JP2008312071A - Optical communication device and optical communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compensate dispersion in an optical fiber transmission path of upward and downward signals on an optical communication device side at one end according to the distance of the optical fiber between optical communication devices on both end sides. <P>SOLUTION: The optical communication device has: a light receiving unit 24 for converting an input light signal to a reception electric signal; a waveform monitor circuit 25 for monitoring the waveform of the reception electric signal; a first dispersion compensator 26 for reception equalizing the reception electric signal; a second dispersion compensator 21 for transmission operating the transmission electric signal; a light source 22 converting the transmission electric signal to the light signal for outputting to the optical fiber transmission path 60; and a controller 27 for controlling the first and second compensators 26, 21, based on an observation result by the waveform monitor circuit 25. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical communication apparatus and an optical communication system that compensate for deterioration due to high-speed optical signal dispersion.

  Currently, with the spread of the Internet, access networks are required to achieve further speedup using economical means. In view of this, an optical communication system such as a PON (Passive Optical Network) system is being introduced that utilizes the broadband property of an optical fiber to share the optical fiber with a plurality of users, thereby achieving economy. In such an optical communication system, the transmission rate per user can be increased by increasing the transmission rate of an optical transceiver that inputs and outputs optical signals.

  However, when the transmission speed of the optical signal increases, the problem that the optical signal after being transmitted through the optical fiber is deteriorated due to the dispersion of the optical fiber (wavelength dispersion or polarization mode dispersion) is generally reported by Non-Patent Document 1 or the like. Are known.

  Therefore, many means have been studied so far in order to restore the waveform deteriorated by dispersion to the original waveform. Conventionally, it has been common to use a dispersion compensating fiber having a characteristic opposite to the dispersion characteristic of the optical fiber transmission line, or a dispersion shifted fiber having a zero dispersion wavelength shifted so that the dispersion becomes zero at the wavelength of the optical signal. there were.

  However, the method using these optical components is expensive and the network design is complicated. Therefore, a dispersion compensator (Electronic Dispersion Compensator: EDC) using an electric circuit as a means for performing dispersion compensation using an economical means by automatically changing the compensation dispersion amount for optical fiber transmission lines of different distances. ) As this dispersion compensator is, as disclosed in Non-Patent Document 2, a method using a transversal filter type feedforward equalizer (FFE) or a decision feedback equalizer (DFE) is generally used.

FIG. 6 shows a configuration example of a conventional optical communication system using this method. The optical communication system includes a remote node 10 which is one of the optical communication apparatus, the center node 0 is the other optical communication apparatus, an optical fiber transmission line 601,60 ₂ connected between them.

Center node 20 includes an optical transmitter 29 for outputting a downlink optical signal to the optical fiber transmission line 60 _2, and the light receiver 24 which converts the upstream optical signal input from the optical fiber transmission path 60 ₁ on the upstream electrical signal, upstream A waveform monitor circuit 25 that monitors the electrical signal, a dispersion compensator 26 that equalizes the upstream electrical signal, and a controller 27 that controls the dispersion compensator 26 are provided. Remote node 10 includes an optical transmitter 13 for outputting upstream optical signal to the optical fiber transmission line 60 _1, and the light receiver 1 for converting the downstream optical signals inputted from the optical fiber transmission line 60 ₂ to downstream electric signals, downlink A waveform monitor circuit 17 that monitors the electrical signal, a dispersion compensator 18 that equalizes the downstream electrical signal, and a controller 19 that controls the dispersion compensator 18 are provided.

In this configuration, the present optical communication system operates as follows. The downstream electrical signal input to the center node 20 is converted into a downstream optical signal by the optical transmitter 29 and output to the optical fiber transmission line 602. Downstream optical signal transmitted through the optical fiber transmission line 60 ₂ is deteriorated under the influence of dispersion, it is input to the remote node 10. The downstream optical signal input to the remote node 10 is converted into a downstream electrical signal by the light receiver 16 and input to the dispersion compensator 18. The downstream electrical signal equalized by the dispersion compensator 18 is monitored by the waveform monitor circuit 17, the controller 19 transmits the control signal a to the dispersion compensator 18, and the dispersion compensator 18 converts the downstream electrical signal. Equalize so that the waveform is equivalent to the waveform not affected by dispersion.

Upstream electric signals inputted to the remote node 10 in the same manner is converted into the upstream optical signal by the optical transmitter 13 is output to the optical fiber transmission line 60 _1. Upstream optical signal transmitted through the optical fiber transmission line 60 ₁ is deteriorated under the influence of dispersion, is input to the center node 20. The upstream optical signal input to the center node 20 is converted into an upstream electrical signal by the light receiver 24 and input to the dispersion compensator 26. The upstream electrical signal equalized by the dispersion compensator 26 is monitored by the waveform monitor circuit 25, the controller 27 transmits the control signal b to the dispersion compensator 26, and the dispersion compensator 26 disperses the upstream electrical signal. So that the waveform is equivalent to the waveform that is not affected by.

