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

Abstract

This optical power distribution estimation device comprises: a coherent receiver that receives, via an optical transmission path, a signal transmitted from an optical transmission device; and an optical power distribution estimation unit that estimates an optical power distribution on the basis of a signal resulting from at least the characteristics of an optical reception device have been compensated or applied to a received signal received by the coherent receiver or to a signal restored on the basis of the received signal and transmitted from the optical transmission device.　

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, reducing the signal-to-noise ratio (hereinafter referred to as "SNR"). If the loss is too high, the optical power attenuates accordingly, reducing the 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. [Prior art documents] [Non-patent literature]

[0006] [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]

[0007] As mentioned above, DLM is a technology that estimates the response of various devices in a digital coherent optical transmission system to a received signal in the optical transmission system using only digital signal processing. However, the estimation accuracy of the above-mentioned estimation target is inferior to that of an analog measuring instrument. This point will be explained. In Non-Patent Documents 1 and 2, as shown in Figure 8, a received signal A[L], which is the actual optical transmission line output, and a simulated signal A[L] propagated through an optical transmission line in the digital domain (Digital-twin link) are compared. ref The optical power is estimated by comparing it with [L].

[0008] Here, as a technique for estimating optical power, an estimation method using a correlation method described in Non-Patent Document 1 and an estimation method using a least squares method described in Non-Patent Document 2 have been proposed. In the estimation method using a correlation method described in Non-Patent Document 1, a received signal A[L] and a simulated signal A ref The optical power is estimated by obtaining the correlation between the received signal A[L] and the simulated signal A[L]. ref The optical power is estimated by determining the optical transmission line parameters so that the square error with [L] is minimized.

[0009] When estimating optical power using the above-mentioned DLM, it is desirable that the characteristics of the actual optical transmission line and the optical transmission line in the digital domain are identical. However, with conventional methods, the optical transmission line in the digital domain cannot adequately simulate the characteristics of the actual optical transmission line. Therefore, although simpler measurements are possible compared to analog measuring instruments, there are problems with lower spatial resolution and estimation accuracy.

[0010] In view of the above circumstances, an object of the present invention is to provide a technique for estimating optical power distribution using digital signal processing, which is capable of estimating optical power distribution with high spatial resolution and high accuracy. [Means for solving the problem]

[0011] One aspect of the present invention is an optical power distribution estimation device comprising: a coherent receiver that receives a signal transmitted from an optical transmitting device via an optical transmission path; and an optical power distribution estimation unit that estimates an optical power distribution based on a received signal received by the coherent receiver or a signal transmitted from the optical transmitting device that has been restored based on the received signal and after at least the characteristics of the optical receiving device have been compensated for or applied to the signal.

[0012] One aspect of the present invention is an optical power distribution estimation method that receives a signal transmitted from an optical transmitting device via an optical transmission path, and estimates an optical power distribution based on the received signal or a signal transmitted from the optical transmitting device that has been restored based on the received signal and after at least the characteristics of an optical receiving device have been compensated for or applied to the signal.

[0013] One aspect of the present invention is a computer program for causing a computer to execute a receiving step of receiving a signal transmitted from an optical transmitting device via an optical transmission path, and an optical power distribution estimation step of estimating an optical power distribution based on the received signal or a signal transmitted from the optical transmitting device that has been restored based on the received signal and after at least the characteristics of the optical receiving device have been compensated for or applied to the signal. [Effects of the Invention]

