Optical transmission line monitoring apparatus and optical transmission line monitoring method

Abstract

To provide an optical transmission line monitoring device for highly accurately estimating the distribution of optical power.SOLUTION: A first compensation unit configured to compensate for a part of chromatic dispersion of an optical transmission line and a part of high-order chromatic dispersion with respect to an electric field signal indicating an optical electric field component of an optical signal digitally coherently received from the optical transmission line; The optical transmission device includes a nonlinear compensation unit that compensates for deterioration due to a nonlinear optical effect of an optical transmission path, a second compensation unit that compensates for a remaining portion of chromatic dispersion and a remaining portion of higher-order chromatic dispersion with respect to an electric field signal after compensation by the nonlinear compensation unit, a generation unit that generates a reference signal indicating a photoelectric field component of an optical signal at a transmission end of the optical transmission path based on the electric field signal, and an estimation unit that estimates a distribution of optical power based on a correlation between the electric field signal after compensation by the second compensation unit and the reference signal.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an optical transmission line monitoring device and an optical transmission line monitoring method. [Background technology]

[0002] An optical transmission system is known that includes multiple optical transmitters and multiple optical receivers. The multiple optical transmitters and multiple optical receivers are communicatively connected via an optical transmission path. The optical transmission path includes optical fibers. The optical transmission system communicates using wavelength division multiplexing (WDM) using the multiple optical transmitters and multiple optical receivers (see, for example, Patent Document 1).

[0003] For example, when an optical transmitter transmits an optical signal, the optical signal is transmitted via an optical transmission line. As a result, an optical receiver receives the optical signal transmitted via the optical transmission line (see, for example, Patent Document 2). When an optical signal is transmitted via WDM, the chromatic dispersion of the optical fiber limits the transmission distance. Therefore, optical receivers have been proposed that include dispersion compensators that compensate for such chromatic dispersion (see, for example, Patent Document 3). It is also known that chromatic dispersion can be reduced by using a dispersion compensation module (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2023 / 037553 [Patent Document 2] Japanese Patent Application Publication No. 2023-177783 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-262452 [Patent Document 4] U.S. Patent No. 6,330,381 Summary of the Invention [Problem to be solved by the invention]

[0005] In many cases, dispersion compensation units such as dispersion compensators and dispersion compensation modules compensate for chromatic dispersion across the entire signal band of an optical signal at the center frequency of the optical signal. This can result in a difference between the amount of chromatic dispersion to be compensated for and the actual amount of chromatic dispersion at both ends of the signal band.

[0006] When large-capacity transmission is achieved in an optical transmission system, the symbol rate, which is the number of times digital modulation is performed per unit time, increases, which tends to increase the difference in the amount of chromatic dispersion described above. When the difference in the amount of chromatic dispersion increases, signal distortion increases after chromatic dispersion compensation, degrading the transmission performance of the optical transmission system. This degradation in transmission performance becomes more pronounced as the transmission distance of the optical signal increases.

[0007] For this reason, when dispersion compensation is performed at high symbol rates, compensation for dispersion slope is also performed in addition to compensation for chromatic dispersion. Dispersion slope is the gradient when the wavelength dependence of chromatic dispersion is approximated by a linear function, i.e., it corresponds to the value obtained by differentiating chromatic dispersion once with respect to wavelength. Values ​​obtained by differentiating chromatic dispersion once or more with respect to wavelength are called higher-order chromatic dispersion. By compensating for both chromatic dispersion and dispersion slope, degradation in the transmission performance of optical transmission systems is suppressed, even when the symbol rate is high.

[0008] Furthermore, in addition to the dispersion compensator described above, some optical receivers may also include an optical transmission line monitoring device that monitors the optical transmission line and estimates the location of losses occurring in the optical transmission line. The optical transmission line monitoring device captures an electric field signal corresponding to the optical signal received by the optical receiver and estimates the distribution of optical power in the optical transmission line based on the electric field signal. The optical transmission line monitoring device can estimate the location of losses occurring in the optical transmission line based on the distribution of optical power.

[0009] However, when estimating the optical power distribution, the optical transmission line monitoring device takes into account the effect of chromatic dispersion but does not take into account the effect of dispersion slope, resulting in a problem of low accuracy in the optical power distribution.

