Optical transmission characteristic estimation device

Abstract

An optical transmission path characteristic estimation device used in an optical transmission system that uses a wide band in which stimulated Raman scattering between bands occurs, the optical transmission path characteristic estimation device comprising: a nonlinear phase rotation amount estimation unit that estimates a nonlinear phase rotation amount on the basis of a reception signal obtained by receiving an optical signal by a coherent detection method; a nonlinear coefficient estimation unit that estimates a non-linear coefficient on the basis of a measurement value of optical power measured in advance at a predetermined position in the longitudinal direction of the optical transmission path and a nonlinear phase rotation amount; and a transmission characteristic estimation unit that estimates an optical power distribution on the basis of the nonlinear phase rotation amount estimated by the nonlinear phase rotation amount estimation unit and the nonlinear coefficient estimated by the non-linear coefficient estimation unit.　

Description

Optical transmission characteristics estimation device

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

[0002] In current optical transmission systems, demand continues to increase exponentially, making it essential to increase transmission capacity. One way to increase transmission capacity is to broaden the bandwidth. Broadening the bandwidth is a method of using multiple different bandwidths for communication. The bandwidths that are commonly used are the C band and the C+L band, which minimize fiber loss. Broadening the bandwidth means further increasing these bandwidths and using the S+C+L band, etc.

[0003] As the bandwidth becomes wider, inter-band stimulated Raman scattering (SRS) and other phenomena become more pronounced, causing optical power transitions between bands. This makes it difficult to manage the signal-to-noise ratio (SNR) and nonlinearity for each band, which in turn makes optimizing transmission performance and system management difficult. Inter-band SRS is a nonlinear phenomenon in optical fiber, and in broadband transmission, it refers to the phenomenon in which energy transitions from short wavelengths to long wavelengths, resulting in a decrease in optical power at short wavelengths and an increase in optical power at long wavelengths. To accurately manage the SNR and nonlinearity, it is necessary to monitor changes in optical power along the longitudinal direction.

[0004] One method for monitoring optical power changes is to use the power profile estimation (PPE) technique (see, for example, Patent Documents 1 and 2, and Non-Patent Documents 1 and 2). The PPE technique estimates the optical power distribution in the longitudinal direction of an optical fiber by simply processing the received signal. By using the PPE technique, it is possible to estimate the optical power distribution in a multi-span optical transmission line without using a dedicated measuring instrument such as a spectrum analyzer. This makes it possible to reduce CAPEX / OPEX (equipment costs and operation and maintenance costs).

[0005] International Publication No. 2021 / 124415 International Publication No. 2023 / 037553

[0006] 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.

[0007] However, in the PPE technology, the nonlinear coefficient, which is inherently wavelength-dependent, is treated as a constant, and therefore there is a problem in that true power changes cannot be obtained in broadband optical transmission systems.

[0008] In view of the above circumstances, an object of the present invention is to provide a technique capable of estimating the true optical power distribution in the distance direction in an optical transmission system that uses a wide band in which stimulated Raman scattering between bands occurs.

[0009] One aspect of the present invention is an optical transmission line characteristics estimation device used in an optical transmission system that utilizes a wide bandwidth such that inter-band stimulated Raman scattering occurs, the optical transmission line characteristics estimation device comprising: a nonlinear phase rotation estimation unit that estimates a nonlinear phase rotation based on a received signal obtained by receiving an optical signal using a coherent detection method; a nonlinear coefficient estimation unit that estimates a nonlinear coefficient based on a measured value of optical power measured in advance at a predetermined position in the longitudinal direction of the optical transmission line and the nonlinear phase rotation; and a transmission characteristics estimation unit that estimates an optical power distribution based on the nonlinear phase rotation estimated by the nonlinear phase rotation estimation unit and the nonlinear coefficient estimated by the nonlinear coefficient estimation unit.

