Optical power distribution estimation device, optical power distribution estimation method, and computer program

Abstract

The present invention provides an optical power distribution estimation device comprising: a partial chromatic dispersion application unit that applies, to a signal, partial chromatic dispersion corresponding to a distance from an optical transmission device to an optical power measurement position; a nonlinear arithmetic operation unit that performs a nonlinear arithmetic operation on the signal to which the partial chromatic dispersion is applied, the nonlinear arithmetic operation using a first-order term obtained by applying the Taylor expansion to an arithmetic expression used for phase rotation; a residual dispersion application unit that applies, to the signal after the nonlinear arithmetic operation by the nonlinear arithmetic operation unit, residual dispersion corresponding to a distance from the optical power measurement position to an optical reception device; and a correlation calculation unit that estimates an optical power distribution of an optical transmission line by obtaining correlation, at each optical power measurement position, between the signal to which the residual dispersion is applied and a received signal based on an optical signal transmitted from the optical transmission device and received through the optical transmission line.

Description

[Technical Field]

[0001] The present invention relates to an optical power distribution estimation device, an optical power distribution estimation method, and a computer program. [Background technology]

[0002] When operating an optical transmission system, the basic characteristics of the optical fiber that makes up the optical transmission path have a significant impact on transmission performance. Here, the basic characteristics of optical fiber include optical power, distribution of loss and dispersion, and location of fault points. For example, if the optical power is too high, the influence of nonlinear optical effects in the optical fiber increases, resulting in a decrease in the signal-to-noise ratio (hereinafter referred to as "SNR" (Signal-to-Noise Ratio)). If the loss is too high, the optical power attenuates accordingly, resulting in a decrease in SNR.

[0003] Therefore, it is important to know the characteristics of optical fibers in the operation, maintenance, and monitoring of optical transmission systems. Optical transmission paths are composed of various devices other than optical fibers, such as optical amplifiers and optical filters. Knowing the characteristics of these devices is also important in the operation, maintenance, and monitoring of optical transmission systems.

[0004] The characteristics of devices such as optical fibers, optical amplifiers, and optical filters can generally be measured using analog measuring instruments such as OTDRs (Optical Time Domain Reflectometers) and optical spectrum analyzers. However, measurements using analog measuring instruments require direct measurement of each optical node and optical fiber, which poses the problem of high equipment and operating costs.

[0005] To solve this problem, in recent years, digital longitudinal monitoring (DLM) has been proposed as a technology that detects the characteristics of various devices in an optical transmission system by digital signal processing on the receiving side of the system, instead of measurements using analog measuring instruments (see, for example, Non-Patent Documents 1 and 2). DLM is based on a digital coherent optical transmission system, and monitors the optical power and other characteristics of the optical transmission line by performing digital signal processing on the received signal obtained by coherently detecting the optical signal transmitted by the optical transmission line.

[0006] Non-Patent Document 1 uses a technique that uses correlation, and in the following description it will be referred to as the correlation method. FIG. 6 is a diagram showing an example configuration of an optical receiving device 10 that uses the correlation method for estimating optical power distribution. The optical receiving device 10 includes a coherent receiver 11, a demodulation / decoding unit 12, a transmission signal restoration unit 13, a chromatic dispersion application unit 14, an absolute value calculation unit 15, and an optical power distribution estimation unit 16. The coherent receiver 11 receives an optical signal transmitted through an optical transmission path and performs coherent detection. The coherent receiver 11 outputs the received signal obtained by coherent detection to the demodulation / decoding unit 12.

[0007] The demodulation and decoding unit 12 decodes the received signal output from the coherent receiver 11. The demodulation and decoding unit 12 includes a chromatic dispersion compensator 121, a polarization fluctuation compensator 122, a frequency offset compensator 123, a carrier phase compensator 124, a symbol decision unit 125, and a decoder 126. The chromatic dispersion compensator 121 estimates chromatic dispersion suffered in the optical transmission path, and compensates for the estimated chromatic dispersion in the received signal output from the coherent receiver 11. The polarization fluctuation compensator 122 compensates for distortion occurring in the waveform of the received signal in the optical transmission path, using the received signal whose chromatic dispersion has been compensated for by the chromatic dispersion compensator 121.

[0008] The frequency offset compensator 123 compensates for the frequency offset of the received signal that has been compensated for by the polarization fluctuation compensator 122. The carrier phase compensator 124 compensates for the phase offset of the received signal after frequency offset compensation. The symbol determiner 125 performs symbol determination on the received signal after phase offset compensation. The decoder 126 decodes the received signal based on the result of the symbol determination by the symbol determiner 125. The transmission signal restorer 13 restores the transmission signal using the received signal decoded by the demodulation and decoding unit 12. The transmission signal restorer 13 includes a mapping unit 131 and a Nyquist filter 132. The mapping unit 131 maps the decoded received signal. The Nyquist filter 132 restores the transmission signal by performing filtering on the mapped received signal.

