Brillouin scattering measuring device

Abstract

The purpose of the present invention is to provide a Brillouin scattering measuring device capable of compensating for fluctuations in a frequency component of broadband probe light and performing highly accurate measurement.　A Brillouin scattering measuring device according to the present invention: acquires broadband probe light that includes Brillouin scattering light and broadband probe light that does not include Brillouin scattering light by using two broadband pulsed light beams having the same optical characteristics; compensates for fluctuations in a frequency component of the broadband probe light that includes Brillouin scattering light on the basis of the broadband probe light that does not include Brillouin scattering light; and performs Lorentzian fitting on a signal obtained by dividing the broadband probe light that includes Brillouin scattering light by the broadband probe light that does not include Brillouin scattering light to determine a peak position in a BGS.

Description

Brillouin scattering measurement device

[0001] The present disclosure relates to a reflectometry technique for sensing by measuring scattered light of light incident on an optical fiber.

[0002] 1 is a diagram illustrating the configuration of a Brillouin scattering measurement device (see, for example, Non-Patent Document 1). The Brillouin scattering measurement device 300 includes a scattered light generation unit 41 that generates pulsed pump light Lpn and probe light Lpr with broadband frequency components to generate scattered light, and a scattered light acquisition unit 42 that acquires the generated scattered light by heterodyne detection. The Brillouin scattering measurement device 300 can acquire a Brillouin Gain Spectrum (BGS) with a single pulsed pump light Lpn by performing optical heterodyne detection using the broadband probe light Lpr, thereby enabling vibration measurement.

[0003] 2 and 3 are diagrams illustrating the measurement method performed by the Brillouin scattering measurement device 300. The Brillouin scattering measurement device 300 causes Brillouin scattering by counter-propagating pulsed pump light Lpn and probe light Lpr with a wideband frequency component within the optical fiber under test 50, and converts the probe light containing Brillouin scattering into an electrical signal using the scattered light acquisition unit 42. The scattered light acquisition unit 42 then detects the Brillouin scattered light component through frequency analysis and calculates the BGS at each point to perform vibration measurement using Brillouin scattering (FIG. 3). In this way, the Brillouin scattering measurement device 300 achieves high-speed sensing by using wideband light.

[0004] T. Ishimaru, et al. , OFC2023, W3J. 6, (2023)

[0005] However, some light sources may output fluctuating light, with intensities that vary by frequency and change over time, as shown in Figure 4. Hereinafter, such fluctuations will be referred to as "fluctuations in frequency components," and such light will be referred to as "light with fluctuations in frequency components." In the case of light with fluctuations in frequency components, the frequency components of the underlying broadband probe light fluctuate, causing the peak position of the scattered light to change depending on the fluctuations, posing a fundamental problem of making it difficult to maintain measurement accuracy.

[0006] To solve the above basic problem, there is a Brillouin scattering measurement device that can compensate for the fluctuation of the frequency component of the broadband probe light and enable high-precision measurement.

[0007] The Brillouin scattering measurement device uses two broadband pulsed lights having the same optical characteristics to acquire broadband probe light including Brillouin scattered light and broadband probe light not including Brillouin scattered light, and compensates for fluctuations in the frequency components of the broadband probe light including Brillouin scattered light based on the broadband probe light not including Brillouin scattered light.

[0008] Specifically, the Brillouin scattering measurement device includes: a pump light generator that generates pump light by pulsing continuous light of a single frequency from a laser; a probe light generator that generates probe light by pulsing broadband continuous light from a broadband light source, the broadband continuous light having frequency components broader than the frequency of the continuous light output by the laser, with a time width wider than that of the pump light; a modulator that generates local light by shifting the frequency of the continuous light from the laser by an arbitrary frequency; a detector that coherently detects the probe light containing Brillouin scattered light generated by counter-propagating the pump light and the probe light through an optical fiber under test, using the local light to generate a measurement signal, and that coherently detects the probe light not containing Brillouin scattered light using the local light to generate a reference signal; and a calculator that compensates for fluctuations in the frequency components of the probe light contained in the measurement signal based on the reference signal.

