Method for adjusting measuring device and method for measuring

Abstract

Provided is a measuring device etc. making it possible to simplify the device configuration while shortening the measuring time.　The measuring device includes a splitter that splits light from a laser light source into two, an optical frequency shifter that shifts the frequency of either of the two split light beams, a first optical modulator that generates probe light having two frequency components by intensity modulating one of the split light beams, a second optical modulator that pulses the other split light beam to generate pump light, a photodetector that detects the light emitted from the other end side of an optical fiber, which is to be measured, when the probe light is incident from one end side of the optical fiber and the pump light is incident from the other end side of the optical fiber, and a processing unit that measures the temperature or strain of the optical fiber on the basis of the light intensity detected by the photodetector, wherein the frequency of the lower frequency component of the two frequency components is the frequency at which Brillouin gain occurs, and the frequency of the higher frequency component is the frequency at which Brillouin loss occurs.

Description

[Technical Field]

[0001] The present invention relates to a measuring device for measuring the temperature or strain of an optical fiber, a method for adjusting the measuring device, and a measuring method. [Background technology]

[0002] Numerous dispersive sensor technologies utilizing Brillouin scattering in optical fibers have been studied. Dispersive Brillouin sensing takes advantage of the fact that the Brillouin gain spectrum, which is the frequency range in which Brillouin scattering occurs strongly, changes in proportion to distortion and temperature. Many methods involve frequency sweeping of the probe light to observe the change in the Brillouin gain spectrum. Methods have also been proposed to acquire the Brillouin gain spectrum all at once using pump and probe light consisting of multi-frequency light, or to use pump and probe light consisting of multi-frequency light and appropriately shape the probe light spectrum, thereby utilizing the fact that the final received optical power changes in proportion to temperature and distortion. Furthermore, methods that utilize the region in which the change in the Brillouin gain spectrum can be considered linear with respect to frequency have been investigated. However, such a region is narrow. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Y. Tanaka and Y. Ozaki, “Brillouin frequency shift measurement with virtually controlled sensitivity,” Appl. Phys. Exp. 10, 062504 (2017). [Non-Patent Document 2] Y. Endo and Y. Tanaka, “Sensitivity enhancement of distributed Brillouin fiber optic sensing using two-frequency pump and probe,” SPIE Conf 11525. on Future Sensing Technologies, Paper 11525-3 (2020). [Non-Patent Document 3] A. Voskoboinik, J.Wang, B. Shamee, S. R. Nuccio, L. Zhang, MChitgarha, A. E. Willner, and M. Tur, “SBS-based fiber optical sensing using frequency-domain simultaneous tone interrogation,” J. Lightwave Technol. 29, 1729-1735 (2011). [Non-Patent Document 4] C. Jin, L. Wang, Y. Chen, N. Guo, W. Chung, H. Au, Z. Li, H-Y. Tam, and C. Lu, “Singlemeasurement digital optical frequency comb based phase-detection Brillouin optical time domain analyzer,” Opt. Exp. 25, 9213-9224 (2017). [Non-Patent Document 5] Y. Tanaka, Y. Ozaki, and Y. So, “Scanless Brillouin gain spectrum measurement based on multiheterodyne detection,” in Tech. Digest of International Cof. on Optical Fiber Sensors 2018,TuE88 (2018). [Non-Patent Document 6] Y. Tanaka and T. Hasegawa, “Brillouin optical time domain analysis using spectrally reshaped 12-GHz spacing multimode pump and probe,” Conference on Lasers and Electro-Optics (CLEO) 2020, paper SF3P.7 (2020). [Non-Patent Document 7] Y. Peled, A. Motil, L. Yaron, and M. Tur, “Slope-assisted fast distributed sensing in optical fibers with arbitrary Brillouin profile,” Opt. Express 19, 19845-19854 (2011). [Non-Patent Document 8] H. Lee, N. Hayashi, Y. Mizuno, and K. Nakamura, “Slope-assisted Brillouin optical correlation domain reflectometry: proof of concept,” Photon. Jour. 8, 6802807 (2016). [Overview of the project] [Problems that the invention aims to solve]

[0004] Methods that use frequency sweeping of probe light inherently require long measurement times, and complex control of the light source frequency sweep is necessary. Furthermore, methods that shape the spectrum of light consisting of numerous frequency components require equipment for spectrum shaping, resulting in a large number of system components, and the adjustment of modulation for spectrum generation becomes complex.

