Relative phase difference compensation device, relative phase difference compensation method, and program

Abstract

In optical communications, this contributes to reducing the amount of calculation in the fitting process performed on the interference signal between the signal light and the reference light. [Solution] A relative phase difference compensation device according to the present disclosure separates signal light and reference light from an optical signal, generates inverse function data indicating the inverse function of a specific function indicated by an interference output signal generated by homodyne detection, modulates the separated reference light, combines the separated signal light and modulated reference light, separates the polarization component of the signal light and the polarization component of the reference light from the combined signal light and reference light, performs homodyne detection on the polarization component of the separated signal light and the polarization component of the reference light to generate an interference output signal, estimates the relative phase difference between the signal light and the reference light based on the generated interference output signal, and generates offset value data that cancels out the relative phase difference between the signal light and the reference light based on the estimated relative phase difference between the signal light and the reference light.

Description

[Technical field]

[0001] The present disclosure relates to a relative phase difference compensation device, a relative phase difference compensation method, and a program. [Background technology]

[0002] In the field of optical communications using coherent signal light such as laser beams, homodyne detection is used to detect phase information from signal light modulated with reference light. Homodyne detection is also generally called homodyne detection (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-180668 A Summary of the Invention [Problem to be solved by the invention]

[0004] The disclosures of the above-mentioned prior art documents are incorporated herein by reference. The following analysis was conducted by the present inventors.

[0005] Here, a fitting process is performed to obtain a relative phase difference between the signal light and the reference light from an interference signal obtained by interfering the signal light and the reference light using a homodyne detection method. However, the amount of calculation processing for the fitting process is large, and this calculation process requires a lot of time. Therefore, in order to transmit high-speed, wide-band data by optical communication, it is desirable to reduce the amount of calculation processing for the fitting process and shorten the time required for the calculation process.

[0006] An object of the present disclosure is to reduce the amount of calculations in the fitting process that is performed on an interference signal between signal light and reference light obtained by homodyne detection in optical communications to determine the relative phase difference between signal light and reference light, thereby contributing to shortening the calculation time. [Means for solving the problem]

[0007] In a first aspect of the present disclosure, there is provided a relative phase difference compensation device that includes a polarization controller, a modulator, a balanced receiver, a polarization beam splitter, a phase difference estimator, and an offset value controller, and that compensates for a relative phase difference between a signal light and a reference light that are included in an optical signal and have orthogonal polarizations. The polarization controller is configured to separate the signal light and the reference light from the optical signal. The modulator is configured to modulate the separated reference light with a received modulation signal indicated by inverse function data indicating an inverse function of a specific function indicated by an interference output signal generated by homodyne detection by the balanced receiver. The polarization beam splitter is configured to combine the signal light separated by the polarization controller and the modulated reference light, and to separate a polarization component of the signal light and a polarization component of the reference light from the combined signal light and reference light. The balanced receiver is configured to perform the homodyne detection on the separated polarization component of the signal light and the polarization component of the reference light to generate the interference output signal. The phase difference estimator is configured to estimate a relative phase difference between the signal light and the reference light based on the generated interference output signal, and the offset value controller is configured to generate offset value data that cancels the relative phase difference between the signal light and the reference light based on the estimated relative phase difference between the signal light and the reference light.

[0008] In a second aspect of the present disclosure, a relative phase difference compensation device is provided that includes a polarization controller, a modulator, and a polarization beam splitter, and compensates for a relative phase difference between a signal light and a reference light, which are included in an optical signal and have orthogonal polarizations, and includes an inverse function data generating step, an interference output signal generating step, a relative phase difference estimating step, and an offset value data generating step. The polarization controller is configured to separate the signal light and the reference light from the optical signal. The modulator is configured to modulate the separated reference light with a received modulation signal indicated by inverse function data indicating an inverse function of a specific function indicated by an interference output signal generated by homodyne detection using a balanced receiver. The polarization beam splitter is configured to combine the signal light separated by the polarization controller and the modulated reference light, and to separate a polarization component of the signal light and a polarization component of the reference light from the combined signal light and reference light. The inverse function data generating step generates inverse function data indicating an inverse function of a specific function indicated by an interference output signal generated by homodyne detection. The interference output signal generating step performs the homodyne detection on the separated polarization component of the signal light and the polarization component of the reference light to generate the interference output signal. The relative phase difference estimating step estimates a relative phase difference between the signal light and the reference light based on the generated interference output signal. The offset value data generating step generates offset value data that cancels the relative phase difference between the signal light and the reference light based on the estimated relative phase difference between the signal light and the reference light.

[0009] In a third aspect of the present disclosure, there is provided a relative phase difference compensation program executed in a relative phase difference compensation device that includes a polarization controller, a modulator, and a polarization beam splitter and compensates for a relative phase difference between a signal light and a reference light that are included in an optical signal and have orthogonal polarizations, the program including an inverse function generation process, an interference output signal generation process, a relative phase difference estimation process, and an offset value data generation process. The polarization controller is configured to separate the signal light and the reference light from the optical signal. The modulator is configured to modulate the separated reference light with a received modulation signal indicated by inverse function data indicating an inverse function of a specific function indicated by an interference output signal generated by homodyne detection using a balanced receiver. The polarization beam splitter is configured to combine the signal light separated by the polarization controller and the modulated reference light, and to separate a polarization component of the signal light and a polarization component of the reference light from the combined signal light and reference light. The inverse function generation process generates inverse function data indicating an inverse function of a specific function indicated by an interference output signal generated by homodyne detection. The interference output signal generation process performs the homodyne detection on the separated polarization components of the signal light and the reference light to generate the interference output signal. The relative phase difference estimation process estimates a relative phase difference between the signal light and the reference light based on the generated interference output signal. The offset value data generation process generates offset value data that cancels the relative phase difference between the signal light and the reference light based on the estimated relative phase difference between the signal light and the reference light. Effect of the Invention

