JP2018174413A - Polarization state estimation method and polarization state estimation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce calculation load when estimating changing speed of polarization state in polarization multiplexed optical signal.SOLUTION: The polarization state estimation method includes: an acquisition step of acquiring plural tap coefficients of an FIR (Finite Impulse Response) filter which is used for adaptive equalization on plural signals included in a polarization multiplexed optical signal; an addition step of calculating the sum of the amount of change of each of the tap coefficients; a detection step of detecting the frequency at which the absolute value of frequency elements in time sequence on the sum; and an estimation step of estimating the changing speed of the polarization state in the polarization multiplexed optical signal from the detected frequency.SELECTED DRAWING: Figure 1

Description

  The present invention mainly relates to a polarization state estimation method and a polarization state estimation apparatus.

  In recent optical transmission systems, digital coherent technology combining coherent optical communication technology and digital signal processing technology is used. In the transmission method using the digital coherent technology, a transmission-side device outputs a phase-modulated optical signal, and a receiving-side coherent receiver outputs a highly sensitive electric signal acquired by the coherent detection technology. The device on the receiving side converts the electrical signal into a digital signal by an AD (Analog to Digital) converter, and then compensates the received waveform distorted in the transmission path by digital signal processing in the digital domain (Non-Patent Document 1). Since correction of waveform distortion can be performed with a simple configuration by digital signal processing, a large-capacity and high-speed transmission system can be realized.

  In the digital coherent transmission method, an optical signal that is polarization-multiplexed on the transmitting side can be separated by a receiving-side device by digital signal processing. Therefore, a polarization-multiplexed optical signal is generally used for transmission. Polarization separation using digital signals is one of the important technologies in digital coherent transmission systems. Since the fluctuation of the polarization state in the transmission path affects the polarization separation caused by the digital signal, obtaining the fluctuation of the polarization state occurring in the transmission path is important in the evaluation of reception tolerance.

  In digital coherent transmission, an FIR (Finite Impulse Response) filter is generally used as an adaptive equalizer in a digital signal processing apparatus. By adaptively controlling the tap coefficient of the FIR filter using an arbitrary algorithm, polarization separation and waveform distortion compensation are realized (Non-Patent Document 1).

  Non-Patent Document 2 describes a method of calculating the fluctuation speed of the polarization state of an optical signal from the tap coefficient of an FIR filter used in an adaptive equalizer in a digital signal processing device. In this method, the Stokes parameter expressing the polarization state of the optical signal is calculated from the tap coefficient of the FIR filter, and the change speed of the polarization state of the optical signal is calculated from the time change of the Stokes parameter. However, with this method, there is a problem that the calculation load becomes remarkably large due to the frequent use of trigonometric functions when calculating the Stokes parameters from the tap coefficients.

S. J. Savory, "Digital filters for coherent optical receivers," Optics Express, vol.16, no.2, pp.804-814, 2008. Calvin C. K. Chan, "Optical Performance Monitoring: Advanced Techniques for Next-Generation Photonic Networks," Academic Press, pp.287-288, 2010.

  In view of the above-described circumstances, the present invention provides a polarization state estimation method and a polarization state estimation device that can reduce a calculation load when estimating a polarization state change speed in a polarization multiplexed optical signal. The purpose is to do.

  The polarization state estimation method in one aspect of the present invention includes an acquisition step of acquiring a plurality of tap coefficients of an FIR filter used for adaptive equalization for a plurality of signals included in a polarization multiplexed optical signal, and the tap coefficient An addition step for calculating the sum of the respective changes, a detection step for detecting a frequency at which the absolute value of the frequency component in the time series of the sum is maximum, and the polarization multiplexed optical signal from the detected frequency Estimating a polarization state fluctuation speed at.

  Further, according to one aspect of the present invention, in the polarization state estimation method, two optical signals having different polarization planes are multiplexed on the polarization multiplexed optical signal, and the FIR filter includes: First and second signals obtained from the polarization multiplexed optical signal are respectively input, and the plurality of tap coefficients are first and second components for the respective components of the two optical signals included in the first signal. A second tap coefficient vector, and third and fourth tap coefficient vectors for the respective components of the two optical signals included in the second signal. In the adding step, the first, second, second The sum is calculated by adding the amount of change of each element of at least one of the third and fourth tap coefficient vectors.