[0010] According to the present invention, it becomes possible to estimate the true optical power distribution in the distance direction in an optical transmission system that uses a wide band in which stimulated Raman scattering between bands occurs.

[0011] FIG. 1 is a diagram illustrating an example of the configuration of an optical transmission system in a first embodiment. FIG. 2 is a diagram illustrating an example of the configuration of an optical receiving device in a first embodiment. FIG. 3 is a sequence diagram illustrating a processing flow of the optical transmission system in a first embodiment. FIG. 4 is a diagram illustrating an example of the configuration of an optical transmission system in a second embodiment. FIG. 5 is a diagram illustrating an example of the configuration of an optical transmission system in a third embodiment. FIG. 6 is a diagram illustrating an example of the configuration of a control device in a third embodiment. FIG. 7 is a flowchart illustrating the processing flow of an optimization method (part 1) performed by the control device in a third embodiment. FIG. 8 is a diagram illustrating the optimization method performed by the control device in a third embodiment. FIG. 9 is a diagram illustrating the processing flow of an optimization method (part 2) performed by the control device in a third embodiment. FIG. 10 is a diagram illustrating the experimental results of the present invention. FIG. 11 is a diagram illustrating the experimental results of the present invention. FIG. 12 is a diagram illustrating the experimental results of the present invention.

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] First Embodiment FIG. 1 is a diagram illustrating an example of the configuration of an optical transmission system 100 according to a first embodiment. The optical transmission system 100 is a system that utilizes a wide band in which inter-band stimulated Raman scattering occurs. For example, the optical transmission system 100 is a system that utilizes a wide band such as the S+C+L band. The optical transmission system 100 includes multiple optical transmitters 10, multiple optical receivers 20, a wavelength multiplexing / demultiplexing unit 30, and a wavelength multiplexing / demultiplexing unit 40. The wavelength multiplexing / demultiplexing unit 30 and the wavelength multiplexing / demultiplexing unit 40 are connected by an optical transmission path 50. The optical transmission path 50 includes an optical fiber, one or more optical amplifiers, and one or more wavelength selective switches. The one or more optical amplifiers amplify optical signals. The one or more wavelength selective switches have the function of dynamically switching any wavelength path from a wavelength-multiplexed optical signal to any port.

[0014] The optical transmitters 10 transmit optical signals in different wavelength bands. For example, the optical transmitter 10-0 transmits optical signals in a channel angular frequency ω ０ The optical transmitter 10-k transmits an optical signal of a channel angular frequency ωｋ The optical transmitter 10-K transmits an optical signal of a channel angular frequency ω Ｋ The value k is a value between 0 and K, where K represents the maximum number of channels used in wavelength division multiplexing. Note that it is not necessary to use all channels, and some of the channels may be used.

[0015] The plurality of optical receiving devices 20 receive optical signals transmitted by the optical transmitting device 10 associated with the optical receiving device 20 itself, among the optical signals transmitted from the plurality of optical transmitting devices 10. The plurality of optical receiving devices 20 estimate the optical power distribution in the distance direction in the optical transmission path 50 based on the received optical signals. For example, the optical receiving device 20-0 receives the optical signal transmitted from the optical transmitting device 10-0, the optical receiving device 20-k receives the optical signal transmitted from the optical transmitting device 10-k, and the optical receiving device 20-K receives the optical signal transmitted from the optical transmitting device 10-K.

[0016] In each optical receiving device 20, an optical power distribution in the distance direction based on optical signals with different channel angular frequencies is estimated. Therefore, an optical power distribution in the distance direction and wavelength direction can be obtained based on the optical power distribution in the distance direction estimated in each optical receiving device 20. The optical power distribution in the distance direction and wavelength direction is obtained by estimating the optical power distribution in the wavelength direction (for example, wavelength λ ０ ~λ Ｋ ) in the distance direction (the distance direction of the optical transmission line 50).

