Optical transmission medium measurement method, optical transmission medium measurement apparatus, optical transmission medium measurement program, and storage medium

Abstract

In the optical transmission medium measurement method, the optical transmission medium is subjected to a plurality of light inputs having different characteristics and equal center wavelengths, and measured values of intensity spectra of a plurality of light outputs from the optical transmission medium corresponding to the plurality of light inputs, respectively, are obtained. The nonlinear coefficient and the wavelength dispersion value are varied and an error between a calculated value of an intensity spectrum calculated based on an intensity spectrum and a phase spectrum of each of the plurality of light inputs, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium, and a measured value of an intensity spectrum of each of the plurality of light outputs is calculated. Then, a difference between the plurality of light inputs due to the difference in characteristics based on a relationship between the nonlinear coefficient and the wavelength dispersion value and the error is determined. Thus, a measurement method of obtaining the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium with high accuracy is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical transmission medium measurement method, an optical transmission medium measurement apparatus, an optical transmission medium measurement program, and a storage medium. BACKGROUND

[0002] In Patent Literature 1, a technique relating to a method of estimating a distribution of optical physical constants in an optical transmission medium is disclosed. The method includes a step of acquiring power spectra and phase spectra of a plurality of input light signals having mutually different intensities, a step of measuring power spectra of output light signals outputted after the input light signals propagate in the optical transmission medium, for each intensity of the input light signals, and a step of estimating respective optical physical constants of the optical transmission medium, based on a result of propagation simulation based on a model in which each of the input light signals propagates in the optical transmission medium.

[0003] In the above method, the respective optical physical constants are estimated by, in the estimating step, performing a search for each of the optical physical constants using an evaluation function that evaluates a difference between the measured power spectrum of the output light signal and a power spectrum of the output light signal obtained as a result of the propagation simulation.

[0004] In Non-Patent Literature 1, a method of measuring a nonlinear optical constant of an optical fiber using a spectral change of nonlinearity generated in the optical fiber is described. Further, in Non-Patent Literature 2, a method of measuring a wavelength dispersion value of an optical fiber using a spectral change of nonlinearity generated in the optical fiber is described.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: International Publication No. 2014 / 112020

[0008] NON-PATENT LITERATURE

[0009] Non-Patent Literature 1: R. H. Stolen and Chinlon Lin, “Self-phase-modulation in silica optical fibers”, Physical Review A, Vol. 17 No. 4, pp. 1448-1453, 1978

[0010] Non-Patent Literature 2: Julius Vengelis, Vygandas Jarutis, and Valdas Sirutkaitis, "Estimation of photonic crystal fiber dispersion by means of supercontinuum generation", Optics Letters, Vol. 42 No. 9, pp. 1844-1847, 2017 SUMMARY

[0011] PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] When an optical system is configured using an optical transmission medium, it is sometimes desirable to accurately obtain a nonlinear coefficient and a wavelength dispersion value, which are parameters of the optical transmission medium. For example, when an optical pulse having an extremely short time width of several picoseconds (hereinafter referred to as an ultrashort optical pulse) is controlled to output a time waveform, sometimes, a desired accuracy of the time waveform is not obtained due to a control error and distortion of the time waveform of the optical pulse output from an optical pulse generating device, and distortion of the time waveform of the optical pulse caused by an optical system disposed at a stage subsequent to the optical pulse generating device.

[0013] In such a case, it is considered to feed back the optical pulse generating device in a manner that the time waveform of the optical pulse is measured with high accuracy to approach a desired time waveform. In order to accurately measure the time waveform of the optical pulse, it is important to accurately obtain a nonlinear coefficient and a wavelength dispersion value of an optical transmission medium used in measurement of the time waveform.

[0014] An object of the embodiments is to provide an optical transmission medium measurement method, an optical transmission medium measurement device, an optical transmission medium measurement program, and a storage medium, which can accurately obtain a nonlinear coefficient and a wavelength dispersion value of an optical transmission medium.

[0015] TECHNICAL MEANS FOR SOLVING PROBLEMS

[0016] The embodiment is an optical transmission medium measurement method. The optical transmission medium measurement method is a method of measuring a nonlinear coefficient and a wavelength dispersion value of an optical transmission medium, including: a measured value acquisition step of acquiring measured values of intensity spectra of multiple light outputs from the optical transmission medium corresponding to multiple light inputs to the optical transmission medium having different characteristics and equal center wavelengths, respectively; an error calculation step of changing the nonlinear coefficient and the wavelength dispersion value and calculating errors of estimated values of the intensity spectra calculated based on intensity spectra and phase spectra of the multiple light inputs, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium, and the intensity spectra of the multiple light outputs, respectively, from the intensity spectra of the multiple light outputs and the measured values; and a parameter determination step of determining the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium based on differences between the multiple light inputs due to differences in the characteristics, from a relationship between the nonlinear coefficient and the wavelength dispersion value and the errors.

[0017] The embodiment is an optical transmission medium measurement device. The optical transmission medium measurement device is a device of measuring a nonlinear coefficient and a wavelength dispersion value of an optical transmission medium, including: a light source section of performing multiple light inputs to the optical transmission medium having different characteristics and equal center wavelengths; a spectrum acquisition section of acquiring measured values of intensity spectra of multiple light outputs from the optical transmission medium corresponding to the multiple light inputs, respectively; and an arithmetic section of changing the nonlinear coefficient and the wavelength dispersion value and calculating errors of estimated values of the intensity spectra calculated based on intensity spectra and phase spectra of the multiple light inputs, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium, and the intensity spectra of the multiple light outputs, respectively, from the intensity spectra of the multiple light outputs and the measured values, determining the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium based on differences between the multiple light inputs due to differences in the characteristics, from a relationship between the nonlinear coefficient and the wavelength dispersion value and the errors.

[0018] The embodiment is an optical transmission medium measurement program. The optical transmission medium measurement program is a program of measuring a nonlinear coefficient and a wavelength dispersion value of an optical transmission medium, which causes a computer to function as a calculation section and a determination section, in which the calculation section changes the nonlinear coefficient and the wavelength dispersion value and calculates errors of estimated values of intensity spectra calculated based on intensity spectra and phase spectra of multiple light inputs having different characteristics and equal center wavelengths, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium, and intensity spectra of multiple light outputs from the optical transmission medium corresponding to the multiple light inputs, respectively, from the intensity spectra of the multiple light outputs and measured values of the intensity spectra of the multiple light outputs, and the determination section determines the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium based on differences between the multiple light inputs due to differences in the characteristics, from a relationship between the nonlinear coefficient and the wavelength dispersion value and the errors.

[0019] The embodiment is a storage medium. The storage medium is a computer-readable medium in which the above-described optical transmission medium measurement program is stored.

[0020] By measuring the intensity spectrum of the light output resulting from the input of light to the optical transmission medium, and inferring the intensity spectrum of the output light from the theoretical relationship of the characteristics of the input light, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium, the nonlinear coefficient and the wavelength dispersion value are theoretically obtained, for which the error of the inferred value with respect to the measured value is minimized.

