Estimation device, filter generation device, estimation method, and filter generation method

Abstract

This inference apparatus comprises: an electric field inference unit that infers, by using a filter having a tap coefficient which is generated for each combination of the optical intensity and the transmission distance of a first input electric field waveform at the input end of a transmission path on the basis of the first input electric field waveform and an output electric field waveform at the output end of the transmission path and by using a generated second input electric field waveform, a simulation signal having the output electric field waveform; and an error rate inference unit that infers the error rate of a code sequence at the output end of the transmission path on the basis of a simulation signal having the output electric field waveform. This filter generation device comprises a filter unit that generates a tap coefficient for a filter for each combination of the optical intensity and the transmission distance of an input electric field waveform at the input end of a transmission path so as to minimize the difference between the shape of a first output electric field waveform at the output end of the transmission path and the shape of a second output electric field waveform outputted from the filter.

Description

[Technical Field]

[0001] The present invention relates to an estimation device, a filter generation device, an estimation method, and a filter generation method. [Background technology]

[0002] In an optical communication system using ROADM (reconfigurable optical add / drop multiplexer) (see Non-Patent Document 1), each node in the transmission path forwards the optical signal transmitted from the first communication device to the second communication device using an optical path. Furthermore, in an All Photonics Network (APN), the optical paths are connected end-to-end without any photoelectric conversion being performed on the optical signals.

[0003] Figure 11 shows an example of the configuration of an optical communication system. The optical communication system illustrated in Figure 11 comprises a first communication device, a second communication device, and a transmission line. The transmission line illustrated in Figure 11 comprises a first node, a second node, a third node, a fourth node, and a fifth node. Each node also includes an optical switch (not shown).

[0004] Each node transmits the optical signal without performing photoelectric conversion. As a result, the optical signal transmitted from the first communication device is transmitted to the second communication device while remaining as light (electric field waveform).

[0005] In an all-photonics network, when a signal requesting connection to a second communication device is transmitted from the first communication device, an appropriate optical path from the first communication device to the second communication device is selected from among several optical paths in the transmission line.

[0006] Here, since the modulation method of the optical signal, the transmission rate, the transmission distance (length of the transmission path), the type of optical fiber used in the transmission path, and the gain of the optical amplifier through which the optical signal is transmitted differ for each optical path, the code error rate in the second communication device also differs for each optical path. For this reason, it is necessary to select an optical path capable of error-free transmission (an optical path in which the code error rate is less than a predetermined value) from among multiple optical paths.

[0007] The optical paths may be selected based on the results of verifying whether each optical path is error-free by actually transmitting an optical signal through it. However, in this case, it takes time for multiple optical paths to be covered, so an enormous amount of time is required to activate the optical paths. Therefore, in order to activate the optical paths in a short time, it is effective to select the optical path that is capable of error-free transmission based on the pre-estimated code error rate for each optical path.

[0008] One method for estimating the code error rate in optical communication systems is to have an estimation device estimate the code error rate through propagation simulation. For example, the estimation device estimates the electric field waveform of an optical signal transmitted through a transmission path having an optical fiber using propagation simulation. The estimation device simulates the electric field waveform in a second communication device by adding appropriate noise to the electric field waveform. The estimation device identifies the code sequence received by the second communication device (received code sequence) by performing a threshold judgment process on the simulation result. The estimation device estimates the code error rate based on the difference between the identified received code sequence and the code sequence transmitted from the first communication device (transmitted code sequence).

[0009] The estimation device accurately estimates the change in the electric field waveform of an optical signal transmitted through a transmission path by performing a predetermined algorithmic processing (e.g., the Split Step Fourier Method (SSFM)) on the nonlinear Schrödinger equation. In this case, the estimation device estimates the electric field waveform (simulated signal) that has undergone linear changes (wavelength dispersion) and nonlinear changes (self-phase modulation) due to transmission. This makes it possible to accurately estimate the change in the electric field waveform of an optical signal transmitted through a transmission path even when nonlinear waveform distortion occurs in the electric field waveform.

[0010] However, in methods based on the split-step Fourier method, the fiber section transmitting the optical signal is divided, and the calculation of the electric field waveform for each divided fiber section is repeated sequentially. Therefore, the calculation time increases as the transmission distance increases. Consequently, it is difficult to apply this estimation method to all-photonic networks that require real-time operation.