[0017] The wavelength multiplexing / demultiplexing unit 30 multiplexes optical signals transmitted from a plurality of optical transmitters 10. As a result, the wavelength multiplexing / demultiplexing unit 30 generates a multiplexed signal.

[0018] The wavelength multiplexing / demultiplexing unit 40 demultiplexes the multiplexed signal generated by the wavelength multiplexing / demultiplexing unit 30 according to wavelength.

[0019] Next, an example of the configuration of the optical receiving device 20 will be described. Fig. 2 is a diagram showing an example of the configuration of the optical receiving device 20 in the first embodiment. Note that, since the multiple optical receiving devices 20 have the same configuration, they will be described as an optical receiving device 20. The optical receiving device 20 includes a coherent receiving unit 210, a nonlinear phase rotation amount estimating unit 220, a nonlinear coefficient estimating unit 230, and a transmission characteristics estimating unit 240. Note that the nonlinear phase rotation amount estimating unit 220, the nonlinear coefficient estimating unit 230, and the transmission characteristics estimating unit 240 constitute an optical transmission path characteristics estimating device.

[0020] The coherent receiving unit 210 is connected to the optical transmission line and receives and coherently detects an optical signal transmitted through the optical transmission line. The coherent receiving unit 210 separates the received optical signal into X-polarized and Y-polarized waves. The coherent receiving unit 210 detects the I- and Q-components of each of the X- and Y-polarized waves by causing interference between each of the polarization-separated X- and Y-polarized optical signals and a laser beam emitted from a local oscillator light source provided inside the coherent receiving unit 210. The coherent receiver 11 converts each of the I- and Q-component optical signals of each of the X- and Y-polarized waves into four analog electrical signals, and then converts the converted four analog signals into four digital signals using four internal analog-to-digital converters and outputs them. Hereinafter, the four digital signals output by the coherent receiving unit 210 will be referred to as received signals.

[0021] The nonlinear phase rotation estimation unit 220 estimates the nonlinear phase rotation γ′(z, ω) based on the received signal output from the coherent receiving unit 210. ｋ Here, ω is the angular frequency of the channel, and k is the wavelength (k=0 to K). For example, the nonlinear phase rotation estimation unit 220 estimates the nonlinear phase rotation γ'(z, ω) using the PPE technique described in Patent Document 1. ｋ ) is estimated.

[0022] The nonlinear coefficient estimator 230 estimates z=z measured by a measuring instrument such as an optical spectrum analyzer or an optical power meter. ０ The true value of the optical power P(z ０ , ω ｋ ) and the nonlinear phase rotation amount γ′(z, ω ｋ) z = z ０ The value γ′(z ０ , ω ｋ ) and the nonlinear coefficient γ(ω ｋ For example, the nonlinear coefficient estimation unit 230 estimates the nonlinear coefficient γ(ω ｋ ) is estimated.

[0023]

[0024] In addition, the nonlinear coefficient γ (ω ｋ The method for estimating the nonlinear coefficient γ(ω ｋ ) can be estimated, other methods may be used.

[0025] The transmission characteristic estimator 240 estimates the true optical power distribution (optical transmission characteristics) of the optical transmission path. Specifically, the transmission characteristic estimator 240 estimates the nonlinear phase rotation amount γ'(z, ω) estimated by the nonlinear phase rotation amount estimator 220. ｋ ) is calculated based on the nonlinear coefficient γ(ω ｋ ) to obtain the true power distribution value P(z,ω).

[0026] The transmission characteristic estimator 240 corrects the optical power based on, for example, the following equation (2) to obtain the true power distribution value P(z, ω) ｋ ) to obtain the

[0027]

[0028] Thereafter, the optical receiving device 20 acquires the value P(z, ω) of the optical power distribution in the distance direction by sweeping (k=0 to K) in the wavelength direction. Note that the process of sweeping in the wavelength direction may be performed by the transmission characteristics estimating unit 240, or may be performed by a sweeping unit provided downstream of the transmission characteristics estimating unit 240.

