JPWO2014119270A1 - Optical receiving apparatus, optical communication system, optical receiving method, and optical receiving apparatus control program - Google Patents

Abstract

In order to reduce signal quality degradation due to phase fluctuations of the light source, the optical receiver performs coherent detection on each of the optical signals received from different optical transmission paths using local oscillation light supplied from the same light source. , Coherent detection means for outputting a plurality of detection signals corresponding to each of the optical signals, phase error detection means for detecting a phase error of a carrier wave component included in the detection signal, and averaging for obtaining an average value of the plurality of phase errors Means, and phase compensation means for performing phase compensation of the detection signal based on the average value.

Description

  The present invention relates to an optical receiver, an optical communication system, an optical reception method, and a recording medium for a control program for the optical receiver, and in particular, an optical receiver, an optical communication system, an optical having a function of receiving an optical signal from a plurality of paths The present invention relates to a receiving method and a recording medium for a control program of an optical receiving apparatus.

  Against the background of a significant increase in data traffic in recent years, there is a strong demand for a large capacity even in a backbone optical transmission system. However, optical transmission using a single mode fiber is approaching the limit of transmission capacity due to signal quality degradation caused by nonlinear effects in the fiber. For this reason, studies on spatial multiplex transmission are being pursued in which the capacity is further increased by spatially multiplexing signals.

  A multi-core fiber is one of transmission lines used in such spatial multiplexing transmission, and has a plurality of cores in one clad. By spatially multiplexing the transmission path with these multiple cores, the transmission capacity per fiber can be increased.

  On the other hand, high-order multilevel modulation is being studied as another means for increasing the capacity. For example, 16-QAM (Quadrature Amplitude Modulation) modulation having 16 signal points can transmit 4-bit information in one symbol as compared with QPSK (Quadrature Phase Shift Keying) modulation in which 2-bit information is transmitted in one symbol. That is, with 16QAM modulation, a double transmission capacity can be achieved in the same band. Since the spatial multiplexing technique and the multi-level modulation technique can be applied to the optical transmission system at the same time, the expansion of the transmission capacity using these techniques is being studied.

  However, in a high-order multilevel modulation system such as 16QAM modulation, the distance between signal points when compared with a constant average signal strength is smaller than that in a low-order modulation system, and thus is resistant to various types of noise. Lower.

  For example, as noise generated in optical transmission, there is phase fluctuation of laser light used for a light source. Laser light is used as a carrier wave of modulated light, and is also used as an LO (local oscillator) during coherent detection. For this reason, the phase fluctuation of the laser beam affects the signal quality. In general, the laser beam with a larger line width has a larger phase fluctuation and a greater influence on the signal quality.

  In order to estimate and compensate for such phase fluctuations of laser light, digital signal processing techniques are used in conjunction with coherent detection.

  Patent Document 1 describes a configuration in which an average phase error is estimated for each block and phase compensation is performed for the next block. Further, in Non-Patent Documents 1 and 2, when an M-phase PSK (phase shift keying) signal is received, the received signal is raised to the Mth power and a component due to the original signal phase is removed, and then time-averaged. A configuration for estimating and compensating for components due to phase fluctuation is described. Non-Patent Document 3 describes a configuration in which a phase fluctuation component is compensated using a digital PLL (phase locked loop) circuit constituted by a phase error calculation, a loop filter, and a VCO (voltage controlled oscillator).

JP 2012-170061 A

A. J. Viterbi and A. M. Viterbi, "Nonlinear Estimation of PSK-Modulated Carrier Phase with Application to Burst Digital Transmission," IEEE Transaction on Information Theory Vol. IT-29, No.4, pp. 543-551 (1983). D.-S. Ly-Gagnon et al., "Coherent Detection of Optical Quadrature Phase-Shift Keying Signals With Carrier Phase Estimation," IEEE Journal of Lightwave Technology Vol. 24, No.1, pp. 12-21 (2006) . F. Derr, "Coherent Optical QPSK Intradyne System: Concept and Digital Receiver Realization," IEEE Journal of Lightwave Technology Vol. 10, No. 9, pp. 1290-1296 (1992).