  There is also a means called predistortion in which a dispersion compensator is arranged on the transmission side. As seen in Non-Patent Document 3, this is a method in which the waveform is intentionally deteriorated in advance on the transmission side so that the waveform after transmission through the optical fiber is the same as the waveform transmitted without being subjected to dispersion.

FIG. 7 shows a configuration example of a conventional optical communication system using this method. The center node 20, a dispersion compensator 21 to predistortion a downstream electric signal inputted, the inputted light source 22 to convert the downstream electric signal predistortion downstream optical signal from the optical fiber transmission line 60 ₁ up An optical receiver 30 for receiving an optical signal is provided. Remote node 10, a dispersion compensator 14 to predistortion an upstream electric signal which is input, is input to the light source 15 to convert the upstream electric signal predistortion upstream optical signal from the optical fiber transmission path 60 ₂ downlink And an optical receiver 12 for receiving an optical signal.

In this configuration, the present optical communication system operates as follows. Downstream electric signal inputted to the center node 20 receives the waveform deterioration at the dispersion compensator 21 at the light source 22 is converted into downstream optical signals, and output to the optical fiber transmission line 60 _2. Downstream optical signal transmitted through the optical fiber transmission line 60 ₂ is influenced by the dispersion is input to the remote node 10. The downstream optical signal input to the remote node 10 cancels the waveform degradation caused by the dispersion compensator 21 and the waveform degradation due to the influence of dispersion, and returns to a waveform state equivalent to the waveform not affected by the dispersion. Received by the receiver 12.

Upstream electric signal inputted to the remote node 10 receives the waveform deterioration at the dispersion compensator 14, is converted into the upstream optical signal by the light source 15 is output to the optical fiber transmission line 60 _1. Upstream optical signal transmitted through the optical fiber transmission line 60 ₁ is influenced by dispersion is input to the center node 20. The upstream optical signal input to the center node 20 cancels the waveform deterioration received by the dispersion compensator 14 and the waveform deterioration due to the influence of dispersion, and returns to a waveform state equivalent to the waveform not affected by the dispersion. Received by the receiver 30.

  In this method, in order to automatically set the compensation dispersion amount, the waveform on the receiving side optical receivers 12 and 30 is monitored and fed back to the controllers of the dispersion compensators 21 and 14 on the transmitting side. Means are needed.

Govind P. Agrawal "Fiber-Optic Commnication Systems", Jobn Wiley & Sons, INC. Ali Ghiasi et al., "Experimental Results of EDC Based Receivers for 2400 ps / nm at lO.7Gb / s for Emerging Te1ecom Standards", OFC2006, 0TuE3,2006. R.I.Li11ey et al., "Electronic dispersion compensation by signal predistortion", OFC2006, OWB3, 2006.

  As described above, dispersion compensation by an electric circuit is more economical than dispersion compensation using an optical fiber such as a dispersion compensation fiber or dispersion shift fiber, and the setting of the compensation dispersion amount is simplified. However, the method of disposing the dispersion compensator on the receiver side or the transmission side has a problem that a controller is required at both end nodes, resulting in high costs. Further, the method of arranging the dispersion compensator in FIG. 7 on the transmission side has a problem that means for feeding back the waveform state on the reception side to the transmission side is required.

  In view of the above points, the object of the present invention is to use an economical means to distribute the upstream and downstream optical fiber transmission paths on one end of the optical communication apparatus side and on the both ends of the optical communication apparatus. An object of the present invention is to provide an optical communication apparatus and an optical communication system that can compensate according to the distance between optical fibers.

