JP5189558B2 - Optical wavelength multiplexing transmission system - Google Patents

Description

  The present invention relates to an optical wavelength multiplexing transmission system that multiplexes intensity-modulated optical signals and phase-modulated optical signals of different wavelengths to perform high-speed and large-capacity transmission.

  When the data transmission speed is about 10 Gbps or less, it is common to modulate the intensity of the optical signal with the transmission data and transmit it over the optical transmission path. For multiple series of transmission data, the intensity of the optical signals of different wavelengths is different. An optical wavelength multiplexing transmission system that modulates and multiplexes and transmits is applied. In addition, when performing high-speed transmission at a data transmission rate of about 40 Gbps, RZ-DQPSK (Return to Zero-Differential Quadrature Phase Shift Keying) method, NRZ-DPSK (Non-Return to Zero-Different Modulation method, etc.) Has been applied.

  Since the optical fiber constituting the optical transmission line has a nonlinear optical effect, waveform deterioration in the case of long-distance transmission becomes a problem. As this nonlinear optical effect, a self phase modulation effect, a mutual phase modulation effect, a four-wave mixing effect, and the like are known. The self-phase modulation effect is a phenomenon in which the refractive index of an optical fiber changes depending on the intensity of the optical signal, resulting in a phase change of the optical signal. The cross-phase modulation effect is a phenomenon in which optical signals of different wavelengths are simultaneously in the same direction. This is a phenomenon in which the intensity of one optical signal undergoes a phase change depending on the intensity of the other optical signal. The four-wave mixing effect is a phenomenon in which optical signal components corresponding to respective wavelength differences are generated when optical signals having different wavelengths are transmitted in the same direction. Both cause S / N degradation in long-distance high-speed transmission.

  Also, when an optical signal based on intensity modulation with a transmission rate of 2.5 Gbps and an optical signal based on intensity modulation of 10 Gbps are wavelength-multiplexed and transmitted, assuming that the respective transmission optical signal levels are the same, S / N deteriorates. Therefore, when the transmission light intensity is increased in order to avoid S / N degradation of a high-speed 10 Gbps optical signal, the nonlinear optical effect is increased, and the transmission characteristics of the optical signals of any transmission speed are degraded. In order to avoid such deterioration of transmission characteristics, when the transmission speed is 1: n, optical wavelength multiplexing is performed in which the transmission light intensity of the low-speed optical signal is transmitted as 1 / n of the transmission light intensity of the high-speed optical signal. There has been proposed a system for performing digitized transmission (see, for example, Patent Document 1).

Japanese Patent No. 3769172

  Conventionally, an optical signal having a data transmission rate of 10 Gbps or less constitutes an optical wavelength multiplexing transmission system to which intensity modulation and optical wavelength multiplexing are applied as described above. A transmission system that uses such a transmission system and multiplexes and transmits the above-described optical signal with a transmission rate of 40 Gbps modulated by the phase modulation method is considered. That is, a system capable of economically performing high-speed and large-capacity communication by transmitting an optical signal of 40 Gbps by a phase modulation method by wavelength multiplexing using an existing optical transmission line is considered.

  However, due to the non-linear optical effect, particularly the cross-phase modulation effect, the intensity of an optical signal having a transmission rate of 10 Gbps or less to which an intensity modulation method is applied greatly affects a 40 Gbps optical signal to which a phase modulation method is applied. However, there is a problem that the phase modulation characteristic of an optical signal having a transmission rate of 40 Gbps is greatly deteriorated, and the S / N reduction is increased. In this case, if the wavelength interval between the optical signal wavelength of 10 Gbps and the optical signal wavelength of 40 Gbps is widened, it is possible to reduce the influence of the optical signal intensity of 10 Gbps of the intensity modulation method on the optical signal of 40 Gbps of the phase modulation method. It is. However, widening the wavelength interval between the optical wavelength group assigned to the optical signal of 10 Gbps and the optical wavelength group assigned to the optical signal of 40 Gbps increases the number of unused wavelengths and effectively uses the wavelength band of the optical signal. There is a problem that makes it impossible to plan. Furthermore, it is necessary to preset the allocation of the optical signal wavelength to the 10 Gbps optical signal and the allocation of the optical signal wavelength to the 40 Gbps optical signal, and there is a problem of the allocation limitation of the optical signal wavelength. Therefore, the optical signal of the intensity modulation method and the optical signal of the phase modulation method are transmitted by separate optical transmission lines so as not to be affected by the mutual phase modulation effect. There is a problem that the transmission path is laid and the cost is increased.