[0005] This invention has been made in view of the above-mentioned problems, and its objective is to provide a measuring device that can shorten the measurement time while simplifying the device configuration. [Means for solving the problem]

[0006] (1) The present invention relates to a measuring device comprising: a branching unit that branches light from a laser light source into two; an optical frequency shifting unit that shifts the frequency of one of the two branched lights; a first optical modulation unit that generates probe light having two frequency components by intensity modulating one of the branched lights; a second optical modulation unit that generates pump light by pulsed the other branched light; an optical detection unit that detects light emitted from the other end of an optical fiber when the probe light is incident from one end of the optical fiber to be measured and the pump light is incident from the other end of the optical fiber; and a processing unit that measures the temperature or strain of the optical fiber based on the light intensity detected by the optical detection unit, wherein the frequency of the lower of the two frequency components is the frequency at which Brillouin gain occurs in interaction with the pump light, and the frequency of the higher of the two frequency components is the frequency at which Brillouin loss occurs in interaction with the pump light.

[0007] The present invention also relates to a measurement method comprising: a branching step of splitting light from a laser light source into two; an optical frequency shifting step of shifting the frequency of one of the two branched lights; a first optical modulation step of intensity-modulating one of the branched lights to generate probe light having two frequency components; a second optical modulation step of pulsed the other branched light to generate pump light; an optical detection step of detecting light emitted from the other end of an optical fiber when the probe light is incident from one end of the optical fiber to be measured and the pump light is incident from the other end of the optical fiber; and a processing step of measuring the temperature or strain of the optical fiber based on the optical intensity detected in the optical detection step, wherein the frequency of the lower of the two frequency components is the frequency at which Brillouin gain occurs in interaction with the pump light, and the frequency of the higher of the two frequency components is the frequency at which Brillouin loss occurs in interaction with the pump light.

[0008] According to the present invention, by using probe light having two frequency components—one that generates Brillouin gain and another that generates Brillouin loss—it becomes possible to measure temperature and distortion from the received light intensity without the need for frequency sweeping. Furthermore, according to the present invention, the equipment required for spectral shaping of probe light and pump light can be eliminated, thus simplifying the apparatus configuration.

[0009] (2) In addition, in the measuring apparatus and measuring method according to the present invention, the processing unit (in the processing step) may measure the temperature or strain of the optical fiber based on the light intensity within a range in which the relationship between the light intensity detected by the light detection unit and the temperature or strain of the optical fiber is a predetermined relationship.

[0010] (3) In addition, in the measuring apparatus and measuring method according to the present invention, the processing unit (in the processing step) may measure the temperature distribution or strain distribution of the optical fiber based on the time change of light intensity detected by the light detection unit.

[0011] According to the present invention, it is possible to measure temperature distribution and strain distribution from the time change of light intensity without requiring frequency sweeping.

[0012] (4) In addition, in the measuring apparatus and measuring method according to the present invention, the first optical modulation unit (in the first optical modulation step) may generate the probe light by intensity modulation of the light frequency shifted by the optical frequency shift unit.

