as a method of suppressing the influence of PMD, there is a method of constantly controlling the polarization state of incidence on an optical fiber so that the influence of PMD on a received signal is minimized (see, for example, Patent Document 1).

  The configuration of this polarization control method is shown in FIG. The apparatus configuration and operation will be described with reference to FIG. The signal light frequency-modulated by the frequency f 0 output from the optical transmitter 21 passes through the polarization control means 22 and then enters the optical transmission line (optical fiber) 24.

  On the receiving side, the signal light is distributed by the light distribution means 26, and one is input to the optical receiver 25. The other is passed through the polarization control means 27 and then separated into two orthogonal polarizations by the polarization separation means 28.

  The polarization separated signal light is received by the balanced optical receiver 29 and converted into an electric signal, and the intensity signal of the component of the frequency f0 in the electric signal is detected by the intensity detector 30. The controller 32 controls the polarization control means 22 so that the intensity signal always becomes maximum, and the controller 31 controls the polarization control means 27 so that the intensity signal always becomes minimum. By performing these polarization controls, the incident polarization to the optical fiber coincides with the main axis of the optical fiber, and waveform deterioration due to PMD can be suppressed.

JP-A-6-284093

  In the conventional method, the incident polarization to the optical fiber is constantly controlled. In an optical communication system in which the PMD state of the optical fiber fluctuates with time, the PMD fluctuation cannot follow the PMD fluctuation or deviates from the optimum incident polarization state. There is a risk of incorrect control.

  Since the optical device for polarization control is always operated, it is a big problem to ensure long-term operation reliability. In addition, in order to always optimally control the incident polarization, a function that always returns a control signal from the reception side to the transmission side that is not included in a normal optical communication system is required.

  The present invention reduces the failure time of the system by minimizing the control of the incident polarization to the optical fiber, reduces the risk of transmission quality degradation due to erroneous polarization control, and further improves the reliability of the optical device. An object of the present invention is to provide an optical transmission method and system that can alleviate the demand.

  In order to achieve the above object, in the present invention, an optical signal output from an optical transmitter passes through a polarization control means and is then input to an optical fiber, and the reception side monitors error rate information or PMD of the received signal. .

  Only when the transmission quality deterioration due to PMD becomes large and the error rate or PMD becomes larger than a certain threshold, the incident polarization to the optical fiber is polarized on the transmission side to suppress the waveform deterioration due to PMD.

  There is a high probability that transmission quality deterioration will occur when the DGD is large and the incident polarization is close to the worst condition. Therefore, transmission quality deterioration due to PMD can be suppressed by changing the incident polarization at this time.

In addition, since incident polarization is not always controlled, and control is performed only when transmission quality degradation has increased to some extent, it is not necessary to always have a function to notify the transmission side of the reception status, and it will be used widely in future optical networks. BDI (backward defect indication) signal for notifying frame transmission interruption to the transmission side mounted on the terminal equipment of the optical transport network (OTN) to be transmitted and BEI (backward error) notifying the transmission side of the occurrence of an error
indication) signal can be used for input polarization control.

  A first aspect of the present invention is an optical transmission applied to an optical transmission system including an optical transmitter that transmits an optical signal, an optical transmission path that transmits the optical signal, and an optical receiver that receives the optical signal. Is the method.

  Here, the feature of the present invention is that the optical transmitter transmits an optical signal, which is transmitted to the optical transmission line after passing through the polarization control means, and propagates through the optical transmission line. The optical signal is received by the optical receiver, the optical receiver detects the error rate of the optical signal, notifies the detected error rate information to the control means provided on the optical transmitter side, and notifies When the error rate information exceeds the threshold value, the control means controls the polarization control means to change the state of incident polarization to the optical transmission line (claim 1).

  Alternatively, in the optical transmission method of the present invention, the optical transmitter transmits an optical signal, and the optical signal is transmitted to the optical transmission path after passing through the polarization control means, and propagates through the optical transmission path. Is distributed to two paths by the optical distribution means, the optical signal of one of the paths is received by the optical receiver, and the optical signal of the other path is input to the PMD measurement means, and this PMD measurement means Notifies the measured PMD information to the control means provided on the optical transmitter side, and when the notified PMD exceeds a threshold value, the control means controls the polarization control means to control the optical transmission line. The incident polarization state is changed (claim 2).

  Alternatively, in the optical transmission method of the present invention, the optical transmitter transmits an optical signal, and the optical signal is transmitted to the optical transmission path after passing through the polarization control means, and propagates through the optical transmission path. Is distributed to two paths by the optical distribution means, the optical signal of one of the paths is received by the optical receiver, and the optical receiver is provided with the detected error rate information on the optical transmitter side. The control means is notified, and the optical signal in the other direction is input to the PMD measuring means. The PMD measuring means notifies the measured PMD information to the control means, and the notified error rate information is related to the error rate. If the PMD information exceeds a predetermined threshold and the PMD information exceeds a threshold determined for PMD, the control means controls the polarization control means to change the incident polarization state to the optical transmission line (Claim 3).

  Thus, as a method for the polarization control means, a more reliable polarization mode dispersion compensation system can be configured by using the error rate at the receiving end and PMD together. Although the error rate alone cannot be used to discriminate degradation factors other than PMD (wavelength dispersion, ASE, etc.), degradation due to PMD can be clearly extracted by using the synchronization as the criterion for increasing PMD. . By changing the incident polarization based on this criterion, transmission quality deterioration due to PMD can be prevented more reliably. Furthermore, unnecessary control without error rate deterioration can be eliminated, and high reliability can be realized.

  Alternatively, the present invention is applied to an optical transmission system including N optical transmitters that transmit optical signals, an optical transmission path that transmits optical signals, and N optical receivers that receive optical signals. This is an optical transmission method.

  Here, a feature of the present invention is that the N optical transmitters respectively transmit N optical signals having different wavelengths, and the N optical signals are transmitted to the N optical transmitters. After passing through N polarization control means connected in series, the light is multiplexed by the wavelength multiplexing means and transmitted to the optical transmission path, and the optical signal propagated through the optical transmission path is transmitted to each wavelength by the wavelength separation means. The optical signals of the respective wavelengths are respectively received by the N optical receivers, and the N optical receivers detect error rates of the optical signals, respectively, and detect the detected error rate information. Each of the control means provided on the optical transmitter side is notified, and when the notified error rate information exceeds a threshold, the control means controls the N polarization control means to control the optical transmission line. The state of polarization of the incident light is changed (claims) ).

  Alternatively, in the optical transmission method of the present invention, the N optical transmitters transmit N optical signals having different wavelengths, respectively, and the N optical signals are serially connected to the N optical transmitters, respectively. After passing through the N polarization control means connected to the optical signal, it is multiplexed by the wavelength multiplexing means and sent to the optical transmission line, and the optical signal propagated through the optical transmission line is separated into each wavelength by the wavelength separation means The optical signals of each wavelength are distributed to two paths by N optical distributing means, and the optical signals of one path are respectively received by the N optical receivers, and the other one is transmitted. The optical signals of the path are respectively input to N PMD measuring means, and the N PMD measuring means notify the measured PMD information to the control means provided on the optical transmitter side, and the notified PMD When the threshold is exceeded, the control means Serial and controls the polarization control means and changes each incident polarization state to said optical transmission line (Claim 5).

  Alternatively, in the optical transmission method of the present invention, the N optical transmitters transmit N optical signals having different wavelengths, respectively, and the N optical signals are serially connected to the N optical transmitters, respectively. After passing through the N polarization control means connected to the optical signal, it is multiplexed by the wavelength multiplexing means and sent to the optical transmission line, and the optical signal propagated through the optical transmission line is separated into each wavelength by the wavelength separation means The optical signals of each wavelength are distributed to two paths by N optical distributing means, and the optical signals of one path are respectively received by the N optical receivers, and the other one is transmitted. The optical signal of the path is input to the optical switching means, and the optical switching means inputs the selected optical signal to the PMD measuring means, and the PMD measuring means provides the measured PMD information to the control means provided on the optical transmitter side. When the notified PMD exceeds the threshold , And the control means to change each incident polarization state to the optical transmission line by controlling the N sets of the polarization control means (claim 6).

  As a result, since one PMD measuring means can be provided, the hardware configuration can be simplified and the hardware cost can be reduced.

  Alternatively, in the optical transmission method of the present invention, the N optical transmitters transmit N optical signals having different wavelengths, respectively, and the N optical signals are serially connected to the N optical transmitters, respectively. After passing through the N polarization control means connected to the optical signal, the optical signal is multiplexed by the wavelength multiplexing means and sent to the optical transmission path, and the optical signal propagated through the optical transmission path is divided into two paths by the optical distribution means. The optical signal of one path is separated into each wavelength by the wavelength separation means, and the optical signal of each wavelength is received by each of the N optical receivers, and the optical signal of the other path Is input to variable wavelength selection means for selecting and outputting an optical signal of one wavelength from the combined optical signal, and this variable wavelength selection means inputs the optical signal of the selected wavelength to PMD measurement means. The measuring means sets the measured PMD information on the optical transmitter side. When the notified PMD exceeds a threshold value, the control means controls the N polarization control means to change the state of incident polarization to the optical transmission line, respectively. (Claim 7).

  As a result, the light distribution means and the PMD measurement means can be combined into one, so that the hardware configuration can be simplified and the hardware cost can be reduced.

  The PMD measuring means notifies the measured PMD information to the control means, and the optical receiver notifies the detected error rate information to the control circuit, and the notified error rate information defines the error rate. The control circuit controls the N polarization control means connected to the optical transmission line when the notified PMD information exceeds the threshold value determined for PMD. The incident polarization state can be changed (claim 8).

  Thus, as a method for the polarization control means, a more reliable polarization mode dispersion compensation system can be configured by using the error rate at the receiving end and PMD together. Although the error rate alone cannot be used to discriminate degradation factors other than PMD (wavelength dispersion, ASE, etc.), degradation due to PMD can be clearly extracted by using the synchronization as the criterion for increasing PMD. . By changing the incident polarization based on this criterion, transmission quality deterioration due to PMD can be prevented more reliably. Furthermore, unnecessary control without error rate deterioration can be eliminated, and high reliability can be realized.

  Alternatively, in the optical transmission method of the present invention, the N optical transmitters respectively transmit N optical signals having different wavelengths, and the N optical signals are multiplexed by wavelength multiplexing means, The combined optical signal is transmitted to the optical transmission path after passing through the polarization control means, and the optical signal propagated through the optical transmission path is separated into each wavelength by the wavelength separation means, and the optical signal of each wavelength is Each of the N optical receivers respectively receives the error rate of the optical signal, and the detected error rate information is provided on the optical transmitter side. And when the notified error rate information exceeds a threshold value, the control means controls the polarization control means to change the state of incident polarization to the optical transmission line. (Claim 9).

  Thereby, since the polarization control means can be made one, the hardware configuration can be simplified and the hardware cost can be reduced.

  Alternatively, in the optical transmission method of the present invention, the N optical transmitters respectively transmit N optical signals having different wavelengths, and the N optical signals are multiplexed by wavelength multiplexing means, The combined optical signal is transmitted to the optical transmission path after passing through the polarization control means, and the optical signal propagated through the optical transmission path is separated into each wavelength by the wavelength separation means, and the optical signal of each wavelength is Each of the N optical distribution means distributes the signal to two paths, the optical signal of one path is received by each of the N optical receivers, and the optical signal of the other path is N PMD. Each of the N PMD measurement means respectively inputs the measured PMD information to the control means provided on the optical transmitter side. When the notified PMD exceeds a threshold value, the N PMD measurement means Means controls the polarization control means to control the optical transmission. And changes the incident polarization state of the road (claim 10).

  Thereby, since the polarization control means can be made one, the hardware configuration can be simplified and the hardware cost can be reduced.

  Alternatively, in the optical transmission method of the present invention, the N optical transmitters respectively transmit N optical signals having different wavelengths, and the N optical signals are multiplexed by wavelength multiplexing means, The combined optical signal is transmitted to the optical transmission path after passing through the polarization control means, and the optical signal propagated through the optical transmission path is separated into each wavelength by the wavelength separation means, and the optical signal of each wavelength is Each of the N optical distribution means distributes the signal to two paths, the optical signal of one of the paths is received by each of the N optical receivers, and the optical signal of the other path is transmitted to the optical switching means. The optical switching means inputs the selected optical signal to the PMD measuring means, and the PMD measuring means notifies the measured PMD information to the control means provided on the optical transmitter side, and the notified PMD When the threshold is exceeded, the control means controls the polarization control. Wherein the controlling means changes the incident polarization state to said optical transmission line (Claim 11).

  As a result, one PMD measurement unit and one polarization control unit can be provided, so that the hardware configuration can be simplified and the hardware cost can be reduced.

  Alternatively, in the optical transmission method of the present invention, the N optical transmitters respectively transmit N optical signals having different wavelengths, and the N optical signals are multiplexed by wavelength multiplexing means, The combined optical signal is transmitted to the optical transmission path after passing through the polarization control means, and the optical signal propagated through the optical transmission path is distributed into two paths by the optical distribution means, and one of the paths Are separated into wavelengths by the wavelength separation means, the optical signals of each wavelength are respectively received by the N optical receivers, and the optical signals in the other direction are input to the variable wavelength selection means, The variable wavelength selection means inputs the optical signal of the selected wavelength to the PMD measurement means, and the PMD measurement means notifies the measured PMD information to the control means provided on the optical transmitter side, and the notified PMD When the threshold is exceeded, the control means And controls the control means and changes the incident polarization state to said optical transmission line (Claim 12).

  As a result, the PMD measuring means, the polarization control means, and the light distribution means can be provided one by one, so that the hardware configuration can be simplified and the hardware cost can be reduced. .

  The PMD measuring means notifies the measured PMD information to the control means, and the optical receiver notifies the detected error rate information to the control means, and the notified error rate information defines the error rate. The control means controls the connected polarization control means to enter the optical transmission line when the notified threshold value exceeds the threshold value determined for PMD. The polarization state can be changed (claim 13).

  As described above, since the PMD measuring unit, the polarization control unit, or the optical distribution unit can be integrated, the hardware configuration can be simplified and the hardware cost can be reduced. In addition, as a method for the polarization control means, a more reliable polarization mode dispersion compensation system can be configured by using an error rate at the receiving end or PMD together. Although the error rate alone cannot be used to discriminate degradation factors other than PMD (wavelength dispersion, ASE, etc.), degradation due to PMD can be clearly extracted by using the synchronization as the criterion for increasing PMD. . By changing the incident polarization based on this criterion, transmission quality deterioration due to PMD can be prevented more reliably. Furthermore, unnecessary control without error rate deterioration can be eliminated, and high reliability can be realized.

Further, as the PMD measuring means, DOP (degree of polarization: Degree of
Polarization) measuring means can be used (claim 14). When the PMD of the transmission path increases, the DOP of the received signal decreases. By using the fact that the DOP of the received signal is below the threshold value as a criterion for starting polarization control, it is possible to distinguish the signal degradation due to other causes such as optical SNR degradation and waveform degradation due to chromatic dispersion, and monitor the signal degradation due to PMD. Therefore, when transmission quality degradation due to other causes occurs, it is possible to control the incident polarization to the optical transmission line and avoid the phenomenon of changing to a polarization state where transmission quality degradation is greater.