[0010] According to each aspect of the present disclosure, in optical communications, the fitting process is performed on an interference signal between signal light and reference light obtained by homodyne detection to determine the relative phase difference between the signal light and the reference light, which can contribute to reducing the amount of calculation and shortening the calculation time. [Brief description of the drawings]

[0011] [Figure 1]FIG. 1 is a diagram illustrating an example of the configuration of an optical communication system that transmits and receives data using coherent light such as a laser beam. [Diagram 2] FIG. 2 is a diagram illustrating a configuration of an optical communication system. [Diagram 3] FIG. 3 is a diagram illustrating the processing of a sign fitting processor in the optical signal receiving and processing device shown in FIG. [Figure 4] FIG. 4 is a diagram illustrating a configuration of an optical communication system according to an embodiment of the present disclosure. [Figure 5A] 5A is a diagram illustrating an example of a waveform of a voltage value indicated by cosine wave data output by an inverse cosine wave data generator of the optical signal receiving processing device shown in FIG. [Figure 5B] FIG. 5B is a diagram illustrating waveforms of interference output signals output under three different conditions by the balanced receiver of the optical signal receiving processing device shown in FIG. [Figure 5C] 5 is a diagram illustrating sample points selected from interference output signals output under three different conditions by the balanced receiver of the optical signal receiving processing device shown in FIG. 4. [Figure 6] FIG. 6 is a diagram illustrating one configuration of an information processing device capable of implementing all or part of the functions of the components of the transmission modulation signal generator and the optical signal receiving and processing device of the optical communication system shown in FIGS. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the embodiments described below. In addition, in each drawing, the same or corresponding elements and processes are appropriately labeled with the same reference numerals. Furthermore, it should be noted that the drawings are schematic, and the dimensional relationship of each element, the ratio of each element, and the details of each process may differ from those in the present disclosure when implemented. In addition, there may be parts in which the dimensional relationship and details of each process are different between the drawings.

[0013] First, an optical communication system 1 used for continuous variable quantum key distribution (CV-QKD) used to enhance the security of optical communication in quantum cryptography communication will be described with reference to Fig. 1. Fig. 1 is a diagram illustrating an example of a configuration of an optical communication system 1 that transmits and receives data using coherent light such as a laser beam. As illustrated in Fig. 1, the optical communication system 1 includes a transmitting device 2 and a receiving device 3 connected via an optical transmission path 100 formed of an optical fiber cable.

[0014] The transmitting device 2 includes a laser diode (LD) 200, a non-polarization beam splitter (NPBS) 202, a polarization beam splitter (PBS) 206, and a phase modulator (PM) 204, all of which are connected to each other by an optical fiber cable. With these components, the transmitting device 2 phase-modulates coherent light such as a laser beam with the voltage value of a transmission modulation signal input from the outside to generate signal light S (signal light), and transmits the signal light S to the receiving device 3 via the optical transmission path 100.

[0015] The receiving device 3 includes a polarization controller (PC) 300, a non-polarizing beam splitter 302, a phase modulator (PM) 304, variable optical attenuators (VOAs) 306 and 308, and a balance receiver (BR) 310. With these components, the transmitting device 2 receives the signal light S from the transmitting device 2, demodulates the transmission modulated signal by homodyne detection, and outputs it to the outside as a voltage value of an interference output signal.

[0016] In the transmitting device 2, the laser diode 200 generates a laser beam as coherent light and outputs it to the non-polarizing beam splitter 202. The non-polarizing beam splitter 202 splits the laser beam input from the laser diode 200 into two components, for example, with an intensity of 99% and an intensity of 1%, outputs the reference light LO with an intensity of 99% to the polarizing beam splitter 206, and outputs the signal light S with an intensity of 1% to the phase modulator 204.

[0017] The phase modulator 204 modulates the signal light S having an intensity of 1% of the laser beam input from the non-polarizing beam splitter 202 with a transmission modulation signal, and outputs the modulated signal to the polarizing beam splitter 206. The polarizing beam splitter 206 combines the signal light S modulated by the phase modulator 204 and the polarized reference light LO input from the polarizing beam splitter 206 so that the polarized lights are orthogonal to each other, and outputs the combined signal to the optical transmission line 100. Note that the optical transmission line 100 is a quantum channel that transmits light by an optical fiber cable, and the polarization of the optical signal output from the transmitter 2 is not preserved in the optical transmission line 100.

[0018] When an optical signal is input from the optical transmission line 100 to the receiving device 3, the polarization controller 300 separates the optical signal into a polarization component of the signal light S and a polarization component of the reference light LO, outputs the polarization component of the signal light S to a non-polarizing beam splitter 302, and outputs the polarization component of the reference light LO to a phase modulator 304. A random received modulation signal is input to the phase modulator 304, which randomly phase-modulates the polarization component of the reference light LO input from the polarization controller 300 and outputs it to the non-polarizing beam splitter 302.

[0019] The non-polarizing beam splitter 302 is a half-mirror beam splitter, which combines the polarization component of the signal light S input from the polarization controller 300 with the polarization component of the reference light LO modulated by the phase modulator 304. The non-polarizing beam splitter 302 splits the intensity of the signal light S obtained by this combination into two optical signals orthogonal to each other and having 50% intensity, outputs one of the polarized optical signals with 50% intensity to the variable optical attenuator 306, and outputs the other polarized optical signal with 50% intensity to the variable optical attenuator 308.

[0020] The variable optical attenuators 306 and 308 equalize the intensities of the optical signals input thereto and output the equalized signals to the balanced receiver 310. The balanced receiver 310 performs homodyne detection on the optical signals input from the variable optical attenuators 306 and 308, detecting amplitude and phase information of the signal light by utilizing the interference of two lights, generates an interference output signal indicating the result of the homodyne detection as a voltage value, and outputs the signal light output signal to the outside. Note that in FIG. 1 and other figures, the path of the signal light S component is indicated by a fine dotted line, and the path of the reference light LO component is indicated by a coarse dotted line.