[0011] To solve these problems, "GNPy" is provided as a method for estimating the code error rate in a short time (see Non-Patent Document 2). In "GNPy", the nonlinear change is approximated by random Gaussian noise (see Non-Patent Documents 3 and 4), which allows for the estimation of the nonlinear change in a short time. [Prior art documents] [Non-patent literature]

[0012] [Non-Patent Document 1] M. Birk et al., “The OpenROADM initiative [Invited]”, Journal of Optical Communications and Networking, vol.12, no.6, pp.C58-67, June 2020. [Non-Patent Document 2] A. Ferrari et al., “GNPy: an open source application for physical layer aware open optical networks”, Journal of Optical Communications and Networking, vol.12, no.6, pp.C31-C40, June 2020. [Non-Patent Document 3] P. Poggiolini et al., “A Detailed Analytical Derivation of the GN Model of Non-Linear Interference in Coherent Optical Transmission Systems” [Non-Patent Document 4] P. Poggiolini et al., “The GN Model of Non-Linear Propagation in Uncompensated Coherent Optical Systems”, Journal of Lightwave Technology, vol.30, no.24, pp.3857-3879, DECEMBER 2012. [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] However, the Gaussian noise approximation for nonlinear changes only holds true when the transmission distance of the optical signal is greater than or equal to a predetermined distance. Therefore, when the transmission distance of the optical signal is less than the predetermined distance, the Gaussian noise approximation for nonlinear changes cannot be applied. Consequently, for example, the Gaussian noise approximation for nonlinear changes cannot be applied to communications within a data center where the transmission distance of the optical signal is relatively short.

[0014] Thus, when the transmission distance of an optical signal is less than a predetermined distance, there is a problem in that the code error rate cannot be estimated in a short time based on the nonlinearly changing electric field waveform.

[0015] In view of the above circumstances, the present invention aims to provide an estimation device, a filter generation device, an estimation method, and a filter generation method that can improve the accuracy of estimating the code error rate in a short time based on a nonlinearly changing electric field waveform, even when the transmission distance of an optical signal is less than a predetermined distance. [Means for solving the problem]

[0016] One aspect of the present invention is an estimation device comprising: an electric field estimation unit that estimates a simulated signal of the output electric field waveform using a filter of tap coefficients generated for each combination of the optical intensity of the first input electric field waveform and the transmission distance based on the input end of the transmission line and the output electric field waveform at the output end of the transmission line, and the generated second input electric field waveform; and an error rate estimation unit that estimates the error rate of the code sequence at the output end of the transmission line based on the simulated signal of the output electric field waveform.

[0017] One aspect of the present invention is a filter generation device comprising a filter unit that generates tap coefficients for a second filter for each combination of optical intensity of the input field waveform at the input end of the transmission line and transmission distance, so as to reduce the difference between the shape of the first output field waveform at the output end of the transmission line and the shape of the second output field waveform output from the first filter.

[0018] One aspect of the present invention is an estimation method performed by an estimation device, comprising the steps of: estimating a simulated signal of the output electric field waveform using a filter of tap coefficients generated for each combination of optical intensity of the first input electric field waveform and transmission distance based on a first input electric field waveform at the input end of a transmission line and an output electric field waveform at the output end of the transmission line, and a generated second input electric field waveform; and estimating the error rate of the code sequence at the output end of the transmission line based on the simulated signal of the output electric field waveform.

[0019] One aspect of the present invention is a filter generation method performed by a filter generation device, which includes the step of generating a tap coefficient for the filter for each combination of the optical intensity of the input electric field waveform at the input end of the transmission line and the transmission distance, such that the difference between the shape of the first output electric field waveform at the output end of the transmission line and the shape of the second output electric field waveform output from the filter is reduced. [Effects of the Invention]

[0020] The present invention makes it possible to improve the accuracy of estimating the code error rate in a short time based on a nonlinearly changing electric field waveform, even when the transmission distance of the optical signal is less than a predetermined distance. [Brief explanation of the drawing]

[0021] [Figure 1] This figure shows an example of the configuration of the estimation system in the first embodiment. [Figure 2] This figure shows an example of the configuration of an optical communication system in the first embodiment. [Figure 3] This figure shows an example of the configuration of the filter generating device in the first embodiment. [Figure 4] This figure shows an example of a lookup table in the first embodiment. [Figure 5] This is a flowchart showing an example of the operation of the estimation device in the first embodiment. [Figure 6] This figure shows an example of the configuration of the estimation system in the second embodiment. [Figure 7] This figure shows an example of the configuration of the filter generation device in the second embodiment. [Figure 8] This figure shows an example of the configuration of the estimation system in the third embodiment. [Figure 9] This figure shows an example of the configuration of the filter generating device in the third embodiment. [Figure 10] This figure shows an example of the hardware configuration of the estimation system in each embodiment. [Figure 11] This is a diagram showing an example configuration of an optical communication system. [Modes for carrying out the invention]

[0022] Embodiments of the present invention will be described in detail with reference to the drawings. (First Embodiment) Figure 1 shows an example configuration of the estimation system 1a in the first embodiment. The estimation system 1a is a system that estimates the code error rate in real time (within a predetermined delay time) according to the change in the electric field waveform of an optical signal transmitted through the transmission path of an optical communication system. In other words, the estimation system 1a calculates the electric field waveform when it arrives at the second communication device based on the optical signal corresponding to the transmitted code sequence transmitted from the first communication device, and estimates the code error rate in the second communication device in real time based on the calculated electric field waveform.

