WO2024171332A1 - Brillouin gain analysis device, and brillouin gain analysis method - Google Patents

Brillouin gain analysis device, and brillouin gain analysis method Download PDF

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WO2024171332A1
WO2024171332A1 PCT/JP2023/005179 JP2023005179W WO2024171332A1 WO 2024171332 A1 WO2024171332 A1 WO 2024171332A1 JP 2023005179 W JP2023005179 W JP 2023005179W WO 2024171332 A1 WO2024171332 A1 WO 2024171332A1
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light
frequency
optical fiber
brillouin gain
brillouin
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PCT/JP2023/005179
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French (fr)
Japanese (ja)
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貴大 石丸
佳史 脇坂
央 高橋
優介 古敷谷
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日本電信電話株式会社
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Priority to PCT/JP2023/005179 priority Critical patent/WO2024171332A1/en
Publication of WO2024171332A1 publication Critical patent/WO2024171332A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre

Definitions

  • This disclosure relates to reflectometry, which performs sensing by measuring the scattered light of light incident on an optical fiber.
  • BOTDA Brillouin Optical Time Domain Analysis
  • BGS Brillouin Gain Spectrum
  • BFS Brillouin Frequency Shift
  • the frequency of the probe light Lpr is fixed, so in order to measure the entire BGS, it is necessary to change the frequency of the probe light Lpr and inject the pulsed pump light Lpn multiple times.
  • BOTDA Brillouin scattered light of any frequency, as shown by the dashed line 22 in Figure 2, is acquired over the entire length of the fiber in a single measurement.
  • the sweep range 23 of the probe light frequency In order to obtain optical information at all frequencies in the BGS range, the sweep range 23 of the probe light frequency must be set to the BGS range, which takes time to measure. For this reason, BOTDA has the problem that it is difficult to measure high-speed strain changes in optical fiber.
  • Non-Patent Document 1 discloses a measurement method that changes the frequency of the probe light and avoids multiple incidences of pulsed pump light.
  • Figure 3 is a diagram explaining the BOTDA disclosed in Non-Patent Document 1.
  • the measurement target of the BOTDA disclosed in Non-Patent Document 1 is a network NW where optical fibers branch.
  • a reflecting device Mr that reflects light is installed at the far end (the end face opposite to the incident end) of the optical fiber after branching.
  • the BOTDA disclosed in Non-Patent Document 1 is configured to measure the loss of each optical fiber after branching from the incident end.
  • the BOTDA disclosed in Non-Patent Document 1 performs BOTDA measurements using the probe light reflected by the reflecting device Mr and the pump light that is incident with a delayed timing relative to the probe light.
  • the BOTDA in Non-Patent Document 1 uses ASE (Amplified Spontaneous Emission) containing a wideband frequency component as the probe light, extracts the intensity of the Brillouin gain without relying on the variation of BFS (Brillouin Frequency Shift), and measures the loss of the optical fiber.
  • ASE Amptonified Spontaneous Emission
  • BFS Band Frequency Shift
  • the BOTDA in Non-Patent Document 1 is intended to measure branched optical fibers in a network NW, and since both the pump light and the probe light are pulsed, it cannot perform distributed measurement of the entire optical fiber.
  • the BOTDA in Non-Patent Document 1 can measure the loss of an optical fiber at high speed, it has the problem that it is difficult to measure the high-speed strain change of the optical fiber in a distributed manner.
  • the present invention aims to solve the above problems by providing a Brillouin gain analysis device and a Brillouin gain analysis method that can measure high-speed strain changes in an optical fiber in a distributed manner.
  • the BOTDA of the present invention uses ASE, which is a broadband continuous light rather than a pulsed light, as the probe light, and obtains Brillouin scattering by optical heterodyne detection.
  • the Brillouin gain analysis device comprises: A laser that outputs continuous light of a single frequency; an amplified spontaneous emission (ASE) light source that generates continuous light having a frequency component in a broader band than the frequency of the continuous light output by the laser and inputs the continuous light into one end of the optical fiber to be measured; a pulse generator that pulses the continuous light from the laser and inputs the pulsed light to the other end of the optical fiber; a modulator that generates local light by shifting the frequency of the continuous light from the laser by an arbitrary frequency; a detector for heterodyne detecting the Brillouin scattered light generated in the optical fiber and the local light; Equipped with.
  • ASE amplified spontaneous emission
  • the Brillouin gain analysis method comprises: A continuous amplified spontaneous emission (ASE) light having a frequency component in a broader band than a single-frequency laser light is input as a probe light to one end of an optical fiber to be measured; Pulsing the laser light and inputting the pulsed laser light as pump light to the other end of the optical fiber;
  • the present invention is characterized in that the frequency of the laser light is shifted by an arbitrary frequency to generate local light, and Brillouin scattered light generated in the optical fiber and the local light are heterodyne detected.
  • the present invention can provide a Brillouin gain analysis device and a Brillouin gain analysis method that can measure high-speed strain changes in an optical fiber in a distributed manner.
  • the Brillouin gain analysis device is characterized by further comprising a signal processing unit that performs a Fourier transform on the signal heterodyne detected by the detector to detect the Brillouin gain spectrum (BGS) and obtains the vibration distribution of the optical fiber from the time series changes in the peaks of the BGS.
  • a signal processing unit that performs a Fourier transform on the signal heterodyne detected by the detector to detect the Brillouin gain spectrum (BGS) and obtains the vibration distribution of the optical fiber from the time series changes in the peaks of the BGS.
  • BGS Brillouin gain spectrum
  • the Brillouin gain analysis method comprises: The heterodyne detected signal is subjected to a Fourier transform to detect a Brillouin Gain Spectrum (BGS); and a vibration distribution of the optical fiber is obtained from a time series change in a peak of the BGS.
  • BGS Brillouin Gain Spectrum
  • the acquired Brillouin scattered light contains multiple frequency components. Therefore, the BGS is calculated by setting a window function for the Brillouin scattered light and performing processing such as Fourier transform to obtain the frequency components. By spectralizing the Brillouin scattered light, it is possible to obtain the vibrations acting on the optical fiber.
  • the above-described Brillouin gain analysis apparatus operates as follows.
  • the scattered light generating section the laser, the ASE light source, and the pulse generator
  • a single-frequency laser is pulsed by an AOM and used as pump light for the BOTDA
  • the ASE which is a light source having a wide frequency component, is used as a probe light for the BOTDA, thereby acquiring Brillouin scattering without frequency sweeping of the probe light.
  • a single-frequency light branched from the laser is generated by an SSB modulator to generate local light shifted by several hundred MHz from the Brillouin scattering, and the Brillouin scattering obtained in the scattered light generating section is subjected to heterodyne detection with light multiplied by a BPF.
  • the frequency component of the Brillouin scattering can be converted into an electrical signal without losing it.
  • the converted electrical signal is converted into a digital signal by an ADC, and a Fourier transform is performed to acquire the BGS, which is the frequency component of the Brillouin scattering.
  • the strain temperature applied to the fiber is measured by the peak frequency of this BGS.
  • the frequency analysis of the signal processing unit includes: dividing the detection signal into predetermined time intervals on a time axis to obtain a section signal;
  • the method is characterized in that zero data is inserted before and after each of the section signals to increase the signal length, and the section signals with increased signal length are Fourier transformed to obtain the BGS.
  • the zero data it is preferable to insert the zero data so that the signal length has a minimum frequency accuracy.
  • This method takes advantage of the fact that there is only one BGS frequency peak in the acquired Brillouin scattered light data, and estimates the BGS frequency peak by performing frequency analysis on the Brillouin scattered light data at fixed distances after zero padding.
  • this method it is possible to measure vibrations from the BGS obtained in a single measurement using pulsed pump light, and to perform analysis with sufficient frequency resolution while maintaining the time resolution.
  • the Brillouin gain analysis device of the present invention can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network.
  • the present invention provides a Brillouin gain analysis device and a Brillouin gain analysis method that can measure high-speed strain changes in an optical fiber in a distributed manner.
  • FIG. 1 is a diagram illustrating BOTDA.
  • FIG. 2 is a diagram illustrating the measurement principle of BOTDA.
  • FIG. 1 is a diagram illustrating an application example of BOTDA.
  • FIG. 1 is a diagram illustrating a Brillouin gain analysis device according to the present invention.
  • FIG. 13 is a diagram for explaining a comparison of probe lights.
  • FIG. 2 is a diagram illustrating the configuration of a detector.
  • 1 is a diagram for explaining the measurement principle of a Brillouin gain analysis device according to the present invention;
  • FIG. 2 is a diagram for explaining a Brillouin gain analysis method according to the present invention.
  • FIG. 1 is a diagram illustrating an experimental system for obtaining Brillouin scattered light by using ASE light.
  • FIG. 1A and 1B are diagrams illustrating experimental results of obtaining Brillouin scattered light by using ASE light.
  • 4 is a diagram for explaining a frequency analysis method performed by a signal processing unit 43 of the Brillouin gain analysis device according to the present invention.
  • FIG. 4 is a diagram for explaining a frequency analysis method performed by a signal processing unit 43 of the Brillouin gain analysis device according to the present invention.
  • FIG. 1 is a diagram illustrating a trade-off between time resolution and frequency resolution.
  • 4 is a flowchart illustrating a frequency analysis method performed by the Brillouin gain analysis device according to the present invention.
  • 1 is a diagram for explaining the results of frequency analysis of Brillouin scattering acquired by the Brillouin gain analysis device according to the present invention;
  • FIG. 2 is a diagram illustrating an optical fiber under test.
  • FIG. 2 is a diagram illustrating an optical fiber under test.
  • 1A and 1B are diagrams illustrating the results of frequency analysis of Brillouin scattering when vibration is applied to an optical fiber under test.
  • 1 is a diagram for explaining that the Brillouin gain analysis apparatus according to the present invention can detect vibrations applied to an optical fiber under test.
  • FIG. 1 is a diagram for explaining that the Brillouin gain analysis apparatus according to the present invention can detect vibrations applied to an optical fiber under test.
  • the Brillouin gain analysis device 301 includes: A laser 11 that outputs continuous light of a single frequency; an ASE (amplified spontaneous emission) light source 13 that generates continuous light having a frequency component in a broader band than the frequency of the continuous light output by the laser 11 and inputs the continuous light into one end of an optical fiber 50 to be measured; a pulse generator 12 which converts the continuous light from the laser 11 into a pulse and inputs the pulsed light to the other end of the optical fiber 50; a modulator 14 for generating local light obtained by shifting the frequency of the continuous light from the laser 11 by an arbitrary frequency; a detector 15 for heterodyne detecting the Brillouin scattered light generated in the optical fiber and the local light; Equipped with.
  • a laser 11 that outputs continuous light of a single frequency
  • an ASE (amplified spontaneous emission) light source 13 that generates continuous light having a frequency component in a broader band than the frequency of the continuous light output by the laser 11 and inputs the continuous light into one end of an optical fiber
  • the Brillouin gain analysis device 301 includes a scattered light generation unit 41 and a scattered light acquisition unit 42 .
  • the scattered light generating section 41 generates two lights, pump light Lpn and probe light Lpr, and causes them to propagate in counter directions through the optical fiber 50 under test.
  • the pump light Lpn is generated by pulsing the continuous light of a single frequency output by the laser 11 through intensity modulation by the AOM of the pulse generator 12.
  • the power of the pump light Lpn is amplified by the EDFA 61.
  • the probe light Lpr is generated by amplifying, by the EDFA 62, broadband light generated by the ASE light source 13. Fig.
  • FIG. 5 is a diagram comparing the probe light Lpr of the Brillouin gain analysis device 300 (Fig. 5(A)) with the probe light Lpr of the Brillouin gain analysis device 301 (Fig. 5(B)).
  • the pump light Lpn and the probe light Lpr interact with each other in the optical fiber under test 50. Due to this interaction, light in which the Brillouin scattered light due to the pump light Lpn is superimposed on the probe light Lpr is sent to the scattered light acquisition unit 42 by the circulator 63.
  • the scattered light acquisition unit 42 converts the light sent from the scattered light generation unit 41 into an electrical signal.
  • the Rayleigh scattered light component of this light is removed by the BPF 64, and the signal light Lsig is made up of only Brillouin scattered light.