In the techniques described in Patent Document 1 and Non-Patent Documents 1 to 3 for estimating and compensating for the phase fluctuation of the laser beam, it is used that the time fluctuation of the phase fluctuation is slower than the symbol rate of the signal. That is, the influence of other noise components on the compensation for phase fluctuation is reduced by incorporating a time averaging process or a low-pass loop filter. On the other hand, it is known that the power spectrum of laser light is a Lorentz type. The Lorentz-type distribution includes a relatively large amount of high-speed time fluctuation. However, in the techniques described in Patent Document 1 and Non-Patent Documents 1 to 3, the phase fluctuation is reduced by a time average process or a low-pass filter loop filter process. Therefore, in the techniques described in Patent Document 1 and Non-Patent Documents 1 to 3, since the response sensitivity to the high-speed phase fluctuation is small, the phase fluctuation of the laser beam that fluctuates at high speed is estimated and compensated. There is a problem that is difficult.
(Object of invention)
An object of the optical receiver, optical communication system, optical receiver method, and control program recording medium of the present invention is to provide a technique for reducing deterioration in signal quality due to phase fluctuations of a light source.

  The optical receiver of the present invention performs coherent detection on each optical signal received from different optical transmission paths using local oscillation light supplied from the same light source, and outputs a detection signal corresponding to each of the optical signals Coherent detection means, phase error detection means for detecting a phase error of a carrier component of the optical signal included in the detection signal, averaging means for obtaining an average value of the phase error, and using the average value Phase compensation means for performing phase compensation of the detection signal.

  In the optical communication system of the present invention, different data signals are coherently modulated using carrier waves supplied from the same light source, and transmission signals corresponding to the data signals are output to different optical transmission lines. And the transmission signal received as a plurality of optical signals from the different optical transmission lines, each of the received optical signals is coherently detected using local oscillation light supplied from the same light source, and the optical signal Coherent detection means for outputting a detection signal corresponding to each of the above, a phase error detection means for detecting a phase error of a carrier component of the optical signal included in the detection signal, and an average for obtaining an average value of the plurality of phase errors An optical receiving apparatus comprising: a converting means; and a phase compensating means for performing phase compensation of the detection signal using the average value; the optical transmitting apparatus; Comprising a transmission line connecting the receiving device.

  The optical receiving method of the present invention performs coherent detection on each of optical signals received from different optical transmission paths using local oscillation light supplied from the same light source, and detects a detection signal corresponding to each of the optical signals. Outputting, detecting a phase error of a carrier component of the optical signal included in the plurality of detection signals, obtaining an average value of the phase error, and performing phase compensation of the detection signal using the average value. Features.

  The recording medium for the control program of the optical receiver according to the present invention coherently detects each of the optical signals received from different optical transmission paths using the local oscillation light supplied from the same light source to the computer of the optical receiver. A procedure for outputting a plurality of detection signals corresponding to each of the optical signals, a procedure for detecting a phase error of a carrier component of the optical signal included in the plurality of detection signals, and an average value of the phase errors And a program for executing a procedure for performing phase compensation of the detection signal based on the average value.

  The present invention can reduce deterioration of signal quality due to phase fluctuation of a light source.

It is a block diagram of the multi-core fiber optical transmission system of a 1st embodiment. It is a block diagram of an optical transmitter. It is a block diagram of an optical receiver. It is a figure which shows the simulation result of the receiving characteristic of a multi-core fiber optical transmission system. It is a block diagram of the multi-core fiber optical transmission system of 2nd Embodiment. It is a block diagram of 15 A of optical receivers. It is a block diagram of the multi-core fiber optical transmission system of 3rd Embodiment. It is a block diagram of the optical receiver of 4th Embodiment.

(First embodiment)
FIG. 1 is a block diagram of a multi-core fiber optical transmission system 100 according to the first embodiment of this invention. The multi-core fiber optical transmission system 100 includes an optical transmitter 11, a fan-in 12, a multi-core fiber transmission line 13, a fan-out 14, and an optical receiver 15.

  The multicore fiber transmission line 13 is a multicore fiber in which a plurality of cores are formed in one clad. As the multi-core fiber, a 7-core multi-core fiber in which seven cores are arranged in a clad and a 19-core multi-core fiber in which 19 cores are arranged in a clad are known. In the first embodiment, for simplicity, a case will be described in which spatial multiplexing transmission is performed using two cores (core 1 and core 2) among a plurality of cores included in the multi-core fiber transmission line 13. The number of cores provided in the multi-core fiber transmission line 13 is not limited to two, and the configuration of the present embodiment can be applied to an optical transmission system using a multi-core fiber having three or more cores.