[0023] Here, when an optical signal corresponding to the transmitted code sequence (input optical signal) is transmitted to the transmission line, waveform distortion (linear waveform distortion and nonlinear waveform distortion) occurs in the input optical signal waveform due to the effects of linear and nonlinear changes caused by propagation in the transmission line. The output optical signal (hereinafter referred to as "output electric field waveform") containing this waveform distortion is output from the output end of the transmission line to the receiving communication device. Furthermore, the effect of self-phase modulation, which is one of the nonlinear changes, is uniquely determined according to a predetermined set of parameters. These predetermined parameters are, for example, the electric field waveform of the optical signal (main signal) input to the transmission line, its intensity (optical intensity), and the transmission distance of the optical signal. A linear change is, for example, a change due to wavelength dispersion.

[0024] Figure 2 shows an example configuration of the optical communication system 100 in the first embodiment. The optical communication system 100 is a system that communicates using optical signals. The optical communication system 100 comprises one or more first communication devices 110, a second communication device 120, and a transmission line 130.

[0025] Hereinafter, the electric field waveform of the optical signal at the input terminal of a transmission line, etc., will be referred to as the "input electric field waveform". Symbol "E in " represents the input electric field waveform. Symbol "Eout " represents the output electric field waveform. The input electric field waveform "E in " and the output electric field waveform "E out " are both time waveforms. The symbol "P in " represents the time average "<>" of the optical intensity "|E in | 2 " of the input electric field waveform.

[0026] The first communication device 110 (the first user terminal) transmits an optical signal corresponding to the transmission code sequence to the second communication device 120 (the second user terminal) using the optical path in the transmission line 130 (for example, an optical fiber) with the transmission distance "L". Here, the input electric field waveform "E in " of the optical signal is input to the transmission line 130. The second communication device 120 (the second user terminal) acquires the output electric field waveform "E out " that has undergone linear and non-linear changes in the transmission line 130.

[0027] Returning to FIG. 1, the description of the configuration example of the estimation system 1a is continued. The estimation system 1a includes a filter generation device 2a, a storage device 3, a sequence generation device 4, and an electric field generation device 5. The estimation system 1a includes an electric field estimation device 6a and an error rate estimation device 7a as an estimation device 8a. That is, the estimation device 8a includes an electric field estimation device 6a and an error rate estimation device 7a.

[0028] The electric field estimation device 6a (electric field estimation unit) includes a selection unit 61 and a filter 62. The error rate estimation device 7a includes a photoelectric conversion unit 71, a noise processing unit 72, a determination unit 73, and an error rate estimation unit 74.

[0029] At the stage of the estimation process, the sequence generation device 4 pre-generates the transmission code sequence transmitted from the first communication device 110 (the transmission-side communication device) toward the second communication device 120 (the reception-side communication device). The sequence generation device 4 transmits the generated transmission code sequence to the electric field generation device 5. The electric field generation device 5 generates the input electric field waveform "E in " of the optical signal corresponding to the transmission code sequence based on the characteristics of the first communication device 110 (for example, the modulation method and transmission characteristics).

[0030] The estimation device 8a outputs the electric field waveform "E out Based on the difference between the received code sequence identified based on "E" and the transmitted code sequence transmitted from the first communication device 110, the code error rate in the second communication device 120 is estimated in real time. The electric field generator 5 generates an input electric field waveform "E" in The input electric field waveform "E" is transmitted to the electric field estimation device 6a. in By applying a filter 62 having the characteristics of the transmission line 130 to the output electric field waveform "E out We estimate that this is the case.

[0031] In the first embodiment, the selection unit 61 determines the tap coefficients of the filter according to the waveform characteristics of linear and nonlinear changes when an optical signal is transmitted through a transmission path 130 (optical fiber) with a transmission distance "L", and the optical intensity "P" of the input electric field waveform at the input end of the transmission path 130. in =<|E in | 2 Based on the ">" and the transmission distance "L", the selection unit 61 selects from the candidate tap coefficients registered in the lookup table pre-stored in the storage device 3. The selection unit 61 sets the selected tap coefficient in the filter 62.