  • continuous light of a single frequency branched off from the laser 11 is also sent to the scattered light acquisition unit 42.
  • the SSB modulator 14 modulates the continuous light to near the Brillouin Frequency Shift (BFS) and outputs it as local light Lo.
  • the detector 15 performs heterodyne detection using the signal light Lsig and the local light Lo.
  • Fig. 6 is a diagram comparing the detector of the Brillouin gain analysis device 300 (Fig.
  • the detector of the Brillouin gain analysis device 300 is a photodiode
  • the detector 15 of the Brillouin gain analysis device 301 includes a 50:50 coupler 15a and a balanced photodiode (BPD) 15b.
  • BPD balanced photodiode
  • FIG. 7 is a diagram explaining the measurement principle of the Brillouin gain analysis device 301.
  • the probe light Lpr is broadband and can fully cover the frequency range 23 of the BGS. Therefore, while the conventional BOTDA required multiple measurements by changing the frequency of the probe light Lpr, the Brillouin gain analysis device 301 can obtain the BGS in a single measurement.
  • the Brillouin gain analysis device 301 further includes a signal processing unit 43 that performs a Fourier transform on the signal heterodyne detected by the detector 15 to detect the Brillouin gain spectrum (BGS) and obtains the vibration distribution of the optical fiber 50 from the time series changes in the peaks of the BGS.
  • BGS Brillouin gain spectrum
  • ASE Amplified spontaneous emission
  • continuous light having a frequency component in a broader band than a single-frequency laser light is input as a probe light Lpr to one end of an optical fiber 50 to be measured (step S01);
  • the laser light is pulsed and pump light Lpn is input to the other end of the optical fiber 50 (step S02); Shifting the frequency of the laser light by an arbitrary frequency to generate local light Lo (step S03); and heterodyne detecting the Brillouin scattered light Lsig and the local light Lo generated in the optical fiber 50 (step S04).
  • ASE Amplified spontaneous emission
  • BGS Brillouin Gain Spectrum
  • step S01 light from the ASE light source 13 within a range taking into consideration the BFS of the BGS is continuously input to one end of the optical fiber 50 as the probe light Lpr.
  • step S02 pump light Lpn having a single frequency is input to the other end of the optical fiber 50, and the probe light Lpr and the pump light Lpn interact with each other within the optical fiber 50 to generate Brillouin scattered light.
  • step S03 the frequency of the light branched from the pump light source is shifted by an arbitrary frequency to generate local light Lo having a frequency near the BFS.
  • step S04 the Brillouin scattered light Lsig and the local light Lo are heterodyne detected.
  • Steps S02 to S04 are repeated for a period of time for which vibration is desired to be detected. After that time has elapsed, in step S05, a Fourier transform is performed on the acquired signal to form a BGS. Finally, in step S06, the vibration is obtained by observing the time series changes in the BGS peaks.
  • the pump light is a pulse and the probe light is a continuous light, and one incidence of the pump light corresponds to one measurement of the entire optical fiber 50. Then, this pulsed pump light is incident for the time desired to measure, and vibration measurement is performed.
  • the optical fiber 50 to be tested in this experimental system is a single mode optical fiber SSMF and a low bending loss optical fiber BIF connected in series.
  • the probe light Lpr is input to one end of the optical fiber 50
  • the pump light Lpn is input to the other end, but in this experimental system, the probe light Lpr, which is an ASE light, and the pump light Lpn, which is a pulse light consisting of a single frequency, are input to one end of the optical fiber 50.
  • a mirror Mr is installed at the other end of the optical fiber 50, and the probe light Lpr is input prior to the pump light Lpn in terms of time.
  • the pump light Lpn input later interacts with the probe light Lpr reflected by the mirror Mr at the other end, causing Brillouin scattering.
  • FIG. 10 is a diagram for explaining the result (waveform RL2) of heterodyne detection by the detector 15 of return light including Brillouin scattered light from the optical fiber 50 in the experimental system of FIG.
  • waveform RL2 the result of heterodyne detection by the detector 15 of return light including Brillouin scattered light from the optical fiber 50 in the experimental system of FIG.
  • Non-Patent Document 1 pulsed ASE light was used as the probe light to obtain the BGS of a branched optical fiber.
  • the probe light in order to perform high-speed measurement in an optical fiber without a branch, the probe light is made to be continuous ASE light, and the obtained signal is converted to BGS using a method such as Fourier transform. This method makes it possible to obtain a distributed BGS with a single pulse of pump light.
  • the feature of the present invention is that, in order to shorten the measurement time required for vibration measurement, continuous ASE light is used as the probe light, and the obtained signal is converted to BGS using a frequency analysis method.
  • the signal processing unit 43 performs frequency analysis on the acquired Brillouin scattering data (detection signal) at regular distances, and calculates the BGS at each point by: dividing the detection signal into predetermined time intervals on a time axis to obtain a section signal; Zero data is inserted before and after each of the section signals to lengthen the signal length, and the section signals with the lengthened signal length are Fourier transformed to produce the BGS.
  • FIG. 11 is a diagram for explaining the frequency analysis method performed by the signal processing unit 43.
  • Step S11 is a process in which the signal processing unit 43 receives a detection signal from the scattered light acquisition unit 42. The detection signal is sampled by an A/D converter.
  • Step S12 is a process in which the signal processing unit 43 divides the detection signal into predetermined sections (sections divided in the longitudinal direction of the optical fiber under test 50). The detection signal divided into the predetermined sections is referred to as a "section signal.”
  • Step S13 is a process in which the signal processing unit 43 inserts zero data before and after the section signal (zero padding) to increase the signal length.
  • step S14 the signal processing unit 43 detects the BGS by performing a Fourier transform on the section signal with the increased signal length. Note that in this step, the peak frequency of the BGS is also obtained.
  • Fig. 12 is a diagram for explaining the procedure for performing distance resolution by frequency analysis on the Brillouin scattered light acquired by the BOTDA using an ASE light source.
  • the detection signal ds1 acquired in step S11 has a time axis corresponding to distance, and is 100 ns per 10 m.
  • the sampling rate of the A/D converter is set to 1 Gsample/s.
  • FFT Fast Fourier Transform
  • step S12 the detection signal ds1 is divided into 100 ns intervals. In this case, vibration data is acquired every 10 m in the longitudinal direction of the optical fiber 50 under test.
  • step S13 zero data is inserted on both sides of the divided detection signal (section signal dss) (zero padding).
  • the length of the zero data to be inserted is set so that the signal length after zero padding is the minimum frequency accuracy in optical fiber sensing technology using Brillouin scattering.
  • sl is the signal division length [sample]
  • sa is the sampling rate [sample/s]
  • fa is the minimum frequency accuracy [Hz]
  • Tr is the time resolution [s]
  • Fr is the frequency resolution [Hz].
  • Tr Tr x sa.
  • FIG. 13 (B2) shows the result of FFT on the section signal dss when the section length of the detection signal ds1 is short.
  • Each plot contains information of 10 Hz before and after. In other words, when the sampling rate is constant, if the section signal dss is short (increasing the distance resolution), the frequency resolution decreases.
  • Reason 2 In BOTDA measurements, it can be assumed that the frequency component of Brillouin scattering is a single peak.
  • BGS is estimated from each plot obtained by performing FFT on the section signal dss (FIGS. 13(A2) and (B2)).
  • the estimation method is a general estimation method such as quadratic function fitting by the least squares method. (Reason 3) Fig.
  • FIG. 13(C1) shows a signal with a length of 1 second, with zero data added before and after the 0.1 second section signal dss as in Fig. 13(B1). Since the signal length of the signal in Fig. 13(C1) is as long as 1 second, information of 10 Hz before and after each plot is included, and the frequency resolution is improved compared to the case of Fig. 13(B1). The insertion of zero data reduces the overall strength of the BGS waveform, but since the waveform obtained by FFTing the section signal dss is a single peak, it can be said that the peak found here is the only peak of the BGS.
  • FIG. 14 is a flowchart for explaining the frequency analysis method performed by the Brillouin gain analysis device 301 of this embodiment.
  • step S21 one pulse is sent as pump light to the optical fiber 50 under test, and Brillouin scattering is obtained by causing interference with probe light from the ASE light source passing through the optical fiber 50 under test.
  • step S21 is repeated for a desired measurement time T (step S21a). According to the sampling theorem, 1/(2 ⁇ pump light pulse sending period) It is possible to measure vibrations of this frequency.
  • step S22 a BGS is generated for Brillouin scattering for each pump light pulse, as described in Figure 11.
  • step S23 the maximum value of the BGS generated in step S22 is taken for each distance along the longitudinal direction of the optical fiber 50 under test, and the peak frequency (BFS) for each distance is estimated.
  • Figure 15 is a diagram (display example) showing the BFS for each distance corresponding to a certain time t. Additional explanation of Figure 15 is provided below.
  • FIG. 16 is a diagram explaining the optical fiber 50 under test.
  • the optical fiber 50 under test is an optical fiber in which a single mode optical fiber 50-1 and a single mode optical fiber 50-2 are connected in series.
  • the single mode optical fiber 50-1 is 50 m long, and generates a BFS of 10.840 GHz in the absence of temperature change or vibration.
  • the single mode optical fiber 50-2 is 50 m long, and generates a BFS of 10.821 GHz in the absence of temperature change or vibration.
  • the single mode optical fiber 50-1 side is the incident side of the probe light Lpr
  • the single mode optical fiber 50-2 side is the incident side of the pump light Lpn.
  • Fig. 15 shows the BFS for each distance for the Brillouin scattering obtained from the optical fiber 50 under test in Fig. 16.
  • the horizontal axis is the longitudinal distance of the optical fiber 50 under test (the input end of the pump light Lpn is set to zero).
  • the color bar indicates the intensity of the BGS.
  • the vertical axis indicates the frequency.
  • the black circles indicate the BFS estimated at each distance. It is estimated that the BFS at the shorter distance of 50 m is about 10.82 GHz, and the BFS at the longer distance is about 10.84 GHz. Therefore, it can be said that the Brillouin gain analyzer 301 can measure the BFS at each distance of the optical fiber under test.
  • step S22a steps S22 and S23 are repeated for the number of pump light pulses sent out in step S21 (measurement time T) to estimate the BFS.
  • the transition of the BFS during measurement time T can be known.
  • the change that has occurred in the optical fiber 50 under test due to the transition of the BFS can be estimated.
  • FIG. 17 is a diagram for explaining the optical fiber under test 50 used in this analysis.
  • the optical fiber under test 50 has a structure in which three single mode optical fibers (50-3, 50-4, 50-5) are connected by an optical switch 55.
  • the single mode optical fiber 50-3 is 50 m long, and generates a BFS of 10.840 GHz in the absence of temperature change or vibration.
  • the single mode optical fiber 50-4 is 50 m long, and generates a BFS of 10.821 GHz in the absence of temperature change or vibration.
  • the single mode optical fiber 50-5 is 50 m long, and generates a BFS of 10.833 GHz in the absence of temperature change or vibration.
  • the single mode optical fibers (50-3, 50-4) are the probe light Lpr input side, and the single mode optical fiber 50-5 is the pump light Lpn input side.
  • the optical switch 55 is driven at 25 Hz to alternately switch the single mode optical fiber 50-5 to be connected to the single mode optical fibers 50-3 and 50-4. That is, the BFS is artificially changed by switching the optical switch 55, thereby simulating a state in which the optical fiber 50 under test is subjected to vibration (see, for example, Non-Patent Document 4).
  • the single mode optical fibers (50-3, 50-4) are connected by a coupler 56 with a branching ratio of 50:50.
  • the coupler 56 inputs the probe light Lpr with equal power into each of the single mode optical fibers (50-3, 50-4).
  • FIG. 15 shows the BGS at a certain time for the Brillouin scattering from the optical fiber 50 under test in FIG. 17.
  • FIG. 18 shows the maximum frequency for each distance for that BGS (BFS for each distance).
  • the horizontal axis is the distance along the length of the optical fiber 50 under test (the input end of the pump light Lpn is set to zero).
  • the color bar is the frequency.
  • the vertical axis is the measurement time. Looking at the 50-100m section in the time direction, the color map changes periodically.
  • Figure 19 shows the results of a Fourier transform performed on the time axis of Figure 18.