In order to achieve the above object, an invention according to claim 1 is an optical communication device connected to one end of an optical fiber transmission line, and converts a received optical signal received from the optical fiber transmission line into a received electrical signal. In the optical communication device that communicates with the device on the other end of the optical fiber transmission line by converting the transmission electrical signal into a transmission optical signal and sending it to the optical fiber transmission line, the received light A photoreceiver that converts a signal into the received electrical signal, a waveform monitor circuit that monitors a waveform of the received electrical signal, a first dispersion compensator for reception that equalizes the received electrical signal, and the transmitted electrical signal A second dispersion compensator for transmission that operates, a light source that converts the transmission electrical signal into the transmission optical signal and sends it to the optical fiber transmission line, the first dispersion compensator, and the first dispersion compensator Dispersion compensation The characterized in that it comprises a controller for controlling, based on the observation results of the waveform monitoring circuit.
According to a second aspect of the present invention, in the optical communication apparatus according to the first aspect, the controller estimates the dispersion amount of the optical fiber transmission line from the waveform of the received electrical signal observed by the waveform monitor circuit. Then, the first dispersion compensator is controlled to equalize the received electrical signal deteriorated due to dispersion.
The invention according to claim 3 is the optical communication device according to claim 2, wherein the controller controls the second dispersion compensator based on the estimated dispersion amount, and The transmission electric signal that can be normally received by the apparatus is generated.
According to a fourth aspect of the present invention, in the optical communication apparatus according to the third aspect, the controller has information for associating the dispersion amount with the set values of the dispersion compensators for transmission and reception. And
In the invention according to claim 5, the first optical communication device and the second optical communication device are connected one-to-one via an optical fiber transmission line, and communicate using an optical signal having a predetermined wavelength. In the communication system, one of the first and second optical communication devices includes the optical communication device according to any one of claims 1 to 4.
According to a sixth aspect of the present invention, a first optical communication device and a plurality of second optical communication devices are connected in a star shape via an optical multiplexer / demultiplexer and an optical fiber transmission line, and each of the second communication devices 5. In an optical communication system in which an apparatus communicates with the first optical communication apparatus using a wavelength assigned to each apparatus, each of the second optical communication apparatuses is according to claim 1. It is characterized by comprising an optical communication device.
According to a seventh aspect of the present invention, a first optical communication device and a plurality of second optical communication devices are connected in a star shape via an optical multiplexer / demultiplexer and an optical fiber transmission line, and each of the second communication In the optical communication system in which the apparatuses communicate with the first optical communication apparatus using wavelengths assigned to the respective apparatuses, the number of the first optical communication apparatuses is the same as the number of the second optical communication apparatuses. 4. The optical communication device according to any one of 4 is provided.

  According to the present invention, by using economical means, the dispersion of the optical fiber transmission path of the upstream signal and the downstream signal is set to the distance of the optical fiber between the optical communication devices at both ends on the one end optical communication device side. Accordingly, it is possible to compensate for this. In the conventional method, a controller is required for the optical communication device at both ends. However, according to the present invention, by arranging the dispersion compensator and the controller only in the optical communication device at one end, both the upstream signal and the downstream signal can be obtained. Dispersion compensation can be realized. Further, the feedback means from the reception side to the transmission side, which is necessary in the conventional predistortion method, can be eliminated.

<First embodiment>
FIG. 1 shows an optical communication system according to a first embodiment of the present invention. In the optical communication system of the present embodiment, one remote node 10 which is one optical communication device, one center node 20 which is the other optical communication device, and the remote node 10 and the center node 20 are connected by one core. And an optical fiber transmission line 60. Here, a signal transmitted from the center node 20 to the remote node 10 is referred to as a “downstream signal”, and a signal transmitted from the remote node 10 to the center node 20 is referred to as an “upstream signal”.

  The center node 20 includes a dispersion compensator 21 for a downstream signal that predistorts an input downstream electrical signal, a single light source 22 that converts the predistorted downstream electrical signal into a downstream optical signal, a downstream optical signal, and an upstream optical signal. One wavelength filter 23 that multiplexes and demultiplexes the optical signal, one light receiver 24 that converts the upstream optical signal degraded by dispersion into an upstream electrical signal, and one waveform monitor circuit 25 that monitors the waveform of the upstream electrical signal, , One upstream signal dispersion compensator 26 for equalizing the waveform of the upstream electrical signal, the compensation dispersion amount is calculated from the waveform monitor circuit 25, and the upstream signal dispersion compensator 21 and the downstream signal dispersion compensator And a single controller 27 for controlling 26 to the optimum compensation dispersion amount.

  Here, “predistortion” means that even if the downstream optical signal is affected by the dispersion of the optical fiber transmission line 60, the remote node 10 can receive it as a waveform equivalent to the waveform not affected by the dispersion. It means that the signal waveform is deteriorated in advance.

  The remote node 10 includes a filter 11 that multiplexes and demultiplexes a downstream optical signal and an upstream optical signal, an upstream optical signal transmitter 13, and a downstream optical receiver 12. The light source for the upstream optical signal and downstream optical signal used in the remote node 10 and the center node 20 may use an external modulator and a semiconductor laser. However, in order to reduce costs, the amount of current injected into the semiconductor laser is reduced. In many cases, a direct modulation type semiconductor laser that generates a transmission optical signal by using a change is used.

  The dispersion compensators 21 and 26 are configured by an electric circuit capable of returning a waveform deteriorated due to dispersion in the optical fiber transmission line 60 to a waveform equivalent to a waveform not subjected to dispersion. As the dispersion compensators 21 and 26, for example, the Maximum Likelihood Sequence Estimation (MLSE) method (Document A: M. Rubsamen et al., “MLSE Receivers for Narrow-band Optical Filtering”, OFC 2006, OWB 6, 2006.) A feedforward equalizer (FFE) including a transversal filter, a decision feedback equalizer (DFE) (Non-Patent Document 2), and the like are well known. FFE and DFE can change the compensation dispersion amount by changing their tap coefficients, and are often used in general. The dispersion to be compensated here refers to either or both of chromatic dispersion and polarization mode dispersion (PMD).