[0021] However, according to the present inventor's insight, in practice, it is difficult to uniquely determine the nonlinear coefficient and the wavelength dispersion value using this method due to measurement error or rounding error of the computer, etc. However, when the error of the inferred value with respect to the measured value is near the minimum value, there is an effective correlation between the nonlinear coefficient and the wavelength dispersion value. Moreover, this correlation varies in correspondence with the characteristics of the light input (intensity spectrum, phase spectrum, etc.).

[0022] Therefore, in the above-described measurement method, measurement device, and measurement program, the optical transmission medium is subjected to a plurality of light inputs having different characteristics with the center wavelengths equal to each other, the nonlinear coefficient and the wavelength dispersion value are varied, and the error of the inferred value with respect to the measured value of the intensity spectrum of the resulting plurality of light outputs is calculated. Then, based on the difference between the plurality of light inputs in the relationship of the nonlinear coefficient and the wavelength dispersion value and the error, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium are determined. According to such a measurement method, measurement device, and measurement program, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium can be obtained with high precision.

[0023] Effects of the Invention

[0024] According to the embodiments, it is possible to provide a measurement method of an optical transmission medium, a measurement device of an optical transmission medium, a measurement program of an optical transmission medium, and a storage medium, which can obtain the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium with high precision. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a block diagram schematically showing the structure of a measurement device 1A of an optical transmission medium according to an embodiment.

[0026] Figure 2 is a diagram showing a hardware structure example in the case where the parameter calculation section 6 is constituted by a computer.

[0027] Figure 3 is a flowchart showing a measurement method according to an embodiment.

[0028] Figure 4 (a) of FIG. 10 is a graph showing one example of a test pulse, and (b) is a graph showing a measured value of the intensity spectrum of the light output corresponding to the input of the test pulse having the characteristics shown in (a). The curve G11 shows the intensity spectrum of the test pulse, and the curve G12 shows the phase spectrum of the test pulse.

[0029] Figure 5 (a) is a graph showing one example of a test pulse, (b) is a graph showing measured values of an intensity spectrum of an optical output corresponding to an optical input of the test pulse shown in (a), the curve G21 shows an intensity spectrum of the test pulse, and the curve G22 shows a phase spectrum of the test pulse.

[0030] Figure 6 is a graph showing one example of a relationship between a nonlinear coefficient and a wavelength dispersion value and an intensity spectrum estimation error with respect to two test pulses, (a) shows a relationship between a nonlinear coefficient and a wavelength dispersion value and an intensity spectrum estimation error with respect to a first generated test pulse, and (b) shows a relationship between a nonlinear coefficient and a wavelength dispersion value and an intensity spectrum estimation error with respect to a second generated test pulse.

[0031] Figure 7 is a graph in which a value of a nonlinear coefficient at which an intensity spectrum estimation error becomes the smallest among wavelength dispersion values is extracted, and in which a horizontal axis is a wavelength dispersion value and a vertical axis is a nonlinear coefficient.

[0032] Figure 8 is a graph showing (a) wavelength dependency of a nonlinear coefficient and (b) wavelength dependency of a wavelength dispersion value in a certain optical transmission medium 4.

[0033] Figure 9 is a flowchart showing a measurement method according to a modification example. DETAILED DESCRIPTION

[0034] Hereinafter, embodiments of an optical transmission medium measurement method, an optical transmission medium measurement apparatus, an optical transmission medium measurement program, and a storage medium will be described in detail with reference to the drawings. In the description of the drawings, the same elements are marked by the same reference numerals, and repetitive description is omitted. The present application is not limited to these examples.

[0035] Figure 1 is a block diagram schematically showing a structure of an optical transmission medium measurement apparatus (hereinafter, simply referred to as a measurement apparatus) 1A according to an embodiment. The measurement apparatus 1A is an apparatus that measures a nonlinear coefficient and a wavelength dispersion value of an optical transmission medium 4 that is a nonlinear initiating medium. When light is transmitted in a nonlinear initiating medium, a nonlinear spectrum change is induced. The spectrum change is a change depending on parameters of the nonlinear initiating medium, particularly, a nonlinear coefficient and a wavelength dispersion value.

[0036] Therefore, the measuring device 1A sets hypothetical values ​​for the nonlinear coefficient and wavelength dispersion, and estimates the changed intensity spectrum through theoretical calculations, calculating the error between the estimated and measured values ​​of the changed intensity spectrum. The measuring device 1A repeats this calculation with varying hypothetical values ​​for the nonlinear coefficient and wavelength dispersion. Then, by changing the characteristics of the light (intensity spectrum, phase spectrum, etc.), the above calculation is performed again. Based on the relationship between the error between the estimated and measured values ​​of the intensity spectrum obtained in this way and the nonlinear coefficient and wavelength dispersion, the measuring device 1A determines the nonlinear coefficient and wavelength dispersion.

[0037] The optical transmission medium 4, which is the object of measurement, is composed of a medium that induces nonlinear spectral changes, such as an optical waveguide. In one embodiment, the optical transmission medium 4 is a highly nonlinear optical fiber or a narrow-line waveguide formed on a substrate such as a silicon substrate. The narrow-line waveguide is, for example, a channel waveguide, a slab waveguide, or a ribbed waveguide. The constituent material of the optical transmission medium 4 is, for example, SiO2, Si, Si3N4, etc.

[0038] The optical transmission medium 4 is used, for example, to measure the time waveform of ultrashort optical pulses with a time width of several femtoseconds to hundreds of femtoseconds. Specifically, at one end of the optical transmission medium 4, where parameters such as the nonlinear coefficient and wavelength dispersion are known, a pulsed light source, the object of measurement, is coupled via an intensity modulator, and at the other end of the optical transmission medium 4, a beam splitter is coupled. Then, the light intensity is varied, and an optical pulse is input into the optical transmission medium 4, and the intensity spectrum of the optical pulse output from the optical transmission medium 4 is measured.

[0039] Because the shape of the intensity spectrum changes depending on the time waveform, the time waveform of the optical pulse can be determined by analyzing the optical fiber transmission simulation. The measuring device 1A of this embodiment is, for example, a device for preparing for such a measurement, and for accurately determining the nonlinear coefficient and wavelength dispersion value of the optical transmission medium 4.

[0040] like Figure 1 As shown, the measuring device 1A of this embodiment includes a light source unit 2, a spectrum acquisition unit 5, and a parameter calculation unit 6. The output terminal 2a of the light source unit 2 is optically coupled to one end 4a of the light transmission medium 4. The light source unit 2 performs multiple light inputs to the light transmission medium 4. The light used in the light input is, for example, a light pulse with a time width of 10 femtoseconds or more and 100 picoseconds or less.