[0014] According to the present invention, it is possible to estimate an optical power distribution with high spatial resolution and high accuracy in an optical power distribution estimation technique using digital signal processing. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 3 is a diagram for explaining an outline of an optical power distribution estimation process in the first embodiment. [Figure 2] 1 is a diagram illustrating an example of the configuration of an optical receiving device according to a first embodiment. [Figure 3] 2 is a diagram illustrating an example of the configuration of an optical transmitter characteristic application unit and an optical receiver characteristic application unit according to the first embodiment. FIG. [Figure 4]4 is a flowchart showing a flow of processing performed by the optical receiving device according to the first embodiment. [Figure 5] FIG. 10 is a diagram illustrating an example of the configuration of an optical transmission system according to a modified example of the first embodiment. [Figure 6] FIG. 10 is a diagram for explaining an outline of an optical power distribution estimation process in the second embodiment. [Figure 7] FIG. 10 is a diagram illustrating an example of the configuration of an optical transmission system according to a second embodiment. [Figure 8] FIG. 1 is a diagram for explaining an outline of a conventional optical power distribution estimation process. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (First embodiment) Fig. 1 is a diagram for explaining an outline of an optical power distribution estimation process in the first embodiment. In the first embodiment, as shown in Fig. 1, characteristics (for example, frequency characteristics (amplitude / phase), inter-lane crosstalk, skew, gain imbalance, etc.) of an optical transmitting device and an optical receiving device provided in an optical transmission system are estimated in advance, and the estimated characteristics of the optical transmitting device and the optical receiving device are simulated on an optical transmission path in the digital domain (digital-twin link). Specifically, in an actual optical transmission path, a transmission signal A[0] is affected by the characteristics of the optical transmitting device and the characteristics of the optical receiving device from the time it is generated by the optical transmitting device until it is received by the optical receiving device.

[0017] Conventional methods have not been able to estimate optical power distributions that take into account the characteristics of such optical transmitting devices and optical receiving devices. Therefore, in the first embodiment, the estimated characteristics of the optical transmitting device and optical receiving device are applied to a signal propagating through an optical transmission path in the digital domain, just like an actual optical transmission path. This brings the characteristics of the actual optical transmission path and the optical transmission path in the digital domain closer to being identical. As a result, estimation accuracy and resolution can be improved.

[0018] The characteristics of the optical transmitting device and the optical receiving device may be measured or estimated by any method before use. For example, analog devices may be measured one by one using a measuring instrument, or they may be estimated by system identification using digital signal processing based on the received signal and the transmitted signal. This makes it possible to estimate the optical power distribution shown in the figure on the right. A specific configuration for realizing the above processing will be described below.

[0019] 2 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, an optical transmitting device characteristic application unit 24, a pre-processing unit 25, and an optical power distribution estimation unit 26. The transmission signal restoration unit 23, the optical transmitting device characteristic application unit 24, the pre-processing unit 25, and the optical power distribution estimation unit 26 are configured as an optical power distribution estimation device.

[0020] 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.

[0021] 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.

[0022] 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 .

[0023] 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.

[0024] 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 .

[0025] The carrier phase compensation unit 224 performs a process of compensating for the phase offset of the received signal after frequency offset compensation.

[0026] The symbol decision unit 225 makes a symbol decision on the received signal after phase offset compensation.

[0027] The decoding unit 226 decodes the received signal based on the result of the symbol decision made by the symbol decision unit 225 .

[0028] The transmission signal restoration unit 23 restores the transmission signal using the received 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.

[0029] The optical transmission device characteristic application unit 24 applies the characteristics of the optical transmission device to the restored transmission signal. The optical transmission device characteristic application unit 24 applies the characteristics of the optical transmission device by convolving the previously estimated characteristics of the optical transmission device into the restored transmission signal using a convolution operation. In this way, the optical transmission device characteristic application unit 24 can make the restored transmission signal closer to the transmission signal transmitted by the optical transmission device.

[0030] The pre-processing unit 25 performs a predetermined process on the transmission signal to which the optical transmission device characteristics have been applied by the optical transmission device characteristics application unit 24. 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 25 includes a polarization fluctuation application unit 251, a carrier phase application unit 252, and a frequency offset application unit 253.

[0031] The polarization fluctuation applying unit 251 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 .

[0032] The carrier phase applying unit 252 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 251 has applied the same value as the distortion.

[0033] The frequency offset applying unit 253 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 252 .

[0034] As described above, the pre-processing unit 25 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 25 will be referred to as the pre-processed transmission signal.