[0009] This Brillouin scattering measurement device generates two broadband probe lights with pulse shapes and identical optical characteristics, separated by a time lag, as shown in Figure 5. The method for generating the two probe lights will be described later. The first probe light Lpr1 is used to measure Brillouin scattering by causing it to interact with pump light Lpn. The second probe light Lpr2 is measured directly (without Brillouin scattering) and used as reference light to compensate for fluctuations in the frequency components of the broadband light. The pulse width of the broadband probe light is subject to the following restrictions: (1) The upper limit of the pulse width of the broadband probe light is the maximum width at which the probe light Lpr1 and the probe light Lpr2 do not overlap. (2) The lower limit of the pulse width of the broadband probe light is wider than the pulse width of the pump light Lpn. (3) When the broadband probe BOTDA (see Patent Document 1) is applied to the entire fiber, the pump light and the probe light must propagate counter-propagatingly throughout the entire range of the optical fiber 50 under test. Therefore, the pulse width of the broadband probe light must be twice the width of the time it takes for the pump light Lpn to propagate through the optical fiber 50 under test.

[0010] 6 is a diagram illustrating the measured waveform Mpr1 of probe light Lpr1 and the measured waveform Mpr2 of probe light Lpr2 measured by the scattered light acquisition unit 42, as well as their frequency analysis results (FA1, FA2). As shown in Fig. 6, the difference between the two lights measured by the scattered light acquisition unit 42 is the presence or absence of Brillouin scattering due to the presence or absence of pump light Lpn. Therefore, by calculating the difference between the two, it is possible to eliminate fluctuations in the frequency component of the probe light, and highly accurate Brillouin scattering information can be obtained.

[0011] Therefore, the Brillouin scattering measurement device can compensate for fluctuations in the frequency components of the broadband probe light, enabling highly accurate measurements.

[0012] As one method for generating two probe lights, the Brillouin scattering measurement device further includes an optical delay device that splits the probe light generated by the probe light generator into two, delays one of the probe lights, and inputs it together with the other probe light into the optical fiber under test, and causes Brillouin scattering between the pump light and one of the probe lights.

[0013] As another method for generating two probe lights, the Brillouin scattering measurement device further includes an optical branching device that branches the probe light generated by the probe light generator into two, and inputs one of the probe lights into the optical fiber under test and the other probe light into a reference optical fiber, and the detector generates the reference signal from the local light that has passed through the reference optical fiber.

[0014] In order to further improve the measurement accuracy, the probe light generator of the Brillouin scattering measurement device may generate the probe light by randomizing the polarization using a polarization scrambler, and the detector may perform polarization diversity heterodyne detection as the coherent detection.

[0015] However, the spectral shapes of the probe light Lpr1 and the probe light Lpr2 are slightly different. This Brillouin scattering measurement device compensates for fluctuations in the frequency components of the broadband probe light by dividing the measurement waveform Mpr1 by the measurement waveform Mpr2. However, due to differences in the spectral shapes of the probe lights, unnecessary side peaks occur during division, making it difficult to accurately determine the BGS peak position. In particular, when the shapes differ at points where the spectral intensity is close to 0, the division result becomes a locally large value. As a result, the side peaks have an adverse effect when detecting the Brillouin frequency shift (BFS), which is the BGS peak.

[0016] Therefore, in order to solve the above problems, an object of the present invention is to provide a Brillouin scattering measurement device that can correctly determine the BGS peak position regardless of the difference in the spectral shape between the measurement probe light and the compensation probe light.

[0017] In order to achieve the above object, the Brillouin scattering measurement device according to the present invention divides the measurement waveform including scattered light by a compensation waveform including no scattered light, and then determines the peak position by fitting using an arbitrary waveform. Specifically, the Brillouin scattering measurement device according to the present invention comprises: a pump light generator that generates pump light by pulsing continuous light of a single frequency from a laser; a probe light generator that generates probe light by pulsing broadband continuous light from a broadband light source, the broadband continuous light having frequency components broader than the frequency of the continuous light output by the laser, with a time width wider than that of the pump light; a modulator that generates local light by shifting the frequency of the continuous light from the laser by an arbitrary frequency; a detector that coherently detects the probe light containing Brillouin scattered light, generated by counter-propagating the pump light and the probe light through an optical fiber under test, using the local light to generate a measurement signal, and that coherently detects the probe light not containing the Brillouin scattered light using the local light to generate a reference signal; and a calculator that divides the frequency-analyzed measurement signal by the frequency-analyzed reference signal to obtain the Brillouin gain spectrum.