  Further, according to one aspect of the present invention, in the polarization state estimation method described above, in the addition step, the amount of change in each element of the first and second tap coefficient vectors, and the third and fourth The sum is calculated by adding any one of the change amounts of the elements of the tap coefficient vector.

  In addition, according to the aspect of the present invention, in the polarization state estimation method described above, in the adding step, all the variations of the elements of the first, second, third, and fourth tap coefficient vectors are added. To calculate the sum.

According to an aspect of the present invention, in the polarization state estimation method, the number of taps of the FIR filter is M, and the elements of the first, second, third, and fourth tap coefficient vectors are h. _{xx, i} (n), h _{xy, i} (n), h _{yx, i} (n), h _{yy, i} (n), and the amount of change of each element is Δh _{xx, i} (n) = h _{xx, i} (N) -h _{xx, i} (n-1),
Δh _{xy, i} (n) = h _{xy, i} (n) −h _{xy, i} (n−1),
Δh _{yx, i} (n) = h _{yx, i} (n) −h _{yx, i} (n−1),
Δh _{yy, i} (n) = h _{yy, i} (n) −h _{yy, i} (n−1)
If the, in the adding step, calculating _S xx _(n) in the formula of paragraph _{0034 (2), S xy (} n), S yx (n), at least one of _S yy (n) as the sum .

  The polarization state estimation apparatus according to an aspect of the present invention includes an acquisition unit that acquires a plurality of tap coefficients of an FIR filter used for adaptive equalization for a plurality of signals included in a polarization multiplexed optical signal; An adder that calculates the sum of the change amounts of the tap coefficients, a detector that detects a frequency at which the absolute value of the frequency component in the time series of the sum is maximum, and the polarization multiplexed from the detected frequency An estimation unit for estimating a polarization state fluctuation speed in the optical signal.

  ADVANTAGE OF THE INVENTION According to this invention, the calculation load at the time of estimating the change speed of the polarization state in the polarization multiplexed optical signal can be reduced.

It is a block diagram which shows the structural example of the optical receiver in embodiment. It is a block diagram which shows the structural example of the adaptive equalization part in embodiment. It is a flowchart which shows the estimation process which the polarization state fluctuation speed estimation part in embodiment performs. It is a 1st graph which shows the result of having estimated the polarization state fluctuation speed of the optical fiber transmission line using the optical receiver of embodiment. It is a 2nd graph which shows the result of having estimated the polarization state fluctuation speed of the optical fiber transmission line using the optical receiver of embodiment. It is a 3rd graph which shows the result of having estimated the polarization state fluctuation speed of the optical fiber transmission line using the optical receiver of embodiment.

  Hereinafter, a polarization state estimation method and a polarization state estimation device according to an embodiment of the present invention will be described with reference to the drawings. The polarization state estimation apparatus according to the embodiment estimates a speed at which the polarization state of an optical signal changes using a tap coefficient when adaptively equalizing digital signal processing.

  FIG. 1 is a block diagram illustrating a configuration example of an optical receiver 1 according to an embodiment of the present invention. The optical receiver 1 receives an optical signal transmitted through an optical fiber transmission line. The optical signal received by the optical receiver 1 is an optical signal obtained by polarization-multiplexing two optical signals whose polarization planes are orthogonal to each other on the transmission side device.

  The optical receiver 1 includes an optical coherent receiver 11 and a digital signal processing unit 12. The optical coherent receiver 11 converts an optical signal input to the optical receiver 1 into a baseband optical signal by local light. The optical coherent receiver 11 separates the baseband optical signal into two optical signals having orthogonal polarization planes. The optical coherent receiver 11 performs photoelectric conversion and AD conversion on each of the two optical signals. The optical coherent receiver 11 outputs two digital signals obtained by photoelectric conversion and AD conversion to the digital signal processing unit 12. The digital signal processing unit 12 demodulates the transmitted binary information from two digital signals, and estimates the polarization state fluctuation speed of the optical signal in the optical fiber transmission line.