  Alternatively, as the PMD measurement means, a photoelectric conversion means and a specific frequency intensity measurement means connected in series with the photoelectric conversion means can be used (claim 15). When the waveform of the received signal deteriorates due to PMD on the optical transmission line, the intensity of frequency B decreases (B: bit rate). B / 2, B / 4, etc. can also be used as the specific frequency, and the amount of PMD that can be observed increases as the frequency decreases. By using the fact that the intensity of a specific frequency (for example, frequency B) of the received signal is below the threshold value as a criterion for starting polarization control, waveform deterioration due to PMD can be detected with higher sensitivity compared to DOP.

  Alternatively, the receiving side has chromatic dispersion compensating means, and the PMD measuring means separates and extracts at least two different frequency components from the optical spectrum components of the optical signal, and the relative position between the extracted components. Detecting the phase difference, calculating the chromatic dispersion amount that the optical signal suffered in the optical transmission path based on the detected relative phase difference information, and measuring the intensity of at least one of the extracted optical spectrum components The measurement result is used as a PMD measurement result, and the chromatic dispersion compensation means can compensate the chromatic dispersion of the optical transmission line based on the calculation result of the chromatic dispersion amount.

  Thus, by compensating the chromatic dispersion of the optical transmission line based on the calculation result of the chromatic dispersion amount, the intensity information obtained by measuring the intensity of the optical signal is prevented from being lowered due to the influence of the chromatic dispersion, and the influence of the PMD Only can be detected. By using this intensity information as a criterion for starting polarization control, waveform deterioration due to PMD can be distinguished from deterioration due to chromatic dispersion and detected with high sensitivity.

  In addition, the optical transmitter superimposes a tone signal having a frequency lower than the bit rate on the signal light as intensity modulation, and performs phase comparison and intensity detection of the frequency component of the tone signal, thereby increasing the detection range of PMD and chromatic dispersion. It becomes possible to enlarge.

  Further, the optical transmitter and the optical receiver each have an error correction unit, and the error number information detected by the error correction unit is used as error rate information notified from the optical receiver to the control unit. (Claim 17).

  Further, when the error rate information or the PMD information is notified from the optical receiver to the control means, the error rate information or the PMD information can be mounted on a BDI signal or a BEI signal. .

  As a result, signal quality degradation due to PMD can be suppressed without adding a special information notification function from the reception side to the transmission side for polarization control.

  Further, when the polarization control means changes the incident polarization to the optical fiber, it can transition between three polarization states where the incident polarization is 90 degrees on the Poincare sphere (claims). Item 19).

  Further, when changing the incident polarization to the optical fiber constituting the optical transmission line by the polarization control means, the angle on the Poincare sphere to be changed in one control unit is set minutely, and the incident polarization is changed. If the error rate or PMD detected on the receiving side increases, the incident polarization is controlled in the direction opposite to the previous setting, and the error rate or PMD detected on the receiving side decreases due to the change of the incident polarization. In this case, the procedure for controlling the incident polarization in the same direction as the previous setting can be repeatedly executed (claim 20).

  That is, when changing the incident polarization to the optical fiber by the polarization control means, first make a slight change, and observe the error rate or PMD increase / decrease state at this time. If it increases, by controlling the incident polarization in the opposite direction, a significant change in the wrong direction can be avoided, and an appropriate change can be made quickly and appropriately. Furthermore, the target error rate or PMD can be achieved by repeatedly executing this procedure.

  In addition, the control means performs a control operation of changing the incident polarization to the optical fiber constituting the optical transmission line by the polarization control means, when the error rate or PMD detected on the receiving side is minimized. (Claim 21). Thereby, the control frequency of incident polarization can be reduced by changing the incident polarization to the best condition.

  Alternatively, the control means performs a control operation for changing the incident polarization to the optical fiber constituting the optical transmission line by the polarization control means, and an error rate or PMD detected on the receiving side sets a control end threshold. The process can be terminated when it falls below (claim 22). Thereby, the control time of incident polarization can be shortened by terminating the control when transmission quality degradation due to PMD can be suppressed to some extent.

  A second aspect of the present invention is an optical transmission system including an optical transmitter that transmits an optical signal, an optical transmission path that transmits the optical signal, and an optical receiver that receives the optical signal.

  Here, a feature of the present invention is that a polarization control means and a control means for controlling the polarization control means are provided between the optical transmitter and the optical transmission line, The optical signal transmitted from the transmitter is transmitted to the optical transmission path after passing through the polarization control means, and the optical signal propagated through the optical transmission path is received by the optical receiver, and the optical receiver Comprises means for detecting the error rate of the optical signal and means for notifying the control means of error rate information detected by the means for detecting, wherein the control means has the notified error rate information. When a threshold value is exceeded, there is provided means for controlling the polarization control means to change the state of incident polarization to the optical transmission line (claim 23).

  Alternatively, in the optical transmission system of the present invention, a polarization control means and a control means for controlling the polarization control means are provided between the optical transmitter and the optical transmission path, and the optical transmission path Between the optical receiver and the optical receiver is provided with optical distribution means for distributing the optical signal arriving from the optical transmission path into two paths, and the optical receiver is provided on one of the paths of the optical distribution means PMD measuring means is provided in the other path, and an optical signal transmitted from the optical transmitter is transmitted to the optical transmission path after passing through the polarization control means, and the optical transmission path Is distributed to two paths by the optical distribution means, the optical signal of one of the paths is received by the optical receiver, and the optical signal of the other path is received by the PMD measuring means. The PMD measurement means notifies the measured PMD information to the control means. And the control means includes means for controlling the polarization control means to change the state of incident polarization to the optical transmission line when the notified PMD information exceeds a threshold value. (Claim 24).

  Alternatively, in the optical transmission system of the present invention, a polarization control means and a control means for controlling the polarization control means are provided between the optical transmitter and the optical transmission path, and the optical transmission path Between the optical receiver and the optical receiver is provided with optical distribution means for distributing the optical signal arriving from the optical transmission path into two paths, and the optical receiver is provided on one of the paths of the optical distribution means PMD measuring means is provided in the other path, and an optical signal transmitted from the optical transmitter is transmitted to the optical transmission path after passing through the polarization control means, and the optical transmission path Is distributed to two paths by the optical distribution means, the optical signal of one of the paths is received by the optical receiver, and the optical signal of the other path is received by the PMD measuring means. The optical receiver is configured to detect an error rate of the optical signal and to detect the error rate. Means for notifying the control means of the error rate information detected by the means, and the PMD measuring means comprises means for notifying the control means of the measured PMD information, the control means being notified When the error rate information exceeds a threshold defined for the error rate and the notified PMD information exceeds a threshold defined for PMD, the polarization control means is controlled to the optical transmission line. Means for changing the incident polarization state of the light beam (claim 25).

  Alternatively, an optical transmission system according to the present invention includes an optical transmission including N optical transmitters that transmit optical signals, an optical transmission path that transmits optical signals, and N optical receivers that receive optical signals. System.

  Here, a feature of the present invention is that N polarization controls connected in series to the N optical transmitters are connected between the N optical transmitters and the optical transmission line. Means, a control means for controlling each of the N polarization control means, and a wavelength multiplexing means for wavelength multiplexing optical signals output from the N polarization control means. Between the optical path and the N optical receivers, there is provided wavelength separation means for wavelength-separating the optical signals combined by the wavelength multiplexing means, and the optical signals transmitted from the N optical transmitters are mutually connected. An optical signal having a different wavelength passes through each of the N polarization control units, is multiplexed by the wavelength multiplexing unit and transmitted to the optical transmission path, and the optical signal propagated through the optical transmission path is: The wavelength separation means separates each wavelength, and the optical signal of each wavelength is divided into N preceding signals. Each of the N optical receivers respectively receives the error rate of the received optical signal and notifies the control unit of the error rate information detected by the detecting unit. The control means controls the N polarization control means to change the state of incident polarization to the optical transmission line when the notified error rate information exceeds a threshold value. (Claim 26).

  Alternatively, the optical transmission system of the present invention includes N polarization control means connected in series to each of the N optical transmitters, between the N optical transmitters and the optical transmission line. A control means for controlling each of the N polarization control means; and a wavelength multiplexing means for wavelength-multiplexing optical signals output from the N polarization control means. Between the N optical receivers, wavelength separation means for wavelength-separating the optical signal combined by the wavelength multiplexing means, and the optical signal separated by each wavelength in two paths, respectively. N optical distribution means for distributing are provided, N optical receivers are connected to one of the N optical distribution means, and N PMD measurement is connected to the other path. Each of which is provided with optical signals having different wavelengths transmitted from the N optical transmitters. Passes through the N polarization control means, and then is multiplexed by the wavelength multiplexing means and transmitted to the optical transmission path. The optical signals propagated through the optical transmission path are respectively transmitted by the wavelength separation means. The optical signals of the respective wavelengths are divided into two paths by the N optical distribution means, and the optical signals of one of the paths are respectively received by the N optical receivers. The optical signals of the other directions are respectively input to the N PMD measurement means, and the PMD measurement means includes means for notifying the control means of the measured PMD information, and the control means The PMD information is provided with means for controlling the N polarization control means to change the state of incident polarization to the optical transmission line when the PMD information exceeds a threshold value (claims). Item 27).

  Alternatively, the optical transmission system of the present invention includes N polarization control means connected in series to each of the N optical transmitters, between the N optical transmitters and the optical transmission line. A control means for controlling each of the N polarization control means; and a wavelength multiplexing means for wavelength-multiplexing optical signals output from the N polarization control means. Between the N optical receivers, wavelength separation means for wavelength-separating the optical signal combined by the wavelength multiplexing means, and the optical signal separated by each wavelength in two paths, respectively. N optical distribution means for distribution are provided, N optical receivers are connected to one of the N optical distribution means, and an optical switching means is provided to the other path. PMD measuring means to which the output of the optical switching means is input is provided, and the N optical transmitters are provided. The optical signals having different wavelengths transmitted from the optical signal pass through the N polarization control units, and then are multiplexed by the wavelength multiplexing unit and transmitted to the optical transmission path, and propagate through the optical transmission path. The optical signal is separated into each wavelength by the wavelength separation means, and the optical signal of each wavelength is distributed into two paths by the N optical distribution means, and the optical signal in one of the paths is The optical signals received by the N optical receivers, respectively, are input to the optical switching means, the optical signal selected by the optical switching means is input to the PMD measuring means, and the PMD The measurement means includes means for notifying the control means of the measured PMD information, and the control means controls the N polarization control means when the notified PMD information exceeds a threshold value. Incident polarization to the optical transmission line Characterized by comprising means for changing the state of each (claim 28).

  Alternatively, the optical transmission system of the present invention includes N polarization control means connected in series to each of the N optical transmitters, between the N optical transmitters and the optical transmission line. A control means for controlling each of the N polarization control means; and a wavelength multiplexing means for wavelength-multiplexing optical signals output from the N polarization control means. Between the N optical receivers, there is provided optical distribution means for distributing the optical signal combined by the wavelength multiplexing means into two paths, and one of the optical distribution means is provided in one of the paths. Is provided with wavelength separation means for separating the combined optical signal into each wavelength, and selects and outputs an optical signal of one wavelength from the combined optical signal on the other path of the optical distribution means PMD to which variable wavelength selection means and an optical signal having a wavelength selected by the variable wavelength selection means are input And optical signals having different wavelengths transmitted from the N optical transmitters are multiplexed by the wavelength multiplexing unit after passing through the N polarization control units, respectively. The optical signal transmitted to the optical transmission path and propagated through the optical transmission path is distributed into two paths by the optical distribution means, and the optical signal in one path is separated into each wavelength by the wavelength separation means. The optical signals of the other path are selected by the variable wavelength selection means and input to the PMD measurement means, and the PMD measurement is performed. The means includes means for notifying the control means of the measured PMD information, and the control means controls the N polarization control means to control the N polarization control means when the notified PMD information exceeds a threshold value. Incident polarization to optical transmission line Characterized by comprising means for changing state, respectively (claim 29).

  The PMD measurement means includes means for notifying the control means of the measured PMD information, and the control means is notified when the notified error rate information exceeds a threshold defined for the error rate. When the PMD information exceeds a threshold value determined for PMD, the PMD information can be provided with means for controlling the polarization control means to change the state of incident polarization to the optical transmission line (claim 30). .

  Alternatively, the optical transmission system of the present invention includes wavelength multiplexing means for wavelength multiplexing optical signals of the N optical transmitters between the N optical transmitters and the optical transmission path, Polarization control means for controlling the polarization of the optical signal combined by the wavelength multiplexing means and control means for controlling the polarization control means are provided, and the optical transmission line and the N optical receivers are provided. Are provided with wavelength separation means for wavelength-separating the optical signals combined by the wavelength multiplexing means, and the optical signals having different wavelengths transmitted from the N optical transmitters are After being multiplexed by the wavelength multiplexing means, transmitted through the polarization control means to the optical transmission path, the optical signal propagated through the optical transmission path is separated into each wavelength by the wavelength separation means, The optical signals of each wavelength are respectively received by the N optical receivers, and the N optical receivers The receiver includes means for detecting the error rate of the optical signal, and means for notifying the control means of the error rate information detected by the detecting means, respectively. When error rate information exceeds a threshold value, there is provided means for controlling the polarization control means to change the incident polarization state to the optical transmission line (claim 31).

  Alternatively, the optical transmission system of the present invention includes wavelength multiplexing means for wavelength multiplexing optical signals of the N optical transmitters between the N optical transmitters and the optical transmission path, Polarization control means for controlling the polarization of the optical signal combined by the wavelength multiplexing means and control means for controlling the polarization control means are provided, and the optical transmission line and the N optical receivers are provided. The wavelength separation means for wavelength-separating the optical signal combined by the wavelength multiplexing means, and the optical signal of each wavelength wavelength-separated by the wavelength separation means are distributed to two paths, respectively. N optical distribution means, N optical receivers are connected to one of the N optical distribution means, and N PMD measurement means are connected to the other path. Each of the optical signals having different wavelengths transmitted from the N optical transmitters The optical signal that has been combined by the wavelength combining unit, transmitted through the polarization control unit and then transmitted to the optical transmission line, and propagated through the optical transmission line is separated into each wavelength by the wavelength separation unit. Are distributed to two paths by N optical distributing means, and the optical signals of one path are respectively received by the N optical receivers, and the optical signals of the other path are respectively received. Is input to each of the N PMD measuring means, and the N PMD measuring means includes means for notifying each of the measured PMD information to the control means, and the control means includes the notified PMD information. When a threshold value is exceeded, there is provided means for controlling the polarization control means to change the state of incident polarization to the optical transmission line (Claim 32).

