Estimation device and program

Abstract

This estimation device comprises: an interval determination unit that determines, as mutually different values, intervals between integration grids in an integration based on a first frequency and a second frequency that affect the efficiency of a nonlinear optical effect, said intervals being intervals between integration grids for self-phase modulation components of optical signals, intervals between integration grids for cross-phase modulation components of the optical signals, and intervals between integration grids for four light-wave mixing components of the optical signals; and an estimation unit that, by performing integration, estimates signal distortion generated in the optical signals due to the nonlinear optical effect.

Description

Estimation device and program

[0001] The present invention relates to an estimation device and a program.

[0002] To increase the capacity of optical communication systems, technologies to expand the bandwidth of wavelength division multiplexing (WDM) signals are being studied. Expanding the bandwidth of WDM signals transmitted using optical signals is expected to increase the total transmission capacity of optical communication systems. However, the wavelength dependency of optical fiber transmission lines (hereinafter referred to as "optical transmission lines") and optical amplifiers becomes more pronounced, complicating simulations used in the design of optical communication systems.

[0003] In order to maximize the total transmission capacity of an optical communication system, simulations that take into account the wavelength dependence of optical transmission lines and optical amplifiers are necessary. Loss and chromatic dispersion in optical transmission lines are wavelength dependent and affect signal quality.

[0004] In optical transmission lines, the power of WDM signals is transferred from short-wavelength channels to long-wavelength channels due to stimulated Raman scattering (SRS). The effective loss of an optical transmission line varies depending on the power and wavelength allocation of the WDM signals. In optical amplifiers, the wavelength dependence of gain and noise figure affects signal quality. If wavelength dependence is not taken into account, simulation results will be inaccurate, making it difficult to optimize optical communication systems.

[0005] Furthermore, the optimal operating conditions of an optical communication system also have wavelength dependency. For example, the optimal power of a transmitted WDM signal is not flat with respect to wavelength. Therefore, when considering the power transition from short wavelengths to long wavelengths due to stimulated Raman scattering, the power of the WDM signal transmitted on the short wavelength side must be stronger than the power of the WDM signal transmitted on the long wavelength side. This increases the number of simulation trials required for optimization compared to when optical signal transmission is designed for a narrow band, where wavelength dependency can be ignored. Therefore, when optical signal transmission is designed for a wide band, a simulation technique that takes wavelength dependency into account, is important, and is highly accurate and requires a short estimation time.

[0006] As a simulation technology for designing broadband optical signal transmission, a technology for estimating signal quality using a Gaussian noise (GN) model is being investigated. In the Gaussian noise model, nonlinear interference (NLI), which corresponds to signal distortion caused by nonlinear optical effects in optical signals in optical transmission paths, is treated as additive white Gaussian noise. The Gaussian noise model is a theoretical model that quantifies the power of additive white Gaussian noise.

[0007] Additionally, several estimation methods have been proposed that can quantify NLI in a shorter time than when analyzing the nonlinear wave propagation equation. These estimation methods use a Gaussian noise model. By taking into account the amplified spontaneous emission (ASE) from the optical amplifier, the transmitter characteristics, the receiver characteristics, and the NLI, the signal-to-noise ratio (SNR) of the transmitted WDM signal can be estimated for each channel. The transmission capacity of the optical communication system is determined based on the estimated SNR. Therefore, the parameters of the optical communication system can be optimized by repeatedly performing simulations while changing the parameters.

[0008] Methods for estimating NLI using a Gaussian noise model include estimation methods using numerical integration and estimation methods using a closed form in which the numerical integration is approximated. Estimation methods using numerical integration require a relatively long estimation time. In contrast, there are several estimation methods using a closed form in which the numerical integration is approximated that require a relatively short estimation time. Therefore, from the perspective of estimation time, estimation methods using a closed form in which the numerical integration is approximated are superior to estimation methods using numerical integration.

[0009] On the other hand, in the estimation method using a closed form, the closed form is derived using approximation, so the configuration of the optical communication system to which the closed form can be applied is limited. Therefore, depending on the configuration of the optical communication system to which the NLI is to be estimated, the NLI may not be estimated using the estimation method using a closed form. When the optical communication system has a configuration to which the NLI cannot be estimated by applying the closed form, an estimation method other than the estimation method using a closed form needs to be adopted.

[0010] Some estimation methods do not address low-dispersion fiber and distributed Raman amplification, and even when they exist, the assumptions and approximations used to derive them must be well understood by the user in order for the method to be properly employed.

[0011] However, the derivation of the mathematical formulas used in the estimation methods is difficult, and it is unrealistic for anyone other than specialized researchers and engineers to derive the formulas. In contrast, numerical integration has a wide range of applicability. Therefore, estimation methods using numerical integration can be used under a variety of conditions and system configurations.

[0012] Since estimation methods using numerical integration require a long estimation time, the requirements for the NLI estimation time may be strict depending on the application. Therefore, if the estimation time can be shortened, it will be possible to expand the scope of application of estimation methods using numerical integration.

[0013] The power spectral density of NLI "G ＮＬＩ " is expressed as equation (1) using equation (2) by an estimation method using numerical integration (see Non-Patent Document 1).

[0014]

[0015]

[0016] Here, "G ＮＬＩ " represents the power spectral density of nonlinear interference (NLI), which corresponds to signal distortion due to nonlinear optical effects. ＴＸ " represents the power spectral density of the WDM signal input to the optical transmission line. １ ", "f ２ " and "f" each represent the frequency of a WDM signal transmitted using an optical signal. １ " is called the "first frequency." ２ " is referred to as the "second frequency." Note that by changing the frequency "f" in equations (1) and (2), the WDM channel used to estimate the signal distortion (NLI) is changed.