[0032] In a paragraph preceding the estimation processing stage (lookup table generation stage), the filter generation device 2a (filter section) generates the output electric field waveform "E" at the output terminal of the transmission line 130. out To minimize the difference between the shape of the input field waveform and the shape of the output field waveform simulated using filter 62, the transmission distance "L" and the optical intensity "P" of the input field waveform are set. in For each combination of "", the filter 62 tap coefficients are generated. The filter generation device 2a registers the generated tap coefficients in the lookup table. The storage device 3 stores the lookup table (tap coefficients of filter 62) and the input electric field waveform light intensity "P in It is memorized for each combination with "[ ]".

[0033] Filter 62 is, for example, a Volterra filter (Reference 1: NP. Diamantopoulos et al., “On the Complexity Reduction of the Second-Order Volterra Nonlinear Equalizer for IM / DD Systems”, Journal of Lightwave Technology, vol. 37, no. 4, pp.1214-1224, FEBRUARY 15, 2019). Filter 62 may also be, for example, a finite-time impulse response filter (FIR filter), which is a first-order Volterra filter.

[0034] Filter 62 takes the transmission path 130 with a transmission distance "L" as the input electric field waveform "E" in The output electric field waveform "E" is affected by the linear and nonlinear waveform characteristics when "E" is transmitted. out This is output to the error rate estimation device 7a.

[0035] The electric field estimation device 6a outputs the electric field waveform "E out This is transmitted to the error rate estimation device 7a. The photoelectric conversion unit 71 converts the output electric field waveform into an electrical waveform. The photoelectric conversion unit 71 (detection unit) may be, for example, a direct detection type receiver (e.g., a single photodiode) or a coherent receiver.

[0036] The noise processing unit 72 adds a predetermined appropriate noise to the electrical signal. The predetermined appropriate noise is, for example, Gaussian noise (Reference 2: W. Freude et al., “Quality Metrics for Optical Signals: Eye Diagram, Q-factor, OSNR, EVM and BER”, Mo.B1.5, ICTON 2012). Examples of Gaussian noise include thermal noise in the receiving communication device and noise due to spontaneous emission (ASE).

[0037] The determination unit 73 identifies the received code sequence in the output electric field waveform received by the photoelectric conversion unit 71 by performing a threshold determination process on the noisy electrical signal. The error rate estimation unit 74 estimates the code error rate in the second communication device 120 based on the difference between the identified received code sequence and the transmitted code sequence transmitted from the first communication device 110.

[0038] Figure 3 shows an example of the configuration of the filter generation device 2a in the first embodiment. The filter generation device 2a comprises a delay processing unit 21, an error calculation unit 22, and a filter unit 23.

[0039] The filter generation device 2a generates the light intensity "P" of the input electric field waveform. in " and transmission distance "L" and input electric field waveform "E in " and output electric field waveform "E out Based on the dataset which is a combination of "P", the appropriate tap coefficient of the filter unit 23 is calculated as the appropriate tap coefficient of the filter 62. The filter unit 23 is calculated based on the light intensity "P in The tap coefficient for the combination of " and transmission distance "L" is set to optical intensity "P in The output electric field waveform "E" is recorded in the storage device 3 along with the transmission distance "L". The delay processing unit 21 records the output electric field waveform "E" out This output electric field waveform "E out The waveform may be one obtained in an actual experiment using coherent reception or a received power receiver (PR receiver), or it may be one calculated using high-precision waveform simulation. High-precision waveform simulation refers to, for example, a waveform simulation using the split-step Fourier method.

[0040] The delay processing unit 21 outputs the electric field waveform "E out By applying a predetermined delay to the input electric field waveform "E in " and output electric field waveform "E out The " is synchronized. Meanwhile, the filter section 23 processes the input electric field waveform "E in The output electric field waveform "E" is generated by applying a predetermined transfer function to "". outThe error calculation unit 22 outputs '.

[0041] The error calculation unit 22 calculates the output electric field waveform "E" output from the delay processing unit 21. out Output electric field waveform "E" for the shape of "" out Error in the shape of '" e=|E out -E out The error calculation unit 22 calculates the error "e". The error calculation unit 22 feeds the error "e" back to the filter unit 23. The filter unit 23 updates the tap coefficients of its filter using a predetermined algorithm so that the error "e=0". The predetermined algorithm is, for example, the Least Mean Square (LMS) algorithm.

[0042] As a result, the filter unit 23 sets tap coefficients according to the waveform characteristics of linear and nonlinear changes in the transmission line 130, and the optical intensity "P" of the input electric field waveform. in It generates for each combination of the input electric field waveform and the transmission distance "L". In this way, the filter unit 23 generates the optical intensity "P" of the input electric field waveform. in The calculation is repeatedly performed for combinations of " and transmission distance "L". The filter section 23 is used to determine the light intensity "P in The appropriate tap coefficient for each combination of " " and the transmission distance "L" is registered in the lookup table.