  In such a configuration, the optical communication system operates as follows. The upstream optical signal output from the remote node 10 is transmitted through the optical fiber transmission line 60, undergoes waveform deterioration due to dispersion, and then converted into an upstream electrical signal by the light receiver 24 of the center node 10. The upstream electrical signal is branched, and one is input to the waveform monitor circuit 25. The other of the branched upstream electrical signals is input to the dispersion compensator 26 for upstream signals.

  The controller 27 monitors the upstream electrical signal input to the waveform monitor circuit 25, obtains a dispersion amount to be compensated based on the upstream electrical signal, and corresponds to the dispersion compensators 21 and 26 for downstream signals and upstream signals corresponding thereto. Can be calculated. This is because the center node 20 and the remote node 11 communicate with each other through a single optical fiber transmission line 60, and the upstream optical signal and the downstream optical signal are transmitted through the same distance. This is because the compensation dispersion amount of the signal can be obtained.

  Based on the monitoring result of the waveform monitor circuit 25, the controller 27 transmits dispersion setting values corresponding to the dispersion amounts to be compensated to the dispersion compensators 21 and 26 for the upstream signal and downstream signal as control signals A and B. . As a method for determining the dispersion setting value, the controller 27 has a correspondence table between the compensation dispersion amount and the dispersion setting value, and obtains the dispersion setting value based on the correspondence table. That is, since the waveform monitor circuit 25 can measure the waveform degradation amount β indicating that the eye opening is reduced due to dispersion, the waveform degradation amount β measured here and the waveform degradation amount created in advance by actual measurement or the like The transmission distance is estimated from the correspondence with the transmission distance, the dispersion compensation amount is calculated from the estimated distance, and the dispersion setting value is determined based on the dispersion compensation amount.

  The dispersion compensator 26 for the upstream signal sets a dispersion setting value based on the control signal A from the controller 27, equalizes and outputs the upstream electrical signal degraded by the dispersion. The dispersion compensator 21 for downstream signals sets a dispersion set value based on the control signal B from the controller 27, and transmits the optical fiber transmission line 60 to correct the amount deteriorated by dispersion before transmission. Predistort and output.

  The predistorted downstream electrical signal is converted into a downstream optical signal by the light source 22, output to the optical fiber transmission line 60, and received by the optical receiver 12 in the remote node 10. The downstream optical signal received by the optical receiver 12 is received as a waveform equivalent to a waveform that is not affected by the dispersion because the predistortion and the dispersion of the optical fiber transmission line 60 cancel each other. Accordingly, there is no need for means for dispersion compensation at the nodes at both ends, and dispersion compensation for both upstream and downstream signals can be automatically performed only by the center node 20 according to the distance of the optical fiber transmission line 60. Here, although the optical fiber transmission line 60 is a single-core optical fiber, as long as the transmission distance is the same, the optical fiber for upstream optical signal and the optical fiber for downstream optical signal may use a two-core optical fiber.

  With the above configuration, using an economical means, the dispersion of the optical fiber transmission line 60 for the upstream signal and the downstream signal is distributed between the center node 20 and each remote node 10 on the node 20 side. It becomes possible to compensate according to the distance of the optical fiber transmission line 60.

<Second embodiment>
FIG. 2 shows a second embodiment of the present invention. The optical communication system of the present embodiment includes one center node 20 that is one optical communication device, one wavelength splitter 40, a plurality of remote nodes 10 ₁ to 10 _n that are the other optical communication devices, and a center node. 20 and a single optical fiber transmission line 60 to a wavelength splitter 40 connects with one core, a plurality of optical fiber transmission lines ₅₀ 1 - connecting the wavelength splitter 40 and a plurality of remote nodes ₁₀ 1 to 10 _n by one core 50 _n . Here, "down signal" a signal transmitted from the center node 20 to Rimotodo ₁₀ 1 to 10 _n, the signal transmitted from the remote node ₁₀ 1 to 10 _n to the center node 20 and "upstream signal".

The center node 20 includes dispersion compensators 21 _{1 to} 21 _n for downstream signals that predistort the input downstream electrical signals, and a plurality of light sources 22 _{1 to} 22 that convert the predistorted downstream electrical signals into downstream optical signals. _n , one wavelength filter 23 that multiplexes and demultiplexes the downstream optical signal and the upstream optical signal, a plurality of light receivers 24 _{1 to} 24 _n that convert the upstream optical signal deteriorated due to dispersion into an upstream electrical signal, and the upstream electrical signal A plurality of waveform monitor circuits 25 _{1 to} 25 _n for monitoring the waveforms of the signals, a plurality of upstream signal dispersion compensators 26 _{1 to} 26 _n for equalizing the waveforms of the upstream electrical signals, and waveform monitor circuits 25 _{1 to} 25 _n. the monitoring result by the calculated compensation amount of dispersion, the optimal compensation amount of dispersion dispersion compensator 26 ₁ ~ 26 _n for the dispersion compensator 21 ₁ through 21 _n and the downlink signal for the uplink signal And a plurality of controllers ₂₇ 1 ~ 27 _n for controlling, differs from the WDM filter 28 ₁ wavelength multiplexing output downstream optical signal at a wavelength, and a WDM filter 28 ₂ for demultiplexing upstream optical signal wavelength-multiplexed .