[0021] CV-QKD differs from standard quantum key distribution (QKD) in the method of detecting weak signal light S, and has advantages over QKD in terms of practical application and implementation, making it a hot research topic in quantum cryptography communication technology. The optical communication system 1 basically has the same configuration as a Mach-Zehnder interferometer. Therefore, the relative phase difference Φ caused by the difference between the optical path length (optical path length) of the signal light S from the laser diode 200 to the balanced receiver 310 and the optical path length of the reference light LO is ps must be stable to within one wavelength of these lights.

[0022] In addition, when implementing CV-QKD using the optical communication system 1, the relative phase difference Φ between the signal light S and the reference light LO is set to 1 in order to suppress excess noise. ps In addition, the fluctuation of the relative phase difference Φ between the signal light S and the reference light LO, which can always vary, must be minimized. psIn order to always accurately estimate and correct the relative phase difference Φ ps The detection of the relative phase difference Φ is performed for about 0.1 seconds at a time interval of 1 second, for example. ps It is necessary to constantly perform compensation for the phase difference between the signal light S and the reference light LO at time intervals of 1 second based on the relative phase difference Φ ps and the estimated relative phase difference Φ ps The compensation of the phase difference based on is a method for single capture offline processing. In the case of streaming data processing, the relative phase difference Φ ps Another approach is taken to estimate and compensate for

[0023] Next, the relative phase difference Φ between the signal light S and the reference light LO is calculated using the optical communication system 1 shown in FIG. ps and estimate the estimated relative phase difference Φ ps An optical communication system 4 that transmits data from a transmitting device 2 to a receiving device 3 while performing compensation using the above every second will be described. FIG. 2 is a diagram illustrating one configuration of the optical communication system 4.

[0024] 2, the optical communication system 4 includes the optical communication system 1 shown in FIG 1, a transmission modulation signal generator (TMSG) 40, and an optical signal reception processing device 42. The optical signal reception processing device 42 includes a modulation data generator (MDG) 420, an adder 422, a selector (SEL) 424, a saw wave data generator (SWDG) 426, a reception modulation signal generator (RMSG) 428, a sine fitting processor (SFP) 430, an offset value controller (OVC) 432, and a post selection processor (PSP) 434.

[0025] With these components, the transmission modulation signal generator 40 and the transmitting device 2 of the optical communication system 4 modulate an optical signal with transmission data input from the outside to generate signal light S, and transmit it to the receiving device 3 together with the reference light LO used to demodulate the transmission data from the signal light S. Also, the optical signal receiving processing device 42 of the optical communication system 4 calculates the relative phase difference Φ between the signal light S and the reference light LO based on the interference output signal output from the balanced receiver 310 of the receiving device 3. ps Furthermore, the optical signal receiving device 42 calculates the relative phase difference Φ ps Phase offset value data V offset and the relative phase difference Φ between these two reference beams LO ps Furthermore, the optical signal receiving processor 42 performs hard decision on the interference output signal output from the balanced receiver 310, demodulates the transmission data, and outputs it to the outside as received data.

[0026] The transmission modulation signal generator 40 generates a transmission modulation signal that indicates the externally input transmission data by a voltage value, and outputs it to the phase modulator 204 of the transmitting device 2. The phase modulator 204 modulates an optical signal by the transmission modulation signal input from the transmission modulation signal generator 40, and outputs it to the polarizing beam splitter 206.

[0027] Fig. 3 is a diagram illustrating the processing of the sine fitting processor 430 in the optical signal receiving processing device 42 shown in Fig. 2. In the optical signal receiving processing device 42, the sine fitting processor 430 fits the voltage value of the cosine-wave interference output signal represented by a trigonometric function, for example, a cosine function, to the voltage value represented by a cosine function by the nonlinear least squares Marquardt-Levenberg algorithm, as shown in Fig. 3. Note that the nonlinear least squares Marquardt-Levenberg algorithm fits the voltage value of the input interference output signal to a specific function, a cosine function in the optical communication system 4, and calculates the relative phase difference Φ ps The sine fitting processor 430 estimates the relative phase difference Φ psto the offset value controller 432.

[0028] The offset value controller 432 calculates the relative phase difference Φ ps Phase offset value data V indicating the voltage value for compensating for offset and outputs it to the adder 422. The modulation data generator 420 generates a random number, generates random reception modulation data indicating the generated random number, and outputs it to the adder 422.

[0029] The adder 422 outputs the phase offset value data V offset The adder 422 adds the received modulated data to generate added data, and outputs the added data to the selector 424. The adder 422 outputs the phase offset value data V offset By subtracting offset In other words, whether the adder 422 adds or subtracts these data is essentially the same.

[0030] The sawtooth wave data generator 426 generates sawtooth wave data whose voltage value waveform indicates a sawtooth wave, and outputs the data to the selector 424. Before the optical communication system 4 starts operating (first period), the selector 424 selects the sawtooth wave data input from the sawtooth wave data generator 426, and outputs the data to the reception modulation signal generator 428. On the other hand, after the optical communication system 4 starts operating (second period), the selector 424 selects the added data input from the adder 422. The selector 424 outputs the selected data to the reception modulation signal generator 428.

[0031] The reception modulation signal generator 428 generates a modulation signal that indicates the sawtooth wave data or added data input from the selector 424 as a voltage value, and outputs it to the phase modulator 304 of the receiving device 3. The post-selection processor 434 demodulates the transmission data by performing hard decision on the voltage value of the interference output signal input from the balanced receiver 310 of the receiving device 3, and outputs it as reception data. Note that when the reception modulation signal generator 428 outputs a modulation signal that indicates the sawtooth wave data as a voltage value to the phase modulator 304 of the receiving device 3, and the phase modulator 304 modulates the reference light LO with this modulation signal, the waveform of the voltage value of the interference output signal output by the balanced receiver 310 becomes a cosine wave, as described below.

[0032] The optical signal received by the receiver 3 is E s and the reference light LO is E LO Ignoring the amplitude, these optical signals E s and reference beam E LO The phase shifts caused by ps1 ,Φ ps2 Then, these are expressed by the following equation (1).