  • the horizontal axis is the longitudinal distance of the optical fiber 50 under test (the input end of the pump light Lpn is set to zero).
  • the color bar represents the signal intensity.
  • the vertical axis represents the frequency.
  • the 25 Hz vibration (the optical path switched by the optical switch 55) applied to the optical fiber under test appears around 50-100 m.
  • ASE Amplified spontaneous emission
  • PD Photo Detector
  • AOM Acousto optic modulator
  • EDFA Erbium doped fiber amplifier
  • A/D Analog Digital
  • BGS Brillouin Gain Spectrum
  • BFS Brillouin Frequency Shift
  • BPD Balanced Photo Detector SSB: Single Side Band
  • Detector 15a 50: 50 coupler 15b: Balanced photodiode 21: Change in BGS peak 22: Arbitrary frequency 23: Sweep range 41: Scattered light generator 42: Scattered light acquirer 50: Optical fiber under test 50-1 to 50-5: Optical fiber 55: Optical switch 56: Coupler 61, 62: Optical amplifier 63: Optical circulator 73: Frequency range of probe light 91: Optical multiplexer 300, 301: Brillouin gain analysis device

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Abstract

The objective of the present invention is to provide a Brillouin gain analysis device and a Brillouin gain analysis method with which it is possible for high-speed strain changes in an optical fiber to be measured distributionally.　A Brillouin gain analysis device 301 according to the present invention comprises: a laser 11 that outputs continuous light having a single frequency; a pulse generator 12 that pulsates the continuous light and inputs the resulting light into one end of an optical fiber 50 to be measured; an ASE light source 13 that generates ASE having a frequency component of a wider band than that of the frequency of the continuous light and inputs the ASE into the other end of the optical fiber 50; a modulator 14 that generates local light obtained by shifting the frequency of the continuous light by a given frequency; a wave detector 15 that performs heterodyne detection on Brillouin scattering light generated in the optical fiber and the local light; and a signal processing unit 43 that detects a Brillouin gain spectrum (BGS) by Fourier transform of a signal obtained by the heterodyne detection, and acquires vibrational distribution of the optical fiber from the time-series change in peaks of the BGS.

Description

ブリルアン利得解析装置及びブリルアン利得解析方法Brillouin gain analysis device and Brillouin gain analysis method
　本開示は、光ファイバに入射した光の散乱光を計測することでセンシングを行う、反射計測に関する。 This disclosure relates to reflectometry, which performs sensing by measuring the scattered light of light incident on an optical fiber.
　光ファイバセンシング技術として、図１のようなＢＯＴＤＡ（Ｂｒｉｌｌｏｕｉｎ　Ｏｐｔｉｃａｌ　Ｔｉｍｅ　Ｄｏｍａｉｎ　Ａｎａｌｙｓｉｓ）という測定手法が存在する。この手法は、光ファイバ５０の歪みや温度を測定するために図２のようなブリルアンゲインスペクトラム（ＢＧＳ；Ｂｒｉｌｌｏｕｉｎ　Ｇａｉｎ　Ｓｐｅｃｔｒｕｍ）を取得する。ＢＧＳのピークの変化２１で光ファイバの歪みや温度を分布的に取得することができる。ＢＧＳのピークの変化２１のずれ量であるブリルアン周波数シフト（ＢＦＳ；Ｂｒｉｌｌｏｕｉｎ　Ｆｒｅｑｕｅｎｃｙ　Ｓｈｉｆｔ）を捉えるためにプローブ光Ｌｐｒの周波数掃引を行う必要がある。１回のパルス化したポンプ光Ｌｐｎを光ファイバ５０に入射する時は、プローブ光Ｌｐｒの周波数を固定するため、ＢＧＳ全体を計測するためには、プローブ光Ｌｐｒの周波数を変更し、パルス化したポンプ光Ｌｐｎを複数回の入射する必要がある。 As an optical fiber sensing technology, there is a measurement technique called BOTDA (Brillouin Optical Time Domain Analysis) as shown in Figure 1. This technique acquires a Brillouin Gain Spectrum (BGS) as shown in Figure 2 in order to measure the strain and temperature of an optical fiber 50. The strain and temperature of the optical fiber can be obtained in a distributed manner by measuring the change in the BGS peak 21. It is necessary to perform a frequency sweep of the probe light Lpr in order to capture the Brillouin Frequency Shift (BFS), which is the deviation amount of the BGS peak change 21. When a single pulsed pump light Lpn is injected into the optical fiber 50, the frequency of the probe light Lpr is fixed, so in order to measure the entire BGS, it is necessary to change the frequency of the probe light Lpr and inject the pulsed pump light Lpn multiple times.
　ＢＯＴＤＡでは、１回の測定でファイバの長さ方向全体に対して、図２の破線２２のような任意周波数のブリルアン散乱光を取得する。ＢＧＳの範囲すべての周波数における光情報を得るためには、プローブ光の周波数の掃引範囲２３をＢＧＳの範囲とする必要があり測定に時間がかかる。このため、ＢＯＴＤＡは、光ファイバの高速な歪み変化を計測することが困難という課題があった。 With BOTDA, Brillouin scattered light of any frequency, as shown by the dashed line 22 in Figure 2, is acquired over the entire length of the fiber in a single measurement. In order to obtain optical information at all frequencies in the BGS range, the sweep range 23 of the probe light frequency must be set to the BGS range, which takes time to measure. For this reason, BOTDA has the problem that it is difficult to measure high-speed strain changes in optical fiber.
　光ファイバの高速な歪み変化を計測するために、例えば、非特許文献１では、プローブ光の周波数を変更すること、及びパルス化したポンプ光を複数回入射することを回避する測定方法を開示する。図３は、非特許文献１が開示するＢＯＴＤＡを説明する図である。非特許文献１が開示するＢＯＴＤＡの測定対象は光ファイバが分岐するネットワークＮＷである。分岐後の光ファイバの遠端（入射端とは逆の端面）には、光を反射する反射装置Ｍｒを設置する。非特許文献１が開示するＢＯＴＤＡは、分岐後のそれぞれの光ファイバの損失を入射端から測定する装置構成である。非特許文献１が開示するＢＯＴＤＡは、反射装置Ｍｒで反射したプローブ光と、プローブ光に対してタイミングを遅らせて入射したポンプ光でＢＯＴＤＡの計測を行う。 In order to measure high-speed strain changes in optical fibers, for example, Non-Patent Document 1 discloses a measurement method that changes the frequency of the probe light and avoids multiple incidences of pulsed pump light. Figure 3 is a diagram explaining the BOTDA disclosed in Non-Patent Document 1. The measurement target of the BOTDA disclosed in Non-Patent Document 1 is a network NW where optical fibers branch. A reflecting device Mr that reflects light is installed at the far end (the end face opposite to the incident end) of the optical fiber after branching. The BOTDA disclosed in Non-Patent Document 1 is configured to measure the loss of each optical fiber after branching from the incident end. The BOTDA disclosed in Non-Patent Document 1 performs BOTDA measurements using the probe light reflected by the reflecting device Mr and the pump light that is incident with a delayed timing relative to the probe light.
　非特許文献１のＢＯＴＤＡは、広帯域の周波数成分を含む、ＡＳＥ（Ａｍｐｌｉｆｉｅｄ　Ｓｐｏｎｔａｎｅｏｕｓ　Ｅｍｉｓｓｉｏｎ）をプローブ光として用い、ＢＦＳ（Ｂｒｉｌｌｏｕｉｎ　Ｆｒｅｑｕｅｎｃｙ　Ｓｈｉｆｔ）のばらつきに依存せずにブリルアン利得の強度を抽出し、光ファイバの損失を測定している。しかし、非特許文献１のＢＯＴＤＡは、ネットワークＮＷ内の分岐した光ファイバを計測することを目的としており、ポンプ光とプローブ光の双方をパルス化しているため、光ファイバ全体の分布測定を行うことができない。つまり、非特許文献１のＢＯＴＤＡは、光ファイバの損失を高速に計測することはできるが、光ファイバの高速な歪み変化を分布的に計測することが困難という課題があった。 The BOTDA in Non-Patent Document 1 uses ASE (Amplified Spontaneous Emission) containing a wideband frequency component as the probe light, extracts the intensity of the Brillouin gain without relying on the variation of BFS (Brillouin Frequency Shift), and measures the loss of the optical fiber. However, the BOTDA in Non-Patent Document 1 is intended to measure branched optical fibers in a network NW, and since both the pump light and the probe light are pulsed, it cannot perform distributed measurement of the entire optical fiber. In other words, although the BOTDA in Non-Patent Document 1 can measure the loss of an optical fiber at high speed, it has the problem that it is difficult to measure the high-speed strain change of the optical fiber in a distributed manner.
　そこで、本発明は、上記課題を解決するために、光ファイバの高速な歪み変化を分布的に計測することができるブリルアン利得解析装置及びブリルアン利得解析方法を提供することを目的とする。 The present invention aims to solve the above problems by providing a Brillouin gain analysis device and a Brillouin gain analysis method that can measure high-speed strain changes in an optical fiber in a distributed manner.
　上記目的を達成するために、本発明に係るＢＯＴＤＡは、プローブ光をパルスではなく広帯域な連続光のＡＳＥを利用し、ブリルアン散乱を光ヘテロダイン検波により取得することとした。 To achieve the above objective, the BOTDA of the present invention uses ASE, which is a broadband continuous light rather than a pulsed light, as the probe light, and obtains Brillouin scattering by optical heterodyne detection.
　具体的には、本発明に係るブリルアン利得解析装置は、
　単一周波数の連続光を出力するレーザと、
　前記レーザが出力する連続光の周波数より広帯域な周波数成分を持つ連続光を発生し、測定対象の光ファイバの一端に入射するＡＳＥ（Ａｍｐｌｉｆｉｅｄ　ｓｐｏｎｔａｎｅｏｕｓ　ｅｍｉｓｓｉｏｎ）光源と、
　前記レーザからの前記連続光をパルス化して前記光ファイバの他端に入射するパルス生成器と、
　前記レーザからの前記連続光の周波数を任意の周波数だけシフトしたローカル光を生成する変調器と、
　前記光ファイバで発生したブリルアン散乱光と前記ローカル光とをヘテロダイン検波する検波器と、
を備える。 Specifically, the Brillouin gain analysis device according to the present invention comprises:
A laser that outputs continuous light of a single frequency;
an amplified spontaneous emission (ASE) light source that generates continuous light having a frequency component in a broader band than the frequency of the continuous light output by the laser and inputs the continuous light into one end of the optical fiber to be measured;
a pulse generator that pulses the continuous light from the laser and inputs the pulsed light to the other end of the optical fiber;
a modulator that generates local light by shifting the frequency of the continuous light from the laser by an arbitrary frequency;
a detector for heterodyne detecting the Brillouin scattered light generated in the optical fiber and the local light;
Equipped with.
　また、本発明に係るブリルアン利得解析方法は、
　単一周波数のレーザ光より広帯域な周波数成分を持つＡＳＥ（Ａｍｐｌｉｆｉｅｄ　ｓｐｏｎｔａｎｅｏｕｓ　ｅｍｉｓｓｉｏｎ）連続光を測定対象の光ファイバの一端にプローブ光として入射すること、
　前記レーザ光をパルス化して前記光ファイバの他端にポンプ光として入射すること、
　前記レーザ光の周波数を任意の周波数だけシフトしてローカル光を生成すること、及び
　前記光ファイバで発生したブリルアン散乱光と前記ローカル光とをヘテロダイン検波すること
を特徴とする。 Further, the Brillouin gain analysis method according to the present invention comprises:
A continuous amplified spontaneous emission (ASE) light having a frequency component in a broader band than a single-frequency laser light is input as a probe light to one end of an optical fiber to be measured;
Pulsing the laser light and inputting the pulsed laser light as pump light to the other end of the optical fiber;
The present invention is characterized in that the frequency of the laser light is shifted by an arbitrary frequency to generate local light, and Brillouin scattered light generated in the optical fiber and the local light are heterodyne detected.