Here, “predistortion” means that even if the downstream optical signal is affected by the dispersion of the optical fiber transmission lines 60 and 50 ₁ to 50 _n , the remote nodes 10 ₁ to 10 _n are not affected by the dispersion. It means deteriorating the signal waveform so that it can be received as a waveform equivalent to the waveform.

Each of the remote nodes 10 ₁ to 10 _n includes wavelength filters 11 _{1 to} 11 _n that multiplex and demultiplex an upstream optical signal and a downstream optical signal, optical receivers 12 _{1 to} 12 _n for downstream optical signals, and an upstream optical signal, respectively. Optical transmitters 13 _{1 to} 13 _n . The optical transmitters 13 _{1 to} 13 _n for upstream optical signals output optical signals having different wavelengths. Others are the same as the first embodiment.

In such a configuration, the optical communication system operates as follows. The upstream optical signals having different wavelengths output from the optical transmitters 13 _{1 to} 13 _{n of the} remote nodes 10 ₁ to 10 _n are transmitted through the optical fiber transmission lines 50 ₁ to 50 _n, and the remote node 10 ₁ is transmitted by the wavelength splitter 40. ˜10 _n wavelength-multiplexed with other upstream optical signals, further transmitted through the optical fiber transmission line 60, and subjected to waveform degradation due to dispersion before being input to the center node 20.

The upstream optical signal input to the center node 20 is demultiplexed by the wavelength filter 23 and converted into upstream electrical signals by the light receivers 24 _{1 to} 24 _n corresponding to the remote nodes 10 ₁ to 10 _n . The upstream electrical signal is branched, and one is input to the waveform monitor circuits 25 _{1 to} 25 _n . The other of the branched upstream electrical signals is input to dispersion compensators 26 _{1 to} 26 _n for upstream signals. The controllers 25 _{1 to} 25 _n monitor the upstream electrical signals input to the waveform monitor circuits 25 _{1 to} 25 _n , obtain dispersion amounts to be compensated based on the monitoring results, and correspond to the downstream signals and upstream signals corresponding thereto. The set values of the signal dispersion compensators 21 _{1 to} 21 _n and 26 _{1 to} 26 _n can be calculated. This is because the center node 20 and the remote nodes 10 ₁ to 10 _n communicate with each other through a single optical fiber transmission line, and the upstream optical signal and the downstream optical signal are transmitted through the same distance. This is because the compensation dispersion amount of the downlink signal can be obtained.

The controllers 27 _{1 to} 27 _n compensate the dispersion compensators 26 _{1 to} 26 _n and 21 _{1 to} 21 _n for the upstream signal and the downstream signal from the monitoring results of the waveform monitor circuits 25 _{1 to} 25 _n . The dispersion setting values corresponding to the power dispersion amount are transmitted as control signals A _{1 to An} and B _{1 to} B _n . As a method for determining the dispersion setting value, the controllers 27 _{1 to} 27 _n have a correspondence table between the compensation dispersion amount and the dispersion setting value, and obtain the dispersion setting value based on the correspondence table. That is, since the amount of waveform deterioration β _{1 ~} β ₂ indicating that the eye opening is reduced by receiving dispersion the waveform monitor circuit 25 ₁ to 25 _n can be measured, the amount of waveform deterioration β _{1 ~} β ₂ as measured here from the correspondence between the transmission distance in advance the amount of waveform deterioration created by actual measurement or the like, it estimates the transmission distance L ₁ ~L _n, calculates a dispersion compensation amount d ₁ to d _n from the estimated distance, the dispersion compensation The dispersion setting value is determined based on the amount. FIG. 8 shows information stored in the controllers 27 _{1 to} 27 _n .

Set the variance set point control signals _A 1 to A _n based on the dispersion compensator ₂₆ 1 ~ 26 _n for uplink signals from the controller ₂₇ 1 ~ 27 _n, equalizes the upstream electric signals deteriorated by dispersion Output. The dispersion compensators 21 _{1 to} 21 _n for downstream signals set dispersion set values based on the control signals B _{1 to} B _n from the controllers 27 _{1 to} 27 _n , and the optical fiber transmission lines 60 and 50 ₁ to 50 _n are set. _n is transmitted and predistorted before transmission so as to correct the amount of deterioration caused by dispersion.

