JP5891099B2 - Optical phase monitor circuit, optical receiver, optical transmission / reception system - Google Patents

Description

  The present invention relates to an optical phase monitor circuit that monitors nonlinear phase noise of an optical multilevel modulation signal.

  In recent years, optical multilevel modulation systems using digital coherent receivers have been studied and put into practical use. The optical multilevel modulation scheme is a technique that enables transmission of a large amount of information using the phase and amplitude of light, and is a quaternary phase modulation scheme (PSK), quadrature amplitude modulation scheme ( Different multi-level modulation schemes such as QAM: Quadrature Amplitude Modulation (APSK) and Amplitude Phase Shift Keying (APSK) have been studied.

  When an optical multilevel modulation signal is passed through an optical fiber transmission line, signal waveform degradation such as chromatic dispersion and polarization mode dispersion occurs. These waveform degradations cause an increase in bit errors in transmission and hinder communication. However, these can be compensated by using an optical compensator or a compensation circuit using a digital signal processing technique on the receiving side.

  One example of signal waveform degradation is phase noise. Phase noise is classified into two types: linear phase noise (ASE optical noise, phase noise due to laser line width, etc.) and nonlinear phase noise. Nonlinear phase noise is caused by a nonlinear optical effect and is difficult to compensate even using an optical device or a digital signal processing circuit. The nonlinear optical effect is a phenomenon in which the refractive index changes according to the light intensity of the transmitted optical signal itself or the light intensity of the adjacent optical signal, and this changes the optical phase of the transmitted optical signal, resulting in a nonlinear phase. It appears as noise and the waveform deteriorates. In particular, in wavelength-division long-distance transmission, the effect of crosstalk between adjacent optical channels (XPM: Cross Phase Modulation) is received, so that the reception sensitivity is deteriorated and the transmission distance is greatly limited.

  In the technique described in Patent Document 1 below, electric field data after coherent reception of an optical multilevel modulation signal and phase synchronization is displayed on a signal point arrangement, and the amplitude of the optical signal is based on the distribution on the display. The nonlinear phase noise is monitored based on the ratio of the standard deviation in the direction and the standard deviation in the phase direction.

JP 2009-198364 A

  In the technique described in Patent Document 1, since the nonlinear phase noise and the linear phase noise are monitored on the signal point arrangement display without being separated, it is difficult to accurately monitor the nonlinear phase noise.

  The present invention has been made in view of the above problems, and extracts nonlinear phase noise from the phase noise of an optical multilevel modulation signal that has deteriorated after passing through an optical fiber transmission line. The objective is to monitor nonlinear phase noise.

  An optical phase monitor circuit according to the present invention extracts a phase error by erasing a data phase modulation component from electrical data obtained by coherent reception of an optical multilevel modulation signal, and a phase having no phase error or data phase modulation component A change in the phase or the shape of the spectrum of the electric field acquired when the electric field data having the error as a phase component is converted into the frequency domain is detected, and the nonlinear phase noise of the optical multilevel modulation signal is monitored.

  The optical phase monitor circuit according to the present invention can accurately monitor the nonlinear phase noise of the optical multilevel modulation signal.

1 is a configuration diagram of an optical receiver 10 that includes an optical phase monitor circuit 360 according to Embodiment 1. FIG. 3 is a block diagram illustrating a configuration example of an optical phase monitor circuit 360. FIG. 6 is a block diagram illustrating a second configuration example of an optical phase monitor circuit 360. FIG. 6 is a block diagram illustrating a third configuration example of an optical phase monitor circuit 360. FIG. 12 is a block diagram illustrating a fourth configuration example of the optical phase monitor circuit 360. FIG. 1 is a configuration diagram of an optical receiver 10 when an optical multilevel modulation signal is a polarization multiplexed optical multilevel modulation signal. FIG. It is a graph which shows the transmission simulation result of 128 Gbit / s PM-QPSK (polarization multiplexing 4 value phase modulation) optical signal. In the optical transmission simulation of FIG. 7, it is a spectrum of a quadruple phase error obtained by using the optical phase monitor circuit 360 shown in FIG. In the optical transmission simulation of FIG. 7, it is a spectrum of electric field data obtained by using the optical phase monitor circuit 360 shown in FIG. 8 is a result of simulating the operation of the optical phase monitor circuit 360 shown in FIG. 2 under the optical transmission simulation conditions of FIG. 8 is a result of simulating the operation of the optical phase monitor circuit 360 shown in FIG. 3 under the optical transmission simulation conditions of FIG. It is a figure which shows the structural example of the optical receiver 10 which is not provided with the phase estimation part 340 and the data decompression | restoration part 350 in case an optical multilevel modulation signal is an optical multilevel modulation signal of a single polarization. It is a figure which shows the structural example of the optical receiver 10 which is not provided with the phase estimation part 340 and the data restoration part 350 in case an optical multilevel modulation signal is an optical multilevel modulation signal of polarization multiplexing. 6 is a configuration diagram of an optical receiver 10 including an optical phase monitor circuit 360 according to Embodiment 2. FIG. 6 is a diagram illustrating a configuration example of an optical phase monitor circuit 360 in Embodiment 2. FIG. 6 is a diagram illustrating a second configuration example of an optical phase monitor circuit 360 according to Embodiment 2. FIG. 1 is a configuration diagram of an optical receiver 10 when an optical multilevel modulation signal is a polarization multiplexing multilevel modulation signal. FIG. It is a figure which shows the structural example of the optical receiver 10 which is not provided with the data decompression | restoration part 350 in case an optical multilevel modulation signal is an optical multilevel modulation signal of a single polarization. It is a figure which shows the structural example of the optical receiver 10 which is not provided with the data decompression | restoration part 350 in case an optical multilevel modulation signal is an optical multilevel modulation signal of polarization multiplexing. It is a block diagram of the optical transmission / reception system 200 which concerns on Embodiment 3. FIG. It is a block diagram of the optical transmitter 40 in case an optical multilevel modulation signal is single polarization. It is a block diagram of the optical transmitter 40 in case an optical multilevel modulation signal is polarization multiplexing. 5 is a flowchart illustrating an initialization procedure of the optical transmission / reception system 200. It is a figure which shows the structure of the lookup table T1 with which the optical transmitter control part 50 and the optical receiver control part 20 are provided, and the lookup table T2. It is a flowchart explaining the procedure in which the optical transmission / reception system 200 recovers from a failure. It is a block diagram of the optical transmission / reception system 200 which concerns on Embodiment 4. FIG.