  Japanese Patent Application Laid-Open No. H10-260260 shows problems and solutions based on a difference in transmission speed of 10 Gbps or less when an optical signal is modulated by the same intensity modulation method and transmitted by optical wavelength multiplexing. Problems in the case where an optical signal modulated by an intensity modulation method with a transmission rate of 10 Gbps or less is wavelength-multiplexed with an optical signal modulated by a high-speed phase modulation method of 40 Gbps, and transmission is performed using the same optical transmission line No solution is suggested.

  The present invention solves the above-described problems. An optical signal having a transmission rate of 10 Gbps or less by an intensity modulation method and an optical signal having a transmission rate of 40 Gbps by a phase modulation method are selected by selecting an arbitrary optical wavelength. Is to multiplex and transmit in accordance with the optical wavelength multiplexing system, and to maintain the transmission quality of the optical signals of both modulation systems.

Optical wavelength multiplex transmission system of the present invention is different optical wavelengths, respectively, and the transmission rate and high-speed phase modulation optical signal, the wavelength of the transmission rate from the phase-modulated optical signal obtained by multiplexing the low-speed intensity modulation optical signal An optical wavelength multiplex transmission system for transmitting a multiplexed optical signal through an optical transmission line, a demultiplexer for demultiplexing the wavelength multiplexed optical signal corresponding to the wavelength, and a wavelength corresponding to the wavelength demultiplexed by the demultiplexer An optical attenuator capable of attenuating and controlling the optical intensity of each optical signal and a filter, and whether the optical signal corresponding to the wavelength is a phase modulated optical signal or an intensity modulated optical signal is input / output optical signal via the filter determination means according to the magnitude of the level difference, based on the determination information from the determination unit, a control for controlling the optical attenuator so as to reduce the light intensity of the intensity-modulated optical signal than the light intensity of the phase-modulated optical signal and the part, the control unit Thus has a configuration in which an optical signal outputted through the optical attenuator is controlled by multiplexing by including a multiplexer for outputting the wavelength-multiplexed optical signal.

  In addition, it receives and separates information on whether it is a wavelength-corresponding phase-modulated optical signal or intensity-modulated optical signal transmitted superimposed on the wavelength-multiplexed optical signal, and based on this received and separated information, the phase-modulated optical signal A control unit for controlling the optical attenuator so as to reduce the light intensity of the intensity-modulated optical signal from the light intensity of

  Also, a determination unit for determining whether the optical signal demultiplexed by the demultiplexer according to the wavelength is a phase modulation optical signal or an intensity modulation optical signal, and the light of the phase modulation optical signal determined by the determination unit A control unit for controlling the optical attenuator is provided so as to reduce the light intensity of the intensity-modulated optical signal rather than the intensity.

  The determination unit detects the level of the optical signal between the input side and the output side of the optical filter and compares the level. When the level difference is equal to or less than a predetermined value, the determination unit determines that the signal is an intensity-modulated optical signal. Comparing / determining means for determining a phase-modulated optical signal when the value exceeds a large value is provided.

  The phase-modulated optical signal is transmitted at a transmission rate of 40 Gbps, and the intensity-modulated optical signal is in accordance with a modulation scheme for transmission at a transmission rate of 10 Gbps or lower. Compared to the level, the transmission level of the intensity-modulated optical signal is reduced by the optical attenuator and transmitted by wavelength multiplexing, so that the mutual phase modulation effect when transmitting by wavelength multiplexing through the same optical transmission line It is possible to suppress the deterioration of the characteristics of the phase-modulated optical signal due to.

It is explanatory drawing of Example 1 of this invention. It is explanatory drawing of Example 2 of this invention. It is explanatory drawing of the transmission-rate determination part of Example 2 of this invention.

Referring to FIG. 2 , the optical wavelength multiplexing transmission system of the present invention has a phase-modulated optical signal having a different optical wavelength and a high transmission rate, and an intensity-modulated optical signal having a transmission rate lower than that of the phase-modulated optical signal. the an optical wavelength multiplex transmission system for transmitting the optical transmission line wavelength-multiplexed optical signal obtained by multiplexing, a demultiplexer 3 demultiplexes the wavelength multiplexed optical signal to the wavelength corresponding, this demultiplexer 3 each the optical attenuators 6-1 to 6-n of the light intensity attenuation controllable demultiplexed wavelength corresponding optical signals, a filter, said wavelength corresponding optical signal phase-modulated optical signal or intensity modulated Based on the determination information (transmission speed determination unit 21) for determining whether the optical signal is an input / output optical signal level difference through the filter or not based on the determination information by the determination unit , the light intensity of the phase-modulated optical signal is determined. the light intensity of the strength-modulated optical signal As reduced, a control unit 22 for controlling the optical attenuator 6-1 to 6-n, light output through the optical attenuator 6-1 to 6-n which are controlled by the control unit 22 And a multiplexer 7 that multiplexes the signals and outputs them as a wavelength multiplexed optical signal.