[0018] The fitting process can eliminate unnecessary side peaks that occur during division, allowing the BGS peak position to be determined correctly. Therefore, the present invention can provide a Brillouin scattering measurement device that can correctly determine the BGS peak position regardless of the difference in the spectral shapes of the measurement probe light and the compensation probe light.

[0019] Since the BGS has a Lorentzian shape, the computing unit of the Brillouin scattering measurement device according to the present invention preferably performs Lorentzian fitting on the Brillouin gain spectrum to determine the peak position, and more preferably performs the Lorentzian fitting using a weighted Lorentzian function.

[0020] The present invention is a program for causing a computer to function as the computing unit. The computing unit of the Brillouin scattering measurement apparatus 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.

[0021] The above inventions can be combined as much as possible.

[0022] The present invention can provide a Brillouin scattering measurement device that can correctly determine the BGS peak position regardless of the difference in the spectral shape between the measurement probe light and the compensation probe light.

[0023] FIG. 1 is a diagram illustrating the configuration of a Brillouin scattering measurement device. FIG. 2 is a diagram illustrating a method for measuring Brillouin scattered light. FIG. 3 is a diagram illustrating the problem of the present invention. FIG. 4 is a diagram illustrating the measurement principle of the Brillouin scattering measurement device according to the present invention. FIG. 5 is a diagram illustrating the measurement principle of the Brillouin scattering measurement device according to the present invention. FIG. 6 is a diagram illustrating the Brillouin scattering measurement device according to the present invention. FIG. 7 is a diagram illustrating the Brillouin scattering measurement device according to the present invention. FIG. 8 is a diagram illustrating a technique for generating two probe beams with pulse shapes having the same characteristics but shifted in time in the Brillouin scattering measurement device according to the present invention. FIG. 9 is a diagram illustrating a method for measuring Brillouin scattered light in the Brillouin scattering measurement device according to the present invention. FIG. 10 is a diagram illustrating the Brillouin scattering measurement device according to the present invention. FIG. 11 is a diagram illustrating the operation of the Brillouin scattering measurement device according to the present invention. FIG. 12 is a diagram illustrating the spectral shapes of two probe beams. (A) is a diagram comparing the spectral shape of probe beam Lpr1, (B) is a diagram comparing the spectral shape of probe beam Lpr2, and (C) is a diagram comparing the fluctuations of the frequency components of both probe beams. FIG. 13 is a diagram illustrating the Brillouin scattering measurement device according to the present invention and signal processing performed by a computing unit.

[0024] The following description of the preferred embodiments of the present invention will be given with reference to the accompanying drawings. The preferred embodiments described below are examples of the present invention, and the present invention is not limited to the preferred embodiments. In this specification and the drawings, components having the same reference numerals are intended to represent the same components.

[0025] First Embodiment FIG. 7 is a diagram illustrating a Brillouin scattering measurement device 301 according to this embodiment. The Brillouin scattering measurement device 301 includes: a pump light generator 10 that pulses continuous light of a single frequency from a laser 11 to generate pump light Lpn; a probe light generator 20 that pulses broadband continuous light from a broadband light source 13, having frequency components broader than the frequency of the continuous light output by the laser 11, with a time width wider than that of the pump light Lnp, to generate probe light Lpr; a modulator 14 that generates local light by shifting the frequency of the continuous light from the laser 11 by an arbitrary frequency; a detector 15 that coherently detects the probe light containing Brillouin scattered light generated by counter-propagating the pump light Lpn and the probe light Lpr through an optical fiber 50 under test, using the local light to generate a measurement signal, and that coherently detects the probe light not containing the Brillouin scattered light using the local light to generate a reference signal; and a calculator 43 that compensates for fluctuations in the frequency components of the probe light contained in the measurement signal based on the reference signal.