  The digital signal processing unit 12 includes a chromatic dispersion compensation unit 13, an adaptive equalization unit 14, a carrier phase compensation unit 15, a received data demodulation unit 16, and a polarization state fluctuation speed estimation unit 17. The chromatic dispersion compensation unit 13 performs chromatic dispersion compensation on each of the two digital signals output from the optical coherent receiver 11. The chromatic dispersion compensation unit 13 outputs a digital signal obtained by chromatic dispersion compensation to the adaptive equalization unit 14. The adaptive equalization unit 14 performs waveform equalization that suppresses interference and distortion between two digital signals output from the chromatic dispersion compensation unit 13. The adaptive equalization unit 14 outputs the two digital signals subjected to waveform equalization to the carrier phase compensation unit 15.

  FIG. 2 is a block diagram illustrating a configuration example of the adaptive equalization unit 14 in the present embodiment. The adaptive equalization unit 14 illustrated in FIG. 2 is configured using an FIR filter having a tap number of M (M is a natural number of 2 or more). The adaptive equalization unit 14 includes delay units 21-1 to 21- (M-1), 233-1 to 23- (M-1), 25-1 to 25- (M-1), and 27-1 to 27. -(M-1), multipliers 22-1 to 22-M, 24-1 to 24-M, 26-1 to 26-M, 28-1 to 28-M, adders 31, 32, Tap coefficient updating units 33 and 34.

The delay units 21-i and 25-i (1 ≦ i ≦ M−1, i is a natural number) are digital signals x _in (first signal) of two digital signals input to the adaptive equalization unit 14. ) Is output after being delayed. The delay amount given to the digital signal x _in by the delay devices 21-i and 25-i is i × (unit time). The unit time may be the same as the AD conversion sampling interval in the optical coherent receiver 11 or may be an interval determined based on the sampling interval.

The multipliers 22-i and 26-i store tap coefficients h _{xx, i} and h _{yx, i} , respectively. The multiplier 22-1 multiplies the digital signal x _in by the tap coefficient h _{xx, 1} and outputs the multiplication result. The multiplier 22-i (2 ≦ i ≦ M) multiplies the digital signal x _in output from the delay device 21- (i−1) by the tap coefficient h _{xx, i} and outputs the multiplication result. The multiplier 26-1 multiplies the digital signal x _in by the tap coefficient h _{yx, 1} and outputs the multiplication result. The multiplier 26-i (2 ≦ i ≦ M) multiplies the digital signal x _in output from the delay unit 25- (i−1) by the tap coefficient h _{yx, i} and outputs the multiplication result.

The delay units 23-i and 27-i (1 ≦ i ≦ M−1) delay the other digital signal y _in (second signal) of the two digital signals input to the adaptive equalization unit 14. Output after. The delay amount given to the digital signal y _in by the delay units 23-i and 27-i is i × (unit time).

The multipliers 24-i and 28-i store tap coefficients h _{xy, i} , h _{yy, i} , respectively. The multiplier 24-1 multiplies the digital signal y _in by the tap coefficient h _{xy, 1} and outputs the multiplication result. The multiplier 24-i (2 ≦ i ≦ M) multiplies the digital signal y _in output from the delay unit 23- (i−1) by the tap coefficient h _{xy, i} and outputs the multiplication result. The multiplier 28-1 multiplies the digital signal y _in by the tap coefficient h _{yy, 1} and outputs the multiplication result. The multiplier 28-i (2 ≦ i ≦ M) multiplies the digital signal y _in output from the delay device 27- (i−1) by the tap coefficient h _{yy, i} and outputs the multiplication result.

The adder 31 adds the multiplication results output from the multipliers 22-i and 24-i (1 ≦ i ≦ M−1), and outputs the addition result as a digital signal _xout . The adder 32 adds the multiplication results output from the multipliers 26-i and 28-i (1 ≦ i ≦ M−1), and outputs the addition result as a digital signal y _out . The digital signals x _out and y _out are digital signals output from the adaptive equalization unit 14.