  FIG. 1 is an explanatory diagram of a first embodiment of the present invention, in which 1 and 9 are signal processing units for transmitting and receiving an OSC (Optical Supervisor Channel) signal as a control signal, 2 and 8 are optical amplifiers, and 3 is an optical wavelength. Demultiplexers for demultiplexing to λ1 to λn, 4-1 to 4-n are optical switch circuits (2 × 2SW) for switching to an optical signal drop / insert or through state, and 5-1 to 5-n are optical signals 6-1 to 6-n are optical attenuators, 7 is a multiplexer that multiplexes optical signals of wavelengths λ1 to λn, and 9 is a signal processing that transmits and receives OSC signals. , 10 is a control processing unit, 11 is a demultiplexer, and 12 is a multiplexer, which is an optical wavelength multiplex having functions of insertion of a transmission optical signal and separation of a received optical signal (OADM). Transmission system Showing a main part of the arm of the relay device. For example, this repeater is connected in sequence by a ring-shaped optical transmission line, performs transmission / reception with an optical signal between optical transceivers connected to each repeater, and wavelength-multiplexes optical signals between the optical transceivers. This constitutes a system for relay transmission.

  The signal processing unit 1 on the receiving side transfers the information on the modulation method and transmission speed corresponding to the wavelength of the optical wavelength multiplexed signal by the OSC (Optical Supervisor Channel) signal demultiplexed by the demultiplexer 11 to the control processing unit 10. The control processing unit 10 holds information on the modulation method and transmission speed corresponding to the wavelength in a memory (not shown), and updates the memory contents in accordance with those changes. The optical wavelength multiplexed signal after the OSC signal is demultiplexed by the demultiplexer 11 is amplified by the optical amplifier 2 and demultiplexed by the demultiplexer 3 so as to correspond to the wavelengths λ1 to λn. The control processing unit 10 identifies whether the optical signal corresponding to the wavelengths λ1 to λn is dropped or through based on the information by the OSC signal from the signal processing unit 1, and in the case of through, sets the optical switch to the through state. In the case of switching or dropping, the optical switch is switched to the drop / insert state, the optical signal dropped by the optical switch is transferred to the optical transceiver, and the optical signal from the optical transceiver is inserted to the optical attenuator. 6-1 to 6-n side.

  The control processing unit 10 receives information indicating the transmission rate of the optical signal corresponding to the wavelengths λ1 to λn at 10 Gbps or 40 Gbps, the modulation method of the intensity modulation signal or the phase modulation signal by the signal processing unit 1, and corresponds to the information. Then, the case where the attenuation amount of the optical attenuators 6-1 to 6-n is controlled via a control path (not shown) is shown. Then, the optical signal having the wavelengths λ1 to λn is multiplexed by the multiplexer 7, amplified by the optical amplifier 8, and notified to the next relay device from the signal processing unit 9 according to the control from the signal processing unit 10. The information on the modulation method and the transmission speed is multiplexed as an OSC signal by the multiplexer 12 and transmitted.

  With regard to the transmission speed and modulation method, even if the optical intensity of the 10 Gbps intensity modulation signal is reduced by about 6 dB with respect to the 40 Gbps phase modulation signal, the same transmission distance can be transmitted with the same characteristics. Therefore, the optical attenuators 6-1 to 6-n are controlled in accordance with the modulation method corresponding to the wavelengths λ1 to λn recognized by the control processing unit 10, that is, the transmission rate, and 10 Gbps for the phase modulation signal of 40 Gbps. Is attenuated by about 6 dB. As a result, a 10 Gbps optical signal and a 40 Gbps optical signal can be transmitted with the same S / N tolerance. In this case, a required number of arbitrary wavelengths among the n wavelengths λ1 to λn is allocated for transmission at a transmission rate of 40 Gbps by the phase modulation method, and other wavelengths are assigned at a transmission rate of 10 Gbps or less by the intensity modulation method. Can be allocated for transmission.