The predistorted downstream electric signal is converted into a downstream optical signal by the light sources 22 _{1 to} 22 _n . Downstream optical signals having different wavelengths corresponding to the remote nodes 10 ₁ to 10 _n are wavelength-multiplexed by the WDM filter 28 ₁ and output to the optical fiber transmission line 60. The wavelength-multiplexed downstream optical signal transmitted through the optical fiber transmission line 60 is demultiplexed by the wavelength splitter 40, and only downstream optical signals having wavelengths corresponding to the remote nodes 10 ₁ to 10 _n are remote nodes 10 ₁ to 10. optical receiver in _{n 12} is input to the 1 to 12 _n. The downstream optical signal input to the optical receivers 12 _{1 to} 12 _n has a waveform equivalent to a waveform that is not affected by the dispersion because the predistortion and the dispersion of the optical fiber transmission lines 60 and 50 ₁ to 50 _n cancel each other. Received.

Accordingly, there is no need for means for dispersion compensation at the nodes at both ends, and dispersion compensation for both upstream and downstream signals is automatically possible at the node 20 at one end. Here, although the optical fiber transmission lines 60 and 50 ₁ to 50 _n are single-core optical fibers, if the transmission distance is the same, the optical fibers for the upstream optical signal and the downstream optical signal are two optical fibers. May be used.

With the configuration as described above, the distribution of the optical fiber transmission lines 50 ₁ to 50 _n and 60 for the upstream signal and the downstream signal is distributed between the center node 20 and the node 20 on one end using economical means. it is possible to compensate in accordance with the distance of the optical fiber transmission line 60, 50 ₁ to 50 _n between the remote nodes ₁₀ 1 to 10 _n.

<Third embodiment>
FIG. 3 shows a third embodiment of the present invention. The optical communication system of the present embodiment uses an optical power splitter (optical distributor) 40A instead of the wavelength splitter 40 in the second embodiment.

<Fourth embodiment>
FIG. 4 shows a fourth embodiment of the present invention. The optical communication system of this embodiment includes one center node 20 that is one optical communication device, one wavelength splitter 40, a plurality of remote nodes 10 ₁ to 10 _n that are the other optical communication devices, and a center node. 20 and the wavelength splitter 40 with one optical fiber transmission line 60, and the wavelength splitter 40 and the plurality of remote nodes 10 ₁ to 10 _n with one optical fiber transmission line 50 ₁ to 50. 50 _n . Here, a signal transmitted from the center node 20 to the remote nodes 10 ₁ to 10 _{n is referred} to as a “downstream signal”, and a signal transmitted from the remote nodes 10 ₁ to 10 _n to the center node 20 is referred to as an “upstream signal”.

The remote nodes 10 ₁ to 10 _n include upstream signal dispersion compensators 14 _{1 to} 14 _n that predistort the input upstream electrical signal, and a light source 15 ₁ that converts the predistorted upstream electrical signal into an upstream optical signal. ˜15 _n , wavelength filters 11 _{1 to} 11 _n for multiplexing and demultiplexing upstream optical signals and downstream optical signals, and light receivers 16 _{1 to} 16 _n for converting downstream optical signals degraded by wavelength dispersion into downstream electrical signals, From waveform monitor circuits 17 _{1 to} 17 _n that monitor the waveform of the downstream electrical signal, dispersion compensators 18 ₁ to 18 _n for downstream signals that equalize the waveform of the downstream electrical signal, and waveform monitor circuits 17 _{1 to} 17 _n A controller 19 _{1 that} calculates the compensation dispersion amount and controls the dispersion compensators 18 ₁ to 18 _n for the downlink signal and the dispersion compensators 14 _{1 to} 14 _n for the uplink signal to the optimum compensation dispersion amount. To 19 _n . Here, “predistortion” means that the signal waveform is deteriorated so that the upstream optical signal can be normally received even if it is affected by the chromatic dispersion of the optical fiber transmission lines 60 and 50 ₁ to 50 _n. .

The center node 20 includes a wavelength filter 23 that multiplexes and demultiplexes downstream optical signals and upstream optical signals, a plurality of downstream optical transmitters 29 _{1 to} 29 _n that output different wavelengths, and downstream outputs that are output at different wavelengths. a WDM filter 28 ₁ to the wavelength multiplexing optical signal, a WDM filter 28 ₂ for demultiplexing upstream optical signal wavelength-multiplexed, demultiplexed and a plurality of optical receivers ₃₀ 1 to 30 _n for receiving an upstream optical signal Is provided. In addition, the light source for the upstream optical signal and the downstream optical signal may use an external modulator and a semiconductor laser, but in order to reduce the cost, the transmission optical signal is changed by changing the amount of current injected into the semiconductor laser. Often, a direct modulation semiconductor laser is used. Others are the same as the first embodiment.