  The optical transmission device 11 generates two optical signals (core 1 transmission light 24-1 and core 2 transmission light 24-2) to be sent to the core 1 and the core 2. The core 1 transmission light 24-1 and the core 2 transmission light 24-2 transmitted from the optical transmission device 11 are input to the fan-in 12 and transmitted through the core 1 and the core 2 of the multi-core fiber transmission path 13, respectively. The fan-in 12 is a device for coupling the core 1 transmission light 24-1 and the core 2 transmission light 24-2 to the core 1 and the core 2 of the multi-core fiber transmission path 13, respectively.

  The multi-core fiber transmission line 13 may include an optical amplifier or the like. The core 1 transmission light 24-1 and the core 2 transmission light 24-2 that have propagated through the multi-core fiber transmission line 13 are received as light via the fan-out 14 as core 1 reception light 41-1 and core 2 reception light 41-2. Received by device 15. The fan-out 14 is a device for coupling the core 1 transmission light 24-1 and the core 2 transmission light 24-2 propagated through the core 1 and the core 2 of the multi-core fiber transmission line 13 with the optical receiver 15.

  FIG. 2 is a block diagram of the optical transmitter 11. In the optical transmitter 11, a common light source 21 is used as a light source for modulation in the optical modulators 23-1 and 23-2 that modulate an optical signal transmitted to the multi-core fiber transmission line 13.

  A part of the light branched by the output of the light source 21 is modulated by the optical modulator 23-1 by the data signal 22-1. The light modulated by the optical modulator 23-1 becomes the core 1 transmission light 24-1. Another part of the light branched at the output of the light source 21 is modulated by the optical modulator 23-2 by the data signal 22-2. The light modulated by the optical modulator 23-2 becomes the core 2 transmission light 24-2.

  The optical modulators 23-1 and 23-2 each have a polarization multiplexing function. The optical modulator 23-1 can polarization-multiplex two different data included in the data signal 22-1 and transmit it as the core 1 transmission light 24-1 by the polarization multiplexing function. Similarly, the optical modulator 23-2 can polarization-multiplex two different data included in the data signal 22-2 and transmit it as the core 1 transmission light 24-2.

  In this way, the data signals 22-1 and 22-2 are transmitted by the multi-core fiber transmission line 13.

FIG. 3 is a block diagram of the optical receiver 15. The optical receiver 15 includes a light source 31, optical front ends 32-1 and 32-2, ADCs (analog to digital converters) 33-1 and 33-2, wavelength dispersion compensators 34-1 and 34-2, and polarization separation. The units 35-1 and 35-2 are provided. Furthermore, the optical receiver 15 includes phase error detection units 36-1 and 36-2, an averaging unit 37, phase compensation units 38-1 and 38-2, and symbol identification units 39-1 and 39-2.
The optical receiver 15 may further include a CPU (central processing unit) 501 and a memory 502. The memory 502 is a fixed storage medium that stores a program executed by the CPU 501. The CPU 501 may realize the function of the optical receiver 15 by executing a program stored in the memory 502. Furthermore, a DSP (digital signal processor) may be used as the CPU 501.
Wavelength dispersion compensation units 34-1 and 34-2, polarization separation units 35-1 and 35-2, phase error detection units 36-1 and 36-2, averaging unit 37, phase compensation units 38-1 and 38- 2. The symbol identification units 39-1 and 39-2 are arithmetic circuits that perform an operation on the input electric signal and output an operation result. The functions of these arithmetic circuits may be controlled by the CPU 501.

  Hereinafter, a mode in which the optical receiver 15 receives the core 1 transmission lights 24-1 and 24-2 that are polarization-multiplexed in the optical transmitter 11 will be described. The light source 31, optical front ends 32-1 and 32-2, ADCs 33-1 and 33-2, chromatic dispersion compensation units 34-1 and 34-2, and polarization separation units 35-1 and 35-2 are generally Is called a coherent detector. The general configuration of the coherent detector and the configurations of the symbol identification units 39-1 and 39-2 are well known as the configuration of the optical receiver that performs coherent detection, and thus detailed description thereof is omitted.

  The core 1 transmission light 24-1 that has propagated through the core 1 is received by the optical receiver 15 as the core 1 reception light 41-1. The core 1 received light 41-1 is input to the optical front end 32-1 together with the light (LO light) branched at the output of the light source 31, and is subjected to coherent detection. As is well known, the optical front end 32-1 includes, for example, a polarization multiplexing type 90-degree optical hybrid, a balanced photodiode, and a transimpedance amplifier.