[0029] 3 is a sequence diagram showing the flow of processing in the optical transmission system 100 according to the first embodiment. Each optical transmitter 10 transmits an optical signal with a different channel angular frequency (step S11). For example, the optical transmitter 10-0 transmits an optical signal with a channel angular frequency ω ０and the optical transmitter 10-k transmits an optical signal of channel angular frequency ω ｋ and the optical transmitter 10-K transmits an optical signal of channel angular frequency ω Ｋ The optical signals transmitted from the optical transmitters 10 are input to the wavelength multiplexing / demultiplexing unit 30.

[0030] The wavelength multiplexing / demultiplexing unit 30 multiplexes the optical signals transmitted from each optical transmitting device 10 to generate a multiplexed signal (step S12). The multiplexed signal generated by the wavelength multiplexing / demultiplexing unit 30 is input to the wavelength multiplexing / demultiplexing unit 40 via the optical transmission line 50. The wavelength multiplexing / demultiplexing unit 40 demultiplexes the input multiplexed signal according to wavelength and outputs the demultiplexed signal to each optical receiving device 20 (step S13). As a result, the optical receiving device 20-0 receives a signal with a channel angular frequency ω ０ The optical signal of channel angular frequency ω is input to the optical receiving device 20-k. ｋ The optical signal of channel angular frequency ω is input to the optical receiving device 20-K. Ｋ An optical signal of is input.

[0031] Here, the same processing is performed in each of the optical receiving devices 20-0, 20-k, and 20-K, so the optical receiving device 20-k will be used as an example for explanation. The coherent receiving unit 210-k of the optical receiving device 20-k receives a signal with a channel angular frequency ω ｋ (Step S14). The coherent receiver 210-k receives an optical signal of channel angular frequency ω ｋ The coherent receiver 210-k outputs the received signal to the nonlinear phase rotation estimator 220-k. The nonlinear phase rotation estimator 220-k estimates the nonlinear phase rotation γ'(z, ω) based on the received signal output from the coherent receiver 210-k. ｋ ) is estimated (step S15).

[0032] The nonlinear phase rotation amount estimator 220-k estimates the estimated nonlinear phase rotation amount γ'(z, ω ｋ The nonlinear coefficient estimator 230-k outputs information indicating the amount of nonlinear phase rotation γ'(z, ω) output from the nonlinear phase rotation estimator 220-k to the nonlinear coefficient estimator 230-k and the transmission characteristic estimator 240-k. ｋ) and z = z measured in advance by a measuring device ０ The true value of the optical power P(z ０ , ω ｋ ) and the nonlinear coefficient γ(ω ｋ The nonlinear coefficient estimation unit 230-k estimates the estimated nonlinear coefficient γ(ω ｋ ) to the transmission characteristic estimation unit 240-k.

[0033] The transmission characteristic estimator 240-k estimates the nonlinear phase rotation amount γ'(z, ω) output from the nonlinear phase rotation amount estimator 220-k. ｋ ) and the nonlinear coefficient γ(ω) output from the nonlinear coefficient estimation unit 230-k. ｋ The transmission characteristic estimation unit 240-k receives information indicating the input amount of nonlinear phase rotation γ'(z, ω ｋ ) and the nonlinear coefficient γ(ω ｋ ) based on the information indicating the nonlinear phase rotation amount γ'(z, ω ｋ ) is expressed as the nonlinear coefficient γ(ω ｋ For example, the transmission characteristic estimator 240-k uses the nonlinear phase rotation amount γ'(z, ω ｋ ) as the nonlinear coefficient γ(ω ｋ ) to correct the optical power. As a result, the transmission characteristic estimator 240-k obtains the true power distribution value P(z, ω ｋ ) is acquired (step S104).