<Embodiment 1: Device configuration>
FIG. 1 is a configuration diagram of an optical receiver 10 including an optical phase monitor circuit 360 according to Embodiment 1 of the present invention. The optical multilevel modulation signal may be any of a single polarization M-value phase modulation signal, an M-value quadrature amplitude phase modulation signal, and an M-value amplitude phase modulation signal. M is assumed to be an integer of 2 or more. The optical receiver 10 includes a coherent light detection unit 110 and a digital signal processing unit 120. The optical receiver 10 is connected to the optical receiver control unit 20, and the optical receiver control unit 20 is connected to the control network 30.

  The coherent detection unit 110 is a functional unit that coherently receives an optical multilevel modulation signal and converts it into electric field data. The optical frequency mixer 210, the local light source 220, the photoelectric detectors 230a and 230b, and the analog / digital converter 240a. And 240b.

  The digital signal processing unit 120 is a functional unit that performs signal processing on the electric field data converted by the coherent light detection unit 110, and includes a timing extraction unit 310, a dispersion compensation unit 320, a frequency estimation unit 330, a phase estimation unit 340, and a data restoration unit. 350 and an optical phase monitor circuit 360.

  The optical multilevel modulation signal input to the optical receiver 10 is input to the coherent light detection unit 110. The optical signal input to the coherent light detection unit 110 is input to the optical frequency mixer 210. The optical frequency mixer 210 optically mixes the unmodulated (CW) light of the local light source 220 and the optical signal received by the coherent light detection unit 110. The optical frequency mixer 210 outputs an I-phase component optical signal and a Q-phase optical signal, which are input to the photoelectric detectors 230a and 230b, respectively. The optical signals input to the photoelectric detectors 230a and 230b are converted into I-phase component electrical signals and Q-phase component electrical signals, respectively, and input to the analog / digital converters 240a and 240b, respectively. The electric signals input to the analog / digital converters 240a and 240b are respectively output as digital electric signals and converted into electric field data described as I + jQ. This electric field data is input to the digital signal processing unit 120.

  The electric field data input to the digital signal processing unit 120 is input to the timing extraction unit 310. The timing extraction unit 310 performs timing extraction processing by bandpass filter processing in the frequency domain. An output from the timing extraction unit 310 is input to the dispersion compensation unit 320. The dispersion compensation unit 320 performs chromatic dispersion compensation processing using an FIR (Finite Impulse Response) filter or the like. An output from the dispersion compensation unit 320 is input to the frequency estimation unit 330. The frequency estimation unit 330 performs frequency offset compensation processing such as frequency offset component extraction in the frequency domain. The output from the frequency estimation unit 330 is branched into two and is input to the phase estimation unit 340 and the optical phase monitor circuit 360, respectively. The phase estimation unit 340 performs phase error detection and compensation using a phase estimation algorithm such as VVA (Viterbi & Viterbi Algorithm) and decision-directed (Decision-Directed). The optical phase monitor circuit 360 monitors nonlinear phase noise. An output from the optical phase monitor circuit 360 is input to the optical receiver control unit 20. The optical receiver control unit 20 changes settings such as the input optical power, the multi-value number, the modulation speed, and the modulation method of the optical signal received by the optical receiver 10, and transmits / receives control information for that purpose via the control network 30. To do. The output from the phase estimation unit 340 is input to the data restoration unit 350. The data restoration unit 350 restores the input signal to digital data. The data restoration unit 350 outputs output data signals O1 and O2. At this time, the data restoration unit 350 may or may not perform the differential encoding process.

  FIG. 2 is a block diagram illustrating a configuration example of the optical phase monitor circuit 360. As shown in FIG. 2, the optical phase monitor circuit 360 includes a resample unit 410, a power multiplier 420, a phase detector 430, a frequency domain converter 440, and a nonlinear phase measurement unit 450. The “phase error detector” in the first embodiment corresponds to the resampler 410, the power multiplier 420, and the phase detector 430.

  The electric field data input to the optical phase monitor circuit 360 is input to the resample unit 410. The resample unit 410 performs a resample process such as waveform interpolation. An output from the resample unit 410 is input to a power multiplier 420.

  The power multiplier 420 power-processes the resampled electric field data. As a result, the phase component of the modulation data disappears, and only the phase error corresponding to the power remains in the phase component. The output from the power multiplier 420 is input to the phase detector 430. The power process needs to be performed for each amplitude value of the resampled electric field data.

  The phase detector 430 detects the phase component of the electric field data in which the phase component of the data modulation has been eliminated by being a power, that is, a phase error that is a multiple of the power. The output from the phase detector 430 is input to the frequency domain converter 440. The frequency domain converter 440 converts the input signal into the frequency domain by fast Fourier transform or the like, and outputs a phase error spectrum that is a multiple of a power. At this time, the number of samples to be processed by the frequency domain converter 440 may be fixedly set in advance, or may be changed freely. The output from the frequency domain converter 440 is input to the nonlinear phase measurement unit 450, which measures the spectral width or dispersion or standard deviation and monitors the nonlinear phase noise of the optical multilevel modulation signal. Thereby, the change of the spectrum shape can be detected. The monitored non-linear phase noise is input to the optical receiver control unit 20.

  FIG. 3 is a block diagram illustrating a second configuration example of the optical phase monitor circuit 360. The optical phase monitor circuit 360 shown in FIG. 3 includes a resample unit 410, a power multiplier 420, a frequency domain converter 440, and a nonlinear phase measurement unit 450. Below, it demonstrates centering on a different part from FIG.

  The electric field data from which the phase component of the data modulation has disappeared, which is an output from the power multiplier 420, is input to the frequency domain converter 440. The frequency domain converter 440 converts the electric field data that has been raised to a power and the phase component of the data modulation has disappeared into the frequency domain by fast Fourier transform or the like, and outputs the spectrum of the electric field data that has been raised to the power and the phase component of the data modulation has disappeared . At this time, the number of samples to be processed by the frequency domain converter 440 may be fixedly set in advance, or may be changed freely. The output from the frequency domain converter 440 is input to the nonlinear phase measurement unit 450, which measures the spectral width or dispersion or standard deviation and monitors the nonlinear phase noise of the optical multilevel modulation signal. Thereby, the change of the spectrum shape can be detected. The monitored nonlinear phase noise amount is input to the optical receiver controller 20.

  FIG. 4 is a block diagram illustrating a third configuration example of the optical phase monitor circuit 360. The optical phase monitor circuit 360 shown in FIG. 4 includes a resample unit 410, a power multiplier 420, a phase detector 430, a divider 460, a frequency domain converter 440, and a nonlinear phase measurement unit 450. Below, it demonstrates centering on a different part from FIG.

  The multiplier phase error, which should be an output from the phase detector 430, is input to the divider 460. Divider 460 divides a phase error that is a multiple of a power and detects the phase error. The output from the divider 460 is input to the frequency domain converter 440. The following configuration is the same as in FIG.