[0017] "LF" represents the efficiency of the nonlinear optical effect (Link function) that reflects the characteristics of the optical transmission line. "γ" represents the nonlinear optical coefficient. "β ２ " represents the second-order dispersion. "β ３ " represents third-order dispersion. "z" represents the distance from the input end of the optical transmission line in the longitudinal direction of the optical transmission line. "ρ" represents the normalized power profile.

[0018] Equations (1) and (2) are basic equations for estimating the NLI. Equation (1) includes two numerical integrals in the frequency direction. Equation (2) includes one numerical integral in the longitudinal direction of the optical transmission line.

[0019] A method for approximating the integral in the longitudinal direction of the optical transmission line in equation (2) is disclosed in Non-Patent Document 2 for the purpose of shortening the estimation time. In the method disclosed in Non-Patent Document 2, the frequency dependency of the efficiency "LF" of the nonlinear optical effect is estimated. In addition, １ ” and the second frequency “f ２ " is used to estimate the NLI.

[0020] M. Cantono et al., "On the Interplay of Nonlinear Interference Generation With Stimulated Raman Scattering for QoT Estimation," in Journal of Lightwave Technology, vol. 36, no. 15, pp. 3131-3141, August 1, 2018, doi: 10.1109 / JLT.2018.2814840. M. Ranjbarzefreh, P. Poggiolini, "Characterization of the Link Function in GN and EGN Methods for Nonlinearity Assessment of Ultrawideband Coherent Fiber Optic Communication Systems with Raman Effect," arXiv:2009.12687 [eess.SP], [online], October 2020, [Retrieved May 24, 2024], Internet<URL: https: / / doi.org / 10.48550 / arXiv.2009.12687>

[0021] When numerical integration is performed by the estimation method disclosed in Non-Patent Document 2, the definition of the interval of the integration grid is important for shortening the estimation time. If the interval of the integration grid is wide, the NLI estimation time can be shortened, but the NLI estimation error increases. If the interval of the integration grid is narrow, the NLI estimation time becomes long. Thus, there is a problem in that it is not possible to shorten the time required for estimation while suppressing a decrease in the estimation accuracy of the signal distortion (NLI).

[0022] In view of the above circumstances, an object of the present invention is to provide an estimation device and a program that can reduce the time required for estimation while suppressing a decrease in the accuracy of signal distortion estimation.

[0023] One aspect of the present invention is an estimation device comprising: a spacing determination unit that determines integration grid spacings for integration based on a first frequency and a second frequency that affect the efficiency of a nonlinear optical effect, the integration grid spacing for a self-phase modulation component of an optical signal, the integration grid spacing for a cross-phase modulation component of the optical signal, and the integration grid spacing for a four-wave mixing component of the optical signal to be different values; and an estimation unit that estimates signal distortion caused in the optical signal by the nonlinear optical effect by performing the integration.

[0024] One aspect of the present invention is a program for causing a computer to execute the steps of: determining integration grid spacings in an integration based on a first frequency and a second frequency that affect the efficiency of a nonlinear optical effect, the integration grid spacing for a self-phase modulation component of an optical signal, the integration grid spacing for a cross-phase modulation component of the optical signal, and the integration grid spacing for a four-wave mixing component of the optical signal to be different values; and estimating signal distortion caused in the optical signal by the nonlinear optical effect by performing the integration.

[0025] According to the present invention, it is possible to reduce the time required for estimation while suppressing a decrease in the accuracy of signal distortion estimation.

[0026] 1 is a diagram illustrating an example of the configuration of an estimation device according to a first embodiment. １ ” and the second frequency “f ２ 1 is a diagram showing an example of the relationship between the first frequency "f" and a 1 THz WDM signal when the frequency "f" is 0 THz in the first embodiment. １ ” and the second frequency “f ２ 1 is a diagram illustrating an example of the exponential dependence of the first frequency "f" when the frequency "f" is -0.3 THz in the first embodiment. １ ” and the second frequency “f ２ 1 is a diagram illustrating an example of the exponential dependence of the first frequency "f" when the frequency "f" is 0.2 THz in the first embodiment. １ ” and the second frequency “f ２1 is a diagram illustrating an example of the exponential dependence of the first frequency "f" when the frequency "f" is 0 THz in the first embodiment. １ ” and the second frequency “f ２ 10 is a diagram illustrating an example of the exponential dependence of "|LF|" on "|LF|" and the SPM component, the XPM component, and the FWM component in the first embodiment. ２ 1 is a diagram showing a first example of an integration grid for an SPM component by a three-dimensional plot of "|LF|" and its overhead view (two-dimensional plot). FIG. 2 is a diagram showing an example of NLI (SPM) power spectral density with respect to the number of integration grids in the first embodiment. ２ 10 is a diagram showing a second example of an integration grid for the SPM component by a three-dimensional plot of "|LF|" and its overhead view (two-dimensional plot). ２ 10 is a diagram showing an example of an integration grid for the XPM component by a three-dimensional plot of "|LF|" and its overhead view (two-dimensional plot). ２ 1 is a diagram showing an example of an integration grid for an FWM component by using a three-dimensional plot example of " and its overhead view (two-dimensional plot). FIG. 2 is a flowchart showing an example of the operation of an estimation device in a first embodiment. FIG. 3 is a diagram showing an example of the configuration of an estimation device in a second embodiment. FIG. 4 is a diagram showing an example of the configuration of an optical transmission system in a second embodiment. FIG. 5 is a diagram showing an example of the configuration of an optical network in a third embodiment.

[0027]

[0023] Embodiments of the present invention will be described in detail with reference to the drawings. (First Embodiment) Fig. 1 is a diagram showing an example of the configuration of an estimation device 1 in the first embodiment. The estimation device 1 (analysis device) is a device that estimates the power spectral density of nonlinear interference (NLI), which corresponds to signal distortion of an optical signal transmitted through an optical transmission line.

