Optical transmission line characteristic estimation device and optical transmission line characteristic estimation method

Abstract

This optical transmission line characteristic estimation device comprises an optical transmission line characteristic estimation unit that estimates an optical transmission line characteristic on the basis of a reception waveform of a reference light wave, a transmission waveform of the reference light wave, and a transmission waveform of one or more light waves other than the reference light wave.　

Description

Optical transmission path characteristic estimation device and optical transmission path characteristic estimation method

[0001] The present invention relates to an optical transmission path characteristics estimation device and an optical transmission path characteristics estimation method.

[0002] When operating an optical transmission system, the fundamental characteristics of the optical transmission path greatly affect the transmission performance. Here, the fundamental characteristics of the optical transmission path include the optical signal power in the optical fiber, the distribution of loss and dispersion in the optical fiber, and the location of fault points. For example, if the optical power is too high, the influence of nonlinear optical effects in the optical fiber becomes large, causing the signal-to-noise ratio (SNR) to decrease. If the loss is too high, the attenuation of optical power increases accordingly, causing the SNR to decrease.

[0003] Therefore, understanding the characteristics of optical fibers is crucial for the operation, maintenance, and monitoring of optical transmission systems. Optical transmission lines consist of various devices other than optical fibers, such as optical amplifiers and optical filters. Understanding the characteristics of these devices is also important for 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 specialized measuring instruments such as OTDRs (Optical Time Domain Reflectometers) and optical spectrum analyzers. However, measurements using specialized instruments require direct measurement for each optical node and optical fiber, which presents challenges in terms of equipment and operational costs.

[0005] To address this challenge, DLM (Digital Longitudinal Monitoring) has recently been proposed as a technology that detects the characteristics of various devices within an optical transmission system by performing digital signal processing on the receiving side of the optical transmission system (see, for example, Non-Patent Documents 1 and 2). DLM is based on a digital coherent optical transmission system and monitors the characteristics of the optical transmission line, such as the optical power distribution along the longitudinal direction of the optical fiber, by performing digital signal processing on the received signal obtained by coherent detection of the optical signal transmitted by the optical transmission line. This makes it possible to measure the distribution of optical power and pinpoint the location of abnormal loss in the optical fiber without using dedicated measuring instruments. As a result, the time and cost required for the design and maintenance of optical transmission systems can be reduced.

[0006] The spatial resolution of DLM depends on the signal bandwidth and chromatic dispersion of the estimated channel and has so far been limited to approximately 1 km (example conditions: 128 GBd, chromatic dispersion parameter D = 17 ps / nm / km). As a result, when multiple anomalous losses exist within 1 km, such as within a node where loss events are concentrated, their locations cannot be resolved. In addition, techniques such as those described in Non-Patent Documents 3 and 4 have been proposed in the past.

[0007] T. Tanimura, et al., “Fiber-Longitudinal Anomaly Position Identification Over Multi-Span Transmission Link Out of Receiver-end Signals”, JLT, 38(9), 2020.T. Sasai, et al., “Digital longitudinal monitoring of Optical Fiber Communication Link”, JLT, 40(8), 2022.P. Serena.,” Locating Fiber Loss Anomalies with a Receiver-side Monitoring Algorithm exploiting Cross-Phase Modulation” OFC2023, W1H.3.I. Kim et al., “Multi-Channel Longitudinal Power Profile Estimation,” ECOC2023, Tu.A.2.4.

[0008] However, the technologies described in Non-Patent Documents 1 to 4 above had the problem that they could not perform optical power distribution estimation with high spatial resolution while reducing computational costs.

[0009] In view of the above circumstances, the present invention aims to provide a technology that can perform optical power distribution estimation with high spatial resolution while reducing computational costs.

[0010] One aspect of the present invention is an optical transmission path characteristic estimation device comprising an optical transmission path characteristic estimation unit that estimates optical transmission path characteristics based on a received waveform of a reference optical wave, a transmitted waveform of the reference optical wave, and the transmitted waveforms of one or more optical waves other than the reference optical wave.

[0011] One aspect of the present invention is an optical transmission path characteristics estimation method that estimates optical transmission path characteristics based on the received waveform of a reference optical wave, the transmitted waveform of the reference optical wave, and the transmitted waveforms of one or more optical waves other than the reference optical wave.

[0012] This invention makes it possible to perform optical power distribution estimation with high spatial resolution while reducing computational costs.

[0013] This figure shows an example configuration of an optical transmission system in the first embodiment. This figure shows an example configuration of an optical transmission path characteristic estimation device in the first embodiment. This is a sequence diagram showing the processing flow of the optical transmission system in the first embodiment. This is a flowchart showing the optical transmission path characteristic estimation process performed by the optical transmission path characteristic estimation device in the first embodiment. This figure shows an example experiment performed with the configuration of the first embodiment. This figure shows an example configuration of an optical transmission path characteristic estimation device in the second embodiment. This figure shows an example configuration of an optical transmission system in the third embodiment. This figure shows an example configuration of an optical transmission system in the fourth embodiment.

[0014] One embodiment of the present invention will be described below with reference to the drawings.

[0015] (First Embodiment) Figure 1 shows an example of the configuration of an optical transmission system 100 in the first embodiment. The optical transmission system 100 includes an optical transmitter 10, an optical multiplexer 20, an optical demultiplexer 30, an optical receiver 40, a demodulation unit 41, a signal reconstruction unit 42, and an optical transmission path characteristic estimation device 43. The optical multiplexer 20 and the optical demultiplexer 30 are connected by an optical transmission path 50. The optical transmission path 50 is, for example, an optical fiber. The optical transmission path 50 may also be equipped with one or more optical amplifiers that amplify the amplitude of the optical signal. In this way, wavelength division multiplexing transmission is performed in the optical transmission system 100.