[0035] The optical power distribution estimator 26 estimates the optical power distribution (optical transmission characteristics) of the optical transmission path using a predetermined estimation algorithm. Here, an estimation algorithm based on a correlation method will be described as an example of the predetermined estimation algorithm. The optical power distribution estimator 26 includes a partial chromatic dispersion applicator 261, a nonlinear calculator 262, a residual dispersion applicator 263, an optical receiving device characteristic applicator 264, and a correlation calculator 265.

[0036] The partial chromatic dispersion application unit 261 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. k For example, when k=10, the partial chromatic dispersion application unit 261 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.

[0037] 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 261 performs the above process at all optical power measurement positions.

[0038] The nonlinear calculation unit 262 performs nonlinear calculation on the transmission signal to which the partial chromatic dispersion value has been applied by the partial chromatic dispersion application unit 261. More specifically, the nonlinear calculation unit 262 may use the following equation (1) used for phase rotation on the transmission signal to which the partial chromatic dispersion value has been applied, or may use nonlinear calculation based on equation (2) using a first-order term obtained by Taylor expansion of equation (1). In equations (1) and (2), uout represents the output from the nonlinear calculation unit, and u in represents the transmitted signal to which a value of partial chromatic dispersion has been applied.

[0039]

number

[0040]

number

[0041] The residual dispersion application unit 263 is k The residual dispersion applying unit 263 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 263 applies a chromatic dispersion value corresponding to the remaining distance not applied by the partial chromatic dispersion applying unit 261. 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.

[0042] The optical receiving device characteristic applying unit 264 applies the characteristic of the optical receiving device 20 to the transmission signal to which the residual chromatic dispersion value output from the residual dispersion applying unit 263 has been applied. The optical receiving device characteristic applying unit 264 applies the characteristic of the optical receiving device 20 by convolving the characteristic of the optical receiving device 20, which has been estimated in advance, by a convolution operation to the transmission signal to which the residual chromatic dispersion value has been applied. In this way, the optical receiving device characteristic applying unit 264 can make the transmission signal closer to the reception signal received by the optical receiving device.

[0043] The correlation calculation unit 265 calculates the correlation between the received signal output from the coherent receiver 21 and the transmitted signal to which the optical receiving device characteristics have been applied by the optical receiving device characteristics application unit 264. The correlation calculation unit 265 performs this process for each optical power measurement position. At this time, an operation of taking the absolute value may be performed before calculating the correlation between the two signals. The correlation calculation unit 265 estimates the estimated power distribution by plotting the correlation results (correlation values) obtained for each optical power measurement position. At this time, if the absolute value has not been calculated before calculating the correlation, the estimated power output by the correlation calculation unit 265 will be a complex value. In this case, when plotting, the real part of the estimated power or the absolute value is calculated before plotting.

[0044] In addition, the explanation here is of a method in which partial chromatic dispersion, nonlinear operation, and residual chromatic dispersion are "applied" to the restored transmitted signal, but it is also possible to use a method in which partial chromatic dispersion, nonlinear operation, and residual chromatic dispersion are "compensated" for the received signal.

[0045] Fig. 3 is a diagram showing an example of the configuration of the optical transmitting device characteristic application unit 24 and the optical receiving device characteristic application unit 264 in the first embodiment. Note that the optical transmitting device characteristic application unit 24 and the optical receiving device characteristic application unit 264 have the same configuration and perform the same processing except for the characteristics they apply, and therefore Fig. 3 will explain the optical transmitting device characteristic application unit 24 as an example. The optical transmitting device characteristic application unit 24 performs MIMO calculations, including inter-lane crosstalk, on four series of optical signals of the I component and Q component of each of the X polarization and the Y polarization.

[0046] The 〇〇 shown in Figure 3 in From 〇〇 out Each line extending to represents convolution by an FIR filter. Note that XX can be any of XI, XQ, YI, or YQ. For example, XI in From XI out The line extending to represents the operation shown in equation (3) below.