　ＢＯＴＤＡにおいて、プローブ光を広帯域化し、光ヘテロダイン検波を用いることで、パルス化した１つのポンプ光で光ファイバ上のブリルアン散乱光を分布的に取得することができる。このため、プローブ光の周波数掃引やポンプ光を複数回入射する必要がない。従って、本発明は、光ファイバの高速な歪み変化を分布的に計測することができるブリルアン利得解析装置及びブリルアン利得解析方法を提供することができる。 In BOTDA, by broadening the bandwidth of the probe light and using optical heterodyne detection, it is possible to obtain a distributed Brillouin scattered light in an optical fiber with a single pulsed pump light. This eliminates the need to sweep the frequency of the probe light or to input the pump light multiple times. Therefore, the present invention can provide a Brillouin gain analysis device and a Brillouin gain analysis method that can measure high-speed strain changes in an optical fiber in a distributed manner.
　本発明に係るブリルアン利得解析装置は、前記検波器でヘテロダイン検波された信号をフーリエ変換してブリルアンゲインスペクトラム（ＢＧＳ）を検出し、前記ＢＧＳのピークの時系列変化から前記光ファイバの振動分布を取得する信号処理部をさらに備えることを特徴とする。 The Brillouin gain analysis device according to the present invention is characterized by further comprising a signal processing unit that performs a Fourier transform on the signal heterodyne detected by the detector to detect the Brillouin gain spectrum (BGS) and obtains the vibration distribution of the optical fiber from the time series changes in the peaks of the BGS.
　また、本発明に係るブリルアン利得解析方法は、
　前記ヘテロダイン検波された信号をフーリエ変換してブリルアンゲインスペクトラム（ＢＧＳ）を検出すること、及び
　前記ＢＧＳのピークの時系列変化から前記光ファイバの振動分布を取得すること
をさらに行う。 Further, the Brillouin gain analysis method according to the present invention comprises:
The heterodyne detected signal is subjected to a Fourier transform to detect a Brillouin Gain Spectrum (BGS); and a vibration distribution of the optical fiber is obtained from a time series change in a peak of the BGS.
　取得したブリルアン散乱光は複数の周波数成分を含む。そこで、ブリルアン散乱光に対し、窓関数を設定してフーリエ変換などの周波数成分を求める処理を行うことでＢＧＳを計算する。ブリルアン散乱光をスペクトル化することで光ファイバに加わる振動を取得することができる。 The acquired Brillouin scattered light contains multiple frequency components. Therefore, the BGS is calculated by setting a window function for the Brillouin scattered light and performing processing such as Fourier transform to obtain the frequency components. By spectralizing the Brillouin scattered light, it is possible to obtain the vibrations acting on the optical fiber.
　つまり、上述したブリルアン利得解析装置は、次のように動作する。
　散乱光生成部（前記レーザ、前記ＡＳＥ光源及び前記パルス生成器）では、単一周波数のレーザをＡＯＭにてパルス化し、ＢＯＴＤＡのポンプ光として使用し、広帯域な周波数成分を持つ光源であるＡＳＥをＢＯＴＤＡのプローブ光として活用することでプローブ光の周波数掃引なしでブリルアン散乱を取得する。散乱光取得部（前記変調器及び前記検波器）では、レーザから分岐した単一周波数の光をＳＳＢ変調器によりブリルアン散乱から数百ＭＨｚ程度ずらしたローカル光を生成し、散乱光生成部で得たブリルアン散乱に対してＢＰＦを掛けた光とヘテロダイン検波する。ヘテロダインを行うことで、ブリルアン散乱の周波数成分を失うことなく電気信号に変換できる。変換した電気信号をＡＤＣにてデジタル信号に変換し、フーリエ変換を行うことで、ブリルアン散乱の周波数成分であるＢＧＳを取得する。このＢＧＳのピーク周波数によりファイバに加わる歪み温度を測定する。 In other words, the above-described Brillouin gain analysis apparatus operates as follows.
In the scattered light generating section (the laser, the ASE light source, and the pulse generator), a single-frequency laser is pulsed by an AOM and used as pump light for the BOTDA, and the ASE, which is a light source having a wide frequency component, is used as a probe light for the BOTDA, thereby acquiring Brillouin scattering without frequency sweeping of the probe light. In the scattered light acquiring section (the modulator and the detector), a single-frequency light branched from the laser is generated by an SSB modulator to generate local light shifted by several hundred MHz from the Brillouin scattering, and the Brillouin scattering obtained in the scattered light generating section is subjected to heterodyne detection with light multiplied by a BPF. By performing heterodyning, the frequency component of the Brillouin scattering can be converted into an electrical signal without losing it. The converted electrical signal is converted into a digital signal by an ADC, and a Fourier transform is performed to acquire the BGS, which is the frequency component of the Brillouin scattering. The strain temperature applied to the fiber is measured by the peak frequency of this BGS.
　ここで、ＡＳＥ連続光によるＢＯＴＤＡにて取得したデータからＢＧＳを計算しピークを探す際の周波数解析手法を説明する。特に時間分解能と周波数分解能にトレードオフがあるため、時間分解能を維持したまま十分な周波数分解能で解析を行うことが困難であり、課題となる。下の手法を採用することで当該課題も解決できる。 Here, we explain the frequency analysis method used to calculate BGS and search for peaks from data acquired by BOTDA using ASE continuous light. In particular, since there is a trade-off between time resolution and frequency resolution, it is difficult and challenging to perform analysis with sufficient frequency resolution while maintaining time resolution. This challenge can be solved by adopting the method below.
　前記信号処理部の前記周波数解析は、
　時間軸上において前記検波信号を所定時間毎に区切り、区間信号とすること、
　それぞれの前記区間信号の前後にゼロデータを挿入して信号長を長くすること、及び
　信号長を長くした前記区間信号をフーリエ変換して前記ＢＧＳとすること
であることを特徴とする。 The frequency analysis of the signal processing unit includes:
dividing the detection signal into predetermined time intervals on a time axis to obtain a section signal;
The method is characterized in that zero data is inserted before and after each of the section signals to increase the signal length, and the section signals with increased signal length are Fourier transformed to obtain the BGS.
　ここで、前記信号長が最小周波数確度となるように前記ゼロデータの挿入を行うことが好ましい。 Here, it is preferable to insert the zero data so that the signal length has a minimum frequency accuracy.
　本手法は、取得したブリルアン散乱光のデータについて、ＢＧＳの周波数ピークが１つのみであることを利用して、一定距離ごとのブリルアン散乱光のデータに対してゼロ・パディングを行ったデータを周波数解析することでＢＧＳの周波数ピークを推定する。
　本手法を採用することで、パルス化したポンプ光による１回の測定で得たＢＧＳから振動を計測することができ、かつ時間分解能を維持したまま十分な周波数分解能で解析を行うことができる。 This method takes advantage of the fact that there is only one BGS frequency peak in the acquired Brillouin scattered light data, and estimates the BGS frequency peak by performing frequency analysis on the Brillouin scattered light data at fixed distances after zero padding.
By adopting this method, it is possible to measure vibrations from the BGS obtained in a single measurement using pulsed pump light, and to perform analysis with sufficient frequency resolution while maintaining the time resolution.
　本発明のブリルアン利得解析装置は、コンピュータとプログラムによっても実現でき、プログラムを記録媒体に記録することも、ネットワークを通して提供することも可能である。 The Brillouin gain analysis device of the present invention can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network.
　なお、上記各発明は、可能な限り組み合わせることができる。 The above inventions can be combined as much as possible.
　本発明は、光ファイバの高速な歪み変化を分布的に計測することができるブリルアン利得解析装置及びブリルアン利得解析方法を提供することができる。 The present invention provides a Brillouin gain analysis device and a Brillouin gain analysis method that can measure high-speed strain changes in an optical fiber in a distributed manner.
ＢＯＴＤＡを説明する図である。FIG. 1 is a diagram illustrating BOTDA. ＢＯＴＤＡの測定原理を説明する図である。FIG. 2 is a diagram illustrating the measurement principle of BOTDA. ＢＯＴＤＡの応用例を説明する図である。FIG. 1 is a diagram illustrating an application example of BOTDA. 本発明に係るブリルアン利得解析装置を説明する図である。FIG. 1 is a diagram illustrating a Brillouin gain analysis device according to the present invention. プローブ光の比較を説明する図である。FIG. 13 is a diagram for explaining a comparison of probe lights. 検波器の構成を説明する図である。FIG. 2 is a diagram illustrating the configuration of a detector. 本発明に係るブリルアン利得解析装置の測定原理を説明する図である。1 is a diagram for explaining the measurement principle of a Brillouin gain analysis device according to the present invention; 本発明に係るブリルアン利得解析方法を説明する図である。FIG. 2 is a diagram for explaining a Brillouin gain analysis method according to the present invention. ＡＳＥ光によりブリルアン散乱光を取得する実験系を説明する図である。FIG. 1 is a diagram illustrating an experimental system for obtaining Brillouin scattered light by using ASE light. ＡＳＥ光によりブリルアン散乱光を取得する実験結果を説明する図である。1A and 1B are diagrams illustrating experimental results of obtaining Brillouin scattered light by using ASE light. 本発明に係るブリルアン利得解析装置の信号処理部４３が行う周波数解析手法について説明する図である。4 is a diagram for explaining a frequency analysis method performed by a signal processing unit 43 of the Brillouin gain analysis device according to the present invention. FIG. 本発明に係るブリルアン利得解析装置の信号処理部４３が行う周波数解析手法について説明する図である。4 is a diagram for explaining a frequency analysis method performed by a signal processing unit 43 of the Brillouin gain analysis device according to the present invention. FIG. 時間分解能と周波数分解能がトレードオフの関係であることを説明する図である。FIG. 1 is a diagram illustrating a trade-off between time resolution and frequency resolution. 本発明に係るブリルアン利得解析装置が行う周波数解析方法を説明するフローチャートである。4 is a flowchart illustrating a frequency analysis method performed by the Brillouin gain analysis device according to the present invention. 本発明に係るブリルアン利得解析装置が取得したブリルアン散乱に対して周波数解析を行った結果を説明する図である。1 is a diagram for explaining the results of frequency analysis of Brillouin scattering acquired by the Brillouin gain analysis device according to the present invention; 被試験光ファイバを説明する図である。FIG. 2 is a diagram illustrating an optical fiber under test. 被試験光ファイバを説明する図である。FIG. 2 is a diagram illustrating an optical fiber under test. 被試験光ファイバに振動を与えたときのブリルアン散乱に対して周波数解析を行った結果を説明する図である。1A and 1B are diagrams illustrating the results of frequency analysis of Brillouin scattering when vibration is applied to an optical fiber under test. 本発明に係るブリルアン利得解析装置が被試験光ファイバに与えた振動を検出できていることを説明する図である。1 is a diagram for explaining that the Brillouin gain analysis apparatus according to the present invention can detect vibrations applied to an optical fiber under test. FIG.
　添付の図面を参照して本発明の実施形態を説明する。以下に説明する実施形態は本発明の実施例であり、本発明は、以下の実施形態に制限されるものではない。なお、本明細書及び図面において符号が同じ構成要素は、相互に同一のものを示すものとする。 The following describes an embodiment of the present invention with reference to the attached drawings. The embodiment described below is an example of the present invention, and the present invention is not limited to the following embodiment. Note that components with the same reference numerals in this specification and drawings are mutually identical.
（実施形態１）
　図４は、本実施形態のブリルアン利得解析装置３０１を説明する図である。ブリルアン利得解析装置３０１は、
　単一周波数の連続光を出力するレーザ１１と、
　レーザ１１が出力する連続光の周波数より広帯域な周波数成分を持つ連続光を発生し、測定対象の光ファイバ５０の一端に入射するＡＳＥ（Ａｍｐｌｉｆｉｅｄ　ｓｐｏｎｔａｎｅｏｕｓ　ｅｍｉｓｓｉｏｎ）光源１３と、
　レーザ１１からの前記連続光をパルス化して光ファイバ５０の他端に入射するパルス生成器１２と、
　レーザ１１からの前記連続光の周波数を任意の周波数だけシフトしたローカル光を生成する変調器１４と、
　前記光ファイバで発生したブリルアン散乱光と前記ローカル光とをヘテロダイン検波する検波器１５と、
を備える。 (Embodiment 1)
4 is a diagram illustrating the Brillouin gain analysis device 301 of this embodiment. The Brillouin gain analysis device 301 includes:
A laser 11 that outputs continuous light of a single frequency;
an ASE (amplified spontaneous emission) light source 13 that generates continuous light having a frequency component in a broader band than the frequency of the continuous light output by the laser 11 and inputs the continuous light into one end of an optical fiber 50 to be measured;
a pulse generator 12 which converts the continuous light from the laser 11 into a pulse and inputs the pulsed light to the other end of the optical fiber 50;
a modulator 14 for generating local light obtained by shifting the frequency of the continuous light from the laser 11 by an arbitrary frequency;
a detector 15 for heterodyne detecting the Brillouin scattered light generated in the optical fiber and the local light;
Equipped with.