  FIG. 5 is a block diagram illustrating a fourth configuration example of the optical phase monitor circuit 360. The optical phase monitor circuit 360 shown in FIG. 5 includes a resample unit 410, a power multiplier 420, a phase detector 430, a divider 460, an electric field regenerator 470, a frequency domain converter 440, and a nonlinear phase measurement unit 450. Below, it demonstrates centering on a different part from FIG.

  The multiplier phase error, which should be an output from the phase detector 430, is input to the divider 460. Divider 460 divides a phase error that is a multiple of a power and detects the phase error. The output from the divider 460 is input to the electric field regenerator 470, and is regenerated into electric field data having a phase error having no phase component of data modulation as a phase component. The output from the electric field regenerator 470 is input to the frequency domain converter 440. The following configuration is the same as in FIG.

  Up to this point, the monitoring of the amount of nonlinear phase noise has been described. By increasing the number of samples targeted by the frequency domain converter 440 in the optical phase monitor circuit 360, the line widths of the lasers on the transmitter side and the receiver side are increased. Can also be monitored. The same applies to the embodiments described later.

  FIG. 6 is a configuration diagram of the optical receiver 10 when the optical multilevel modulation signal is a polarization multiplexed signal. The optical receiver 10 shown in FIG. 6 is different from FIG. 1 in that it includes a functional unit that processes an optical multilevel modulation signal for each polarization. Hereinafter, a description will be given focusing on differences from FIG.

  The coherent light detection unit 110 includes a polarization separator 250, optical frequency mixers 210a and 210b, a local light source 220, photoelectric detectors 230a and 230b, photoelectric detectors 230c and 230d, analog / digital converters 240a and 240b, analog -Digital converters 240c and 240d are provided.

  The digital signal processing unit 120 includes a timing extraction unit 310, a dispersion compensation unit 320, a polarization separation unit 370, a frequency estimation unit 330, a phase estimation unit 340, a data restoration unit 350, and optical phase monitor circuits 360a and 360b.

  The optical multilevel modulation signal input to the optical receiver 10 in FIG. 6 is input to the coherent detection unit 110. The optical multilevel modulation signal input to the coherent light detection unit 110 is input to the polarization separator 250. The polarization separator 250 extracts two orthogonal polarization components from the optical multilevel modulation signal and outputs them to the optical frequency mixers 210a and 210b, respectively. The optical frequency mixer 210a outputs an I-phase component optical signal and a Q-phase optical signal in TE polarization, which are input to the photoelectric detectors 230a and 230b, respectively. The optical frequency mixer 210b outputs an I-phase component optical signal and a Q-phase optical signal in TM polarization, which are input to the photoelectric detectors 230c and 230d, respectively. The optical signals input to the photoelectric detectors 230a and 230b are converted into an I-phase component electrical signal and a Q-phase component electrical signal in TE polarization, respectively, and input to the analog / digital converters 240a and 240b, respectively. The optical signals input to the photoelectric detectors 230c and 230d are converted into an I-phase component electrical signal and a Q-phase component electrical signal in TM polarization, respectively, and input to the analog / digital converters 240c and 240d, respectively. The electric signals input to the analog / digital converters 240a and 240b are converted into digital electric signals, respectively, and converted into electric field data described as I + jQ. The electric signals input to the analog / digital converters 240c and 240d are converted into digital electric signals, respectively, and converted into electric field data described as I + jQ. The electric field data in each polarization is input to the digital signal processing unit 120.

  The electric field data input to the digital signal processing unit 120 is input to the polarization separation unit 370 via the timing extraction unit 310, the dispersion compensation unit 320, and the frequency estimation unit 330. The polarization separation unit 370 separates the polarization of the polarization multiplexed signal using a polarization separation algorithm such as CMA (Constant Modulus Algorithm) or MMA (Multiple Modulus Algorithm), and generates PMD (Polarization Mode) generated in the transmission path. Dispersion (polarization mode dispersion) is compensated. The output from the polarization separation unit 370 is branched into two and input to the data restoration unit 350 and the optical phase monitor circuits 360a and 360b. The data restoration unit 350 restores each polarization signal to digital data and outputs output data signals O1, O2, O3, and O4. The optical phase monitor circuit 360a monitors the nonlinear phase noise of the TE polarization, and the optical phase monitor circuit 360b monitors the nonlinear phase noise of the TM polarization. Outputs from the optical phase monitor circuits 360 a and 360 b are input to the optical receiver control unit 20. The optical phase monitor circuits 360a and 360b may have any of the configurations shown in FIGS.

<Embodiment 1: Operation Principle and Evaluation Result of Optical Phase Monitor Circuit 360>
FIG. 7 is a graph showing a transmission simulation result of a 128 Gbit / s PM-QPSK (polarization multiplexed four-level phase modulation) optical signal. The vertical axis represents the bit error rate (BER), and the horizontal axis represents the input optical power (Launched Power) for each channel. Centering on PM-QPSK optical signals, 10 Gbit / s optical intensity modulation signals at 100 GHz intervals, 8 waves on the right side and 8 waves on the left side, were arranged as a precondition. Since the polarization state of the 10 Gbit / s light intensity modulation signal is a linear polarization with a polarization angle of π / 4, the TE polarization and TM polarization in FIG. 7 are affected by the almost uniform nonlinear optical effect. Yes. The optical fiber transmission line is 6 span DSF 50 km, and the transmission distance is 300 km in total. The optical signal-to-noise ratio (OSNR, Optical Signal-to-Noise Ratio) is fixed at 17 dB.

  According to the result shown in FIG. 7, it can be seen that the BER starts to deteriorate when the input power per wave is about −12 dBm, and rapidly deteriorates from −10 dBm. This is because a nonlinear optical effect starts to appear from −10 dBm and nonlinear phase noise is generated.

  FIG. 8 shows a spectrum of a quadruple phase error obtained by converting the quadruple phase error into the frequency domain by FFT using the optical phase monitor circuit 360 shown in FIG. 2 in the optical transmission simulation of FIG. is there. The vertical axis is the spectral power, and the horizontal axis is the frequency. In this simulation, both TE polarization and TM polarization are affected by a substantially uniform nonlinear optical effect, so a phase error spectrum of 4 times is picked up only for TE polarization.

  In the case of input power per wave of -14 dBm and -12 dBm, peaks rise near the DC and symbol rates. However, when the input power per wave is increased, the spectrum width starts to appear in the vicinity of the direct current and the symbol rate, and the spectrum width increases in the case of the input power per wave of −6 dBm. This is because the spectrum of the nonlinear phase noise is generated around the direct current and the symbol rate, and the spectrum of the nonlinear phase noise spreads as the input power per wave increases.