In such a configuration, the optical communication system operates as follows. The downstream optical signals having different wavelengths output from the optical transmitters 29 _{1 to} 29 _{n of the} center node 20 are wavelength-multiplexed by the WDM filter 28 ₁ and output to the optical fiber transmission line 60. The wavelength-multiplexed downstream optical signal transmitted through the optical fiber transmission line 60 is demultiplexed by the wavelength splitter 40, and the downstream optical signals having wavelengths corresponding to the remote nodes 10 ₁ to 10 _n are transmitted to the optical fiber transmission lines 50 ₁ to 50 ₁ . 50 _n is output. Downstream optical signals that have undergone waveform degradation due to wavelength dispersion are converted into downstream electrical signals by the light receivers 16 _{1 to} 16 _n of the remote nodes 10 ₁ to 10 _n . The downstream electric signal is branched, and one is input to the waveform monitor circuits 17 _{1 to} 17 _n . The other of the branched downstream electrical signals is input to dispersion compensators 18 ₁ to 18 _n for downstream signals.

The controllers 19 _{1 to} 19 _n monitor the downstream electrical signals input to the waveform monitor circuits 17 _{1 to} 17 _n , obtain the dispersion amount to be compensated based on the downstream electrical signals, and correspond to the downstream signals and upstream signals. Dispersion set values of the dispersion compensators 18 ₁ to 18 _n and 14 _{1 to} 14 _n for use can be calculated. This is because the center node 20 and the remote nodes 10 ₁ to 10 _n communicate with each other through a single-core optical fiber transmission line, and the upstream optical signal and the downstream optical signal are transmitted through the same distance, and therefore the waveform of the downstream electrical signal is monitored. This is because the compensation dispersion amount of the uplink signal can be obtained.

Based on the monitoring results of the waveform monitor circuits 17 _{1 to} 17 _n , the controllers 19 _{1 to} 19 _n are dispersions to be compensated for the dispersion compensators 14 _{1 to} 14 _n and 18 ₁ to 18 _n for the upstream signal and the downstream signal. The dispersion set values corresponding to the amounts are transmitted as control signals C _{1 to} C _n and D _{1 to} Dn. As a method for determining the dispersion setting value, the controllers 19 _{1 to} 19 _n have a correspondence table between the compensation dispersion amount and the dispersion setting value, and obtain the dispersion setting value based on the correspondence table. That is, since the amount of waveform deterioration β _{1 ~} β ₂ indicating that the eye opening is reduced by receiving dispersion the waveform monitor circuit 17 ₁ to 17 _n can be measured, the amount of waveform deterioration β _{1 ~} β ₂ as measured here from the correspondence between the transmission distance in advance the amount of waveform deterioration created by actual measurement or the like, it estimates the transmission distance L ₁ ~L _n, calculates a dispersion compensation amount d ₁ to d _n from the estimated distance, the dispersion compensation The dispersion setting value is determined based on the amount. FIG. 9 shows information stored in the controllers 19 _{1 to} 19 _n .

The dispersion compensators 18 ₁ to 18 _n for downlink signals set dispersion setting values based on the control signals C _{1 to} C _n 1 from the controllers 19 _{1 to} 19 _n , and the downlink electrical signals deteriorated due to dispersion are set. Equalize and output. The dispersion compensators 14 _{1 to} 14 _n for upstream signals set dispersion set values based on the control signals D _{1 to} Dn from the controllers 19 _{1 to} 19 _n , and the optical fiber transmission lines 50 ₁ to 50 _n and 60 is transmitted and predistorted before transmission so as to correct the amount of deterioration due to dispersion and output.

Predistorted the upstream electric signal is converted into the upstream optical signal by the light source ₁₅ 1 to 15 _n, is output to the optical fiber transmission line ₅₀ 1 to 50 _n. The upstream optical signals transmitted through the optical fiber transmission lines 50 ₁ to 50 _n are combined by the wavelength splitter 40 and output to the optical fiber transmission line 60. Upstream optical signal input from the optical fiber transmission path 60 to the center node 20, after passing through the wavelength filter 23 is demultiplexed by the WDM filter 28 _2, up having a wavelength corresponding to each remote node ₁₀ 1 to 10 _n Optical signals are input to the optical receivers 30 ₁ to 30 _n . The upstream optical signals input to the optical receivers 30 ₁ to 30 _n are received in a waveform equivalent to a waveform that is not affected by the dispersion because the predistortion and the dispersion of the optical fiber transmission line cancel each other.

Therefore, no means for dispersion compensation is required at the nodes at both ends, and dispersion compensation for both the upstream signal and the downstream signal is automatically possible at the nodes 10 ₁ to 10 _n at one end. Here, although the optical fiber transmission lines 60 and 50 ₁ to 50 _n are single-core optical fibers, if the transmission distance is the same, the optical fibers for the upstream optical signal and the downstream optical signal are two optical fibers. May be used.

With the configuration as described above, the dispersion of the optical fiber transmission lines 50 ₁ to 50 _n and 60 of the upstream signal and the downstream signal can be distributed on the node 10 ₁ to 10 _n side at one end by using economical means. Compensation can be made according to the distances of the optical fiber transmission lines 60 and 50 ₁ to 50 _n between the center node 20 and the remote nodes 10 ₁ to 10 _n .

<Fifth embodiment>
FIG. 5 shows a fifth embodiment of the present invention. The optical communication system of this embodiment uses an optical power splitter 40A instead of the wavelength splitter 40 in the fourth embodiment.