[0034] The above-described processes from step S14 to step S17 are executed in each optical receiving device 20. As a result, the true power distribution value P(z, ω) in the distance direction is obtained for each optical receiving device 20. ０ ) ~ P(z, ω Ｋ The true power distribution value P(z, ω) in the distance direction obtained for each optical receiving device 20 is obtained. ０ ) ~ P(z, ω Ｋ ) the value P(z, ω) of the true power distribution in the distance direction and wavelength direction is obtained.

[0035] According to the optical transmission system 100 configured as described above, the optical receiving device 20 includes a nonlinear phase rotation estimator 220 that estimates a nonlinear phase rotation based on a received signal obtained by receiving an optical signal using coherent detection, a nonlinear coefficient estimator 230 that estimates a nonlinear coefficient based on a measured optical power value measured in advance at a predetermined position in the longitudinal direction of the optical transmission path and the nonlinear phase rotation, and a transmission characteristic estimator 240 that estimates an optical power distribution based on the nonlinear phase rotation estimated by the nonlinear phase rotation estimator 220 and the nonlinear coefficient estimated by the nonlinear coefficient estimator 230. As a result, a wavelength-dependent nonlinear coefficient that has conventionally been treated as a constant is determined by estimation rather than as a constant, and the optical power distribution is estimated based on the nonlinear phase rotation determined by conventional technology and the estimated nonlinear coefficient. This makes it possible to estimate the true optical power distribution in the distance direction in an optical transmission system that utilizes a wide bandwidth in which inter-band SRS occurs.

[0036] By using the true optical power distribution P(z, ω) in the distance direction estimated in the optical receiving device 20, it becomes possible to monitor the optical power distribution in the longitudinal direction in the presence of inter-band SRS, the spectral tilt due to inter-band SRS, and the amount of transition in optical power due to inter-band SRS.

[0037] Second Embodiment In the first embodiment, a configuration was shown in which optical signals of multiple channels were transmitted using multiple optical transmitters. In the second embodiment, a configuration will be described in which a single optical transmitter is used to estimate a true optical power distribution in the distance direction based on an optical signal of one arbitrary channel.

[0038] 4 is a diagram showing an example of the configuration of an optical transmission system 100a according to the second embodiment. The optical transmission system 100a is a system that uses a wide band in which inter-band stimulated Raman scattering occurs. For example, the optical transmission system 100a is a system that uses a wide band such as the S+C+L band. The optical transmission system 100a includes one optical transmitting device 10, one optical receiving device 20, a wavelength multiplexing / demultiplexing unit 30, and a wavelength multiplexing / demultiplexing unit 40. The wavelength multiplexing / demultiplexing unit 30 and the wavelength multiplexing / demultiplexing unit 40 are connected by an optical transmission path 50.

[0039] 4, the optical transmission system 100a differs in configuration from the optical transmission system 100 in that it does not include a plurality of optical transmitters 10 and optical receivers 20. The following description will focus on the differences from the optical transmission system 100.

[0040] The optical transmitter 10 is a device for transmitting an optical signal of an arbitrary wavelength band. For example, the optical transmitter 10 transmits an optical signal of a channel angular frequency ω ｋ transmits an optical signal.

[0041] The optical receiving device 20 receives the channel angular frequency ω ｋ The optical receiver 20 receives an optical signal of the received channel angular frequency ω ｋ The optical power distribution in the distance direction in the optical transmission line 50 is then estimated based on the optical signal ω. ０ From ω Ｋ The optical power distribution in the distance direction and the wavelength direction is estimated by sweeping in the wavelength direction up to The optical receiving device 20 has the same configuration as that of the first embodiment.

[0042] According to the optical transmission system 100a configured as above, even when a one-channel optical signal is used, it is possible to obtain the same effects as in the first embodiment.

[0043] (Third Embodiment) In the third embodiment, a configuration will be described in which the functions of each device and optical transmitting device provided in the optical transmission path are optimized using the optical power distribution in the distance direction and wavelength direction obtained by the configuration of the first embodiment or the second embodiment.