  From the optical front end 32-1, generally, four electric signals of in-phase component (I) and quadrature component (Q) are output for two polarized waves (X, Y), respectively. These electric signals are expressed in a complex number format for each polarization, with the I component being a real part and the Q component being an imaginary part. In FIG. 3, the X-polarized signal and the Y-polarized signal are each described by one line.

  The output of the optical front end 32-1 is quantized by the ADC 33-1, and digital signal processing is performed in the subsequent blocks. The processing in the chromatic dispersion compensation unit 34-1 and the polarization separation unit 35-1 is the same as the processing in general polarization multiplexing coherent detection. For example, the chromatic dispersion compensator 34-1 compensates for waveform degradation caused by chromatic dispersion generated in the transmission path. Further, the polarization separation unit 35-1 performs compensation of the polarization state of the signal transmitted by polarization multiplexing and phase compensation of the carrier. In the polarization separation unit 35-1, the influence of noise components such as ASE (amplified spontaneous emission) on the carrier phase is reduced by time averaging or the like.

  Similarly, the core 2 transmission light 24-2 propagated through the core 2 is received as the core 2 reception light 41-2. The core 2 received light 41-2 is input to the optical front end 32-2 together with the LO light and subjected to coherent detection. The coherently detected signal is quantized by the ADC 33-2. Then, in the chromatic dispersion compensation unit 34-2 and the polarization separation unit 35-2, digital signal processing is performed on the quantized signal by the same procedure as that of the core 1 received light 41-1.

  Here, in the optical front end 32-2, the output of the light source 31 is branched and used for coherent detection of the core 1 received light 41-1 and the core 2 received light 41-2. That is, the light source 31 that generates LO light for coherent detection of the core 2 received light 41-2 is common to the core 1 received light 41-1. With such a configuration, the influence of the phase fluctuation of the light source 31 on the result of the coherent detection of the core 1 received light 41-1 and the core 2 received light 41-2 is synchronized.

  Next, operations of the phase error detection units 36-1 and 36-2, the averaging unit 37, and the phase compensation units 38-1 and 38-2 will be described.

  The polarization separation unit 35-1 outputs the output of the separated polarization (X, Y) as detection signals 40-1 and 40-2. The detection signal 40-1 is branched into two and input to the phase compensation unit 38-1 and the phase error detection unit 36-1. Similarly, the detection signal 40-2 is input to the phase compensation unit 38-2 and the phase error detection unit 36-2.

  The phase error detector 36-1 detects the phase error of the carrier from the most probable signal point of the detection signal 40-1. For example, the phase error detector 36-1 performs symbol determination on the input signal to obtain the most probable signal point and obtains complex conjugate data thereof. The phase error detection unit 36-1 calculates the deflection angle after multiplying the obtained complex conjugate data by the input signal. The carrier phase error is obtained from the calculated declination. The phase error detection unit 36-1 detects a phase error for each of the two polarization components (X, Y).

  Similarly, in the detection signal 40-2, the phase error detection unit 36-2 detects the respective phase errors for the two polarization components (X, Y).

  That is, the phase error detection unit 36-1 detects each phase error of the polarization component (X, Y) included in the detection signal 40-1 and outputs it to the averaging unit 37. Further, the phase error detection unit 36-2 detects each phase error of the polarization component (X, Y) included in the detection signal 40-2 and outputs it to the averaging unit 37.

  And the averaging part 37 calculates | requires the average value of each phase error calculated | required by the phase error detection parts 36-1 and 36-2, and calculates the average value (averaged phase error) to the phase compensation part 38-1. And 38-2.

  Here, the correlation between the cores regarding noise such as ASE is considered to be small. On the other hand, the phase error due to the phase fluctuation of the light source 31 has simultaneity in all the detection signals output from the phase error detection units 36-1 and 36-2. In addition, it is considered that the phase error caused by the phase fluctuation of the light source 31 has simultaneity with respect to two polarization components. Here, since the process in the averaging unit 37 is performed at each timing, unlike the time average process or the low-pass filter process, the frequency component having a high phase fluctuation is not cut off. For this reason, the averaged phase error includes the influence of the phase fluctuation of the light source 31 that fluctuates at high speed. Therefore, the phase error caused by the phase fluctuation of the light source 31 is extracted by averaging the phase error in the averaging unit 37.