[0013] (5) The present invention also relates to a method for adjusting the above-described measuring device, the method including: setting a frequency shift amount in the optical frequency shift unit so that two frequency components of the probe light do not simultaneously receive gain due to Brillouin gain and loss due to Brillouin loss; obtaining the light intensity detected by the light detection unit each time the frequency of the modulation signal of the first optical modulation unit is changed; obtaining a Brillouin gain spectrum and a Brillouin frequency shift based on the relationship between the frequency of the modulation signal and the light intensity; and adjusting the frequency shift amount based on the Brillouin gain spectrum and the Brillouin frequency shift. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] [Figure 1] FIG. 1 is a diagram showing the configuration of the measuring device according to the present embodiment. [Figure 2] FIG. 2 is a diagram showing a pump light, a probe light, a Brillouin gain spectrum, and a Brillouin loss spectrum. [Figure 3] FIG. 3 is a diagram showing the relationship between the total of the amplification of the probe light due to Brillouin gain and the loss of the probe light due to Brillouin loss, and νprobe - νBFS. [Figure 4] FIG. 4 is a diagram showing an experimental system of an experiment for verifying the principle of the method of the present embodiment. [Figure 5] FIG. 5 is a diagram showing the experimental results of an experiment for measuring the temperature distribution of an optical fiber. [Figure 6] FIG. 6 is a diagram showing a fiber under measurement in an experiment for measuring the strain distribution of an optical fiber. [Figure 7] FIG. 6 is a diagram showing the experimental results of an experiment for measuring the strain distribution of an optical fiber. [Figure 8] FIG. 8 is a flowchart showing the flow of a method for adjusting the frequency shift amount. [Figure 9] FIG. 9 is a graph plotting the light intensity obtained when the frequency shift amounts are 60 MHz, 40 MHz, 25 MHz, and 20 MHz against the frequency of the modulation signal. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described below. Note that the embodiments described below are not intended to unduly limit the scope of the present invention as described in the claims. Furthermore, not all of the configurations described in these embodiments are necessarily essential components of the present invention.

[0016] Figure 1 shows the configuration of the measuring device according to this embodiment. The measuring device 1 is a device for measuring the temperature or strain of the sensing area SA (measurement target) of the optical fiber 2, and includes a single-wavelength laser light source 10, an optical splitter 11 (branching section), an optical frequency shifter 20 (optical frequency shifting section), optical modulators 30, 31 (first optical modulation section, second optical modulation section), an optical isolator 40, an oscillator 50, a pulse signal generator 60, an optical circulator 70, a photodetector 80 (photodetection section), and a data processing device 90 (processing section).

[0017] The optical splitter 11 splits the light (center frequency ν0) from the laser light source 10 into two beams at a predetermined splitting ratio (for example, 1:1).

[0018] The optical frequency shifter 20 shifts the frequency of one of the two beams of light split by the optical splitter 11. In the example shown in Figure 1, the frequency of the beam incident on the optical modulator 30 is shifted. Let Δν be the amount of frequency shift by the optical frequency shifter 20. The frequency shift amount Δν is set so that the relationship between the light intensity detected by the photodetector 80 (the light intensity of the probe light AP, described later) and the temperature or strain is within a predetermined range and satisfies a predetermined relationship (fits a predetermined function).

[0019] The optical modulator 30 modulates the intensity of one of the branched light components (light emitted from the optical frequency shifter 20) to generate a probe light Pr having two frequency components. The frequency of the lower of the two frequency components is set to the frequency at which Brillouin gain occurs due to interaction with the pump light Pm, and the frequency of the higher of the two frequency components is set to the frequency at which Brillouin loss occurs due to interaction with the pump light Pm. The probe light Pr passes through the optical isolator 40 and is incident from one end of the sensing region SA of the optical fiber 2. The oscillator 50 generates an intensity-modulated signal to drive the optical modulator 30.

[0020] The optical modulator 31 generates pump light Pm by applying intensity modulation to the other branched light using a periodic gate pulse to pulse it. The pulse signal generator 60 generates an intensity modulated signal (pulse signal) to drive the optical modulator 31.

[0021] The optical circulator 70 outputs the pump light Pm, which is input to the first port, from the second port to guide it to the other end of the sensing region SA, and outputs the light (probe light AP, which has been affected by Brillouin gain and Brillouin loss) emitted from the other end of the sensing region SA and input to the second port from the third port to guide it to the photodetector 80. The photodetector 80 detects the probe light AP and outputs the detected light intensity as an electrical signal.

[0022] The data processing unit 90 is a computer equipped with a processor (CPU, etc.) and a memory unit (RAM, hard disk, etc.), and calculates the temperature or strain of the optical fiber 2 (sensing region SA) based on the signal intensity from the photodetector 80 (light intensity detected by the photodetector 80). For example, a function approximating the relationship between the light intensity of the probe light AP and the temperature or strain (e.g., a proportional relationship) is determined by pre-calibration, and the temperature or strain of the sensing region SA is calculated by substituting the light intensity detected by the photodetector 80 (light intensity within a range where the relationship between the light intensity of the probe light AP and the temperature or strain is a predetermined relationship) into this function. The data processing unit 90 also calculates the temperature distribution or strain distribution of the sensing region SA based on the time change of the light intensity detected by the photodetector 80. For example, the relationship between the generation timing of each pulse of the pump light Pm (count of generated pulses) and the position in the sensing region SA is determined by pre-calibration, and the temperature or strain for each position in the sensing region SA is calculated using this relationship based on the light intensity at the generation timing of each pulse of the pump light Pm. The timing of each pulse of the pump light Pm is supplied as a trigger signal from the pulse signal generator 60.