Based on the digital signals x _in , y _in and the digital signal x _out , the tap coefficient updating unit 33 performs tap coefficient vector h _xx = [h _{xx, 1} , h _{xx, 2} ,..., H _{xx, M} ], h _xy = [h _{xy, 1} , h _{xy, 2} ,..., h _{xy, M} ] is updated. The tap coefficient updating unit 33 stores the updated tap coefficient in each of the multipliers 22-i and 24-i. Based on the digital signals x _in , y _in and the digital signal y _out , the tap coefficient update unit 34 tap coefficients h _yx = [h _{yx, 1} , h _{yx, 2} ,..., H _{yx, M} ], h _yy = [H _{yy, 1} , h _{yy, 2} ,..., H _{yy, M} ] is updated. The tap coefficient updating unit 34 stores the updated tap coefficient in each of the multipliers 26-i and 28-i.

Tap coefficient updating unit 33 and 34, using equation (1), the tap coefficient vector _{h xx, h xy, h yx} , updates the _{h yy.} The tap coefficient update units 33 and 34 output the tap coefficient vectors h _xx , h _xy , h _yx , and h _yy to the polarization state fluctuation speed estimation unit 17.

In Expression (1), μ is a step size parameter, and ε _x (n) and ε _y (n) are error evaluation functions. The vectors x _in ^* and y _in ^* are complex conjugate time series of the digital signals x _in and y _in , and x _in ^* = [x _in (n), x _in (n−1),..., X _in ( n−M + 1)] ^* and y _in ^* = [y _in (n), y _in (n−1),..., y _in (n−M + 1)] ^* . Tap coefficient vector _{h xx (n), h xy} (n), h yx (n), h yy (n) is the tap coefficient vector obtained by (n-1) -th update. For example, the tap coefficient vector h _xx (n) is [h _{xx, 1} (n), h _{xx, 2} (n),..., H _{xx, M} (n)]. The step size parameter μ may be a predetermined value or a value determined based on the fluctuation speed of the polarization state.

Incidentally, the tap coefficient updating unit 33 applies a known algorithm such as RLS (Recursive Least-Squares) and CMA (Constant Modulus Algorithm), the tap coefficient vector _{h xx, h xy, h yx} , the _{h yy} You may update sequentially.

In the adaptive equalization unit 14, the tap coefficient updating units 33 and 34 change the tap coefficients h _{xx, i} , h _{xy, i} , h _{yx, i} , h _{yy, i} according to changes in transmission characteristics in the optical fiber transmission line. Update sequentially. Digital signal _{x in,} by each tap coefficient in accordance with _{y in} is updated, the two digital signals _{x in,} and the waveform equalization and polarization isolation for between _{y in} is performed.

  Returning to FIG. 1, the description of the configuration of the digital signal processing unit 12 will be continued. The carrier phase compensation unit 15 estimates frequency offset and phase noise for the two digital signals output from the adaptive equalization unit 14. The carrier phase compensation unit 15 compensates for two digital signals based on the estimation result. The carrier phase compensation unit 15 outputs the two compensated digital signals to the reception data demodulation unit 16. The reception data demodulation unit 16 acquires the transmitted binary information by performing demodulation and decoding on the two digital signals output from the carrier phase compensation unit 15.

Polarization state variation speed estimation unit 17 as a polarization state estimating apparatus, the tap coefficient vector _h xx output from the adaptive equalizer _{14, h xy, h yx,} h yy ( first to fourth tap coefficient vectors ) To estimate the fluctuation speed of the polarization state. The tap coefficient of the FIR filter of the adaptive equalization unit 14 updated by adaptive equalization has a relationship with the Stokes parameter as described in Non-Patent Document 2. That is, the time change of the tap coefficient indicates a change in the polarization state. Therefore, using the tap coefficients h _{xx, i} , h _{xy, i} , h _{yx, i} , h _{yy, i} , the polarization state variation S (n) is expressed by Equation (2).

In Expression (2), M is the number of taps of the FIR filter. Each of Δh _{xx, i} (n), Δh _{xy, i} , Δh _{yx, i} , Δh _{yy, i} represents the amount of time variation of the tap coefficient.
Δh _{xx, i} (n) = h _{xx, i} (n) −h _{xx, i} (n−1)
Δh _{xy, i} (n) = h _{xy, i} (n) −h _{xy, i} (n−1)
_{Δh yx, i (n) =} h yx, i (n) -h yx, i (n-1)
Δh _{yy, i} (n) = h _{yy, i} (n) −h _{yy, i} (n−1)

That is, S _xx (n) is a value obtained by adding the absolute value of the time change amount of each element of the tap coefficient vector h _xx . _{Similarly, S xy (n), S} yx (n), a value obtained by adding the absolute value of the time variation of each element of the _S yy (n) be the tap coefficient vector _{h xy, h yx, h yy} . _{S (n), S xx (} n) in a predetermined _{period, S xy (n), S} yx (n), by sequentially calculating the _S yy (n), each time series is obtained.