[0028] The estimation device 1 includes a storage device 11, a memory 12, a communication unit 13, and an execution unit 14. The communication unit 13 includes an acquisition unit 131 and an output unit 132. The execution unit 14 includes an interval determination unit 141 and an estimation unit 142.

[0029] The device of the present invention can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network.

[0030] The estimation device 1 is realized as software by a processor such as a CPU (Central Processing Unit) executing a program stored in a storage device 11 having a non-volatile recording medium (non-transitory recording medium) and a memory 12. The program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), and CD-ROMs (Compact Disc Read Only Memory), and non-transitory recording media such as storage devices built into a computer system, such as hard disks or solid state drives (SSDs). The communication unit 13 executes predetermined communication processing.

[0031] The estimation device 1 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).

[0032] The storage device 11 stores a program to be executed by the execution unit 14. When the estimation device 1 is started up, the program is loaded from the storage device 11 into the memory 12.

[0033] The acquisition unit 131 acquires system data for estimating the power spectral density of the NLI from each functional unit (not shown) of an optical communication system such as an optical transmission system having an optical transmission path and an optical network.

[0034] The output unit 132 outputs the estimated power spectral density of the NLI to an external device (not shown). The output unit 132 may output the integration grid spacing to the external device (not shown). The output unit 132 may transmit control signals to each functional unit (not shown) of the optical communication system.

[0035] The interval determination unit 141 determines the interval of the integration grid in the estimation process of the power spectral density of the NLI. Here, the interval determination unit 141 determines the interval of the integration grid for the self-phase modulation component of the optical signal, the interval of the integration grid for the cross-phase modulation component of the optical signal, and the interval of the integration grid for the four-wave mixing component of the optical signal to be different values ​​from one another. The interval of the integration grid is determined based on the first frequency "f" that affects the efficiency of the nonlinear optical effect. １ ” and the second frequency “f ２ is the spacing of the integration grid in the integration based on

[0036] The interval determination unit 141 determines the first frequency "f １ ” and the second frequency “f ２ For both of the above, the interval of the integration grid for the self-phase modulation component is made narrower than the interval of the integration grid for the four-wave mixing component.

[0037] The interval determination unit 141 determines the first frequency "f １ ” and the second frequency “f ２ ", the interval of the integration grid for the cross-phase modulation component is made narrower than the interval of the integration grid for the four-wave mixing component, and the first frequency "f １ ” and the second frequency “f ２ For the other of "," the interval of the integration grid for the cross-phase modulation component is made wider than the interval of the integration grid for the self-phase modulation component.

[0038] The interval determination unit 141 determines the first frequency "f １ ” and the second frequency “f ２ For both of the above, the interval of the integration grid for the four-wave mixing component is made wider than the interval of the integration grid for the self-phase modulation component.

[0039] The estimation unit 142 estimates the power spectral density of the NLI, which corresponds to the signal distortion caused in the optical signal by the nonlinear optical effect, by performing integration such as double integration as shown in equations (1) and (2) based on the determined integration grid spacing.

[0040] Next, the frequency dependency of the efficiency "LF" of the nonlinear optical effect, which reflects the characteristics of the optical transmission line, will be described.

[0041] The frequency dependence of the efficiency "LF" of the nonlinear optical effect is caused by a part corresponding to the phase fluctuation of the optical signal and a part corresponding to the power change of the optical signal. The part corresponding to the phase fluctuation of the optical signal is expressed by the exponential function "exp()" in equation (2). The part corresponding to the power change of the optical signal is expressed by the square root "√" in equation (2).

[0042] Regarding the part corresponding to the power change of the optical signal (the √ part), it is assumed that the power of each optical signal is the same (constant) in the same WDM channel, and that the power of each optical signal is different in different WDM channels.

[0043] Furthermore, the frequency dependence of the portion corresponding to the phase fluctuation of the optical signal is higher than the frequency dependence of the portion corresponding to the power change of the optical signal (the √ portion). Therefore, in the portion corresponding to the phase fluctuation of the optical signal, the phase fluctuation in each WDM channel must also be taken into consideration. In the following, the frequency dependence of the exponential function in the portion corresponding to the phase fluctuation of the optical signal is also taken into consideration when determining the spacing of the integration grid.

[0044] FIG. 2 shows the frequency “f” and the first frequency “f １ ” and the second frequency “f ２ 1 is a diagram showing an example of the relationship between the first frequency "f" in equation (1) and a 1 THz WDM signal. １ ”, second frequency “f ２ 2, the band range of the WDM signal ranges from -0.5 THz to 0.5 THz, for example.

[0045] Varying the variable frequency "f" changes the WDM channel used to estimate the signal distortion (NLI). That is, by varying the frequency "f", the first frequency "f １ ” and the second frequency “f ２ The distribution of the exponential function changes on the plane spanned by ".

[0046] FIG. 3 shows the first frequency “f” when the frequency “f” is 0 THz in the first embodiment. １ ” and the second frequency “f ２ 3 shows an example of the frequency dependence of the exponential function on the frequency "f". That is, in FIG. 3, a first example of the frequency dependence of the exponential function in Equation (2) is shown using normalized contours. When the frequency "f" is 0 THz, the peak of the exponential function is in the central region (f １ = f = 0, f ２ = f = 0).

[0047] First frequency “f １ ” axis area and the second frequency “f ２ The areas of the first frequency "f" and the second frequency "f" are areas where the value of the exponential function is large. １ The further away from the axis region of the second frequency "f", the smaller the value of the exponential function. ２ The further away from the axis region, the smaller the value of the exponential function.

[0048] FIG. 4 shows the first frequency "f" when the frequency "f" is -0.3 THz in the first embodiment. １ ” and the second frequency “f ２ 4 shows an example of the exponential dependence on ". That is, FIG. 4 shows a second example of the frequency dependence of the exponential function in equation (2) using normalized contours. When the frequency "f" is -0.3 THz, the peak of the exponential function appears in the lower left region of FIG. 4.