[0043] Figure 4 shows an example of a lookup table in the first embodiment. In a paragraph prior to the estimation processing stage, the lookup table is generated for each input electric field waveform of the optical signal transmitted from the first communication device (transmitting communication device). The lookup table contains tap coefficients generated by the filter unit 23, which are used for the optical intensity "P" of the input electric field waveform. in-n " and transmission distance "L n Each combination with "" (where "n" is the index of the combination, an integer greater than or equal to 1) is registered.

[0044] Next, we will explain an example of the operation of the estimation device 8a. Figure 5 is a flowchart showing an example of the operation of the estimation device 8a in the first embodiment. The selection unit 61 selects the input electric field waveform "E" at the input terminal of the transmission line 130. in " and its input electric field waveform "E in Light intensity of "P in " and the transmission distance "L" and the output electric field waveform "E" at the output terminal of the transmission line 130. out Based on this, the tap coefficients (lookup table) generated by the filter generation device 2a are obtained. The selection unit 61 obtains the light intensity "P" of the input electric field waveform. in Based on the transmission distance "L", a tap coefficient is selected (step S101).

[0045] The filter 62 with the selected tap coefficients sets the input electric field waveform "E" at the input terminal of the transmission line 130. in The input electric field waveform "E" is obtained from the electric field generator 5 (step S102). Filter 62 processes the input electric field waveform "E" in The simulated signal "E" of the output electric field waveform at the output terminal of the transmission line 130 to which " is input. out The error rate estimation device 7a estimates the transmission code sequence and the output electric field waveform at the input terminal (first communication device 110) of the transmission line 130, and the simulated signal "E out Based on the comparison results with the above, the error rate of the received code sequence at the output terminal of the transmission line 130 (second communication device 120) is estimated (step S104).

[0046] As described above, the filter generation device 2a generates the input electric field waveform "E" at the input terminal of the transmission line 130. in (First input electric field waveform) and the output electric field waveform "E" at the output terminal of the transmission line 130 out Based on (first output electric field waveform), the optical intensity of the input electric field waveform at the input terminal of the transmission line 130 is "P in For each combination of " and the transmission distance "L", the filter unit 23 (filter) generates tap coefficients. Here, the filter unit 23 generates tap coefficients for the output electric field waveform "E" at the output terminal of the transmission line 130. out The shape of the (first output electric field waveform) and the output electric field waveform "E" output from the filter section 23 (filter). outThe tap coefficients of the filter section 23 (filter) are generated as the tap coefficients of the filter 62 in such a way that the difference between them and the shape of the second output electric field waveform is minimized.

[0047] Furthermore, the tap coefficients selected from the generated tap coefficients are set in the filter 62. The electric field estimation device 6a (electric field estimation unit) (electric field simulation unit) uses the filter 62 and the input electric field waveform "E" generated by the electric field generator 5. in Using the (second input electric field waveform), the output electric field waveform is simulated as the signal "E out The error rate estimation device 7a (error rate estimation unit) estimates the error rate of the received code sequence at the output terminal (second communication device 120) of the transmission line 130 using a simulated signal of the output electric field waveform "E out It is estimated based on the following.

[0048] This makes it possible to improve the accuracy of estimating the code error rate in a short time based on a nonlinearly changing electric field waveform, even when the transmission distance of the optical signal is less than a predetermined distance. Furthermore, in methods based on the split-step Fourier method, the amount of computation required to estimate the code error rate increases as the transmission distance increases. In contrast, in estimation system 1a, the amount of computation required to estimate the code error rate does not increase even if the transmission distance increases. Therefore, the computation time required to estimate the code error rate can be reduced.

[0049] (Second Embodiment) In the second embodiment, the main differences from the first embodiment are that the first linear change generation unit is provided by the electric field estimation device, and the second linear change generation unit is provided by the filter generation device. The second embodiment will be explained focusing on the differences from the first embodiment.

[0050] Of the linear and nonlinear changes, the linear change can be calculated in a shorter time than the nonlinear change by solving the linear term of the nonlinear Schrödinger equation. Therefore, in the second embodiment, a linear change in the electric field waveform is generated in the first stage using a method based on the Schrödinger equation (the linear term of the nonlinear Schrödinger equation). In the second stage, the filter 62 imparts the characteristics of a nonlinear change (nonlinear degradation) to the electric field waveform from which the linear change was generated.

[0051] Figure 6 shows an example configuration of the estimation system 1b in the second embodiment. The estimation system 1b comprises a filter generation device 2b, a memory device 3, a sequence generation device 4, and an electric field generation device 5. The estimation system 1a comprises an electric field estimation device 6b and an error rate estimation device 7b as the estimation device 8b.