  The average value of the phase error output from the averaging unit 37 is a phase error mainly caused by the phase fluctuation of the light source 31. The phase error output from the averaging unit 37 is used for phase correction of the detection signals 40-1 and 40-2 in the phase compensation units 38-1 and 38-2.

  The phase compensation unit 38-1 compensates for the phase error by rotating the phase of the detection signal 40-1 in the direction opposite to the averaged phase error. Specifically, the phase compensation unit 38-1 multiplies the detection signal 40-1 by the signal having the opposite phase of the averaged phase error output from the averaging unit 37, thereby obtaining the phase of the light source 31. Reduce phase error due to fluctuations.

  The phase compensation unit 38-2 performs the same process as the phase compensation unit 38-1 on the detection signal 40-2.

  Symbol identification is performed in the symbol identification units 39-1 and 39-2 on the outputs of the phase compensation units 38-1 and 38-2 from which the influence of the phase error has been removed. The symbol identification units 39-1 and 39-2 output data in which symbols are identified.

  As described above, the multi-core fiber optical transmission system 100 according to the first embodiment obtains the average value of the phase errors detected by the phase error detectors 36-1 and 36-2 by calculation, and based on the obtained average value. Thus, phase compensation is performed by the phase compensation units 38-1 and 38-2. As a result, the influence of the phase fluctuation of the light source 31 is reduced including the fluctuation component that fluctuates at high speed. That is, the multi-core fiber optical transmission system 100 according to the first embodiment has an effect that it is possible to reduce deterioration in signal quality due to phase fluctuation of the light source.

  In the present embodiment, the mode in which the transmitted optical signal is polarization multiplexed has been described. However, polarization multiplexing may not be performed on the transmitted optical signal. When polarization multiplexing is not performed, one detection signal is output from each of the core 1 received light and the core 2 received light. Then, the phase error detectors 36-1 and 36-2 obtain the phase error of these detection signals, the averaging unit 37 obtains the average value of the phase errors, and the phase compensators 38-1 and 38-2. Output to. The phase compensation units 38-1 and 38-2 perform phase compensation of the detection signal based on the obtained average value. As a result, even when polarization multiplexing is not performed, the influence of the phase fluctuation of the light source 31 is reduced including a component that fluctuates at high speed.

  In the present embodiment, the optical transmission by the two cores has been described. However, for three or more cores, phase error detection is performed for each core, and the results are averaged to perform phase compensation, so that the same effect can be obtained even when the multi-core transmission line includes three or more cores. Is obtained.

  FIG. 4 is a diagram illustrating a simulation result of reception characteristics of the multi-core fiber optical transmission system. FIG. 4 shows the result of simulating reception characteristics in the case of performing multiplex transmission of an 80 Gb / s (gigabit per second) polarization multiplexed 16QAM signal using a multi-core fiber having seven cores. In the simulation, the modulated light propagating through all the cores is set to be received using the same laser light having a line width of 1 MHz as LO light. A (solid line) in FIG. 4 is a simulation result when phase compensation according to the present embodiment, that is, an average value of phase errors detected by different cores is obtained and phase compensation is performed using the average value. Further, B (broken line) in FIG. 4 is a simulation result when the phase compensation is not performed by the average value of the phase error between the cores.

  The horizontal axis of FIG. 4 is an OSNR (optical signal to noise ratio), and the vertical axis is a Q value (quality factor). The Q value is an index generally used as a value indicating the quality of a digital optical signal. A large Q value indicates a higher signal transmission quality.

  From FIG. 4, it can be confirmed that in the multi-core fiber optical transmission system, the Q value, that is, the quality of the received signal is improved by performing the phase compensation based on the average value of the phase errors detected by different cores.

(Second Embodiment)
FIG. 5 is a block diagram of a multi-core fiber optical transmission system 200 according to the second embodiment. The multi-core fiber optical transmission system 200 includes an optical transmitter 11, a fan-in 12, a multi-core fiber transmission line 13, a fan-out 14, and an optical receiver 15A. The configuration of the multi-core fiber optical transmission system 200 is the same as that of the multi-core fiber optical transmission system 100 shown in FIG. 1 except for the optical receiver 15A. It should be noted that the same components as those described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the multi-core fiber transmission line 13, there is a possibility that a difference occurs in propagation delay between cores due to a difference in refractive index of each core. If there is a difference in propagation delay between the cores, in the optical receiver 15A, the simultaneity between the cores of the influence of the phase fluctuation of the light source 21 (see FIG. 2) included in the optical transmitter 11 is maintained. I can't beat it.