  9 is obtained by using the optical phase monitor circuit 360 shown in FIG. 3 in the optical transmission simulation of FIG. 7 to convert the electric field data, which has been raised to the fourth power and the phase component of data modulation has been eliminated, into the frequency domain by FFT. This is a spectrum of electric field data in which the phase component of data modulation disappears after being raised to the fourth power. The vertical axis is the spectral power, and the horizontal axis is the frequency. In this simulation, both TE polarization and TM polarization are affected by a substantially uniform nonlinear optical effect. Therefore, the spectrum of electric field data in which only the TE polarization is raised to the fourth power and the phase component of data modulation disappears is taken up.

  In the case of input power per wave of -14 dBm and -12 dBm, peaks rise near the DC and symbol rates. However, when the input power per wave is increased, the spectrum width starts to appear in the vicinity of the direct current and the symbol rate, and the spectrum width increases in the case of the input power per wave of −6 dBm. This is because the spectrum of the nonlinear phase noise is generated around the direct current and the symbol rate, and the spectrum of the nonlinear phase noise spreads as the input power per wave increases.

  FIG. 10 shows the result of simulating the operation of the optical phase monitor circuit 360 shown in FIG. 2 under the optical transmission simulation conditions of FIG. The vertical axis represents the standard deviation of the spectrum of the nonlinear phase noise calculated by the nonlinear phase measurement unit 450, and the horizontal axis represents the input power for each channel. According to the result of FIG. 10, when the input power per wave increases from −12 dBm to −10 dBm, the standard deviation of the spectrum of the nonlinear phase noise increases sharply, and when the input power per wave is further increased, −8 dB is obtained. It can be seen that the standard deviation of the spectrum of the nonlinear phase noise decreases as an inflection point. Similar results are seen in FIG.

  The optical phase monitor circuit 360 shown in FIGS. 4 to 5 converts the phase error obtained by dividing the M-fold phase error by the M value into the frequency domain by FFT. Since a simulation result similar to that of FIG. 11 was obtained, description thereof is omitted.

  According to the results shown in FIGS. 10 to 11, it can be seen that the input power having a standard deviation of the spectrum width of the nonlinear phase noise changes sharply starting from the input power.

<Embodiment 1: Modification of optical receiver 10>
In the above description, the configuration of the optical receiver 10 provided with the data reception function by the optical phase monitor circuit 360, the phase estimation unit 340, and the data restoration unit 350 has been described. In the configuration of the optical receiver 10 including only the monitor circuit 360, the same configuration as described above can be adopted.

  FIG. 12 is a diagram illustrating a configuration example of the optical receiver 10 that does not include the phase estimation unit 340 and the data restoration unit 350 when the optical multilevel modulation signal is a single-polarization optical phase modulation signal.

  FIG. 13 is a diagram illustrating a configuration example of the optical receiver 10 that does not include the phase estimation unit 340 and the data restoration unit 350 when the optical multilevel modulation signal is a polarization multiplexed optical phase modulation signal.

<Embodiment 1: Summary>
As described above, in the optical phase monitor circuit 360 according to the first embodiment, the frequency domain conversion unit 440 converts the electric field data that has been raised to a power and the phase component of the data modulation has disappeared, or the phase component thereof into a spectrum, thereby converting the nonlinear phase The measuring unit 450 measures the spectral width or dispersion or standard deviation from the spectrum, and monitors the nonlinear phase noise of the optical multilevel modulation signal.

<Embodiment 2>
FIG. 14 is a configuration diagram of the optical receiver 10 including the optical phase monitor circuit 360 according to the second embodiment of the present invention. In the optical receiver 10 shown in FIG. 14, the configuration of the digital signal processing unit 120 is different from that of the first embodiment.

  In the second embodiment, the optical multilevel modulation signal may be any of a single polarization M-value phase modulation signal, an M-value quadrature amplitude phase modulation signal, and an M-value amplitude phase modulation signal. M is assumed to be an integer of 2 or more. The output from the frequency estimation unit 330 is input to the phase estimation unit 340. The phase estimation unit 340 performs phase error detection and compensation using a phase estimation algorithm such as VVA (Viterbi & Viterbi Algorithm) and decision-directed (Decision-Directed). The output from the phase estimation unit 340 is branched into two and input to the data restoration unit 350 and the optical phase monitor circuit 360.

  FIG. 15 is a diagram illustrating a configuration example of the optical phase monitor circuit 360 according to the second embodiment. The optical phase monitor circuit 360 shown in FIG. 15 includes a phase error detector 480, a frequency domain converter 440, and a nonlinear phase measuring unit 450. The “phase error detector” in the second embodiment corresponds to the phase error detector 480.

  The electric field data input to the optical phase monitor circuit 360 is input to the phase error detector 480. The phase error detector 480 holds in advance the signal point arrangement when the electric field data of the optical multilevel modulation signal before passing through the optical fiber transmission line is arranged on the constellation. By comparing, the phase estimation unit 340 detects a phase error that could not be compensated. The output from the phase error detector 480 is input to the frequency domain converter 440. The following configuration is the same as in FIG.

  FIG. 16 is a diagram illustrating a second configuration example of the optical phase monitor circuit 360 according to the second embodiment. The optical phase monitor circuit 360 illustrated in FIG. 16 includes a phase error detector 480, an electric field regenerator 470, a frequency domain converter 440, and a nonlinear phase measurement unit 450.

  The output from the phase error detection unit 480 is input to the electric field regenerator 470, and is regenerated into electric field data having the phase error that the phase estimation unit 340 cannot compensate for as a phase component. The output from the electric field regenerator 470 is input to the frequency domain converter 440. The following configuration is the same as in FIG.

  FIG. 17 is a configuration diagram of the optical receiver 10 when the optical multilevel modulation signal is a polarization multiplexed signal. The optical receiver 10 shown in FIG. 17 is different from FIG. 14 in that it includes a functional unit that processes an optical multilevel modulation signal for each polarization. Hereinafter, a description will be given focusing on differences from FIG.

  The coherent light detection unit 110 includes a polarization separator 250, optical frequency mixers 210a and 210b, a local light source 220, photoelectric detectors 230a and 230b, photoelectric detectors 230c and 230d, analog / digital converters 240a and 240b, analog -Digital converters 240c and 240d are provided.

  The digital signal processing unit 120 includes a timing extraction unit 310, a dispersion compensation unit 320, a polarization separation unit 370, a frequency estimation unit 330, a phase estimation unit 340, a data restoration unit 350, and optical phase monitor circuits 360a and 360b.