[0009] The chromatic dispersion application unit 14 estimates the chromatic dispersion suffered in the optical transmission path and applies the estimated chromatic dispersion value to the received signal output from the polarization fluctuation compensation unit 122. This restores the received signal from the signal output from the coherent receiver 11, with only the polarization fluctuation compensated for. The chromatic dispersion application unit 14 outputs the restored received signal to the optical power distribution estimation unit 16. The absolute value calculation unit 15 takes the absolute value of the restored transmitted signal and outputs it to the optical power distribution estimation unit 16.

[0010] The optical power distribution estimation unit 16 includes a partial chromatic dispersion compensation unit 161, a nonlinear calculation unit 162, a residual dispersion compensation unit 163, an absolute value calculation unit 164, and a correlation calculation unit 165. The partial chromatic dispersion compensation unit 161 receives the optical power measurement position z k (k is a natural number equal to or greater than 0), and compensates for the estimated partial chromatic dispersion on the received signal to which the chromatic dispersion value has been applied. The nonlinear calculation unit 162 performs nonlinear calculation shown in the following equation (1) on the received signal whose partial chromatic dispersion has been compensated for by the partial chromatic dispersion compensator 161. In equation (1), u out represents the output from the nonlinear calculation unit 162, and u in represents the received signal with the partial chromatic dispersion value applied.

[0011]

number

[0012] The residual dispersion compensator 163 measures the optical power at the optical power measurement position z k The residual chromatic dispersion corresponding to the distance from the transmission source to the optical transmitter is estimated, and the received signal after nonlinear calculation is compensated for the estimated residual chromatic dispersion. The absolute value calculation unit 164 calculates the absolute value of the received signal with the residual chromatic dispersion compensated for and outputs it to the correlation calculation unit 165. The correlation calculation unit 165 calculates the correlation between the absolute value of the restored transmission signal output from the absolute value calculation unit 15 and the absolute value of the received signal with the residual chromatic dispersion compensated for output from the absolute value calculation unit 164. The optical power distribution estimation unit 16 performs the above processing for all optical power measurement positions. The estimated power distribution obtained by plotting the correlation results obtained by the correlation calculation unit 165 for each optical power measurement position has the form P0(offset)+aP(z). Here, a represents a real number, and P(z) represents the estimated power for each position z. [Prior art documents] [Non-patent literature]

[0013] [Non-Patent Document 1] T. Tanimura, et al., “Fiber-Longitudinal Anomaly Position Identification Over Multi-Span Transmission Link Out of Receiver-end Signals”, JLT, 38(9), 2020. [Non-patent document 2] T. Sasai, et al., “Digital longitudinal monitoring of Optical Fiber Communication Link”, JLT, 40(8), 2022. Summary of the Invention [Problem to be solved by the invention]

[0014] Figure 7 is a diagram illustrating the problems with optical power distribution estimation using the conventional correlation method. In the conventional configuration, because an offset P0 exists in the estimated power distribution, even if the estimated output is plotted on a logarithmic axis as 10log10(P0+aP(z)), it is not possible to estimate a correct power level diagram (amount of power change) as shown in Figure 7. Furthermore, if the received signal contains a lot of noise, the noise increases when nonlinear calculations are performed, resulting in a deterioration in the accuracy of the optical power distribution estimation.

[0015] As described above, in the conventional configuration, the power change amount (dB) cannot be estimated due to the presence of an unnecessary power offset in the estimated optical power distribution, making it difficult to estimate the loss amount.

[0016] In view of the above circumstances, an object of the present invention is to provide a technique capable of estimating the amount of power change. [Means for solving the problem]

[0017] One aspect of the present invention is an optical power distribution estimation device comprising: a partial chromatic dispersion application unit that applies partial chromatic dispersion to a signal, the partial chromatic dispersion corresponding to the distance from an optical transmitting device to an optical power measurement position; a nonlinear calculation unit that performs nonlinear calculation on the signal to which the partial chromatic dispersion has been applied, using a first-order term obtained by Taylor expansion of a formula used for phase rotation; a residual dispersion application unit that applies residual chromatic dispersion, the residual chromatic dispersion corresponding to the distance from the optical power measurement position to an optical receiving device, to the signal after the nonlinear calculation by the nonlinear calculation unit; and a correlation calculation unit that estimates the optical power distribution of the optical transmission path by calculating, for each optical power measurement position, a correlation between the signal to which the residual chromatic dispersion has been applied and a received signal that is based on an optical signal transmitted from the optical transmitting device and received via an optical transmission path.

[0018] One aspect of the present invention is an optical power distribution estimation method that applies partial chromatic dispersion corresponding to the distance from an optical transmitting device to an optical power measurement position to a signal, performs a nonlinear operation on the signal to which the partial chromatic dispersion has been applied using a first-order term obtained by Taylor expansion of an equation used for phase rotation, applies residual chromatic dispersion corresponding to the distance from the optical power measurement position to an optical receiving device to the signal after the nonlinear operation, and estimates the optical power distribution of the optical transmission path by taking a correlation, for each optical power measurement position, between the signal to which the residual chromatic dispersion has been applied and a received signal that is based on an optical signal transmitted from the optical transmitting device and received via the optical transmission path.