[0010] Therefore, in one aspect, an object of the present invention is to provide an optical transmission line monitoring device and an optical transmission line monitoring method that estimate the distribution of optical power with high accuracy. [Means for solving the problem]

[0011] In one embodiment, an optical transmission line monitoring device includes a first compensating unit that compensates for a part of the chromatic dispersion of the optical transmission line and a part of higher-order chromatic dispersion with respect to an electric field signal that indicates an optical field component of an optical signal digitally coherently received from the optical transmission line; a nonlinear compensating unit that compensates for degradation due to a nonlinear optical effect of the optical transmission line with respect to the electric field signal after compensation by the first compensating unit; a second compensating unit that compensates for a remainder of the chromatic dispersion and a remainder of the higher-order chromatic dispersion with respect to the electric field signal after compensation by the nonlinear compensating unit; a generating unit that generates a reference signal that indicates an optical field component of the optical signal at a transmitting end of the optical transmission line based on the electric field signal; and an estimating unit that estimates an optical power distribution based on a correlation between the electric field signal after compensation by the second compensating unit and the reference signal. [Effects of the Invention]

[0012] The optical power distribution can be estimated with high accuracy. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is an example of an optical transmission system. [Figure 2] 2 is an example of a hardware configuration of an optical receiver and an optical transmission line monitoring device. [Figure 3] This is an example of the functional configuration of a DSP and FPGA. [Figure 4] 1A is an example of a power profile according to a comparative example, and FIG. 1B is an example of a power profile according to an example. [Figure 5] 1 is an example of a power profile from a transmitting end to a receiving end and an enlarged view of a portion thereof; [Figure 6]10A is another example of a power profile according to a comparative example, and FIG. 10B is an example of a moving average of an anomaly score distribution according to a comparative example. [Figure 7] 10(a) is another example of a power profile according to an embodiment, and FIG. 10(b) is an example of a moving average of an anomaly score distribution according to an embodiment. [Figure 8] 10 is a flowchart illustrating an example of the operation of the optical transmission line monitoring device. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0015] As shown in FIG. 1, the optical transmission system ST includes an optical transmitter 100 and an optical receiver 200. The optical transmitter 100 and the optical receiver 200 are connected by an optical transmission line 50. The optical transmitter 100 is provided at the transmitting end of the optical transmission line 50, and the optical receiver 200 is provided at the receiving end of the optical transmission line 50. When transmission data is input, the optical transmitter 100 transmits an optical signal obtained by modulating the transmission data to the optical transmission line 50. The optical signal propagates through the optical transmission line 50. The optical receiver 200 receives the optical signal transmitted from the optical transmitter 100 from the optical transmission line 50, demodulates it, and outputs the demodulated data.

[0016] A plurality of optical amplifiers 51A, 52A, and 53A are provided on the optical transmission line 50. Therefore, the optical transmission line 50 is divided into a plurality of transmission sections (hereinafter referred to as spans) SP#1, SP#2, SP#3, and SP#4 by the optical amplifiers 51A, 52A, and 53A. In other words, the optical transmission line 50 is a multi-span optical transmission line including a plurality of spans SP#1, SP#2, SP#3, and SP#4 (hereinafter referred to as SP#1, . . . , SP#4 as appropriate).

[0017] Optical fibers 51F, 52F, 53F, and 54F are laid in each of the spans SP#1, ..., SP#4. For example, SSMF (Standard Single Mode Fiber) is laid as the optical fiber in the spans SP#1, ..., #SP#4. DSF (Dispersion Shifted Fiber) may be laid as the optical fiber in some or all of the spans SP#1, ..., #SP#4.

[0018] The optical receiver 200 includes an optical transmission line monitoring device 300. The optical transmission line monitoring device 300 may be provided as a separate unit from the optical receiver 200. In this case, the optical transmission line monitoring device 300 may be included in an optical network controller that manages the optical transmission system ST. The optical transmission line monitoring device 300 monitors the characteristics of the optical transmission line 50. As will be described in detail later, the optical transmission line monitoring device 300 acquires an electric field signal that indicates an optical electric field component of the optical signal received by the optical receiver 200.

[0019] The optical receiver 200 may be provided with an OTDR (Optical Time Domain Reflectometer). The OTDR can monitor the characteristics of the optical transmission line 50. However, providing the optical receiver 200 with an OTDR may increase the manufacturing cost of the optical receiver 200, for example. Furthermore, the monitoring pulse light used in the OTDR may have a nonlinear effect on the optical signal. For this reason, it is difficult to use the OTDR while the optical communication service is in operation. For these reasons, the optical receiver 200 in this embodiment does not include an OTDR.

[0020] When the optical transmission line monitoring device 300 acquires the electric field signal, it calculates estimated values ​​of the optical power of the optical signal at multiple positions on the optical transmission line 50 based on the electric field signal, and estimates a power profile, which is the distribution of the optical power. As will be described in detail later, the power profile is, for example, a graph or distribution with the distance from the optical transmitter 100 on the horizontal axis and the estimated value of the optical power on the vertical axis. The characteristics of the optical transmission line 50 can be represented by the power profile.