[0047]

number

[0048] Here h xi―xi is the XI of the optical transmitter in From XI out In the case of the optical receiver characteristic application unit 264, h xi―xi is the XI of the optical receiving device 20 in From XI out The n in equation (3) represents the response characteristic between the optical transmitter characteristic application unit 24 and the optical receiver characteristic application unit 264. in From 〇〇 out By performing this on each line extending in the direction perpendicular to the optical axis, the frequency characteristics of the optical transmitter and receiver and the imbalance between lanes can be simulated.

[0049] FIG. 4 is a flowchart showing the flow of processing 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 26 (step S102).

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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 optical transmission device characteristic application unit 24. The optical transmission device characteristic application unit 24 applies the characteristics of the optical transmission device to the transmission signal output from the transmission signal restoration unit 23 (step S110). The optical transmission device characteristic application unit 24 outputs the transmission signal after application of the characteristics of the optical transmission device to the polarization fluctuation application unit 251.

[0054] The polarization fluctuation application unit 251 applies the same value as the distortion that occurred in the waveform of the received signal compensated for by the polarization fluctuation compensation unit 222 to the transmission signal after application of the characteristics of the optical transmission device output from the optical transmission device characteristic application unit 24 (step S111). The polarization fluctuation application unit 251 outputs the transmission signal after application to the carrier phase application unit 252.

[0055] The carrier phase applying unit 252 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 251 (step S112). The carrier phase applying unit 252 outputs the transmission signal after application to the frequency offset applying unit 253. The frequency offset applying unit 253 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 S113). The frequency offset applying unit 253 outputs the transmission signal after application to the optical power distribution estimating unit 26.

[0056] The partial chromatic dispersion application unit 261 sets k=0 (step S114) and outputs the optical power measurement position z k The partial chromatic dispersion application unit 261 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 S114, the partial chromatic dispersion application unit 261 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 261 applies the estimated partial chromatic dispersion value to the transmission signal after application that is output from the frequency offset application unit 253 (step S115). The partial chromatic dispersion application unit 261 outputs the transmission signal to which the partial chromatic dispersion value has been applied to the nonlinear operation unit 262.

[0057] The nonlinear calculation unit 262 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 261 (step S116). The nonlinear calculation unit 262 outputs the transmission signal after the nonlinear calculation to the residual dispersion application unit 263. The residual dispersion application unit 263 calculates the nonlinearity of the transmission signal at the optical power measurement position z k The residual dispersion applying unit 263 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 263 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 263 applies the estimated residual chromatic dispersion value to the transmission signal after nonlinear operation output from the nonlinear operation unit 262 (step S117). The residual dispersion applying unit 263 outputs the transmission signal to which the residual chromatic dispersion value has been applied to the optical receiving device characteristic applying unit 264.

[0058] The optical receiving device characteristic applying unit 264 applies the characteristic of the optical receiving device 20 to the transmission signal after the residual chromatic dispersion value has been applied and output from the residual dispersion applying unit 263 (step S118). The optical receiving device characteristic applying unit 264 outputs the transmission signal after the characteristic of the optical receiving device 20 has been applied to the correlation calculating unit 265. The correlation calculating unit 265 calculates the correlation between the reception signal output from the coherent receiver 21 and the transmission signal after the characteristic of the optical receiving device 20 has been applied and output from the optical receiving device characteristic applying unit 264 (step S119). Thereafter, the correlation calculating unit 265 determines whether or not a termination condition is satisfied (step S120). 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.

[0059] If the correlation calculation unit 265 determines that the termination condition is not satisfied (step S120-NO), it adds a value of 1 to k (step S121). Thereafter, the optical receiving device 20 repeatedly executes the processes from step S115 onwards. For example, if the value after the addition is k=1, the partial chromatic dispersion application unit 261 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 S115. The partial chromatic dispersion application unit 261 applies the estimated partial chromatic dispersion value to the applied transmission signal output from the frequency offset application unit 253.