  The optical multilevel modulation signal input to the optical receiver 10 in FIG. 17 is input to the coherent detection unit 110. The optical multilevel modulation signal input to the coherent light detection unit 110 is input to the polarization separator 250. The polarization separator 250 extracts two orthogonal polarization components from the optical multilevel modulation signal and outputs them to the optical frequency mixers 210a and 210b, respectively. The optical frequency mixer 210a outputs an I-phase component optical signal and a Q-phase optical signal in TE polarization, which are input to the photoelectric detectors 230a and 230b, respectively. The optical frequency mixer 210b outputs an I-phase component optical signal and a Q-phase optical signal in TM polarization, which are input to the photoelectric detectors 230c and 230d, respectively. The optical signals input to the photoelectric detectors 230a and 230b are converted into an I-phase component electrical signal and a Q-phase component electrical signal in TE polarization, respectively, and input to the analog / digital converters 240a and 240b, respectively. The optical signals input to the photoelectric detectors 230c and 230d are converted into an I-phase component electrical signal and a Q-phase component electrical signal in TM polarization, respectively, and input to the analog / digital converters 240c and 240d, respectively. The electric signals input to the analog / digital converters 240a and 240b are converted into digital electric signals, respectively, and converted into electric field data described as I + jQ. The electric signals input to the analog / digital converters 240c and 240d are converted into digital electric signals, respectively, and converted into electric field data described as I + jQ. The electric field data in each polarization is input to the digital signal processing unit 120.

  The electric field data input to the digital signal processing unit 120 is input to the polarization separation unit 370 via the timing extraction unit 310, the dispersion compensation unit 320, and the frequency estimation unit 330. The polarization separation unit 370 separates the polarization of the polarization multiplexed signal using a polarization separation algorithm such as CMA (Constant Modulus Algorithm) or MMA (Multiple Modulus Algorithm), and generates PMD (Polarization Mode) generated in the transmission path. Dispersion (polarization mode dispersion) is compensated. The output from the polarization separation unit 370 is branched into two and input to the data restoration unit 350 and the optical phase monitor circuits 360a and 360b. The data restoration unit 350 restores each polarization signal to digital data and outputs output data signals O1, O2, O3, and O4. The optical phase monitor circuit 360a monitors the nonlinear phase noise of the TE polarization, and the optical phase monitor circuit 360b monitors the nonlinear phase noise of the TM polarization. Outputs from the optical phase monitor circuits 360 a and 360 b are input to the optical receiver control unit 20. The optical phase monitor circuits 360a and 360b may have any of the configurations shown in FIGS.

<Embodiment 2: Modification of optical receiver 10>
In the above description, the configuration of the optical receiver 10 having the data reception function by the optical phase monitor circuit 360 and the data restoration unit 350 has been described. However, the optical receiver 10 has no data reception function, and only the optical phase monitor circuit 360 is provided. Also in the configuration of the optical receiver 10 provided, the same configuration as above can be adopted.

  FIG. 18 is a diagram illustrating a configuration example of the optical receiver 10 that does not include the data restoration unit 350 when the optical multilevel modulation signal is a single-polarization optical phase modulation signal.

  FIG. 19 is a diagram illustrating a configuration example of the optical receiver 10 that does not include the data restoration unit 350 when the optical multilevel modulation signal is a polarization multiplexed optical phase modulation signal.

<Embodiment 2: Summary>
As described above, the optical phase monitor circuit 360 according to the second embodiment receives the electric field data after the phase estimation unit 340 estimates and compensates the phase of the optical multilevel modulation signal, and the phase estimation unit 340 can fully compensate. The non-existing phase error or electric field data having the phase error as a phase component is converted into a spectrum, and the non-linear phase measurement unit 450 measures the spectral width or variance or standard deviation from the spectrum and monitors the non-linear phase noise.

<Embodiment 3>
FIG. 20 is a configuration diagram of an optical transmission / reception system 200 according to Embodiment 3 of the present invention. The optical transmission / reception system 200 includes an optical receiver 10, an optical transmitter 40, an optical repeater 70, an optical receiver control unit 20, an optical transmitter control unit 50, an optical repeater control unit 80, an optical fiber transmission line 60, a control network. 30. The optical receiver 10 has been described in any one of the first and second embodiments. The optical transmitter 40 has a function of changing the input power, the multi-value number, the modulation speed, and the modulation method in accordance with an instruction from the optical transmitter control unit 50. The optical fiber transmission line 60 is an optical path that connects the optical transmitter 40 and the optical receiver 10. The optical repeater 70 is connected after the optical fiber transmission line 60 and has a function of changing the input power in accordance with an instruction from the optical repeater control unit 80. The control network 30 is a communication network that transmits and receives control information between the optical receiver controller 20, the optical repeater controller 80, and the optical transmitter controller 50.

  FIG. 21 is a configuration diagram of the optical transmitter 40 when the optical multilevel modulation signal has a single polarization. The optical transmitter 40 shown in FIG. 21 includes a variable multilevel modulation speed signal generator 401, a laser light source 260, an optical modulator 270, and a variable optical power attenuator 280. The variable multilevel modulation speed signal generator 401 and the variable optical power attenuator 280 are connected to the optical transmitter controller 50 via the control network 30.

  Non-modulated (CW: Continuous Wave) light generated from the laser light source 260 is input to the optical modulator 270. In parallel with this, the variable multilevel modulation speed signal generator 401 inputs the data signal I1 to the optical modulator 270. The optical modulator 270 modulates the CW light based on the data signal I1 and outputs an optical modulation signal. The output from the optical modulator 270 is input to the variable optical power attenuator 280. The variable optical power attenuator 280 sets the optical power of the optical modulation signal to the optical transmission power value specified by the control information received from the optical transmitter control unit 50. The output from the variable optical power attenuator 280 is input to the optical fiber transmission line 60, and the output of the optical fiber transmission line is input to the optical repeater 70.

  The variable multilevel modulation rate signal generator 401 can change the setting of the multilevel number of the optical multilevel modulation signal and the modulation rate based on control information from the optical transmitter control unit 50. When the variable multilevel modulation rate signal generator 401 changes the setting of the multilevel number or the modulation rate, the variable multilevel modulation rate signal generator 401 transmits control information indicating that the setting of the optical receiver 10 should be changed to the optical transmitter control unit 50. When receiving the control information, the optical transmitter controller 50 transmits the control information to the optical receiver controller 20 through the control network 30. As a modulation method, any one of a phase modulation method, a quadrature amplitude phase modulation method, and an amplitude phase modulation method may be employed. The input data signal I1 may be a signal obtained by separating one data signal into two, or may be separate data that is completely unrelated. The optical modulator 270 may be, for example, an LN phase modulator, a Mach Zender (MZ) modulator, and an quadrature (IQ) modulator in which two MZ modulators are configured in parallel. An IQ modulator is suitable when transmission of m-PSK, m-QAM, and m-APSK (m is 4 or more) is assumed.