[0021] Therefore, if the power profile can be estimated accurately, the optical transmission line monitoring device 300 can accurately estimate the location of loss occurring in the optical transmission line 50 based on the power profile. For example, the optical transmission line monitoring device 300 can accurately estimate the location of abnormal loss that affects transmission characteristics, such as vibration caused by construction or traffic or aging of optical fiber. Note that a monitoring monitor that displays the power profile, the location of loss, etc. may be connected to the optical transmission line monitoring device 300. This allows, for example, an operator of the optical transmission system ST to check the power profile, the location of abnormal loss, etc.

[0022] Next, the optical receiver 200 and the optical transmission line monitoring device 300 will be described in detail with reference to FIGS.

[0023] As shown in Fig. 2, the optical receiver 200 includes an ICR (Integrated Coherent Receiver) 210 and an ITLA (Integrable Tunable Laser Assembly) 220. Although not shown, the ICR 210 includes a 90° optical hybrid circuit, a BPD (Balanced Photo Diode), and a TIA (Transimpedance Amplifier). The ICR 210 is an integrated circuit that houses the 90° optical hybrid circuit, the BPD, and the TIA in a single package. The optical receiver 200 also includes an ADC (Analogue Digital Converter) 230 and a DSP (Digital Signal Processor) 240.

[0024] An optical signal is input to the ICR 210 via the optical fiber 54F. The ITLA 220 includes a local light source that outputs local light (i.e., laser light). The ICR 210 receives the optical signal using the local light in a digital coherent system, converts the received optical signal into an electric field signal (specifically, an electric field information signal) corresponding to the optical signal, and outputs the electric field signal to the ADC 230. The ADC 230 converts the electric field signal from analog format to digital format and outputs the signal to the DSP 240.

[0025] The DSP 240 receives the electric field signal output from the ADC 230 and performs various digital signal processing on the received electric field signal. As shown in Fig. 3, the DSP 240 includes a fixed equalization unit 241, a high-order compensation unit 242, an adaptive equalization unit 243, a frequency compensation unit 244, a phase estimation unit 245, a discrimination unit 246, and an error correction unit 247.

[0026] The fixed equalization unit 241 totally compensates for the chromatic dispersion suffered by the optical signal propagating through the optical transmission line 50, for the electric field signal received by the DSP 240. The fixed equalization unit 241 outputs the electric field signal after compensating for the chromatic dispersion to the high-order compensation unit 242.

[0027] The high-order compensation unit 242 totally compensates for the dispersion slope of the electric field signal output from the fixed equalization unit 241. The dispersion slope is a value obtained by differentiating chromatic dispersion once with respect to wavelength, and is an example of high-order chromatic dispersion. High-order chromatic dispersion may include a value obtained by differentiating chromatic dispersion twice or more with respect to wavelength. For example, when the high-order compensation unit 242 takes into account the influence of only the dispersion slope, the transfer function H(ω,z) for calculating the amount of dispersion slope compensation is expressed by the following formula. Note that β3 is the third-order dispersion coefficient (ps 3 / km), where ω is the angular frequency.

number

[0028] Therefore, the total length of the optical transmission line 50 is Z total (km), the dispersion slope transfer function H(ω,Z total ) is expressed by the following formula: Transfer function H(ω,Z total ) is included in the high-order compensation unit 242 in advance. The high-order compensation unit 242 calculates the transfer function H(ω,Z total ) to globally compensate for the dispersion slope.

number

[0029] The adaptive equalization unit 243 adaptively compensates for residual dispersion in the electric field signal output from the high-order compensation unit 242. The residual dispersion is chromatic dispersion that remains after not being completely compensated for by the fixed equalization unit 241 and the high-order compensation unit 242. The adaptive equalization unit 243 outputs the electric field signal after compensating for the residual dispersion to the frequency compensation unit 244.

[0030] The frequency compensation unit 244 compensates for a frequency offset in the electric field signal output from the adaptive equalization unit 243. The frequency offset is the difference (or deviation) between the optical frequency of a transmission light source (not shown) provided in the optical transmitter 100 and the optical frequency of the ITLA 220. The frequency compensation unit 244 outputs the electric field signal after compensating for the frequency offset to the phase estimation unit 245. The phase estimation unit 245 compensates for a phase offset in the electric field signal output from the frequency compensation unit 244 and estimates the phase of the optical signal. The phase offset is the difference (or deviation) between the phases of the transmission light source and the ITLA 220. The phase estimation unit 245 outputs the electric field signal after compensating for the phase offset to the discrimination unit 246.

[0031] The discrimination unit 246 demodulates the transmission data by discriminating the value of each symbol based on the electric field signal output from the phase estimation unit 245, and outputs the demodulated data to the error correction unit 247. The error correction unit 247 corrects bit errors in the demodulated data and outputs the demodulated data after the errors are corrected.