[0016] In Figure 1, the optical transmission system 100 includes n (where n is an integer of 2 or more) optical transmitters 10-1 to 10-n, n optical receivers 40-1 to 40-n, n demodulation units 41-1 to 41-n, and n signal reconstruction units 42-1 to 42-n. The optical receivers 40, demodulation units 41, and signal reconstruction units 42 are provided in, for example, one optical receiving device R. In Figure 1, as an example, n optical receiving devices Rn are shown, and the functional units provided in each optical receiving device R are denoted with sub-numbers "-1" to "-n" for distinction. Note that the number of optical transmitters 10 and the number of combinations of optical receivers 40, demodulation units 41, and signal reconstruction units 42 may be different.

[0017] Each of the optical transmitters 10 transmits optical signals in different orthogonal modes, for example, different frequencies (different wavelengths) or different spatial modes. For example, the optical transmitter 10-1 transmits an optical signal of frequency f1, and the optical transmitter 10-n transmits an optical signal of frequency fn. A configuration example using optical signals of different frequencies will be described below, but a configuration using other different orthogonal modes such as different spatial modes may also be adopted.

[0018] The optical multiplexer 20 multiplexes input optical signals. For example, the optical multiplexer 20 multiplexes the optical signals transmitted from the respective optical transmitters 10 to generate a multiplexed optical signal. The optical multiplexer 20 outputs the generated multiplexed optical signal to the optical transmission line 50.

[0019] The optical demultiplexer 30 demultiplexes the input optical signal according to wavelength. For example, the optical demultiplexer 30 demultiplexes the multiplexed optical signal transmitted through the optical transmission line 50 according to wavelength. It is assumed that an optical receiver 40-1 is connected to the port of the optical demultiplexer 30 that outputs an optical signal of wavelength λ1 (optical signal of frequency f1), and an optical receiver 40-n is connected to the port of the optical demultiplexer 30 that outputs an optical signal of wavelength λn (optical signal of frequency fn).

[0020] The optical receiver 40 receives the optical signal demultiplexed by the optical demultiplexer 30. The optical receiver 40 converts the received optical signal into an electrical signal (for example, a digital signal) and outputs the converted signal to the demodulation unit 41.

[0021] The demodulation unit 41 performs compensation processing on the electrical signal (for example, a digital signal) output from the optical receiver 40. The compensation processing includes, for example, chromatic dispersion compensation, adaptive equalization, frequency offset compensation, and carrier phase recovery. Part or all of the compensation processing may be omitted or added as necessary. Hereinafter, a signal that has been subjected to compensation processing by the demodulation unit 41 is referred to as a demodulated signal. In order to distinguish the demodulated signals output from the respective demodulation units 41, in the following description, the demodulated signal output from the demodulation unit 41-1 is referred to as a first demodulated signal, and the demodulated signal output from the demodulation unit 41-n is referred to as an n-th demodulated signal.

[0022] The signal reconstruction unit 42 performs signal reconstruction processing on the electrical signal (e.g., a digital signal) that has been compensated by the demodulation unit 41. Signal reconstruction processing is the process of restoring the waveform of the optical signal transmitted by the optical transmitter 10. Signal reconstruction processing includes, for example, symbol determination, error correction decoding, re-error correction coding, upsampling, and Nyquist shaping. Some or all of the signal reconstruction processing may be omitted or added as needed. Hereinafter, the signal that has undergone signal reconstruction processing by the signal reconstruction unit 42 will be referred to as the reconstructed signal. In order to distinguish the reconstructed signals output from each signal reconstruction unit 42, in the following description the reconstructed signal output from signal reconstruction unit 42-1 will be referred to as the first reconstructed signal, and the reconstructed signal output from signal reconstruction unit 42-n will be referred to as the nth reconstructed signal.

[0023] The processing performed by these signal reconstruction units 42 is for reconstructing the transmission signals transmitted from each of the optical transmitters 10-1 to 10-n. Therefore, if each transmission signal is a known signal, the signal reconstruction unit 42 is not necessarily required, and the known signal may be used as the reconstructed signal. In other words, if each transmission signal is a known signal, each optical receiver R does not need to be equipped with a signal reconstruction unit 42. One such configuration is to transmit a specific signal from the optical transmitter for the purpose of estimating the optical transmission path characteristics without using the signal being communicated. In this case, since the user inserts a specific signal into the optical transmitter 10, the transmission signal becomes known, and the user can use the known transmission signal as a substitute for the first to nth reconstructed signals.

[0024] The optical transmission line characteristic estimation device 43 estimates optical transmission line characteristics based on cross-channel interference (XCI: cross-channel interference), which is interference between a target channel and another channel. That is, the optical transmission line characteristic estimation device 43 uses a demodulated signal (e.g., a first demodulated signal) and a reconstructed signal (e.g., a first reconstructed signal) obtained from an optical receiver R of the target channel (e.g., optical receiver R1), and a reconstructed signal (e.g., an n-th reconstructed signal) obtained from an optical receiver R of another channel (e.g., optical receiver Rn) to estimate the optical transmission line characteristics. The optical transmission line characteristic is, for example, optical power distribution.

[0025] Here, the target channel is a channel serving as a reference used for estimating optical transmission line characteristics. Another channel is a channel other than the target channel. However, the optical transmission line characteristic estimation device 43 only needs to use at least one channel other than the target channel as another channel. For example, in the case of an optical transmission system 100 multiplexing N channels, (N-1) channels excluding the target channel are candidates for another channel, and at least one channel among the (N-1) channels serves as another channel.