[0023] In optical fiber 2, thermally induced acoustic waves create a refractive index distribution (moving diffraction grating). Pump light Pm incident on the other end of optical fiber 2 (sensing region SA) is reflected by this, generating stroke light with a downshifted frequency that propagates backward (to the other end of optical fiber 2). Furthermore, electrostriction occurs due to the beat between the stroke light and pump light Pm, creating a refractive index distribution. This series of processes is repeated, and a Brillouin gain spectrum (BGS) is generated at frequencies lower than the frequency ν0 of pump light Pm. Also, a Brillouin loss spectrum (BLS) is generated at frequencies higher than the frequency ν0 of pump light Pm. When probe light Pr is incident opposite to pump light Pm (on one end of optical fiber 2), probe light AP, which has been amplified by the Brillouin gain spectrum and attenuated by the Brillouin loss spectrum, is emitted from the other end of optical fiber 2.

[0024] Figure 2 shows the pump light, probe light, Brillouin gain spectrum, and Brillouin loss spectrum. In Figure 2, the horizontal axis represents frequency (ν). As shown in Figure 2, in optical fiber 2 (sensing region SA), a Brillouin gain spectrum (BGS) is generated in a certain frequency range lower than the pump light frequency ν0, and a Brillouin loss spectrum (BLS) is generated in a certain frequency range higher than the pump light frequency ν0. The frequency difference ν between the pump light frequency ν0 and the center frequency of the Brillouin gain spectrum (and Brillouin loss spectrum) is... BFS This is called the Brillouin frequency shift (BFS). For example, when the wavelength of the pump light (laser light source) is 1.5 μm, the Brillouin gain spectrum is generated at a frequency approximately 11 GHz lower than the pump light frequency ν0, and the Brillouin loss spectrum is generated at a frequency approximately 11 GHz higher than the pump light frequency ν0. BFS This changes in proportion to the temperature and strain of the sensing region SA.

[0025] The probe light has two frequency components. The frequency of the lower frequency component (Probe1) is set to a frequency within the frequency range of the Brillouin gain spectrum, and the frequency of the higher frequency component (Probe2) is set to a frequency within the frequency range of the Brillouin loss spectrum. As a result, the lower frequency component of the probe light is amplified by the Brillouin gain, and the higher frequency component of the probe light is attenuated (loss occurs) by the Brillouin loss. The frequency difference between the frequency (ν0 + Δν) of the light incident on the optical modulator 30 (light emitted from the optical frequency shifter 20) and the frequencies of the two frequency components of the probe light is ν probe Let's assume that, for example, when the wavelength of the pump light (laser light source) is 1.5 μm, ν probe Let it be approximately 11 GHz. Brillouin frequency shift ν BFS and ν probeWhen they are equal, the sum of the amplification of the probe light due to Brillouin gain and the loss of the probe light due to Brillouin loss (the value obtained by subtracting the light intensity of the probe light Pr from the light intensity of the probe light AP) becomes 0.

[0026] Here, when the frequency shift amount Δν at the optical frequency shifter 20 is appropriately set, as shown in FIG. 3, an area can be approximated where the sum (Probe gain) of the amplification of the probe light due to Brillouin gain and the loss of the probe light due to Brillouin loss changes proportionally to the temperature and strain of the optical fiber 2. In the example shown in FIG. 3, the temperature and strain of the optical fiber 2 are represented by ν probe -ν BFS and when the frequency shift amount Δν is 25 MHz, ν probe -ν BFS In the range of -0.02 GHz to 0.02 GHz (40 MHz), Probe gain (equivalent to the light intensity of the probe light AP) can be regarded as changing proportionally (linearly responding) to temperature and strain. Therefore, if the relationship between the light intensity of the probe light AP and the temperature or strain in the sensing region SA is calibrated and obtained in advance, the temperature and strain in the sensing region SA can be obtained from the light intensity detected by the light receiver 80 (the light intensity within the range linearly responding to temperature or strain) using this calibration result. Note that by changing the frequency shift amount Δν, the region where Probe gain linearly responds to temperature and strain can be translated parallel to the frequency axis on the frequency axis, so the measurable temperature and strain ranges can be flexibly changed. Also, since the pump light is pulsed, the temporal change in the light intensity of the probe light AP detected by the light receiver 80 corresponds to the spatial temperature distribution or strain distribution in the sensing region SA. Therefore, the temperature distribution and strain distribution in the sensing region SA can be obtained by measuring the temporal change in the light intensity detected by the light receiver 80.