[0032] 2, the optical transmission line monitoring device 300 has a field programmable gate array (FPGA) 310 as a hardware circuit. The optical transmission line monitoring device 300 may have an application specific integrated circuit (ASIC) as a hardware circuit instead of the FPGA 310. The optical transmission line monitoring device 300 may have a processor including a central processing unit (CPU) and a memory instead of the FPGA 310.

[0033] The FPGA 310 receives the electric field signal output from the DSP 240 and performs various digital signal processing on the received electric field signal. As shown in Fig. 3, the FPGA 310 includes a capture memory 311 and a first compensation unit (referred to as CPS#1 in Fig. 3) 312. The FPGA 310 also includes a nonlinear compensation unit 313 and a second compensation unit (referred to as CPS#2 in Fig. 3) 314.

[0034] The first compensating section 312 includes a first CD (Chromatic Dispersion) compensating section 401 and a first DS (Dispersion Slope) compensating section 402. The second compensating section 314 includes a second CD compensating section 405 and a second DS compensating section 406.

[0035] Furthermore, the FPGA 310 includes a generating unit 315, a parameter DB (DataBase) 316, an estimating unit 317, and a calculating unit 318. The first compensating unit 312, the nonlinear compensating unit 313, the second compensating unit 314, the generating unit 315, the estimating unit 317, and the calculating unit 318 are realized by the FPGA 310 executing a program according to a flowchart described later. Also, the optical transmission line monitoring method of the present invention is realized by the FPGA 310 executing a program according to a flowchart described later.

[0036] The capture memory 311 holds the electric field signal output from the phase estimation unit 245 as a capture signal. The electric field signal output from the phase estimation unit 245 is a signal after chromatic dispersion has been compensated for by the fixed equalization unit 241 and dispersion slope has been compensated for by the high-order compensation unit 242. Therefore, the amount of chromatic dispersion contained in the capture signal is close to 0 (zero) ps / nm (picoseconds / nanometer). In addition, the amount of dispersion slope contained in the capture signal is also close to 0 (zero) ps / nm 32 It will be close.

[0037] As shown in FIG. 3, the first CD compensator 401 acquires a capture signal from the capture memory 311. Upon acquiring the capture signal, the first CD compensator 401 compensates for a portion of the chromatic dispersion of the optical transmission line 50 to the capture signal. More specifically, the first CD compensator 401 adds chromatic dispersion to the entire optical transmission line 50, i.e., from the transmitting end to the receiving end, and compensates for chromatic dispersion from the receiving end to the monitoring position. On the other hand, because chromatic dispersion can be added, it can also be said that the first CD compensator 401 adds chromatic dispersion from the transmitting end to the monitoring position. This is because the difference between compensation and addition is merely the sign of the amount of dispersion. The first CD compensator 401 outputs the capture signal after adding (or compensating for) a portion of the chromatic dispersion of the optical transmission line 50 to the first DS compensator 402 as a monitor signal.

[0038] The first DS compensating unit 402 compensates for part of the dispersion slope, which is higher-order chromatic dispersion of the optical transmission line 50, based on a first compensation amount described below, for the monitor signal compensated by the first CD compensating unit 401. More specifically, the first DS compensating unit 402 adds the dispersion slope of the entire optical transmission line 50 and compensates for the dispersion slope from the receiving end to the monitoring position. However, since the dispersion slope can also be added, it can also be said that the first DS compensating unit 402 adds the dispersion slope from the transmitting end to the monitoring position. The first DS compensating unit 402 outputs the monitor signal after adding (or compensating for) the dispersion slope of the optical transmission line 50 to the nonlinear compensating unit 313.

[0039] As shown in FIG. 3 , the nonlinear compensator 313 compensates for degradation due to the nonlinear optical effect of the optical transmission line 50 in the monitor signal compensated for by the first DS compensator 402. An example of a nonlinear optical effect is the Kerr effect. When the Kerr effect occurs, the refractive index of the optical fiber of the optical transmission line 50 changes in proportion to the square of the power of the optical signal. As a result, self-phase modulation occurs in the optical signal, causing the pulse width to narrow due to a change in the phase velocity of light, resulting in signal errors. The nonlinear compensator 313 compensates for degradation due to the nonlinear optical effect of the optical transmission line 50 by performing phase rotation by an amount equal to the square of the amplitude of the monitor signal multiplied by a predetermined value. The nonlinear compensator 313 outputs the monitor signal after compensation for degradation due to the nonlinear optical effect to the second CD compensator 405.

[0040] The second CD compensator 405 compensates for the remaining chromatic dispersion of the optical transmission line 50 in the monitor signal after compensation by the nonlinear compensator 313. More specifically, the second CD compensator 405 compensates for the remaining chromatic dispersion from the monitor position to the transmitting end. The second CD compensator 405 outputs the monitor signal after compensation for the remaining chromatic dispersion of the optical transmission line 50 to the second DS compensator 406.