[0044] 5 is a diagram showing an example of the configuration of an optical transmission system 100b according to the third embodiment. The optical transmission system 100b is a system that uses a wide band in which inter-band stimulated Raman scattering occurs. For example, the optical transmission system 100b is a system that uses a wide band such as the S+C+L band. The optical transmission system 100b includes a plurality of optical transmitters 10, a plurality of optical receivers 20, a wavelength multiplexing / demultiplexing unit 30, a wavelength multiplexing / demultiplexing unit 40, and a control device 60. The wavelength multiplexing / demultiplexing unit 30 and the wavelength multiplexing / demultiplexing unit 40 are connected by an optical transmission path 50.

[0045] The optical transmission system 100b differs in configuration from the optical transmission system 100 in that it additionally includes a control device 60. The optical transmission system 100b is similar to the optical transmission system 100 in the processing up to obtaining the value P(z, ω) of the true power distribution in the distance direction and wavelength direction. The following description will focus on the differences from the optical transmission system 100.

[0046] The control device 60 optimizes each device and each optical transmitter 10 included in the optical transmission path 50 of the optical transmission system 100b based on the value P(z, ω) of the true power distribution in the distance direction and wavelength direction. Methods for optimizing each device and each optical transmitter 10 included in the optical transmission path 50 include a method of optimizing to minimize spectral tilt and a method of optimizing to maximize the optical signal-to-noise ratio (OSNR) or the generalized signal-to-noise ratio (GSNR). The control device 60 performs optimization using one or two of the above methods.

[0047] Next, a description will be given of the functional configuration of the control device 60. Fig. 6 is a diagram showing an example of the configuration of the control device 60 according to the third embodiment. The control device 60 includes an acquisition unit 610, an optimization unit 620, and an optimization control unit 630.

[0048] The acquisition unit 610 acquires the true power distribution value P(z, ω) in the distance direction obtained by each optical receiving device 20. ０ ) ~ P(z, ω Ｋ ) to obtain the value P(z, ω) of the true power distribution in the distance and wavelength directions.

[0049] The optimization unit 620 calculates control values ​​for optimizing each device included in the optical transmission line 50 and each optical transmission device 10, based on the value P(z, ω) of the true power distribution in the distance direction and wavelength direction acquired by the acquisition unit 610. The optimization unit 620 estimates the amount of nonlinear noise using, for example, the optical power distribution P(z, ω), predicts the generalized signal-to-noise ratio GSNR, and calculates a control value for the modulation format that is optimal for the optical transmission device 10 based on the predicted total SNR for automatic optimization of performance.

[0050] The optimization control unit 630 controls each device included in the optical transmission path 50 and each optical transmitting device 10 to be optimized based on the control value calculated by the optimization unit 620. Specifically, the optimization control unit 630 controls each device included in the optical transmission path 50 and each optical transmitting device 10 to be optimized by feeding back the control value to each device included in the optical transmission path 50 or each optical transmitting device 10.

[0051] 7 is a flowchart showing the flow of processing of the optimization method (part 1) performed by the control device 60 in the third embodiment. The acquisition unit 610 acquires the true power distribution value P(z, ω) in the distance direction obtained by each optical receiving device 20. ０ ) ~ P(z, ω Ｋ ) is obtained (step S201). An example of the true power distribution value P(z, ω) in the distance and wavelength directions is shown in FIG. 8A. Note that, although an example is shown in which the true power distribution in the distance direction obtained for all channels used in wavelength division multiplexing is used, only some of the channels may be used.

[0052] The optimization unit 620 uses the value P(z, ω) of the true power distribution in the distance direction and wavelength direction acquired by the acquisition unit 610 to calculate the power distribution at the distance z ０ The power at the wavelength is extracted in the wavelength direction to check the spectral tilt (step S202). ０ This represents the angle of the spectrum obtained by extracting the power in the wavelength direction.