  Alternatively, the optical transmission system of the present invention includes wavelength multiplexing means for wavelength multiplexing optical signals of the N optical transmitters between the N optical transmitters and the optical transmission path, Polarization control means for controlling the polarization of the optical signal combined by the wavelength multiplexing means and control means for controlling the polarization control means are provided, and the optical transmission line and the N optical receivers are provided. The wavelength separation means for wavelength-separating the optical signal combined by the wavelength multiplexing means, and the optical signal of each wavelength wavelength-separated by the wavelength separation means are distributed to two paths, respectively. N optical distribution means, N optical receivers are connected to one path of the N optical distribution means, and optical switching means are provided to the other path, PMD measuring means that receives the output of this optical switching means is provided and transmitted from N optical transmitters. The optical signals having different wavelengths are multiplexed by the wavelength multiplexing means and transmitted to the optical transmission path after passing through the polarization control means, and the optical signal propagated through the optical transmission path is the wavelength separation The optical signal of each wavelength is divided into two paths by N optical distribution means, and the optical signal of one path is respectively divided by the N optical receivers. The received optical signal in the other direction is input to the optical switching unit, the optical switching unit inputs the selected optical signal to the PMD measuring unit, and the PMD measuring unit receives the measured PMD information. Means for notifying the control means, and when the notified PMD information exceeds a threshold value, the control means controls the polarization control means to change the state of incident polarization to the optical transmission line. Characterized by having means for Claim 33).

  Alternatively, the optical transmission system of the present invention includes wavelength multiplexing means for wavelength multiplexing optical signals of the N optical transmitters between the N optical transmitters and the optical transmission path, Polarization control means for controlling the polarization of the optical signal combined by the wavelength multiplexing means and control means for controlling the polarization control means are provided, and the optical transmission line and the N optical receivers are provided. Is provided with optical distribution means for distributing the optical signal combined by the wavelength multiplexing means into two paths, and the combined optical signal is provided in one of the paths of the optical distribution means A wavelength separation means for separating the light into each wavelength, variable wavelength selection means for selecting and outputting an optical signal of one wavelength from the multiplexed optical signal on the other path of the optical distribution means, PMD measuring means to which an optical signal having a wavelength selected by the variable wavelength selecting means is input is provided. Optical signals having different wavelengths transmitted from the optical transmitter are multiplexed by the wavelength multiplexing unit, transmitted to the optical transmission path after passing through the polarization control unit, and propagated through the optical transmission path A signal is distributed into two paths by the optical distribution means, and an optical signal in one of the paths is separated into wavelengths by the wavelength separation means, and the optical signals of the respective wavelengths are divided into N optical receivers. And the optical signal of the other path is input to the variable wavelength selection unit, the optical signal of the selected wavelength is input to the PMD measurement unit, and the PMD measurement unit measures the measured PMD information. The control means controls the polarization control means to determine the incident polarization state to the optical transmission line when the notified PMD information exceeds a threshold value. That we have the means to change The characters (claim 34).

  Further, together with PMD information measured by the PMD measuring means, error rate information detected by the optical receiver is notified to the control means, and the control means determines the notified error rate information regarding the error rate. Means for controlling the polarization control means to change the state of incident polarization to the optical transmission line when the notified threshold value exceeds the threshold value determined for PMD. (Claim 35).

  Further, the PMD measuring means may comprise DOP measuring means (claim 36). Alternatively, the PMD measurement means can include a photoelectric conversion means for converting an optical signal into an electrical signal, and a specific frequency intensity measurement means connected in series with the photoelectric conversion means (Claim 37). Alternatively, the optical signal of each wavelength separated by the wavelength separation means is input and N chromatic dispersion compensation means for compensating the chromatic dispersion are provided, and the PMD measurement means includes at least one of optical spectrum components of the optical signal. A means for separating and extracting two different frequency components, a phase comparing means for detecting a relative phase difference between the components extracted by the extracting means, and relative phase difference information obtained from the phase comparing means. Based on the chromatic dispersion measuring means for calculating the chromatic dispersion amount that the optical signal has suffered in the optical transmission line, and the intensity of at least one of the optical spectrum components extracted by the extracting means, the measurement result is obtained. An intensity measurement unit configured as a PMD measurement result, and the chromatic dispersion compensation unit compensates the chromatic dispersion of the optical transmission line based on the measurement result of the chromatic dispersion measurement unit. It can comprise a stage (claim 38).

  The optical transmitter and the optical receiver each include error correction means, the means for detecting the error rate includes means for detecting the number of errors by the error correction means, and the notifying means includes the The error rate information notified to the control means may include means for using information on the number of errors detected by the detecting means (claim 39).

  The notifying means may comprise means for mounting the error rate information or the PMD information in a BDI signal or BEI signal when notifying the control means of the error rate information or the PMD information ( 40).

  In addition, when the polarization control means changes the incident polarization to the optical fiber, the polarization control means includes means for transitioning between three polarization states each having an angle of 90 degrees on the Poincare sphere. (Claim 41).

  Further, the control means, when changing the incident polarization to the optical fiber constituting the optical transmission line by the polarization control means, to set a small angle on the Poincare sphere to be changed in one control unit, If the error rate or PMD detected on the receiving side increases due to the change in incident polarization, the incident polarization is controlled in the opposite direction to the previous setting, and the error rate detected on the receiving side due to the change in incident polarization. Alternatively, it is possible to provide means for repeatedly executing the procedure of controlling the incident polarization in the same direction as the previous setting when PMD decreases (claim 42).

  The polarization control means is a means for ending the control operation for changing the incident polarization to the optical fiber constituting the optical transmission line when the error rate or PMD detected on the receiving side is minimized. (Claim 43). Alternatively, the control means performs a control operation for changing the incident polarization to the optical fiber constituting the optical transmission line in the polarization control means, and an error rate or PMD detected on the receiving side sets a threshold value for completion of control. Means may be provided for terminating when it falls below (claim 44).

  According to the present invention, it is possible to reduce the failure time of the system by the minimum control of the incident polarization to the optical fiber, and to reduce the risk of transmission quality deterioration due to erroneous polarization control.

  Furthermore, the requirements for the reliability of the optical device can be relaxed. Further, signal quality deterioration due to PMD can be suppressed without adding a special information notification function from the reception side to the transmission side for incident polarization control.

(First Example)
The optical transmission system of the first embodiment will be described with reference to FIG. FIG. 1 is an overall configuration diagram of the optical transmission system according to the first embodiment.

  As shown in FIG. 1, the first embodiment includes an optical transmitter 1 that transmits an optical signal, an optical transmission path 4 that transmits the optical signal, and an optical receiver 5 that receives the optical signal. System.

  Here, the feature of the first embodiment is that between the optical transmitter 1 and the optical transmission line 4, there is a polarization control means 2 and a control circuit 3 for controlling the polarization control means 2. The optical signal transmitted from the optical transmitter 1 is transmitted to the optical transmission path 4 after passing through the polarization control means 2, and the optical signal propagated through the optical transmission path 4 is received by the optical receiver 5. The optical receiver 5 includes means for detecting the error rate of the optical signal and means for notifying the control circuit 3 of the error rate information detected by the detecting means. When the error rate information exceeds a certain threshold value, there is provided means for controlling the polarization control means 2 to change the state of incident polarization to the optical transmission line 4 (claim 23).

  Next, the optical transmission method of the first embodiment will be described. In the optical transmission method of the first embodiment, the optical transmitter 1 transmits an optical signal, and this optical signal is transmitted to the optical transmission line 4 after passing through the polarization control means 2 and propagated through the optical transmission line 4. The signal is received by the optical receiver 5, and the optical receiver 5 detects the error rate of the optical signal and notifies the detected error rate information to the control circuit 3 provided on the optical transmitter 1 side. When the error rate information exceeds the threshold value, the control circuit 3 controls the polarization control means 2 to change the incident polarization state to the optical transmission line 4 (claim 1).

  That is, in the first embodiment, the optical signal transmitted from the optical transmitter 1 is transmitted to the optical transmission path 4 after passing through the polarization control means 2, and the signal light propagated through the optical transmission path 4 is transmitted to the optical receiver 5. Receive at. The error rate information detected by the optical receiver 5 is notified to the control circuit 3, and when the notified error rate information exceeds a certain threshold, the control circuit 3 controls the polarization control means 2 to control the optical transmission line 4. The incident polarization state is changed to reduce the influence of the PMD of the optical transmission line on the optical signal.

  FIG. 2 is a diagram for explaining the operation of the present invention. Since the PMD of the optical transmission line 4 varies with time, the error rate of the system also varies accordingly. Normally, a margin is assigned to transmission degradation in an optical transmission system, and a certain degree of transmission degradation is allowed. However, if an error rate is exceeded, a system failure occurs. When the error rate becomes extremely bad and a system failure occurs, the DGD of the optical transmission path becomes large and the incident polarization state is likely to be close to the worst condition.

  Therefore, when the error rate deteriorates to a certain threshold, the transmission quality deterioration due to PMD can be suppressed by changing the incident polarization. For notification of error rate information to the transmission side, since the optical communication system is normally an opposite system, the overhead for managing the line in the reverse direction may be used. Since the incident polarization is not always controlled and the transmission quality deteriorates, that is, the control action is performed only when the incident polarization becomes a waveform deterioration, the risk of transmission quality deterioration due to incorrect polarization control is reduced. it can. In addition, since the polarization control means 2 is not required to operate at all times, it is possible to relax the requirements for the reliability of the optical device.

(Second embodiment)
The optical transmission system of the second embodiment will be described with reference to FIG. FIG. 3 is an overall configuration diagram of the optical transmission system according to the second embodiment.

  As shown in FIG. 3, the second embodiment includes an optical transmitter 1 that transmits an optical signal, an optical transmission line 4 that transmits the optical signal, and an optical receiver 5 that receives the optical signal. System.

  Here, the feature of the second embodiment is that between the optical transmitter 1 and the optical transmission line 4, there is a polarization control means 2 and a control circuit 3 for controlling the polarization control means 2. Provided between the optical transmission path 4 and the optical receiver 5 is an optical distribution means 6 that distributes an optical signal arriving from the optical transmission path 4 into two paths. An optical receiver 5 is connected to this path, PMD measuring means 7 is provided on the other path, and an optical signal transmitted from the optical transmitter 1 passes through the polarization control means 2 and is optically transmitted. The optical signal transmitted to the path 4 and propagated through the optical transmission path 4 is distributed to two paths by the optical distribution means 6, and the optical signal of one of the paths is received by the optical receiver 5, and the other one is received. The optical signal of the route is input to the PMD measuring unit 7, and the PMD measuring unit 7 includes a unit that notifies the control circuit 3 of the measured PMD information. The control circuit 3 is provided with means for controlling the polarization control means 2 to change the incident polarization state to the optical transmission line 4 when the notified PMD information exceeds a threshold (claim) Item 24).

  Next, the optical transmission method of the second embodiment will be described. In the optical transmission method of the second embodiment, the optical transmitter 1 transmits an optical signal, and this optical signal is transmitted to the optical transmission line 4 after passing through the polarization control means 2 and propagated through the optical transmission line 4. The optical distribution means 6 distributes the signal into two paths, the optical signal of one of the paths is received by the optical receiver 5, and the optical signal of the other path is input to the PMD measurement means 7, The PMD measuring unit 7 notifies the measured PMD information to the control circuit 3 provided on the optical transmitter 1 side, and the control circuit 3 controls the polarization control unit 2 when the notified PMD exceeds a threshold value. Thus, the influence of PMD of the optical transmission line 4 on the optical signal is reduced by changing the state of incident polarization to the optical transmission line 4 (claim 2).

  The second embodiment is different from the first embodiment in that PMD is used instead of using error rate information of a received signal for polarization control. This makes it possible to distinguish signal degradation due to other causes such as optical SNR degradation and waveform degradation due to chromatic dispersion, and to monitor signal degradation due to PMD. Therefore, when transmission quality degradation due to other causes occurs, optical transmission It is possible to avoid the phenomenon of controlling the polarization incident on the path and changing to a polarization state in which transmission quality deterioration is further increased.

(Third embodiment)
An optical transmission system according to a third embodiment will be described with reference to FIG. FIG. 4 is an overall configuration diagram of the optical transmission system according to the third embodiment.

  As shown in FIG. 4, the third embodiment is an optical transmission including an optical transmitter 1 for transmitting an optical signal, an optical transmission line 4 for transmitting the optical signal, and an optical receiver 5 for receiving the optical signal. System.

  Here, the feature of the third embodiment is that between the optical transmitter 1 and the optical transmission line 4, there is a polarization control means 2 and a control circuit 3 for controlling the polarization control means 2. Provided between the optical transmission path 4 and the optical receiver 5 is an optical distribution means 6 that distributes an optical signal arriving from the optical transmission path 4 into two paths. An optical receiver 5 is connected to this path, PMD measuring means 7 is provided on the other path, and an optical signal transmitted from the optical transmitter 1 passes through the polarization control means 2 and is optically transmitted. The optical signal transmitted to the path 4 and propagated through the optical transmission path 4 is distributed to two paths by the optical distribution means 6, and the optical signal of one of the paths is received by the optical receiver 5, and the other one is received. The optical signal of the route is input to the PMD measuring means 7, and the optical receiver 5 includes means for detecting the error rate of the optical signal and means for detecting the error rate. Means for notifying the control circuit 3 of the detected error rate information, the PMD measuring means 7 is provided with means for notifying the control circuit 3 of the measured PMD information, and the control circuit 3 includes the notified error rate. When the information exceeds a threshold value defined for the error rate and the notified PMD information exceeds the threshold value defined for the PMD, the polarization control means 2 is controlled to control the incident polarization on the optical transmission line 4. A means for changing the wave state is provided (claim 25).

  Next, the optical transmission method of the third embodiment will be described. In the optical transmission method of the third embodiment, the optical transmitter 1 transmits an optical signal, and this optical signal is transmitted to the optical transmission line 4 after passing through the polarization control means 2 and propagated through the optical transmission line 4. The signal is distributed by the optical distribution means 6 into two paths, the optical signal of one of the paths is received by the optical receiver 5, and the optical receiver 5 notifies the detected error rate information to the control circuit 3, The optical signal of the other path is input to the PMD measuring means 7, and the PMD measuring means 7 notifies the measured PMD information to the control circuit 3, and the notified error rate information sets a threshold value defined for the error rate. If the PMD information exceeds the threshold value determined for PMD, the control circuit 3 controls the polarization control means 2 to change the state of incident polarization to the optical transmission line 4 (claim 3). ).

  The third embodiment is different from the second embodiment in that not only PMD values measured on the receiving side but also error rate information of received signals are used for polarization control. As a result, when transmission quality deterioration due to a cause other than PMD occurs, it is possible to control the incident polarization to the optical transmission line and avoid the phenomenon of changing to a polarization state where transmission quality deterioration is greater. Furthermore, by using the error rate information together for control, unnecessary control in a state where there is no error rate degradation can be eliminated, and high reliability can be realized.

(Fourth embodiment)
The optical transmission system of the fourth embodiment will be described with reference to FIG. FIG. 5 is an overall configuration diagram of the optical transmission system according to the fourth embodiment.

  In the fourth embodiment, as shown in FIG. 5, N optical transmitters 1-1 to 1-N for transmitting optical signals, an optical transmission line 4 for transmitting optical signals, and N for receiving optical signals. This is an optical transmission system including a plurality of optical receivers 5-1 to 5-N.