[0041] The light source unit 2 ensures that the center wavelengths of the multiple light inputs are equal to each other, and that the characteristics of the multiple light inputs are different from each other. Here, the characteristics of the light inputs refer to, for example, at least one selected from intensity spectrum, phase spectrum, and light pulse energy. Light pulse energy refers to the value obtained by integrating the intensity (power) of a light pulse over time from the rise to the fall of the light pulse.

[0042] The light source section 2 of the present embodiment is configured to include a light source 21 and a light property control section 22. The light source 21 outputs light (e.g., light pulses) having a certain property with a center wavelength equal to each other a plurality of times. The light source 21 is, for example, an ultrashort pulse laser light source such as a femtosecond laser light source. The input end 22a of the light property control section 22 is optically coupled with the output end 21a of the light source 21, and the output end 22b of the light property control section 22 is optically coupled with one end 4a of the light transmission medium 4.

[0043] The light property control section 22 changes the property of the light output from the light source 21 each time and inputs the changed light from the output end 22b to the one end 4a of the light transmission medium 4. The light property control section 22, for example, changes at least one selected from the intensity spectrum, the phase spectrum, and the pulse energy of the light output from the light source 21 to an arbitrary value (or shape).

[0044] The light property control section 22 can be configured, for example, by an optical system including a pulse shaper, a wavelength filter, an optical fiber, an ND (Neutral Density) filter, a wavelength plate, and a polarizing plate, an acousto-optic element (AO modulator), an AO tunable filter (AOTF), an aperture structure (aperture), or a chopper. Alternatively, the light property control section 22 can be configured by combining at least two of them.

[0045] The input end 5a of the spectrum acquisition section 5 is optically coupled with the other end 4b of the light transmission medium 4. The spectrum acquisition section 5 receives the light output from the other end 4b of the light transmission medium 4 at the input end 5a in correspondence with the plurality of light inputs to the light transmission medium 4. Then, the spectrum acquisition section 5 acquires measured values of the intensity spectra of the plurality of light outputs from the light transmission medium 4 corresponding to the plurality of light inputs, respectively.

[0046] The spectrum acquisition section 5 includes, for example, a spectrometer that spectrally splits the output light from the light transmission medium 4 and a light detector that detects the intensity of the spectrally split output light for each wavelength. Alternatively, the spectrum acquisition section 5 can be a spectrometer or a Fourier transform type spectrophotometer. The signal output end 5b of the spectrum acquisition section 5 is electrically connected with the signal input end 6a of the parameter calculation section 6. The spectrum acquisition section 5 outputs data on the measured values of the intensity spectra obtained from the signal output end 5b to the parameter calculation section 6.

[0047] The parameter calculation section 6 receives data on the measured values of the intensity spectra of the plurality of light outputs from the spectrum acquisition section 5. The parameter calculation section 6 is an example of the operation section of the present embodiment. The parameter calculation section 6 determines the nonlinear coefficient and the wavelength dispersion value of the light transmission medium 4 on the basis of the measured values of the intensity spectra of the plurality of light outputs.

[0048] In one example, the parameter calculation section 6 is constituted by a computer including a CPU (Central Processing Unit) and a memory or a programmable integrated circuit such as an FPGA (Field Programmable Gate Array). In these computers or FPGAs, a light transmission medium measurement program (hereinafter, simply referred to as a measurement program) for implementing the process of the parameter calculation section 6 described below is written and stored.

[0049] The measurement program can be stored in the computer or FPGA at the time of shipment of the measurement apparatus 1A, can be acquired via a communication line after shipment and stored in the computer or FPGA, or can be recorded in a storage medium readable by a computer and stored in the computer or FPGA. The storage medium is arbitrary, and examples include a floppy disk, a CD-ROM, a DVD-ROM, a BD-ROM, a USB memory, and the like.

[0050] Figure 2 is a diagram schematically showing a hardware configuration example in the case where the parameter calculation section 6 is constituted by a computer. As shown in Figure 2 the parameter calculation section 6 can be constituted as a general computer physically including a processor (CPU) 61, a main storage device such as a ROM 62 and a RAM 63, an input device 64 such as a keyboard, a mouse, and a touch panel, an output device 65 such as a display (including a touch panel), a communication module 66 such as a network card for exchanging data with other apparatuses, a secondary storage device 67 such as a hard disk, and the like.

[0051] The processor 61 of the computer can implement the function of the parameter calculation section 6 by the measurement program. In other words, the measurement program causes the processor 61 of the computer to function as the parameter calculation section 6. The measurement program is stored in a storage device (storage medium) inside or outside the computer, such as the secondary storage device 67, for example. The storage device can also be a non-transitory storage medium. As the storage medium, a floppy disk, a CD, a DVD, and the like, a storage medium such as a ROM, a semiconductor memory, a cloud server, and the like can be exemplified.

[0052] Here, a light transmission medium measurement method (hereinafter, simply referred to as a measurement method) related to the present embodiment, in which the processing content of the parameter calculation section 6 (measurement program), that is, the determination of the nonlinear coefficient and the wavelength dispersion value, is described in detail.

[0053] Figure 3 is a flowchart showing the measurement method of the present embodiment. In addition, this measurement method is a method in the case where the phase spectrum of the light output from the light source section 2 is unknown and the calculation is directly performed. Furthermore, by using this measurement method, the nonlinear coefficient and the wavelength dispersion value are obtained by performing light input twice to the light transmission medium 4.

[0054] As shown in (a) of FIG. 10, first, as a step Sll, a light (test pulse) is generated at the light source section 2. Specifically, a light pulse is output from the light source 21, and the light characteristic control section 22 controls the characteristic (one or both of the phase spectrum and the intensity spectrum) of the light pulse, whereby the test pulse is generated at the light characteristic control section 22. Figure 3

[0055] Figure 4 (a) of FIG. 10, the intensity spectrum of the test pulse has a shape symmetrical about a center wavelength (900 nm in this example), and has a unimodal shape having a peak at the center wavelength. Further, the phase spectrum of the test pulse has a flat shape where the phase is substantially constant within the wavelength range Λ1 of the intensity spectrum. Such a light pulse is generally called a Transform Limited (TL) pulse. Figure 4

[0056] Further, the wavelength range of the intensity spectrum refers to a range where the value of the intensity is, for example, 1% or more with respect to the peak intensity. In this example, the width of the wavelength range Λ1 of the intensity spectrum is, for example, 25 nm. Outside the wavelength range Λ1 of the intensity spectrum, the phase value is a value virtually assumed in calculation and hardly contributes to the characteristic of the test pulse, and thus can have an arbitrary value.

[0057] Next, as a step S12, the intensity spectrum of the generated test pulse is measured. Specifically, the test pulse output from the light source section 2 is input to the spectrum acquisition section 5 without passing through the optical transmission medium 4, and the measured value of the intensity spectrum of the test pulse is acquired at the spectrum acquisition section 5. The data on the measured value of the intensity spectrum is provided to the parameter calculation section 6 as the intensity spectrum data on the light input.