<Other embodiments>
The first to fifth embodiments described above are examples in which the present invention is applied to point-to-point type and star type networks, but an optical fiber transmission line for transmitting upstream optical signals and downstream optical signals. Can be applied to a bus-type network and a ring-type network.

It is a block diagram which shows the structure of the optical communication system of 1st Example of this invention. It is a block diagram which shows the structure of the optical communication system of the 2nd Example of this invention. It is a block diagram which shows the structure of the optical communication system of the 3rd Example of this invention. It is a block diagram which shows the structure of the optical communication system of the 4th Example of this invention. It is a block diagram which shows the structure of the optical communication system of the 5th Example of this invention. It is a block diagram which shows the structure of the conventional optical communication system. It is a block diagram which shows the structure of another conventional optical communication system. It is explanatory drawing of the information preserve | saved at the controller of the optical communication system of 2nd Example of this invention. It is explanatory drawing of the information preserve | saved at the controller of the optical communication system of the 4th Example of this invention.

Explanation of symbols

10, 10 ₁ to 10 _n : Remote node 11, 11 _{1 to} 11 _n : Wavelength filter 12, 12 _{1 to} 12 _n : Optical receiver 13, 13 _{1 to} 13 _n : Optical transmitter 14 _{1 to} 14 _n : Dispersion compensation vessel 15 ₁ to 15 _n: the light source 16 ₁ ~ 16 _n: photoreceiver 17 ₁ to 17 _n: waveform monitor circuit 18 ₁ ~ 18 _n: dispersion compensator 20: center node 21, 21 ₁ through 21 _n: dispersion compensator 22 , 22 _{1 to} 22 _n : light source 23: wavelength filter 24, 24 _{1 to} 42 _n : light receiver 25, 25 _{1 to} 25 _n : waveform monitor circuit 26, 26 _{1 to} 26 _n : dispersion compensator 27, 27 _{1 to} 27 _n: The controller _{28 1,} 28 2: WDM filter 29, 29 ₁ ~ 29 _n: an optical transmitter 30, 30 ₁ to 30 _n: an optical receiver 40: wavelength splitter 40A: light Pawasupu Jitter 50 ₁ to 50 _n: an optical fiber transmission line 60, 60 _1, 60 _2: optical fiber transmission lines

Claims (7)

An optical communication device connected to one end of an optical fiber transmission line, which converts a received optical signal received from the optical fiber transmission line into a received electrical signal and extracts it, and converts a transmitted electrical signal into a transmitted optical signal. In an optical communication device that communicates with a device on the other end of the optical fiber transmission line by sending it to the optical fiber transmission line,
A photoreceiver that converts the received optical signal into the received electrical signal; a waveform monitor circuit that monitors a waveform of the received electrical signal; a first dispersion compensator for reception that equalizes the received electrical signal; A second dispersion compensator for transmission that manipulates a transmission electric signal; a light source that converts the transmission electric signal into the transmission optical signal and sends it to the optical fiber transmission line; the first dispersion compensator; An optical communication apparatus comprising: a controller that controls the first dispersion compensator based on an observation result of the waveform monitor circuit. The optical communication device according to claim 1,
The controller estimates the amount of dispersion of the optical fiber transmission line from the waveform of the received electrical signal observed by the waveform monitor circuit, controls the first dispersion compensator, and receives the received electrical power deteriorated by dispersion. An optical communication apparatus characterized by equalizing a signal. The optical communication device according to claim 2,
The controller controls the second dispersion compensator based on the estimated dispersion amount, and generates the transmission electrical signal that can be normally received by the device on the other end side. Optical communication device. The optical communication apparatus according to claim 3.
The optical controller is characterized in that the controller has information for associating the dispersion amount with the set values of the dispersion compensators for transmission and reception. In an optical communication system in which a first optical communication device and a second optical communication device are connected one-to-one via an optical fiber transmission line and communicate using an optical signal having a predetermined wavelength.
One of said 1st and 2nd optical communication apparatuses consists of an optical communication apparatus as described in any one of Claims 1-4, The optical communication system characterized by the above-mentioned. A first optical communication device and a plurality of second optical communication devices are connected in a star shape via an optical multiplexer / demultiplexer and an optical fiber transmission line, and each of the second communication devices has a wavelength assigned to each of them. In an optical communication system that communicates with the first optical communication device using
Each said 2nd optical communication apparatus consists of an optical communication apparatus as described in any one of Claims 1-4, The optical communication system characterized by the above-mentioned. A first optical communication device and a plurality of second optical communication devices are connected in a star shape via an optical multiplexer / demultiplexer and an optical fiber transmission line, and each of the second communication devices has a wavelength assigned to each of them. In an optical communication system that communicates with the first optical communication device using
The first optical communication apparatus includes the same number of optical communication apparatuses as claimed in any one of claims 1 to 4 as the second optical communication apparatus.

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