  Here, a feature of the fourth embodiment is that N optical transmitters 1-1 to 1- 1 are arranged between the N optical transmitters 1-1 to 1-N and the optical transmission line 4. N polarization control means 2-1 to 2-N connected in series to N, a control circuit 3 for controlling the N polarization control means 2-1 to 2-N, and N Wavelength multiplexing means 8 for wavelength multiplexing optical signals output from the polarization control means 2-1 to 2-N is provided, and an optical transmission line 4 and N optical receivers 5-1 to 5 are provided. -N is provided with wavelength demultiplexing means 9 for wavelength demultiplexing the optical signals combined by the wavelength multiplexing means 8, and mutually transmitted from the N optical transmitters 1-1 to 1-N. The optical signals having different wavelengths pass through the N polarization control units 2-1 to 2-N, and then are multiplexed by the wavelength multiplexing unit 8 and transmitted to the optical transmission line 4. The propagated optical signal is separated into wavelengths by the wavelength separation means 9, and the optical signals of the respective wavelengths are received by the N optical receivers 5-1 to 5 -N, respectively, and the N optical receivers 5. -1 to 5-N include means for detecting the error rate of the received optical signal and means for notifying the control circuit 3 of the error rate information respectively detected by the detecting means. When the notified error rate information exceeds a certain threshold, the N polarization control units 2-1 to 2-N connected to each of them are controlled to enter the polarization state of incidence on the optical transmission line 4 Are provided with means for changing each of them (claim 26).

  Next, an optical transmission method according to the fourth embodiment will be described. In the optical transmission method of the fourth embodiment, N optical transmitters 1-1 to 1-N transmit N optical signals having different wavelengths, respectively, and these N optical signals are N optical signals. After passing through N polarization control means 2-1 to 2-N connected in series to the transmitters 1-1 to 1-N, they are multiplexed by the wavelength multiplexing means 8 and sent to the optical transmission line 4. Then, the optical signal propagated through the optical transmission line 4 is separated into each wavelength by the wavelength demultiplexing means 9, and the optical signals of each wavelength are received by the N optical receivers 5-1 to 5-N, respectively. The optical receivers 5-1 to 5-N respectively detect the error rate of the optical signal, and send the detected error rate information to the control circuit 3 provided on the optical transmitters 1-1 to 1-N side. When the notified error rate information exceeds a certain threshold value, the control circuit 3 controls the N polarization control units 2-1 to 2-N. By changing the incident polarization state of the optical transmission path 4, respectively, to reduce the influence of PMD of the optical transmission path 4 with respect to the optical signal (claim 4).

(Fifth embodiment)
The optical transmission system of the fifth embodiment will be described with reference to FIG. FIG. 6 is an overall configuration diagram of the optical transmission system according to the fifth embodiment.

  In the fifth embodiment, as shown in FIG. 6, N optical transmitters 1-1 to 1-N for transmitting optical signals, an optical transmission line 4 for transmitting optical signals, and N for receiving optical signals. This is an optical transmission system including a plurality of optical receivers 5-1 to 5-N.

  Here, a feature of the fourth embodiment is that N optical transmitters 1-1 to 1- 1 are arranged between the N optical transmitters 1-1 to 1-N and the optical transmission line 4. N polarization control means 2-1 to 2-N connected in series to N, a control circuit 3 for controlling the N polarization control means 2-1 to 2-N, and N Wavelength multiplexing means 8 for wavelength multiplexing optical signals output from the polarization control means 2-1 to 2-N is provided, and an optical transmission line 4 and N optical receivers 5-1 to 5 are provided. -N, wavelength separation means 9 for wavelength-separating the optical signal combined by the wavelength multiplexing means 8, and N pieces of optical signals separated into the respective wavelengths distributed to two paths The optical distribution means 6-1 to 6-N are provided, and N optical receivers 5-1 to 5-N are provided in one of the N optical distribution means 6-1 to 6-N. Each connected The other path is provided with N PMD measuring means 7-1 to 7-N, and optical signals having different wavelengths transmitted from the N optical transmitters 1-1 to 1-N are as follows: An optical signal that has passed through each of the N polarization control units 2-1 to 2-N, is combined by the wavelength combining unit 8 and transmitted to the optical transmission line 4, and propagates through the optical transmission line 4, is wavelength-separated. The optical signal of each wavelength is distributed by N optical distribution units 6-1 to 6-N, one of which is divided into N optical receivers 5-1 to 5-5. -N is received respectively, and the other is input to N PMD measuring means 7-1 to 7-N. The PMD measuring means 7-1 to 7-N send the measured PMD information to the control circuit 3. The control circuit 3 includes a means for notifying each of them, and when the notified PMD information exceeds a threshold, There is to provided with a means for changing each incident polarization state of the optical transmission path 4 by controlling the N sets of the polarization control means 2-1 to 2-N (claim 27).

  Next, an optical transmission method according to the fifth embodiment will be described. In the optical transmission method of the fifth embodiment, N optical transmitters 1-1 to 1-N transmit N optical signals having different wavelengths, respectively. The N optical signals are N optical signals. After passing through N polarization control means 2-1 to 2-N connected in series to the transmitters 1-1 to 1-N, they are multiplexed by the wavelength multiplexing means 8 and sent to the optical transmission line 4. Then, the optical signal propagated through the optical transmission line 4 is separated into each wavelength by the wavelength separation means 9, and the optical signals of each wavelength are divided into two paths by N light distribution means 6-1 to 6-N, respectively. The optical signals in one direction are received by N optical receivers 5-1 to 5-N, respectively, and the optical signals in the other direction are received by N PMD measuring means 7-1 to 7-7. -N, and the N PMD measuring means 7 notify the control circuit 3 of the measured PMD information, respectively, and the notified PM When the information exceeds the threshold value, the control circuit 3 controls the N polarization control means 2-1 to 2-N to change the state of incident polarization to the optical transmission line 4 (Claim 5). .

  That is, the fifth embodiment is different from the fourth embodiment in that a PMD value is used instead of using error rate information of a received signal for polarization control. This makes it possible to distinguish signal degradation due to other causes such as optical SNR degradation and waveform degradation due to chromatic dispersion, and to monitor signal degradation due to PMD. Therefore, when transmission quality degradation due to other causes occurs, optical transmission It is possible to avoid the phenomenon of controlling the polarization incident on the path and changing to a polarization state in which transmission quality deterioration is further increased.

(Sixth embodiment)
The optical transmission system of the sixth embodiment will be described with reference to FIG. FIG. 7 is an overall configuration diagram of the optical transmission system according to the sixth embodiment.

  In the sixth embodiment, as shown in FIG. 7, N optical transmitters 1-1 to 1-N for transmitting optical signals, an optical transmission line 4 for transmitting optical signals, and N for receiving optical signals. This is an optical transmission system including a plurality of optical receivers 5-1 to 5-N.

  Here, the sixth embodiment is characterized in that N optical transmitters 1-1 to 1- 1 are arranged between the N optical transmitters 1-1 to 1-N and the optical transmission line 4. N polarization control means 2-1 to 2-N connected in series to N, a control circuit 3 for controlling the N polarization control means 2-1 to 2-N, and N Wavelength multiplexing means 8 for wavelength multiplexing optical signals output from the polarization control means 2-1 to 2-N is provided, and an optical transmission line 4 and N optical receivers 5-1 to 5 are provided. -N, wavelength separation means 9 for wavelength-separating the optical signal combined by the wavelength multiplexing means 8, and N signals for distributing the optical signals separated by each wavelength to two paths, respectively. The optical distribution means 6-1 to 6-N are provided, and N optical receivers 5-1 to 5-N are provided in one of the N optical distribution means 6-1 to 6-N. Each connected An optical switching means 10 is provided on the other path, and a PMD measuring means 7 to which an output of the optical switching means 10 is input is provided and transmitted from N optical transmitters 1-1 to 1-N. The optical signals having different wavelengths pass through the N polarization control units 2-1 to 2-N, and are multiplexed by the wavelength multiplexing unit 8 and transmitted to the optical transmission line 4. Are separated into wavelengths by the wavelength separation means 9, and the optical signals of each wavelength are distributed to two paths by N light distribution means 6-1 to 6-N, respectively. The optical signal of one route is received by each of the N optical receivers 5-1 to 5-N, and the optical signal of the other route is input to the optical switching unit 10 and selected by the optical switching unit 10. The optical signal is input to the PMD measuring means 7, and the PMD measuring means 7 The control circuit 3 includes means for notifying the control circuit 3, and the control circuit 3 controls the N polarization control means 2-1 to 2 -N to control the optical transmission line when the notified PMD information exceeds a threshold value. 4 is provided with means for changing the polarization state of incident light on each of them (claim 28).

  Next, an optical transmission method according to the sixth embodiment will be described. In the optical transmission method of the sixth embodiment, N optical transmitters 1-1 to 1-N transmit N optical signals having different wavelengths, respectively, and these N optical signals are N optical signals. After passing through N polarization control means 2-1 to 2-N connected in series to the transmitters 1-1 to 1-N, they are multiplexed by the wavelength multiplexing means 8 and sent to the optical transmission line 4. Then, the optical signal propagated through the optical transmission line 4 is separated into each wavelength by the wavelength separation means 9, and the optical signals of each wavelength are divided into two paths by N light distribution means 6-1 to 6-N, respectively. The optical signals in one direction are received by the N optical receivers 5-1 to 5-N, respectively, and the optical signals in the other direction are input to the optical switching means 10, and this optical switching is performed. The means 10 inputs the selected optical signal to the PMD measuring means 7, and the PMD measuring means 7 passes the measured PMD information to the control circuit 3. When the notified PMD exceeds the threshold value, the control circuit 3 controls the N polarization control units 2-1 to 2-N to change the incident polarization state to the optical transmission line 4, respectively. (Claim 6).

  The sixth embodiment differs from the fifth embodiment in that each wavelength is temporally selected by the light switching means 10 and PMD information is measured by the PMD measuring means 7. As a result, the PMD measuring means 7 can be shared by all wavelengths, so that the number of parts can be greatly reduced and the cost can be reduced.

(Seventh embodiment)
The optical transmission system of the seventh embodiment will be described with reference to FIG. FIG. 8 is an overall configuration diagram of the optical transmission system according to the seventh embodiment.

  As shown in FIG. 8, the optical transmission system of the seventh embodiment includes N optical transmitters 1-1 to 1-N that transmit optical signals, an optical transmission line 4 that transmits optical signals, and an optical signal. Is an optical transmission system including N optical receivers 5-1 to 5-N.

  Here, a feature of the sixth embodiment is that N optical transmitters 1-1 to 1- 1 are arranged between the N optical transmitters 1-1 to 1-N and the optical transmission line 4. N polarization control means 2-1 to 2-N connected in series to N, a control circuit 3 for controlling the N polarization control means 2-1 to 2-N, and N Wavelength multiplexing means 8 for wavelength multiplexing optical signals output from the polarization control means 2-1 to 2-N is provided, and an optical transmission line 4 and N optical receivers 5-1 to 5 are provided. -N is provided with an optical distribution means 6 for distributing the optical signal combined by the wavelength multiplexing means 8 into two paths, and one of the optical distribution means 6 is combined with one of the paths. A wavelength separation means 9 is provided for separating the optical signal into wavelengths, and a variable wavelength for selecting and outputting an optical signal of one wavelength from the multiplexed optical signal on the other path of the optical distribution means 6 Selecting means 11 and PMD measuring means 7 to which an optical signal having a wavelength selected by the variable wavelength selecting means 11 is input, and are transmitted from the N optical transmitters 1-1 to 1-N. The optical signals having different wavelengths pass through the N polarization control units 2-1 to 2-N, and then are combined by the wavelength combining unit 8 and transmitted to the optical transmission line 4. The propagated optical signal is distributed into two paths by the optical distribution means 6, and the optical signal in one of the paths is separated into each wavelength by the wavelength separation means 9, and N optical receivers 5-1 to 5-5. -N is received respectively, and the optical signal of the other path is selected by the variable wavelength selection unit 11 and input to the PMD measurement unit 7, and the PMD measurement unit 7 receives the measured PMD information. Is provided to the control circuit 3, and the control circuit 3 Provided with means for controlling the N polarization control means 2-1 to 2-N to change the incident polarization state to the optical transmission line 4 when the PMD information exceeds a threshold value, respectively. (Claim 29).

  Next, the optical transmission method of the seventh embodiment will be described. In the optical transmission method of the seventh embodiment, N optical transmitters 1-1 to 1-N transmit N optical signals having different wavelengths, respectively, and these N optical signals are N optical signals. After passing through N polarization control means 2-1 to 2-N connected in series to the transmitters 1-1 to 1-N, they are multiplexed by the wavelength multiplexing means 8 and sent to the optical transmission line 4. Then, the optical signal propagated through the optical transmission line 4 is distributed into two paths by the optical distribution means 6, and the optical signal in one of the directions is separated into each wavelength by the wavelength separation means 9, and the light of each wavelength. A signal is received by each of N optical receivers 5-1 to 5-N, and an optical signal in the other direction is a variable wavelength that selects and outputs an optical signal having one wavelength from the combined optical signal. The variable wavelength selection unit 11 inputs an optical signal having the selected wavelength to the PMD measurement unit 7 and inputs the PM signal to the PMD measurement unit 7. The measuring means 7 notifies the measured PMD information to the control circuit 3, and when the notified PMD exceeds the threshold value, the control circuit 3 controls the N polarization control means 2-1 to 2-N. Each incident polarization state to the optical transmission line 4 is changed.

  The seventh embodiment is different from the sixth embodiment in that selection of each wavelength is realized by the variable wavelength selection means 11 instead of the light switching means 10. Thereby, the number of parts can be significantly reduced by sharing the PMD measuring means 7 for all wavelengths. Furthermore, since light distribution for PMD measurement is performed before wavelength separation, the number of light distribution means 6 can be reduced, and a significant cost reduction can be realized.

(Eighth Example)
The optical transmission system of the eighth embodiment will be described with reference to FIG. FIG. 9 is an overall configuration diagram of the optical transmission system according to the eighth embodiment.

  In the eighth embodiment, as shown in FIG. 9, the PMD measuring means 7-1 to 7-N include means for notifying the control circuit 3 of the measured PMD information, and the optical receivers 5-1 to 5-N include Means for notifying the control circuit 3 of the detected error rate information, and the control circuit 3 exceeds the threshold value determined for the error rate, and the notified PMD information is related to PMD. When a predetermined threshold value is exceeded, there is provided means for controlling the polarization control means 2-1 to 2-N to change the polarization state of incidence on the optical transmission line 4 (claim 30).

  The example of FIG. 9 shows a configuration example in the case where error rate information and PMD information are used together in the optical transmission system of the fifth embodiment shown in FIG. 6, but the sixth example shown in FIG. 7 or FIG. Alternatively, error rate information and PMD information can be used together in the optical transmission system of the seventh embodiment.

  That is, the optical transmission system of FIG. 7 or FIG. 8 is different from the optical transmission system of FIG. 6 in that the number of PMD measuring means 7 is one, and the point that error rate information and PMD information are used together. Can be similarly applied to the optical transmission systems shown in FIG. 6, FIG. 7, and FIG.

  Next, an optical transmission method according to the eighth embodiment will be described. In the optical transmission method of the eighth embodiment, the PMD measuring means 7 or 7-1 to 7-N notifies the measured PMD information to the control circuit 3, and the optical receivers 5-1 to 5-N detect the detected error. Rate information is notified to the control circuit 3, and the control is performed when the notified error rate information exceeds a threshold value defined for the error rate and the notified PMD information exceeds a threshold value defined for PMD. The circuit 3 changes the incident polarization state to the optical transmission line 4 by controlling the N polarization control means 2-1 to 2-N connected thereto (Claim 8).