[0041] The second DS compensator 406 compensates for the remainder of the dispersion slope, which is higher-order chromatic dispersion in the optical transmission line 50, of the monitor signal after compensation by the second CD compensator 405, based on a second compensation amount described below. More specifically, the second DS compensator 406 compensates for the remainder of the dispersion slope from the monitor position to the transmitting end. The second DS compensator 406 outputs the monitor signal after compensation for the remainder of the dispersion slope in the optical transmission line 50 to the estimation unit 317.

[0042] The calculation unit 318 uses Z as the distance for estimating the optical power. estimate When Z is set in the calculation unit 318, β3, which is the third-order dispersion coefficient stored in the parameter DB 316, is acquired. estimatecorresponds to the distance from the transmitting end to the monitoring position. When the calculation unit 318 acquires β3, it calculates a first compensation amount and a second compensation amount. After calculating the first compensation amount and the second compensation amount, the calculation unit 318 sets the first compensation amount in the first DS compensator 402 and sets the second compensation amount in the second DS compensator 406.

[0043] The calculation unit 318 can calculate the first compensation amount using the following formula.

number

[0044] Furthermore, the calculation unit 318 can calculate the second compensation amount using the following formula.

number

[0045] The generator 315 acquires the capture signal held in the capture memory 311. Upon acquiring the capture signal, the generator 315 recovers symbols from the capture signal and demodulates the capture signal by identifying the value of each symbol to generate a reference signal that is a replica of the transmission data. The generator 315 may use transmission data prepared in advance as the reference signal instead of generating a reference signal. Upon generating the reference signal, the generator 315 outputs the reference signal to the estimation unit 317.

[0046] The estimation unit 317 calculates a correlation value between the complex amplitude of the monitor signal and the reference signal for each amount of dispersion (specifically, the amount of accumulated dispersion) based on the monitor signal output from the second DS compensation unit 406 and the reference signal output from the generation unit 315. After calculating the correlation value, the estimation unit 317 outputs the calculated correlation value as an estimate of optical power for each amount of dispersion. Since the magnitude of self-phase modulation corresponds to the optical power at the monitor position, the estimation unit 317 can output the correlation value as an estimate of optical power. The estimation unit 317 can estimate a power profile based on the estimate of optical power. For example, JP 2023-178193 A can be referenced for estimating the power profile.

[0047] Next, an example of the effect of the present invention will be described in comparison with a comparative example with reference to Figures 4(a) and (b). The horizontal axis of each power profile shown in Figures 4(a) and (b) represents the distance from the transmitting end, and the vertical axis of each power profile represents the estimated value of optical power. The horizontal axis of the power profile may also represent the amount of accumulated dispersion from the transmitting end. Note that the comparative example shows a case where the above-mentioned first compensator 312 does not include the first DS compensator 402, and the second compensator 314 does not include the second DS compensator 406.

[0048] First, the peak value of the estimated optical power can be relatively clearly identified in both the power profile according to the comparative example as shown in Fig. 4(a) and the power profile according to the embodiment as shown in Fig. 4(b). For example, at a distance D1 in the power profile according to the comparative example, the peak value of the estimated optical power is uniquely identified. At a distance D2 in the power profile according to the embodiment, the peak value of the estimated optical power is also uniquely identified.

[0049] On the other hand, with respect to the bottom value of the optical power estimation value (specifically, the highest value appearing at the bottom portion of the optical power estimation value), the noise level 60 becomes high in the power profile according to the comparative example, as shown in FIG. 4(a). The reason for the high noise level 60 is that the influence of nonlinearity becomes weaker. As a result, the optical power estimation value becomes buried in the noise level 60, and the noise ratio calculated based on the peak value and the bottom value tends to become smaller.

[0050] In the comparative example where dispersion slope compensation is not performed in the optical transmission line monitoring device 300, the accuracy of the power profile decreases. That is, there is a risk that the power profile may deviate from the ideal power profile based on the design and specifications. Therefore, with such a power profile, the optical transmission line monitoring device 300 may not be able to accurately detect the location of the loss occurring in the optical transmission line 50.

[0051] However, in the power profile according to the embodiment, as shown in FIG. 4(b), the nonlinear effect is not weakened, and the noise level 70 is lowered. Therefore, the estimated value of the optical power is less likely to be buried in the noise level 70, and the noise ratio calculated based on the peak value and the bottom value tends to be larger. That is, in the embodiment in which dispersion slope compensation is performed in the optical transmission line monitoring device 300, the accuracy of the power profile is improved. Therefore, the optical transmission line monitoring device 300 can accurately detect the location of a loss occurring in the optical transmission line 50 based on such an accurate power profile.