[0033]

number

[0034] A phase modulator 304 receives the optical signal E s and reference beam E LO The modulation signal Φ saw When phase modulation is performed by (t), the optical signal E LO_PM is obtained.

[0035]

number

[0036] The balanced receiver 310 receives the optical signal E s and optical signal E LO_PM When these are interfered with, the optical signal EBR is obtained.

[0037]

number

[0038] In the above formula (3), Φ ps =Φ ps1 -Φ ps2 It is.

[0039] As described above, the optical signal E s and reference beam E LO The modulation signal Φ saw When modulation is performed using (t), the optical signal obtained by the modulation is E BR The waveform of is a cosine wave.

[0040] In the optical communication system 4, the phase modulator 304 of the receiver 3 modulates the reference light LO with a modulation signal that indicates sawtooth wave data in voltage value before the receiver 3 starts operating. As a result, in the optical signal receiver 42, the relative phase difference Φ ps and phase offset value data V offset The optical communication system 4 being in an operating state means that in the optical communication system 4, the transmitting device 2 transmits an optical signal indicating significant transmission data to the receiving device 3 via the optical transmission path 100, and the receiving device 3 and the optical signal receiving processing device 50 are in a state where they can demodulate the significant transmission signal from the optical signal.

[0041] On the other hand, after the operation of the receiving device 3 is started, the phase modulator 304 of the receiving device 3 receives the reference light LO, and transmits the reception modulation data and the phase offset value data V offset The balanced receiver 310 modulates the signal light S and the reference light LO by the voltage value of the sum of the signal light S and the reference light LO. ps The post-selection processor 434 thus generates an interference output signal that has been compensated for the relative phase difference Φ ps The transmission data is demodulated from the interference output signal from which the interference has been compensated, and is further output as the reception data.

[0042] As described above, the sine fitting processor 430 converts the optical signal E having a cosine waveform output from the balanced receiver 310 into a BR The sine fitting processor 430 performs fitting processing using the nonlinear least squares Marquardt-Levenberg algorithm for the sine difference Φ. The amount of calculation required for fitting processing in the sine fitting processor 430 is large, and therefore the fitting processing in the sine fitting processor 430 requires a long calculation time. Therefore, when the optical signal receiving and processing device 42 is used, the relative phase difference Φ ps It is not possible to detect and compensate for this in approximately 0.1 seconds.

[0043] [Embodiment] Hereinafter, an embodiment according to the present disclosure will be described. In an optical communication system 5 according to an embodiment of the present disclosure described below, when demodulating transmission data from the signal light received from the transmitting device side on the receiving device side, a modulation signal that indicates an inverse trigonometric function, for example, an inverse cosine function, in voltage is input to a receiving modulation signal generator 428, and the reference light LO is modulated. As a result, an interference output signal whose voltage value is triangular is output from the balance receiver 310 of the receiving device 3, and it is no longer necessary to perform fitting processing of the voltage value of the interference output signal to a cosine wave function, but rather it is sufficient to fit to a triangular wave function.

[0044] This eliminates the need for fitting using the nonlinear least-squares Marquardt-Levenberg algorithm, and instead requires linear zero-crossing phase difference estimation to find the zero-crossing time of the voltage value that represents a triangular wave function. This reduces the amount of calculation required for the fitting process and shortens the calculation time, which speeds up the estimation of the relative phase difference between the signal light S and the reference light LO. Note that the "estimate" of the relative phase difference is also commonly called the "measurement" of the relative phase difference.

[0045] FIG. 4 is a diagram illustrating a configuration of an optical communication system 5 according to an embodiment of the present disclosure. As shown in FIG. 4, the optical communication system 5 has a configuration in which the optical signal receiving processing device 42 of the optical communication system 4 shown in FIG. 2 is replaced with an optical signal receiving processing device 50. The optical signal receiving processing device 50 has a configuration in which the sawtooth wave data generator 426 of the optical signal receiving processing device 42 is replaced with an arccosine wave data generator (ACWDG; ArcCosineWave Data Generator) 500, and the sine fitting processor 430 is replaced with a linear zero-crossing phase difference estimator (LZCPDE; Linear Zero-Crossing Phase Difference Estimator) 502. FIG. 5A is a diagram illustrating a waveform of a voltage value indicated by the cosine wave data output by the arccosine wave data generator 500 of the optical signal receiving processing device 50 shown in FIG. 4. As shown in FIG. 5A, the voltage value indicated by the arccosine wave data output by the arccosine wave data generator 500 has an arccosine wave waveform.

[0046] The inverse cosine wave data generator 500 generates modulation data whose voltage value indicates a waveform of an inverse cosine function, and outputs the data to the selector 424. The linear zero-crossing phase difference estimator 502 performs linear zero-crossing phase difference estimation on the voltage value of the interference output signal input from the balanced receiver 310. With these components, the optical communication system 5 transmits, similarly to the optical communication system 4, signal light S modulated by a modulation signal indicating transmission data by a voltage value from the transmitter 2 to the receiver 3. Furthermore, the optical communication system 5 detects the relative phase difference between the signal light S and the reference light LO, and corrects the relative phase difference between the signal light S and the reference light LO.

[0047] The processing of the optical communication system 5 will be described in detail below, focusing on the processing of the optical signal receiving processing device 50, and further referring to mathematical expressions as necessary. The transmitting device 2 and the receiving device 3 perform the processing described with reference to Fig. 1. The relative phase difference Φ between the signal light S and the reference light LO in the optical signal receiving processing device 50 ps The estimation is performed before the start of operation of the optical communication system 5. In addition, before the start of operation, an unmodulated optical signal is transmitted from the transmitting device 2 to the receiving device 3.

[0048] Relative phase difference Φ ps While the estimation of is being performed, the linear zero-crossing phase difference estimator 502 estimates the relative phase difference Φ ps and outputs it to the offset value controller 432. The offset value controller 432 estimates the relative phase difference Φ ps and outputs the offset value data to the adder 422.