[0027] Figure 4 shows the experimental setup for an experiment to verify the principle of the method of this embodiment. In Figure 4, LD is a single-wavelength laser light source, PM is a phase modulator (optical frequency shift section), IM1 and IM2 are optical intensity modulators (first optical modulation section and second optical modulation section), PS is a polarization scrambler, ISO is an optical isolator, FG is an arbitrary waveform generator (signal generator), EDFA is an optical amplifier, PD is a photodetector, and FUT is the fiber under test (sensing region SA).

[0028] Light from a single-wavelength laser light source (LD) with a wavelength of 1.55 μm was split into two using an optical fiber coupler (3 dB coupler). The upper optical path in the experimental system generates probe light Pr, and the lower optical path generates pump light Pm.

[0029] In the upper optical path of the experimental system, one of the branched beams was frequency-shifted by a phase modulator PM driven by a sawtooth wave modulation signal, and then intensity-modulated at a frequency near the Brillouin frequency by a Mach-Zehnder type optical intensity modulator IM1 driven by a sinusoidal wave modulation signal. Here, by setting the modulation operating point of the optical intensity modulator IM1 to the point where the output optical intensity is minimized (leaving only the intensity-modulated frequency component), a probe light Pr having two frequency components (a frequency component that produces Brillouin gain and a frequency component that produces Brillouin loss) is obtained. In this experiment, the frequency shift amount (Δν) in the phase modulator PM was set to 25 MHz, and the intensity modulation frequency (ν) in the optical intensity modulator IM1 was set to 25 MHz. probe The frequency was set to 10.805 GHz. In the lower optical path of the experimental system, the other branched light was subjected to intensity modulation by an optical intensity modulator IM2 driven by a pulsed modulation signal to generate a pulse (pump light Pm) with a pulse duration width of 30 ns.

[0030] Here, the spatial resolution is given by Δz = cw / 2n, where c is the speed of light in a vacuum, n is the effective refractive index of the optical fiber, and w is the pulse duration. The speed of light c is approximately 3 × 10⁻⁶. 8The speed is m / s, and the effective refractive index n of the optical fiber is approximately 1.5, so the spatial resolution Δz of the experimental system is approximately 3m. The repetition frequency of the pump light Pm was set to 2.2MHz. In this case, the maximum measurement range is 45m.

[0031] In this experiment, a 30m optical fiber was used as the fiber under test (FUT) for temperature distribution measurement. The central 5m region of the fiber under test (the section from 12.5m to 17.5m from the end) was placed in an incubator and its temperature was varied from 25.7°C to 41.1°C. The rest of the fiber under test was left at room temperature. The experimental results are shown in Figure 5. The graph in Figure 5 shows the distribution of the sum of the amplification of the probe light due to Brillouin gain and the loss of the probe light due to Brillouin loss (Probe gain) measured when the temperature of the central region of the fiber under test was 25.7°C, 29.1°C, 32.2°C, 35.0°C, 37.8°C, and 41.1°C. In the central region of the fiber under test, the Probe gain changes more significantly as the temperature increases. Furthermore, the graph shown within Figure 5 illustrates the relationship between the temperature at the center of the central region of the fiber FUT under test (15 m from the end) and the probe gain, showing that the probe gain changes in proportion to the temperature.