[0058] Next, as a step S13, the light input of the test pulse is performed to the optical transmission medium 4, and the measured value of the intensity spectrum of the light output from the optical transmission medium 4 corresponding to the light input is acquired (measured value acquisition step).

[0059] Figure 4 (b) of FIG. 10 is a graph showing the intensity spectrum of the light output from the optical transmission medium 4 corresponding to the light input of the test pulse. As shown in (b) of FIG. 10, the intensity spectrum of the light output from the optical transmission medium 4 has a shape symmetrical about the center wavelength (900 nm in this example), and has a unimodal shape having a peak at the center wavelength. Further, the phase spectrum of the light output from the optical transmission medium 4 has a flat shape where the phase is substantially constant within the wavelength range Λ1 of the intensity spectrum. Figure 4 ​​a graph of the measured value of the intensity spectrum of the corresponding light output of the test pulse of the light input of the characteristics shown in (a). Specifically, the test pulse output from the light source section 2 is input to one end 4a of the optical transmission medium 4, and the measured value of the intensity spectrum of the test pulse transmitted within the optical transmission medium 4 and output from the other end 4b of the optical transmission medium 4 is acquired at the spectrum acquisition section 5. This measured value is provided to the parameter calculation section 6 as the measured value data of the intensity spectrum of the light output.

[0060] In addition, in this step S13, the test pulse can also be input to the optical transmission medium 4 multiple times while changing the light intensity of the test pulse, and the measured values of the intensity spectrum are acquired respectively.

[0061] Next, the parameter calculation section 6 (measurement program) calculates the estimated value of the intensity spectrum based on the theoretical relationship between the intensity spectrum and the phase spectrum of the light input, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium 4, and the intensity spectrum of the light output. At this time, the nonlinear coefficient and the wavelength dispersion value are individually changed and a plurality of estimated values are calculated. Then, the error (hereinafter, referred to as the intensity spectrum estimation error) of the plurality of estimated values from the measured value is calculated (error calculation step, calculation section in the measurement program).

[0062] Specifically, as the step S14, the parameter calculation section 6 sets the assumed value of the parameter (nonlinear coefficient and wavelength dispersion value) of the optical transmission medium 4. Also, as the step S15, the parameter calculation section 6 sets the assumed spectrum of the phase spectrum of the test pulse output from the light source section 2 (before input to the optical transmission medium 4).

[0063] Then, as the step S16, the parameter calculation section 6 estimates the intensity spectrum of the light output from the assumed value of the nonlinear coefficient and the wavelength dispersion value, and the assumed spectrum of the phase spectrum, according to the theoretical relationship. The theoretical relationship refers to the relationship shown in the following mathematical expression, for example.

[0064] [Math. 1]

[0065]

[0066] where A denotes the amplitude of the electric field, z denotes the transmission distance, β n denotes the n-th dispersion, a denotes the loss coefficient, γ denotes the nonlinear coefficient, ω0 denotes each frequency, and t denotes time. The result of Fourier transform of A corresponds to the phase spectrum and the intensity spectrum. Since A can be estimated from the above mathematical expression, the intensity spectrum obtained by this Fourier transform can also be estimated.

[0067] Next, as in step S17, the parameter calculation unit 6 compares the estimated value of the intensity spectrum of the light output with the measured value of the intensity spectrum of the light output. The parameter calculation unit 6 changes the hypothetical spectrum and performs the above steps S15 to S17 until the intensity spectrum estimation error does not change (convergence) (step S18: No), and takes the hypothetical spectrum when the intensity spectrum estimation error does not change (becomes minimal) as the phase spectrum of the light input (step S18: Yes).

[0068] Furthermore, the parameter calculation unit 6 uses the estimated value of the intensity spectrum at this time as the estimated value of the intensity spectrum corresponding to the nonlinear coefficient and wavelength dispersion value set in step S14, and records the estimated error of the intensity spectrum at this time as the estimated error of the intensity spectrum corresponding to the nonlinear coefficient and wavelength dispersion value set in step S14 (step S19).

[0069] Afterwards, the parameter calculation unit 6 returns to step S14 (step S22) and repeats steps S15 to S19 after changing the hypothetical values ​​of the parameters (nonlinear coefficient and wavelength dispersion value) of the optical transmission medium 4. In this way, the parameter calculation unit 6 changes the hypothetical values ​​of the parameters (nonlinear coefficient and wavelength dispersion value) of the optical transmission medium 4 and calculates the estimated value of the intensity spectrum and the intensity spectrum estimation error corresponding to each hypothetical value.

[0070] Then, returning to step S11, a test pulse is generated again in the light source unit 2. This test pulse is a light pulse with the same center wavelength as the previously generated test pulse but a different intensity spectrum.

[0071] Figure 5 Figure (a) is a graph representing an example of a test pulse, where curve G21 represents the intensity spectrum of the test pulse, and curve G22 represents the phase spectrum of the test pulse. For example... Figure 5 As shown in (a), the intensity spectrum of this test pulse is similar to that of the previous test pulse (refer to...). Figure 4 Like (a), it has a shape that is symmetrical about the center wavelength (900 nm in this example) and has a unimodal shape with a peak of intensity at the center wavelength.

[0072] Among them, the width of the wavelength range Λ2 of the intensity spectrum, i.e., the intensity spectrum width, is smaller than that of the previously tested pulse ( Figure 4 (a)). In this example, the width of the wavelength range Λ2 is, for example, 7 nm. Furthermore, the phase spectrum of the test pulse has a flat shape with approximately a fixed phase within the wavelength range of the intensity spectrum.

[0073] After generating such a test pulse, repeat steps S12 to S19 above. Figure 5 (b) indicates that it is related to having Figure 5The graph in (a) shows the measured intensity spectrum of the light output corresponding to the light input of the test pulse. After the above processing, the relationship between the nonlinear coefficient and wavelength dispersion value and the intensity spectrum estimation error of two test pulses with the same center wavelength but different characteristics can be obtained.

[0074] Figure 6 This is a graph illustrating an example of the relationship between the nonlinear coefficients and wavelength dispersion values ​​of two test pulses and the intensity spectrum estimation error. Figure 6 (a) represents the relationship between the nonlinear coefficient and wavelength dispersion of the initially generated test pulse and the intensity spectrum estimation error. Figure 6 (b) represents the relationship between the nonlinear coefficient and wavelength dispersion of the second generated test pulse and the intensity spectrum estimation error.

[0075] In these graphs, the vertical axis represents the wavelength dispersion (unit: ps). 2 The horizontal axis represents the nonlinear coefficient (unit: / W / km), and the intensity spectrum estimation error is indicated by the shade of color. The darker the color, the smaller the intensity spectrum estimation error. In the figure, the areas B1 and B2 enclosed by dashed lines represent areas where the error is close to the minimum value (in other words, areas where the intensity spectrum estimation error is less than a certain threshold).