Incidentally, _S xx _(n) in equation _{(2), S xy (n} ), S yx (n), in calculating the _S yy (n), without any M number of tap coefficients and addition target, M Some tap coefficients among the tap coefficients may be added. For example, the tap coefficient to be added may be a tap coefficient in a range from the Pth to the Qth out of M tap coefficients. P and Q are natural numbers that satisfy 1 <P <Q <M. Further, the tap coefficient to be added may be a plurality of predetermined tap coefficients among the M tap coefficients. By reducing the number of tap coefficients to be added, the amount of calculation when calculating the polarization state fluctuation S (n) is reduced.

  The polarization state fluctuation speed estimation unit 17 calculates the fluctuation S (n) according to the equation (2), and calculates the cycle of the calculated fluctuation S (n). The polarization state fluctuation speed estimation unit 17 estimates the fluctuation speed of the polarization state by calculating the reciprocal (frequency) of the calculated S (n) period. Alternatively, the polarization state fluctuation speed estimation unit 17 may perform a Fourier transform on the fluctuation S (n) to estimate the polarization state fluctuation speed. Specifically, the polarization state fluctuation speed estimation unit 17 detects the frequency at which the absolute value of the intensity is maximum in the frequency spectrum obtained by Fourier transform, and estimates the fluctuation speed of the polarization state from the detected frequency.

FIG. 3 is a flowchart showing an estimation process performed by the polarization state fluctuation speed estimation unit 17 in the present embodiment. Polarization state changing speed estimating unit 17 starts the estimation process, the tap coefficient vector _h xx from the adaptive equalizer _14, h _xy, h _yx, acquires _{h yy} (step S101). The polarization state fluctuation speed estimation unit 17 calculates the sum S _xx (n), S _xy (n), S _ix (n), and S _yy (n) of the time variation amounts of each element of the tap coefficient vector for each tap coefficient vector. (Step S102). As described above, the polarization state fluctuation speed estimation unit 17 adds some elements for each tap coefficient vector and adds S _xx (n), S _xy (n), S _ix (n), and S _yy. (N) may be calculated.

  The polarization state fluctuation speed estimation unit 17 calculates the polarization state fluctuation S (n), and detects the frequency at which the absolute value of the frequency component in the fluctuation S (n) is maximum (step S103). The polarization state fluctuation speed estimation unit 17 estimates the detected frequency as the polarization state fluctuation speed (step S104).

  Since the polarization state fluctuation speed estimation unit 17 estimates the change speed of the polarization state based on the tap coefficient vector of the FIR filter used in the adaptive equalization unit 14, it is not necessary to calculate the Stokes parameter. The calculation of the polarization state fluctuation S (n) using the tap coefficient (equation (2)) can be performed by a relatively simple calculation compared to the calculation of the Stokes parameter, and therefore the calculation load is small. Therefore, the polarization state fluctuation speed estimation unit 17 can reduce the calculation load when estimating the polarization state change speed.

Incidentally, the polarization state variation speed estimation unit 17, instead of the variation _{S (n), S xx (} n), S xy (n), S yx (n), S yy (n) of the polarization state from each The fluctuation speed may be estimated. Alternatively, the polarization state fluctuation speed estimation unit 17 may estimate the fluctuation speed of the polarization state from a combination of S _xx (n), S _xy (n), S _ix (n), and S _yy (n). .

When there is no crosstalk between the X polarization and the Y polarization of the optical signal in the optical fiber transmission line, each element (tap coefficient) of the tap coefficient vectors h _xy and h _yx is almost zero. Further, when the X polarization and the Y polarization are switched in the optical signal input by the optical receiver 1, the elements (tap coefficients) of the tap coefficient vectors h _xx and h _yy are almost zero. Thus, as can also be estimated variation speed of the polarization state is in any polarization _{state, S xx (n), S} xy (n), S yx (n), S obtained by adding the _S yy (n) ( It is desirable to estimate the fluctuation speed of the polarization state using n).