[0049] FIG. 5 shows the first frequency "f" when the frequency "f" is 0.2 THz in the first embodiment. １ ” and the second frequency “f ２5 shows an example of the exponential dependence on ". That is, FIG. 5 shows a third example of the frequency dependence of the exponential function in equation (2) using normalized contours. When the frequency "f" is 0.2 THz, the peak of the exponential function appears in the upper right region of FIG. 5.

[0050] In this way, the value of the frequency "f" is changed, so that the first frequency "f １ ” and the second frequency “f ２ The position of the peak of the exponential function moves along the diagonal line to the right on the plane spanned by "f". Here, the tendency of the distribution of the exponential function is maintained. １ =f" and "f ２ The relationship "=f" is maintained, and the position of the peak of the exponential function moves.

[0051] Even if the value of the frequency "f" is changed, "f １ = f ２ The exponential function reaches its maximum at "f = f" １ =f" or "f ２ The value of the exponential function increases on the axis of "f = f". Also, the value of the frequency "f" is changed, and "f １ =f" and "f ２ The further away from each axis of "=f", the smaller the value of the exponential function.

[0052] "f １ =f" and "f ２ The closer you get to the "f = f" axis, the closer the intervals between the contour lines are, so the greater the change in the value of the exponential function relative to frequency. １ =f" and "f ２ The further away from each axis of "=f", the wider the interval between the contour lines, so the change in the value of the exponential function with respect to frequency is smaller.

[0053] Below, “f １ = f ２ NLI corresponding to "f = f" is called "self-phase modulation (SPM)" or "self-channel interference (SCI)." １ =f" or "f ２NLI corresponding to "f = f" is called "cross-phase modulation," "XPM (cross-phase modulation)," or "XCI (cross-channel interference)." １ = f ２ =f” and “f １ =f” and “f ２ NLI that does not correspond to either "f = f" or "four-wave mixing (FWM)" or "multi-channel interference (MCI)."

[0054] FIG. 6 shows the first frequency “f” when the frequency “f” is 0 THz in the first embodiment. １ ” and the second frequency “f ２ 1 is a diagram showing an example of an exponential dependence on the first frequency "f" and the SPM, XPM and FWM components. １ ” and the second frequency “f ２ On the plane spanned by ", the shape of the integral domain of the NLI component becomes a hexagon as shown in FIG. 6. This is because "f" in Eq. １ +f ２ -f" is the first frequency "f １ ” and the second frequency “f ２ This is because it corresponds to the direction of the right diagonal in the plane spanned by ". When the bandwidth of each WDM channel is taken into consideration, the shape of the integral region of the NLI component becomes a rhombus rather than a square.

[0055] The NLI components of the SPM component, the XPM component, and the FWM component have the following characteristics (A1), (A2), and (A3) in terms of the frequency dependence of the exponential function values.

[0056] (A1) First frequency “f １ ” and the second frequency “f ２ The exponential dependence of the SPM component on both σ and σ is strong, i.e., the contours in the region of the SPM component are closely spaced.

[0057] (A2) First frequency “f １ ” and the second frequency “f ２The exponential dependence of the XPM component on one of the first frequencies "f １ ” axis and the second frequency “f ２ ' axis, the contours in the region of the XPM component are closely spaced.

[0058] (A3) First frequency “f １ ” and the second frequency “f ２ The exponential dependence of the FWM component on both σ and σ is small, i.e. the contour spacing in the region of the FWM component is wide.

[0059] To perform accurate numerical integration in a short time, the interval of the integration grid needs to be narrow in regions where the interval of the contour lines is narrow, and the interval of the integration grid needs to be wide in regions where the interval of the contour lines is wide. Therefore, the interval of the integration grid is determined for each of the SPM component, the XPM component, and the FWM component.

[0060] Next, a method for determining the interval of the integration grid will be explained for each of the SPM component, the XPM component, and the FWM component.

[0061] <Method of Determining Integration Grid Spacing for SPM Component (First Example)> FIG. 7 shows the method of determining the spacing of the integration grid for the SPM component in the first embodiment. ２ 1 shows a first example of an integration grid for SPM components, with a three-dimensional plot of "LF" and its overhead view (two-dimensional plot). The power of each optical signal in the same WDM channel is assumed to be the same (constant), and the efficiency of the nonlinear optical effect, "LF," is estimated. The bandwidth of the WDM channel is, for example, 100 GHz.

[0062] First frequency “f １ The intervals of the integration grid in the axis direction of the second frequency "f" are equal. ２ The intervals of the integration grid in the axial direction of the first frequency "f １ " axis and the second frequency "f ２ " axis and "|LF| ２" changes significantly. Therefore, the interval determination unit 141 increases the number of integration grids until the vicinity of each axis can be expressed sufficiently accurately. In other words, the interval determination unit 141 narrows the intervals of the integration grids until the vicinity of each axis can be expressed sufficiently accurately.

[0063] The efficiency of the nonlinear optical effect for the SPM component, "LF", is １ ” axis direction and the second frequency “f ２ ” axis direction. Therefore, the first frequency “f １ the number of integration grids in the axis direction of the second frequency "f ２ The number of integration grids in the "axis direction" and "axis direction" may be the same.

[0064] FIG. 8 is a diagram showing an example of the NLI (SPM) power spectral density versus the number of integration grids in the first embodiment. １ ” axis from −50 to 50 GHz, and the second frequency “f ２ The power spectral density [dBm / Hz] of the NLI is plotted for the range from -50 to 50 GHz on the " axis and for varying the number of integration grids.