  However, the difference in propagation delay between the cores of the multi-core fiber transmission line 13 depends mainly on variations in the production of the multi-core fiber and the installation environment of the transmission line, so it is considered that it does not vary greatly in time. Therefore, by adjusting the delay difference between the cores optically or using digital signal processing, even when there is a propagation delay difference between the cores, the influence of the phase fluctuation of the light source 31 of the optical transmitter is reduced. it can.

  FIG. 6 is a block diagram of the optical receiver 15A. The optical receiver 15A is different from the optical receiver 15 shown in FIG. 3 in that it includes a delay adjustment unit 50.

  That is, the optical receiver 15A includes delay adjustment units 50-1 and 50-2 immediately after the output of the polarization separation unit 35-1. The delay adjustment units 50-1 and 50-2 adjust the delay amount so that the correlation between the output of the phase error detection unit 36-1 and the output of the phase error detection unit 36-2 becomes large.

  For example, the delay adjustment unit 50-1 receives an average value of two phase errors corresponding to the detection signal 40-1 from the phase error detection unit 36-1, and receives the detection signal 40-2 from the phase error detection unit 36-2. The average value of the two phase errors corresponding to is received. Then, the delay adjustment unit 50-1 may change the delay amount so that the difference between the average values of the received phase errors becomes small. Also, the delay adjustment unit 50-2 may have the same function as the delay adjustment unit 50-1, and the delay amount may be adjusted in one or both of the delay adjustment units 50-1 and 50-2.

  The phase error detection units 36-1 and 36-2 detect the phase error in consideration of the phase fluctuation of the light source 21 even if the delay amounts of the core 1 and the core 2 are different by adjusting the delay amount. it can.

  As a result, similarly to the first embodiment, the multi-core fiber optical transmission system 200 of the second embodiment can reduce signal quality degradation due to phase fluctuations of the light source. Furthermore, the multi-core fiber optical transmission system 200 of the second embodiment can improve the received signal quality including the reduction of the influence of the phase fluctuation of the light source of the optical transmission device.

  Instead of the delay adjustment units 50-1 and 50-2, the delay adjustment unit that optically adjusts the delay amount of the core 1 reception light 41-1 and the core 2 reception light 41-2 is replaced with the fan-out 14 and the light. It may be provided between the front ends 32-1 and 32-2.

(Third embodiment)
FIG. 7 is a block diagram of a multi-core fiber optical transmission system 300 according to the third embodiment. The multi-core fiber optical transmission system 300 has a configuration for transmitting a modulated optical signal through a multi-core fiber transmission line by wavelength multiplexing.

  The multi-core fiber optical transmission system 300 includes optical transmitters 111 to 11n, multiplexers 121-1 and 121-2, fan-in 12, multi-core fiber transmission path 13, fan-out 14, and duplexers 122-1 and 122-2. And optical receivers 151 to 15n. n indicates that there are n optical transmitters and optical receivers (n is an integer of 2 or more). In FIG. 7, the configurations of the fan-in 12, the multi-core fiber transmission line 13, and the fan-out 14 are the same as those in FIGS.

  The optical transmitters 111 to 11n have the same configuration as the optical transmitter 11 shown in FIG. Each of the optical transmission devices 111 to 11n outputs the core 1 transmission light 24-1 to the multiplexer 121-1, and outputs the core 2 transmission light 24-2 to the multiplexer 121-2. Here, the wavelengths of light output from the optical transmission apparatuses 111 to 11n are different, and the wavelengths of the optical transmission apparatuses 111 to 11n are λ1 to λn, respectively.

  The optical receivers 151 to 15n have the same configuration as the optical receiver 15 shown in FIG. 3 or the optical receiver 15A shown in FIG. The optical receivers 151 to 15n receive received light having wavelengths λ1 to λn, respectively.

  The optical multiplexer 121-1 wavelength-multiplexes the core 1 transmission light 24-1 having the wavelengths λ1 to λn output from the optical transmission devices 111 to 11n, and inputs the wavelength-multiplexed light to the fan-in 12 as the core 1 transmission light 124-1. . The optical multiplexer 121-2 wavelength-multiplexes the core 2 transmission light 24-2 having the wavelengths λ1 to λn output from the optical transmission apparatuses 111 to 11n, and inputs the wavelength-multiplexed light to the fan-in 12 as the core 1 transmission light 124-2. .