[0026] In this embodiment, the Brillouin scattering measurement device 301 further includes an optical delay device 17 that splits the probe light Lpr generated by the probe light generator 20 into two, delays one of the probe lights Lpr, and inputs it together with the other probe light Lpr into the optical fiber 50 to be measured, and is characterized in that Brillouin scattering is caused between the pump light Lpn and one of the probe lights Lpr.

[0027] The Brillouin scattering measurement device 301 is composed of a scattered light generator 41 and a scattered light acquirer 42. The scattered light generator 41 generates pump light Lpn consisting of a pulsed single frequency and probe light Lpr consisting of two pulsed broadband frequencies. The pump light Lpn is generated by modulating single-frequency light emitted from a laser 11 into a pulsed shape using an intensity modulator 12 and amplifying the light using an optical amplifier 61 as needed. The optical filter 18a removes noise due to the optical amplifier 61. On the other hand, the probe light Lpr is generated by pulsing light emitted from a broadband light source 13 using an intensity modulator 16. For example, the broadband light source 13 outputs light obtained by exciting ASE light using an EDFA.

[0028] 9 is a diagram illustrating a method for generating two probe beams with the same pulse shape characteristics at different times in this embodiment. In this embodiment, an optical delayer 17 is used. In this embodiment, a delay optical fiber 17b is disposed in one of the branched paths, thereby generating two probe beams with the same pulse shape characteristics at different times. Any desired delay amount can be achieved by changing the length of the delay optical fiber 17b.

[0029] Specifically, the optical delay 17 splits one pulsed probe light Lpr into two by a coupler 17a, adds a delay to one probe light Lpr by a delay optical fiber 17b arranged in one path R1, and recombines the delayed probe light Lpr and the non-delayed probe light Lpr by a coupler 17c. The optical delay 17 outputs pulse-shaped probe lights Lpr (Lpr1, Lpr2) having the same characteristics with a time difference.

[0030] The scattered light generating unit 41 inputs the pump light Lpn to one end of the measured optical fiber 50 and inputs both probe light Lpr to the other end of the measured optical fiber 50. Here, the scattered light generating unit 41 adjusts the input timing of the pump light Lpn and both probe light Lpr to the measured optical fiber 50 so that one probe light Lpr and the pump light Lpn do not collide within the measured optical fiber 50 and the other probe light Lpr and the pump light Lpn do not collide within the measured optical fiber 50.

[0031] The scattered light acquisition unit 42 is a device that uses local light to perform coherent detection of the probe light Lpr output from one end of the optical fiber 50 under test. The local light is obtained by modulating light branched from the laser 11 to near BFS using a frequency modulator 14. If necessary, the local light may be amplified using an optical amplifier. Coherent detection is performed by combining the probe light Lpr and the local light and detecting them using a BPD. The detected signal is then converted into digital data by an ADC, and frequency analysis processing is performed by a PC.

[0032] To generate Brillouin scattering stably without polarization dependence, a configuration such as that shown in Fig. 8 may be used. The Brillouin scattering measurement device 302 of Fig. 8 differs from the Brillouin scattering measurement device 301 of Fig. 7 in that the probe light generator 20 generates probe light Lpr by randomizing polarization using a polarization scrambler 19, and the detector 15 performs polarization diversity heterodyne detection as the coherent detection. The optical filter 18b removes light of unnecessary optical frequencies based on changes in the Brillouin frequency shift (BFS) (extracting only light of frequency components necessary to cause Brillouin scattering). Specifically, the optical filter 18b extracts light of a predetermined band that is separated from the optical frequency of the pump light by approximately the optical frequency of the BFS as the probe light.

[0033] 10 is a diagram illustrating a method for measuring Brillouin scattered light performed by the scattered light acquisition unit 42. Of the two probe lights obtained by the optical delay unit 17, one (e.g., Lpr1) is made to collide with the pump light Lpn in the measured optical fiber 50, and the other (e.g., Lpr2) is made to pass through the measured optical fiber 50 without colliding with the pump light Lpn, and both probe lights are coherently detected by the detector 15.