[0065] The larger the number of integration grids, the smaller the value of "|LF|" in Equation (1). ２ Since the frequency dependence of " can be accurately represented, the power spectral density of the estimated NLI decreases. As a method for optimizing the number of integration grids (grid spacing), the spacing determination unit 141 reduces the number of integration grids within a range in which the power spectral density of the NLI does not change depending on the number of integration grids. In FIG. 8 , the range in which the power spectral density of the NLI does not change is a range in which the number of integration grids is from 140 to 180. Therefore, the spacing determination unit 141 determines the number of integration grids to be a predetermined number between 140 and 160. This enables the estimation unit 142 to accurately estimate the signal distortion (power spectral density of the NLI) caused in the optical signal by the nonlinear optical effect in a short time.

[0066] The chromatic dispersion value is large in WDM channels on the longer wavelength side. The larger the chromatic dispersion value, the greater the change in the efficiency of the nonlinear optical effect (LF) with respect to frequency. Therefore, the spacing determiner 141 narrows the spacing of the integration grid for WDM channels on the longer wavelength side. For this reason, the spacing determiner 141 determines the spacing of the integration grid for the SPM component for each WDM channel as shown in (B1), (B2), or (B3) below.

[0067] (B1) The interval determination unit 141 determines the interval of the integration grid for the WDM channel with the longest wavelength. The interval determination unit 141 and the estimation unit 142 apply the interval of the integration grid determined for the WDM channel with the longest wavelength to the estimation of the SPM components in all other WDM channels.

[0068] (B2) The interval determination unit 141 determines the intervals of the integration grids for the WDM channel with the shortest wavelength, the WDM channel with the central wavelength, and the WDM channel with the longest wavelength. The interval determination unit 141 and the estimation unit 142 also apply the determined intervals of the integration grids to the estimation of the SPM components in the WDM channel near the shortest wavelength, the WDM channel near the central wavelength, and the WDM channel near the longest wavelength, respectively.

[0069] (B3) The interval determination unit 141 determines the intervals of the integration grids for the WDM channel with the shortest wavelength, the WDM channel with the central wavelength, and the WDM channel with the longest wavelength. The interval determination unit 141 determines the intervals of the integration grids for each WDM channel by interpolation processing on the intervals of the integration grids so that the intervals of the integration grids are different from each other.

[0070] <Method of Determining Integration Grid Spacing for SPM Component (Second Example)> FIG. 9 shows the method of determining the spacing of the integration grid for the SPM component in the first embodiment. ２ 10 shows a second example of an integration grid for SPM components, with a three-dimensional plot of " " and its overhead view (two-dimensional plot).

[0071] The interval determination unit 141 determines the first frequency "f １ The second frequency "f = 0" ２ ” is the axis of symmetry, and the first frequency “f１ The interval determining unit 141 determines the interval of the integration grid on the axis of the second frequency "f ２ The first frequency "f = 0" １ ” is the axis of symmetry, and the second frequency “f ２ Determine the spacing of the integration grid on the " axis to be logarithmically spaced.

[0072] In this way, the intervals of the integration grids are narrow in the range where the change in efficiency "LF" is large. On the other hand, the intervals of the integration grids are wide in the range where the change in efficiency "LF" is small. This reduces the amount of calculation compared to when the number of integration grids is determined at equal intervals, and therefore makes it possible to shorten the estimation time.

[0073] As a method for optimizing the number of integration grids (grid spacing), the spacing determiner 141 may reduce the number of integration grids within a range in which the power spectral density of the NLI does not change depending on the number of integration grids, as illustrated in Fig. 8. Furthermore, the spacing determiner 141 may determine the spacing of the integration grid for the SPM component for each WDM channel as illustrated in (B1), (B2), or (B3) above.

[0074] <Method of Determining Integration Grid Spacing for XPM Component> FIG. 10 shows the method of determining the spacing of the integration grid for the XPM component in the first embodiment. ２ 1 is a diagram showing an example of an integration grid for the XPM component, with a three-dimensional plot of the XPM component and its overhead view (two-dimensional plot). The change in the efficiency of the nonlinear optical effect "LF" for the XPM component is １ ” axis and the second frequency “f ２ " axis and one of them is larger.

[0075] Therefore, the interval determination unit 141 determines the interval of the integration grid to be axially symmetric logarithmic intervals in the direction of the axis along which the change in the efficiency "LF" is large. That is, the interval determination unit 141 narrows the interval of the integration grid in the vicinity of the axis along which the change in the efficiency "LF" is large. In FIG. 10, the interval determination unit 141 determines the interval of the integration grid to be axially symmetric logarithmic intervals in the direction of the axis along which the change in the efficiency "LF" is large. １ The spacing of the integration grid in the direction of the axis of the first frequency "f １ The second frequency "f = 0"２ The logarithmic spacing is determined to be symmetric about the axis of ".

[0076] Furthermore, the interval determination unit 141 determines the intervals of the integration grids in the direction of an axis where the change in efficiency "LF" is small to be equal intervals. That is, the interval determination unit 141 widens the intervals of the integration grids in the direction of an axis where the change in efficiency "LF" is small. This reduces the total number of integration grids.

[0077] As a method for optimizing the number of integration grids (grid spacing), the spacing determination unit 141 determines the first frequency “f ” within a range in which the power spectrum density of the NLI does not change depending on the number of integration grids, as illustrated in FIG. １ Alternatively, the number of integration grids on the axis of the second frequency "f" may be reduced. In addition, the interval determination unit 141 may determine the number of integration grids on the axis of the second frequency "f" within a range in which the power spectrum density of the NLI does not change depending on the number of integration grids, as illustrated in FIG. ２ The number of integration grids on the axis of " may be reduced. That is, the interval determination unit 141 reduces the number of integration grids within a range in which the power spectral density of the NLI is not overestimated.

[0078] The spacing determination unit 141 determines the spacing of the integration grid for the XPM component for each WDM channel as shown in (C1), (C2), or (C3) below.