　ブリルアン利得解析装置３０１は、散乱光生成部４１と散乱光取得部４２を備える。
　散乱光生成部４１は、ポンプ光Ｌｐｎとプローブ光Ｌｐｒの２つの光を生成し、被試験光ファイバ５０にて対向伝搬させる。
　ポンプ光Ｌｐｎは、レーザ１１が出力した単一周波数の連続光をパルス生成器１２のＡＯＭでの強度変調でパルス化されて生成される。ポンプ光Ｌｐｎは、ＥＤＦＡ６１でパワーが増幅される。一方、プローブ光Ｌｐｒは、ＡＳＥ光源１３を用いて発生させた広帯域な光をＥＤＦＡ６２で増幅させて生成する。図５は、ブリルアン利得解析装置３００のプローブ光Ｌｐｒ（図５（Ａ））とブリルアン利得解析装置３０１のプローブ光Ｌｐｒ（図５（Ｂ））とを比較した図である。
　ポンプ光Ｌｐｎとプローブ光Ｌｐｒは、被試験光ファイバ５０内で、相互作用を起こす。当該相互作用により、プローブ光Ｌｐｒにポンプ光Ｌｐｎによるブリルアン散乱光が重畳した光が、サーキュレータ６３により散乱光取得部４２に送られる。 The Brillouin gain analysis device 301 includes a scattered light generation unit 41 and a scattered light acquisition unit 42 .
The scattered light generating section 41 generates two lights, pump light Lpn and probe light Lpr, and causes them to propagate in counter directions through the optical fiber 50 under test.
The pump light Lpn is generated by pulsing the continuous light of a single frequency output by the laser 11 through intensity modulation by the AOM of the pulse generator 12. The power of the pump light Lpn is amplified by the EDFA 61. On the other hand, the probe light Lpr is generated by amplifying, by the EDFA 62, broadband light generated by the ASE light source 13. Fig. 5 is a diagram comparing the probe light Lpr of the Brillouin gain analysis device 300 (Fig. 5(A)) with the probe light Lpr of the Brillouin gain analysis device 301 (Fig. 5(B)).
The pump light Lpn and the probe light Lpr interact with each other in the optical fiber under test 50. Due to this interaction, light in which the Brillouin scattered light due to the pump light Lpn is superimposed on the probe light Lpr is sent to the scattered light acquisition unit 42 by the circulator 63.
　散乱光取得部４２は、散乱光生成部４１から送られてくる光を電気信号に変換する。当該光は、まず、ＢＰＦ６４でレイリー散乱光の成分が除かれ、ブリルアン散乱光のみの信号光Ｌｓｉｇとなる。
　また、散乱光取得部４２には、レーザ１１レーザから分岐された単一周波数の連続光も送られてくる。ＳＳＢ変調器１４は当該連続光をブリルアン周波数シフト（ＢＦＳ；Ｂｒｉｌｌｏｕｉｎ　Ｆｒｅｑｕｅｎｃｙ　Ｓｈｉｆｔ）付近に変調し、ローカル光Ｌｏとして出力する。
　検波器１５は、信号光Ｌｓｉｇとローカル光Ｌｏとを用いてヘテロダイン検波を行う。図６は、ブリルアン利得解析装置３００の検波器（図６（Ａ））とブリルアン利得解析装置３０１の検波器１５（図５（Ｂ））とを比較した図である。ブリルアン利得解析装置３００の検波器はフォトダイオードであるが、ブリルアン利得解析装置３０１の検波器１５は５０：５０カプラ１５ａとバランス型フォトダイオード（ＢＰＤ；Ｂａｌａｎｃｅｄ　Ｐｈｏｔｏ　Ｄｅｔｅｃｔｏｒ）１５ｂを備える。 The scattered light acquisition unit 42 converts the light sent from the scattered light generation unit 41 into an electrical signal. First, the Rayleigh scattered light component of this light is removed by the BPF 64, and the signal light Lsig is made up of only Brillouin scattered light.
In addition, continuous light of a single frequency branched off from the laser 11 is also sent to the scattered light acquisition unit 42. The SSB modulator 14 modulates the continuous light to near the Brillouin Frequency Shift (BFS) and outputs it as local light Lo.
The detector 15 performs heterodyne detection using the signal light Lsig and the local light Lo. Fig. 6 is a diagram comparing the detector of the Brillouin gain analysis device 300 (Fig. 6A) with the detector 15 of the Brillouin gain analysis device 301 (Fig. 5B). The detector of the Brillouin gain analysis device 300 is a photodiode, while the detector 15 of the Brillouin gain analysis device 301 includes a 50:50 coupler 15a and a balanced photodiode (BPD) 15b.
　図７は、ブリルアン利得解析装置３０１の測定原理を説明する図である。図２の従来のＢＯＴＤＡと比較すると、プローブ光Ｌｐｒが広帯域となっており、ＢＧＳの周波数範囲２３を十分カバーできている。このため、従来のＢＯＴＤＡではプローブ光Ｌｐｒの周波数を変化させて測定を複数回行わなければならなかったところ、ブリルアン利得解析装置３０１では１回の測定でＢＧＳを取得できる。 FIG. 7 is a diagram explaining the measurement principle of the Brillouin gain analysis device 301. Compared to the conventional BOTDA in FIG. 2, the probe light Lpr is broadband and can fully cover the frequency range 23 of the BGS. Therefore, while the conventional BOTDA required multiple measurements by changing the frequency of the probe light Lpr, the Brillouin gain analysis device 301 can obtain the BGS in a single measurement.
　ブリルアン利得解析装置３０１は、検波器１５でヘテロダイン検波された信号をフーリエ変換してブリルアンゲインスペクトラム（ＢＧＳ）を検出し、前記ＢＧＳのピークの時系列変化から光ファイバ５０の振動分布を取得する信号処理部４３をさらに備える。 The Brillouin gain analysis device 301 further includes a signal processing unit 43 that performs a Fourier transform on the signal heterodyne detected by the detector 15 to detect the Brillouin gain spectrum (BGS) and obtains the vibration distribution of the optical fiber 50 from the time series changes in the peaks of the BGS.
　図８は、信号処理部４３を含めたブリルアン利得解析装置３０１の動作を説明するフローチャートである。本ブリルアン利得解析方法は、
　単一周波数のレーザ光より広帯域な周波数成分を持つＡＳＥ（Ａｍｐｌｉｆｉｅｄ　ｓｐｏｎｔａｎｅｏｕｓ　ｅｍｉｓｓｉｏｎ）連続光を測定対象の光ファイバ５０の一端にプローブ光Ｌｐｒとして入射すること（ステップＳ０１）、
　前記レーザ光をパルス化して光ファイバ５０の他端にポンプ光Ｌｐｎ入射すること（ステップＳ０２）、
　前記レーザ光の周波数を任意の周波数だけシフトしてローカル光Ｌｏを生成すること（ステップＳ０３）、及び
　光ファイバ５０で発生したブリルアン散乱光Ｌｓｉｇとローカル光Ｌｏとをヘテロダイン検波すること（ステップＳ０４）
を特徴とする。 8 is a flowchart for explaining the operation of the Brillouin gain analysis device 301 including the signal processing unit 43.
Amplified spontaneous emission (ASE) continuous light having a frequency component in a broader band than a single-frequency laser light is input as a probe light Lpr to one end of an optical fiber 50 to be measured (step S01);
The laser light is pulsed and pump light Lpn is input to the other end of the optical fiber 50 (step S02);
Shifting the frequency of the laser light by an arbitrary frequency to generate local light Lo (step S03); and heterodyne detecting the Brillouin scattered light Lsig and the local light Lo generated in the optical fiber 50 (step S04).
It is characterized by:
　そして、信号処理部４３において、
　前記ヘテロダイン検波された信号をフーリエ変換してブリルアンゲインスペクトラム（ＢＧＳ）を検出すること（ステップＳ０５）、及び
　前記ＢＧＳのピークの時系列変化から光ファイバ５０の振動分布を取得すること（ステップＳ０６）
をさらに行う。 Then, in the signal processing unit 43,
Detecting a Brillouin Gain Spectrum (BGS) by Fourier transforming the heterodyne detected signal (step S05); and acquiring a vibration distribution of the optical fiber 50 from a time series change in the peak of the BGS (step S06).
Further steps will be taken.
　まず、ステップＳ０１で、ＢＧＳのＢＦＳを考慮した範囲のＡＳＥ光源１３の光をプローブ光Ｌｐｒとして連続に光ファイバ５０の一端に入射する。
　次に、ステップＳ０２で、光ファイバ５０の他端に単一周波数からなるポンプ光Ｌｐｎを入射し、光ファイバ５０内でプローブ光Ｌｐｒとポンプ光Ｌｐｎとを相互作用させてブリルアン散乱光を発生させる。
　ステップＳ０３で、ポンプ光の光源より分岐させた光の周波数を任意の周波数だけシフトしてＢＦＳ付近の周波数のローカル光Ｌｏを生成する。
　ステップＳ０４で、ブリルアン散乱光Ｌｓｉｇとローカル光Ｌｏとをヘテロダイン検波する。ここまでで、１回のポンプ光パルスで分布的にＢＧＳを形成するために必要な信号が受信できる。
　振動を検出したい時間だけステップＳ０２からステップＳ０４を繰り返す。
　当該時間を経過した後、ステップＳ０５で、取得した信号にフーリエ変換を行い、ＢＧＳを形成する。
　最後に、ステップＳ０６で、ＢＧＳのピークの時系列変化を見ることで振動を取得する。 First, in step S01, light from the ASE light source 13 within a range taking into consideration the BFS of the BGS is continuously input to one end of the optical fiber 50 as the probe light Lpr.
Next, in step S02, pump light Lpn having a single frequency is input to the other end of the optical fiber 50, and the probe light Lpr and the pump light Lpn interact with each other within the optical fiber 50 to generate Brillouin scattered light.
In step S03, the frequency of the light branched from the pump light source is shifted by an arbitrary frequency to generate local light Lo having a frequency near the BFS.
In step S04, the Brillouin scattered light Lsig and the local light Lo are heterodyne detected. Up to this point, a signal required to form a distributed BGS with one pump light pulse can be received.
Steps S02 to S04 are repeated for a period of time for which vibration is desired to be detected.
After that time has elapsed, in step S05, a Fourier transform is performed on the acquired signal to form a BGS.
Finally, in step S06, the vibration is obtained by observing the time series changes in the BGS peaks.
　つまり、ポンプ光はパルスで、プローブ光は連続光であり、ポンプ光１回の入射が、光ファイバ５０全体の１回の測定に対応する。そして、このパルスのポンプ光を計測したい時間だけ入射し、振動測定を行う。 In other words, the pump light is a pulse and the probe light is a continuous light, and one incidence of the pump light corresponds to one measurement of the entire optical fiber 50. Then, this pulsed pump light is incident for the time desired to measure, and vibration measurement is performed.
（実施例）
　本実施例では、ＡＳＥ光によりブリルアン散乱光を取得する実験結果を説明する。
　図９は、本実施例での実験系を説明する図である。本実験系の被試験光ファイバ５０はシングルモード光ファイバＳＳＭＦと低曲げ損失光ファイバＢＩＦを直列に接続したものである。実施形態のブリルアン利得解析装置３０１は、光ファイバ５０の一端にプローブ光Ｌｐｒ、他端にポンプ光Ｌｐｎを入射したが、本実験系では、光ファイバ５０の一端にＡＳＥ光であるプローブ光Ｌｐｒと、単一周波数からなるパルス光であるポンプ光Ｌｐｎを入射する。ブリルアン利得解析装置３０１と同じ状態を形成するために光ファイバ５０の他端にはミラーＭｒを設置し、ポンプ光Ｌｐｎに対し、プローブ光Ｌｐｒを時間的に先に入射する。後に入射するポンプ光Ｌｐｎは、他端のミラーＭｒで反射したプローブ光Ｌｐｒと相互作用し、ブリルアン散乱が起こる。 (Example)
In this embodiment, the results of an experiment in which Brillouin scattered light is obtained by using ASE light will be described.