[0026] When estimating optical transmission line characteristics using optical waveforms of different frequencies, the center frequency between the target channel and another channel may be separated by any distance. By increasing the optical band involving nonlinear interference in this manner, a large walk-off due to chromatic dispersion can be obtained, and spatial resolution can be improved. Similarly, even when estimating optical transmission line characteristics using optical waveforms of different orthogonal modes, spatial resolution can be improved by obtaining a large walk-off effect between different orthogonal modes. In the following description, it is assumed that the optical receiver R1 is a receiver that receives an optical signal of the target channel, and the optical receiver Rn is a receiver that receives an optical signal of another channel. Therefore, in the following description, a configuration using two channels is taken as an example for explanation, but the present invention is applicable to a case where the number of channels is three or more.

[0027] Figure 2 shows an example of the configuration of the optical transmission path characteristic estimation device 43 in the first embodiment. The optical transmission path characteristic estimation device 43 includes a wavelength dispersion application unit 431, a wavelength dispersion application unit 432, a perturbation component estimation unit 433, an XCI perturbation basis generation unit 434, and an optical power distribution estimation unit 435.

[0028] The wavelength dispersion application unit 431 estimates the wavelength dispersion occurring in the optical transmission path and applies the estimated wavelength dispersion to the demodulated signal output from the demodulation unit 41 of the optical receiver R that receives the optical signal of the channel of interest. For example, the wavelength dispersion application unit 432 applies the wavelength dispersion occurring in the optical transmission path 50 to the first demodulated signal output from the demodulation unit 41-1. As a result, the wavelength dispersion application unit 431 generates a signal from which polarization rotation, frequency offset, phase noise, etc., have been removed from the received signal received by the optical receiver 40. The signal generated by the wavelength dispersion application unit 431 is the signal before wavelength dispersion compensation, from which polarization rotation, frequency offset, phase noise, etc., have been removed. Hereinafter, the signal generated by the wavelength dispersion application unit 431 will be referred to as signal A(L,t).

[0029] The wavelength dispersion application unit 432 estimates the wavelength dispersion occurring in the optical transmission path and applies the estimated wavelength dispersion to the reconstructed signal output from the signal reconstruction unit 42 of the optical receiver R that receives the optical signal of the channel of interest. For example, the wavelength dispersion application unit 432 applies the wavelength dispersion occurring in the optical transmission path 50 to the first reconstructed signal output from the signal reconstruction unit 42-1. As a result, the wavelength dispersion application unit 432 generates a signal from which polarization rotation, frequency offset, phase noise, etc., have been removed from the received signal received by the optical receiver 40. The signal generated by the wavelength dispersion application unit 432 is the signal before wavelength dispersion compensation, from which polarization rotation, frequency offset, phase noise, etc., have been removed. Hereinafter, the signal generated by the wavelength dispersion application unit 432 will be referred to as signal A. ０ Let (L,t).

[0030] The perturbation component estimation unit 433 uses the signal A(L,t) generated by the wavelength dispersion application unit 431 and the signal A generated by the wavelength dispersion application unit 432. ０ The input is (L,t). The perturbation component estimation unit 433 calculates the signal A from the input signal A(L,t). ０ Perturbation component A excluding the (L,t) component１ (L,t) is estimated. In this way, the perturbation component estimation unit 433 estimates signal A from signal A(L,t). ０ Subtracting (L,t) gives the perturbation component A １ Estimate (L,t).

[0031] The XCI perturbation basis generation unit 434 includes a high-frequency wavelength dispersion application unit 436, a nonlinear calculation unit 437, and a residual wavelength dispersion application unit 438. The high-frequency wavelength dispersion application unit 436 receives a reconstructed signal output from a signal reconstruction unit 42 of an optical receiver R that receives an optical signal from another channel. The high-frequency wavelength dispersion application unit 436 applies a wavelength dispersion to the input reconstructed signal that corresponds to the range from the optical transmitter 10 to position k (=0, 1, ..., K-1), according to the frequency difference between the channel of interest and the other channel. K is an integer of 1 or more. For example, the high-frequency wavelength dispersion application unit 436 applies a wavelength dispersion to the input nth reconstructed signal that corresponds to the range from the optical transmitter 10 to position k (=0, 1, ..., K-1), according to the frequency difference (fn-f1) between the channel of interest (f1) and the other channel (fn).

[0032] The nonlinear calculation unit 437 performs nonlinear calculations on the signal to which wavelength dispersion has been applied by the high-frequency wavelength dispersion application unit 436. For example, the nonlinear calculation unit 437 applies 2j(|・| ２ -rms(・) ２ The operation )(・) is performed. Here, j is the imaginary unit, and rms(・) is the root mean square (RMS) of the signal. As a result, the nonlinear calculation unit 437 performs a phase shift due to the nonlinear effect on the signal to which wavelength dispersion has been applied.

[0033] The residual wavelength dispersion application unit 438 applies wavelength dispersion to the signal that has been nonlinearly calculated by the nonlinear calculation unit 437, corresponding to the distance from position k to the optical receiver 40 that receives the optical signal of the reference channel. For example, the residual wavelength dispersion application unit 438 applies wavelength dispersion to the signal that has been nonlinearly calculated by the nonlinear calculation unit 437, corresponding to the distance from position k to the optical receiver 40-1.

[0034] The XCI perturbation basis generation unit 434 repeatedly executes the above processing by changing the position k from 0, 1, ..., to K-1. Thereby, the XCI perturbation basis generation unit 434 obtains the signal x ０ , x １ , ..., x Ｋ－１ . The signal x ０ is a signal obtained by the processing of the high-frequency chromatic dispersion applying unit 436, the nonlinear calculation unit 437, and the residual chromatic dispersion applying unit 438 when the position is set to 0. Hereinafter, the signals x ０ , x １ , ..., x Ｋ－１ obtained by the XCI perturbation basis generation unit 434 are collectively referred to as signal X. As described above, the XCI perturbation basis generation unit 434 generates a signal of cross-channel interference component.