[0076] Referring to the ranges of regions B1 and B2, it can be seen that the combination of the nonlinear coefficient that minimizes the intensity spectrum estimation error has a linear relationship with the wavelength dispersion value. Therefore, comparing these graphs, when the characteristics of the two test pulses (in this example, the intensity spectrum width) differ, differences arise in the relationship between the nonlinear coefficient and the wavelength dispersion value and the intensity spectrum estimation error (specifically, the proportional coefficient in the linear relationship, etc.). In other words, this difference in the relationship between the nonlinear coefficient and the wavelength dispersion value and the intensity spectrum estimation error stems from the differences in the characteristics of the initial and second optical inputs.

[0077] Figure 7 It is a curve plotted with the nonlinear coefficient that minimizes the intensity spectrum estimation error from the dispersion values ​​of each wavelength, with the transverse axis representing the long dispersion value and the vertical axis representing the nonlinear coefficient. Figure 7 In the diagram, multiple plots of the rhombus P1 correspond to... Figure 6 (a), multiple circular plots P2 correspond to Figure 6 (b)

[0078] Further, the straight line G1 is an approximate straight line based on the plurality of plots P1, and the straight line G2 is an approximate straight line based on the plurality of plots P2. That is, the straight line G1 represents a linear relationship of the nonlinear coefficient and the wavelength dispersion value which minimizes the intensity spectrum estimation error corresponding to the first light input. Further, the straight line G2 represents a linear relationship of the nonlinear coefficient and the wavelength dispersion value which minimizes the error corresponding to the second light input.

[0079] The parameter calculation section 6 (measurement program) determines the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium 4 based on a difference between the first and second light inputs with respect to the nonlinear coefficient and the wavelength dispersion value and the intensity spectrum estimation error of such a relationship (parameter determination step, determination section in the measurement program) in step S20. Figure 3 Specifically, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium 4 are determined from the intersection point Q of the two approximate straight lines G1, G2.

[0080] In this example, the approximate straight line G1 is represented by y = 5.7072x + 106.04, and the approximate straight line G2 is represented by y = 0.3751x + 104.54 when the nonlinear coefficient is x and the wavelength dispersion value is y. Therefore, the intersection point thereof is calculated as (x, y) = (101.2, -0.84), and the nonlinear coefficient and the wavelength dispersion value are determined as 101.2 [ / W / km], -0.84 [ps 2 / km], respectively.

[0081] Further, in the above example, the nonlinear coefficient and the wavelength dispersion value are determined by the second light input to the optical transmission medium 4, but the nonlinear coefficient and the wavelength dispersion value can also be determined by three or more light inputs. In this case, a situation in which the intersection points of the straight lines cannot be uniquely obtained, which is different from that shown in Figure 7 (b), and (c) of FIG. 6, but for example, an average of the plurality of intersection points can be made the nonlinear coefficient and the wavelength dispersion value, or the like, and the optimal nonlinear coefficient and wavelength dispersion value can be determined based on the plurality of intersection points.

[0082] Further, in the above example, the intensity spectrum is estimated (step S16) after the measured intensity spectrum (step S12), but the order thereof can also be reversed. That is, the intensity spectrum can also be measured after the intensity spectrum is estimated.

[0083] Further, with reference to Figure 6 (b) and Figure 7The approximate straight line G2, in the combination of the nonlinear coefficient and the wavelength dispersion value that minimizes the intensity spectrum estimation error, has a roughly constant nonlinear coefficient. Thus, the intensity spectrum estimation error becomes less sensitive to changes in the wavelength dispersion value, depending on the intensity spectrum width of the light input. Therefore, by varying the intensity spectrum width of the light input and determining the relationship between the nonlinear coefficient, the wavelength dispersion value, and the intensity spectrum estimation error, it is possible to determine that the wavelength dispersion value represents a constant intensity spectrum width.

[0084] In addition, in the above example, the nonlinear coefficient is approximately constant when the intensity spectral width is 7 nm, but the magnitude of the intensity spectral width, which is assumed to have an approximately constant nonlinear coefficient, varies depending on the various parameters of the optical transmission medium 4.

[0085] According to the measurement method described above, the nonlinear coefficient and wavelength dispersion of the optical transmission medium 4 at a specified wavelength (900 nm in the example above) can be measured. Then, by varying this specified wavelength (i.e., by making...) Figure 4 (a) and Figure 5 The intensity spectrum shown in (a) shows the change in the center wavelength. The measurement was repeated, and the nonlinear coefficient and wavelength dispersion of the optical transmission medium 4 were also measured.

[0086] Figure 8 This is a graph showing the wavelength dependence of (a) the nonlinear coefficient and (b) the wavelength dispersion value in a certain optical transmission medium 4. Figure 8 In the diagram, the horizontal axis of (a) and (b) represents wavelength (unit: nm), the vertical axis of (a) represents the nonlinear coefficient (unit: / W / km), and the vertical axis of (b) represents the wavelength dispersion (unit: ps). 2 / km). In these graphs, the specified wavelengths are varied to 800nm, 850nm, 900nm, 950nm, and 1000nm, and the nonlinear coefficient and wavelength dispersion are measured. Thus, according to this embodiment, the wavelength characteristics of the nonlinear coefficient and wavelength dispersion can also be measured with high precision.

[0087] The effects obtained by the measuring device 1A, measuring method and measuring procedure according to the above-described embodiment will be explained.

[0088] For example, in the prior art described in Patent Document 1, the intensity spectrum of the light output obtained by inputting light into the light transmission medium 4 is measured, and the intensity spectrum of the output light is estimated based on the characteristics of the input light, the theoretical relationship between the nonlinear coefficient and wavelength dispersion value of the light transmission medium 4, and the nonlinear coefficient and wavelength dispersion value with the smallest error relative to the measured value are explored. Thus, theoretically, the nonlinear coefficient and wavelength dispersion value of the light transmission medium 4 can be uniquely determined.

[0089] However, according to the present inventors' insight, it is actually difficult to uniquely determine the nonlinear coefficient and the wavelength dispersion value using this method due to measurement errors and computer rounding errors, etc. However, as shown in Figure 6 , when the intensity spectrum estimation error is near the minimum value, there is a significant correlation between the nonlinear coefficient and the wavelength dispersion value. Moreover, as shown in Figure 6 , the correlation varies depending on the characteristics of the light input (intensity spectrum, phase spectrum, optical pulse energy, etc.).

[0090] Thus, in the present embodiment, the nonlinear coefficient and the wavelength dispersion value are varied by performing multiple light inputs to the optical transmission medium 4 with different characteristics for which the center wavelengths are equal to each other, and the intensity spectrum estimation error of the obtained multiple light outputs is calculated. Then, based on the difference between the nonlinear coefficient and the wavelength dispersion value and the intensity spectrum estimation error, which is caused by the difference in characteristics, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium 4 are determined based on the relationship between the nonlinear coefficient and the wavelength dispersion value and the intensity spectrum estimation error. Thus, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium 4 can be obtained with high precision.