[0049] Before the operation of the optical communication system 5 is started, the selector 424 selects the sum of the random modulation data input from the adder 422 and the offset value data, and outputs it to the reception modulation signal generator 428. When the operation of the optical communication system 5 is started, the selector 424 selects the inverse cosine wave data input from the inverse cosine wave data generator 500, and outputs it to the reception modulation signal generator 428. The reception modulation signal generator 428 generates a reception data modulation signal indicating, as a voltage value, the sum of the random modulation data selected by the selector 424 and the offset value, or the inverse cosine wave data generated by the inverse cosine wave data generator 500, and outputs it to the phase modulator 304.

[0050] Before the optical communication system 5 starts operating, the phase modulator 304 phase-modulates the reference light LO input from the polarization controller 300 and controls the phase, as shown in the following equation (4).

[0051]

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[0052] In the above formula (4), E in (t) is the reference light LO input from the polarization controller 300, and E out (t) is the modulated reference light LO output from the phase modulator 304, V(t) is the voltage value of the received data modulation signal, and V pl is the change in the voltage value of the received data modulated signal required to change the phase of the reference light LO by π (radian; 180°).

[0053] V pl When =π is substituted into the above equation (4), the modulated reference light LO output from the balanced receiver 310 is expressed by the following equation (5).

[0054]

number

[0055] The reference light LO modulated as shown in equation (5) and the signal light S are input to the balanced receiver 310. When the balanced receiver 310 performs general homodyne detection, the balanced receiver 310 adds the reference light LO input from the variable optical attenuator 306 and the reference light LO input from the variable optical attenuator 308, and outputs an interference output signal I(t) whose voltage value is represented by the following equation (6).

[0056]

number

[0057] As described above, before operation is started, no significant transmission data is input to the transmitting device 2, and transmission data indicating a value of 0 or 1 is input, and as a result, an unmodulated optical signal is input from the transmitting device 2 to the receiving device 3. If the difference in optical path length between the signal light S and the reference light LO is equal, no phase difference occurs between these reference lights LO.

[0058] In this case, E denotes the reference light LO input from the polarization controller 300. in (t) is Ae jωt (E in (t)=Ae jωt ) can be written as: out (t)=E in (t)·e jV(t) and E in (t)=Ae jωt Substituting these values, the voltage value of the interference output signal I(t) output from the balanced receiver 310 is expressed by the following equation (7).

[0059]

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[0060] In the above equation (7), B is the amplitude of the voltage value of the interference output signal output from the balanced receiver 310.

[0061] Fig. 5B is a diagram illustrating waveforms of interference output signals output under three different conditions by the balanced receiver 310 of the optical signal receiving processing device 50 shown in Fig. 4. In the optical communication system 5, when a reception modulation signal indicating the voltage of the inverse cosine wave data V(t) shown in the following formula (8) is input from the inverse cosine wave data generator 500 to the phase modulator 304, the balanced receiver 310 outputs an interference output signal whose voltage waveform is a triangular wave (period=1) as shown in Fig. 5B.

[0062]

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[0063] The period of the inverse cosine function is π(V PI =π), whereas the period of a cosine function is 2π. If the period of the inverse cosine wave data V(t) is expanded to be 2π, the inverse cosine wave data V(t) can be expressed as a combination of two types of inverse cosine wave data V(t) with a phase difference of π, as shown in the following equation (9).

[0064]

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[0065] On the other hand, when the balanced receiver 310 subtracts the reference light LO input from the variable optical attenuator 308 from the reference light LO input from the variable optical attenuator 306, and performs homodyne detection using the resulting difference between these reference lights LO, the interference output signal I(t) is expressed by the following equation (10), similar to equation (9).

[0066]

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[0067] In this case, in the optical signal receiving processing device 50, an inverse sine wave data generator (not shown) is used instead of the inverse cosine wave data generator 500, which generates modulation data whose voltage value indicates a waveform of an inverse sine function and outputs the data to the selector 424. That is, when the balanced receiver 310 calculates the difference between the reference light LO that has passed through the variable optical attenuator 306 and the reference light LO that has passed through the variable optical attenuator 308 to perform homodyne detection, an inverse sine wave data generator is used instead of the inverse cosine wave data generator 500, and a received modulation signal whose voltage value is indicated by the inverse sine wave data V(t) shown in the following formula (11) is input to the phase modulator 304.

[0068]

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[0069] When the optical communication system 5 is implemented, a difference may occur between the optical path length of the signal light S and the optical path length of the reference light LO. The relative phase difference occurring between the signal light S and the reference light LO due to this difference in optical path length is defined as Φ ps Then, the voltage value of the interference output signal I(t) is expressed by the following equation (12). In other words, due to the above-mentioned difference, the phase of the waveform indicated by the voltage value of the interference output signal I(t) is the relative phase difference Φ ps The relative phase difference is estimated by calculating the relative phase difference Φ from the interference output signal I(t) shown in the following equation (12). ps The aim is to seek...

[0070]

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[0071] Next, the optical signal receiving device 50 calculates the relative phase difference Φ using the time (zero crossing time) when the positive and negative voltage values ​​of the interference output signal output by the balance receiver 310 are switched. psThe estimation process of is described below. Fig. 5C is a diagram illustrating sample points selected from each of the interference output signals output under three different conditions by the balanced receiver 310 of the optical signal receiving processing device 50 shown in Fig. 4. In Fig. 5C, two sample points selected at an interval of less than 1 / 2 period from the waveform of a triangular wave are marked with circles, and a sample point (Interference Signal) that may be an interference signal in the waveform of the triangular wave is marked with a triangle.

[0072] Specifically, as shown in Fig. 5C, the linear zero crossing phase difference estimator 502 selects two sample points included in the waveform at an interval of less than 1 / 2 period of the waveform of the voltage value of the interference output signal output by the balanced receiver 310. In this way, by selecting two sample points at an interval of less than 1 / 2 period from the waveform of the interference output signal and performing linear interpolation, it is possible to estimate the zero crossing time T0 of the waveform of the triangular wave as shown in Fig. 5C.