[0035] The optical power distribution estimation unit 435 estimates an optical power distribution based on the perturbation component A １ (L, t) obtained by the perturbation component estimation unit 433 and the signal X obtained by the XCI perturbation basis generation unit 434. Various estimation methods are conceivable for the estimation of the optical power distribution by the optical power distribution estimation unit 435.

[0036] For example, the optical power distribution estimation unit 435 estimates the power distribution vector γ' using any one of the estimators shown in the following formulas (1) to (4). In formulas (1) to (4), let X = [x ０ , x １ , ..., x Ｋ－１ , R be an arbitrary K×K matrix, and λ be an arbitrary real number. It should be noted that the optical power distribution estimation unit 435 does not need to perform estimation using any one of formulas (1) to (4), and may use a combination of any of formulas (1) to (4), or may use a combination excluding Re, or take an absolute value instead of Re, etc.

[0037]

[0038]

[0039]

[0040]

[0041] (Operation of Optical Transmission System 100) Figure 3 is a sequence diagram showing the processing flow of the optical transmission system 100 in the first embodiment. At the start of processing in Figure 3, it is assumed that an optical signal of frequency f1 is transmitted from optical transmitter 10-1 and an optical signal of frequency fn is transmitted from optical transmitter 10-n. The optical receiver 40-1 of the first optical receiving device R1 receives the optical signal of wavelength λ1 that has been separated from the optical demultiplexer 30 (step S101). The optical receiver 40-1 converts the received optical signal of wavelength λ1 into a digital signal and outputs it to the demodulation unit 41-1.

[0042] The demodulation unit 41-1 generates a first demodulated signal based on the digital signal output from the optical receiver 40-1 (step S102). The demodulation unit 41-1 outputs the generated first demodulated signal to the optical transmission path characteristic estimation device 43 and the signal reconstruction unit 42-1 (step S103). The signal reconstruction unit 42-1 generates a first reconstructed signal based on the first demodulated signal output from the demodulation unit 41-1 (step S104). The signal reconstruction unit 42-1 outputs the generated first reconstructed signal to the optical transmission path characteristic estimation device 43 (step S105).

[0043] The optical receiver 40-n of the nth optical receiver Rn receives the optical signal of wavelength λn that has been delimited from the optical demultiplexer 30 (step S106). The optical receiver 40-n converts the received optical signal of wavelength λn into a digital signal and outputs it to the demodulation unit 41-n. The demodulation unit 41-n generates the nth demodulated signal based on the digital signal output from the optical receiver 40-n (step S107). The demodulation unit 41-n outputs the generated nth demodulated signal to the signal reconstruction unit 42-n. The signal reconstruction unit 42-n generates the nth reconstructed signal based on the nth demodulated signal output from the demodulation unit 41-n (step S108). The signal reconstruction unit 42-n outputs the generated nth reconstructed signal to the optical transmission path characteristic estimation device 43 (step S109).

[0044] The optical transmission path characteristic estimation device 43 receives the first demodulated signal output from the demodulation unit 41-1, the first reconstructed signal output from the signal reconstruction unit 42-1, and the nth reconstructed signal output from the signal reconstruction unit 42-n. Based on the input first demodulated signal, first reconstructed signal, and nth reconstructed signal, the optical transmission path characteristic estimation device 43 performs optical transmission path characteristic estimation processing (step S110). Optical transmission path characteristic estimation processing is a process that estimates the optical transmission path characteristics. Details of the optical transmission path characteristic estimation processing are explained in Figure 4.

[0045] (Operation of Optical Transmission Path Characteristic Estimation Device 43) Figure 4 is a flowchart showing the flow of the optical transmission path characteristic estimation process performed by the optical transmission path characteristic estimation device 43 in the first embodiment. The wavelength dispersion application unit 431 applies wavelength dispersion to the input first demodulated signal (step S201). As a result, the wavelength dispersion application unit 431 generates signal A(L,t). The wavelength dispersion application unit 431 outputs the generated signal A(L,t) to the perturbation component estimation unit 433. The wavelength dispersion application unit 432 applies wavelength dispersion to the input first reconstructed signal (step S202). As a result, the wavelength dispersion application unit 432 generates signal A ０ (L,t) is generated. The wavelength dispersion application unit 432 generates the signal A ０ (L,t) is output to the perturbation component estimation unit 433.

[0046] The perturbation component estimation unit 433 calculates the signal A from the input signal A(L,t). ０ By subtracting (L,t), the perturbation component A is obtained. １ (L,t) is estimated (step S203). The perturbation component estimation unit 433 estimates the perturbation component A １ (L,t) is output to the optical power distribution estimation unit 435. The XCI perturbation basis generation unit 434 initializes the value of k (step S204). For example, the XCI perturbation basis generation unit 434 sets the value of k to 0. The high-frequency wavelength dispersion application unit 436 applies wavelength dispersion to the input nth reconstruction signal (step S205). For example, the high-frequency wavelength dispersion application unit 436 applies wavelength dispersion to the input nth reconstruction signal that corresponds to the frequency difference between the channel of interest and another channel, from the optical transmitter 10-n to position k.

[0047] The high-frequency wavelength dispersion application unit 436 outputs the nth reconstructed signal to which wavelength dispersion has been applied to the nonlinear calculation unit 437. The nonlinear calculation unit 437 performs a nonlinear calculation on the nth reconstructed signal after wavelength dispersion application output from the high-frequency wavelength dispersion application unit 436 (step S206). The nonlinear calculation unit 437 outputs the nth reconstructed signal after nonlinear calculation to the residual wavelength dispersion application unit 438. The residual wavelength dispersion application unit 438 applies wavelength dispersion corresponding to the distance from position k to the optical receiver 40-1 to the nth reconstructed signal after nonlinear calculation output from the nonlinear calculation unit 437 (step S207). As a result, the residual wavelength dispersion application unit 438 calculates the signal x ｋ The signal x is obtained. For example, when k = 0, the residual wavelength dispersion application unit 438 obtains the signal x ０ Obtain it.