  FIG. 22 is a configuration diagram of the optical transmitter 40 when the optical multilevel modulation signal is polarization multiplexed. The optical transmitter 40 shown in FIG. 22 includes a variable multilevel modulation speed signal generator 401, a laser light source 260, an optical splitter 290, optical modulators 270a and 270b, a polarization multiplexer 300, and a variable optical power attenuator 280. . A polarization maintaining fiber (PMF) is connected between the optical modulator 270a and the polarization multiplexer 300, and between the optical modulator 270b and the polarization multiplexer 300. The variable multilevel modulation speed signal generator 401 and the variable optical power attenuator 280 are connected to the optical transmitter controller 50 via the control network 30.

  Unmodulated (CW, Continuous Wave) light generated from the laser light source 260 is input to the optical splitter 290. The optical splitter 290 splits the CW light and inputs it to the optical modulators 270a and 270b, respectively. The optical modulator 270a modulates the CW light according to the data signal I1 from the variable multi-level modulation speed signal generator 401. The optical modulator 270b modulates the CW light according to the data signal I2 from the variable multi-level modulation speed signal generator 401. The optical modulators 270a and 270b each output an optical modulation signal. The input data signals I1 and I2 may be signals obtained by separating one data signal into two, or may be separate data that are not related at all. The bit rates of the input data signals I1 and I2 may be the same or different.

  The polarization multiplexer 300 is a polarization state in which the optical modulation signal modulated by the optical modulator 270a and the optical modulation signal modulated by the optical modulator 270b are orthogonal to each other (for example, TE polarization and TM polarization). To generate a polarization multiplexed optical signal. The output from the polarization multiplexer 300 is input to the variable optical power attenuator 280.

  Further, instead of the control network 30, a supervisory control optical signal (OSC, Optical Supervisor Call) is input to the optical fiber transmission line 60, and the supervisory control optical signal from the optical fiber transmission line 60 is optically provided with a light detection unit. The setting information may be acquired by receiving between the receiver control unit 20, the optical repeater control unit 80, and the optical transmitter control unit 50.

<Third Embodiment: System Operation>
FIG. 23 is a flowchart for explaining an initialization procedure of the optical transmission / reception system 200. This flowchart is performed when setting the optical receiver 10 to an initial state, such as when setting up the optical receiver 10 or when returning from a failure. It is assumed that the optical transmitter control unit 50 and the optical receiver control unit 20 include a lookup table described later.

  In step S5, the optical transmitter control unit 50 and the optical receiver control unit 20 transmit information about the multilevel number, modulation speed, modulation scheme, and polarization multiplexing scheme of the optical multilevel modulation signal to the optical transmitter 40, respectively. Set to optical receiver 10.

  In step S10, the optical transmitter control unit 50 and the optical receiver control unit 20 set a reference value of a nonlinear phase corresponding to the optical multilevel modulation signal. In step S <b> 15, the optical transmitter control unit 50 and the optical receiver control unit 20 set the operating range of the input optical power to the optical transmitter 40 and the optical receiver 10.

  In step S <b> 20, the optical transmitter control unit and the optical repeater control unit 80 set the input optical power to the optical transmitter 10 and the optical repeater 70.

  In step S25, the optical receiver control unit 20 monitors the nonlinear phase (TE polarized wave, TM polarized wave) of the optical receiver 10, and stores the monitoring result in the lookup table T2. The object to be monitored is the spectral width or standard deviation.

  In step S30, the optical receiver control unit 20 determines whether or not the nonlinear phase (TE polarized wave, TM polarized wave) is approximately equal to the reference value. If it is the same level, the flow ends. If not, the process proceeds to step S35.

  In step S35, the optical receiver control unit 20 determines whether or not the measurement of the nonlinear phase (TE polarized wave, TM polarized wave) is completed within the operating range of the input optical power set in step S15. If not completed, the process proceeds to step 40, and the input optical power not yet measured through the optical transmitter controller 50 and the optical repeater controller 80 is set on the optical transmitter 40 and the optical repeater 70. Returning to step S20, similar processing is performed. If the measurement has been completed, the process proceeds to step S45.

  In step S45, the optical receiver control unit 20 determines whether or not the nonlinear phase is equal to or less than a reference value within the measurement range set in step S15. If there is anything below the reference value, the input optical power corresponding to the nonlinear phase closest to the reference value is set, and the flow ends. If not below the reference value, the process proceeds to step S50. In step S50, the optical receiver control unit 20 changes the multilevel number, modulation speed, modulation method, and polarization multiplexing method of the optical transmitter 40 via the optical transmitter control unit 50, and updates T1. Returning to step S5, the same flow is repeated. This flowchart is complete | finished above.

  FIG. 24 is a diagram illustrating a configuration of a lookup table (LUT: Look Up Table) T1 and a lookup table T2 included in the optical transmitter control unit 50 and the optical receiver control unit 20. Hereinafter, each table will be described.

  The look-up table T1 grasps the multilevel number of the optical multilevel modulation signal output from the optical transmitter 40, the modulation speed, the modulation scheme, the polarization multiplexing scheme, the input optical power operating range, and the nonlinear phase reference value. It is a table to keep. The optical transmitter control unit 50 and the optical receiver control unit 20 change the above-described parameters of the optical multilevel modulation signal output from the optical receiver 10 via the optical transmitter control unit 50 in steps S5, S50, and the like. At that time, the change contents are recorded in the lookup table T1.

  The lookup table T2 is a table for recording the input optical power and nonlinear phase measurement results of the optical multilevel modulation signal received by the optical receiver 10 for each polarization. When the optical multilevel modulation signal has a single polarization, the nonlinear phase may be recorded as a TE polarization. The measurement result recorded in the lookup table T2 is used when referring to the measurement result in steps S30, S45, and the like.

  FIG. 25 is a flowchart for explaining a procedure for the optical transmission / reception system 200 to recover from a failure. In FIG. 25, it is assumed that the flowchart described in FIG. 23 has been performed in advance.

  In step S55, the optical receiver control unit 20 performs the following steps when a failure (deterioration of the BER in the optical receiver 10) is detected, and if not detected, waits at this step to detect the failure. I wait. The failure of the optical receiver 10 may be notified from the optical receiver 10 to the optical receiver control unit 20 at the time of occurrence, or even after the operation of the optical receiver 10 starts, the optical receiver control unit 20 10 may be constantly monitored and detected.