[0073] The linear zero-crossing phase difference estimator 502 calculates the relative phase difference Φ by the following equation (13) based on the estimated zero-crossing time T0 and the ideal zero-crossing time T when there is no difference between the optical path length of the signal light S and the optical path length of the reference light LO. ps can be calculated efficiently.

[0074]

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[0075] Here, when the zero crossing times T and T0 shown in equation (13) have a relationship of T-T0>0, the relative phase difference Φ ps When the relationship T-T0<0 exists in the delay direction, the relative phase difference Φ ps occurs in the forward direction.

[0076] As described above, the relative phase difference Φ psSince the waveform of the voltage value of the interference output signal output by the balanced receiver 310 is a triangular wave, linear interpolation is very easy. Therefore, the relative phase difference Φ ps The amount of calculation required to estimate the relative phase difference Φ described above can be reduced, and the calculation time can be shortened. ps According to the estimation method, the relative phase difference Φ ps Therefore, phase correction can be easily achieved to make the absolute value of φ as close to 0 as possible.

[0077] As described above, the linear zero-crossing phase difference estimator 502 estimates the relative phase difference Φ ps and outputs the calculation result to the offset value controller 432. The offset value controller 432 outputs the phase offset value data V offset The voltage indicated by is calculated using the following formula (14).

[0078]

number

[0079] The offset value controller 432 receives the phase offset value data V offset The adder 422 outputs data indicating the voltage value of the received modulation data input from the modulation data generator 420 and the phase offset value data V offset Adding these together gives the relative phase difference Φ ps The adder 422 outputs the corrected received modulation data to the selector 424. Note that if the received modulation data includes phase offset value data V offset Adding the phase offset data V offset The relative phase difference Φ ps can be set to 0°.

[0080] The selector 424 selects the relative phase difference Φps While the estimation of is being performed, the adder 422 selects the inverse cosine wave data input from the inverse cosine wave data generator 500 and outputs it to the reception modulation signal generator 428. On the other hand, after the operation of the optical communication system 5 is started, the adder 422 selects the reception modulation data input from the adder 422 and the phase offset value data V offset The sum of the data indicating the voltage value of the selected signal is selected and output to the reception modulation signal generator 428.

[0081] The reception modulation signal generator 428 generates a reception modulation signal of a voltage value indicated by the data input from the selector 424, and outputs it to the phase modulator 304. After the optical communication system 5 starts operating, the post-selection processor 434 demodulates the transmission data by hard decision of mapping the interference output signal input from the balanced receiver 310 to the closest reference signal, and outputs it to the outside as reception data. When the interference output signal includes QPSK-modulated transmission data, the post-selection processor 434 demodulates the transmission data by performing quadrant decision.

[0082] According to the optical communication system 5 described above, the relative phase difference Φ ps Since it is possible to estimate the relative phase difference Φ ps This reduces the amount of calculation required to estimate the relative phase difference Φ ps Since the estimation of can be performed by hardware such as an FPGA, the relative phase difference Φ ps Therefore, the relative phase difference Φ can be estimated within a short time, for example, within 0.1 seconds. ps The time required for compensation is also shorter.

[0083] [Information processing device that can be used to implement the embodiment of the present disclosure] All or part of the functions of the transmission modulation signal generator 40 and the optical signal receiving and processing devices 42, 50 of the optical communication systems 4, 5 described above can be implemented by an information processing device (computer) 6 described below. Fig. 6 is a diagram illustrating one configuration of an optical communication system 5 capable of implementing all or part of the functions of the components of the transmission modulation signal generator 40 and the optical signal receiving and processing devices 42, 50 of the optical communication systems 4, 5 shown in Figs. 2 and 4.

[0084] As illustrated in Fig. 6, the information processing device 6 includes a CPU (Central Processing Unit) 600, a main storage device 602, an auxiliary storage device 604, and an interface (IF; InterFace) 606, which are interconnected via a bus so as to be capable of inputting and outputting information. However, the information processing device 6 may include hardware components other than those illustrated in Fig. 6, and the components of the information processing device 6 may be distributed across multiple devices. In other words, the configuration of the information processing device 6 is not limited to the configuration illustrated in Fig. 6.

[0085] The CPU 600 executes instructions included in a program that is executed by the information processing device 6 and is required for processing of each component of the transmission modulation signal generator 40 and the optical signal receiving and processing devices 42 and 50. The main storage device 602 includes storage elements such as a RAM (Random Access Memory) and a ROM (Read Only Memory), and temporarily stores data used by the CPU 600 to execute the program.

[0086] The auxiliary storage device 604 includes a non-volatile storage device such as a hard disk drive (HDD), a solid state drive (SSD), and a flash memory, and stores the programs executed by the CPU 600 on a medium to long term basis. The programs stored in the auxiliary storage device 604 may be provided and distributed as products stored on non-transitory computer-readable recording media such as magnetic storage media, CDs, and DVDs. The IF device 606 provides an interface for inputting and outputting information between the drive control device and the like and the transmission modulation signal generator 40 and the optical signal reception processing devices 42 and 50.

[0087] As described above, each of the components of the transmission modulation signal generator 40 and the optical signal receiving and processing devices 42, 50 can be realized by a program executed in the information processing device 6, except for components that must be configured by hardware due to their nature. On the other hand, these components may be realized by dedicated hardware, or by an appropriate combination of hardware and software (program) executed in the information processing device 6. Furthermore, as described above, at least a portion of the components of the transmission modulation signal generator 40 and the optical signal receiving and processing devices 42, 50 can be realized by a program, and therefore the content of the processing executed by such components can be understood as a method.