[0060] Thereafter, the processes from steps S115 to S119 are executed with k=1. Then, the correlation calculation unit 265 determines again whether the termination condition is met (step S120). In this way, the processes from steps S115 to S119 are repeatedly executed until correlations are acquired at all optical power measurement positions.

[0061] In the process of step S120, if it is determined that the termination condition is satisfied (step S120-YES), the correlation calculation unit 265 performs optical power estimation using the correlation results acquired for each optical power measurement position (step S122). Specifically, the correlation calculation unit 265 plots the correlation results acquired for each optical power measurement position to estimate the estimated power distribution.

[0062] The optical receiving device 20 configured as described above can estimate the optical power distribution while taking into account the characteristics of the optical transmitting device and the optical receiving device, which could not be simulated in the conventional optical transmission path in the digital domain. Therefore, it becomes possible to estimate the optical power distribution with high spatial resolution and high accuracy.

[0063] (Variation 1) In the above-described embodiment, the optical transmitting device characteristic application unit 24 and the optical receiving device characteristic application unit 264 are configured to apply all characteristics. The optical transmitting device characteristic application unit 24 and the optical receiving device characteristic application unit 264 may be configured to apply only some of the characteristics. In this configuration, the optical transmitting device characteristic application unit 24 and the optical receiving device characteristic application unit 264 do not perform MIMO calculations for all combinations, but perform MIMO calculations excluding some of the characteristics (for example, setting them to 0).

[0064] (Variation 2) In the above-described embodiment, a configuration using a correlation method has been described as a technique for estimating optical power distribution, but the optical power distribution estimator 26 may be configured to estimate the optical power distribution using the least squares method. When configured in this manner, the optical power distribution estimator 26 estimates the optical power by determining optical transmission path parameters so as to minimize the square error between the received signal output from the coherent receiver 21 and the transmitted signal to which the optical receiving device characteristic applying unit 264 has applied the characteristics of the optical receiving device.

[0065] (Variation 3) The optical power distribution estimation process may be performed in a network controller that manages the optical transmission system. Fig. 5 is a diagram showing an example of the configuration of an optical transmission system 100 according to a modification of the first embodiment. The optical transmission system 100 includes an optical transmitting device (not shown), an optical receiving device 20a, and a network controller 30. The optical transmission system 100 may include a plurality of optical receiving devices 20a. The optical transmitting device (not shown) and the optical receiving device 20a are connected by an optical transmission path, and the optical receiving device 20a and the network controller 30 are connected by an electric line. The optical receiving device 20a 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.

[0066] The optical receiving device 20a includes a coherent receiver 21 and a demodulation / decoding unit 22. The network controller 30 includes a transmission signal restoration unit 23, an optical transmission device characteristic application unit 24, a pre-processing unit 25, and an optical power distribution estimation unit 26. The processes performed by the coherent receiver 21, demodulation / decoding unit 22, transmission signal restoration unit 23, optical transmission device characteristic application unit 24, pre-processing unit 25, and optical power distribution estimation unit 26 are basically the same as those in the above-described embodiment. Below, differences from the above-described embodiment will be described.

[0067] 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 26 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.

[0068] Each functional unit included in the network controller 30 performs the same processing as in the above-described embodiment.

[0069] 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 20a.

[0070] Furthermore, when multiple optical receiving devices 20a are connected to the network controller 30, the network controller 30 can estimate the optical power distribution for each optical receiving device 20a. This eliminates the need for each optical receiving device 20a to estimate its optical power distribution, and each optical receiving device 20a does not need to be equipped with a function for estimating the optical power distribution. Furthermore, since a single network controller 30 estimates the optical power distributions for multiple optical receiving devices 20a, efficient optical power distribution estimation becomes possible.

[0071] (Second embodiment) In the second embodiment, a configuration using the inverse characteristics of an optical transmitting device and an optical receiving device will be described.