[0052] The electric field estimation device 6b comprises a selection unit 61, a filter 62, and a linear change generation unit 63. The error rate estimation device 7b comprises a photoelectric conversion unit 71, a noise processing unit 72, a determination unit 73, and an error rate estimation unit 74.

[0053] During the estimation processing stage, the linear change generation unit 63 (first linear change generation unit) generates the input electric field waveform "E in The linear change generator 63 generates the input electric field waveform "E" by a method based on the Schrödinger equation. in Compared to the calculation time for the nonlinear change of "", the input electric field waveform "E" transmitted through the optical fiber over a transmission distance "L" is calculated in a shorter time. in The linear change of the input electric field waveform "E" is calculated. That is, the linear change generation unit 63 solves the linear term of the nonlinear Schrödinger equation for the electric field waveform, and generates a linear change of the electric field waveform in a shorter time compared to the generation time of the nonlinear change of the electric field waveform. The linear change generation unit 63 applies only a linear change to the electric field waveform transmitted through the optical fiber, and does not need to apply a nonlinear change. The linear change generation unit 63 calculates the linear change of the input electric field waveform "E" after the linear change processing has been performed. in This is output to filter 62.

[0054] During the estimation process, the selection unit 61 sets the tap coefficients in the filter 62 based on the characteristics of the nonlinear change of the electric field waveform of the transmitted optical signal. The filter 62 processes the input electric field waveform "E" which has undergone linear change processing by the linear change generation unit 63. in A nonlinear change processing is performed on the result. As a result, filter 62 estimates a simulated signal of the output electric field waveform after the nonlinear change processing has been performed. Filter 62 outputs the simulated signal of the output electric field waveform after the nonlinear change processing has been performed to the photoelectric conversion unit 71.

[0055] Figure 7 shows an example of the configuration of the filter generation device 2b in the second embodiment. The filter generation device 2b comprises a delay processing unit 21, an error calculation unit 22, a filter unit 23, and a linear change generation unit 24.

[0056] In the paragraph preceding the estimation processing stage (the lookup table generation stage), the linear change generation unit 24 (second linear change generation unit) receives the input electric field waveform "E in The linear change generation unit 24 generates the input electric field waveform "E" by a method based on the Schrödinger equation. in Compared to the calculation time for the nonlinear change of "", the input electric field waveform "E" transmitted through the optical fiber over a transmission distance "L" is calculated in a shorter time. in The linear change of the input electric field waveform "E" is calculated. That is, the linear change generation unit 24 generates a linear change of the electric field waveform in a shorter time compared to the generation time of the nonlinear change of the electric field waveform by solving the linear term of the nonlinear Schrödinger equation for the electric field waveform. Based on the linear change generation result, the linear change generation unit 24 performs linear change processing on the electric field waveform. The linear change generation unit 24 does not need to apply a nonlinear change to the electric field waveform transmitted through the optical fiber, but only a linear change. The linear change generation unit 24 calculates the linear change of the input electric field waveform "E" after the linear change processing has been performed. in "The output electric field waveform "E out The output "''" is sent to the filter unit 23.

[0057] The filter section 23 filters the input electric field waveform "E in Output electric field waveform "E" corresponding to " outThe error calculation unit 22 receives the error "E out '" and "E" from the delay processing unit out Based on this, the error "e" is calculated. The error calculation unit 22 transmits the error "e" to the filter unit 23. The filter unit 23 minimizes the error "e" by updating the tap coefficients of the filter unit 23 using an algorithm such as least squares mean (LMS).

[0058] The filter section 23 determines the optimal tap coefficient of the filter 62 that minimizes the error "e", based on the light intensity "P" of the input electric field waveform. in The result is derived for each combination of " and the transmission distance "L".

[0059] As described above, the linear change generation unit 63 generates the input electric field waveform "E in Linear change processing is performed on the input electric field waveform "E" which has undergone linear change processing by the linear change generation unit 63. Filter 62 performs linear change processing on the input electric field waveform "E" which has undergone linear change processing by the linear change generation unit 63. in By performing a nonlinear change processing on "", the simulated signal of the output electric field waveform "E out The error rate estimation device 7b derives the simulated signal "E" of the output electric field waveform. out Based on this, the error rate of the received code sequence at the output terminal (second communication device 120) of the transmission line 130 is estimated.

[0060] This makes it possible to improve the convergence characteristics of the least-squares mean in the tap coefficient derivation process, even when the transmission distance of the optical signal is less than a predetermined distance, and to improve the accuracy of estimating the code error rate in a short time based on the nonlinearly changing electric field waveform.