[0052] With reference to Fig. 5, another example of the effect of the present invention will be described in comparison with a comparative example. Fig. 5 shows a power profile in a submarine transmission system that is prone to the effects of dispersion slope. That is, the power profile is shown when the optical transmission system ST is provided with a large number of optical amplifiers, including multiple optical amplifiers 51A, 52A, and 53A, and the optical transmission line 50 includes a large span. The power profile shown in the lower part of Fig. 5 represents an estimated value of the optical power from the transmitting end to the receiving end. The power profile shown in the upper part of Fig. 5 represents an estimated value of the optical power near the receiving end.

[0053] As shown in the upper part of Fig. 5, in the comparative example, the noise ratio calculated based on the peak value and the bottom value tends to be smaller. That is, in the comparative example in which dispersion slope compensation is not performed in the optical transmission line monitoring device 300, the accuracy of the power profile decreases. On the other hand, in the embodiment, the noise ratio calculated based on the peak value and the bottom value tends to be larger. That is, in the embodiment in which dispersion slope compensation is performed in the optical transmission line monitoring device 300, the accuracy of the power profile improves.

[0054] An example of the effect of the present invention depending on the presence or absence of loss will be explained in comparison with a comparative example with reference to Figures 6(a) and 6(b) and Figures 7(a) and 7(b). The loss is generated at a position X0 (km) away from the transmitting end. The magnitude of the loss is about several dB (decibels).

[0055] First, as shown in Figure 6(a), in the comparative example where dispersion slope is not compensated, the waveform of the power profile differs depending on whether or not there is loss. For example, near a position X0 (km) away from the transmitting end, the peak value of the estimated optical power when there is loss is smaller than the peak value of the estimated optical power when there is no loss. In other words, near a position X0 (km) away from the transmitting end, the occurrence of loss causes the estimated optical power to decrease.

[0056] Next, as shown in Figure 6(b), in the comparative example where dispersion slope is not compensated, the peak value of the anomaly score corresponds to the peak value of the estimated optical power. This is because the anomaly score is the difference between the estimated optical power when there is no loss and the estimated optical power when there is loss. Here, the difference between the peak value of the anomaly score in the comparative example and a position X0 (km) away from the transmitting end is X1 (km). In other words, if a loss occurs at a position X0 (km) away from the transmitting end, the location of the loss that can be detected by the anomaly score will differ from the actual location of the loss. Specifically, in the comparative example, an error of X1 (km) occurs in the location of the loss.

[0057] On the other hand, as shown in Figure 7(a), in the case of an embodiment in which dispersion slope is compensated, the waveform of the power profile differs depending on whether or not there is loss. Near a position X0 (km) away from the transmitting end, the peak value of the estimated optical power when there is loss is smaller than the peak value of the estimated optical power when there is no loss. In other words, near a position X0 (km) away from the transmitting end, the occurrence of loss causes the estimated optical power to decrease.

[0058] Next, as shown in Figure 7(b), in the case of the embodiment in which the dispersion slope is compensated, the peak value of the anomaly core also corresponds to the peak value of the estimated optical power. Here, the difference between the peak value of the anomaly core in the embodiment and a position X0 (km) away from the transmitting end is X2 (km). In other words, if a loss occurs at a position X0 (km) away from the transmitting end, the location of the loss that can be detected by the anomaly core differs from the actual location of the loss. Specifically, in the case of the comparative example, an error of X2 (km) occurs in the location of the loss.

[0059] The error of X2 (km) in this example is smaller than the error of X1 (km) in the comparative example. That is, since the error is smaller in the example than in the comparative example, the loss occurrence position can be detected with high accuracy based on the anomaly score. In this way, by taking dispersion slope compensation into consideration when generating the power profile, the loss occurrence position can be detected with high accuracy.

[0060] The operation of the optical transmission line monitoring device 300 will be described with reference to FIG.

[0061] First, the calculation unit 318 receives a distance setting (step S1). estimate This allows the calculation unit 318 to accept the setting of Z estimate is set. When the calculation unit 318 receives the distance setting, it then acquires a coefficient (step S2). Specifically, Z estimate When this is set, the calculation unit 318 acquires β3, which is the third-order dispersion coefficient stored in the parameter DB 316.

[0062] When the calculation unit 318 acquires the coefficient, it calculates the compensation amount (step S3). estimate The calculation unit 318 calculates the first compensation amount based on the third-order dispersion coefficient β3 and the above-mentioned formula 3. estimate The second compensation amount is calculated based on β3, which is the third-order dispersion coefficient, and the above-mentioned formula 4.