[0088] The present application may include the following forms, but is not limited to these. [Appendix 1] A relative phase difference compensation device, comprising a polarization controller, a modulator, a balanced receiver, a polarization beam splitter, a phase difference estimator, and an offset value controller, for compensating for a relative phase difference between a signal light and a reference light, which are included in an optical signal and have orthogonal polarizations. The polarization controller is configured to separate the signal light and the reference light from the optical signal. The modulator is configured to modulate the separated reference light with a received modulation signal indicated by inverse function data indicating an inverse function of a specific function indicated by an interference output signal generated by homodyne detection by the balanced receiver. The polarization beam splitter is configured to combine the signal light separated by the polarization controller and the modulated reference light, and to separate a polarization component of the signal light and a polarization component of the reference light from the combined signal light and reference light. The balanced receiver is configured to perform the homodyne detection on the separated polarization component of the signal light and the polarization component of the reference light to generate the interference output signal. The phase difference estimator is configured to estimate a relative phase difference between the signal light and the reference light based on the generated interference output signal, and the offset value controller is configured to generate offset value data that cancels the relative phase difference between the signal light and the reference light based on the estimated relative phase difference between the signal light and the reference light. [Appendix 2] The relative phase difference compensation device further includes an adder and a selector. The adder is configured to generate an added value by adding modulation data and the offset value data. The selector is configured to select the inverse function data at least during a first period during which the offset value data is generated, and to select the generated added value during a second period different from the first period. The modulator is configured to modulate the reference light separated by the received modulation signal indicated by the inverse function data when the selector selects the inverse function data, and to modulate the reference light separated by the received modulation signal indicated by the added value when the selector selects the added value, thereby compensating for the relative phase difference. [Appendix 3] 3. The relative phase difference compensation device according to claim 1 or 2, further comprising a post-selection processor configured to combine data represented by the signal light by performing hard decisions on the interference output signal. [Appendix 4] 4. The relative phase difference compensation device according to claim 1, wherein the specific function is a cosine function and the inverse function is an inverse cosine function. [Appendix 5] 5. The relative phase difference compensation device according to any one of claims 1 to 4, wherein the specific function is a sine function, and the inverse function is an arcsine function. [Appendix 6] 6. The relative phase difference compensation device according to any one of claims 1 to 5, wherein a waveform of the interference output signal is a triangular wave, and the phase difference estimator is configured to estimate the relative phase difference between the signal light and the reference light by performing linear zero-crossing phase difference estimation on the interference output signal. [Appendix 7] A relative phase difference compensation method for a relative phase difference compensation device, which includes a polarization controller, a modulator, and a polarization beam splitter, and compensates for a relative phase difference between a signal light and a reference light, which are included in an optical signal and have orthogonal polarizations, includes an inverse function data generating step, an interference output signal generating step, a relative phase difference estimating step, and an offset value data generating step. The polarization controller is configured to separate the signal light and the reference light from the optical signal. The modulator is configured to modulate the separated reference light with a received modulation signal indicated by inverse function data indicating an inverse function of a specific function indicated by an interference output signal generated by homodyne detection using a balanced receiver. The polarization beam splitter is configured to combine the signal light separated by the polarization controller and the modulated reference light, and to separate a polarization component of the signal light and a polarization component of the reference light from the combined signal light and reference light. The inverse function data generating step generates inverse function data indicating an inverse function of a specific function indicated by an interference output signal generated by homodyne detection. The interference output signal generating step performs the homodyne detection on the separated polarization component of the signal light and the polarization component of the reference light to generate the interference output signal. The relative phase difference estimating step estimates a relative phase difference between the signal light and the reference light based on the generated interference output signal. The offset value data generating step generates offset value data that cancels the relative phase difference between the signal light and the reference light based on the estimated relative phase difference between the signal light and the reference light. [Appendix 8] A program executed in a relative phase difference compensation device that includes a polarization controller, a modulator, and a polarization beam splitter and compensates for a relative phase difference between a signal light and a reference light that are included in an optical signal and have orthogonal polarizations, the program comprising an inverse function generation process, an interference output signal generation process, a relative phase difference estimation process, and an offset value data generation process. The polarization controller is configured to separate the signal light and the reference light from the optical signal. The modulator is configured to modulate the separated reference light with a received modulation signal indicated by inverse function data indicating an inverse function of a specific function indicated by an interference output signal generated by homodyne detection using a balanced receiver. The polarization beam splitter is configured to combine the signal light separated by the polarization controller and the modulated reference light, and to separate the polarization component of the signal light and the polarization component of the reference light from the combined signal light and reference light. The inverse function generation process generates inverse function data indicating an inverse function of a specific function indicated by an interference output signal generated by homodyne detection. The interference output signal generation process performs the homodyne detection on the separated polarization components of the signal light and the reference light to generate the interference output signal. The relative phase difference estimation process estimates a relative phase difference between the signal light and the reference light based on the generated interference output signal. The offset value data generation process generates offset value data that cancels the relative phase difference between the signal light and the reference light based on the estimated relative phase difference between the signal light and the reference light. It goes without saying that combinations of the various forms described in the appendix of the present disclosure, or any combination of the elements described in each aspect and embodiment (including the non-selection of some elements) can be made by those skilled in the art at any time in accordance with the basic concept of the present disclosure.

[0089] The disclosures of the cited patent documents and the like are incorporated herein by reference. Within the scope of all disclosures (including the scope of claims), modifications and adjustments of the embodiments and examples are possible based on the basic technical ideas. Furthermore, within the scope of all disclosures, various combinations and selections (including partial deletions) of various disclosed elements (including each element of each claim, each element of the embodiments and examples, each element of each drawing, etc.) are possible. In other words, this disclosure naturally includes various modifications and corrections that a person skilled in the art would be able to make in accordance with the entire disclosure, including the scope of claims, and the technical ideas. In particular, with regard to the numerical ranges described in this document, any numerical value or small range included within the range should be construed as being specifically described even if not otherwise specified. Furthermore, the disclosures of the above patent documents, if necessary, in accordance with the spirit of this disclosure, may be used in part or in whole in combination with the disclosures in this document as part of this disclosure, and are deemed to be included in the disclosures of this application. [Explanation of symbols]

