Assay device and assay method

Abstract

Provided are a measurement device and the like that can simplify the configuration of a device and improve convenience. A measurement device branches light from a laser light source into two light beams, generates pump light as pulsed light composed of two frequency components by intensity-modulating one of the branched light beams, generates probe light by shifting the frequency of the other branched light beam, combines light emitted from one end of an optical fiber on which the pump light is incident from the one end of the optical fiber with the probe light, detects a beat signal between the probe light and Brillouin scattered light generated in a frequency band between the two frequency components, and measures the temperature or strain of the optical fiber based on the detected beat signal. The interval of the two frequency components is set so that a Brillouin gain spectrum generated on the low-frequency side of the higher one of the frequency components and a Brillouin loss spectrum generated on the high-frequency side of the lower one of the frequency components have overlap on the frequency axis.

Description

Technical Field

[0001] This invention relates to a measuring device and method for measuring the temperature or strain of optical fibers. Background Technology

[0002] Previously, much research has been conducted on distributed sensor technology utilizing Brillouin scattering within optical fibers. Distributed Brillouin sensing leverages the fact that the frequency region where Brillouin scattering occurs strongly, i.e., the Brillouin gain spectrum, changes proportionally with strain and temperature. In the Brillouin analytical method, one of the representative methods, probe light is incident from the opposite side of the fiber (the side opposite to the side of the incident pump light) to observe changes in the Brillouin gain spectrum with a relatively high signal-to-noise ratio. However, to observe the Brillouin gain spectrum, a frequency scan of the probe light is required, which is time-consuming. In Brillouin reflection measurements such as BOTDR (Brillouin Optical Time Domain Reflectometry), another representative method, the probe light is not incident on the fiber but is heterodyne-interfered with the Brillouin scattered light from the fiber. The beat signal obtained by photoelectric conversion in a photodetector is input to an electrical spectrum analyzer to observe changes in the Brillouin gain spectrum. However, electrical spectrum analyzers, which consist of high-frequency circuitry, are expensive.

[0003] Furthermore, the following methods have been proposed: a method using pump light and probe light composed of multi-frequency light to obtain the Brillouin gain spectrum; and a method using pump light and probe light composed of multi-frequency light, and utilizing the fact that the final received optical power varies proportionally with temperature and strain by appropriately shaping the spectrum of the probe light. While these methods achieve a configuration without frequency scanning, the method of shaping the spectrum of light composed of many frequency components increases the number of system components due to the need for spectrum shaping equipment. Additionally, a method utilizing a region where the change in the Brillouin gain spectrum is considered linear with respect to frequency has been explored. However, such a region is narrow.

[0004] In addition, a method is proposed to simplify the measurement with fewer system components by using the Brillouin gain spectrum and Brillouin loss spectrum obtained by a single-frequency pump light and a dual-frequency probe light. Existing technical documents Non-patent literature

[0005] 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, M.Chitgarha, 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, “Single-measurement digital optical frequency comb based phase-detection Brillouin optical time domain analyzer,” Opt. Exp. 25, 9213-9224 (2017). Empty Range 5:Y. Tanaka , Y. Ozaki , and Y. So , “ Scanless Brillouin Gain Spectrum Measurement Based multiheterodyne detection,” in Tech. Empty Range 6:Y. Tanaka and T. Hasegawa, “Brillouin optical time domain analysis using spectrally reshaped 12-GHz spacing multimode pump and probe,” Conference on Lasers andElectro-Optics (CLEO) 2020, paper SF3P.7 (2020). Empty Range 7:Y. Peled, A. Motil, L. Yaron, and M. Tur, “Slope-assisted fast distributed sensing in optical fibers with arbitrary Brillouin profile,” Opt. Empty Range 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). Empty Range 9:K. Hoshino , D. Saito , Y. Endo , T. Hasegawa , and Y. Tanaka , “ Brillouin gain spectrum manipulation using multifrequency pump and probe for slope-assisted BOTDA with wider dynamic range," Applied Physics Express, vol.15,022009, 2022. Summary of the Invention The problem the invention aims to solve

[0006] The method of using dual-frequency probe light has room for improvement from a convenience point of view because the probe light is incident from the opposite side of the optical fiber (the side opposite to the side of the incident pump light).