[0079] (C1) The spacing determiner 141 estimates the power transition of the XPM component from a predetermined number of WDM channels adjacent to the WDM channel with the longest wavelength to the WDM channel with the longest wavelength. The spacing determiner 141 determines the integration grid spacing for the WDM channel with the shortest wavelength to be equal spacing and logarithmic spacing. As a method for optimizing the number of integration grids (grid spacing), the spacing determiner 141 may reduce the number of integration grids to the extent that the power spectral density of the NLI does not change depending on the number of integration grids, as illustrated in FIG. 8. The spacing determiner 141 and the estimation unit 142 also apply the determined integration grid spacing to the estimation of the XPM component in all other WDM channels.

[0080] (C2) The spacing determiner 141 estimates the power transition of the XPM component from a predetermined number of WDM channels adjacent to the WDM channel with the shortest wavelength to the WDM channel with the shortest wavelength. The spacing determiner 141 estimates the power transition of the XPM component from a predetermined number of WDM channels adjacent to the WDM channel with the central wavelength to the WDM channel with the central wavelength. The spacing determiner 141 estimates the power transition of the XPM component from a predetermined number of WDM channels adjacent to the WDM channel with the longest wavelength to the WDM channel with the longest wavelength. The spacing determiner 141 determines the intervals of the integration grids for the WDM channel with the shortest wavelength, the WDM channel with the central wavelength, and the WDM channel with the longest wavelength to be equal intervals and logarithmic intervals. Here, as a method of optimizing the number of integration grids (grid intervals), the spacing determiner 141 may reduce the number of integration grids within a range in which the power spectral density of the NLI does not change depending on the number of integration grids, as illustrated in FIG. 8 . The spacing determination unit 141 and the estimation unit 142 also apply the determined integration grid spacing to the estimation of the XPM components in the WDM channels near the shortest wavelength, the WDM channels near the central wavelength, and the WDM channels near the longest wavelength.

[0081] (C3) The spacing determiner 141 estimates the power transition of the XPM component from a predetermined number of WDM channels adjacent to the WDM channel with the shortest wavelength to the WDM channel with the shortest wavelength. The spacing determiner 141 estimates the power transition of the XPM component from a predetermined number of WDM channels adjacent to the WDM channel with the central wavelength to the WDM channel with the central wavelength. The spacing determiner 141 estimates the power transition of the XPM component from a predetermined number of WDM channels adjacent to the WDM channel with the longest wavelength to the WDM channel with the longest wavelength. The spacing determiner 141 determines the intervals of the integration grids for the WDM channel with the shortest wavelength, the WDM channel with the central wavelength, and the WDM channel with the longest wavelength to be equal intervals and logarithmic intervals. Here, as a method of optimizing the number of integration grids (grid intervals), the spacing determiner 141 may reduce the number of integration grids within a range in which the power spectral density of the NLI does not change depending on the number of integration grids, as illustrated in FIG. 8 . The interval determining unit 141 determines the interval of the integration grid for each WDM channel by interpolation processing on the interval of the integration grid so that the intervals of the integration grid are different from each other.

[0082] <Method of Determining Integration Grid Spacing for FWM Component> FIG. 11 shows the method of determining the spacing of the integration grid for the FWM component, which is the same as the method of determining the spacing of the integration grid for the FWM component. ２ 1 is a diagram showing an example of an integration grid for the FWM component by a three-dimensional plot of the first frequency "f" and a perspective view (two-dimensional plot) of the first frequency "f" and the second frequency "f" of the FWM component. １ ” axis and the second frequency “f ２ " is small relative to both the axis and the inside.

[0083] Therefore, the interval determination unit 141 determines the first frequency "f １ ” axis and the second frequency “f ２ The integration grid is spaced equally for both the first frequency "f" and the second frequency "f" axes. １ the number of integration grids on the axis of the second frequency "f ２ The number of integration grids on the " axis may be the same.

[0084] As a method for optimizing the number of integration grids (grid spacing), the spacing determination unit 141 may reduce the number of integration grids within a range in which the power spectral density of the NLI does not change depending on the number of integration grids, as illustrated in Fig. 8. In other words, the spacing determination unit 141 reduces the number of integration grids within a range in which the power spectral density of the NLI is not overestimated.

[0085] The spacing determination unit 141 determines the spacing of the integration grid for the FWM component for each WDM channel as shown in (D1), (D2), or (D3) below.

[0086] (D1) The spacing determiner 141 estimates the power transition of the FWM component from a predetermined number of WDM channels adjacent to the WDM channel with the longest wavelength to the WDM channel with the longest wavelength. The spacing determiner 141 determines equal integration grid spacing for the WDM channel with the shortest wavelength. As a method for optimizing the number of integration grids (grid spacing), the spacing determiner 141 may reduce the number of integration grids to a range in which the power spectral density of the NLI does not change depending on the number of integration grids, as illustrated in FIG. 8. The spacing determiner 141 and the estimation unit 142 also apply the determined integration grid spacing to the estimation of the FWM component in all other WDM channels.

[0087] (D2) The spacing determiner 141 estimates the power transition of the FWM component from a predetermined number of WDM channels adjacent to the WDM channel with the shortest wavelength to the WDM channel with the shortest wavelength. The spacing determiner 141 estimates the power transition of the FWM component from a predetermined number of WDM channels adjacent to the WDM channel with the central wavelength to the WDM channel with the central wavelength. The spacing determiner 141 estimates the power transition of the FWM component from a predetermined number of WDM channels adjacent to the WDM channel with the longest wavelength to the WDM channel with the longest wavelength. The spacing determiner 141 determines equal intervals between the integration grids for the WDM channel with the shortest wavelength, the WDM channel with the central wavelength, and the WDM channel with the longest wavelength. Here, as a method of optimizing the number of integration grids (grid interval), the spacing determiner 141 may reduce the number of integration grids within a range in which the power spectral density of the NLI does not change depending on the number of integration grids, as illustrated in FIG. 8 . The spacing determination unit 141 and the estimation unit 142 also apply these determined integration grid spacings to the estimation of FWM components in the WDM channels near the shortest wavelength, the WDM channels near the central wavelength, and the WDM channels near the longest wavelength.