[0032] Furthermore, an experiment was conducted to measure the strain distribution of an optical fiber using an experimental setup similar to that shown in Figure 4. As shown in Figure 6, in this experiment, a weight was attached to the 20m fiber under test (FUT) at a distance of 7m (13m) from the ceiling end, and the distribution of tensile strain (fiber elongation) due to the weight was measured. The fiber under test (FUT) was fixed to the ceiling with tape at distances of 15m and 20m, and the lower 13m was rolled up on a table. The frequency shift amount (Δν) in the phase modulator PM was set to 35MHz, and the intensity modulation frequency (ν) in the optical intensity modulator IM1 was set to ν probeThe frequency was set to 10.082 GHz. The spatial resolution of this measurement is 2 m. The experimental results are shown in Figure 7. The graph in Figure 7 shows the distribution of fiber elongation when the weight (load) attached to the fiber under test (FUT) was 360 g, 310 g, 260 g, 210 g, 160 g, and 110 g. At a distance of approximately 13 m from the weight attachment point, the distortion increases with increasing load.

[0033] According to the method of this embodiment, by using probe light having two frequency components—one that generates Brillouin gain and another that generates Brillouin loss—it becomes possible to measure temperature and strain from the received light intensity, or to measure temperature distribution and strain distribution from the time change of the received light intensity, without requiring frequency sweeping. Furthermore, since the equipment required for spectral shaping of the probe light and pump light can be omitted, the apparatus configuration can be simplified. In addition, the modulation signal applied to the first optical modulation section to generate the probe light is a simple sine wave and does not need to be a complex waveform, making it easy to control and highly stable.

[0034] Next, we will explain how to adjust the frequency shift amount Δν in the optical frequency shifter 20 (how to adjust the measuring device). Prior to adjustment, a reference region of the optical fiber 2 is determined. For example, a certain length of fiber (e.g., about 5m) on the measuring device side, including the laser light source and modulator, is kept in a stable state free from large temperature changes and distortions, and this is designated as the reference region.

[0035] Figure 8 is a flowchart illustrating the flow of the adjustment method for the frequency shift amount Δν. First, the frequency shift amount Δν at the optical frequency shifter 20 is set to be large so that when the lower of the two frequency components of the probe light Pr receives gain due to Brillouin gain, the higher frequency component does not receive loss due to Brillouin loss, and when the higher frequency component receives loss due to Brillouin loss, the lower frequency component does not receive gain due to Brillouin gain (i.e., the two frequency components of the probe light Pr do not simultaneously receive gain due to Brillouin gain and loss due to Brillouin loss) (step S10). In the experimental system of this embodiment, the above conditions were met when the frequency shift amount Δν was set to 60 MHz.

[0036] Next, the frequency of the modulation signal of the optical modulator 30 (intensity modulation frequency, ν probe ) is the Brillouin frequency shift ν BFS The frequency range is gradually changed within a range of approximately 11 GHz, and the distribution measurement is performed (step S11). However, only the light intensity corresponding to the position of the reference region is acquired from the light intensity detected by the photodetector 80 (light intensity of probe light AP).

[0037] Next, based on the relationship between the frequency of the modulated signal and the acquired light intensity, the shape of the Brillouin gain spectrum BGS and the Brillouin frequency shift ν are determined. BFS (Step S12) is determined. Figure 9 is a graph plotting the optical intensity obtained when the frequency shift amount Δν is 60MHz, 40MHz, 25MHz, and 20MHz against the frequency of the modulated signal. As shown in Figure 9, the graph when the frequency shift amount Δν is 60MHz consists of peaks and valleys that are sufficiently far apart from each other, and the shape of the Brillouin gain spectrum BGS can be determined from the peak portion, and the Brillouin frequency shift ν can be determined from the frequency of the peak portion (peak frequency) and the frequency shift amount Δν. BFS This can be calculated. If the peaks and valleys overlap (they are not clearly separated), the frequency shift amount Δν is further increased, and the procedure to proceed to step S11 is performed.

[0038] Next, the Brillouin gain spectrum BGS and the Brillouin frequency shift ν BFS Based on this, a frequency shift amount Δν that allows for a wide range in which the light intensity detected by the photodetector 80 changes linearly with temperature and distortion is calculated by calculation on the PC, and the calculated frequency shift amount Δν is set as the adjusted frequency shift amount Δν in the optical frequency shifter 20 (step S13).