[0034] 10A shows a waveform obtained by frequency analysis of a probe light (e.g., Lpr2) that has passed through the measured optical fiber 50 without colliding with the pump light Lpn. This waveform is information on only the broadband probe light. FIG. 10B shows a waveform obtained by frequency analysis of a probe light (e.g., Lpr1) that has been made to collide with the pump light Lpn in the measured optical fiber 50. This waveform is information on the broadband probe light that includes scattered light.

[0035] The purpose is to obtain information on the Brillouin gain corresponding to the strain of the optical fiber under test 50. The waveform in Fig. 10(B) contains information on both the Brillouin gain and the broadband probe light, but the peak positions fluctuate due to fluctuations in the frequency components of the broadband probe light. Therefore, the waveform in Fig. 10(A) (information on the fluctuations in the frequency components of the broadband probe light) obtained for reference is used to obtain the signal in Fig. 10(B) (information on the Brillouin gain) by removing the fluctuation components of the frequency components of the broadband probe light. This calculation is performed by the signal processing unit 43 by unifying the vertical axes of Figs. 10(A) and 10(B) into units of power in dB scale, and dividing or deconvolving the measurement signal of the broadband probe light including the Brillouin scattered light by the reference signal of the broadband probe light not including the Brillouin scattered light.

[0036] 11 is a diagram illustrating a Brillouin scattering measurement device 303 of this embodiment. The Brillouin scattering measurement device 303 further includes an optical branching device 31 that branches the probe light Lpr generated by the probe light generator 20 into two beams, and inputs one of the probe light beams into the measured optical fiber 50 and the other probe light beam into the reference optical fiber 51. This differs from the Brillouin scattering measurement device 301 of FIG. 7 in that the detector 15 generates the reference signal from the probe light that has passed through the reference optical fiber 51.

[0037] The measurement of Brillouin scattered light described in the first embodiment can also be performed in a configuration of the Brillouin scattering measurement device 303 in which separate systems are provided for the measurement signal passing through the measured optical fiber 50 and the reference signal passing through the reference optical fiber 51. The optical branching device 31 branches the probe light Lpr into two, and one (e.g., probe light Lpr1) is incident on the measured optical fiber 50, while the other (e.g., probe light Lpr2) is incident on the reference optical fiber 51. The scattered light acquisition unit 42 has two pairs of detectors 15. One detector 15 coherently detects the probe light Lpr1 that has collided with the pump light Lpn in the measured optical fiber 50 using local light to generate a measurement signal. The other detector 15 coherently detects the probe light Lpr2 that has passed through the reference optical fiber 51 using local light to generate a reference signal. As described in the first embodiment, the calculator 43 compensates for fluctuations in the frequency component of the probe light included in the measurement signal based on the reference signal.

[0038] Even when a reference signal is generated using the reference optical fiber 51, the Brillouin scattering measurement device 304 may have the configuration shown in FIG. 12 in order to generate Brillouin scattering stably without polarization dependency.

[0039] 13 is a flowchart explaining the operation of the Brillouin scattering measurement apparatus (301 to 304) described in the first and second embodiments. In this operation, pulsed pump light Lpn is repeatedly input into the fiber under test 50 until a desired measurement time is reached.

[0040] Step S01: A probe beam is generated by pulsing broadband light in a frequency range that takes into account the BFS of the BGS. The probe beam is then split into two beams. In the Brillouin scattering measurement device (301-302) of embodiment 1, one of the probe beams is delayed, and both beams are incident on the fiber under test 50 so as to counter-propagate with the pulsed pump beam Lpn. In the Brillouin scattering measurement device (303-304) of embodiment 2, one of the probe beams is incident on the reference optical fiber 51, and the other probe beam is incident on the fiber under test 50 so as to counter-propagate with the pulsed pump beam Lpn.