[0091] As in the present embodiment, the combination of the nonlinear coefficient and the wavelength dispersion value for which the intensity spectrum estimation error is close to the minimum value can also be made to have a linear relationship in step S20, and the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium 4 can be determined by the parameter calculation section 6 based on the two linear relationships corresponding to the respective multiple light inputs. In this case, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium 4 can be easily obtained.

[0092] As in steps S15 to S19 of the present embodiment, the relationship between the intensity spectrum estimation error and the hypothetical spectrum can also be obtained by varying the hypothetical spectrum of the phase spectrum input to the theoretical relationship, and the hypothetical spectrum for which the intensity spectrum estimation error is minimized can be calculated as the phase spectrum of each light input. In this case, the present embodiment can be performed using light for which the phase spectrum is unknown, and the measurement of the phase spectrum can be omitted, so the time and effort required for the measurement of the nonlinear coefficient and the wavelength dispersion value can be reduced.

[0093] As shown in (a) of Figure 4 and (a) of Figure 5 , the intensity spectrum of the multiple light inputs can also be different from each other. According to the present inventors' research, in this case, the relationship between the nonlinear coefficient and the wavelength dispersion value and the intensity spectrum estimation error is significantly different between the multiple light inputs. Thus, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium 4 can be determined with even higher precision. This tendency is more significant particularly in the case where the wavelength ranges (spectrum widths) of the intensity spectrum of the multiple light inputs are different from each other.

[0094] Further, in this case, as shown in (a) of Figure 4 and (a) of Figure 5As shown in (a), the phase spectrum of each light input can also be flat within the wavelength range of the intensity spectrum. According to the inventors' research, when the phase spectrum is flat, the change in intensity spectrum estimation error relative to a unit change in the nonlinear coefficient and wavelength dispersion is larger compared to the case where it is not flat. Therefore, the relationship between the nonlinear coefficient and wavelength dispersion and the intensity spectrum estimation error is clearer, and thus the nonlinear coefficient and wavelength dispersion of the optical transmission medium 4 can be determined with higher precision.

[0095] As in this embodiment, in step S13, the light characteristics output from the common light source 21 can be changed by the light characteristic control unit 22, and multiple light inputs can be performed. In other words, the light source unit 2 may also include a light source 21 that outputs light with certain characteristics and a light characteristic control unit 22 that changes the characteristics of the light output from the light source 21 and performs multiple light inputs. In this case, multiple light inputs can be performed using a single light source 21, thus simplifying the structure required for measurement.

[0096] However, this structure can be replaced by, for example, preparing multiple light sources with equal center wavelengths but different characteristics, and sequentially inputting light into the light transmission medium 4 from these light sources. In this case, the nonlinear coefficients and wavelength dispersion values ​​of the light transmission medium 4 can also be obtained with high precision.

[0097] (First variation)

[0098] Figure 9 This is a flowchart illustrating a measurement method involved in a variation of the above-described embodiment. The difference between this variation and the above-described embodiment lies in the method for obtaining the phase spectrum of the light input. In the above-described embodiment, a hypothetical spectrum of the light input is set in step S15, and the hypothetical spectrum with minimal intensity spectrum estimation error is used as the phase spectrum of the light input. In this variation, the phase spectrum of the light input is obtained through actual measurement.

[0099] That is, such as Figure 9 As shown, after step S12 (or possibly before step S12), as step S21, the phase spectrum of the test pulse generated in step S11 is measured. Specifically, the test pulse output from the light source unit 2 is input to the phase spectrum measuring device without passing through the light transmission medium 4, and the phase spectrum measuring device obtains the measured value of the phase spectrum of the test pulse. The data of the measured value of the phase spectrum is provided to the parameter calculation unit 6 as phase spectrum data of the light input.

[0100] In addition, the phase spectrum measurement device used here is a device based on a measurement method such as Frequency Resolved Optical Gating (FROG), OPR (Optical Pulse Ruler), or the like. The structure of the OPR device is a structure obtained by removing the light source 21 and the light property control section 22 from the structure of Figure 1

[0101] Next, as step S13, the optical input of the test pulse is performed to the optical transmission medium 4, and the measured value of the intensity spectrum of the optical output from the optical transmission medium 4 corresponding to the optical input is obtained (measured value obtaining step). The details of step S13 are the same as in the above embodiment.

[0102] Next, the parameter calculation section 6 calculates the estimated value of the intensity spectrum based on the theoretical relationship between the intensity spectrum of the optical input and the phase spectrum, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium 4, and the intensity spectrum of the optical output. At this time, a plurality of estimated values are calculated while changing the nonlinear coefficient and the wavelength dispersion value individually. Then, the error (intensity spectrum estimation error) of the plurality of estimated values from the measured value is calculated (error calculating step, calculation section in the measurement program).

[0103] Specifically, as step S14, the parameter calculation section 6 sets the assumed value of the parameter (nonlinear coefficient and wavelength dispersion value) of the optical transmission medium 4. Then, as step S16, the parameter calculation section 6 estimates the intensity spectrum of the optical output from the theoretical relationship based on the assumed value of the nonlinear coefficient and the wavelength dispersion value, and the measured value of the phase spectrum.

[0104] After that, as step S17, the parameter calculation section 6 compares the estimated value of the intensity spectrum of the optical output with the measured value of the intensity spectrum of the optical output. The parameter calculation section 6 records the error (intensity spectrum estimation error) of the estimated value from the measured value of the intensity spectrum as the intensity spectrum estimation error corresponding to the nonlinear coefficient and the wavelength dispersion value set at step S14 (step S19).

[0105] After that, the parameter calculation section 6 returns to step S14 again (step S22), and repeats the above steps S16, S17, and S19 after changing the assumed value of the parameter (nonlinear coefficient and wavelength dispersion value) of the optical transmission medium 4. In this way, the parameter calculation section 6 changes the assumed value of the parameter (nonlinear coefficient and wavelength dispersion value) of the optical transmission medium 4 and calculates the estimated value of the intensity spectrum and the intensity spectrum estimation error corresponding to each assumed value.

[0106] ​After that, the process returns to step S11 again, and a test pulse is generated again in the light source section 2. This test pulse is an optical pulse different in characteristics (at least one of intensity spectrum, phase spectrum, and optical pulse energy, for example) from the test pulse generated previously, but has the same center wavelength as the test pulse generated previously.

[0107] After generating such a test pulse, the above-described steps S12, S21, S13, S14, S16, S17, and S19 are repeated again. Through the above process, the relationship between the intensity spectrum estimation error of the estimated value and the measured value of the intensity spectrum of two test pulses different in characteristics from each other and the nonlinear coefficient and the wavelength dispersion value can be obtained. In addition, the details of the next step S20 are omitted from the description because they are the same as those of the above-described embodiment.

[0108] As in this modification example, the step S21 of obtaining the measured value of the phase spectrum of the light input can be performed before steps S14 to S19. In this case, the calculation of step S20 can be performed based on the correct phase spectrum, and the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium 4 can be obtained with higher accuracy.