[0053] The optimization unit 620 calculates control values ​​for optimizing each device and each optical transmitting device 10 included in the optical transmission line 50 so as to eliminate the spectral tilt as shown in Fig. 8C. The optimization unit 620 outputs the calculated control values ​​to the optimization control unit 630. The optimization control unit 630 feeds back the control values ​​output from the optimization unit 620 to each device and each optical transmitting device 10 included in the optical transmission line 50 (step S203).

[0054] In this way, by estimating the optical spectrum in the longitudinal direction of the optical fiber, it becomes possible to optimize the amplifiers 51 and wavelength selective switches 52 at each relay node, which makes it possible to receive signals without spectral tilt.

[0055] 9 is a flowchart showing the flow of processing of the optimization method (part 2) performed by the control device 60 in the third embodiment. The acquisition unit 610 acquires the true power distribution value P(z, ω) in the distance direction obtained by each optical receiving device 20. ０ ) ~ P(z, ω Ｋ ) and obtains a value P(z, ω) of the true power distribution in the distance and wavelength directions (step S301). The optimization unit 620 evaluates transmission quality such as OSNR and GSNR using the obtained value P(z, ω) of the true power distribution in the distance and wavelength directions (step S302).

[0056] 7 , the optimization unit 620 checks the spectral tilt and calculates a control value that maximizes the transmission quality by, for example, eliminating the spectral tilt. The optimization unit 620 outputs the calculated control value to the optimization control unit 630. The optimization control unit 630 feeds back the control value output from the optimization unit 620 to each device included in the optical transmission line 50 and each optical transmitting device 10 (step S303).

[0057] According to the optical transmission system 100b of the third embodiment configured as described above, it becomes possible to predict the system performance and automatically optimize the performance in a wideband optical transmission system using the obtained true optical power distribution P(z, ω).

[0058] (Modification of the Third Embodiment) In the above-described embodiment, the optical transmission system 100b has been shown to have a configuration including a plurality of optical transmitting devices 10 and a plurality of optical receiving devices 20. However, the optical transmission system 100b may also be applied to a configuration including one optical transmitting device 10 and one optical receiving device 20, as in the second embodiment. In such a configuration, the nonlinear phase rotation amount estimator 220 acquires a received signal corresponding to a channel frequency corresponding to the optical receiving device 20 and calculates the nonlinear phase rotation amount γ'(z, ω ｋThen, the optical receiving device 20 estimates the optical power distribution in the distance direction and the wavelength direction by sweeping the channel frequency corresponding to the optical receiving device 20 using the optical power distribution estimated by the transmission characteristic estimating unit 240.

[0059] (Experimental Results) Next, experimental results of the optical transmission system 100 according to the present invention will be described. Here, in a system in which the transmission signal is PS 64QAM, the modulation rate is 100 GBud, and the optical transmission line 50 is a 50 km × 2 span LWPF (Low Water Peak Fiber), the power distribution and spectrum were measured as follows.

[0060] A multiband signal in the S+C+L bands as shown in Figure 10 was created (with one monitor channel), and the wavelength of the monitor channel was swept to estimate the longitudinal power distribution for all channels. The results are shown in Figure 11(A). Furthermore, the power at 80 km was extracted from the estimated power distribution, and the spectrum was obtained. The results are shown in Figure 11(B).

[0061] As shown in Figure 12, a single-band signal containing only the main signal was created (when there was one monitor channel), and the wavelength of the monitor channel was swept for the S, C, and L bands to estimate the longitudinal power distribution for all channels. The results are shown in Figure 13(A). Furthermore, the power at 80 km was extracted from the estimated power distribution, and the spectrum was obtained. The results are shown in Figure 13(B).

[0062] From the difference in power obtained by multi-band transmission and single-band transmission, it is possible to estimate the amount of power transition due to SRS between bands, as shown in Figure 14. This suggests that transmission performance can be optimized and system management can be performed.