[0048] Subsequently, the XCI perturbation base generation unit 434 determines whether the termination condition has been met (step S208). The termination condition is the condition for ending the processing by the XCI perturbation base generation unit 434, for example, that k = K-1. That is, in the residual wavelength dispersion application unit 438, the signal x Ｋ－１ The result is obtained. If the XCI perturbation base generation unit 434 determines that the termination condition is not met (step S208-NO), the XCI perturbation base generation unit 434 adds 1 to the value of k (step S209). After that, the XCI perturbation base generation unit 434 executes the processing from step S205 onwards.

[0049] On the other hand, if the XCI perturbation basis generation unit 434 determines that the termination condition has been met (step S208-YES), the XCI perturbation basis generation unit 434 outputs the obtained signal X to the optical power distribution estimation unit 435. In this way, the XCI perturbation basis generation unit 434 acquires the signal at each position by repeatedly changing the position k from 0, 1, ..., K-1. The optical power distribution estimation unit 435 then processes the perturbation component A obtained by the perturbation component estimation unit 433. １ Based on (L,t) and the signal X obtained by the XCI perturbation base generation unit 434, the optical power distribution is estimated using at least one of the above-described equations (1) to (4) (step S210).

[0050] The above description explains the case in which optical transmission path characteristics are estimated using a walk-off due to wavelength dispersion between optical waveforms of different frequencies. However, when using effects other than wavelength dispersion, such as when using different orthogonal modes, the above-mentioned wavelength dispersion application units (for example, wavelength dispersion application units 431, 432, high-frequency wavelength dispersion application unit 436, residual wavelength dispersion application unit 438, etc., which are functional units that apply wavelength dispersion) can be read as physical quantity application units. The same applies to other embodiments. The physical quantity application unit performs an operation to apply the physical quantity to the signal (for example, applying modal dispersion in the case of spatial modes).

[0051] Figure 5 shows an example of an experiment conducted using the configuration of the first embodiment. Equation (1) was used as the estimator in the experiment. The simulation conditions were as follows: Modulation scheme: Probabilistic-constellation-shaped-64QAM; Modulation rate: 128GBd (both channels); Channel spacing: 256GHz; Nyquist roll-off: 0.1; Transmission path configuration: 25 km x 2 spans (split-step method); Loss: 0.2 dB / km; Group velocity dispersion: 17 ps / nm / km; Nonlinear constant: 1.3 W-1km-1; Input optical power: 15 dBm / ch; Spatial granularity: 0.1 km

[0052] As shown in Figure 5, this method can estimate the optical power distribution with high spatial resolution at 0.1 km, and it can be seen that the estimation matches the true transmission path parameter γ'. The 1 dB anomaly losses inserted at 25.3 km and 25.6 km within the 25 km x 2 spans can also be estimated. In other words, it can be seen that the location resolution of the two anomaly losses has been successfully achieved.

[0053] The optical transmission path characteristic estimation device 43 configured as described above includes an optical transmission path characteristic estimation device 43 that estimates optical transmission path characteristics based on a received waveform of a reference optical wave (for example, a first demodulated signal obtained based on the signal of the channel of interest (a reference reference wavelength channel) in the embodiment), a transmitted waveform of a reference optical wave (for example, a first reconstructed signal obtained by reconstructing the transmitted signal based on the first demodulated signal), and a transmitted waveform of one or more optical waves other than the reference optical wave (a second reconstructed signal obtained by reconstructing the transmitted signal based on the received signals of one or more other channels (other wavelength channels) other than the channel of interest used for estimating optical transmission path characteristics).

[0054] Conventionally, estimation was performed using self-channel interference, which is nonlinear interference within the channel of interest in optical fiber transmission. In contrast, the optical transmission path characteristic estimation device 43 performs estimation using inter-channel interference, which is interference between the channel of interest and another channel. This allows for a larger walk-off due to chromatic dispersion when estimating optical transmission path characteristics using optical waveforms of different frequencies, thereby improving spatial resolution. Similarly, when estimating optical transmission path characteristics using optical waveforms of different orthogonal modes, spatial resolution can be improved by performing estimation between modes with large walk-offs. Furthermore, the optical transmission path characteristic estimation device 43 does not reconstruct the entire optical bandwidth, but only reconstructs the signals of each channel used for estimation. Therefore, computational costs can be reduced. As a result, it becomes possible to perform optical power distribution estimation with high spatial resolution while reducing computational costs.

[0055] Furthermore, while Non-Patent Document 4 also describes a signal reconstruction technique, it reconstructs the entire optical bandwidth during signal reconstruction. This is computationally intensive, especially when performing calculations such as Fourier transforms and inverse Fourier transforms. Thus, the optical transmission path characteristic estimation device 43 can achieve high spatial resolution optical power distribution estimation while reducing computational costs compared to the technique described in Non-Patent Document 4.

[0056] (Second Embodiment) In the second embodiment, a configuration for estimating optical transmission path characteristics by taking into account not only mutual channel interference but also self-channel interference (SCI) will be described. In the second embodiment, the system configuration is the same as in the first embodiment. The difference from the first embodiment lies in the configuration of the optical transmission path characteristic estimation device. The following will focus on the differences from the first embodiment.