[0088] (D3) The spacing determiner 141 estimates the power transition of the FWM component from a predetermined number of WDM channels adjacent to the WDM channel with the shortest wavelength to the WDM channel with the shortest wavelength. The spacing determiner 141 estimates the power transition of the FWM component from a predetermined number of WDM channels adjacent to the WDM channel with the central wavelength to the WDM channel with the central wavelength. The spacing determiner 141 estimates the power transition of the FWM component from a predetermined number of WDM channels adjacent to the WDM channel with the longest wavelength to the WDM channel with the longest wavelength. The spacing determiner 141 determines equal intervals between the integration grids for the WDM channel with the shortest wavelength, the WDM channel with the central wavelength, and the WDM channel with the longest wavelength. Here, as a method of optimizing the number of integration grids (grid interval), the spacing determiner 141 may reduce the number of integration grids within a range in which the power spectral density of the NLI does not change depending on the number of integration grids, as illustrated in FIG. 8 . The interval determining unit 141 determines the interval of the integration grid for each WDM channel by interpolation processing on the interval of the integration grid so that the intervals of the integration grid are different from each other.

[0089] Note that the above determination methods for the integration grid spacing for the SPM component, the XPM component, and the FWM component may be combined so as to reduce the total number of integration grids.Furthermore, the above determination method for the integration grid spacing may be combined with any other determination method so as to further reduce the total number of integration grids.

[0090] Next, an example of the operation of the estimation device 1 will be described. Fig. 12 is a flowchart showing an example of the operation of the estimation device 1 in the first embodiment. The interval determination unit 141 determines the interval of an integration grid for a self-phase modulation component (SPM component) of the optical signal, the interval of an integration grid for a cross-phase modulation component (XPM component) of the optical signal, and the interval of an integration grid for a four-wave mixing component (FWM component) of the optical signal to be different from one another (step S101). The estimation unit 142 estimates signal distortion caused in the optical signal by nonlinear optical effects by performing integration such as double integration (step S102).

[0091] As described above, the interval determiner 141 determines the interval of the integration grid for the self-phase modulation component of the optical signal, the interval of the integration grid for the cross-phase modulation component of the optical signal, and the interval of the integration grid for the four-wave mixing component of the optical signal to be different values. The estimator 142 estimates the signal distortion caused in the optical signal by the nonlinear optical effect by performing numerical integration.

[0092] In this way, the total number of integration grids is reduced by determining the intervals of the integration grids in consideration of the frequency dependency of the efficiency "LF" of the nonlinear optical effect that reflects the characteristics of the optical transmission line. This makes it possible to reduce the time required for estimation while suppressing a decrease in the accuracy of signal distortion estimation.

[0093] The time required for estimation can be reduced by several tens to one hundredth compared to when the integration grid intervals for the SPM, XPM, and FWM components are determined to be sufficiently narrow so that the NLI power spectral density is not overestimated. Furthermore, based on an integral-type Gaussian noise model that can be applied to various configurations of optical communication systems, it is possible to reduce the time required for estimation while suppressing a decrease in the accuracy of signal distortion estimation.

[0094] Second Embodiment The second embodiment is mainly different from the first embodiment in that parameters used in the optical transmission system are determined. The second embodiment will be described focusing on the differences from the first embodiment.

[0095] 13 is a diagram showing an example of the configuration of the estimation device 1 in the second embodiment. The execution unit 14 includes an interval determination unit 141, an estimation unit 142, a parameter determination unit 143, and a control unit 144.

[0096] 14 is a diagram showing an example of the configuration of an optical transmission system 2 in the second embodiment. The optical transmission system 2 includes a sending unit 21, M (M is an integer of 2 or more) transmission units 22, and a receiving unit 23. The sending unit 21 includes N (N is an integer of 2 or more) transmitters 211 and a multiplexer 212. The transmission unit 22 includes an optical fiber 221, one or more pumps 222, and an optical amplifier 223. The receiving unit 23 includes a demultiplexer 231 and N receivers 232.

[0097] The transmitter 211 outputs the channel signals to the multiplexer 212. The multiplexer 212 (WDM MUX) generates a WDM signal by multiplexing N channel signals. The multiplexer 212 outputs the WDM signal to an optical fiber 221 using an optical signal. The pump 222 is a distributed Raman amplifier. The pump 222 generates pump light based on a control signal related to the Raman pump light. The pump 222 amplifies the power of the WDM signal using the pump light. The optical amplifier 223 is a lumped optical amplifier. The demultiplexer 231 (WDM DEMUX) demultiplexes the WDM signal into N channel signals. The receiver 232 obtains the channel signals from the demultiplexer 231.

[0098] The interval determination unit 141 determines the interval of an integration grid in the process of estimating the power spectral density of the NLI. The estimation unit 142 acquires system parameters necessary for estimating signal quality based on signal distortion from the optical transmission system 2. The estimation unit 142 estimates the signal-to-noise ratio (SNR) as the signal quality for each WDM channel based on the acquired system parameters. Here, the estimation unit 142 may estimate the SNR based not only on signal distortion (NLI) as one of the signal quality penalties but also on various other signal quality penalties. The various signal quality penalties include, for example, the spontaneous emission noise of the optical amplifier 223, the characteristics of the transmitter 211, and the characteristics of the receiver 232. There is a correlation between the SNR and the transmission capacity of the optical transmission system 2, and the SNR and the transmission capacity change depending on the system parameters.