  In step S60, the optical receiver control unit 20 monitors the current nonlinear phase (TE polarized wave, TM polarized wave). In step S65, the optical receiver control unit 20 compares the current nonlinear phase noise amount (TE polarization, TM polarization) with the nonlinear phase reference value recorded in the lookup table T1. If the current nonlinear phase noise amount (TE polarized wave, TM polarized wave) is about the same as the reference value, the process proceeds to step S100. If not, the process proceeds to step S70.

  In step S70, the optical receiver control unit 20 changes the input optical power of the optical transmitter 40 and the optical repeater 70 via the optical transmitter control unit 50 and the optical repeater control unit 80 so as to approach the reference value. In step S75, the input optical power is set to the optical transmitter 40 and the optical repeater 70.

  In step S80, the optical receiver control unit 20 monitors the nonlinear phase (TE polarized wave, TM polarized wave) after changing the input optical power. In step S85, the optical receiver control unit 20 compares the nonlinear phase (TE polarization, TM polarization) after changing the input optical power with the nonlinear phase reference value recorded in the lookup table T1. If the nonlinear phase (TE polarized wave, TM polarized wave) after changing the input optical power is approximately the same as the reference value, the flow ends. If not, the process proceeds to step S90.

  In step S90, the optical receiver control unit 20 determines whether or not the measurement of the nonlinear phase (TE polarized wave, TM polarized wave) is completed within the operation range of the input optical power. If not completed, the process returns to step S70, and the input optical power not yet measured via the optical transmitter controller 50 and the optical repeater controller 80 is set on the optical transmitter 40 and the optical repeater 70. Similar processing is performed. If the measurement has been completed, the process proceeds to step S95.

  In step S95, the optical receiver control unit 20 determines whether or not the nonlinear phase is equal to or less than a reference value within the operating range of the input optical power. If there is anything below the reference value, the input optical power corresponding to the nonlinear phase closest to the reference value is set, and the flow ends. If not below the reference value, the process proceeds to step S100. In step S100, the optical receiver control unit 20 changes the multi-level number, modulation speed, modulation method, and polarization multiplexing method of the optical transmitter 40 via the optical transmitter control unit 50, and proceeds to step S105. Processing equivalent to S5 of 23 is performed. This flowchart is complete | finished above.

<Embodiment 3: Summary>
As described above, the optical transmission / reception system 200 according to the third embodiment can operate the optical transmitter 40, the optical repeater 70, and the optical receiver 10 by monitoring the nonlinear phase.

  Further, when the optical transmission / reception system 200 according to the third embodiment detects the deterioration of the BER, the optical transmission / reception system 200 determines whether or not the cause is due to nonlinear phase noise, and automatically performs an appropriate recovery process according to the cause. Can be implemented. That is, when the BER of the optical receiver 10 is deteriorated, the return process can be automatically performed, so that the burden on operation can be reduced.

  The reason why the above processing can be performed by the non-linear phase noise is that the influence of the non-linear phase noise signal changes significantly according to the modulation method, the optical transmitter, or the input optical power. Therefore, in the present invention, the non-linear phase is monitored, the multi-level number of the optical multi-level modulation signal, the modulation speed, the input optical power, etc. are switched adaptively and applied to the automatic failure recovery. It was decided to investigate the deterioration factor. Thus, it is considered that the present invention is useful in that it can be applied to various uses by monitoring the nonlinear phase.

<Embodiment 4>
FIG. 26 is a configuration diagram of an optical transmission / reception system 200 according to Embodiment 4 of the present invention. In the fourth embodiment, it is assumed that wavelength multiplexed optical signals are transmitted and received. An optical transmission / reception system 200 shown in FIG. 26 includes a wavelength multiplexing optical transmitter 90 that transmits wavelength multiplexed optical signals, a wavelength multiplexing optical receiver 100 that receives wavelength multiplexed optical signals, an optical repeater 70, an optical receiver control unit 20, An optical repeater control unit 80, an optical transmitter control unit 50, an optical fiber transmission line 60, and a control network 30 are provided.

  The wavelength division multiplexing optical transmitter 90 includes optical transmitters 40-1, 40-2,..., 40-n having functions of changing input optical power, multi-value number, modulation speed, modulation method, and the like. A device 510 is provided. The optical multiplexer 510 wavelength-multiplexes and outputs an optical multilevel modulation signal output from each optical transmitter. The wavelength multiplexing optical receiver 80 includes optical receivers 10-1, 10-2,..., 10-n, and an optical demultiplexer 520. The optical demultiplexer 520 demultiplexes the wavelength multiplexed optical signal transmitted by the wavelength multiplexed optical transmitter 90 and distributes it to each optical receiver. Each optical transmitter and each optical receiver are the same as those described in any of the above embodiments.

  The optical repeater 70 is connected after the optical fiber transmission line 60 and has a function of changing the input power in accordance with an instruction from the optical repeater control unit 80. The input power of the optical multilevel modulation signal for each wavelength corresponding to the optical transmitters 40-1, 40-2,..., 40-n included in the wavelength multiplexing transmitter 90 may be set individually.

  The optical transmitter control unit 50 and the optical receiver control unit 20 include optical transmitters 40-1, 40-2,..., 40-n included in the wavelength division multiplexing transmitter 90, and the wavelength division multiplexing optical receiver 100, respectively. The control information for setting change is transmitted / received to / from the optical receivers 10-1, 10-2,. Each optical transmitter and each optical receiver changes the setting according to the control information.

  In the fourth embodiment, for the initialization procedure and the failure recovery procedure of the wavelength division multiplexing optical transmitter 90 and the wavelength division multiplexing optical receiver 100, the flowchart described in FIG. 23 and FIG. 25 is used for each optical transmitter and each optical receiver. It can be done individually.

  Further, instead of the control network 30, a supervisory control optical signal (OSC, Optical Supervisor Call) is input to the optical fiber transmission line 60, and the supervisory control optical signal from the optical fiber transmission line 60 is optically provided with a light detection unit. The setting information may be acquired by receiving between the receiver control unit 20, the optical repeater control unit 80, and the optical transmitter control unit 50.

  The present invention is not limited to the embodiments described above, and includes various modifications. The above embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. A part of the configuration of one embodiment can be replaced with the configuration of another embodiment. The configuration of another embodiment can be added to the configuration of a certain embodiment. Further, with respect to a part of the configuration of each embodiment, another configuration can be added, deleted, or replaced.

  Each of the above-described configurations, functions, processing units, processing means, and the like may be realized in hardware by designing a part or all of them, for example, with an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files for realizing each function can be stored in a memory, a hard disk, a recording device such as an SSD (Solid State Drive), a recording medium such as an IC card, an SD card, or a DVD.