[0039] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible. The present invention includes configurations that are substantially identical to those described in the embodiments (for example, configurations with the same function, method, and result, or configurations with the same purpose and effect). The present invention also includes configurations in which non-essential parts of the configuration described in the embodiments are replaced. Furthermore, the present invention includes configurations that produce the same effects or achieve the same purpose as the configuration described in the embodiments. Furthermore, the present invention includes configurations that add known technology to the configuration described in the embodiments. [Explanation of symbols]

[0040] 1... Measuring device, 2... Optical fiber, 10... Laser light source, 11... Optical splitter, 20... Optical frequency shifter, 30, 31... Optical modulator, 40... Optical isolator, 50... Oscillator, 60... Pulse signal generator, 70... Optical circulator, 80... Photodetector, 90... Data processing device

Claims

1. A branching section that splits the light from the laser light source into two, A light frequency shifting unit that shifts the frequency of one of the two branched light beams, A first optical modulation unit generates probe light having two frequency components by intensity modulation of one of the branched light streams, A second optical modulation unit generates pump light by pulsing the other branched light, A light detection unit detects light emitted from the other end of an optical fiber when the probe light is incident on one end of the optical fiber to be measured and the pump light is incident on the other end of the optical fiber. The processing unit includes a unit that measures the temperature or strain of the optical fiber based on the light intensity detected by the light detection unit, A method for adjusting a measuring device, wherein the frequency of the lower of the two frequency components is the frequency at which Brillouin gain occurs due to interaction with the pump light, and the frequency of the higher of the two frequency components is the frequency at which Brillouin loss occurs due to interaction with the pump light, The steps include setting the frequency shift amount in the optical frequency shift unit so that the two frequency components of the probe light do not simultaneously suffer gain due to Brillouin gain and loss due to Brillouin loss, The steps include acquiring the light intensity detected by the light detection unit each time the frequency of the modulation signal of the first light modulation unit is changed, The steps include determining the Brillouin gain spectrum and the Brillouin frequency shift based on the relationship between the frequency of the modulated signal and the light intensity, A method for adjusting a measuring device, comprising the step of adjusting the amount of frequency shift based on the Brillouin gain spectrum and the Brillouin frequency shift.

2. In claim 1, The aforementioned processing unit, A method for adjusting a measuring device, which measures the temperature or strain of an optical fiber based on the light intensity within a range where the relationship between the light intensity detected by the light detection unit and the temperature or strain of the optical fiber is a predetermined relationship.

3. In claim 1 or 2, The aforementioned processing unit, A method for adjusting a measuring device, which measures the temperature distribution or strain distribution of the optical fiber based on the time change of light intensity detected by the light detection unit.

4. In any one of claims 1 to 3, The first optical modulation unit is, A method for adjusting a measuring device, which generates probe light by intensity modulating light that has been frequency-shifted in the optical frequency shifting section.

5. A branching step that splits the light from the laser light source into two, An optical frequency shift step in which the frequency of one of the two branched beams of light is shifted by an optical frequency shift unit, A first optical modulation step involves generating probe light having two frequency components by intensity modulation of one of the branched light beams using a first optical modulation unit, A second optical modulation step involves pulsing the other branched light to generate pump light, A photodetection step in which, when the probe light is incident on one end of the optical fiber to be measured and the pump light is incident on the other end of the optical fiber, the light emitted from the other end of the optical fiber is detected by a photodetector, The process includes measuring the temperature or strain of the optical fiber based on the light intensity detected in the light detection step, The frequency of the lower of the two frequency components is the frequency at which Brillouin gain occurs due to interaction with the pump light, and the frequency of the higher of the two frequency components is the frequency at which Brillouin loss occurs due to interaction with the pump light. The steps include setting the frequency shift amount in the optical frequency shift unit so that the two frequency components of the probe light do not simultaneously suffer gain due to Brillouin gain and loss due to Brillouin loss, The steps include acquiring the light intensity detected by the light detection unit each time the frequency of the modulation signal of the first light modulation unit is changed, The steps include determining the Brillouin gain spectrum and the Brillouin frequency shift based on the relationship between the frequency of the modulated signal and the light intensity, A measurement method further comprising the step of adjusting the amount of frequency shift based on the Brillouin gain spectrum and the Brillouin frequency shift.

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