9 is a diagram for explaining the experimental system in this embodiment. The optical fiber 50 to be tested in this experimental system is a single mode optical fiber SSMF and a low bending loss optical fiber BIF connected in series. In the Brillouin gain analysis device 301 of the embodiment, the probe light Lpr is input to one end of the optical fiber 50, and the pump light Lpn is input to the other end, but in this experimental system, the probe light Lpr, which is an ASE light, and the pump light Lpn, which is a pulse light consisting of a single frequency, are input to one end of the optical fiber 50. In order to create the same state as the Brillouin gain analysis device 301, a mirror Mr is installed at the other end of the optical fiber 50, and the probe light Lpr is input prior to the pump light Lpn in terms of time. The pump light Lpn input later interacts with the probe light Lpr reflected by the mirror Mr at the other end, causing Brillouin scattering.
　図１０は、図９の実験系において、光ファイバ５０からのブリルアン散乱光を含む戻り光を検波器１５でヘテロダイン検波した結果（波形ＲＬ２）を説明する図である。
　ポンプ光Ｌｐｎだけ光ファイバ５０に入射し、ＡＳＥ光のプローブ光Ｌｐｒを光ファイバ５０に入射しない場合の戻り光は波形ＲＬ１であり、ブリルアン散乱が発生していないことがわかる。 FIG. 10 is a diagram for explaining the result (waveform RL2) of heterodyne detection by the detector 15 of return light including Brillouin scattered light from the optical fiber 50 in the experimental system of FIG.
When only the pump light Lpn is input to the optical fiber 50 and the probe light Lpr of the ASE light is not input to the optical fiber 50, the return light has a waveform RL1, which indicates that no Brillouin scattering occurs.
　２種類の特性の異なる光ファイバを被試験光ファイバ５０として用いているため、波形ＲＬ２にはブリルアン散乱のピークが２つ観察できる。図１０では、ＡＳＥ光でブリルアン散乱が取得できるか確認するため、光ファイバ５０全体の情報を一つの図で表している。波形ＲＬ２を時間的に区切り周波数スペクトルへ変換すれば、光ファイバ５０の振動を分布的に取得できる。つまり、本実験系より、プローブ光を広帯域化し、光ヘテロダイン検波を用いることで、パルス化した１つのポンプ光で光ファイバ上のブリルアン散乱光を分布的に取得できることがわかる。 Since two types of optical fiber with different characteristics are used as the optical fiber 50 under test, two Brillouin scattering peaks can be observed in the waveform RL2. In Figure 10, the information of the entire optical fiber 50 is shown in a single diagram in order to confirm whether Brillouin scattering can be obtained with ASE light. If the waveform RL2 is divided in time and converted into a frequency spectrum, the vibration of the optical fiber 50 can be obtained in a distributed manner. In other words, this experimental system shows that by broadening the bandwidth of the probe light and using optical heterodyne detection, it is possible to obtain the distributed Brillouin scattering light on the optical fiber with a single pulsed pump light.
（効果）
　従来技術（非特許文献１）では、分岐された光ファイバのＢＧＳを取得するため、プローブ光としてパルスのＡＳＥ光を使用していた。本発明では、分岐のない光ファイバでの高速な測定のため、プローブ光を連続光のＡＳＥ光とし、取得した信号をフーリエ変換等の手法を用いてＢＧＳに変換する。この手法により、１回のパルス化したポンプ光で、分布的なＢＧＳの取得を可能にする。本発明の特徴は、振動計測に必要な測定時間短縮のため、プローブ光としてＡＳＥ光の連続光を用い、取得した信号を周波数解析手法によりＢＧＳに変換する点である。 (effect)
In the prior art (Non-Patent Document 1), pulsed ASE light was used as the probe light to obtain the BGS of a branched optical fiber. In the present invention, in order to perform high-speed measurement in an optical fiber without a branch, the probe light is made to be continuous ASE light, and the obtained signal is converted to BGS using a method such as Fourier transform. This method makes it possible to obtain a distributed BGS with a single pulse of pump light. The feature of the present invention is that, in order to shorten the measurement time required for vibration measurement, continuous ASE light is used as the probe light, and the obtained signal is converted to BGS using a frequency analysis method.
（実施形態２）
　本実施形態では、信号処理部４３が行う、ＡＳＥによるＢＯＴＤＡにて取得したデータからＢＧＳを計算する周波数解析手法について説明する。信号処理部４３は、取得したブリルアン散乱のデータ（検波信号）について、一定距離ごとに周波数解析を行い、各地点でのＢＧＳを計算するときに、
　時間軸上において前記検波信号を所定時間毎に区切り、区間信号とすること、
　それぞれの前記区間信号の前後にゼロデータを挿入して信号長を長くすること、及び
　信号長を長くした前記区間信号をフーリエ変換して前記ＢＧＳとすること
を行う。 (Embodiment 2)
In this embodiment, a frequency analysis method for calculating the BGS from data acquired by the ASE-based BOTDA performed by the signal processing unit 43 will be described. The signal processing unit 43 performs frequency analysis on the acquired Brillouin scattering data (detection signal) at regular distances, and calculates the BGS at each point by:
dividing the detection signal into predetermined time intervals on a time axis to obtain a section signal;
Zero data is inserted before and after each of the section signals to lengthen the signal length, and the section signals with the lengthened signal length are Fourier transformed to produce the BGS.
　図１１は、信号処理部４３が行う周波数解析手法について説明する図である。
　ステップＳ１１は、信号処理部４３が散乱光取得部４２から検波信号を受け取る工程である。なお、検波信号はＡ／Ｄコンバータによりサンプリングされている。
　ステップＳ１２は、信号処理部４３が検波信号を所定区間（被試験光ファイバ５０の長手方向に区分した区間）毎に区切る工程である。所定区間に区切られた検波信号を「区間信号」とする。
　ステップＳ１３は、信号処理部４３が区間信号の前後にゼロデータを挿入（ゼロパディング）して信号長を長くする工程である。
　ステップＳ１４は、信号処理部４３が、信号長を長くした区間信号をフーリエ変換してＢＧＳを検出する工程である。なお、この工程でＢＧＳのピーク周波数も取得する。 FIG. 11 is a diagram for explaining the frequency analysis method performed by the signal processing unit 43. In FIG.
Step S11 is a process in which the signal processing unit 43 receives a detection signal from the scattered light acquisition unit 42. The detection signal is sampled by an A/D converter.
Step S12 is a process in which the signal processing unit 43 divides the detection signal into predetermined sections (sections divided in the longitudinal direction of the optical fiber under test 50). The detection signal divided into the predetermined sections is referred to as a "section signal."
Step S13 is a process in which the signal processing unit 43 inserts zero data before and after the section signal (zero padding) to increase the signal length.
In step S14, the signal processing unit 43 detects the BGS by performing a Fourier transform on the section signal with the increased signal length. Note that in this step, the peak frequency of the BGS is also obtained.
　図１２を用いてより具体的に説明する。図１２は、ＡＳＥ光源を利用したＢＯＴＤＡにより取得したブリルアン散乱光を周波数解析により距離分解する手順について説明する図である。
　ステップＳ１１で取得した検波信号ｄｓ１は時間軸が距離に対応しており、１０ｍあたり１００ｎｓである。また、ＡＳＥ光源を利用したＢＯＴＤＡにてブリルアン散乱光に対して３００ＭＨｚずらした光とヘテロダイン検波を行った信号を十分取得するため、Ａ／Ｄ変換器のサンプリングレートを１Ｇｓａｍｐｌｅ／ｓとした。１Ｇｓａｍｐｌｅ／ｓのサンプリングレートで１００ｎｓ分の検波信号を取得した場合、デジタル化された信号の長さは１×１０９×１００×１０－９＝１００サンプルとなる。ＦＦＴ（Ｆａｓｔ　Ｆｏｕｒｉｅｒ　Ｔｒａｎｓｆｏｒｍ）において、周波数分解能は、サンプリングレート／サンプル数となるため、ここでは周波数分解能は、（１×１０９）／（１００）＝１０ＭＨｚとなる。 This will be described more specifically with reference to Fig. 12. Fig. 12 is a diagram for explaining the procedure for performing distance resolution by frequency analysis on the Brillouin scattered light acquired by the BOTDA using an ASE light source.
The detection signal ds1 acquired in step S11 has a time axis corresponding to distance, and is 100 ns per 10 m. In addition, in order to sufficiently acquire a signal obtained by heterodyne detection with light shifted by 300 MHz from the Brillouin scattered light in the BOTDA using an ASE light source, the sampling rate of the A/D converter is set to 1 Gsample/s. When a detection signal of 100 ns is acquired at a sampling rate of 1 Gsample/s, the length of the digitized signal is 1×10 9 ×100×10 −9 =100 samples. In FFT (Fast Fourier Transform), the frequency resolution is the sampling rate/number of samples, so here the frequency resolution is (1×10 9 )/(100)=10 MHz.
　ステップＳ１２では、検波信号ｄｓ１を１００ｎｓ毎に区切る。この場合、被試験光ファイバ５０の長手方向に１０ｍずつの振動データを取得することになる。 In step S12, the detection signal ds1 is divided into 100 ns intervals. In this case, vibration data is acquired every 10 m in the longitudinal direction of the optical fiber 50 under test.
　ステップＳ１３では、区分された検波信号（区間信号ｄｓｓ）の両側にゼロデータを挿入する（ゼロパディング）。挿入するゼロデータは、ゼロパディング後の信号長がブリルアン散乱による光ファイバセンシング技術での最小周波数確度となる長さとする。
　一例として挿入するゼロパディングの長さｚ１［ｓａｍｐｌｅ］は次式で算出することができる。
ｚｌ＝（ｓａ／Ｆｒ）－ｓｌ
ここで、ｓｌは信号を区切る長さ［ｓａｍｐｌｅ］、ｓａはサンプリングレート［ｓａｍｐｌｅ／ｓ］、ｆａは最小周波数確度［Ｈｚ］、Ｔｒは時間分解能［ｓ］、Ｆｒは周波数分解能［Ｈｚ］である。ただし、ｓｌ＝Ｔｒ×ｓａである。
　例えば、当該最小周波数確度が１ＭＨｚであるならば、区間信号ｄｓｓの左右にそれぞれ１Ｇ×４５０ｎｓ＝４５０ｓａｎｐｌｅ分のゼロデータを挿入し、信号長を１μｓとする。このようにすることで１ＭＨｚ周波数分解能でＢＧＳを取得すること（ステップＳ１４）ができる（例えば、非特許文献３を参照。）。
　なお、ｓｌ＞ｚｌの場合、ゼロパディングする必要はない。 In step S13, zero data is inserted on both sides of the divided detection signal (section signal dss) (zero padding). The length of the zero data to be inserted is set so that the signal length after zero padding is the minimum frequency accuracy in optical fiber sensing technology using Brillouin scattering.
As an example, the length z1 [sample] of the zero padding to be inserted can be calculated by the following formula.
zl=(sa/Fr)-sl
Here, sl is the signal division length [sample], sa is the sampling rate [sample/s], fa is the minimum frequency accuracy [Hz], Tr is the time resolution [s], and Fr is the frequency resolution [Hz]. However, sl = Tr x sa.
For example, if the minimum frequency accuracy is 1 MHz, zero data of 1 G x 450 ns = 450 samples is inserted on both sides of the section signal dss to set the signal length to 1 μs. In this way, it is possible to obtain a BGS with a frequency resolution of 1 MHz (step S14) (see, for example, Non-Patent Document 3).
Note that if sl>zl, there is no need to perform zero padding.