  The fan-out 14 inputs the core 1 transmission light 124-1 propagated through the core 1 of the multi-core fiber transmission line 13 as the core 1 reception light 141-1 to the duplexer 122-1. The demultiplexer 122-1 wavelength-separates the core 1 received light 141-1 into the core 1 received light 41-1 having wavelengths λ1 to λn and inputs the wavelength-separated light to the optical receivers 151 to 15n for each wavelength. Further, the fan-out 14 inputs the core 2 transmission light 124-2 propagated through the core 2 to the demultiplexer 122-2 as the core 2 reception light 141-2. The demultiplexer 122-2 wavelength-separates the core 2 received light 141-2 into the core 2 received light 41-2 having the wavelengths λ1 to λn, and inputs the separated wavelengths to the optical receivers 151 to 15n.

  With such a configuration, the optical receivers 151 to 15n can receive wavelength-multiplexed transmitted optical signals for each wavelength and correct phase errors.

  That is, the multi-core fiber optical transmission system 300 according to the third embodiment has an effect that it is possible to reduce the deterioration of signal quality due to the phase fluctuation of the light source, as in the first and second embodiments.

  Furthermore, the multi-core fiber optical transmission system 300 of the third embodiment transmits an optical signal by wavelength multiplexing and corrects a phase error for each wavelength at the time of reception. For this reason, the multi-core fiber optical transmission system 300 according to the third embodiment can reduce the influence of the phase fluctuation of the light source at each wavelength multiplexed wavelength.

  In the present embodiment, when the optical receiver 15A described in FIG. 6 is used for some or all of the optical receivers 151 to 15n, the optical transmitters 111 to 11n of the optical receiver 15A are used. The influence of the phase error of the light source is reduced.

(Fourth embodiment)
FIG. 8 is a block diagram of an optical receiver 400 according to the fourth embodiment of this invention. The optical receiving device 400 includes a coherent detection unit 401, a phase error detection unit 402, an averaging unit 403, and a phase compensation unit 404.

  The coherent detection unit 401 performs coherent detection on a plurality of optical signals received from different optical transmission paths using local oscillation light supplied from the same light source, and generates a plurality of detection signals corresponding to the received optical signals. Output. The phase error detection unit 402 detects the phase error of the carrier wave component of the received optical signal included in each of the plurality of detection signals output from the coherent detection unit 401. Averager 403 obtains the average value of the phase errors detected by phase error detector 402 and outputs the average value to phase compensator 404. The phase compensation unit 404 performs phase compensation of the detection signal output from the coherent detection unit 401 based on the average value obtained by the averaging unit 403.

  The optical receiver 400 of the fourth embodiment performs coherent detection on a plurality of optical signals using local oscillation light supplied from the same light source. Then, the optical receiver 400 performs phase compensation of the received signal based on the average value of the phase error of the detection signal detected by the phase error detector 402. With such a configuration, the optical receiving device 400 can reduce the influence of the phase fluctuation of the local oscillation light in the coherent reception.

  That is, the optical receiving device 400 according to the fourth embodiment has an effect that it is possible to reduce deterioration in signal quality due to phase fluctuation of the light source.

  The procedure for detecting the phase error of the carrier component of the optical signal included in the detection signal, the procedure for obtaining the average value of the phase error, and the phase of the detection signal based on the average value described in the first to fourth embodiments. The procedure for performing the compensation may be executed by a computer included in each optical receiving apparatus. The computer is, for example, a CPU or a DSP. The CPU and DSP are controlled by a program. The program is recorded on a fixed recording medium such as a memory or a hard disk.

While the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.
This application claims the priority on the basis of Japanese application Japanese Patent Application No. 2013-014422 for which it applied on January 29, 2013, and takes in those the indications of all here.