[0019] One aspect of the present invention is a computer program for causing a computer to execute the following steps: a partial chromatic dispersion application step of applying partial chromatic dispersion to a signal, the partial chromatic dispersion corresponding to the distance from an optical transmitting device to an optical power measurement position; a nonlinear operation step of performing a nonlinear operation on the signal to which the partial chromatic dispersion has been applied, using a first-order term obtained by Taylor expansion of an equation used for phase rotation; a residual chromatic dispersion application step of applying residual chromatic dispersion corresponding to the distance from the optical power measurement position to an optical receiving device to the signal after the nonlinear operation in the nonlinear operation step; and a correlation calculation step of estimating the optical power distribution of the optical transmission path by calculating, for each optical power measurement position, a correlation between the signal to which the residual chromatic dispersion has been applied and a received signal based on an optical signal transmitted from the optical transmitting device and received via an optical transmission path. [Effects of the Invention]

[0020] The present invention makes it possible to estimate the amount of power change. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a diagram illustrating an example of the configuration of an optical receiving device according to a first embodiment. [Figure 2] 4 is a flowchart showing a flow of processing performed by the optical receiving device according to the first embodiment. [Figure 3]FIG. 10 is a diagram showing the results of a comparison between the method of the present invention and the true power in the optical transmission line obtained by simulation. [Figure 4] FIG. 10 is a diagram illustrating a configuration example of an optical receiving device according to a modified example of the first embodiment. [Figure 5] FIG. 10 is a diagram illustrating an example of the configuration of an optical transmission system according to a second embodiment. [Figure 6] FIG. 1 is a diagram illustrating an example of the configuration of an optical receiving device that uses a correlation method for estimating optical power distribution. [Figure 7] 1A and 1B are diagrams for explaining problems with optical power distribution estimation using a conventional correlation method. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0023] (First embodiment) FIG. 1 is a diagram illustrating an example of the configuration of an optical receiving device 20 according to the first embodiment. The optical receiving device 20 is connected to an optical transmitting device provided in an optical transmission system via an optical transmission path. The optical transmission path is, for example, an optical fiber. The optical receiving device 20 receives a transmission signal transmitted from the optical transmitting device via the optical transmission path. The optical receiving device 20 includes a coherent receiver 21, a demodulation / decoding unit 22, a transmission signal restoration unit 23, a pre-processing unit 24, and an optical power distribution estimation unit 25. The transmission signal restoration unit 23, the pre-processing unit 24, and the optical power distribution estimation unit 25 are configured as an optical power distribution estimation device.

[0024] The coherent receiver 21 is connected to the optical transmission line and receives an optical signal (e.g., a transmission signal) transmitted through the optical transmission line and performs coherent detection. The coherent receiver 21 separates the received optical signal into X-polarized and Y-polarized waves. The coherent receiver 21 detects the I- and Q-components of each of the X- and Y-polarized waves by causing interference between each of the X- and Y-polarized optical signals after polarization separation and a laser beam emitted from a local oscillator light source provided inside. The coherent receiver 21 converts each of the I- and Q-component optical signals of the X- and Y-polarized waves into four analog electrical signals. The coherent receiver 21 converts the converted four analog signals into four digital signals using four internal analog-to-digital converters and outputs the converted signals. Hereinafter, the four digital signals output by the coherent receiver 21 will be referred to as received signals.

[0025] The demodulation / decoding unit 22 decodes the received signal output from the coherent receiver 21 while compensating for influences caused by the optical transmission path. Examples of influences caused by the optical transmission path include chromatic dispersion, polarization fluctuation, frequency offset, and carrier phase. The demodulation / decoding unit 22 includes a chromatic dispersion compensator 221, a polarization fluctuation compensator 222, a frequency offset compensator 223, a carrier phase compensator 224, a symbol decision unit 225, and a decoding unit 226.

[0026] The chromatic dispersion compensator 221 estimates the chromatic dispersion experienced in the optical transmission line, and compensates for the estimated chromatic dispersion in the received signal output from the coherent receiver 21 .

[0027] The polarization fluctuation compensator 222 compensates for distortion that occurs in the waveform of the received signal in the optical transmission path, using the received signal whose chromatic dispersion has been compensated for by the chromatic dispersion compensator 221. That is, the polarization fluctuation compensator 222 corrects code errors that occur in the received signal due to inter-symbol interference in the optical transmission path. For example, the polarization fluctuation compensator 222 may perform adaptive equalization processing using an FIR (Finite Impulse Response) filter in accordance with set tap coefficients. Note that the polarization fluctuation compensator 222 may compensate for distortion that occurs in the waveform of the received signal using a method other than the above for adaptively compensating for polarization fluctuation.

[0028] The frequency offset compensator 223 executes a process of compensating for the frequency offset of the received signal that has been compensated for by the polarization fluctuation compensator 222 .

[0029] The carrier phase compensation unit 224 performs a process of compensating for the phase offset of the received signal after frequency offset compensation.

[0030] The symbol decision unit 225 makes a symbol decision on the received signal after phase offset compensation.

[0031] The decoding unit 226 decodes the received signal based on the result of the symbol decision made by the symbol decision unit 225 .