  As described above, the eighth embodiment differs from the fifth to seventh embodiments in that not only the PMD value measured on the receiving side but also the error rate information of the received signal is used for polarization control. . Thereby, when transmission quality deterioration due to causes other than PMD occurs, the incident polarization to the optical transmission line is controlled, and the phenomenon of changing to a polarization state where transmission quality deterioration becomes larger can be avoided. Furthermore, by using the error rate information together for control, unnecessary control in a state where there is no error rate degradation can be eliminated, and high reliability can be realized.

(Ninth Example)
An optical transmission system according to the ninth embodiment will be described with reference to FIG. FIG. 10 is an overall configuration diagram of the optical transmission system according to the ninth embodiment.

  In the ninth embodiment, as shown in FIG. 10, N optical transmitters 1-1 to 1-N for transmitting optical signals, an optical transmission line 4 for transmitting optical signals, and N for receiving optical signals. This is an optical transmission system including a plurality of optical receivers 5-1 to 5-N.

  Here, a feature of the ninth embodiment is that N optical transmitters 1-1 to 1- 1 are arranged between the N optical transmitters 1-1 to 1-N and the optical transmission line 4. Wavelength multiplexing means 8 for wavelength multiplexing N optical signals, polarization control means 2 for controlling the polarization of the optical signal multiplexed by the wavelength multiplexing means 8, and controlling this polarization control means 2 And a wavelength for separating the wavelength of the optical signal combined by the wavelength combining unit 8 between the optical transmission line 4 and the N optical receivers 5-1 to 5-N. Separating means 9 is provided, and optical signals having different wavelengths transmitted from N optical transmitters 1-1 to 1 -N are combined by the wavelength combining means 8 and then passed through the polarization control means 2. The optical signal that has passed through and is transmitted to the optical transmission line 4 and propagated through the optical transmission line 4 is separated into wavelengths by the wavelength separation means 9, and the optical signal of each wavelength is divided into N light beams. The N optical receivers 5-1 to 5-N are respectively detected by means for detecting the error rate of the optical signal and the means for detecting the optical signals. The control circuit 3 controls the polarization control means 2 to the optical transmission line 4 when the notified error rate information exceeds a threshold value. There is provided means for changing the incident polarization state.

  Next, an optical transmission method according to the ninth embodiment will be described. In the optical transmission method according to the ninth embodiment, N optical transmitters 1-1 to 1-N transmit N optical signals having different wavelengths, respectively, and the N optical signals are wavelength multiplexing means. 8, and the combined optical signal is transmitted to the optical transmission line 4 after passing through the polarization control means 2, and the optical signal propagated through the optical transmission line 4 is separated into each wavelength by the wavelength separation means 9. The optical signals of the respective wavelengths are received by the N optical receivers 5-1 to 5-N, respectively, and the N optical receivers 5-1 to 5-N indicate the error rates of the optical signals, respectively. The detected error rate information is notified to the control circuits 3 provided on the optical transmitters 1-1 to 1-N side, respectively, and when the notified error rate information exceeds a threshold value, the control circuit 3 Controls the polarization control means 2 to change the state of incident polarization to the optical transmission line 4 (claim 9).

  That is, the ninth embodiment is different from the fourth embodiment in that the incident polarization to the optical transmission line 4 of the wavelength multiplexed signal is collectively controlled instead of performing the incident polarization control for each wavelength. It is.

  Normally, system design is performed so that the probability of a DGD value causing a large transmission quality degradation that causes a system failure at a certain wavelength of the optical fiber is low, so a large transmission quality degradation occurs simultaneously at a plurality of wavelengths. The probability is very small.

For example, if the system failure probability at a certain wavelength is designed to be 10 ⁻⁶ (22 minutes / year), the probability of simultaneous system failure at two wavelengths is 10 ⁻¹² (0.03 seconds / 100 years). Become. Therefore, it is highly possible that the transmission quality is greatly degraded by one wavelength, and the transmission quality degradation due to PMD can be effectively suppressed by changing the polarization state by one polarization control means 2. By reducing the number of polarization control means 2, the system cost can be reduced, and the reliability of the entire system can be improved by reducing the number of parts.

(Tenth embodiment)
An optical transmission system according to the tenth embodiment will be described with reference to FIG. FIG. 11 is an overall configuration diagram of the optical transmission system according to the tenth embodiment.

  In the tenth embodiment, as shown in FIG. 11, N optical transmitters 1-1 to 1-N for transmitting optical signals, an optical transmission line 4 for transmitting optical signals, and N for receiving optical signals. This is an optical transmission system including a plurality of optical receivers 5-1 to 5-N.

  Here, the sixth embodiment is characterized in that N optical transmitters 1-1 to 1- 1 are arranged between the N optical transmitters 1-1 to 1-N and the optical transmission line 4. Wavelength multiplexing means 8 for wavelength multiplexing N optical signals, polarization control means 2 for controlling the polarization of the optical signal multiplexed by the wavelength multiplexing means 8, and controlling this polarization control means 2 And a wavelength for separating the wavelength of the optical signal combined by the wavelength combining unit 8 between the optical transmission line 4 and the N optical receivers 5-1 to 5-N. Separating means 9 and N light distributing means 6-1 to 6-N for distributing the optical signals of the respective wavelengths separated by the wavelength separating means 9 to two paths are provided. N optical receivers 5-1 to 5-N are respectively connected to one of the optical distribution means 6-1 to 6-N, and N PMD measuring means 7 are connected to the other path. 1 to 7-N are provided, and the optical signals having different wavelengths transmitted from the N optical transmitters 1-1 to 1-N are combined by the wavelength combining unit 8 to be polarization control unit. The optical signal transmitted to the optical transmission path 4 after passing through 2 and propagated through the optical transmission path 4 is separated into wavelengths by the wavelength separation means 9, and the optical signals of the respective wavelengths are divided into N optical distribution means 6. -1 to 6-N are distributed to two paths, and the optical signal of one of the paths is received by N optical receivers 5-1 to 5-N, respectively, and the other path is The optical signals are respectively input to N PMD measuring units 7-1 to 7-N, and the N PMD measuring units 7-1 to 7-N respectively notify the control circuit 3 of the measured PMD information. The control circuit 3 controls the polarization control means 2 when the notified PMD information exceeds a threshold value. There is to provided with a means for changing the incident polarization state of the optical transmission path 4 (claim 32).

  Next, an optical transmission method according to the tenth embodiment will be described. In the optical transmission method of the tenth embodiment, N optical transmitters 1-1 to 1-N transmit N optical signals having different wavelengths, respectively, and the N optical signals are wavelength multiplexing means. 8, and the combined optical signal is transmitted to the optical transmission line 4 after passing through the polarization control means 2, and the optical signal propagated through the optical transmission line 4 is separated into each wavelength by the wavelength separation means 9. The optical signals of the respective wavelengths are distributed to two paths by N optical distribution means 6-1 to 6-N, respectively, and the optical signal of one of the paths is transmitted to N optical receivers 5-1. ˜5-N respectively, and the optical signals in the other directions are respectively input to N PMD measuring means 7-1 to 7-N, and the N PMD measuring means 7-1 to 7-N The measured PMD information is notified to the control circuits 3 provided on the optical transmitters 1-1 to 1-N side, respectively, and the notified PM If the information is beyond the threshold value, the control circuit 3 controls the polarization control unit 2 changes the incident polarization state of the optical transmission path 4 (claim 10).

  That is, the tenth embodiment is different from the ninth embodiment in that PMD values are used instead of using error rate information of received signals for polarization control. This makes it possible to distinguish signal degradation due to other causes such as optical SNR degradation and waveform degradation due to chromatic dispersion, and to monitor signal degradation due to PMD. Therefore, when transmission quality degradation due to other causes occurs, optical transmission It is possible to control the incident polarization to the path 4 and avoid the phenomenon of changing to a polarization state in which transmission quality deterioration is further increased.

(Eleventh Example)
An optical transmission system according to the eleventh embodiment will be described with reference to FIG. FIG. 12 is an overall configuration diagram of the optical transmission system according to the eleventh embodiment.

  In the eleventh embodiment, as shown in FIG. 12, N optical transmitters 1-1 to 1-N that transmit optical signals, an optical transmission line 4 that transmits optical signals, and an optical signal are received. This is an optical transmission system including N optical receivers 5-1 to 5-N.

  Here, the feature of the eleventh embodiment is that there are N optical transmitters 1-1 to 1-1 between the N optical transmitters 1-1 to 1-N and the optical transmission line 4. Wavelength multiplexing means 8 for wavelength multiplexing the -N optical signal, polarization control means 2 for controlling the polarization of the optical signal multiplexed by the wavelength multiplexing means 8, and this polarization control means 2 A control circuit 3 for controlling, and wavelength-separates the optical signal combined by the wavelength combining unit 8 between the optical transmission line 4 and the N optical receivers 5-1 to 5-N. There are provided a wavelength separation means 9 and N light distribution means 6-1 to 6-N for distributing optical signals of respective wavelengths separated by the wavelength separation means 9 to two paths. N optical receivers 5-1 to 5-N are connected to one of the optical distribution means 6-1 to 6-N, respectively, and an optical switching means 10 is provided to the other path. PMD measuring means 7 having the output of the optical switching means 10 as an input is provided, and optical signals having different wavelengths transmitted from the N optical transmitters 1-1 to 1-N are combined with each other. After being combined by the means 8 and passing through the polarization control means 2, it is transmitted to the optical transmission line 4, and the optical signal propagated through the optical transmission line 4 is separated into wavelengths by the wavelength separation means 9. The optical signal is distributed to two paths by N optical distribution means 6-1 to 6-N, respectively, and the optical signal of one path is transmitted by N optical receivers 5-1 to 5-N. The optical signals received in the other directions are input to the optical switching means 10, and the optical switching means 10 inputs the selected optical signal to the PMD measurement means 7, and the PMD measurement means 7 measures the measured PMD information. For notifying the control circuit 3 of the PMD information. There when exceeding the threshold value, there is to provided with a means for changing the incident polarization state of the optical transmission path 4 by controlling the polarization control unit 2 (claim 33).

  Next, an optical transmission method according to the eleventh embodiment will be described. In the optical transmission method according to the eleventh embodiment, N optical transmitters 1-1 to 1-N transmit N optical signals having different wavelengths, respectively, and the N optical signals are wavelength-multiplexed. The combined optical signal is transmitted by the means 8 and transmitted to the optical transmission path 4 after passing through the polarization control means 2, and the optical signal propagated through the optical transmission path 4 is converted into each wavelength by the wavelength separation means 9. The optical signals of the respective wavelengths are divided into two paths by N optical distribution means 6-1 to 6-N, respectively, and the optical signal of one of the paths is divided into N optical receivers 5- 1 to 5-N, respectively, and the optical signal of the other path is input to the optical switching means 10, which inputs the selected optical signal to the PMD measuring means 7, and this PMD measuring means 7 notifies the control circuit 3 of the measured PMD information. When the notified PMD exceeds a threshold value, control is performed. Road 3 controls the polarization control unit 2 changes the incident polarization state of the optical transmission path 4 (claim 11).

  The eleventh embodiment differs from the tenth embodiment in that each wavelength is temporally selected by the light switching means 10 and PMD information is measured by the PMD measuring means 7. As a result, the PMD measuring means 7 can be shared by all wavelengths, so that the number of parts can be greatly reduced and the cost can be reduced.

(Twelfth embodiment)
A twelfth embodiment will be described with reference to FIG. FIG. 13 is an overall configuration diagram of the optical transmission system according to the twelfth embodiment.

  In the twelfth embodiment, as shown in FIG. 13, N optical transmitters 1-1 to 1-N that transmit optical signals, an optical transmission line 4 that transmits optical signals, and an optical signal are received. This is an optical transmission system including N optical receivers 5-1 to 5-N.

  Here, a feature of the twelfth embodiment is that there are N optical transmitters 1-1 to 1-1 between the N optical transmitters 1-1 to 1-N and the optical transmission line 4. Wavelength multiplexing means 8 for wavelength multiplexing the -N optical signal, polarization control means 2 for controlling the polarization of the optical signal multiplexed by the wavelength multiplexing means 8, and this polarization control means 2 A control circuit 3 for controlling the optical signal, and the optical signal combined by the wavelength combining means 8 between the optical transmission line 4 and the N optical receivers 5-1 to 5-N. A light distribution means 6 for distributing the light to the path is provided, and a wavelength separation means 9 for separating the combined optical signal into each wavelength is provided on one of the paths of the light distribution means 6. In this path, a variable wavelength selection unit 11 that selects and outputs an optical signal having one wavelength from the combined optical signals, and a wavelength selected by the variable wavelength selection unit 11 PMD measuring means 7 to which an optical signal is input is provided, and optical signals having different wavelengths transmitted from N optical transmitters 1-1 to 1-N are multiplexed by wavelength multiplexing means 8. The optical signal transmitted to the optical transmission path 4 after passing through the polarization control means 2 and propagated through the optical transmission path 4 is distributed into two paths by the optical distribution means 6, and the optical signal in one of the paths is transmitted. Is separated into wavelengths by the wavelength separation means 9, optical signals of the respective wavelengths are received by the N optical receivers 5-1 to 5-N, respectively, and the optical signals in the other directions are variable wavelength selection means. 11, the optical signal of the selected wavelength is input to the PMD measuring means 7, and the PMD measuring means 7 includes means for notifying the control circuit 3 of the measured PMD information, and the control circuit 3 is notified. When the PMD information exceeds a threshold value, the polarization control means 2 is controlled. There is to provided with a means for changing the incident polarization state of the optical transmission path 4 Te (claim 34).

  Next, an optical transmission method according to the twelfth embodiment will be described. In the optical transmission method according to the twelfth embodiment, N optical transmitters 1-1 to 1-N transmit N optical signals having different wavelengths, respectively, and the N optical signals are wavelength-multiplexed. The optical signal combined by the means 8 is transmitted to the optical transmission line 4 after passing through the polarization control means 2, and the optical signal propagated through the optical transmission line 4 is divided into two by the optical distribution means 6. The optical signal of one of the paths is separated into wavelengths by the wavelength separation means 9, and the optical signals of the respective wavelengths are received by the N optical receivers 5-1 to 5-N, The optical signal of the other path is input to the variable wavelength selection unit 11, and the variable wavelength selection unit 11 inputs the optical signal of the selected wavelength to the PMD measurement unit 7. The PMD measurement unit 7 measures the measured PMD information. Is notified to the control circuit 3, and when the notified PMD exceeds the threshold, the control circuit 3 By controlling the wave control unit 2 changes the incident polarization state of the optical transmission path 4 (claim 12).

  The twelfth embodiment is different from the eleventh embodiment in that selection of each wavelength is realized by variable wavelength selection means instead of light switching means. Thereby, the number of parts can be significantly reduced by sharing the PMD measuring means 7 for all wavelengths. Furthermore, since light distribution for PMD measurement is performed before wavelength separation, the number of light distribution means 6 can be reduced, and a significant cost reduction can be realized.