  FIG. 2 is an explanatory diagram of Embodiment 2 of the present invention, where the same reference numerals as those in FIG. 1 denote the same name parts, 21 denotes a transmission rate determination unit, and 22 denotes a control unit. In the second embodiment, the transmission rate of the optical signal corresponding to the wavelengths λ1 to λn is determined by the transmission rate determination unit 21 without transmitting the information on the transmission rate and the modulation method corresponding to the wavelength by the OSC signal between the relay devices. In accordance with the determination result, the control unit 22 controls the attenuation amount of each of the optical attenuators 6-1 to 6-n. That is, control is performed so that an optical signal based on an intensity modulation method of about 10 Gbps or less is attenuated by about 6 dB with respect to an optical signal based on a phase modulation method at a transmission rate of 40 Gbps. Thereby, it is possible to transmit the optical signals of the respective transmission speeds with the same S / N tolerance.

  Further, the transmission rate determination unit 21 notifies the control unit 22 of information on the transmission rates corresponding to the wavelengths λ1 to λn as a configuration including a transmission rate determination unit corresponding to the wavelengths λ1 to λn. If the transmission rate in this case is 40 Gbps, it is a phase-modulated optical signal, and if the transmission rate is 10 Gbps or less, it is an intensity-modulated optical signal. If the transmission rate does not change frequently, the transmission rate determination unit 21 determines the transmission rate corresponding to the wavelengths λ1 to λn in a time division manner, notifies the control unit 22 of the result, and controls the control unit 22. Is stored in the internal memory (not shown), and when the transmission rate change is detected, the memory content is updated, and the attenuation amount of the optical attenuators 6-1 to 6-n is controlled according to the memory content It is also possible.

  FIG. 3 is an explanatory diagram of a transmission rate determination unit, 31 is a branching unit (CPL), 32 is a filter, 33 and 35 are light detection units (PD), and 35 is a light intensity detector. An optical signal input to the filter 32 is detected by the light detection unit 33, an optical signal output through the filter 32 is detected by the light detection unit 34, and compared by the light intensity detector 35. The spectrum of the 40 Gbps phase modulation signal is broader than the spectrum of the 10 Gbps intensity modulation signal. If the pass characteristic of the filter 32 is almost allowed to pass through the spectrum of the 10 Gbps intensity modulation signal, 40 Gbps. Since the spectrum of the phase modulation signal is broadened, the input / output level difference of the filter 32 becomes large. The light intensity detector 35 determines the magnitude relation of such an input / output level difference by the light intensity detector 35. That is, when the input / output level difference is large, it can be determined as a phase-modulated optical signal with a transmission rate of 40 Gbps, and when the input / output level difference is small, it can be determined as an intensity-modulated optical signal with a transmission rate of 10 Gbps or less. According to the determination result of the transmission rate, the control unit 22 (see FIG. 2) controls the attenuation amount of the optical attenuators 6-1 to 6-n corresponding to the wavelengths λ1 to λn. That is, compared with an optical attenuator that inputs a phase-modulated optical signal having a transmission rate of 40 Gbps, an attenuation amount by an optical attenuator that inputs an intensity-modulated optical signal having a transmission rate of 10 Gbps or less is, for example, as described above. Then, control is performed so as to attenuate about 6 dB. As a result, it is possible to avoid transmission characteristic deterioration that a 40 Gbps phase-modulated optical signal receives from an intensity-modulated optical signal having a transmission rate of 10 Gbps or less.

DESCRIPTION OF SYMBOLS 1,9 Signal processing part 2,8 Optical amplifier 3 Demultiplexer 4-1 to 4-n Optical switch circuit 5-1 to 5-n Optical transmitter / receiver 6-1 to 6-n Optical attenuator 7 Multiplexer 10 Control processing unit 11 demultiplexer 12 multiplexer

Claims (1)

Light that transmits a wavelength-multiplexed optical signal, which is obtained by multiplexing a phase-modulated optical signal having different optical wavelengths and a high transmission rate , and an intensity-modulated optical signal having a transmission rate slower than the phase-modulated optical signal , through an optical transmission line In a wavelength division multiplexing transmission system,
A demultiplexer for demultiplexing the wavelength-multiplexed optical signal corresponding to the wavelength;
An optical attenuator capable of controlling attenuation of each light intensity of the optical signal corresponding to the wavelength demultiplexed by the demultiplexer ;
A determination unit that includes a filter, and determines whether the optical signal corresponding to the wavelength is a phase-modulated optical signal or an intensity-modulated optical signal, based on the level difference of the input / output optical signal through the filter;
Based on the determination information from the determination unit, and a controller for controlling the optical attenuator so as to reduce the light intensity of the intensity-modulated optical signal than the light intensity of the phase-modulated optical signal,
And a multiplexer that multiplexes the optical signals output through the optical attenuator controlled by the control unit and outputs the multiplexed optical signal as a wavelength multiplexed optical signal.

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