[0063] (Modification common to the first to third embodiments) In each of the above-described embodiments, a configuration has been shown in which the optical transmission path characteristics estimation device including the nonlinear phase rotation amount estimator 220, the nonlinear coefficient estimator 230, and the transmission characteristics estimator 240 is provided in the optical receiving device 20. However, the optical transmission path characteristics estimation device including the nonlinear phase rotation amount estimator 220, the nonlinear coefficient estimator 230, and the transmission characteristics estimator 240 may be provided in a device external to the optical receiving device 20. The external device is a control device such as a network controller that controls a communication system in which the optical receiving device 20 is provided (for example, the control device 60 shown in FIG. 5 ). In this configuration, the optical receiving device 20 transmits a received signal to the external device. The external device estimates optical power distribution in the distance direction and wavelength direction using the above-described method based on the received signal transmitted from the optical receiving device 20.

[0064] Some or all of the functional units of the optical receiving device 20 and the control device 60 described above are realized as software by a processor such as a CPU (Central Processing Unit) executing a program stored in a storage device having a non-volatile storage medium (non-transitory storage medium) and a storage unit. The program may be recorded on a computer-readable non-transitory storage medium. Examples of computer-readable non-transitory storage media include portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), and CD-ROMs (Compact Disc Read Only Memory), and storage devices such as hard disks built into computer systems.

[0065] Some or all of the functional units of the optical receiving device 20 and the control device 60 described above may be realized using hardware including an electronic circuit (electronic circuit or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0066] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0067] The present invention can be applied to a technique for estimating transmission characteristics in a digital coherent optical transmission system.

[0068] 10, 10-0 to 10-K... optical transmitting device, 20, 20-0 to 20-K... optical receiving device, 30... wavelength multiplexing / demultiplexing unit, 40... wavelength multiplexing / demultiplexing unit, 50... optical transmission path, 60... control device, 100, 100a, 100b... optical transmission system, 210... coherent receiving unit, 220... nonlinear phase rotation amount estimating unit, 230... nonlinear coefficient estimating unit, 240... transmission characteristic estimating unit, 610... acquisition unit, 620... optimization unit, 630... optimization control unit

Claims

1. An optical transmission line characteristics estimation device used in an optical transmission system that utilizes a wide bandwidth such that inter-band stimulated Raman scattering occurs, comprising: a nonlinear phase rotation estimation unit that estimates a nonlinear phase rotation based on a received signal obtained by receiving an optical signal using a coherent detection method; a nonlinear coefficient estimation unit that estimates a nonlinear coefficient based on a measured value of optical power measured in advance at a predetermined position in the longitudinal direction of the optical transmission line and the nonlinear phase rotation; and a transmission characteristics estimation unit that estimates an optical power distribution based on the nonlinear phase rotation estimated by the nonlinear phase rotation estimation unit and the nonlinear coefficient estimated by the nonlinear coefficient estimation unit.

2. The optical transmission path characteristics estimation device according to claim 1, wherein the received signal is a signal obtained by coherently detecting an optical signal of a specific wavelength that is demultiplexed according to wavelength after optical signals of different frequency bands transmitted by a plurality of optical transmitting devices are multiplexed, and the nonlinear phase rotation amount estimation unit acquires a received signal corresponding to a channel frequency that corresponds to an optical receiving device that includes the device itself or an optical receiving device that is an output source of the received signal.

3. The optical transmission path characteristics estimation device according to claim 1, wherein the optical power distribution estimated by the transmission characteristics estimation unit is used to estimate the optical power distribution in the distance direction and wavelength direction by sweeping the channel frequency corresponding to the optical receiving device that includes the device itself or the optical receiving device that is the output source of the received signal.

4. An optical transmission path characteristics estimation device according to any one of claims 1 to 3, further comprising a control device that optimizes a control value obtained based on the optical power distribution estimated by the transmission characteristics estimation unit by feeding it back to one optical transmitting device that transmits the optical signal or to one or more devices provided on the optical transmission path.

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