[0109] (2nd Modification Example)

[0110] In the above-described embodiment, as an example in which the characteristics of the multiple light inputs are different from each other, the intensity spectrum of the multiple light inputs is made different from each other as shown in (a) of FIG. 6 and (a) of FIG. 7, but the characteristics of the different light inputs are not limited to the intensity spectrum as long as the relationship between the nonlinear coefficient and the wavelength dispersion value and the intensity spectrum estimation error is different between the multiple light inputs. Figure 4 Figure 5 For example, the phase spectrum of the multiple light inputs can be made different from each other, the peak intensity of the multiple light inputs can be made different from each other, and the optical pulse energy of the multiple light inputs can be made different from each other. In addition, two or more of various characteristics such as the intensity spectrum, the phase spectrum, the peak intensity, and the optical pulse energy can be made different between the multiple light inputs. In the case where the phase spectrum of the multiple light inputs is made different from each other, the phase spectrum of one light input can be made flat in the wavelength range of the intensity spectrum.

[0111] In this case, the relationship between the nonlinear coefficient and the wavelength dispersion value and the intensity spectrum estimation error is also different between the multiple light inputs. Therefore, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium 4 can be determined with high accuracy as in the above-described embodiment.

[0112]

[0113] The optical transmission medium measurement method, the optical transmission medium measurement apparatus, the optical transmission medium measurement program, and the storage medium are not limited to the above-described embodiments and configuration examples, and various modifications can be made thereto.

[0114] ​​For example, in the above-described embodiments, a light pulse is used as the light input, but a continuous light can also be used as the light input. Furthermore, in the above-described embodiments, a case where the relationship between the nonlinear coefficient and the wavelength dispersion value and the intensity spectrum estimation error is linear is exemplified, but the effect of the present application can be appropriately obtained even when the relationship is nonlinear.

[0115] The optical transmission medium measurement method of the above-described embodiment is a method of measuring a nonlinear coefficient and a wavelength dispersion value of an optical transmission medium, including: a measured value acquisition step of performing a plurality of light inputs to the optical transmission medium with center wavelengths equal to each other and characteristics different from each other, and acquiring measured values of intensity spectra of a plurality of light outputs from the optical transmission medium corresponding to the plurality of light inputs, respectively; an error calculation step of changing the nonlinear coefficient and the wavelength dispersion value and calculating an error of an estimated value of an intensity spectrum calculated based on an intensity spectrum and a phase spectrum of each of the plurality of light inputs, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium, and a theoretical relationship of an intensity spectrum of each of the plurality of light outputs, from the measured values; and a parameter determination step of determining the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium based on a difference between the plurality of light inputs due to a difference in the characteristics, from a relationship between the nonlinear coefficient and the wavelength dispersion value and the error.

[0116] The optical transmission medium measurement apparatus of the above-described embodiment is an apparatus of measuring a nonlinear coefficient and a wavelength dispersion value of an optical transmission medium, including: a light source section of performing a plurality of light inputs to the optical transmission medium with center wavelengths equal to each other and characteristics different from each other; a spectrum acquisition section of acquiring measured values of intensity spectra of a plurality of light outputs from the optical transmission medium corresponding to the plurality of light inputs, respectively; and an arithmetic section of changing the nonlinear coefficient and the wavelength dispersion value and calculating an error of an estimated value of an intensity spectrum calculated based on an intensity spectrum and a phase spectrum of each of the plurality of light inputs, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium, and a theoretical relationship of an intensity spectrum of each of the plurality of light outputs, from the measured values, determining the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium based on a difference between the plurality of light inputs due to a difference in the characteristics, from a relationship between the nonlinear coefficient and the wavelength dispersion value and the error.

[0117] The optical transmission medium measurement program of the above-described embodiment is a program of measuring a nonlinear coefficient and a wavelength dispersion value of an optical transmission medium, which causes a computer to function as a calculation section and a determination section, in which the calculation section changes the nonlinear coefficient and the wavelength dispersion value and calculates an error of an estimated value of an intensity spectrum calculated based on an intensity spectrum and a phase spectrum of each of a plurality of light inputs with center wavelengths equal to each other and characteristics different from each other, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium, and a theoretical relationship of an intensity spectrum of a plurality of light outputs from the optical transmission medium corresponding to the plurality of light inputs, from measured values of intensity spectra of the plurality of light outputs, and the determination section determines the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium based on a difference between the plurality of light inputs due to a difference in the characteristics, from a relationship between the nonlinear coefficient and the wavelength dispersion value and the error.

[0118] The storage medium of the above embodiment is a computer-readable medium storing the above optical transmission medium measurement program.

[0119] In the above measurement method, a structure can also be adopted in which, in the parameter determination step, the combination of the nonlinear coefficient and the wavelength dispersion value that makes the error close to the minimum value has a linear relationship, and the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium are determined based on a plurality of linear relationships corresponding to a plurality of light inputs, respectively.

[0120] In the above measurement apparatus, a structure can also be adopted in which the combination of the nonlinear coefficient and the wavelength dispersion value that makes the error close to the minimum value has a linear relationship, and the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium are determined by the arithmetic unit based on a plurality of linear relationships corresponding to a plurality of light inputs, respectively.

[0121] According to such a structure, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium can be easily obtained.

[0122] In the above measurement method, a structure can also be adopted in which, before the error calculation step, a step of obtaining a measured value of the phase spectrum of each light input is further included. In this case, the above calculation can be performed based on a correct phase spectrum, and the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium can be obtained with higher accuracy.

[0123] In the above measurement method, a structure can also be adopted in which, in the error calculation step, the error and the hypothetical spectrum are obtained by changing the hypothetical spectrum of the phase spectrum input to the theoretical relationship, and the hypothetical spectrum in which the error is the minimum is calculated as the phase spectrum of each light input to calculate the estimated value.

[0124] In the above measurement apparatus, a structure can also be adopted in which the arithmetic unit changes the hypothetical spectrum of the phase spectrum input to the theoretical relationship to obtain the error and the hypothetical spectrum, and the hypothetical spectrum in which the error is the minimum is calculated as the phase spectrum of each light input to calculate the estimated value.

[0125] According to such a structure, the above measurement can be performed using light whose phase spectrum is unknown, and the measurement of the phase spectrum can be omitted, so the time and effort required for the measurement of the nonlinear coefficient and the wavelength dispersion value can be reduced.

[0126] In the above measurement method and measurement apparatus, a structure can also be adopted in which the intensity spectrum of each of a plurality of light inputs is different. According to the inventor's research, in this case, the relationship between the nonlinear coefficient and the wavelength dispersion value and the error greatly differs between the plurality of light inputs. Therefore, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium can be determined with higher accuracy.

[0127] Further, in the above case, a structure in which the phase spectrum is flat in the wavelength range of the intensity spectrum for multiple light inputs can also be employed. According to the inventors' studies, the relationship between the nonlinear coefficient and the wavelength dispersion value and the error is thereby made clearer, and thus the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium can be determined with higher precision.