[0072] Fig. 6 is a diagram for explaining an outline of the optical power distribution estimation process in the second embodiment. In the second embodiment, as shown in Fig. 6, the inverse characteristics of the optical transmitting device and the optical receiving device provided in the optical transmission system are estimated in advance, and the signal transmitted and received in the actual optical transmission path (the signal transmitted from the optical transmitting device and received by the optical receiving device) is compensated for with the estimated inverse characteristics of the optical transmitting device and the optical receiving device. This makes the actual optical transmission path and the optical transmission path in the digital domain closer to the same characteristics. As a result, it is possible to improve the estimation accuracy and resolution.

[0073] The inverse characteristics of the optical transmitting device and the optical receiving device may be measured or estimated by any method before use. For example, analog devices may be measured one by one using a measuring instrument, or they may be estimated by system identification using digital signal processing based on the received signal and the transmitted signal. This makes it possible to estimate the optical power distribution as shown in the figure on the right. A specific configuration for realizing the above processing will be described below.

[0074] 7 is a diagram illustrating an example of the configuration of an optical transmission system 100b according to the second embodiment. The optical transmission system 100b includes an optical transmitter 10b and an optical receiver 20b. The optical transmitter 10b and the optical receiver 20b are connected via an optical transmission path 40.

[0075] The optical transmitting device 10b includes a transmission signal generating unit 11 and an optical transmitting device characteristic compensating unit 12. The transmission signal generating unit 11 generates a transmission signal to be transmitted. The optical transmitting device characteristic compensating unit 12 compensates for the characteristics of the optical transmitting device 10b in the transmission signal by using the inverse characteristic of the optical transmitting device 10b, which has been estimated in advance, for the transmission signal generated by the transmission signal generating unit 11. Specifically, the optical transmitting device characteristic compensating unit 12 compensates for the characteristics of the optical transmitting device 10b by convolving the transmission signal generated by the transmission signal generating unit 11 with the inverse characteristic of the optical transmitting device 10b, which has been estimated in advance, through a convolution operation.

[0076] The optical receiving device 20b receives the transmission signal transmitted from the optical transmitting device 10b via the optical transmission path 40. The optical receiving device 20b includes a coherent receiver 21, a demodulation / decoding unit 22, a transmission signal restoration unit 23, a pre-processing unit 25, an optical power distribution estimation unit 26b, and an optical receiving device characteristic compensation unit 27. The transmission signal restoration unit 23, the pre-processing unit 25, the optical power distribution estimation unit 26b, and the optical receiving device characteristic compensation unit 27 are configured as an optical power distribution estimation device.

[0077] The optical receiving device 20b differs in configuration from the optical receiving device 20 in that it does not include the optical transmitting device characteristic application unit 24, that it includes an optical power distribution estimating unit 26b instead of the optical power distribution estimating unit 26, and that it further includes an optical receiving device characteristic compensating unit 27. The other configurations of the optical receiving device 20b are the same as those of the optical receiving device 20. The following description will focus on the differences from the optical receiving device 20.

[0078] The optical receiving device characteristic compensating unit 27 compensates for the characteristics of the optical receiving device 20b in the received signal by using the inverse characteristic of the optical receiving device 20b estimated in advance for the received signal output from the coherent receiver 21. The optical receiving device characteristic compensating unit 27 compensates for the characteristics of the optical receiving device 20b by convolving the inverse characteristic of the optical receiving device 20b estimated in advance with the received signal through a convolution operation.

[0079] In the optical transmission system 100b configured as described above, the optical transmitter 10b transmits a signal that has been compensated for the characteristics of the optical transmitter 10b as a transmission signal, and the optical receiver 20b compensates for the characteristics of the optical receiver 20b with respect to the transmission signal transmitted from the optical transmitter 10b. This allows the actual optical transmission path and the optical transmission path in the digital domain to have characteristics that are closer to the same. As a result, estimation accuracy and resolution can be improved.

[0080] (Variation 1) In the above-described embodiment, the optical transmitter characteristic compensator 12 and the optical receiver characteristic compensator 27 are configured to compensate for all characteristics. The optical transmitter characteristic compensator 12 and the optical receiver characteristic compensator 27 may be configured to compensate for only some characteristics. In such a configuration, the optical transmitter characteristic compensator 12 and the optical receiver characteristic compensator 27 do not perform MIMO calculations for all combinations, but perform MIMO calculations excluding some characteristics (for example, setting some characteristics to 0).