(Thirteenth embodiment)
An optical transmission system according to the thirteenth embodiment will be described with reference to FIG. FIG. 14 is an overall configuration diagram of the optical transmission system according to the thirteenth embodiment.

  In the optical transmission system of the thirteenth embodiment, as shown in FIG. 14, the PMD measuring means 7-1 to 7-N include means for notifying the control circuit 3 of the measured PMD information, and the optical receiver 5-1 ˜5-N includes means for notifying the control circuit 3 of the detected error rate information, and the control circuit 3 exceeds the threshold determined for the error rate and the notified error rate information is notified. The PMD information includes means for controlling the polarization control means 2 to change the incident polarization state to the optical transmission line 4 when the PMD information exceeds a threshold defined for PMD (claim 35).

  The example of FIG. 14 shows a configuration example in the case where error rate information and PMD information are used together in the optical transmission system of the tenth embodiment shown in FIG. 11, but the tenth embodiment shown in FIG. 12 or FIG. Similarly, the error rate information and PMD information can be used together in the optical transmission system of the first or twelfth embodiment.

  That is, the optical transmission system of FIG. 12 or 13 is different from the optical transmission system of FIG. 11 in that the number of PMD measuring means 7 is one, and the error rate information and PMD information are used together. Can be similarly applied to the optical transmission systems shown in FIG. 11, FIG. 12, and FIG.

  Next, an optical transmission method according to the thirteenth embodiment will be described. In the optical transmission method of the thirteenth embodiment, the PMD measuring means 7 or 7-1 to 7-N notifies the control circuit 3 of the measured PMD information, and the optical receivers 5-1 to 5-N detect it. Error rate information is notified to the control circuit 3, and when the notified error rate information exceeds a threshold defined for the error rate and the notified PMD information exceeds a threshold defined for PMD, The control circuit 3 controls the polarization control means 2 to change the state of incident polarization to the optical transmission line 4 (claim 13).

  As described above, the thirteenth embodiment is different from the tenth to twelfth embodiments in that not only the PMD value measured on the receiving side but also the error rate information of the received signal is used for the polarization control. It is. Thereby, when transmission quality deterioration due to causes other than PMD occurs, the incident polarization to the optical transmission line is controlled, and the phenomenon of changing to a polarization state where transmission quality deterioration becomes larger can be avoided. Furthermore, by using the error rate information together for control, unnecessary control in a state where there is no error rate degradation can be eliminated, and high reliability can be realized.

(14th embodiment)
The optical transmission system according to the fourteenth embodiment will be described with reference to FIG. FIG. 15 is an overall configuration diagram of the optical transmission system according to the fourteenth embodiment.

  In the fourteenth embodiment, as shown in FIG. 15, the PMD measuring means 7 includes a DOP measuring means 12 (claims 14 and 36). When the PMD of the transmission path increases, the DOP of the received signal decreases. By using the fact that the DOP of the received signal is below the threshold value as a criterion for starting polarization control, it is possible to distinguish the signal degradation due to other causes such as optical SNR degradation and waveform degradation due to chromatic dispersion, and monitor the signal degradation due to PMD. Therefore, when transmission quality deterioration due to other causes occurs, it is possible to control the incident polarization to the optical transmission line 4 and avoid the phenomenon of changing to a polarization state in which the transmission quality deterioration becomes larger.

  Therefore, when using the PDM measuring means 7 in the fourteenth embodiment, the control circuit 3 does not exceed the threshold value but the polarization control means 2 when the value falls below the threshold value. To control.

(15th Example)
An optical transmission system according to the fifteenth embodiment will be described with reference to FIG. FIG. 16 is an overall configuration diagram of an optical transmission system according to the fifteenth embodiment.

  In the optical transmission system of the fifteenth embodiment, as shown in FIG. 16, the PMD measuring means 7 includes a photoelectric conversion means 13 for converting an optical signal into an electrical signal, and a specific connected in series with the photoelectric conversion means 13. Frequency intensity measuring means 14 (claims 15 and 37).

  When the waveform of the received signal deteriorates due to PMD in the optical transmission line 4, the intensity of the frequency B decreases (B: bit rate). B / 2, B / 4, etc. can also be used as the specific frequency, and the amount of PMD that can be observed increases as the frequency decreases. By using the fact that the intensity of a specific frequency (for example, frequency B) of the received signal is below the threshold value as a criterion for starting polarization control, waveform deterioration due to PMD can be detected with higher sensitivity compared to DOP.

(16th Example)
The optical transmission system according to the sixteenth embodiment will be described with reference to FIG. FIG. 17 is a block diagram of an optical transmission system according to the sixteenth embodiment.

  In the optical transmission system of the sixteenth embodiment, as shown in FIG. 17, N wavelength dispersion compensating means 15-for inputting the optical signals of the respective wavelengths separated by the wavelength separating means 9 and compensating the chromatic dispersion thereof. 1 to 15 -N, and the PMD measuring means 7 is extracted by the frequency component separating means 16 for separating and extracting at least two different frequency components from the optical spectrum components of the optical signal, and the frequency component separating means 16. A phase comparison unit 17 for detecting a relative phase difference between the components, and a wavelength for calculating a chromatic dispersion amount that the optical signal suffers in the optical transmission line 4 based on the relative phase difference information obtained from the phase comparison unit 17. An intensity measuring means 19 that measures the intensity of at least one of the optical spectrum components extracted by the dispersion measuring means 18 and the frequency component separating means 16 and uses this measurement result as a PMD measurement result. Comprising a wavelength dispersion compensating unit 151 to 15-N is provided with means for compensating for wavelength dispersion of the measurement results based optical transmission path 4 of the wavelength dispersion measuring unit 18 (claim 16, claim 38).

  By compensating the chromatic dispersion of the optical transmission line 4 based on the measurement result of the chromatic dispersion measuring means 18, the intensity information obtained by the intensity measuring means 19 is prevented from being lowered due to the influence of chromatic dispersion, and only the influence by PMD is obtained. It can be detected. By using this intensity information as a criterion for starting polarization control, waveform deterioration due to PMD can be distinguished from deterioration due to chromatic dispersion and detected with high sensitivity.

  Further, in the optical transmitters 1-1 to 1-N, a tone signal having a frequency lower than the bit rate is superimposed on the signal light as intensity modulation, and phase comparison and intensity detection of frequency components of the tone signal are performed, thereby performing PMD. In addition, the detection range of chromatic dispersion can be expanded.

(17th Example)
In the optical transmission system of the seventeenth embodiment, the optical transmitters 1, 1-1 to 1 -N and the optical receivers 5, 5-1 to 5 -N are each provided with error correction means to detect the error rate. Means for detecting the number of errors by the error correcting means, and the means for notifying is detected by the means for detecting as error rate information to be notified to the control circuit 3, 3-1 to 3-N. Means for using information on the number of errors is provided.

  That is, in the optical transmission method of the seventeenth embodiment, the optical transmitters 1, 1-1 to 1-N and the optical receiver in the first, third, fourth, eighth, ninth, and thirteenth embodiments. 5, 5-1 to 5-N have error correction means, and error rate information notified from the optical receivers 5 and 5-1 to 5-N to the control circuits 3 and 3-1 to 3-N. The number-of-errors information detected by the error correction means is used (claim 17). This makes it possible to control the incident polarization before an error occurs in the signal after error correction, that is, the client signal.

(Eighteenth embodiment)
In the optical transmission system of the eighteenth embodiment, the means for notifying the BDI signal or the BEI signal when the error rate information or the PMD information is notified to the control circuits 3 and 3-1 to 3-N. Means for mounting error rate information or the PMD information is provided.

  That is, in the optical transmission method of the eighteenth embodiment, when the error rate information or the PMD information is notified from the optical receivers 5 and 5-1 to 5 -N to the control circuits 3 and 3-1 to 3 -N. In addition, the error rate information or the PMD information is mounted on the BDI signal or the BEI signal.

As a result, signal quality degradation due to PMD can be suppressed without adding a special information notification function from the reception side to the transmission side for polarization control.
(Nineteenth Example)
In the optical transmission system of the nineteenth embodiment, when the polarization control means 2, 2-1 to 2-N change the incident polarization to the optical fiber, the angles formed by the incident polarization on the Poincare sphere. Means for transitioning between three polarization states with an angle of 90 degrees.

  That is, in the optical transmission method of the ninth embodiment, when the polarization control means 2, 2-1 to 2-N change the incident polarization to the optical fiber, each of the incident polarizations forms on the Poincare sphere. Three polarization states having an angle of 90 degrees are transitioned (claim 19).

  The polarization states of the two principal axes of the optical transmission line are orthogonal, and the angle formed on the Poincare sphere is 180 degrees. The equator when the polarization states of the two principal axes are poles on the Poincare sphere is the worst polarization state. One of the three is the best when two of the three polarizations are on the equator of the worst polarization state by shifting the three polarization states where the angle formed by the incident polarization on the Poincare sphere is 90 degrees. It becomes a polarization state, and the worst polarization state can be avoided. By limiting the number of polarization states to be shifted to three, not only the control is simplified, but also the time until transmission quality is improved can be shortened compared to a method of changing the polarization state little by little.

(20th embodiment)
A procedure for changing the incident polarization angle in the optical transmission system of the twentieth embodiment will be described with reference to the flowchart of FIG. FIG. 18 is a flowchart showing the incident polarization angle changing procedure in the control circuit of the optical transmission system of the twentieth embodiment.

  In the control circuit 3 in the optical transmission system of the twentieth embodiment, the control circuit 3 changes the incident polarization to the optical fiber constituting the optical transmission line 4 by the polarization control means 2, 2-1 to 2-N. In this case, if the angle on the Poincare sphere to be changed in one control unit is set minutely, and the error rate or PMD detected on the receiving side increases due to the change of the incident polarization, the incident polarization is set to the previous setting. Comprises means for repeatedly controlling the incident polarization in the same direction as the previous setting when the error rate or PMD detected on the receiving side is reduced by changing the incident polarization. 42).

  That is, as shown in FIG. 18, when changing the incident polarization to the optical fiber constituting the optical transmission line 4 by the polarization control means 2, 2-1 to 2-N, the Poincare that is changed in one control unit. When the angle on the sphere is set to a very small value (S1) and the error rate or PMD detected on the receiving side increases due to the change of the incident polarization (S2), the incident polarization is set in the opposite direction to the previous setting. If it is controlled (S3) and decreases (S2), the incident polarization is controlled in the same direction as the previous setting (S1). In this way, the change of the incident polarization and the confirmation of increase / decrease in the error rate or PMD are repeated to control the incident polarization (claim 20).

(21st Example)
The procedure for determining the end of control in the optical transmission system of the 21st embodiment will be described with reference to the flowchart of FIG. FIG. 19 is a flowchart showing a control end determination procedure in the control circuit of the optical transmission system of the 21st embodiment.

  The control circuit 3 of the optical transmission system of the twenty-first embodiment performs a control operation for changing the incident polarization to the optical fiber constituting the optical transmission line 4 by the polarization control means 2 and 2-1 to 2-N. And means for ending when the error rate or PMD detected on the receiving side is minimized (claim 43).

  That is, as shown in FIG. 19, the control circuit 3 receives a control operation for changing the incident polarization to the optical fiber constituting the optical transmission line 4 by the polarization control means 2, 2-1 to 2-N. The error rate or PMD detected on the side is observed (S10), and the process ends when the value becomes minimum (S11, S12) (claim 21).

  Thereby, the control frequency of incident polarization can be reduced by changing the incident polarization to the best condition.

(Twenty-second embodiment)
The procedure for determining the end of control in the optical transmission system of the twenty-second embodiment will be described with reference to the flowchart of FIG. FIG. 20 is a flowchart showing a control end determination procedure in the control circuit of the optical transmission system of the twenty-second embodiment, and is common to the twenty-first embodiment.

  The control circuit 3 of the optical transmission system of the twenty-second embodiment performs a control operation for changing the incident polarization to the optical fiber constituting the optical transmission line 4 by the polarization control means 2 and 2-1 to 2-N. And a means for ending when the error rate or PMD detected on the receiving side falls below a control end threshold (claim 44).

  That is, as shown in FIG. 20, the control circuit 3 receives a control operation for changing the incident polarization to the optical fiber constituting the optical transmission line 4 by the polarization control means 2, 2-1 to 2-N. The error rate or PMD detected on the side is observed (S20), and the process ends when the value falls below the control end threshold (S21, S22) (claim 22).

  Thereby, the control time of incident polarization can be shortened by terminating the control when transmission quality degradation due to PMD can be suppressed to some extent.

  The present invention reduces the failure time of the system by the minimum control of the incident polarization to the optical fiber, reduces the risk of transmission quality degradation due to erroneous control of the polarization, and further improves the reliability of the optical device. Since the request can be relaxed, application to OTN or the like can contribute to the construction of an efficient network with high communication quality.

1 is an overall configuration diagram of an optical transmission system according to a first embodiment. FIG. 6 is an operation explanatory diagram of the present invention. The block diagram of the optical transmission system of 2nd Example. The block diagram of the optical transmission system of 3rd Example. The block diagram of the optical transmission system of 4th Example. The block diagram of the optical transmission system of 5th Example. The block diagram of the optical transmission system of 6th Example. The block diagram of the optical transmission system of 7th Example. The block diagram of the optical transmission system of 8th Example. The block diagram of the optical transmission system of 9th Example. The block diagram of the optical transmission system of 10th Example. The block diagram of the optical transmission system of 11th Example. The block diagram of the optical transmission system of 12th Example. The block diagram of the optical transmission system of 13th Example. The block diagram of the optical transmission system of 14th Example. The block diagram of the optical transmission system of 15th Example. The block diagram of the optical transmission system of 16th Example. The flowchart which shows the angle change procedure of the incident polarization in the control circuit of the optical transmission system of 20th Example. The flowchart which shows the control end judgment procedure in the control circuit of the optical transmission system of 21st Example. The flowchart which shows the control end judgment procedure in the control circuit of the optical transmission system of 22nd Example. The block diagram of the conventional optical transmission system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1-1 to 1-N, 21 Optical transmitter 2, 2-1 to 2-N, 22, 27 Polarization control means 3, 3-1 to 3-N Control circuit 4, 24 Optical transmission line 5, 5-1 to 5-N, 25 Optical receiver 6, 6-1 to 6-N, 26 Optical distribution means 7, 7-1 to 7-N PMD measuring means 8 Wavelength multiplexing means 9 Wavelength separation means 10 Optical switching Means 11 Variable wavelength selection means 12 DOP measurement means 13 Photoelectric conversion means 14 Specific frequency intensity measurement means 15-1 to 15-N Wavelength dispersion compensation means 16 Frequency component separation means 17 Phase comparison means 18 Wavelength dispersion measurement means 19 Intensity measurement means 28 Polarization separation means 29 Balanced optical receiver 30 Intensity detectors 31, 32 Controller

Claims (44)