[0041] Step S02 In the Brillouin scattering measurement device (301-302) of embodiment 1, pump light Lpn consisting of a single frequency is incident on the measured optical fiber 50 at a timing when it counter-propagates with only one of the two probe light Lpr. Two signals are generated from the two probe light Lpr output from the measured optical fiber 50: a measurement signal including Brillouin scattering and a reference signal not including Brillouin scattering. In the Brillouin scattering measurement device (303-304) of embodiment 2, pump light Lpn consisting of a single frequency is incident on the measured optical fiber 50 at a timing when it counter-propagates with the probe light Lpr. The pump light Lpn is not incident on the reference optical fiber 51. A measurement signal including Brillouin scattering is generated from the probe light Lpr output from the measured optical fiber 50, and a reference signal not including Brillouin scattering is generated from the probe light Lpr output from the reference optical fiber 51.

[0042] Step S03: The scattered light acquisition unit 41 coherently detects the measurement signal and the reference signal using local light to acquire the respective detection signals. That is, with a single injection of pump light Lpn, two detection signals, one for Brillouin scattering measurement and one for reference, can be acquired, thereby acquiring detection signals that can form a distributed BGS throughout the entire fiber.

[0043] Step S04: If the desired measurement time has not been reached, measurement is restarted from step S01. If the desired measurement time has been reached, step S05 is carried out.

[0044] Step S05: Frequency analysis is performed on the acquired detection signal for each distance on the optical fiber 50 under test, and the BGS at each point is calculated. At this time, fluctuations of the broadband probe light are compensated for using the method described in FIG. 10 . Then, by observing the time-series changes in the peaks of the calculated BGS, the vibration at each point on the optical fiber 50 under test can be obtained. Note that step S05 is an independent process for each pump light, so it can also be executed during the loop of steps S01 to S04 if the calculation time is sufficient.

[0045] (Effects) The Brillouin scattering measurement devices described in the first to third embodiments can compensate for fluctuations in the frequency components of broadband light and reduce BGS peak estimation errors.

[0046] (Embodiment 4) The Brillouin scattering measurement device described above compensates for fluctuations in the frequency components of the broadband probe light by dividing the measurement signal FA1 by the reference signal FA2. Ideally, the fluctuations in the frequency components of the two probe lights (Lpr1, Lpr2) are identical (their spectral shapes match). However, in reality, the spectral shapes of the two probe lights (Lpr1, Lpr2) often differ slightly, as shown in FIG. 14 . Even slight differences in the spectral shapes of the probe lights can result in unwanted side peaks during division. In particular, when the shapes differ at points where the spectral intensity is close to zero, the division result will have locally large values ​​(large side peaks). Such unwanted side peaks can prevent accurate measurement of the BGS peak position, making it difficult to detect the BFS, which is the BGS peak.

[0047] The Brillouin scattering measurement apparatus of this embodiment is capable of accurately measuring the peak position of BGS even when the fluctuations of the frequency components of the two probe beams (Lpr1, Lpr2) are different. The configuration of the Brillouin scattering measurement apparatus of this embodiment is the same as that of the Brillouin scattering measurement apparatuses of Embodiments 1 to 3. First, like the Brillouin scattering measurement apparatuses of Embodiments 1 to 3, the Brillouin scattering measurement apparatus of this embodiment measures signals with and without Brillouin scattering based on the two probe beams (Lpr1, Lpr2) using a scattered light acquisition unit 42 (measurement signal Mpr1 and measurement waveform Mpr2). Then, a calculator 43 divides a measurement signal FA1 obtained by frequency-analyzing the measurement signal Mpr1 by a reference signal FA2 obtained by frequency-analyzing the measurement waveform Mpr2 to obtain a Brillouin gain spectrum.

[0048] Since the BGS has a Lorentzian shape, the calculator 43 performs Lorentzian fitting on the Brillouin gain spectrum to determine the peak position. The Lorentzian fitting can remove unnecessary side peaks that are not Lorentzian. Furthermore, to further reduce the influence of side peaks, the calculator 43 may perform Lorentzian fitting taking into account weights based on errors included in the measurement.