[0032] The transmission signal restoration unit 23 restores the transmission signal using the reception signal decoded by the demodulation and decoding unit 22. That is, the transmission signal restoration unit 23 restores the transmission signal transmitted from the optical transmitting device based on the signal after the influence caused by the optical transmission path has been compensated for. The transmission signal restoration unit 23 includes a mapping unit 231 and a Nyquist filter 232. The mapping unit 231 maps the decoded reception signal. The Nyquist filter 232 restores the transmission signal by performing filtering on the mapped reception signal.

[0033] The pre-processing unit 24 performs a predetermined process on the transmission signal restored by the transmission signal restoration unit 23. Here, the predetermined process is a process of applying a value corresponding to the influence caused by the optical transmission path to the transmission signal in order to make the transmission signal closer to the received signal. The pre-processing unit 24 includes a polarization fluctuation application unit 241, a carrier phase application unit 242, and a frequency offset application unit 243.

[0034] The polarization fluctuation applying unit 241 applies to the transmission signal restored by the transmission signal restoring unit 23 a value that is the same as the distortion that has occurred in the waveform of the reception signal compensated for by the polarization fluctuation compensating unit 222 .

[0035] The carrier phase applying unit 242 applies the same value as the phase offset compensated for by the carrier phase compensating unit 224 to the transmission signal to which the polarization fluctuation applying unit 241 has applied the same value as the distortion.

[0036] The frequency offset applying unit 243 applies the same value as the phase offset compensated by the frequency offset compensating unit 223 to the transmission signal to which the same value as the phase offset has been applied by the carrier phase applying unit 242 .

[0037] As described above, the pre-processing unit 24 generates a signal by removing the chromatic dispersion value from the received signal received by the coherent receiver 21. Hereinafter, the transmission signal processed in the pre-processing unit 24 will be referred to as the pre-processed transmission signal.

[0038] The optical power distribution estimator 25 estimates the optical power distribution (optical transmission characteristics) of the optical transmission path using an estimation algorithm based on a correlation method. The optical power distribution estimator 25 includes a partial chromatic dispersion applicator 251, a nonlinear calculator 252, a residual dispersion applicator 253, and a correlation calculator 254.

[0039] The partial chromatic dispersion application unit 251 applies the optical power from the optical transmitter to the optical power measurement position z k The value of chromatic dispersion corresponding to the distance from the optical transmitter to the optical power measurement position z is applied to the pre-processed transmission signal. kFor example, when k=10, the partial chromatic dispersion application unit 251 applies chromatic dispersion to the optical power measurement position z 10 A partial chromatic dispersion value corresponding to the distance to the target point is estimated, and the estimated partial chromatic dispersion value is applied to the pre-processed transmission signal.

[0040] Optical power measurement position z k The lower limit of is, for example, the position of the optical transmitter (k=0), and the optical power measurement position z k The upper limit is, for example, the position of the optical receiving device 20. The partial chromatic dispersion application unit 251 performs the above process at all optical power measurement positions.

[0041] The nonlinear calculation unit 252 performs nonlinear calculation on the transmission signal to which the partial chromatic dispersion value has been applied by the partial chromatic dispersion application unit 251. More specifically, the nonlinear calculation unit 252 performs nonlinear calculation on the transmission signal to which the partial chromatic dispersion value has been applied, based on equation (2) using first-order terms obtained by Taylor expansion of the equation used for phase rotation. Equation (2) is an equation using first-order terms of Taylor expansion of the conventional nonlinear calculation unit 162. In equation (2), u out represents the output by the nonlinear calculation unit 252, and u in represents the transmitted signal to which a value of partial chromatic dispersion has been applied.

[0042]

number

[0043] The residual dispersion application unit 253 is k The residual dispersion applying unit 253 applies a chromatic dispersion value corresponding to the distance from the optical power measurement position z to the optical receiving device 20 to the transmission signal after nonlinear calculation. In this way, the residual dispersion applying unit 253 applies a chromatic dispersion value corresponding to the remaining distance not applied by the partial chromatic dispersion applying unit 251. Hereinafter, the optical power measurement position z k The value of chromatic dispersion corresponding to the distance from the optical fiber 10 to the optical receiving device 20 is referred to as the residual chromatic dispersion value.

[0044] The correlation calculation unit 254 calculates the correlation between the received signal output from the coherent receiver 21 and the transmitted signal to which the residual chromatic dispersion value output from the residual dispersion application unit 253 has been applied. The correlation calculation unit 254 performs this process for each optical power measurement position. The correlation calculation unit 254 plots the correlation results (correlation values) obtained for each optical power measurement position to estimate the power distribution.

[0045] FIG. 2 is a flowchart showing the flow of processing performed by the optical receiving device 20 in the first embodiment. The coherent receiver 21 receives a transmission signal transmitted from an optical transmitter via an optical transmission path (step S101). The coherent receiver 21 outputs the received signal. The received signal output from the coherent receiver 21 is branched and input to the demodulation / decoding unit 22 and the optical power distribution estimation unit 25 (step S102).