In an optical transmission method applied to an optical transmission system including an optical transmitter that transmits an optical signal, an optical transmission path that transmits the optical signal, and an optical receiver that receives the optical signal,
The optical transmitter transmits an optical signal, the optical signal is transmitted to the optical transmission path after passing through the polarization control means, the optical signal propagated through the optical transmission path is received by the optical receiver, The optical receiver detects the error rate of the optical signal, notifies the detected error rate information to the control means provided on the optical transmitter side, and when the notified error rate information exceeds a threshold value The control means controls the polarization control means to change the incident polarization state to the optical transmission line. In an optical transmission method applied to an optical transmission system including an optical transmitter that transmits an optical signal, an optical transmission path that transmits the optical signal, and an optical receiver that receives the optical signal,
The optical transmitter transmits an optical signal, which is transmitted to the optical transmission path after passing through the polarization control means, and the optical signal propagated through the optical transmission path is divided into two paths by the optical distribution means. The optical signal in one direction is received by the optical receiver, and the optical signal in the other direction is input to PMD (Polarization Mode Dispersion) measuring means, and this PMD measuring means Notifies the measured PMD information to the control means provided on the optical transmitter side, and when the notified PMD exceeds a threshold value, the control means controls the polarization control means to control the optical transmission line. An optical transmission method characterized by changing a polarization state of incident light on the optical fiber. In an optical transmission method applied to an optical transmission system including an optical transmitter that transmits an optical signal, an optical transmission path that transmits the optical signal, and an optical receiver that receives the optical signal,
The optical transmitter transmits an optical signal, which is transmitted to the optical transmission path after passing through the polarization control means, and the optical signal propagated through the optical transmission path is divided into two paths by the optical distribution means. The optical signal of one of the paths is received by the optical receiver, and the optical receiver detects an error rate of the optical signal, and provides the detected error rate information on the optical transmitter side. And the optical signal of the other path is input to the PMD measuring means. The PMD measuring means notifies the measured PMD information to the control means, and the notified error rate information is When the threshold value defined for the error rate is exceeded and the PMD information exceeds the threshold value defined for PMD, the control means controls the polarization control means to control the incident polarization to the optical transmission line. An optical transmission method characterized by changing a state. In an optical transmission method applied to an optical transmission system including N optical transmitters that transmit optical signals, an optical transmission path that transmits optical signals, and N optical receivers that receive optical signals,
The N optical transmitters respectively transmit N optical signals having different wavelengths, and the N optical signals are connected to the N optical transmitters in series, respectively. After passing through the means, the light is combined by the wavelength combining means and transmitted to the optical transmission line, and the optical signal propagated through the optical transmission line is separated into each wavelength by the wavelength separation means, and the optical signal of each wavelength is N The N optical receivers respectively detect the error rate of the optical signal, and the detected error rate information is sent to control means provided on the optical transmitter side, respectively. And when the notified error rate information exceeds a threshold value, the control means controls the N polarization control means to change the state of incident polarization to the optical transmission line, respectively. Optical transmission method. Optical transmission applied to an optical transmission system comprising N optical transmitters for transmitting optical signals, an optical transmission path for transmitting optical signals, and N optical receivers for receiving optical signals In the method
The N optical transmitters respectively transmit N optical signals having different wavelengths, and the N optical signals are connected to the N optical transmitters in series, respectively. After passing through the means, the light is combined by the wavelength combining means and transmitted to the optical transmission line, and the optical signal propagated through the optical transmission line is separated into each wavelength by the wavelength separation means, and the optical signal of each wavelength is N The optical signal is distributed to two paths by one optical distribution means, the optical signal of one path is received by each of the N optical receivers, and the optical signal of the other path is measured by N PMD measurements. Each of the N PMD measurement means notifies the measured PMD information to the control means provided on the optical transmitter side, and when the notified PMD exceeds a threshold value, the control means Controls the N polarization control means to control the light The optical transmission method characterized by changing the incident polarization state of the transmission path, respectively. Optical transmission applied to an optical transmission system comprising N optical transmitters for transmitting optical signals, an optical transmission path for transmitting optical signals, and N optical receivers for receiving optical signals In the method
The N optical transmitters respectively transmit N optical signals having different wavelengths, and the N optical signals are connected to the N optical transmitters in series, respectively. After passing through the means, the light is combined by the wavelength combining means and transmitted to the optical transmission line, and the optical signal propagated through the optical transmission line is separated into each wavelength by the wavelength separation means, and the optical signal of each wavelength is N Each of the optical distribution means distributes the signal to two paths, the optical signal of one of the paths is received by each of the N optical receivers, and the optical signal of the other path is input to the optical switching means. The optical switching means inputs the selected optical signal to the PMD measuring means, and the PMD measuring means notifies the measured PMD information to the control means provided on the optical transmitter side, and the notified PMD is a threshold value. The control means N N polarizations The optical transmission method characterized by controlling the control means to change each incident polarization state to the optical transmission line. Optical transmission applied to an optical transmission system comprising N optical transmitters for transmitting optical signals, an optical transmission path for transmitting optical signals, and N optical receivers for receiving optical signals In the method
The N optical transmitters respectively transmit N optical signals having different wavelengths, and the N optical signals are connected to the N optical transmitters in series, respectively. After passing through the means, the light is combined by the wavelength combining means and transmitted to the optical transmission path, and the optical signal propagated through the optical transmission path is distributed into two paths by the optical distribution means. The optical signal is separated into each wavelength by the wavelength separation means, the optical signals of each wavelength are respectively received by the N optical receivers, and the optical signal in the other direction is one from the combined optical signal. The variable wavelength selection means inputs an optical signal of the selected wavelength to the PMD measurement means, and the PMD measurement means outputs the measured PMD information to the optical signal. Notify the control means provided on the transmitter side and notify And when the PMD exceeds the threshold, the control unit optical transmission method and changing each incident polarization state to the optical transmission line by controlling the N sets of the polarization control means. The PMD measurement means notifies the measured PMD information to the control means, and the optical receiver notifies the detected error rate information to the control means, and the notified error rate information is defined with respect to the error rate. When the threshold value is exceeded and the notified PMD information exceeds a threshold value defined for PMD, the control means controls the N polarization control means connected to the optical transmission line. The optical transmission method according to claim 5, wherein the incident polarization state is changed. In an optical transmission method applied to an optical transmission system including N optical transmitters that transmit optical signals, an optical transmission path that transmits optical signals, and N optical receivers that receive optical signals,
The N optical transmitters respectively transmit N optical signals having different wavelengths, and the N optical signals are combined by wavelength multiplexing means, and the combined optical signals are polarization controlled. After passing through the means, the optical signal transmitted to the optical transmission line and propagated through the optical transmission line is separated into wavelengths by the wavelength separation means, and the optical signals of each wavelength are received by the N optical receivers, respectively. The N optical receivers respectively detect the error rate of the optical signal, notify the detected error rate information to the control means provided on the optical transmitter side, and notify the notified error rate. When the information exceeds a threshold value, the control means controls the polarization control means to change the state of incident polarization to the optical transmission line. In an optical transmission method applied to an optical transmission system including N optical transmitters that transmit optical signals, an optical transmission path that transmits optical signals, and N optical receivers that receive optical signals,
The N optical transmitters respectively transmit N optical signals having different wavelengths, and the N optical signals are combined by wavelength multiplexing means, and the combined optical signals are polarization controlled. After passing through the means, the optical signal transmitted to the optical transmission line and propagated through the optical transmission line is separated into wavelengths by the wavelength separation means, and the optical signals of each wavelength are divided into two by the N optical distribution means. The optical signals in one of the directions are received by the N optical receivers, and the optical signals in the other direction are input to N PMD measuring means, respectively. The PMD measurement means notifies the measured PMD information to the control means provided on the optical transmitter side, and when the notified PMD exceeds a threshold value, the control means controls the polarization control means. To change the polarization state of incident light on the optical transmission line. An optical transmission method characterized by the above. In an optical transmission method applied to an optical transmission system including N optical transmitters that transmit optical signals, an optical transmission path that transmits optical signals, and N optical receivers that receive optical signals,
The N optical transmitters respectively transmit N optical signals having different wavelengths, and the N optical signals are combined by wavelength multiplexing means, and the combined optical signals are polarization controlled. After passing through the means, the optical signal transmitted to the optical transmission line and propagated through the optical transmission line is separated into wavelengths by the wavelength separation means, and the optical signals of each wavelength are divided into two by the N optical distribution means. The optical signal of one of the paths is received by each of the N optical receivers, and the optical signal of the other path is input to the optical switching means, which is selected by the optical switching means. The optical signal is input to the PMD measuring means, and the PMD measuring means notifies the measured PMD information to the control means provided on the optical transmitter side. When the notified PMD exceeds the threshold, the control means Controls the polarization control means to the optical transmission line The optical transmission method characterized by changing the Ihen wave state. In an optical transmission method applied to an optical transmission system including N optical transmitters that transmit optical signals, an optical transmission path that transmits optical signals, and N optical receivers that receive optical signals,
The N optical transmitters respectively transmit N optical signals having different wavelengths, and the N optical signals are combined by wavelength multiplexing means, and the combined optical signals are polarization controlled. The optical signal transmitted to the optical transmission path after passing through the means and propagated through the optical transmission path is distributed into two paths by the optical distribution means, and the optical signal in one of the paths is divided into wavelengths by the wavelength separation means. The optical signals of the respective wavelengths are respectively received by the N optical receivers, and the optical signals of the other directions are input to the variable wavelength selecting means, and the variable wavelength selecting means has the selected wavelength. The optical signal is input to the PMD measuring means, and the PMD measuring means notifies the measured PMD information to the control means provided on the optical transmitter side. When the notified PMD exceeds the threshold, the control means Controls the polarization control means to control the optical transmission line The optical transmission method characterized by changing the incident polarization state of.   The PMD measurement means notifies the measured PMD information to the control means, and the optical receiver notifies the detected error rate information to the control means, and the notified error rate information is defined with respect to the error rate. When the PMD information exceeds the threshold determined for PMD, the control means controls the polarization control means connected to control the incident polarization to the optical transmission line. The optical transmission method according to claim 10, wherein the state is changed.   The optical transmission method according to any one of claims 2, 3, 5, 6, 7, 8, 10, 11, 12, and 13, wherein a DOP (Degree of Polarization) measuring unit is used as the PMD measuring unit.   The photoelectric conversion means and a specific frequency intensity measurement means connected in series with the photoelectric conversion means are used as the PMD measurement means. An optical transmission method according to any one of the above. It has chromatic dispersion compensation means on the receiving side,
The PMD measuring means includes
Separating and extracting at least two different frequency components from the optical spectral components of the optical signal;
Detect the relative phase difference between the extracted components,
Based on the detected relative phase difference information, calculate the amount of chromatic dispersion that the optical signal suffered in the optical transmission line,
The intensity of at least one of the extracted light spectrum components is measured and this measurement result is used as a PMD measurement result.
The chromatic dispersion compensation means compensates chromatic dispersion of the optical transmission line based on a calculation result of the chromatic dispersion amount. Any one of claims 2, 3, 5, 6, 7, 8, 10, 11, 12, and 13 An optical transmission method according to claim 1.   The optical transmitter and the optical receiver each have error correction means, and the error number information detected by the error correction means is used as error rate information notified from the optical receiver to the control means. The optical transmission method according to any one of 3, 4, 8, 9, and 13.   When the error rate information or the PMD information is notified from the optical receiver to the control means, the error rate information or the PMD information is mounted on a BDI (Backward Defect Indication) signal or a BEI (Backward Error Indicator) signal. The optical transmission method according to claim 1.   19. Any one of claims 1 to 18, wherein, when the polarization control means changes the incident polarization to the optical fiber, the incident polarization transitions between three polarization states each having an angle of 90 degrees on the Poincare sphere. An optical transmission method according to claim 1.   When the incident polarization to the optical fiber constituting the optical transmission line is changed by the polarization control means, the angle on the Poincare sphere to be changed in one control unit is set to be small, and reception is performed by changing the incident polarization. When the error rate or PMD detected on the receiving side increases, the incident polarization is controlled in the direction opposite to the previous setting, and when the error rate or PMD detected on the receiving side decreases due to the change of the incident polarization The optical transmission method according to claim 1, wherein the procedure for controlling the incident polarization in the same direction as the previous setting is repeatedly executed.   The control means ends the control operation for changing the incident polarization to the optical fiber constituting the optical transmission line by the polarization control means when the error rate or PMD detected on the receiving side is minimized. The optical transmission method according to claim 1.   In the control means, the error rate or PMD detected on the receiving side is lower than the control end threshold when the polarization control means changes the incident polarization to the optical fiber constituting the optical transmission line. 21. The optical transmission method according to claim 1, wherein the optical transmission method ends at a point in time. In an optical transmission system including an optical transmitter that transmits an optical signal, an optical transmission path that transmits the optical signal, and an optical receiver that receives the optical signal,
Between the optical transmitter and the optical transmission path, a polarization control means and a control means for controlling the polarization control means are provided,
The optical signal transmitted from the optical transmitter is transmitted to the optical transmission line after passing through the polarization control means,
The optical signal propagated through the optical transmission line is received by the optical receiver,
The optical receiver is:
Means for detecting the error rate of the optical signal;
Means for notifying the control means of error rate information detected by the means for detecting,
The control means comprises means for controlling the polarization control means to change the state of incident polarization to the optical transmission line when the notified error rate information exceeds a certain threshold value. Optical transmission system. In an optical transmission system including an optical transmitter that transmits an optical signal, an optical transmission path that transmits the optical signal, and an optical receiver that receives the optical signal,
Between the optical transmitter and the optical transmission path, a polarization control means and a control means for controlling the polarization control means are provided,
Between the optical transmission line and the optical receiver, there is provided an optical distribution means for distributing the optical signal arriving from the optical transmission line into two directions,
The optical receiver is connected to one path of the optical distribution means, and PMD measurement means is provided to the other path,
The optical signal transmitted from the optical transmitter is transmitted to the optical transmission line after passing through the polarization control means,
The optical signal propagated through the optical transmission path is distributed to two paths by the optical distribution means,
The optical signal in one direction is received by the optical receiver, and the optical signal in the other direction is input to the PMD measuring means,
The PMD measuring means includes means for notifying the control means of measured PMD information,
The control means includes means for controlling the polarization control means to change the incident polarization state to the optical transmission line when the notified PMD information exceeds a threshold value. Optical transmission system. In an optical transmission system including an optical transmitter that transmits an optical signal, an optical transmission path that transmits the optical signal, and an optical receiver that receives the optical signal,
Between the optical transmitter and the optical transmission path, a polarization control means and a control means for controlling the polarization control means are provided,
Between the optical transmission line and the optical receiver, there is provided an optical distribution means for distributing the optical signal arriving from the optical transmission line into two directions,
The optical receiver is connected to one path of the optical distribution means, and PMD measurement means is provided to the other path,
The optical signal transmitted from the optical transmitter is transmitted to the optical transmission line after passing through the polarization control means,
The optical signal propagated through the optical transmission path is distributed to two paths by the optical distribution means,
The optical signal in one direction is received by the optical receiver, and the optical signal in the other direction is input to the PMD measuring means,
The optical receiver is:
Means for detecting an error rate of the optical signal;
Means for notifying the control means of error rate information detected by the means for detecting,
The PMD measuring means includes means for notifying the control means of measured PMD information,
When the notified error rate information exceeds a threshold value determined for the error rate and the notified PMD information exceeds a threshold value determined for PMD, the control means controls the polarization control means. An optical transmission system comprising means for controlling and changing the polarization state of incidence on the optical transmission line. In an optical transmission system comprising N optical transmitters for transmitting optical signals, an optical transmission path for transmitting optical signals, and N optical receivers for receiving optical signals,
Between the N optical transmitters and the optical transmission line, there are N polarization control means connected in series to the N optical transmitters, and the N polarization control means. Control means for controlling each, and wavelength multiplexing means for wavelength multiplexing optical signals output from the N polarization control means,
Between the optical transmission line and the N optical receivers, wavelength separation means for wavelength-separating the optical signal multiplexed by the wavelength multiplexing means is provided,
The optical signals having different wavelengths transmitted from the N optical transmitters pass through the N polarization control units, and then are multiplexed by the wavelength multiplexing unit and transmitted to the optical transmission line. ,
The optical signal propagated through the optical transmission line is separated into each wavelength by the wavelength separation means,
The optical signals of each wavelength are received by the N optical receivers,
N optical receivers are:
Means for respectively detecting the error rate of the received optical signal;
Means for notifying the control means of the error rate information respectively detected by the means for detecting,
The control means includes means for controlling the N polarization control means to change the state of polarization incident on the optical transmission line when the notified error rate information exceeds a threshold value. An optical transmission system characterized by In an optical transmission system comprising N optical transmitters for transmitting optical signals, an optical transmission path for transmitting optical signals, and N optical receivers for receiving optical signals,
Between the N optical transmitters and the optical transmission line, there are N polarization control means connected in series to the N optical transmitters, and the N polarization control means. Control means for controlling each, and wavelength multiplexing means for wavelength multiplexing optical signals output from the N polarization control means,
Between the optical transmission line and the N optical receivers, wavelength separation means for wavelength-separating the optical signal combined by the wavelength multiplexing means, and optical signals separated into the respective wavelengths, respectively. N light distribution means for distributing the light in two directions are provided,
N optical receivers are connected to one path of the N optical distribution means, respectively, and N PMD measurement means are provided to the other path, respectively.
The optical signals having different wavelengths transmitted from the N optical transmitters pass through the N polarization control units, and then are multiplexed by the wavelength multiplexing unit and transmitted to the optical transmission line. ,
The optical signal propagated through the optical transmission line is separated into each wavelength by the wavelength separation means,
The optical signals of each wavelength are distributed to two paths by the N light distributing means,
The optical signal of one path is received by each of the N optical receivers, and the optical signal of the other path is input to each of the N PMD measuring means,
The PMD measurement means includes means for notifying the control means of the measured PMD information,
The control means includes means for controlling the N polarization control means to change the state of incident polarization to the optical transmission line when the notified PMD information exceeds a threshold value. An optical transmission system characterized by In an optical transmission system comprising N optical transmitters for transmitting optical signals, an optical transmission path for transmitting optical signals, and N optical receivers for receiving optical signals,
Between the N optical transmitters and the optical transmission line, there are N polarization control means connected in series to the N optical transmitters, and the N polarization control means. Control means for controlling each, and wavelength multiplexing means for wavelength multiplexing optical signals output from the N polarization control means,
Between the optical transmission line and the N optical receivers, wavelength separation means for wavelength-separating the optical signal combined by the wavelength multiplexing means, and optical signals separated into the respective wavelengths, respectively. N light distribution means for distributing the light in two directions are provided,
N optical receivers are connected to one path of the N optical distribution means, and an optical switching means is provided to the other path.
PMD measuring means to which the output of this light switching means is input is provided,
The optical signals having different wavelengths transmitted from the N optical transmitters pass through the N polarization control units, and then are multiplexed by the wavelength multiplexing unit and transmitted to the optical transmission line. ,
The optical signal propagated through the optical transmission line is separated into each wavelength by the wavelength separation means,
The optical signals of each wavelength are distributed to two paths by the N light distributing means,
The optical signal of one path is received by each of the N optical receivers, the optical signal of the other path is input to the optical switching unit, and the optical signal selected by the optical switching unit is Input to the PMD measuring means,
The PMD measuring means includes means for notifying the control means of measured PMD information,
The control means includes means for controlling the N polarization control means to change the state of incident polarization to the optical transmission line when the notified PMD information exceeds a threshold value. An optical transmission system characterized by In an optical transmission system comprising N optical transmitters for transmitting optical signals, an optical transmission path for transmitting optical signals, and N optical receivers for receiving optical signals,
Between the N optical transmitters and the optical transmission line, there are N polarization control means connected in series to the N optical transmitters, and the N polarization control means. Control means for controlling each, and wavelength multiplexing means for wavelength multiplexing optical signals output from the N polarization control means,
Between the optical transmission line and the N optical receivers, there is provided an optical distribution unit that distributes the optical signal combined by the wavelength combining unit into two paths,
One path of this light distribution means is provided with wavelength separation means for separating the combined optical signal into each wavelength,
On the other path of the optical distribution means, there is a variable wavelength selection means for selecting and outputting an optical signal having one wavelength from the combined optical signals, and an optical signal having a wavelength selected by the variable wavelength selection means. PMD measuring means for input is provided,
The optical signals having different wavelengths transmitted from the N optical transmitters pass through the N polarization control units, and then are multiplexed by the wavelength multiplexing unit and transmitted to the optical transmission line. ,
The optical signal propagated through the optical transmission path is distributed into two paths by the optical distribution means, and the optical signal in one of the paths is separated into each wavelength by the wavelength separation means, so that N optical reception signals are received. Each of the optical signals in the other direction is selected by the variable wavelength selection means and input to the PMD measurement means.
The PMD measuring means includes means for notifying the control means of measured PMD information,
The control means includes means for controlling the N polarization control means to change the state of incident polarization to the optical transmission line when the notified PMD information exceeds a threshold value. An optical transmission system characterized by The PMD measurement means includes means for notifying the control means of measured PMD information,
The optical receiver comprises means for notifying the control means of detected error rate information;
When the notified error rate information exceeds a threshold value determined for the error rate and the notified PMD information exceeds a threshold value determined for PMD, the control means controls the polarization control means. 30. The optical transmission system according to claim 27, further comprising means for controlling and changing a polarization state of incident light on the optical transmission line. In an optical transmission system comprising N optical transmitters for transmitting optical signals, an optical transmission path for transmitting optical signals, and N optical receivers for receiving optical signals,
Between the N optical transmitters and the optical transmission line, wavelength multiplexing means for wavelength multiplexing optical signals of the N optical transmitters, and light combined by the wavelength multiplexing means A polarization control means for controlling the polarization of the signal, and a control means for controlling the polarization control means,
Between the optical transmission line and the N optical receivers, wavelength separation means for wavelength-separating the optical signal multiplexed by the wavelength multiplexing means is provided,
The optical signals having different wavelengths transmitted from the N optical transmitters are combined by the wavelength combining unit and then transmitted to the optical transmission path through the polarization control unit,
The optical signal propagated through the optical transmission line is separated into each wavelength by the wavelength separation means,
The optical signals of each wavelength are received by the N optical receivers,
N optical receivers are:
Means for detecting an error rate of each of the optical signals;
Means for notifying the control means of the error rate information respectively detected by the means for detecting,
The control means includes means for controlling the polarization control means to change the state of incident polarization to the optical transmission line when the notified error rate information exceeds a threshold value. Optical transmission system. In an optical transmission system comprising N optical transmitters for transmitting optical signals, an optical transmission path for transmitting optical signals, and N optical receivers for receiving optical signals,
Between the N optical transmitters and the optical transmission line, wavelength multiplexing means for wavelength multiplexing optical signals of the N optical transmitters, and light combined by the wavelength multiplexing means A polarization control means for controlling the polarization of the signal, and a control means for controlling the polarization control means,
Between the optical transmission line and the N optical receivers, wavelength separation means for wavelength-separating the optical signal multiplexed by the wavelength multiplexing means, and each wavelength wavelength-separated by the wavelength separation means N optical distribution means for distributing each of the optical signals to two paths, respectively,
N optical receivers are connected to one path of the N optical distribution means, respectively, and N PMD measurement means are provided to the other path, respectively.
Optical signals having different wavelengths transmitted from N optical transmitters are multiplexed by the wavelength multiplexing unit and transmitted to the optical transmission line after passing through the polarization control unit,
The optical signal propagated through the optical transmission line is separated into each wavelength by the wavelength separation means,
The optical signal of each wavelength is distributed to two paths by N optical distribution means,
The optical signal of one path is received by each of the N optical receivers, and the optical signal of the other path is input to each of the N PMD measuring means,
The N PMD measuring means include means for notifying the control means of the measured PMD information,
The control means includes means for controlling the polarization control means to change the incident polarization state to the optical transmission line when the notified PMD information exceeds a threshold value. Optical transmission system. In an optical transmission system comprising N optical transmitters for transmitting optical signals, an optical transmission path for transmitting optical signals, and N optical receivers for receiving optical signals,
Between the N optical transmitters and the optical transmission line, wavelength multiplexing means for wavelength multiplexing optical signals of the N optical transmitters, and light combined by the wavelength multiplexing means A polarization control means for controlling the polarization of the signal, and a control means for controlling the polarization control means,
Between the optical transmission line and the N optical receivers, wavelength separation means for wavelength-separating the optical signal multiplexed by the wavelength multiplexing means, and each wavelength wavelength-separated by the wavelength separation means N optical distribution means for distributing each of the optical signals to two paths, respectively,
N optical receivers are connected to one path of the N optical distribution means, and an optical switching means is provided to the other path.
PMD measuring means is provided which takes the output of this light switching means as input,
Optical signals having different wavelengths transmitted from N optical transmitters are multiplexed by the wavelength multiplexing unit and transmitted to the optical transmission line after passing through the polarization control unit,
The optical signal propagated through the optical transmission line is separated into each wavelength by the wavelength separation means,
The optical signal of each wavelength is distributed to two paths by N optical distribution means,
The optical signal of one path is received by each of the N optical receivers, the optical signal of the other path is input to the optical switching unit, and the optical switching unit transmits the selected optical signal to the optical switching unit. Input to PMD measuring means,
The PMD measuring means includes means for notifying the control means of measured PMD information,
The control means includes means for controlling the polarization control means to change the incident polarization state to the optical transmission line when the notified PMD information exceeds a threshold value. Optical transmission system. In an optical transmission system comprising N optical transmitters for transmitting optical signals, an optical transmission path for transmitting optical signals, and N optical receivers for receiving optical signals,
Between the N optical transmitters and the optical transmission line, wavelength multiplexing means for wavelength multiplexing optical signals of the N optical transmitters, and light combined by the wavelength multiplexing means A polarization control means for controlling the polarization of the signal, and a control means for controlling the polarization control means,
Between the optical transmission line and the N optical receivers, there is provided an optical distribution unit that distributes the optical signal combined by the wavelength combining unit into two paths,
One path of this light distribution means is provided with wavelength separation means for separating the combined optical signal into each wavelength,
On the other path of the optical distribution means, there is a variable wavelength selection means for selecting and outputting an optical signal having one wavelength from the combined optical signals, and an optical signal having a wavelength selected by the variable wavelength selection means. PMD measuring means for input is provided,
Optical signals having different wavelengths transmitted from the N optical transmitters are multiplexed by the wavelength multiplexing unit and transmitted to the optical transmission line after passing through the polarization control unit,
The optical signal propagated through the optical transmission path is distributed into two paths by the optical distribution means, and the optical signal of one path is separated into each wavelength by the wavelength separation means,
The optical signals of the respective wavelengths are respectively received by the N optical receivers, the optical signals of the other directions are input to the variable wavelength selection unit, and the optical signal of the selected wavelength is the PMD measurement unit. Entered in
The PMD measuring means includes means for notifying the control means of measured PMD information,
The control means includes means for controlling the polarization control means to change the incident polarization state to the optical transmission line when the notified PMD information exceeds a threshold value. Optical transmission system. The PMD measurement means includes means for notifying the control means of measured PMD information,
The optical receiver comprises means for notifying the control means of detected error rate information;
When the notified error rate information exceeds a threshold value determined for the error rate and the notified PMD information exceeds a threshold value determined for PMD, the control means controls the polarization control means. The optical transmission system according to any one of claims 32 to 34, further comprising means for controlling and changing a polarization state of incident light on the optical transmission line.   36. The optical transmission system according to any one of claims 24, 25, 27, 28, 29, 30, 32, 33, 34, and 35, wherein the PMD measurement unit includes a DOP measurement unit.   The PMD measurement unit includes a photoelectric conversion unit that converts an optical signal into an electric signal, and a specific frequency intensity measurement unit that is connected in series with the photoelectric conversion unit, 24, 25, 27, 28, 29, The optical transmission system according to any one of 30, 32, 33, 34, and 35. N wavelength dispersion compensation means for inputting optical signals of respective wavelengths separated by the wavelength separation means and compensating for the chromatic dispersion,
The PMD measuring means includes
Means for separating and extracting at least two different frequency components of the optical spectral components of the optical signal;
Phase comparison means for detecting a relative phase difference between the components extracted by the extraction means;
Chromatic dispersion measuring means for calculating the amount of chromatic dispersion that the optical signal suffered in the optical transmission path based on the relative phase difference information obtained from the phase comparison means;
Intensity measuring means for measuring the intensity of at least one of the optical spectrum components extracted by the extracting means and setting the measurement result as a PMD measurement result; and
The chromatic dispersion compensating means includes means for compensating chromatic dispersion of the optical transmission line based on a measurement result of the chromatic dispersion measuring means. 24, 25, 27, 28, 29, 30, 32, 33, 34 35. The optical transmission system according to any one of the above. The optical transmitter and the optical receiver each include error correction means,
The means for detecting the error rate comprises means for detecting the number of errors by the error correction means,
The means for notifying comprises means for using information on the number of errors detected by the means for detecting as error rate information notified to the control means. Any one of claims 23, 25, 26, 30, 31, and 35 The optical transmission system described in 1.   40. The means for notifying comprises means for mounting the error rate information or the PMD information in a BDI signal or a BEI signal when notifying the error rate information or the PMD information to the control means. An optical transmission system according to any one of the above.   24. A means for changing three polarization states each having an angle of 90 degrees formed on the Poincare sphere when the incident polarization to the optical fiber is changed in the polarization control means. Or an optical transmission system according to any one of 40 to 40. The control means includes
When changing the incident polarization to the optical fiber constituting the optical transmission line by the polarization control means, set the angle on the Poincare sphere to be changed in one control unit,
If the error rate or PMD detected on the receiving side increases due to the change in incident polarization, the incident polarization is controlled in the opposite direction to the previous setting, and the error rate detected on the receiving side due to the change in incident polarization. The optical transmission system according to any one of claims 23 to 41, further comprising means for repeatedly executing a procedure for controlling incident polarization in the same direction as the previous setting when PMD decreases.   The control means ends the control operation for changing the incident polarization to the optical fiber constituting the optical transmission line by the polarization control means when the error rate or PMD detected on the receiving side is minimized. 43. The optical transmission system according to claim 23, further comprising means for   In the control means, the error rate or PMD detected on the receiving side is lower than the control end threshold when the polarization control means changes the incident polarization to the optical fiber constituting the optical transmission line. 43. The optical transmission system according to any one of claims 23 to 42, comprising means for terminating at a time.

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