  10: Optical receiver, 20: Optical receiver controller, 30: Control network, 40: Optical transmitter, 50: Optical transmitter controller, 60: Optical fiber transmission line, 70: Optical repeater, 80: Optical repeater 90: wavelength multiplexed optical transmitter, 100: wavelength multiplexed optical receiver, 110: coherent light detector, 120: digital signal processor, 210: optical frequency mixer, 220: local light source, 230: photoelectric Detector: 240: Analog to digital converter, 250: Polarization separator, 260: Laser light source, 270: Optical modulator, 280: Variable optical power attenuator, 290: Optical splitter, 300: Polarization multiplexer, 310: Timing extraction unit, 320: Dispersion compensation unit, 330: Frequency estimation unit, 340: Phase estimation unit, 350: Data restoration unit, 360: Optical phase monitor circuit, 370: Polarization separation unit, 410: Resampling , 420: power multiplier, 430: phase detector, 440: frequency domain converter, 450: nonlinear phase measurement unit, 460: divider, 470: electric field regenerator, 480: phase error detector, 510: optical multiplexing 520: Optical demultiplexer.

Claims (15)

An optical phase monitor circuit for monitoring an optical multilevel modulation signal,
Phase error that eliminates and extracts data phase modulation components from electric field data obtained by coherent reception of the optical multilevel modulation signal, or phase error electric field data that uses the phase error that does not have the data phase modulation component as a phase component A phase error detector to detect ;
A frequency domain converter that converts the phase error or the phase error electric field data into a frequency domain;
A non-linear phase monitoring unit for monitoring a non-linear phase by detecting a change in a phase or a spectrum shape of an electric field acquired when the frequency domain converting unit converts the phase error or the phase error electric field data into a frequency domain;
Equipped with a,
The phase error detection unit extracts the phase error by performing a power process on the electric field data and deleting the data phase modulation component, or compares the electric field data with a constellation arrangement stored in advance. And detecting the phase error not having the data phase modulation component . The nonlinear phase monitoring unit is
The non-linear phase is monitored by measuring the phase width of the phase or electric field spectrum obtained when the frequency domain conversion unit converts the phase error or the phase error electric field data into the frequency domain as the shape. 2. The optical phase monitor circuit according to claim 1, wherein: The nonlinear phase monitoring unit is
By measuring the phase or electric field spectrum dispersion or standard deviation obtained when the frequency domain conversion unit converts the phase or electric field data having no data phase modulation component into the frequency domain as the shape, a nonlinear phase is obtained. The optical phase monitor circuit according to claim 1, wherein:   4. The optical phase monitor circuit according to claim 2, wherein the phase error or the phase error electric field data is phase error or phase error electric field data of the electric field data before the input of the phase estimation unit. The phase error detector is
A resampler that resamples the electric field data before the phase estimator input;
A power multiplication unit to power the electric field data after the resample acquired by the resample unit;
The optical phase monitor circuit according to claim 4, further comprising: The phase error detector is
The optical phase monitor circuit according to claim 5, further comprising: a division unit that divides a phase detected from the electric field data after the power detected by the power multiplication unit. 4. The optical phase monitor circuit according to claim 2, wherein the phase error or the phase error electric field data is phase error or phase error electric field data of electric field data after being input to a phase estimation unit. 5. A light detection unit for coherently receiving an optical multilevel modulation signal;
An optical phase monitor circuit according to claim 1;
With
The optical phase monitor circuit monitors the optical multilevel modulation signal received by the optical detection unit. An optical transmitter for transmitting an optical multilevel modulation signal;
An optical receiver according to claim 8;
A light receiver control unit for changing the settings of the optical receiver based on the nonlinear phase where the light phase monitor circuit in which the optical receiver is equipped acquired,
An optical transmitter controller that changes the setting of the optical transmitter in accordance with an instruction of the optical receiver controller;
An optical transmission / reception system comprising: The optical receiver controller is
The correspondence relationship between the amount of nonlinear phase noise of the optical multilevel modulation signal and the input optical power is recorded in advance while changing the input optical power of the optical multilevel modulation signal received by the optical receiver. ,
When detecting that the bit error rate of the optical receiver has deteriorated, the amount of nonlinear phase noise acquired by the optical phase monitor circuit included in the optical receiver and the amount of nonlinear phase noise recorded in advance are between Find the difference between
The optical transmission / reception system according to claim 9, wherein when the difference is not within a predetermined range, an input optical power of the optical multilevel modulation signal received by the optical receiver is changed. The optical receiver controller is
When the difference is within the predetermined range, the recording is performed again after changing at least one of the multi-value number, modulation speed, modulation method, and partial multiplexing method of the optical multi-value modulation signal. It implements. The optical transmission / reception system of Claim 10 characterized by the above-mentioned. The optical receiver controller is
The recording is performed for each polarization of the optical multilevel modulation signal,
As the difference, a difference between the nonlinear phase noise amount for each polarization acquired by the optical phase monitor circuit included in the optical receiver and the nonlinear phase noise amount for each polarization recorded in advance is obtained. The optical transmission / reception system according to claim 10. The optical transmission / reception system according to claim 9, further comprising: an optical repeater that changes an optical power of the optical multilevel modulation signal transmitted by the optical transmitter and relays the optical multilevel modulation signal to the optical receiver. A wavelength division multiplexing optical transmitter having a plurality of the optical transmitters;
A wavelength division multiplexing optical receiver having a plurality of the optical receivers;
With
The plurality of optical transmitters transmit the optical multilevel modulation signals of different wavelengths,
The wavelength multiplexing optical transmitter is:
An optical multiplexing unit that multiplexes the optical multilevel modulation signals transmitted by the optical transmitters and outputs a wavelength multiplexed optical signal;
The wavelength multiplexing optical receiver is:
An optical demultiplexing unit that demultiplexes the wavelength-multiplexed optical signal into optical signals of different wavelengths and outputs the optical multilevel modulation signals;
Each said optical receiver
The optical transmission / reception system according to claim 9, wherein each of the optical multilevel modulation signals demultiplexed by the optical demultiplexing unit is received. The optical receiver control unit, with respect to the optical transmitter control unit,
Control information indicating that the optical signal power of the optical transmitter should be changed, control information indicating that the multilevel number of the optical multilevel modulation signal transmitted by the optical transmitter should be changed, and modulation rate of the optical transmitter 10. The optical transmission / reception system according to claim 9, wherein the optical transmission / reception system is at least one of control information indicating that the optical transmitter should be changed and control information for switching whether or not the optical transmitter should perform polarization multiplexing.

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