[0057] Figure 6 shows an example of the configuration of the optical transmission path characteristic estimation device 43a in the second embodiment. The optical transmission path characteristic estimation device 43a includes a wavelength dispersion application unit 431, a wavelength dispersion application unit 432, a perturbation component estimation unit 433, an XCI perturbation basis generation unit 434, an optical power distribution estimation unit 435a, and an SCI perturbation basis estimation unit 439.

[0058] The optical transmission path characteristic estimation device 43a differs from the optical transmission path characteristic estimation device 43 in that it includes an optical power distribution estimation unit 435a instead of the optical power distribution estimation unit 435, and newly includes an SCI perturbation basis estimation unit 439. The other configurations of the optical transmission path characteristic estimation device 43a are the same as those of the optical transmission path characteristic estimation device 43. The differences from the optical transmission path characteristic estimation device 43 will be explained below.

[0059] The SCI perturbation basis estimation unit 439 comprises a wavelength dispersion application unit 440, a nonlinear calculation unit 441, and a residual wavelength dispersion application unit 442. The wavelength dispersion application unit 440 receives a reconstructed signal output from a signal reconstruction unit 42 of an optical receiver R that receives an optical signal of the channel of interest. In the example shown in Figure 6, the wavelength dispersion application unit 440 receives a first reconstructed signal output from a signal reconstruction unit 42-1. The wavelength dispersion application unit 440 applies a wavelength dispersion to the first reconstructed signal output from the signal reconstruction unit 42-1 that corresponds to the frequency difference between the channel of interest and another channel, from the optical transmitter 10-1 to position k (=0, 1, ..., K-1).

[0060] The nonlinear calculation unit 441 performs nonlinear calculations on the signal to which wavelength dispersion has been applied by the wavelength dispersion application unit 440. For example, the nonlinear calculation unit 441 performs 2j(|・| ２-rms(・) ２ Perform the operation )(・).

[0061] The residual wavelength dispersion application unit 442 applies wavelength dispersion to the signal that has been subjected to nonlinear calculations by the nonlinear calculation unit 441, corresponding to the distance from position k to the optical receiver 40 that receives the optical signal of another channel. For example, the residual wavelength dispersion application unit 442 applies wavelength dispersion to the signal that has been subjected to nonlinear calculations by the nonlinear calculation unit 441, corresponding to the distance from position k to the optical receiver 40-1.

[0062] The SCI perturbation basis estimation unit 439 repeatedly performs the above process, changing the position k from 0, 1, ..., K-1. As a result, the SCI perturbation basis estimation unit 439 calculates the signal s ０ ,s １ , ..., s Ｋ－１ Obtain the signal s. ０ This is the signal obtained by the processing of the wavelength dispersion application unit 440, the nonlinear calculation unit 441, and the residual wavelength dispersion application unit 442 when the position is set to 0. The following is the signal s acquired by the SCI perturbation basis estimation unit 439. ０ ,s １ , ..., s Ｋ－１ These are collectively referred to as signal S. In this way, the SCI perturbation basis estimation unit 439 generates a signal of the self-interchannel interference component.

[0063] The optical power distribution estimation unit 435a calculates perturbation component A obtained by the perturbation component estimation unit 433. １ The optical power distribution is estimated based on (L,t), the signal X obtained by the XCI perturbation basis generation unit 434, and the signal S obtained by the SCI perturbation basis estimation unit 439. Various estimation methods can be considered for estimating the optical power distribution by the optical power distribution estimation unit 435a.

[0064] For example, the optical power distribution estimation unit 435a estimates the power distribution vector γ' using one of the estimators shown in equations (5) to (9) below. In equations (5) to (9), X = [x ０ , x １ , ..., x Ｋ－１ Let ] and S = [s ０ ,s １ , ..., s Ｋ－１Let ] be an arbitrary K × K matrix and λ be an arbitrary real number. Note that the optical power distribution estimation unit 435a does not need to use any one of equations (5) to (9) for estimation, and may use a combination of any of equations (5) to (9), or it may use one without Re, or one in which the absolute value is taken instead of Re, etc.

[0065]

[0066]

[0067]

[0068]

[0069]

[0070] (Operation of Optical Transmission Path Characteristic Estimation Device 43a) The optical transmission path characteristic estimation process performed by the optical transmission path characteristic estimation device 43a in the second embodiment is basically the same as the optical transmission path characteristic estimation process performed by the optical transmission path characteristic estimation device 43, except that it includes the processing performed by the SCI perturbation basis estimation unit 439. Therefore, the optical transmission path characteristic estimation process performed by the optical transmission path characteristic estimation device 43a will be explained using Figure 4 as an example. After the processes from step S201 to step S203 are executed, the XCI perturbation basis generation unit 434 and the SCI perturbation basis estimation unit 439 initialize the value of k (step S204). For example, the XCI perturbation basis generation unit 434 and the SCI perturbation basis estimation unit 439 set the value of k to 0.

[0071] The processes from step S205 to step S209 are performed by the XCI perturbation basis generation unit 434 and the SCI perturbation basis estimation unit 439, respectively. First, the operation of the XCI perturbation basis generation unit 434 is the same as in the first embodiment, so its explanation will be omitted. Next, the operation of the SCI perturbation basis estimation unit 439 will be explained. The wavelength dispersion application unit 440 applies wavelength dispersion to the input first reconstructed signal (step S205). For example, the wavelength dispersion application unit 440 applies wavelength dispersion to the input first reconstructed signal that corresponds to the frequency difference between the channel of interest and another channel, from the optical transmitter 10-1 to position k.