[0007] The present invention was made in view of the problems mentioned above, and its object is to provide a measuring device that can simplify the configuration of the device and improve convenience. Solution for solving the problem

[0008] (1) The present invention relates to a measuring device comprising: a branching section that branches light from a laser source into two beams; an optical modulation section that modulates the intensity of one of the branched beams to generate a pump beam, the pump beam being a pulsed beam composed of two frequency components; an optical frequency shifting section that shifts the frequency of the other branched beam to generate a probe beam; an optical detection section that receives light after combining light emitted from one end of the optical fiber when the pump beam is incident from one end of the optical fiber to be measured with the probe beam, and detects a beat signal between the Brillouin scattered light and the probe beam generated in the frequency band between the two frequency components; and a processing section that measures the temperature or strain of the optical fiber based on the beat signal detected by the optical detection section, wherein the interval between the two frequency components is set such that the Brillouin gain spectrum generated on the low-frequency side of the higher frequency component of the two frequency components overlaps with the Brillouin loss spectrum generated on the high-frequency side of the lower frequency component of the two frequency components on the frequency axis.

[0009] Additionally, the present invention relates to a measurement method comprising: a branching step, splitting light from a laser source into two beams; an optical modulation step, modulating the intensity of one branched beam to generate a pump beam, the pump beam being a pulsed beam composed of two frequency components; an optical frequency shifting step, shifting the frequency of the other branched beam to generate a probe beam; an optical detection step, receiving light after combining the light emitted from one end of the optical fiber when the pump beam is incident from that end with the probe beam, and detecting a beat signal between the Brillouin scattered light and the probe beam generated in the frequency band between the two frequency components; and a processing step, based on the beat signal detected by the optical detection step, measuring the temperature or strain of the optical fiber, wherein the interval between the two frequency components is set such that the Brillouin gain spectrum generated on the low-frequency side of the higher frequency component and the Brillouin loss spectrum generated on the high-frequency side of the lower frequency component overlap on the frequency axis.

[0010] According to the present invention, since the incident light into the optical fiber is only the pump light incident from one end of the optical fiber, the device configuration can be simplified and the convenience can be further improved.

[0011] (2) Alternatively, in the measuring apparatus and measuring method of 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 the beat signal detected by the optical detection unit (in the optical detection step).

[0012] According to the present invention, temperature distribution and strain distribution can be determined from the time variation of beat signals without frequency scanning. Attached Figure Description

[0013] Figure 1 This is a diagram showing the configuration of the measuring device according to this embodiment. Figure 2 This is a graph showing the relationship between the pump light, Brillouin gain spectrum, Brillouin loss spectrum, Brillouin scattered light, and probe light. Figure 3 This is a diagram showing the experimental system for verifying the principle of the method of this embodiment. Figure 4 This is a diagram showing the experimental results of the experiment confirming the principle of the method of this embodiment. Figure 5 This is a diagram showing an example of the configuration of a measuring device without using a probe light. Detailed Implementation

[0014] Hereinafter, embodiments of the present invention will be described. Furthermore, the embodiments described below are not intended to unduly limit the scope of the present invention as described in the claims. Additionally, not all configurations described in these embodiments are necessarily essential elements of the present invention.

[0015] Figure 1 This diagram illustrates the configuration of the measuring apparatus according to this embodiment. The measuring apparatus 1 is a device for measuring the temperature or strain of the sensing area SA (the object of measurement) of the optical fiber 2, and includes: a single-wavelength (single-mode) laser source 10; an optical coupler 11 (branch); an optical modulator 20 (optical modulation unit); a pulse signal generator 30; an oscillator 40; an optical circulator 50; an optical frequency shifter 60 (optical frequency shifting unit); an optical coupler 12 (multiplexing unit); an optical receiver 70 (optical detection unit); and a data processing device 80 (processing unit).