[0061] (Third embodiment) In the third embodiment, the main differences from the second embodiment are that the photoelectric conversion unit is provided by the electric field estimation device, the photoelectric conversion unit is provided by the filter generation device, and the photoelectric conversion unit is not provided by the error rate estimation device. The third embodiment will be explained focusing on the differences from the second embodiment.

[0062] Figure 8 shows an example configuration of the estimation system 1c in the third embodiment. The estimation system 1c comprises a filter generation device 2c, a memory device 3, a sequence generation device 4, and an electric field generation device 5. The estimation system 1a comprises an electric field estimation device 6c and an error rate estimation device 7c as the estimation device 8c.

[0063] The electric field estimation device 6c comprises a selection unit 61, a filter 62, a linear change generation unit 63, and a photoelectric conversion unit 64. The error rate estimation device 7b comprises a noise processing unit 72, a determination unit 73, and an error rate estimation unit 74.

[0064] During the estimation process, the linear change generation unit 63 generates the input electric field waveform "E" after the linear change processing has been performed. in The input electric field waveform "E" is output to the photoelectric conversion unit 64. The photoelectric conversion unit 64 (detection unit) processes the input electric field waveform "E" after linear change processing has been performed. in The photoelectric conversion unit 64 converts the input electric field waveform "E" into an electrical signal (intensity waveform). in The electrical signal of '' is output to filter 62.

[0065] During the estimation process, the selection unit 61 sets the tap coefficients in the filter 62 based on the characteristics of the nonlinear change of the electric field waveform of the transmitted optical signal. The filter 62 processes the input electric field waveform "E" which has undergone linear change processing by the linear change generation unit 63. in A nonlinear change processing is performed on the electrical signal. The filter 62 outputs a simulated signal (electrical signal) of the output electric field waveform after the nonlinear change processing has been performed to the noise processing unit 72.

[0066] Figure 9 shows an example of the configuration of the filter generation device 2c in the third embodiment. The filter generation device 2c comprises a delay processing unit 21, an error calculation unit 22, a filter unit 23, a linear change generation unit 24, a photoelectric conversion unit 25-1, and a photoelectric conversion unit 25-2.

[0067] Before the stage of the estimation process (the stage of deriving the look-up table), the linear change generation unit 24 executes a linear change process on the electric field waveform based on the result of deriving the linear change. The linear change generation unit 24 inputs the input electric field waveform "E in " on which the linear change process has been executed to the photoelectric conversion unit 25-1.

[0068] The photoelectric conversion unit 25-1 converts the input electric field waveform "E in " on which the linear change process has been executed into an electrical signal. The photoelectric conversion unit 25-1 outputs the electrical signal of the input electric field waveform "E in " on which the linear change process has been executed to the filter unit 23. The photoelectric conversion unit 25-2 converts the output electric field waveform "E out " into an electrical signal. The photoelectric conversion unit 25-2 outputs the electrical signal of the output electric field waveform "E ` out " to the delay processing unit 21.

[0069] The delay processing unit 21 acquires the electrical signal of the output electric field waveform "E out " from the photoelectric conversion unit 25-2. When a predetermined time has elapsed since the acquisition time of the electrical signal of the output electric field waveform "E out ", the delay processing unit 21 outputs the electrical signal of the output electric field waveform "E out " to the error calculation unit 22.

[0070] The filter unit 23 acquires the electrical signal of the input electric field waveform "E in " on which the linear change process has been executed from the photoelectric conversion unit 25-1. The filter unit 23 acquires the error "e" from the error calculation unit 22. The filter unit 23 derives an appropriate tap coefficient of the filter 62 for each combination of the light intensity "P in " of the input electric field waveform and the transmission distance "L".

[0071] As described above, the linear change generation unit 63 executes a linear change process on the input electric field waveform "E in ". The photoelectric conversion unit 64 converts the input electric field waveform "E in " on which the linear change process has been executed into an electrical signal. The photoelectric conversion unit 64 inputs the input electric field waveform "E inThe electrical signal of "E" is output to filter 62. Filter 62 processes the input electric field waveform "E" after linear change processing has been performed. in By performing a nonlinear change processing on the electrical signal of "E", a simulated signal of the output electric field waveform "E out The error rate estimation device 7c derives the simulated signal "E" of the output electric field waveform. out Based on this, the error rate of the code sequence at the output terminal (second communication device 120) of the transmission line 130 is estimated.

[0072] This makes it possible to improve the accuracy of quickly estimating the code error rate based on a nonlinearly changing electric field waveform, even when the transmission distance of the optical signal is less than a predetermined distance.

[0073] (Hardware configuration) Figure 10 shows examples of the hardware configuration of the estimation system in each embodiment. The estimation system 1 illustrated in Figure 10 corresponds to estimation system 1a in the first embodiment, estimation system 1b in the second embodiment, and estimation system 1c in the third embodiment, respectively.