[0072] The wavelength dispersion application unit 440 outputs the first reconstructed signal to which wavelength dispersion has been applied to the nonlinear calculation unit 441. The nonlinear calculation unit 441 performs a nonlinear calculation on the first reconstructed signal after wavelength dispersion application output from the wavelength dispersion application unit 440 (step S206). The nonlinear calculation unit 441 outputs the first reconstructed signal after nonlinear calculation to the residual wavelength dispersion application unit 442. The residual wavelength dispersion application unit 442 applies wavelength dispersion corresponding to the distance from position k to the optical receiver 40-1 to the first reconstructed signal after nonlinear calculation output from the nonlinear calculation unit 441 (step S207). As a result, the residual wavelength dispersion application unit 442 applies the signal s ｋ The signal s is obtained. For example, when k = 0, the residual wavelength dispersion application unit 442 receives the signal s ０ Obtain it.

[0073] Subsequently, the SCI perturbation basis estimation unit 439 determines whether the termination condition has been met (step S208). The termination condition in the second embodiment is the condition for terminating the processing by the XCI perturbation basis generation unit 434 and the SCI perturbation basis estimation unit 439, respectively, and is, for example, that k = K-1. That is, in the SCI perturbation basis estimation unit 439, the signal s Ｋ－１ The result is obtained. If the SCI perturbation basis estimation unit 439 determines that the termination condition is not met (step S208-NO), the SCI perturbation basis estimation unit 439 adds 1 to the value of k (step S209). After that, the SCI perturbation basis estimation unit 439 executes the processing from step S205 onwards.

[0074] On the other hand, if the SCI perturbation basis estimation unit 439 determines that the termination condition has been met (step S208-YES), the SCI perturbation basis estimation unit 439 outputs the obtained signal S to the optical power distribution estimation unit 435a. In this way, the SCI perturbation basis estimation unit 439 acquires the signal at each position by repeatedly changing the position k from 0, 1, ..., K-1. The optical power distribution estimation unit 435a then processes the perturbation component A obtained by the perturbation component estimation unit 433. １Based on (L,t), the signal X obtained by the XCI perturbation basis generation unit 434, and the signal S obtained by the SCI perturbation basis estimation unit 439, the optical power distribution is estimated using at least one of the above-described equations (5) to (9) (step S210).

[0075] According to the optical transmission path characteristic estimation device 43a in the second embodiment configured as described above, the optical transmission path characteristics are estimated by also taking into account self-interchannel interference. Therefore, although the computational cost is higher than in the first embodiment, it becomes possible to estimate the optical transmission path characteristics with higher accuracy than in the first embodiment.

[0076] (Third Embodiment) In the first and second embodiments, it may be necessary to synchronously acquire the sample time and sampling rate of multiple channels of signals used for estimating optical transmission path characteristics. The third embodiment describes a configuration that assumes such a case.

[0077] Figure 7 shows an example configuration of the optical transmission system 200 in the third embodiment. The optical transmission system 200 includes an optical transmitter 10, an optical multiplexer 20, an optical demultiplexer 30, an optical receiver 40, a demodulation unit 41, a signal reconstruction unit 42, and an optical transmission path characteristic estimation device 43. The optical transmission system 200 shown in Figure 7 has the same system configuration as the optical transmission system 100 in the first embodiment. The differences from the first embodiment will be explained below.

[0078] To acquire signals from multiple channels synchronously, a synchronization signal may be used to synchronize the acquisition timing of each optical receiver 40. The synchronization signal may be output from a device that generates an independent reference signal, or it may be output from any of the optical receivers 40. Also, when transmitting a known sequence between the transmitter and receiver, the transmission timing of the optical transmitters 10 (for example, 10-1 and optical transmitter 10-n) may be synchronized. The targets for synchronization are the optical transmitters 10 and optical receivers 40 used for estimating the optical transmission path characteristics. This configuration may also be applied to the optical transmission system 100 in the second embodiment.

[0079] According to the optical transmission system 200 in the third embodiment configured as described above, the sample time and sampling rate of multiple channels of signals used for estimating optical transmission path characteristics can be acquired synchronously.

[0080] (Fourth Embodiment) In the first and second embodiments, it was necessary to acquire signals from multiple channels in a synchronized manner, and multiple signal reconstruction units were required. To avoid this, the fourth embodiment describes a configuration in which a single optical transmitter is equipped with multiple lasers and outputs light of different frequencies.

[0081] Figure 8 shows an example configuration of the optical transmission system 300 in the fourth embodiment. The optical transmission system 300 includes an optical transmitter 10, an optical multiplexer 20, an optical demultiplexer 30, an optical receiver 40, a demodulation unit 41, a signal reconstruction unit 42, and an optical transmission path characteristic estimation device 43. Unlike the other embodiments, the optical transmission system 300 only needs to include at least one optical transmitter 10 and at least one optical receiver 40. The difference in configuration between the optical transmission system 300 and the optical transmission system 100 lies in the configuration of the optical transmitter 10. This will be explained in detail below.

[0082] The optical transmitter 10 comprises a plurality of lasers 11-1, 11-2, a multiplexer 12, a transmission signal generation unit 13, a digital-to-analog converter 14, and a modulator 15. The optical transmitter 10 may also be equipped with three or more lasers. In this case, all lasers will emit light of different wavelengths. Lasers 11-1 and 11-2 emit light of different frequencies. For example, laser 11-1 emits light of frequency f1, and laser 11-2 emits light of frequency fn. The multiplexer 12 combines the light of frequencies f1 and fn output from lasers 11-1 and 11-2, respectively. As a result, the multiplexer 12 generates a multiplexed optical signal.

[0083] The transmission signal generation unit 13 generates the transmission data (electrical signal) to be transmitted. The digital-to-analog converter 14 generates an analog signal by performing a digital-to-analog conversion on the transmission data generated by the transmission signal generation unit 13. The modulator 15 generates a modulated optical signal by modulating the multiplexed optical signal generated by the multiplexer 12 with the analog signal. The modulator 15 transmits the generated modulated optical signal.