[0128] In the above measurement method and measurement apparatus, a structure in which the phase spectra of the multiple light inputs differ from each other can also be employed. In such a case, the relationship between the nonlinear coefficient and the wavelength dispersion value and the error also differs among the multiple light inputs. Thus, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium can be determined with high precision.

[0129] In the above measurement method, a structure in which, in the measured value acquisition step, the characteristics of the light output from the common light source are changed while the multiple light inputs are performed can also be employed.

[0130] In the above measurement apparatus, a structure in which the light source section includes a light source that outputs light having certain characteristics and a light characteristic control section that performs the multiple light inputs while changing the characteristics of the light output from the light source can also be employed.

[0131] According to such a structure, the multiple light inputs can be performed using a single light source, and thus the structure required for the measurement can be simplified.

[0132] Industrial Applicability

[0133] The embodiments can be utilized as a measurement method of an optical transmission medium, a measurement apparatus of an optical transmission medium, a measurement program of an optical transmission medium, and a storage medium that can acquire the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium with high precision.

[0134] Explanation of Symbols

[0135] 1A... measurement apparatus of an optical transmission medium, 2... light source section, 2a... output end, 4... optical transmission medium, 4a... one end, 4b... other end, 5... spectrum acquisition section, 5a... input end, 5b... signal output end, 6... parameter calculation section, 6a... signal input end, 21... light source, 21a... output end, 22... light characteristic control section, 22a... input end, 22b... output end, B1, B2... region, G1, G2... approximate straight line, Λ1, Λ2... wavelength range.

Claims

1. An optical transmission medium measuring method characterized by: being a method of measuring a nonlinear coefficient and a wavelength dispersion value of an optical transmission medium, including: an actual value acquisition step of performing multiple light inputs to the optical transmission medium with center wavelengths equal to each other and characteristics different from each other, and acquiring actual values of intensity spectra of multiple light outputs from the optical transmission medium corresponding to the multiple light inputs respectively; an error calculation step of changing the nonlinear coefficient and the wavelength dispersion value and calculating errors of the optical transmission medium between estimated values of intensity spectra calculated based on intensity spectra and phase spectra of the multiple light inputs respectively, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium, and intensity spectra calculated based on a theoretical relationship of the multiple light outputs respectively; and a parameter determination step of determining the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium based on differences between the multiple light inputs caused by the differences in the characteristics, from a relationship of the nonlinear coefficient and the wavelength dispersion value and the errors, in the parameter determination step, a combination of the nonlinear coefficient and the wavelength dispersion value that makes the errors close to a minimum value has a linear relationship, and the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium are determined based on multiple linear relationships corresponding to the multiple light inputs respectively.

2. The optical transmission medium measuring method according to claim 1, characterized by: further including a step of acquiring actual values of phase spectra of the light inputs before the error calculation step.

3. The optical transmission medium measuring method according to claim 1, characterized by: in the error calculation step, an assumed spectrum of a phase spectrum input to the theoretical relationship is changed to obtain a relationship of the errors and the assumed spectrum, and the assumed spectrum that makes the errors minimum is calculated as a phase spectrum of each light input to calculate the estimated values.

4. The optical transmission medium measuring method according to any one of claims 1 to 3, characterized in that: intensity spectra of the multiple light inputs are different from each other.

5. The optical transmission medium measuring method according to claim 4, characterized in that: phase spectra of the multiple light inputs are flat in a wavelength range of the intensity spectra.

6. The optical transmission medium measuring method according to any one of claims 1 to 4, characterized in that: phase spectra of the multiple light inputs are different from each other.

7. The optical transmission medium measuring method according to any one of claims 1 to 6, characterized in that: in the actual value acquisition step, the multiple light inputs are performed while changing characteristics of light output from a common light source.

8. An optical transmission medium measuring apparatus characterized by: being an apparatus of measuring a nonlinear coefficient and a wavelength dispersion value of an optical transmission medium, including: a light source section of performing multiple light inputs to the optical transmission medium with center wavelengths equal to each other and characteristics different from each other; a spectrum acquisition section of acquiring actual values of intensity spectra of multiple light outputs from the optical transmission medium corresponding to the multiple light inputs respectively; and an arithmetic unit that changes the nonlinear coefficient and the wavelength dispersion value and calculates an error of an estimated value of an intensity spectrum calculated based on a theoretical relationship of an intensity spectrum of each of a plurality of light inputs, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium, and the intensity spectrum of each of a plurality of light outputs from the optical transmission medium, the plurality of light inputs each having a different characteristic, and a measured value of the intensity spectrum of each of the plurality of light outputs, a combination of the nonlinear coefficient and the wavelength dispersion value that makes the error close to a minimum value has a linear relationship, and the arithmetic unit determines the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium based on a plurality of the linear relationships corresponding to the plurality of light inputs, respectively.

9. The optical transmission medium measuring apparatus according to claim 8, wherein: the arithmetic unit changes a hypothetical spectrum of a phase spectrum input to the theoretical relationship and calculates a relationship of the error and the hypothetical spectrum, and calculates the estimated value using the hypothetical spectrum that makes the error a minimum as the phase spectrum of each light input.

10. The optical transmission medium measuring apparatus according to claim 8 or 9, wherein: the intensity spectra of the plurality of light inputs are different from each other.

11. The optical transmission medium measuring apparatus according to claim 10, wherein: the phase spectra of the plurality of light inputs are flat in a wavelength range of the intensity spectrum.

12. The optical transmission medium measuring apparatus according to any one of claims 8 to 10, wherein: the phase spectra of the plurality of light inputs are different from each other.

13. The optical transmission medium measuring apparatus according to any one of claims 8 to 12, wherein: the light source unit includes: a light source that outputs light having a certain characteristic; and a light characteristic control unit that changes the characteristic of the light output from the light source and performs the plurality of light inputs.

14. An optical transmission medium measuring program, wherein: the program is a program that measures a nonlinear coefficient and a wavelength dispersion value of an optical transmission medium, a computer functions as an arithmetic unit and a determination unit, the arithmetic unit changes the nonlinear coefficient and the wavelength dispersion value and calculates an error of an estimated value of an intensity spectrum calculated based on a theoretical relationship of an intensity spectrum of each of a plurality of light inputs, the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium, and the intensity spectrum of each of a plurality of light outputs from the optical transmission medium, the plurality of light inputs each having a different characteristic and a center wavelength equal to each other, the determination unit determines the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium based on a difference between the plurality of light inputs due to a difference in the characteristic, a relationship of the nonlinear coefficient and the wavelength dispersion value and the error, and The combination of the nonlinear coefficient and the wavelength dispersion value that minimizes the error has a linear relationship, and the determining section determines the nonlinear coefficient and the wavelength dispersion value of the optical transmission medium based on a plurality of the linear relationships corresponding to a plurality of the light inputs.

15. A computer-readable storage medium storing the optical transmission medium measurement program according to claim 14. ​

Images