[0046] The chromatic dispersion compensator 221 estimates the chromatic dispersion suffered in the optical transmission path, and compensates for the estimated chromatic dispersion in the received signal output from the coherent receiver 21 (step S103). The chromatic dispersion compensator 221 outputs the received signal after chromatic dispersion compensation to the polarization fluctuation compensator 222. The polarization fluctuation compensator 222 compensates for distortion occurring in the waveform of the received signal in the optical transmission path, using the received signal after chromatic dispersion output from the chromatic dispersion compensator 221 (step S104). The polarization fluctuation compensator 222 outputs the compensated received signal to the frequency offset compensator 223.

[0047] The frequency offset compensator 223 compensates for the frequency offset of the received signal that has been compensated for by the polarization fluctuation compensator 222 (step S105). The frequency offset compensator 223 outputs the received signal after frequency offset compensation to the carrier phase compensator 224. The carrier phase compensator 224 compensates for the phase offset of the received signal after frequency offset compensation by the frequency offset compensator 223 (step S106). The carrier phase compensator 224 outputs the received signal after phase offset compensation to the symbol decision unit 225.

[0048] The symbol determination unit 225 performs symbol determination on the received signal after phase offset compensation (step S107). The symbol determination unit 225 outputs the result of the symbol determination to the decoding unit 226. The decoding unit 226 decodes the received signal based on the result of the symbol determination by the symbol determination unit 225 (step S108). The decoding unit 226 outputs the decoded received signal to the transmission signal restoration unit 23.

[0049] The transmission signal restoration unit 23 restores the transmission signal using the reception signal decoded by the demodulation and decoding unit 22 (step S109). The transmission signal restoration unit 23 outputs the restored transmission signal to the pre-processing unit 24. The polarization fluctuation application unit 241 applies, to the transmission signal restored by the transmission signal restoration unit 23, a value that is the same as the distortion that occurred in the waveform of the reception signal compensated for by the polarization fluctuation compensation unit 222 (step S110). The polarization fluctuation application unit 241 outputs the applied transmission signal to the carrier phase application unit 242.

[0050] The carrier phase applying unit 242 applies the same value as the phase offset compensated for by the carrier phase compensating unit 224 to the transmission signal after application output from the polarization fluctuation applying unit 241 (step S111). The carrier phase applying unit 242 outputs the transmission signal after application to the frequency offset applying unit 243. The frequency offset applying unit 243 applies the same value as the frequency offset compensated for by the frequency offset compensating unit 223 to the transmission signal after application output from (step S112). The frequency offset applying unit 243 outputs the transmission signal after application to the optical power distribution estimating unit 25.

[0051] The partial chromatic dispersion application unit 251 sets k=0 (step S113), and kThe partial chromatic dispersion application unit 251 estimates a partial chromatic dispersion value that is a chromatic dispersion value that is a distance from the optical transmitter to the optical power measurement position z0. For example, since k=0 in step S113, the partial chromatic dispersion application unit 251 estimates a partial chromatic dispersion value that is a chromatic dispersion value that is a distance from the optical transmitter to the optical power measurement position z0. The partial chromatic dispersion application unit 251 applies the estimated partial chromatic dispersion value to the transmission signal after application that is output from the frequency offset application unit 243 (step S114). The partial chromatic dispersion application unit 251 outputs the transmission signal to which the partial chromatic dispersion value has been applied to the nonlinear operation unit 252.

[0052] The nonlinear calculation unit 252 performs nonlinear calculation based on the above formula (2) using the transmission signal after the partial chromatic dispersion value application output from the partial chromatic dispersion application unit 251 (step S115). The nonlinear calculation unit 252 outputs the transmission signal after the nonlinear calculation to the residual dispersion application unit 253. The residual dispersion application unit 253 calculates the nonlinearity of the transmission signal at the optical power measurement position z k The residual dispersion applying unit 253 estimates a value of chromatic dispersion corresponding to the distance from the optical power measurement position z0 to the optical receiving device 20. For example, the residual dispersion applying unit 253 estimates a residual chromatic dispersion value, which is a value of chromatic dispersion corresponding to the distance from the optical power measurement position z0 to the optical receiving device 20. The residual dispersion applying unit 253 applies the estimated residual chromatic dispersion value to the transmission signal after nonlinear operation output from the nonlinear operation unit 252 (step S116). The residual dispersion applying unit 253 outputs the transmission signal to which the residual chromatic dispersion value has been applied to the correlation calculating unit 254.

[0053] The correlation calculation unit 254 calculates the correlation between the received signal output from the coherent receiver 21 and the transmitted signal after the residual chromatic dispersion value has been applied and output from the residual dispersion application unit 253 (step S117). Thereafter, the correlation calculation unit 254 determines whether or not a termination condition is satisfied (step S118). The termination condition here is a condition for terminating the calculation of the correlation, and may be, for example, that the calculation of the correlation up to all optical power measurement positions has been completed.

[0054] If the correlation calculation unit 254 determines that the termination condition is not satisfied (step S118-NO), it adds 1 to k (step S119). Thereafter, the optical receiving device 20 repeatedly executes the processes from step S114 onwards. For example, if the value after the addition is k=1, the partial chromatic dispersion application unit 251 estimates a value of chromatic dispersion corresponding to the distance from the optical transmitting device to the optical power measurement position z1 in the process of step S114. The partial chromatic dispersion application unit 251 applies the estimated partial chromatic dispersion value to the applied transmission signal output from the frequency offset application unit 243.