[0016] Optical coupler 11 splits the light from laser source 10 into two beams in a manner that is such that a predetermined branching ratio (e.g., 1 to 1) is achieved.

[0017] Optical modulator 20 modulates the intensity of one light beam branched off from optical coupler 11 to generate pump light Pm. Pump light Pm consists of two frequency components (center frequency ν). pump1 ν pump2 The light is composed of pulsed light. A pulse signal generator 30 generates an intensity modulation signal (pulse signal) for pulsed generation, and an oscillator 40 generates an intensity modulation signal for dual-frequency modulation. The pulse signal from the pulse signal generator 30 and the intensity modulation signal from the oscillator 40 are combined and supplied to the optical modulator 20. When a Mach-Zehnder type optical modulator is used as the optical modulator 20, the frequency components of the incident light can be suppressed by controlling the bias voltage, generating only sideband wave components. At this time, the interval (frequency interval) between the two frequency components of the pump light Pm becomes twice the frequency of the oscillator 40. Furthermore, the interval between the two frequency components of the pump light Pm is set such that the higher frequency component (center frequency ν) is... pump2 The Brillouin gain spectrum generated on the low-frequency side of the spectrum and the lower of the two frequency components (center frequency ν) pump1The Brillouin loss spectrum generated on the high-frequency side of the optical modulator overlaps on the frequency axis. Alternatively, the optical modulation unit can be configured with an optical modulator for pulsed modulation (an optical modulator that modulates the intensity based on a pulse signal from the pulse signal generator 30) and an optical modulator for dual-frequency modulation (an optical modulator that modulates the intensity based on an intensity modulation signal from the oscillator 40). In this case, as the optical modulator for pulsed modulation, in addition to a Mach-Zehnder type optical modulator, an acousto-optic modulator (AOM) or an optical modulator based on a semiconductor optical amplifier (SOA) can also be used.

[0018] The optical circulator 50 outputs the pump light Pm input to port 1 from port 2 and guides it to one end of the sensing region SA. It also outputs light (the Brillouin scattered light Br generated in the band between the two frequency components of the pump light Pm) that exits from one end of the sensing region SA and enters port 2 from port 3 and guides it to the optical coupler 12. Alternatively, the optical circulator 50 can also be constructed using an optical isolator and an optical coupler.

[0019] Optical frequency shifter 60 shifts the frequency of the other light branched off from optical coupler 11 to generate probe light Pr. The frequency shift amount performed by optical frequency shifter 60 is set such that the frequency (ν) of probe light Pr... probe It will not overlap with the spectrum of the Brillouin scattered light Br. Furthermore, as an optical frequency shifter 60, an acousto-optic modulator can be used, or it can be constructed from an optical modulator and an optical wavelength filter.

[0020] Optical coupler 12 combines the light emitted from one end of the sensing region SA and the light output from the third port of the optical circulator 50 with the probe light Pr emitted from the optical frequency shifter 60. Optical receiver 70 receives the combined light from optical coupler 12 and detects the beat signal between the Brillouin scattered light Br and the probe light Pr. The intensity of the beat signal detected by optical receiver 70 (after optical heterodyne detection) is output as an electrical signal and input to data processing device 80.

[0021] The data processing device 80 is a computer equipped with a processor (CPU, etc.) and a storage unit (RAM, hard disk, etc.). Based on the signal intensity detected by the optical receiver 70, it calculates the temperature or strain of the optical fiber 2 (sensing region SA). For example, a function approximating the relationship (e.g., proportional relationship) between signal intensity and temperature or strain is pre-calibrated, and the signal intensity detected by the optical receiver 70 is substituted into this function to calculate the temperature or strain of the sensing region SA. Furthermore, the data processing device 80 calculates the temperature distribution or strain distribution of the sensing region SA based on the time variation of the signal intensity detected by the optical receiver 70. The length of light propagating within one cycle of the pump light Pm pulse corresponds to the length of the sensing region SA. That is, the temperature and strain distribution in the sensing region SA can be determined from the change in signal intensity measured within one cycle of the pump light Pm pulse. Moreover, the generation timing of each pulse of the pump light Pm is supplied as a trigger signal from the pulse signal generator 30.