　その理由は次の通りである。
（理由１）図１３のように時間分解能と周波数分解能はトレードオフの関係であること。
　サンプリングレートが一定である場合、周波数分解能は区間信号の長さの逆数に比例する。図１３（Ａ１）は検波信号ｄｓ１について区切る長さが長い場合（本例では１秒）、図１３（Ｂ１）は検波信号ｄｓ１について区切る長さが短い場合（本例では０．１秒）の区間信号ｄｓｓを示している。図１３（Ａ２）は検波信号ｄｓ１について区切る長さが長い場合の区間信号ｄｓｓにＦＦＴを行った結果である。プロット１つに対し、前後１Ｈｚの情報が含まれる。図１３（Ｂ２）は検波信号ｄｓ１について区切る長さが短い場合の区間信号ｄｓｓにＦＦＴを行った結果である。プロット１つに対し、前後１０Ｈｚの情報が含まれる。つまり、サンプリングレートが一定の場合、区間信号ｄｓｓが短い（距離分解能を上げる）と周波数分解能が低下する。
（理由２）ＢＯＴＤＡの測定ではブリルアン散乱の周波数成分がシングルピークであると仮定できること。
　区間信号ｄｓｓにＦＦＴを行って得られた各プロットからＢＧＳを推定する（図１３（Ａ２）及び（Ｂ２））。推定手法は、最小二乗法による２次関数フィッティングなどの一般的な推定手法を用いる。
（理由３）
　図１３（Ｂ１）のような０．１秒の区間信号ｄｓｓの前後にゼロデータを付加し、信号長を１秒としたものを図１３（Ｃ１）に示す。図１３（Ｃ１）の信号の信号長は１秒と長いので、プロット１つに対し、前後１０Ｈｚの情報が含まれるようになり、図１３（Ｂ１）の場合に比べて周波数分解能が向上する。ゼロデータを挿入したためＢＧＳ波形全体の強度は下がるが、区間信号ｄｓｓをＦＦＴした波形はシングルピークであるため、ここで求めたピークはＢＧＳ唯一のピークであるといえる。 The reasons are as follows:
(Reason 1) As shown in FIG. 13, time resolution and frequency resolution are in a trade-off relationship.
When the sampling rate is constant, the frequency resolution is proportional to the inverse of the length of the section signal. Fig. 13 (A1) shows the section signal dss when the section length of the detection signal ds1 is long (1 second in this example), and Fig. 13 (B1) shows the section signal dss when the section length of the detection signal ds1 is short (0.1 seconds in this example). Fig. 13 (A2) shows the result of FFT on the section signal dss when the section length of the detection signal ds1 is long. Each plot contains information of 1 Hz before and after. Fig. 13 (B2) shows the result of FFT on the section signal dss when the section length of the detection signal ds1 is short. Each plot contains information of 10 Hz before and after. In other words, when the sampling rate is constant, if the section signal dss is short (increasing the distance resolution), the frequency resolution decreases.
(Reason 2) In BOTDA measurements, it can be assumed that the frequency component of Brillouin scattering is a single peak.
BGS is estimated from each plot obtained by performing FFT on the section signal dss (FIGS. 13(A2) and (B2)). The estimation method is a general estimation method such as quadratic function fitting by the least squares method.
(Reason 3)
Fig. 13(C1) shows a signal with a length of 1 second, with zero data added before and after the 0.1 second section signal dss as in Fig. 13(B1). Since the signal length of the signal in Fig. 13(C1) is as long as 1 second, information of 10 Hz before and after each plot is included, and the frequency resolution is improved compared to the case of Fig. 13(B1). The insertion of zero data reduces the overall strength of the BGS waveform, but since the waveform obtained by FFTing the section signal dss is a single peak, it can be said that the peak found here is the only peak of the BGS.
　図１４は、本実施形態のブリルアン利得解析装置３０１が行う周波数解析方法を説明するフローチャートである。
　ステップＳ２１では、ポンプ光としてパルスを１つを被試験光ファイバ５０に送出し、被試験光ファイバ５０中を通過するＡＳＥ光源からのプローブ光と干渉させてブリルアン散乱を取得する。なお、ステップＳ２１は所望の計測時間Ｔ分だけ繰り返す（ステップＳ２１ａ）。サンプリング定理より
１／（２×ポンプ光のパルス送出周期）
の周波数の振動を計測可能である。 FIG. 14 is a flowchart for explaining the frequency analysis method performed by the Brillouin gain analysis device 301 of this embodiment.
In step S21, one pulse is sent as pump light to the optical fiber 50 under test, and Brillouin scattering is obtained by causing interference with probe light from the ASE light source passing through the optical fiber 50 under test. Note that step S21 is repeated for a desired measurement time T (step S21a). According to the sampling theorem, 1/(2×pump light pulse sending period)
It is possible to measure vibrations of this frequency.
　ステップＳ２２では、図１１で説明したようにポンプ光１パルス毎にブリルアン散乱についてＢＧＳを生成する。 In step S22, a BGS is generated for Brillouin scattering for each pump light pulse, as described in Figure 11.
　ステップＳ２３では、ステップＳ２２で生成したＢＧＳについて被試験光ファイバ５０の長手方向の各距離で最大値を取り、距離ごとのピーク周波数（ＢＦＳ）を推定する。図１５は、ある時刻ｔに対応する距離ごとのＢＦＳを表示した図（表示例）である。図１５について以下に追加説明を行う。 In step S23, the maximum value of the BGS generated in step S22 is taken for each distance along the longitudinal direction of the optical fiber 50 under test, and the peak frequency (BFS) for each distance is estimated. Figure 15 is a diagram (display example) showing the BFS for each distance corresponding to a certain time t. Additional explanation of Figure 15 is provided below.
　図１６は、被試験光ファイバ５０を説明する図である。被試験光ファイバ５０は、シングルモード光ファイバ５０－１とシングルモード光ファイバ５０－２を直列させた光ファイバである。シングルモード光ファイバ５０－１は、５０ｍであり、温度変化や振動が無い状態で１０．８４０ＧＨｚのＢＦＳが発生する。シングルモード光ファイバ５０－２は、５０ｍであり、温度変化や振動が無い状態で１０．８２１ＧＨｚのＢＦＳが発生する。シングルモード光ファイバ５０－１側をプローブ光Ｌｐｒ入射側、シングルモード光ファイバ５０－２側をポンプ光Ｌｐｎ入射側とする。 FIG. 16 is a diagram explaining the optical fiber 50 under test. The optical fiber 50 under test is an optical fiber in which a single mode optical fiber 50-1 and a single mode optical fiber 50-2 are connected in series. The single mode optical fiber 50-1 is 50 m long, and generates a BFS of 10.840 GHz in the absence of temperature change or vibration. The single mode optical fiber 50-2 is 50 m long, and generates a BFS of 10.821 GHz in the absence of temperature change or vibration. The single mode optical fiber 50-1 side is the incident side of the probe light Lpr, and the single mode optical fiber 50-2 side is the incident side of the pump light Lpn.
　図１５は、図１６の被試験光ファイバ５０から取得したブリルアン散乱について距離ごとのＢＦＳを表示したものである。横軸は、被試験光ファイバ５０の長手方向の距離（ポンプ光Ｌｐｎの入射端をゼロとしている。）である。カラーバーは、ＢＧＳの強度である。縦軸は周波数である。図１５中、黒丸は各距離において推定したＢＦＳである。
　距離５０ｍを境に距離が短い方のＢＦＳが約１０．８２ＧＨｚ、長い方のＢＦＳが約１０．８４ＧＨｚと推定されている。従って、ブリルアン利得解析装置３０１は被試験光ファイバの各距離におけるＢＦＳを測定できているといえる。 Fig. 15 shows the BFS for each distance for the Brillouin scattering obtained from the optical fiber 50 under test in Fig. 16. The horizontal axis is the longitudinal distance of the optical fiber 50 under test (the input end of the pump light Lpn is set to zero). The color bar indicates the intensity of the BGS. The vertical axis indicates the frequency. In Fig. 15, the black circles indicate the BFS estimated at each distance.
It is estimated that the BFS at the shorter distance of 50 m is about 10.82 GHz, and the BFS at the longer distance is about 10.84 GHz. Therefore, it can be said that the Brillouin gain analyzer 301 can measure the BFS at each distance of the optical fiber under test.
　ステップＳ２２ａでは、ステップＳ２１で送出したポンプ光のパルス分（計測時間Ｔ分）だけステップＳ２２とＳ２３を繰り返してＢＦＳを推定する。つまり、計測時間Ｔの間のＢＦＳの推移（周波数が変化した／しない）を知ることができる。そして、ＢＦＳの推移により被試験光ファイバ５０に生じた変化を推定することができる。 In step S22a, steps S22 and S23 are repeated for the number of pump light pulses sent out in step S21 (measurement time T) to estimate the BFS. In other words, the transition of the BFS during measurement time T (whether the frequency has changed or not) can be known. Then, the change that has occurred in the optical fiber 50 under test due to the transition of the BFS can be estimated.
（実施例）
　図１７から図１９を用いて、ブリルアン利得解析装置３０１が被試験光ファイバ５０に与えた振動をどのように解析するかを説明する。
　図１７は、本解析に使用する被試験光ファイバ５０を説明する図である。被試験光ファイバ５０は、３つのシングルモード光ファイバ（５０－３、５０－４、５０－５）を光スイッチ５５で接続した構造である。シングルモード光ファイバ５０－３は、５０ｍであり、温度変化や振動が無い状態で１０．８４０ＧＨｚのＢＦＳが発生する。シングルモード光ファイバ５０－４は、５０ｍであり、温度変化や振動が無い状態で１０．８２１ＧＨｚのＢＦＳが発生する。シングルモード光ファイバ５０－５は、５０ｍであり、温度変化や振動が無い状態で１０．８３３ＧＨｚのＢＦＳが発生する。シングルモード光ファイバ（５０－３、５０－４）側をプローブ光Ｌｐｒ入射側、シングルモード光ファイバ５０－５側をポンプ光Ｌｐｎ入射側とする。そして、光スイッチ５５を２５Ｈｚで駆動し、シングルモード光ファイバ５０－５が交互にシングルモード光ファイバ５０－３と５０－４に接続するように切り替える。つまり、光スイッチ５５の切り替えにより、ＢＦＳを疑似的に変化させることで、被試験光ファイバ５０に振動を与えた状態を模擬する（例えば、非特許文献４を参照。）。 (Example)
17 to 19, how the Brillouin gain analyzer 301 analyzes the vibration applied to the optical fiber 50 under test will be described.
FIG. 17 is a diagram for explaining the optical fiber under test 50 used in this analysis. The optical fiber under test 50 has a structure in which three single mode optical fibers (50-3, 50-4, 50-5) are connected by an optical switch 55. The single mode optical fiber 50-3 is 50 m long, and generates a BFS of 10.840 GHz in the absence of temperature change or vibration. The single mode optical fiber 50-4 is 50 m long, and generates a BFS of 10.821 GHz in the absence of temperature change or vibration. The single mode optical fiber 50-5 is 50 m long, and generates a BFS of 10.833 GHz in the absence of temperature change or vibration. The single mode optical fibers (50-3, 50-4) are the probe light Lpr input side, and the single mode optical fiber 50-5 is the pump light Lpn input side. The optical switch 55 is driven at 25 Hz to alternately switch the single mode optical fiber 50-5 to be connected to the single mode optical fibers 50-3 and 50-4. That is, the BFS is artificially changed by switching the optical switch 55, thereby simulating a state in which the optical fiber 50 under test is subjected to vibration (see, for example, Non-Patent Document 4).
　プローブ光Ｌｐｒ入射側ではシングルモード光ファイバ（５０－３、５０－４）を分岐比率が５０：５０のカプラ５６で接続している。カプラ５６は、シングルモード光ファイバ（５０－３、５０－４）それぞれにプローブ光Ｌｐｒを均等なパワーで入射する。 On the probe light Lpr input side, the single mode optical fibers (50-3, 50-4) are connected by a coupler 56 with a branching ratio of 50:50. The coupler 56 inputs the probe light Lpr with equal power into each of the single mode optical fibers (50-3, 50-4).