[0055] Thereafter, the processes from steps S115 to S117 are executed with k=1. Then, the correlation calculation unit 254 determines again whether the termination condition is met (step S118). In this manner, the processes from steps S114 to S117 are repeatedly executed until correlations are acquired at all optical power measurement positions.

[0056] In the process of step S118, if it is determined that the termination condition is satisfied (step S118-YES), the correlation calculation unit 254 performs optical power estimation using the correlation results acquired for each optical power measurement position (step S120). Specifically, the correlation calculation unit 254 estimates an estimated power distribution by plotting the correlation results acquired for each optical power measurement position. At this time, the estimated power output by the correlation calculation unit 254 is a complex value. When plotting, the correlation calculation unit 254 first takes the real part of the estimated power or the absolute value and then plots it.

[0057] Under the following conditions, the true power in the optical transmission line was determined by simulation, and the determined true power in the optical transmission line was compared with the method of the present invention. (Simulation conditions) Transmission line model: Split-step Fourier method SSFM dz:0.05km Oversampling rate: 40 samples / symbol Loss coefficient: 0.2dB / km Chromatic dispersion coefficient: D=16ps / nm / km Nonlinear coefficient: g=1.3W -1 km -1 Signal: Probabilistically-shaped 64QAM64GBd Measurement interval: 0.25 km

[0058] Figure 3 shows the results of a comparison between the method of the present invention and the true power in the optical transmission line determined by simulation. In Figure 3, L1 represents the true power in the optical transmission line set in the simulation, and L2 represents the relative power determined by the method of the present invention. As shown in Figure 3, by plotting the estimated output on a logarithmic axis as 10log10(P(z)), it is possible to estimate values ​​close to the correct power level diagram (power change amount dB). In other words, the results shown in Figure 3 demonstrate that the method of the present invention can estimate true power change amount (dB) (a physically meaningful value can be estimated).

[0059] The optical receiving device 20 configured as described above includes a partial chromatic dispersion applying unit 251 that applies partial chromatic dispersion to a signal, the partial chromatic dispersion corresponding to the distance from the optical transmitting device to the optical power measurement position; a nonlinear calculation unit 252 that performs nonlinear calculation (the above equation (2)) on the signal to which the partial chromatic dispersion has been applied, using a linear term obtained by Taylor expansion of the equation used for phase rotation; a residual dispersion applying unit 253 that applies residual chromatic dispersion, the residual chromatic dispersion corresponding to the distance from the optical power measurement position to the optical receiving device 20, to the signal after the nonlinear calculation; and a correlation calculation unit 254 that estimates the optical power distribution in the optical transmission line by calculating the correlation between the signal to which residual chromatic dispersion has been applied and a received signal based on an optical signal transmitted from the optical transmitting device and received via the optical transmission line for each optical power measurement position. Conventional configurations use equation (1) for the nonlinear calculation, and an offset P0 occurs due to the constant term (=1) when exp in equation (1) is Taylor expanded. As a result, it is not possible to estimate the amount of power change. In contrast, the optical receiving device 20 uses only the first-order term obtained by Taylor expansion as shown in equation (2) for nonlinear calculation, and eliminates the constant term, so that the offset P0 can be eliminated. As a result, it becomes possible to estimate the amount of power change.

[0060] Furthermore, in the conventional configuration, nonlinear calculation is performed on the received signal. in,x =u in,x_true +N, |u in,x | 2 =|u in,x_true | 2 +|N| 2 +u ※ in,x_true N+u in,x_true N ※ and excessive phase rotation occurs due to the noise (similar to the y polarization). In contrast, the optical receiving device 20 performs nonlinear calculations on the restored transmission signal, so there is no noise N in the signal. Therefore, |u in,x | 2 =|u in,x_true | 2 Since no excessive components appear, it is possible to improve the estimation accuracy of the optical power distribution.

[0061] (Variation 1) The order of compensation by the demodulation / decoding unit 22 and the order of application by the pre-processing unit 24 and the optical power distribution estimating unit 25 are not limited to the above-mentioned order. Any order may be used for compensation by the demodulation / decoding unit 22. In the above-mentioned embodiment, the configuration in which the pre-processing unit 24 applies values ​​corresponding to the polarization fluctuation, frequency offset, and carrier phase to the restored transmission signal has been shown, but it is sufficient that the values ​​corresponding to the polarization fluctuation, frequency offset, and carrier phase are applied before processing by the correlation calculating unit 254.

[0062] (Variation 2) In the above-described embodiment, a process of taking the absolute value may be performed before performing the correlation calculation, as in the conventional case.

[0063] (Variation 3) In the above-described embodiment, the preprocessing unit 24 applies values ​​corresponding to the polarization fluctuation, frequency offset, and carrier phase applied to the transmission signal transmitted from the optical transmitting device via the optical transmission line to the restored transmission signal. In the optical receiving unit 20, it is sufficient that the same amounts of the polarization fluctuation, frequency offset, and carrier phase are added between the two waveforms for which correlation calculation is performed. Therefore, the optical receiving unit 20 may apply the same amount of the polarization fluctuation as added to the received signal to the restored transmission signal, or may compensate from the received signal. Here, the compensation from the received signal method refers to a method in which the correlation calculation unit 254 uses a signal after compensating for the effects of the optical transmission line on the received signal.