On the other hand, in order to reduce the amount of calculation when estimating the fluctuation speed of the polarization state, a combination of tap coefficient vectors in which the tap coefficient does not become 0, specifically, S _xx (n) and S _xy (n) Any one of a combination of S _yx (n) and S _yy (n) may be used.

Because they often crosstalk occurs between the X polarization and the Y polarization is transmitted optical _{signal, S xx (n), S} xy (n), S yx (n), S yy (n ) May be used to estimate the fluctuation speed of the polarization state. The polarization state fluctuation speed estimation unit 17 can reduce the calculation load by reducing the parameters used when estimating the fluctuation speed of the polarization state.

When the quality of the digital signal is deteriorated due to noise, the tap coefficient of the FIR filter updated by adaptive equalization may be affected by the noise. In this case, there is a possibility that the estimation accuracy of the fluctuation speed of the polarization state is lowered. However, the tap coefficient vector _{h xx, h xy, h yx} , h yy or time variation Delta] h _xx tap coefficient vector,, Delta] h _xy, Delta] h _yx, polarization fluctuations from the moving average of the Delta] h _yy S a (n) By calculating, the influence of noise can be reduced. Alternatively, the influence of noise may be reduced by calculating the fluctuation speed of the polarization state using the moving average of the fluctuation S (n) of the polarization state.

  The polarization state fluctuation speed estimation unit 17 may calculate the polarization state fluctuation S (n) based on the moving average of each tap coefficient vector or the moving average of the time change amount of the tap coefficient vector. Alternatively, the polarization state variation speed estimation unit 17 calculates the polarization state variation S (n) from the time variation amount of each tap coefficient vector or each tap coefficient vector, and moves the polarization state variation S (n). The fluctuation speed of the polarization state may be estimated using the average. By estimating the fluctuation speed of the polarization state using the moving average, the polarization state fluctuation speed estimation unit 17 can reduce the influence of noise in the estimation of the fluctuation speed of the polarization state.

  The polarization state fluctuation speed estimation unit 17 includes an acquisition unit that performs Step S101 in the flowchart illustrated in FIG. 3, an addition unit that performs Step S102, a detection unit that performs Step S103, and an estimation unit that performs Step S104. It is good also as a structure provided with.

  FIGS. 4 to 6 show the results of estimating the polarization state fluctuation speed of the optical fiber transmission line using the optical receiver 1 of the present embodiment. 4 to 6, the horizontal axis indicates the frequency as the fluctuation speed of the polarization state, and the vertical axis indicates the intensity of each frequency component. FIG. 4 is a graph plotting the absolute values of the results obtained by Fourier transforming the polarization state fluctuation S (n) when the polarization state fluctuation speed is 1 kHz. In the graph shown in FIG. 4, the frequency at which the absolute value of the intensity is maximum is 1.02 kHz, and the polarization state fluctuation speed estimation unit 17 estimates the polarization state fluctuation speed as 1.02 kHz.

  FIG. 5 is a graph plotting the absolute values of the results obtained by Fourier transforming the polarization state fluctuation S (n) when the polarization state fluctuation speed is 2 kHz. In the graph shown in FIG. 5, the frequency at which the absolute value of the intensity is maximum is 2.04 kHz, and the polarization state fluctuation speed estimation unit 17 estimates the polarization state fluctuation speed to be 2.04 kHz. FIG. 6 is a graph plotting the absolute values of the results obtained by Fourier transforming the fluctuation S (n) of the polarization state when the fluctuation speed of the polarization state is 5 kHz. In the graph shown in FIG. 6, the frequency at which the absolute value of the intensity is maximum is 5.10 kHz, and the polarization state fluctuation speed estimation unit 17 estimates the fluctuation speed of the polarization state as 5.10 kHz.

  As shown in FIGS. 4 to 6, it can be seen that the optical receiver 1 of the present embodiment can accurately estimate the polarization state fluctuation speed of the transmission path. Furthermore, since the optical receiver 1 estimates the polarization state change speed without calculating the Stokes parameters, it is possible to reduce the computation load when estimating the polarization state change speed. Since the optical receiver 1 can estimate the polarization state fluctuation speed by the estimation method with reduced calculation load, it can quickly acquire the polarization state fluctuation speed in the received optical signal. Further, the polarization state estimation method performed by the polarization state fluctuation speed estimation unit 17 is suitable for evaluation of reception tolerance in the optical receiver 1.