[0090] 1,4,5 Optical communication systems 100 Optical transmission line 2. Transmitting device 200 Laser Diode (LD) 202,302 Non-Polarization Beam Splitter (NPBS) 204 Phase Modulator (PM) 206 Polarization Beam Splitter (PBS) 3. Receiving device 300 Polarization Controller (PC) 304 Phase Modulator (PM) 306,308 Variable Optical Attenuator (VOA) 310 Balance Receiver (BR; Balance Receiver) 40 Transmission Modulation Signal Generator (TMSG) 42,50 Optical signal receiving and processing device 420 Modulation Data Generator (MDG) 422 Adder 424 Selector (SEL;SELector) 426 Saw Wave Data Generator (SWDG) 428 Reception Modulation Signal Generator (RMSG) 430 Sine Fitting Processor (SFP) 432 Offset Value Controller (OVC) 434 Post Selection Processor (PSP) 500 ArcCosinWave Data Generator (ACWDG) 502 Linear Zero-Crossing Phase Difference Estimator (LZCPDE) 6. Information processing equipment 600 CPU(Central Processing Unit) 602 Main storage 604 auxiliary storage 606 Interface (IF; InterFace)

Claims

1. A relative phase difference compensation device that includes a polarization controller, a modulator, a balance receiver, a polarization beam splitter, a phase difference estimator, and an offset value controller, and compensates for a relative phase difference between a signal light and a reference light, the signal light and the reference light having mutually orthogonal polarizations, the polarization controller is configured to separate the signal light and the reference light from the optical signal; The modulator is configured to modulate the separated reference light with a received modulation signal represented by inverse function data representing an inverse function of a specific function represented by an interference output signal generated by homodyne detection by the balanced receiver; the polarization beam splitter is configured to combine the signal light separated by the polarization controller with the modulated reference light, and to separate a polarized component of the signal light and a polarized component of the reference light from the combined signal light and reference light; the balanced receiver is configured to perform the homodyne detection on the separated polarization component of the signal light and the polarization component of the reference light to generate the interference output signal; the phase difference estimator is configured to estimate a relative phase difference between the signal light and the reference light based on the generated interference output signal; The offset value controller is configured to generate offset value data that cancels the relative phase difference between the signal light and the reference light, based on the estimated relative phase difference between the signal light and the reference light. Relative phase difference compensation device.

2. An adder and a selector are further included, the adder is configured to add modulation data and the offset value data to generate a sum; the selector is configured to select the inverse function data during at least a first period during which the offset value data is generated, and to select the generated additional value during a second period different from the first period; The modulator is configured to modulate the reference light separated by the reception modulation signal indicated by the inverse function data when the selector selects the inverse function data, and to modulate the reference light separated by the reception modulation signal indicated by the addition value when the selector selects the addition value, thereby compensating for the relative phase difference.

2. A relative phase difference compensation device according to claim 1.

3. a post-selection processor configured to decode data represented by the signal light by performing hard decisions on the interference output signal; The relative phase difference compensation device according to claim 1 , further comprising:

4. the particular function is a cosine function, The inverse function is the inverse cosine function.

2. A relative phase difference compensation device according to claim 1.

5. the particular function is a sine function, The inverse function is the arc sine function 2. A relative phase difference compensation device according to claim 1.

6. the waveform of the interference output signal is a triangular wave; The phase difference estimator is configured to estimate a relative phase difference between the signal light and the reference light by performing a linear zero-crossing phase difference estimation on the interference output signal.

2. A relative phase difference compensation device according to claim 1.

7. A relative phase difference compensation method in a relative phase difference compensation device that includes a polarization controller, a modulator, and a polarizing beam splitter and compensates for a relative phase difference between a signal light and a reference light that are included in an optical signal and have orthogonal polarizations, wherein the polarization controller is configured to separate the signal light and the reference light from the optical signal, the modulator is configured to modulate the separated reference light with a received modulation signal indicated by inverse function data indicating an inverse function of a specific function indicated by an interference output signal generated by homodyne detection using a balanced receiver, and the polarizing beam splitter is configured to combine the signal light separated by the polarization controller and the modulated reference light, and to separate the polarized component of the signal light and the polarized component of the reference light from the combined signal light and reference light, an inverse function data generating step of generating inverse function data indicating an inverse function of a particular function indicated by the interference output signal generated by the homodyne detection; an interference output signal generating step of performing the homodyne detection on the separated polarized component of the signal light and the polarized component of the reference light to generate the interference output signal; a relative phase difference estimating step of estimating a relative phase difference between the signal light and the reference light based on the generated interference output signal; an offset value data generating step of generating offset value data for canceling the relative phase difference between the signal light and the reference light based on the estimated relative phase difference between the signal light and the reference light; A relative phase difference compensation method comprising:

8. A program executed in a relative phase difference compensation device that includes a polarization controller, a modulator, and a polarizing beam splitter, and that compensates for a relative phase difference between a signal light and a reference light that are included in an optical signal and have orthogonal polarizations, wherein the polarization controller is configured to separate the signal light and the reference light from the optical signal, the modulator is configured to modulate the separated reference light with a received modulation signal indicated by inverse function data indicating an inverse function of a specific function indicated by an interference output signal generated by homodyne detection using a balanced receiver, and the polarizing beam splitter is configured to combine the signal light separated by the polarization controller and the modulated reference light, and to separate the polarized component of the signal light and the polarized component of the reference light from the combined signal light and reference light, an inverse function generation process for generating inverse function data indicative of the inverse of a particular function represented by the interference output signal generated by the homodyne detection; an interference output signal generation process for performing the homodyne detection on the separated polarization components of the signal light and the reference light to generate the interference output signal; a relative phase difference estimation process for estimating a relative phase difference between the signal light and the reference light based on the generated interference output signal; an offset value data generation process for generating offset value data for canceling the relative phase difference between the signal light and the reference light based on the estimated relative phase difference between the signal light and the reference light; A program that includes:

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