　図１７の被試験光ファイバ５０からのブリルアン散乱について、図１５のようにある時刻におけるＢＧＳを取得する。そして、図１８は、そのＢＧＳについて距離ごとに周波数の最大値（距離ごとのＢＦＳ）を示した図である。横軸は、被試験光ファイバ５０の長手方向の距離（ポンプ光Ｌｐｎの入射端をゼロとしている。）である。カラーバーは周波数である。縦軸は計測時間である。５０－１００ｍの区間を時間方向に見るとカラーマップが周期的に変化している。 As shown in FIG. 15, the BGS at a certain time is obtained for the Brillouin scattering from the optical fiber 50 under test in FIG. 17. FIG. 18 shows the maximum frequency for each distance for that BGS (BFS for each distance). The horizontal axis is the distance along the length of the optical fiber 50 under test (the input end of the pump light Lpn is set to zero). The color bar is the frequency. The vertical axis is the measurement time. Looking at the 50-100m section in the time direction, the color map changes periodically.
　図１９は、図１８の時間方向に対してフーリエ変換を行った結果である。横軸は、被試験光ファイバ５０の長手方向の距離（ポンプ光Ｌｐｎの入射端をゼロとしている。）である。カラーバーは信号強度である。縦軸は周波数である。図１９に示すように、５０－１００ｍ付近に被試験光ファイバに与えた２５Ｈｚの振動（光スイッチ５５で切り替えた光経路）が現れている。 Figure 19 shows the results of a Fourier transform performed on the time axis of Figure 18. The horizontal axis is the longitudinal distance of the optical fiber 50 under test (the input end of the pump light Lpn is set to zero). The color bar represents the signal intensity. The vertical axis represents the frequency. As shown in Figure 19, the 25 Hz vibration (the optical path switched by the optical switch 55) applied to the optical fiber under test appears around 50-100 m.
（定義）
　本明細書及び図面で使用している略語は次の通りである。
ＡＳＥ　：　Ａｍｐｌｉｆｉｅｄ　ｓｐｏｎｔａｎｅｏｕｓ　ｅｍｉｓｓｉｏｎ
ＰＤ　：　Ｐｈｏｔｏ　Ｄｅｔｅｃｔｏｒ
ＡＯＭ　：　Ａｃｏｕｓｔｏ　ｏｐｔｉｃ　ｍｏｄｕｌａｔｏｒ
ＥＤＦＡ　：　Ｅｒｂｉｕｍ　ｄｏｐｅｄ　ｆｉｂｅｒ　ａｍｐｌｉｆｉｅｒ
Ａ／Ｄ　：　Ａｎａｌｏｇ　Ｄｉｇｉｔａｌ
ＢＧＳ　：　Ｂｒｉｌｌｏｕｉｎ　Ｇａｉｎ　Ｓｐｅｃｔｒｕｍ
ＢＦＳ　：　Ｂｒｉｌｌｏｕｉｎ　Ｆｒｅｑｕｅｎｃｙ　Ｓｈｉｆｔ
ＢＰＤ　：　Ｂａｌａｎｃｅｄ　Ｐｈｏｔｏ　Ｄｅｔｅｃｔｏｒ
ＳＳＢ　：　Ｓｉｎｇｌｅ　Ｓｉｄｅ　Ｂａｎｄ (Definition)
The following abbreviations are used in the present specification and drawings:
ASE: Amplified spontaneous emission
PD: Photo Detector
AOM: Acousto optic modulator
EDFA: Erbium doped fiber amplifier
A/D: Analog Digital
BGS: Brillouin Gain Spectrum
BFS: Brillouin Frequency Shift
BPD: Balanced Photo Detector
SSB: Single Side Band
１１：レーザ
１２：パルス生成器
１３：ＡＳＥ光源
１４：変調器
１５：検波器
１５ａ：５０：５０カプラ
１５ｂ：バランス型フォトダイオード
２１：ＢＧＳのピークの変化
２２：任意周波数
２３：掃引範囲
４１：散乱光生成部
４２：散乱光取得部
５０：被試験光ファイバ
５０－１～５０－５：光ファイバ
５５：光スイッチ
５６：カプラ
６１、６２：光増幅器
６３：光サーキュレータ
７３：プローブ光の周波数範囲
９１：光合波器
３００、３０１：ブリルアン利得解析装置 11: Laser 12: Pulse generator 13: ASE light source 14: Modulator 15: Detector 15a: 50: 50 coupler 15b: Balanced photodiode 21: Change in BGS peak 22: Arbitrary frequency 23: Sweep range 41: Scattered light generator 42: Scattered light acquirer 50: Optical fiber under test 50-1 to 50-5: Optical fiber 55: Optical switch 56: Coupler 61, 62: Optical amplifier 63: Optical circulator 73: Frequency range of probe light 91: Optical multiplexer 300, 301: Brillouin gain analysis device

Claims (4)

  1. 　ブリルアン利得解析装置であって、
    　単一周波数の連続光を出力するレーザと、
    　前記レーザが出力する連続光の周波数より広帯域な周波数成分を持つ連続光を発生し、測定対象の光ファイバの一端に入射するＡＳＥ（Ａｍｐｌｉｆｉｅｄ　ｓｐｏｎｔａｎｅｏｕｓ　ｅｍｉｓｓｉｏｎ）光源と、
    　前記レーザからの前記連続光をパルス化して前記光ファイバの他端に入射するパルス生成器と、
    　前記レーザからの前記連続光の周波数を任意の周波数だけシフトしたローカル光を生成する変調器と、
    　前記光ファイバで発生したブリルアン散乱光と前記ローカル光とをヘテロダイン検波する検波器と、
    　前記検波器でヘテロダイン検波された検波信号について周波数解析を行い、ブリルアンゲインスペクトラム（ＢＧＳ）を検出を行う信号処理部と、
    を備えており、
    　前記信号処理部の前記周波数解析は、
    　時間軸上において前記検波信号を所定時間毎に区切り、区間信号とすること、
    　それぞれの前記区間信号の前後にゼロデータを挿入して信号長を長くすること、及び
    　信号長を長くした前記区間信号をフーリエ変換して前記ＢＧＳとすること
    であることを特徴とするブリルアン利得解析装置。     1. A Brillouin gain analysis apparatus, comprising:
    A laser that outputs continuous light of a single frequency;
    an amplified spontaneous emission (ASE) light source that generates continuous light having a frequency component in a broader band than the frequency of the continuous light output by the laser and inputs the continuous light into one end of the optical fiber to be measured;
    a pulse generator that pulses the continuous light from the laser and inputs the pulsed light to the other end of the optical fiber;
    a modulator that generates local light by shifting the frequency of the continuous light from the laser by an arbitrary frequency;
    a detector for heterodyne detecting the Brillouin scattered light generated in the optical fiber and the local light;
    a signal processing unit that performs frequency analysis on the detection signal heterodyne-detected by the detector and detects a Brillouin gain spectrum (BGS);
    Equipped with
    The frequency analysis of the signal processing unit includes:
    dividing the detection signal into predetermined time intervals on a time axis to obtain a section signal;
    A Brillouin gain analysis device comprising: inserting zero data before and after each of the section signals to lengthen the signal length; and subjecting the section signals with the lengthened signal length to a Fourier transform to obtain the BGS.
  2. 　前記信号処理部は、前記信号長が最小周波数確度となるように前記ゼロデータの挿入を行うことを特徴とする請求項１に記載のブリルアン利得解析装置。 The Brillouin gain analysis device according to claim 1, characterized in that the signal processing unit inserts the zero data so that the signal length has a minimum frequency accuracy.
  3. 　ブリルアン利得解析装置によるブリルアン利得解析方法であって、
    　前記ブリルアン利得解析装置は、
    　単一周波数の連続光を出力するレーザと、
    　前記レーザが出力する連続光の周波数より広帯域な周波数成分を持つ連続光を発生し、測定対象の光ファイバの一端に入射するＡＳＥ（Ａｍｐｌｉｆｉｅｄ　ｓｐｏｎｔａｎｅｏｕｓ　ｅｍｉｓｓｉｏｎ）光源と、
    　前記レーザからの前記連続光をパルス化して前記光ファイバの他端に入射するパルス生成器と、
    　前記レーザからの前記連続光の周波数を任意の周波数だけシフトしたローカル光を生成する変調器と、
    　前記光ファイバで発生したブリルアン散乱光と前記ローカル光とをヘテロダイン検波する検波器と、
    　前記検波器でヘテロダイン検波された検波信号について周波数解析を行い、ブリルアンゲインスペクトラム（ＢＧＳ）を検出を行う信号処理部と、
    を備えており、
    　前記信号処理部が前記周波数解析として、
    　時間軸上において前記検波信号を所定時間毎に区切り、区間信号とすること、
    　それぞれの前記区間信号の前後にゼロデータを挿入して信号長を長くすること、及び
    　信号長を長くした前記区間信号をフーリエ変換して前記ＢＧＳとすること
    を行うことを特徴とするブリルアン利得解析方法。     A Brillouin gain analysis method using a Brillouin gain analysis device, comprising:
    The Brillouin gain analysis device
    A laser that outputs continuous light of a single frequency;
    an amplified spontaneous emission (ASE) light source that generates continuous light having a frequency component in a broader band than the frequency of the continuous light output by the laser and inputs the continuous light into one end of the optical fiber to be measured;
    a pulse generator that pulses the continuous light from the laser and inputs the pulsed light to the other end of the optical fiber;
    a modulator that generates local light by shifting the frequency of the continuous light from the laser by an arbitrary frequency;
    a detector for heterodyne detecting the Brillouin scattered light generated in the optical fiber and the local light;
    a signal processing unit that performs frequency analysis on the detection signal heterodyne-detected by the detector and detects a Brillouin gain spectrum (BGS);
    Equipped with
    The signal processing unit performs the frequency analysis as follows:
    dividing the detection signal into predetermined time intervals on a time axis to obtain a section signal;
    A Brillouin gain analysis method comprising the steps of: inserting zero data before and after each of the section signals to lengthen the signal length; and subjecting the section signals with the lengthened signal length to a Fourier transform to obtain the BGS.
  4. 　前記周波数解析において、前記信号長が最小周波数確度となるように前記ゼロデータの挿入を行うことを特徴とする請求項３に記載のブリルアン利得解析方法。 The Brillouin gain analysis method according to claim 3, characterized in that in the frequency analysis, the zero data is inserted so that the signal length has a minimum frequency accuracy.
PCT/JP2023/005179 2023-02-15 2023-02-15 Brillouin gain analysis device, and brillouin gain analysis method WO2024171332A1 (en)

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06167421A (en) * 1992-07-23 1994-06-14 Fujikura Ltd Measurement of brillouin gain spectrum of optical fiber
JP2000321123A (en) * 1999-05-14 2000-11-24 Akashi Corp Vibration wave analyzing apparatus
JP2007139699A (en) * 2005-11-22 2007-06-07 Tokyo Electric Power Co Inc:The Frequency analyzing method
JP2008216123A (en) * 2007-03-06 2008-09-18 Sumitomo Electric Ind Ltd Pmd characteristics measuring method of optical fiber, line drawing method, abnormal place specifying method and optical fiber transmission path construction method
JP2009042005A (en) * 2007-08-07 2009-02-26 Nippon Telegr & Teleph Corp <Ntt> Method and device for measuring distribution of distortion and temperature using optical fiber
JP2015078859A (en) * 2013-10-15 2015-04-23 日本電信電話株式会社 Branch optical fiber characteristic analyzer and analysis method for the same
WO2022254712A1 (en) * 2021-06-04 2022-12-08 日本電信電話株式会社 Optical fiber testing method and optical fiber testing device

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06167421A (en) * 1992-07-23 1994-06-14 Fujikura Ltd Measurement of brillouin gain spectrum of optical fiber
JP2000321123A (en) * 1999-05-14 2000-11-24 Akashi Corp Vibration wave analyzing apparatus
JP2007139699A (en) * 2005-11-22 2007-06-07 Tokyo Electric Power Co Inc:The Frequency analyzing method
JP2008216123A (en) * 2007-03-06 2008-09-18 Sumitomo Electric Ind Ltd Pmd characteristics measuring method of optical fiber, line drawing method, abnormal place specifying method and optical fiber transmission path construction method
JP2009042005A (en) * 2007-08-07 2009-02-26 Nippon Telegr & Teleph Corp <Ntt> Method and device for measuring distribution of distortion and temperature using optical fiber
JP2015078859A (en) * 2013-10-15 2015-04-23 日本電信電話株式会社 Branch optical fiber characteristic analyzer and analysis method for the same
WO2022254712A1 (en) * 2021-06-04 2022-12-08 日本電信電話株式会社 Optical fiber testing method and optical fiber testing device

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