  A computer including a CPU (Central Processing Unit), a memory, an auxiliary storage device, and the like functions as a device including the polarization state fluctuation speed estimation unit 17 when the CPU executes a program stored in a non-temporary storage device. Also good. All or some of the functions of the polarization state fluctuation speed estimation unit 17 are realized by using hardware such as an application specific integrated circuit (ASIC), a programmable logic device (PLD), and a field programmable gate array (FPGA). May be. The program may be recorded on a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, or a storage device such as a hard disk built in the computer system. The program may be transmitted via a telecommunication line.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

  It can also be applied to applications where it is indispensable to reduce the computation load when estimating the rate of change of the polarization state in a polarization multiplexed optical signal.

DESCRIPTION OF SYMBOLS 1 ... Optical receiver 11 ... Optical coherent receiver 12 ... Digital signal processing part 13 ... Chromatic dispersion compensation part 14 ... Adaptive equalization part 15 ... Carrier phase compensation part 16 ... Received data demodulation part 17 ... Polarization state fluctuation speed estimation part 21, 23, 25, 27 ... delay devices 22, 24, 26, 28 ... multipliers 31, 32 ... adders 33, 34 ... tap coefficient updating unit

Claims (6)

An acquisition step of acquiring a plurality of tap coefficients of an FIR filter used for adaptive equalization with respect to a plurality of signals included in the polarization multiplexed optical signal;
An adding step for calculating the sum of the amount of change of each of the tap coefficients;
A detection step of detecting a frequency at which an absolute value of a frequency component in the sum time series is maximum;
An estimation step for estimating a polarization state fluctuation speed in the polarization multiplexed optical signal from the detected frequency;
A polarization state estimation method including: Two optical signals having different polarization planes are multiplexed in the polarization multiplexed optical signal,
The FIR filter receives first and second signals obtained from the polarization multiplexed optical signal, respectively.
The plurality of tap coefficients include first and second tap coefficient vectors for components of the two optical signals included in the first signal, and components of the two optical signals included in the second signal. And third and fourth tap coefficient vectors for
In the adding step,
Adding the amount of change of each element of at least one of the first, second, third and fourth tap coefficient vectors to calculate the sum;
The polarization state estimation method according to claim 1. In the adding step,
Adding the amount of change of each element of the first and second tap coefficient vectors and the amount of change of each element of the third and fourth tap coefficient vectors to calculate the sum;
The polarization state estimation method according to claim 2. In the adding step,
Adding all the variations of each element of the first, second, third and fourth tap coefficient vectors to calculate the sum;
The polarization state estimation method according to claim 2. The number of taps of the FIR filter is M, and the elements of the first, second, third and fourth tap coefficient vectors are h _{xx, i} (n), h _{xy, i} (n), h _{xy , i} ( n), h _{yy, i} (n), and the change amount of each element is Δh _{xx, i} (n) = h _{xx, i} (n) −h _{xx, i} (n−1),
Δh _{xy, i} (n) = h _{xy, i} (n) −h _{xy, i} (n−1),
Δh _{yx, i} (n) = h _{yx, i} (n) −h _{yx, i} (n−1),
Δh _{yy, i} (n) = h _{yy, i} (n) −h _{yy, i} (n−1)
If
Wherein the adding step calculates _S xx in the formula _{(A) (n), S} xy (n), S yx (n), at least one of _S yy (n) as the sum,

The polarization state estimation method according to claim 2. An acquisition unit for acquiring a plurality of tap coefficients of an FIR filter used for adaptive equalization for a plurality of signals included in a polarization multiplexed optical signal;
An adder that calculates the sum of the amount of change of each of the tap coefficients;
A detection unit for detecting a frequency at which an absolute value of a frequency component in the time series of the sum is maximum;
An estimation unit for estimating a polarization state fluctuation speed in the polarization multiplexed optical signal from the detected frequency;
A polarization state estimation apparatus comprising:

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