[0099] The parameter determination unit 143 determines the system parameters based on the signal-to-noise ratio and, for example, a predetermined conditional expression. The system parameters are parameters used in the optical transmission system 2 and are not limited to specific parameters.

[0100] The system parameters may be, for example, power parameters, wavelength parameters, and modulation format parameters of each WDM channel. The system parameters may be, for example, loss parameters of the optical transmission path, chromatic dispersion parameters, nonlinear coefficients, and Raman gain coefficients. The system parameters may be, for example, wavelength parameters of the pump light for Raman amplification in the pump 222, and power parameters of the pump light for Raman amplification in the pump 222. The system parameters may be, for example, gain parameters of the optical amplifier 223, and noise figure parameters of the optical amplifier 223. The system parameters may be, for example, characteristic parameters of the transmitter 211, and characteristic parameters of the receiver 232.

[0101] The parameter determination unit 143 optimizes the variable system parameters to maximize the transmission capacity of the optical transmission system 2. The variable system parameters include, for example, a power parameter of each WDM channel, a wavelength parameter, a gain parameter of the optical amplifier 223, a noise figure parameter of the optical amplifier 223, a wavelength parameter of the pump light for Raman amplification in the pump 222, and a power parameter of the pump light for Raman amplification in the pump 222. The control unit 144 controls each functional unit of the optical transmission system 2 by feeding back the determined system parameters to the optical transmission system 2.

[0102] As described above, the parameter determining unit 143 determines the system parameters of the optical transmission system 2 based on the signal-to-noise ratio and, for example, a predetermined conditional expression. The control unit 144 feeds back the determined system parameters to the optical transmission system 2 via the output unit 132.

[0103] This makes it possible to suppress a decrease in the accuracy of signal distortion estimation, shorten the time required for estimation, and maximize the total transmission capacity of the optical transmission system 2.

[0104] (Third Embodiment) In the third embodiment, the main difference from the second embodiment is that parameters used in an optical network in which a plurality of nodes are connected to each other are determined. In the third embodiment, the differences from the second embodiment will be mainly described.

[0105] 15 is a diagram showing an example of the configuration of an optical network 3 in the third embodiment. The optical network 3 includes a plurality of nodes 31. Combinations of the plurality of nodes 31 are connected by optical paths. The nodes 31 have the functions of transmitting optical signals, receiving optical signals, amplifying optical signals, gain equalizing optical signals, multiplexing optical signals, demultiplexing optical signals, and switching optical paths (directions) through which optical signals pass.

[0106] The interval determination unit 141 determines the interval of the integration grid in the process of estimating the power spectral density of the NLI. The estimation unit 142 acquires system parameters required for estimating the signal quality based on the signal distortion from each of one or more nodes 31 in the optical network 3.

[0107] The parameter determination unit 143 determines system parameters for switching the optical path through which the optical signal passes. The parameter determination unit 143 may determine each of the system parameters exemplified in the second embodiment. The control unit 144 feeds back the determined system parameters to each node 31 via the output unit 132. In this way, the control unit 144 controls each node 31 of the optical network 3.

[0108] As described above, the parameter determination unit 143 determines the system parameters of the optical network 3 based on the signal-to-noise ratio and, for example, a predetermined conditional expression. The control unit 144 feeds back the determined system parameters to each node 31 of the optical network 3 via the output unit 132.

[0109] This makes it possible to suppress a decrease in the accuracy of signal distortion estimation, shorten the time required for estimation, and maximize the total transmission capacity of the optical network 3.

[0110] Although an embodiment of the present invention has been described in detail above 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.

[0111] The present invention is applicable to optical communication systems.

[0112] 1...Estimation device, 2...Optical transmission system, 3...Optical network, 11...Storage device, 12...Memory, 13...Communication unit, 14...Execution unit, 21...Transmitting unit, 22...Transmitting unit, 23...Receiving unit, 31...Node, 131...Acquisition unit, 132...Output unit, 141...Spacing determination unit, 142...Estimation unit, 143...Parameter determination unit, 144...Control unit, 211...Transmitter, 212...Multiplexer, 221...Optical fiber, 222...Pump, 223...Optical amplifier, 231...Demultiplexer, 232...Receiver

Claims

1. An estimation device comprising: a spacing determination unit that determines the integration grid spacing for an integration based on a first frequency and a second frequency that affect the efficiency of a nonlinear optical effect, the integration grid spacing for a self-phase modulation component of an optical signal, the integration grid spacing for a cross-phase modulation component of the optical signal, and the integration grid spacing for a four-wave mixing component of the optical signal to be different values; and an estimation unit that estimates signal distortion caused in the optical signal by the nonlinear optical effect by performing the integration.

2. The estimation device according to claim 1, wherein the interval determination unit: for both the first frequency and the second frequency, makes the interval of the integration grid for the self-phase modulation component narrower than the interval of the integration grid for the four-wave mixing component; for one of the first frequency and the second frequency, makes the interval of the integration grid for the cross-phase modulation component narrower than the interval of the integration grid for the four-wave mixing component; for the other of the first frequency and the second frequency, makes the interval of the integration grid for the cross-phase modulation component wider than the interval of the integration grid for the self-phase modulation component; and for both the first frequency and the second frequency, makes the interval of the integration grid for the four-wave mixing component wider than the interval of the integration grid for the self-phase modulation component.

3. A program for causing a computer to execute the following steps: determining the intervals of integration grids in integration based on a first frequency and a second frequency that affect the efficiency of the nonlinear optical effect, wherein the intervals of the integration grid for the self-phase modulation component of the optical signal, the integration grid for the cross-phase modulation component of the optical signal, and the integration grid for the four-wave mixing component of the optical signal are different from one another; and estimating the signal distortion caused in the optical signal by the nonlinear optical effect by performing the integration.

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