[0063] After calculating the compensation amount, the calculation unit 318 sets the compensation amount (step S4). More specifically, the calculation unit 318 sets the first compensation amount in the first DS compensator 402. Furthermore, the calculation unit 318 sets the second compensation amount in the second DS compensator 406. After the calculation unit 318 sets the compensation amount, the first CD compensator 401 compensates for part of the chromatic dispersion (step S5). More specifically, the first CD compensator 401 acquires a capture signal from the capture memory 311 and compensates for part of the chromatic dispersion of the optical transmission line 50 for the capture signal.

[0064] After the first CD compensator 401 has compensated for a portion of the chromatic dispersion, the first DS compensator 402 then compensates for a portion of the dispersion slope (step S6). More specifically, the first DS compensator 402 compensates for a portion of the dispersion slope of the optical transmission line 50 based on the first compensation amount for the monitor signal, which is the capture signal after compensation by the first CD compensator 401.

[0065] Once the first DS compensator 402 has compensated for a portion of the dispersion slope, the nonlinear compensator 313 performs nonlinear compensation (step S7). More specifically, the nonlinear compensator 313 compensates for degradation due to the nonlinear optical effect of the optical transmission line 50 by performing a phase rotation by an amount equal to the square of the amplitude of the monitor signal multiplied by a predetermined value. Once the nonlinear compensator 313 has performed nonlinear compensation, the second CD compensator 405 compensates for the remaining chromatic dispersion of the optical transmission line 50 (step S8). More specifically, the second CD compensator 405 compensates for the remaining chromatic dispersion of the optical transmission line 50 for the monitor signal after compensation by the nonlinear compensator 313.

[0066] After the second CD compensator 405 has compensated for the remaining chromatic dispersion, the second DS compensator 406 then compensates for the remaining dispersion slope (step S9). More specifically, the second DS compensator 406 compensates for the remaining dispersion slope of the optical transmission line 50 based on the second compensation amount for the monitor signal after compensation by the second CD compensator 405.

[0067] After the second DS compensator 406 compensates for the remaining dispersion slope, the generator 315 generates a reference signal (step S10). More specifically, the generator 315 acquires the capture signal stored in the capture memory 311, recovers symbols from the capture signal, and demodulates the capture signal by identifying the value of each symbol to generate a reference signal. After generating the reference signal, the generator 315 outputs the reference signal.

[0068] When the generating unit 315 outputs the reference signal, the estimating unit 317 calculates a correlation value (step S11). More specifically, the estimating unit 317 calculates the correlation value between the complex amplitudes of the monitor signal and the reference signal. After calculating the correlation value, the estimating unit 317 outputs the calculated correlation value as an optical power estimation value (step S12) and ends the process. Note that the estimating unit 317 may estimate and output a power profile based on the optical power estimation value before ending the process. Furthermore, the optical transmission line monitoring device 300 may execute the processes of steps S5 to S9 and the process of step S10 in parallel.

[0069] As described above, when estimating a power profile taking into account the influence of nonlinearity, the optical transmission line monitoring device 300 takes into account not only the influence of chromatic dispersion but also the influence of dispersion slope, thereby improving the accuracy of estimating the power profile of the optical transmission line monitoring device 300.

[0070] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims.