[0064] 4 is a diagram showing an example of the configuration of an optical receiving device 20a in a modified example of the first embodiment. The optical receiving device 20a receives a transmission signal transmitted from an optical transmitting device connected via an optical transmission path. The optical receiving device 20a includes a coherent receiver 21, a demodulation / decoding unit 22, a transmission signal restoration unit 23, and an optical power distribution estimation unit 25. The optical receiving device 20a differs from the optical receiving device 20 in that it does not include a pre-processing unit 24. The following describes the processing that differs from that of the optical receiving device 20.

[0065] The optical receiving device 20a also outputs the received signal, the phase offset of which has been compensated for by the carrier phase compensator 224, to the optical power distribution estimator 25. Furthermore, the optical receiving device 20a outputs the transmitted signal restored by the transmitted signal restorer 23 to the optical power distribution estimator 25. The optical power distribution estimator 25 performs the same processing on the restored transmitted signal as that described in the above-described embodiment. The correlation calculator 254 finds the correlation between the received signal output from the demodulator / decoder 22 and the transmitted signal after the residual chromatic dispersion value has been applied, output from the residual dispersion application unit 253. The correlation calculator 254 repeatedly executes this processing until a termination condition is satisfied.

[0066] (Second embodiment) In the second embodiment, a configuration will be described in which the process of estimating the optical power distribution is performed in a network controller that manages an optical transmission system.

[0067] 5 is a diagram showing an example of the configuration of an optical transmission system 100 in the second embodiment. The optical transmission system 100 includes an optical transmitting device (not shown), an optical receiving device 20b, and a network controller 30. The optical transmission system 100 may include a plurality of optical receiving devices 20b. The optical transmitting device (not shown) and the optical receiving device 20b are connected by an optical transmission path, and the optical receiving device 20b and the network controller 30 are connected by an electric line. The optical receiving device 20b receives a transmission signal transmitted from the optical transmitting device connected via the optical transmission path. The network controller 30 is a higher-level device that manages the optical transmission system 100.

[0068] The optical receiving device 20b includes a coherent receiver 21 and a demodulation / decoding unit 22. The network controller 30 includes a transmission signal restoration unit 23, a pre-processing unit 24, and an optical power distribution estimation unit 25. The processes performed by the coherent receiver 21, demodulation / decoding unit 22, transmission signal restoration unit 23, pre-processing unit 24, and optical power distribution estimation unit 25 are basically the same as those in the first embodiment. Below, differences from the first embodiment will be described.

[0069] The coherent receiver 21 outputs the received signal to a demodulation / decoding unit 22, and also outputs the received signal via an electrical line to an optical power distribution estimation unit 25 provided in the network controller 30. The demodulation / decoding unit 22 outputs the decoded received signal via an electrical line to a transmission signal restoration unit 23 provided in the network controller 30.

[0070] Each functional unit included in the network controller 30 performs the same processing as in the first embodiment.

[0071] According to the optical transmission system 100 configured as above, the optical power distribution is estimated in the network controller 30, which is a host device that manages the optical transmission system 100. This makes it possible to reduce the processing load on one optical receiving device 20b.

[0072] Furthermore, when multiple optical receiving devices 20b are connected to the network controller 30, the network controller 30 can estimate the optical power distribution for each optical receiving device 20b. This eliminates the need for each optical receiving device 20b to estimate its own optical power distribution, eliminating the need for each optical receiving device 20b to have a function for estimating its own optical power distribution. Since a single network controller 30 estimates the optical power distributions of multiple optical receiving devices 20b, efficient optical power distribution estimation becomes possible. Furthermore, when each optical receiving device 20b receives a signal with a different wavelength (i.e., in the case of a wavelength division multiplexing (WDM) system), the wavelength dependence of the optical power distribution obtained by the present invention can be obtained. This makes it possible to obtain the wavelength dependence of loss in an optical fiber in an optical transmission system, the gain spectrum of an optical amplifier, and the like.

[0073] (Variation 1) The second embodiment may be modified in the same manner as Modifications 1 to 3 of the first embodiment. For example, when the network controller 30 has the configuration shown in (Modification 3), the network controller 30 only needs to acquire from the optical receiving device 20b the same amount of information as that added to the received signal. Furthermore, in the case of a method of compensation from the received signal, the network controller 30 does not include the pre-processing unit 24, and acquires the received signal after carrier phase compensation from the optical receiving device 20b.

[0074] (Application example of the present invention) The present invention can be applied to the estimation of various optical transmission line characteristics. By applying this power distribution estimation to optical signals of various wavelengths, it is possible to estimate optical power distribution (detection of abnormal fiber), optical amplifier gain spectrum and gain tilt (detection of abnormal amplifier), power distribution in the distance direction and wavelength direction in an optical transmission line, and multipath interference. Furthermore, by acquiring optical power distribution in both X and Y polarizations, it is possible to estimate the amount and location of PDL (Polarization Dependent Loss).