[0022] like Figure 2 As shown, in fiber 2 (sensing region SA), the higher of the two frequency components of the pump light Pm (center frequency ν) pump2 The low-frequency side of the pump light Pm generates the Brillouin Gain Spectrum (BGS), which is the lower of the two frequency components (center frequency ν). pump1 The high-frequency side of the spectrum generates the Brillouin Loss Spectrum (BLS). It has two frequency components (ν). pump1 ,ν pump2 The spacing between BGS and BLS is set so that they overlap on the frequency axis, thereby reducing the gain (Brillouin gain) of BGS and the intensity (power) of the Brillouin scattered light Br generated in the frequency band of BGS. Figure 2 The BSS shown is the spectrum of the Brillouin scattered light Br after power reduction. (The last part, "ν," appears to be a typo and can be omitted.) pump2 The difference ν between the center frequency of BGS and BGS BFS (and ν) pump1 The difference ν between the center frequency and the BLS BFS This is called the Brillouin Frequency Shift. The Brillouin Frequency Shift ν BFS It changes proportionally to the changes in temperature and strain of the sensing region SA. That is, due to changes in temperature and strain of the sensing region SA, ν... BFS Changes in light intensity cause the BGS and BLS to move closer or further apart, thus altering the gain of the BGS and consequently changing the intensity of the Brillouin scattered light Br. This phenomenon allows for the convenient measurement of the temperature and strain of the sensing region SA from optical power measurements.

[0023] Probe light Pr (center frequency ν) probe () is generated by shifting the frequency of light from laser source 10. This frequency shift causes ν to probe It will not overlap with the BSS. In the optical receiver 70, the beat signal between the Brillouin scattered light Br and the probe light Pr is observed. Figure 2 The figure shows the beat frequency BF of the Brillouin scattered light Br and the probe light Pr. In the data processing device 80, the temporal variation of the beat signal components is observed by observing the signal intensity of specific frequency components within the beat signal. Furthermore, the overall intensity variation of the beat signal can also be observed. The intensity of the beat signal changes according to the gain of the BGS (changes in temperature or strain of the sensing region SA). If the relationship between the intensity of the beat signal and the temperature or strain of the sensing region SA is calibrated and determined beforehand, the temperature and strain of the sensing region SA can be determined from the observed beat signal intensity using the calibration result.

[0024] Figure 3 This is a diagram illustrating the experimental system used to verify the principle of the method described in this embodiment. Figure 3 In this diagram, LD is a single-mode laser source, IM1-IM3 are optical intensity modulators, SG1 and SG2 are oscillators, EDFA1-EDFA3 are optical amplifiers, BPF is an optical bandpass filter, OSA is an optical spectrum analyzer, PS is a polarization scrambler, FG is an arbitrary waveform generator, ATT is an attenuator, PD is a photodetector, ESA is an electrical spectrum analyzer, and FUT is the fiber under test (sensing area SA).

[0025] The light from a single-mode laser source (LD) with a wavelength of 1.55 μm was split into two paths using an optical fiber coupler (3 dB coupler). The upper optical path of the experimental system generates the probe light Pr, and the lower optical path generates the pump light Pm. The fiber under test (FUT) was 5 km long and was kept at a constant temperature of 50 °C in an incubator.