[0071] In addition, the following supplementary notes are provided in relation to the above description. (Supplementary Note 1) An optical transmission line monitoring device comprising: a first compensating unit that compensates for a part of chromatic dispersion and a part of higher-order chromatic dispersion of an optical transmission line with respect to an electric field signal that indicates an optical field component of an optical signal that is digitally coherently received from the optical transmission line; a nonlinear compensating unit that compensates for degradation due to a nonlinear optical effect of the optical transmission line with respect to the electric field signal after compensation by the first compensating unit; a second compensating unit that compensates for a remainder of the chromatic dispersion and a remainder of the higher-order chromatic dispersion with respect to the electric field signal after compensation by the nonlinear compensating unit; a generating unit that generates a reference signal that indicates an optical field component of the optical signal at a transmitting end of the optical transmission line based on the electric field signal; and an estimating unit that estimates an optical power distribution based on a correlation between the electric field signal after compensation by the second compensating unit and the reference signal. (Supplementary Note 2) The optical transmission line monitoring device according to Supplementary Note 1, wherein the high-order chromatic dispersion is a value obtained by differentiating the chromatic dispersion with respect to wavelength one or more times. (Supplementary Note 3) The optical transmission line monitoring device according to Supplementary Note 1, wherein the higher-order chromatic dispersion is a dispersion slope. (Supplementary Note 4) The optical transmission line monitoring device according to any one of Supplementary Notes 1 to 3, further comprising a calculation unit that calculates a first compensation amount to be set in the first compensator and a second compensation amount to be set in the second compensator based on a third-order dispersion coefficient, a predetermined transfer function, and a distance from the position of the transmitting end to a position where the optical power is estimated, when the higher-order chromatic dispersion is a dispersion slope, wherein the first compensator compensates for a part of the higher-order chromatic dispersion based on the first compensation amount, and the second compensator compensates for the remaining part of the higher-order chromatic dispersion based on the second compensation amount. (Appendix 5) The optical transmission line monitoring device according to any one of Appendices 1 to 3, wherein the first compensating unit compensates for a portion of the chromatic dispersion and then compensates for a portion of the higher-order chromatic dispersion, and the second compensating unit compensates for the remainder of the chromatic dispersion and then compensates for the remainder of the higher-order chromatic dispersion. (Supplementary Note 6) An optical transmission line monitoring method comprising: compensating an electric field signal indicating an optical field component of an optical signal digitally coherently received from an optical transmission line for a part of chromatic dispersion and a part of higher-order chromatic dispersion of the optical transmission line; compensating the electric field signal after compensating for a part of the chromatic dispersion and a part of the higher-order chromatic dispersion for degradation due to a nonlinear optical effect of the optical transmission line; compensating the electric field signal after compensating for the degradation for a remainder of the chromatic dispersion and a remainder of the higher-order chromatic dispersion; generating a reference signal indicating an optical field component of the optical signal at a transmitting end of the optical transmission line based on the electric field signal; and estimating an optical power distribution based on a correlation between the electric field signal after compensating for the remainder of the chromatic dispersion and the remainder of the higher-order chromatic dispersion and the reference signal. (Supplementary Note 7) The optical transmission line monitoring method according to Supplementary Note 6, characterized in that, when the higher-order chromatic dispersion is a dispersion slope, a first compensation amount for compensating for a part of the higher-order chromatic dispersion and a second compensation amount for compensating for the remainder of the higher-order chromatic dispersion are calculated based on a third-order dispersion coefficient, a predetermined transfer function, and a distance from the position of the transmitting end to a position where the optical power is estimated. [Explanation of symbols]

[0072] ST Optical Transmission System 100 Optical Transmitter 200 Optical Receiver 300 Optical transmission line monitoring device 312 1st Compensation Department 313 Nonlinear Compensation Section 314 Second Compensation Department 315 Generation part 317 Estimation Department 318 Calculation Unit

Claims

1. a first compensation unit that compensates for a part of chromatic dispersion and a part of higher-order chromatic dispersion of an optical transmission line with respect to an electric field signal that indicates an optical electric field component of an optical signal that is digitally coherently received from the optical transmission line; a nonlinear compensation unit that compensates for degradation of the electric field signal after compensation by the first compensation unit due to a nonlinear optical effect of the optical transmission line; a second compensator that compensates for the remainder of the chromatic dispersion and the remainder of the high-order chromatic dispersion in the electric field signal after compensation by the nonlinear compensator; a generator that generates a reference signal indicating an optical electric field component of the optical signal at a transmitting end of the optical transmission line based on the electric field signal; an estimation unit that estimates a distribution of optical power based on a correlation between the electric field signal after compensation by the second compensation unit and the reference signal; An optical transmission line monitoring device comprising:

2. The higher-order chromatic dispersion is a value obtained by differentiating the chromatic dispersion with respect to wavelength one or more times.

2. The optical transmission line monitoring device according to claim 1.

3. further comprising a calculation unit that calculates a first compensation amount to be set in the first compensator and a second compensation amount to be set in the second compensator based on a third-order dispersion coefficient, a predetermined transfer function, and a distance from the position of the transmitting end to a position where the optical power is estimated, when the higher-order chromatic dispersion is a dispersion slope; the first compensator compensates for a part of the higher-order chromatic dispersion based on the first compensation amount; the second compensator compensates for the remainder of the higher-order chromatic dispersion based on the second compensation amount.

3. The optical transmission line monitoring device according to claim 1 or 2.

4. Compensating for a part of the chromatic dispersion and a part of the higher-order chromatic dispersion of an optical transmission line with respect to an electric field signal indicating an optical electric field component of an optical signal digitally coherently received from the optical transmission line; compensate for degradation due to nonlinear optical effects of the optical transmission line with respect to the electric field signal after compensating for a portion of the chromatic dispersion and a portion of the higher-order chromatic dispersion; Compensating for the remaining chromatic dispersion and the remaining higher-order chromatic dispersion in the electric field signal after compensating for the deterioration; generating a reference signal indicating an optical electric field component of the optical signal at a transmitting end of the optical transmission line based on the electric field signal; estimating an optical power distribution based on a correlation between the electric field signal after compensating for the residual chromatic dispersion and the residual higher-order chromatic dispersion and the reference signal; Optical transmission line monitoring method.

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