[0049] 15 is a diagram illustrating the signal processing performed by the calculator 43. To estimate BFS from the acquired signal, the calculator 43 divides the signal FA1 with Brillouin scattering by the signal FA2 without Brillouin scattering to calculate the signal BS1. As described above, the signal BS1 exhibits large differences in spectral intensity even at frequencies other than those containing BGS due to slight differences in the spectra of the signals FA1 and FA2, and unwanted side peaks occur at frequencies with low intensity. Therefore, the calculator 43 performs fitting using a Lorentzian shape, which is characteristic of BGS, to detect the Lorentzian-shaped BGS signal BS2, rather than the unwanted side peaks that are not Lorentzian. The calculator 43 then estimates the BFS from the peak positions of the signal BS2.

[0050] Furthermore, the calculator 43 may perform Lorentz fitting by taking into account weights that take into account the measurement errors contained in the signals FA1 and FA2. This allows for more accurate estimation of the BGS peak position. For example, when the signal FA1 is f and the signal FA2 is g, the weights are calculated as follows in the error propagation equation: , which can be calculated as follows. Alternatively, because side peaks tend to occur at frequencies with low light intensity in the spectrum of broadband light, weighting such as w = g, in which the spectrum of the broadband probe light itself is used as the weight, may be used. [Note] The "weight" in the above-mentioned "Lorentz fitting taking weights into account," refers to the weight used in the optimization calculation when fitting based on a Lorentz function. For example, in the case of fitting processing using fitnlm (Reference 1), the Lorentz function and measurement data are input. In this case, in normal Lorentz fitting (processing that does not take weights into account), all parameters of "Weights - weight of observation value" are set to 1, and all measurement data are treated equally. On the other hand, in Lorentz fitting taking weights into account, the parameters of "Weights - weight of observation value" are set to weights based on Equation (1), and fitting is performed by assigning different weights to each measurement data. (Reference 1) https: / / jp.mathworks. com / help / stats / fitnlm.html [End of supplement]

[0051] (Definitions) The following abbreviations are used in this specification and drawings. ASE: Amplified spontaneous emission PD: Photo Detector AOM: Acousto optical modulator EDFA: Erbium doped fiber Amplifier ADC: Analog-to-digital converter BGS: Brillouin Gain Spectrum BFS: Brillouin Frequency Shift BPD: Balanced Photo Detector SSB: Single Side Band

[0052] 10: Pump light generator 11: Laser 12: Pulse generator 13: Broadband light source 14: Modulator 15: Detector 15a: 50:50 coupler 15b: Balanced photodiode 16: Intensity modulator 17: Delay device 18a, 18b: Optical filter 19: Polarization scrambler 31: Optical branching device 41: Scattered light generation unit 42: Scattered light acquisition unit 43: Computing unit 50: Optical fiber to be measured 51: Reference optical fiber 61, 62: Optical amplifier 63: Optical circulator 64: Optical amplifier 300-304: Brillouin scattering measurement device

Claims

1. A Brillouin scattering measurement device comprising: a pump light generator that generates pump light by pulsing continuous light of a single frequency from a laser; a probe light generator that generates probe light by pulsing broadband continuous light from a broadband light source, the broadband continuous light having frequency components broader than the frequency of the continuous light output by the laser, with a pulse width wider than that of the pump light; a modulator that generates local light by shifting the frequency of the continuous light from the laser by an arbitrary frequency; a detector that coherently detects the probe light, which includes Brillouin scattered light generated by counter-propagating the pump light and the probe light through an optical fiber under test, using the local light to generate a measurement signal, and that coherently detects the probe light, which does not include Brillouin scattered light, using the local light to generate a reference signal; and a calculator that divides the frequency-analyzed measurement signal by the frequency-analyzed reference signal to obtain the Brillouin gain spectrum.

2. The Brillouin scattering measurement device according to claim 1, wherein the computing unit performs Lorentz fitting on the Brillouin gain spectrum to determine the peak position.

3. The Brillouin scattering measurement device according to claim 2, wherein the computing unit performs the Lorentz fitting by weighting the frequency-analyzed measurement signal and the reference signal.

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