[0074] The estimated system 1 is implemented as software by a processor 101, such as a CPU (Central Processing Unit), executing a program stored in a storage device 103 having a non-volatile recording medium (non-temporary recording medium) and memory 102. The program may be recorded on a computer-readable recording medium. A computer-readable recording medium is a non-temporary recording medium such as 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 or solid-state drive (SSD) built into a computer system. The communication unit 104 performs predetermined communication processing.

[0075] The estimation system 1 may be implemented using hardware (accelerator) including an electronic circuit (or circuitry) such as an LSI (Large Scale Integrated Circuit), ASIC (Application Specific Integrated Circuit), PLD (Programmable Logic Device), or FPGA (Field Programmable Gate Array).

[0076] Although 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. [Industrial applicability]

[0077] This invention is applicable to optical communication systems. [Explanation of Symbols]

[0078] 1, 1a, 1b, 1c… Estimation system, 2a, 2b, 2c… Filter generation device, 3… Memory device, 4… Sequence generation device, 5… Field generation device, 6a, 6b, 6c… Field estimation device, 7a, 7b, 7c… Error rate estimation device, 8a, 8b, 8c… Estimation device, 21… Delay processing unit, 22… Error calculation unit, 23… Filter unit, 24… Linear change generation unit, 25… Photoelectric conversion unit, 61… Selection unit, 62… Filter, 63… Linear change generation unit, 64… Photoelectric conversion unit, 71… Photoelectric conversion unit, 72… Noise processing unit, 73… Judgment unit, 74… Error rate estimation unit, 100… Optical communication system, 101… Processor, 102… Memory, 103… Memory device, 104… Communication unit, 110… First communication device, 120… Second communication device, 130… Transmission line

Claims

1. An electric field estimation unit estimates a simulated signal of the output electric field waveform using a filter of tap coefficients generated for each combination of optical intensity and transmission distance of the first input electric field waveform based on the first input electric field waveform at the input end of the transmission line and the output electric field waveform at the output end of the transmission line, and the generated second input electric field waveform. An error rate estimation unit estimates the error rate of the code sequence at the output end of the transmission line based on a simulated signal of the output electric field waveform. Equipped with, The filter is an estimation device that outputs a simulated signal of the output electric field waveform, which is affected by the linear and nonlinear waveform characteristics when the second input electric field waveform is transmitted along the transmission path of the transmission distance, using the tap coefficient selected based on the light intensity of the second input electric field waveform and the transmission distance.

2. The estimation device according to claim 1, wherein the filter applies at least the nonlinear waveform distortion among the linear waveform distortion and nonlinear waveform distortion occurring in the transmission line using the tap coefficient.

3. The estimation device according to claim 1, wherein the simulated signal of the output electric field waveform is an electric field waveform or an intensity waveform.

4. A filter unit that generates a tap coefficient for each combination of light intensity and transmission distance based on a dataset which is a combination of the light intensity and transmission distance of the input electric field waveform at the input end of the transmission line and the output electric field waveform at the output end of the transmission line, The filter unit receives the input electric field waveform, or a waveform obtained by performing linear change processing in the transmission line on the input electric field waveform. The filter unit generates the tap coefficients such that the difference between the shape of the output electric field waveform and the shape of the waveform output from the filter unit is reduced. Filter generating device.

5. The filter generation apparatus according to claim 4, wherein the filter unit registers the tap coefficients in a lookup table.

6. An estimation method performed by an estimation device, A step of estimating a simulated signal of the output electric field waveform using a filter of tap coefficients generated for each combination of optical intensity and transmission distance of the first input electric field waveform based on the first input electric field waveform at the input end of the transmission line and the output electric field waveform at the output end of the transmission line, and the generated second input electric field waveform. The steps include: estimating the error rate of the code sequence at the output terminal of the transmission line based on a simulated signal of the output electric field waveform; Includes, The filter is an estimation method that outputs a simulated signal of the output electric field waveform that is affected by the linear and nonlinear waveform characteristics when the second input electric field waveform is transmitted along the transmission path of the transmission distance, using the tap coefficient selected based on the light intensity of the second input electric field waveform and the transmission distance.

7. A filter generation method performed by a filter generation device, The step includes generating a tap coefficient for each combination of light intensity and transmission distance based on a dataset which is a combination of the light intensity and transmission distance of the input electric field waveform at the input end of the transmission line and the output electric field waveform at the output end of the transmission line. In the generation step described above, the input electric field waveform, or a waveform obtained by performing linear change processing in the transmission line on the input electric field waveform, is input to the filter unit. The filter unit generates the tap coefficients such that the difference between the shape of the output electric field waveform and the shape of the waveform output from the filter unit is reduced. Filter generation method.

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