[0084] As described above, in this embodiment, the optical transmitter 10 combines the light output from two lasers 11-1 and 11-2 with different frequencies using a multiplexer 12, and then inputs it to a modulator 15 to obtain a modulated optical signal. With this configuration, a single signal can be transmitted simultaneously even between different frequencies. Therefore, the signal reconstruction of frequency fn can be replaced by the signal reconstruction unit 42-1 of the first optical transceiver R1. As a result, the restoration of multiple channels and inter-channel synchronization become unnecessary. In this configuration, the optical transmission path characteristic estimation device 43 can use the demodulation unit 41-n and the signal reconstruction unit 42-1 instead of the outputs of the demodulation unit 41-n and the signal reconstruction unit 42-n in the first embodiment. Other processing is the same as in the first embodiment.

[0085] As described above, when light of different frequencies is multiplexed in a single optical transmitter 10, even if the optical demultiplexer 30 separates the signals according to wavelength, inter-channel interference and inter-channel interference are superimposed on the frequency of the channel of interest. Therefore, if a single optical receiver R (for example, a first optical receiver R1) can receive only the channel of the frequency of interest, the optical transmission line characteristics can be determined by taking inter-channel interference into account, similar to the first embodiment.

[0086] With the optical transmission system 300 configured as described above, by using an optical transmitter 10 equipped with multiple lasers, it becomes unnecessary to acquire signals from multiple channels in a synchronized manner. Furthermore, it is sufficient to have only a single signal reconstruction unit 42. As a result, the same effects as in the first embodiment can be obtained even with a configuration different from that of the first embodiment.

[0087] The optical transmission path characteristic estimation device 43 in the optical transmission system 300 may be the optical transmission path characteristic estimation device 43a in the second embodiment. As described above, even if the multiplexed optical signal transmitted from one optical transmitter 10 is decoupled according to wavelength by the optical decoupler 30, inter-channel interference and self-channel interference are superimposed on the frequency of the channel of interest. Therefore, if only the channel of the one frequency of interest can be received by one optical receiver R (for example, the first optical receiver R1), the optical transmission path characteristics can be determined by taking into account inter-channel interference and self-channel interference, similar to the second embodiment.

[0088] (Modification 1 common to the first to fourth embodiments) In the embodiments described above, a configuration in which a communication signal is used as the channel for estimating the optical transmission path characteristics was explained as an example, but special transmitters, signals, and optical waveforms specifically for monitoring may also be used.

[0089] (Modification 2 common to the first to fourth embodiments) The optical transmission path characteristic estimation devices 43, 43a in each embodiment can also acquire the time distribution, wavelength distribution, and polarization distribution of optical power by acquiring the optical power distribution in the time direction, wavelength direction, and polarization direction. In addition, the optical transmission path characteristic estimation devices 43, 43a can also improve the SNR of the estimated power distribution by averaging them.

[0090] Some or all of the functional units of the optical receiver R and optical transmission path characteristic estimation devices 43, 43a described above are realized as software by a processor such as a CPU (Central Processing Unit) executing a program stored in a storage device and a memory unit having a non-volatile recording medium (non-temporary recording medium). The program may be recorded on a computer-readable non-temporary recording medium. A computer-readable non-temporary recording medium is, for example, a portable medium such as a flexible disk, magneto-optical disk, ROM (Read Only Memory), CD-ROM (Compact Disc Read Only Memory), or a storage device such as a hard disk built into a computer system.

[0091] Some or all of the functional units of the optical receiver R and optical transmission path characteristic estimation devices 43, 43a described above may be implemented using hardware including electronic circuits (electronic circuits or circuits) such as LSI (Large Scale Integrated Circuit), ASIC (Application Specific Integrated Circuit), PLD (Programmable Logic Device), or FPGA (Field Programmable Gate Array).

[0092] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention.

[0093] This invention can be applied to techniques for estimating transmission characteristics in wavelength division multiplexing transmission.

[0094] 10, 10-1 to 10-n... Optical transmitter, 11-1 to 11-2... Laser, 12... Multiplexer, 13... Transmit signal generation unit, 14... Digital to analog converter, 15... Modulator, 20... Optical multiplexer, 30... Optical demultiplexer, 40, 40-1 to 40-n... Optical receiver, 41, 41-1 to 41-n... Demodulation unit, 42, 42-1 to 42-n... Signal reconstruction unit, 43, 43a... Optical transmission path characteristic estimation device, 50... Optical transmission path, 431, 432, 440... Wavelength dispersion application unit, 433... Perturbation component estimation unit, 434... XCI perturbation basis generation unit, 435... Optical power distribution estimation unit, 436... High frequency wavelength dispersion application unit, 437, 441... Nonlinear calculation unit, 438, 442...Residual wavelength dispersion application unit, 439...SCI perturbation basis estimation unit, 100, 200, 300...Optical transmission system

Claims

1. An optical transmission path characteristic estimation device comprising: an optical transmission path characteristic estimation unit that estimates optical transmission path characteristics based on the received waveform of a reference optical wave, the transmitted waveform of the reference optical wave, and the transmitted waveforms of one or more optical waves other than the reference optical wave.

2. The optical transmission path characteristic estimation device according to claim 1, wherein the optical transmission path characteristic estimation unit estimates the optical transmission path characteristics by taking into account inter-channel interference.

3. The optical transmission path characteristic estimation device according to claim 2, wherein the optical transmission path characteristic estimation unit estimates the optical transmission path characteristics by further taking into account self-interchannel interference.

4. An optical transmission path characteristics estimation method that estimates optical transmission path characteristics based on the received waveform of a reference optical wave, the transmitted waveform of the reference optical wave, and the transmitted waveforms of one or more optical waves other than the reference optical wave.

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