[0075] Some or all of the functional units of the optical receiving devices 20, 20a, and 20b and the network controller 30 described above are realized as software by a processor such as a CPU (Central Processing Unit) executing a program stored in a storage device having a non-volatile storage medium (non-transitory storage medium) and a storage unit. The program may be recorded on a computer-readable non-transitory storage medium. Examples of computer-readable non-transitory storage media include portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), and CD-ROMs (Compact Disc Read Only Memory), and storage devices such as hard disks built into a computer system.

[0076] Some or all of the functional units of the optical receiving devices 20, 20a, 20b and the network controller 30 described above may be realized using hardware including an electronic circuit (electronic circuit or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0077] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Industrial Applicability]

[0078] The present invention can be applied to a technique for estimating transmission characteristics in a digital coherent optical transmission system. [Explanation of symbols]

[0079] 20, 20a, 20b...optical receiving device, 21...coherent receiver, 22...demodulation and decoding unit, 23...transmission signal restoration unit, 24...preprocessing unit, 25...optical power distribution estimation unit, 30...network controller, 221...chromatic dispersion compensation unit, 222...polarization fluctuation compensation unit, 223...frequency offset compensation unit, 224...carrier phase compensation unit, 225...symbol decision unit, 226...decoding unit, 231...mapping unit, 232...Nyquist filter, 241...polarization fluctuation application unit, 242...carrier phase application unit, 243...frequency offset application unit, 251...partial chromatic dispersion application unit, 252...nonlinear calculation unit, 253...residual dispersion application unit, 254...correlation calculation unit

Claims

1. a partial chromatic dispersion applying unit that applies partial chromatic dispersion to the signal corresponding to the distance from the optical transmitter to the optical power measurement position; a nonlinear calculation unit that performs a nonlinear calculation on the signal to which the partial chromatic dispersion has been applied, using only a first-order term obtained by Taylor expansion of a formula used for phase rotation; a residual dispersion application unit that applies residual chromatic dispersion corresponding to the distance from the optical power measurement position to an optical receiving device to the signal after nonlinear operation by the nonlinear operation unit; a correlation calculation unit that estimates an optical power distribution in the optical transmission line by calculating a correlation between the signal to which the residual chromatic dispersion has been applied and a received signal based on an optical signal transmitted from the optical transmitting device and received via the optical transmission line for each optical power measurement position; and An optical power distribution estimation device comprising:

2. a transmission signal restoration unit that restores a transmission signal transmitted by the optical transmitting device based on the received signal; 2. The optical power distribution estimation device according to claim 1, wherein the partial chromatic dispersion applying unit applies the partial chromatic dispersion to a restored transmission signal or a signal obtained after predetermined processing has been performed on the restored transmission signal.

3. a pre-processing unit that performs the predetermined processing on the transmission signal restored by the transmission signal restoration unit, the received signal is a signal before being compensated for effects caused by the optical transmission path, the transmission signal restoration unit restores the transmission signal based on the signal after the influence caused by the optical transmission path has been compensated for; 3. The optical power distribution estimation device according to claim 2, wherein the preprocessing unit applies a value corresponding to an influence caused by the optical transmission path in order to make the transmission signal closer to the reception signal as the predetermined processing.

4. the received signal is a signal after compensation for effects caused by the optical transmission path; the transmission signal restoration unit restores the transmission signal based on the signal after the influence caused by the optical transmission path has been compensated for; 3. The optical power distribution estimation device according to claim 2, wherein the partial chromatic dispersion applying unit applies the partial chromatic dispersion to the restored transmission signal.

5. applying partial chromatic dispersion to the signal corresponding to the distance from the optical transmitter to the optical power measurement position; performing a nonlinear operation using only a first-order term obtained by Taylor expansion of a mathematical expression used for phase rotation on the signal to which the partial chromatic dispersion has been applied; applying residual chromatic dispersion corresponding to the distance from the optical power measurement position to the optical receiving device to the signal after the nonlinear operation; an optical power distribution estimation method for estimating an optical power distribution in an optical transmission path by calculating, for each optical power measurement position, a correlation between a signal to which the residual chromatic dispersion has been applied and a received signal based on an optical signal transmitted from the optical transmitting device and received via an optical transmission path.

6. On the computer, a partial chromatic dispersion applying step of applying partial chromatic dispersion corresponding to the distance from the optical transmitter to the optical power measurement position to the signal; a nonlinear calculation step of performing a nonlinear calculation on the signal to which the partial chromatic dispersion has been applied, using only a first-order term obtained by Taylor expansion of an equation used for phase rotation; a residual chromatic dispersion applying step of applying residual chromatic dispersion corresponding to a distance from the optical power measurement position to an optical receiving device to the signal after the nonlinear operation in the nonlinear operation step; a correlation calculation step of estimating an optical power distribution in the optical transmission path by calculating a correlation between the signal to which the residual chromatic dispersion has been applied and a received signal based on an optical signal transmitted from the optical transmitting device and received via an optical transmission path at each optical power measurement position; A computer program for executing

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