[0081] (Variation 2) In the above-described embodiment, a configuration using a correlation method has been described as a technique for estimating the optical power distribution, but the optical power distribution estimator 26b may be configured to estimate the optical power distribution using the least squares method. In such a configuration, the optical power distribution estimator 26b estimates the optical power by determining optical transmission path parameters so as to minimize the square error between the received signal in which the characteristics of the optical transmitting device and the optical receiving device have been compensated for and the restored transmitted signal.

[0082] (Modifications common to the first and second embodiments) In each embodiment, a part of the characteristics may be “compensated in the main signal path” and a part may be “applied to the reference signal path.” There are many combinations, and any combination may be used.

[0083] Some or all of the functional units of the optical transmitting device 10b, the optical receiving devices 20, 20a, and 20b, and the network controller 30 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.

[0084] Some or all of the functional units of the optical transmitting device 10b, 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).

[0085] 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]

[0086] The present invention can be applied to a technique for estimating transmission characteristics in a digital coherent optical transmission system. [Explanation of symbols]

[0087] 10b...optical transmitter, 11...transmission signal generation unit, 12...optical transmitter characteristic compensation unit, 20, 20a, 20b...optical receiver, 21...coherent receiver, 22...demodulation and decoding unit, 23...transmission signal restoration unit, 24...optical transmitter characteristic application unit, 25...preprocessing unit, 26, 26b...optical power distribution estimation unit, 27...optical receiver characteristic compensation 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, 251...polarization fluctuation application unit, 252...carrier phase application unit, 253...frequency offset application unit, 261...partial chromatic dispersion application unit, 262...nonlinear calculation unit, 263...residual dispersion application unit 264...optical receiving device characteristic application unit, 265...correlation calculation unit

Claims

1. a coherent receiver that receives a signal transmitted from an optical transmitter via an optical transmission line; a transmission signal restoration unit that restores a signal transmitted from the optical transmitting device based on a reception signal received by the coherent receiver; an optical transmission device characteristic applying unit that applies the characteristics of the optical transmission device to the restored signal; an optical receiving device characteristic applying unit that applies an optical receiving device characteristic to the signal after the optical transmitting device characteristic has been applied; an optical power distribution estimator that estimates an optical power distribution using the received signal and the signal after the characteristics of the optical transmitting device and the characteristics of the optical receiving device have been applied; An optical power distribution estimation device comprising:

2. the optical transmitting device characteristic application unit and the optical receiving device characteristic application unit apply the characteristics of the optical transmitting device and the characteristics of the optical receiving device, which are estimated in advance, to the restored signal by convolving them through a convolution operation.

2. The optical power distribution estimation device according to claim 1.

3. receiving a signal transmitted from an optical transmitter via an optical transmission line; Reconstructing the signal transmitted from the optical transmitter based on the received signal; applying the characteristics of the optical transmitting device to the restored signal; applying a characteristic of an optical receiving device to the signal after the characteristic of the optical transmitting device has been applied; an optical power distribution estimation method for estimating an optical power distribution using the received signal and the signal after the characteristics of the optical transmitting device and the characteristics of the optical receiving device have been applied;

4. On the computer, a receiving step of receiving a signal transmitted from an optical transmitting device via an optical transmission line; a transmission signal restoration step unit that restores a signal transmitted from the optical transmitting device based on the received signal; an optical transmission device characteristic applying step of applying the characteristic of the optical transmission device to the restored signal; an optical receiving device characteristic applying step of applying an optical receiving device characteristic to the signal after the optical transmitting device characteristic has been applied; an optical power distribution estimating step of estimating an optical power distribution using the received signal and the signal after the characteristics of the optical transmitting device and the characteristics of the optical receiving device have been applied; A computer program for executing

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