100, 200, 300 Multi-core fiber optical transmission system 11, 111-11n Optical transmitter 12 Fan-in 121-1, 121-2 multiplexer 122-1, 122-2 Demultiplexer 13 Multi-core fiber transmission line 14 Fan-out 15 , 15A, 151-15n, 400 Optical receiver 21 Light source 22-1, 22-2 Data signal 23-1, 23-2 Optical modulator 24-1, 124-1 Core 1 transmitted light 24-2, 124-2 Core 2 transmission light 31 Light source 32-1, 32-2 Optical front end 33-1, 33-2 ADC
34-1 and 34-2 Wavelength dispersion compensation unit 35-1 and 35-2 Polarization separation unit 36-1 and 36-2 Phase error detection unit 37 Averaging unit 38-1 and 38-2 Phase compensation unit 39-1 39-2 Symbol identification unit 40-1, 40-2 Detection signal 41-1, 141-1 Core 1 received light 41-2, 141-2 Core 2 received light 50-1, 50-2 Delay adjustment unit 401 Coherent Detection unit 402 Phase error detection unit 403 Averaging unit 404 Phase compensation unit 501 CPU
502 memory

Claims (10)

Coherent detection means for coherently detecting each optical signal received from different optical transmission paths using local oscillation light supplied from the same light source, and outputting a detection signal corresponding to each of the optical signals;
Phase error detection means for detecting a phase error of a carrier wave component of the optical signal included in the detection signal;
Averaging means for obtaining an average value of a plurality of the phase errors;
And a phase compensation unit that performs phase compensation of the detection signal using the average value.   The apparatus further comprises delay adjusting means for adjusting a delay amount of the detection signal so that a correlation of phase errors between the detection signals detected by the phase difference detection means is increased, and the detection signal with the adjusted delay amount is provided. The optical receiver according to claim 1, wherein the optical receiver is input to the phase difference detection unit.   3. The optical receiver according to claim 1, wherein each of the different optical transmission lines is a plurality of cores provided in the same cladding in the multi-core fiber. The optical signal is a polarization multiplexed optical signal,
The coherent detection means outputs the detection signal separated for each polarization,
4. The optical receiver according to claim 1, wherein the phase error detection unit detects a phase error of a carrier wave component included in the detection signal separated for each polarization. 5. The optical signal is a wavelength-multiplexed optical signal,
The coherent detection means coherently detects the optical signal using local oscillation light supplied from the same light source for each multiplexed wavelength, and outputs the detection signal.
5. The optical receiver according to claim 1, wherein the phase error detection unit detects a phase error of a carrier wave component included in the detection signal separated for each wavelength. Optical transmission devices that coherently modulate different data signals using carrier waves supplied from the same light source, and output transmission signals corresponding to the data signals to different optical transmission lines, respectively.
The plurality of transmission signals are received as a plurality of optical signals from the different optical transmission lines, each of the received optical signals is coherently detected using local oscillation light supplied from the same light source, and the optical signal Coherent detection means for outputting a detection signal corresponding to each, phase error detection means for detecting a phase error of a carrier component of the optical signal included in the detection signal, and averaging for obtaining an average value of a plurality of the phase errors And an optical receiver comprising: phase compensation means for performing phase compensation of the detection signal using the average value;
An optical communication system comprising: a transmission line that connects the optical transmitter and the optical receiver. Optical transmission devices for coherently modulating different data signals using carrier waves supplied from the same light source and polarization multiplexing and outputting transmission signals respectively corresponding to the data signals to different optical transmission lines,
An optical communication system comprising: the optical receiving device according to claim 4. Optical transmission for coherently modulating different data signals for each wavelength to be multiplexed using a carrier wave supplied from the same light source and wavelength-division-multiplexing and outputting transmission signals corresponding to the data signals to different optical transmission paths Equipment,
An optical communication system comprising: the optical receiver according to claim 5. Each of the optical signals received from different optical transmission paths is coherently detected using local oscillation light supplied from the same light source, and outputs a detection signal corresponding to each of the optical signals,
Detecting a phase error of a carrier component of the optical signal included in the detection signal;
Obtain an average value of a plurality of the phase errors,
An optical receiving method, wherein phase compensation of the detection signal is performed using the average value. In the computer of the optical receiver,
A procedure of coherently detecting each optical signal received from different optical transmission paths using local oscillation light supplied from the same light source, and outputting a plurality of detection signals corresponding to each of the optical signals,
A procedure for detecting a phase error of a carrier component of the optical signal included in the detection signal;
A procedure for obtaining an average value of a plurality of the phase errors;
A procedure for performing phase compensation of the detection signal using the average value, and a control program for the optical receiver for executing the procedure,
Recording medium for control program of optical receiver.

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