[0026] The light from the laser source LD is intensity modulated by optical intensity modulator IM1 to form light composed of two frequency components. After branching, in the upper optical path, the high-frequency component is intercepted by optical bandpass filter BPF and then intensity modulated by optical intensity modulator IM2 to form light composed of two frequency components. The low-frequency component is used as the probe light Pr. The high-frequency component becomes a high-frequency signal during optical heterodyne detection and therefore cannot be detected electrically. The intensity modulation frequency in optical intensity modulator IM1 is set to 10.88 GHz, and the intensity modulation frequency in optical intensity modulator IM2 is set to 10.6 GHz. This shifts the frequency of the light from the laser source LD by 280 MHz (10.88 - 10.6 = 0.28 GHz) to generate the probe light Pr. In the lower optical path, the intensity of the branched light (light composed of two frequency components) is modulated by the light intensity modulator IM3 driven by the pulsed modulation signal, thereby generating a pulse light Pm with a pulse width of 25μs and a period of 50.1μs.

[0027] Figure 3 The spectrum diagram shown in the lower right corner illustrates the situation with optical heterodyne detection (within the dashed lines). This diagram shows the positional relationship between the Brillouin scattered light Br and the probe light Pr on the frequency axis; the scale is not accurate. The beat frequency between the Brillouin scattered light Br and the probe light Pr obtained by optical heterodyne detection is approximately 200 MHz. The frequency interval between the probe light Pr (the lower-frequency component of the two frequency components) and the undetected higher-frequency component is... Figure 3 In the example, it is 21.2GHz.

[0028] In this experiment, the Brillouin gain spectrum (BGS) generated on the low-frequency side of the higher frequency component of the pump light Pm and the Brillouin loss spectrum (BLS) generated on the high-frequency side of the lower frequency component of the pump light Pm were varied along the frequency axis (the gain of BGS changed). This altered the interval between the two frequency components of the pump light Pm, and the signal strength (the integral value of the entire beat signal spectrum) detected by the photodetector PD was measured. Specifically, the distance between the source frequency and the center frequency ν of the high-frequency component of the pump light Pm was measured. pump2 (Center frequency ν of the low-frequency component) pump1 The frequency difference f pump The change in signal strength from 10.88 GHz to 10.89 GHz in 1 MHz increments.

[0029] The experimental results are in Figure 4 As shown in the image. Figure 4 As shown, the experiment demonstrates that as f pumpAs the gain of BGS increases and the overlap between BGS and BLS decreases (the gain of BGS increases), the signal strength (i.e., the power of the Brillouin scattered light Br) increases. Strictly speaking, the interaction between BGS and BLS should be analyzed using the coupled-mode equations. However, if the range is narrower than the half-width of BGS and BLS (100 MHz), the change in the frequency difference between the two frequency components of the pump light Pm is expected to be monotonic, and indeed, the experimental results confirm this.

[0030] According to the method of this embodiment, by using pump light composed of two frequency components, the frequency interval is set such that the BGS generated on the low-frequency side of the higher frequency component and the BLS generated on the high-frequency side of the lower frequency component overlap on the frequency axis. Temperature and strain can be measured from signal intensity, or temperature and strain distributions can be measured from the time variation of signal intensity, without frequency scanning. Furthermore, since the equipment required for spectral shaping of the pump light and probe light can be eliminated, the device configuration can be simplified. Additionally, since the incident light into the optical fiber is only pump light incident from one end of the fiber, convenience is improved compared to the case where probe light is incident from the other end of the fiber.

[0031] Figure 5 An example of the configuration of a measuring apparatus without using the probe light Pr is shown. Figure 5 In China, for the sake of Figure 1 The components shown are identical, and the same reference numerals are used in the accompanying drawings; their descriptions are omitted where appropriate. Figure 5In the example shown, light from the laser source 10 is incident unbranched onto the optical modulator 20. Additionally, light exiting from one end of the sensing region SA and incident on the second port of the optical circulator 50, and outputting from the third port, is incident on the optical filter 90 (optical wavelength filter). The optical filter 90 allows only the Brillouin scattered light Br generated in the band between the two frequency components of the pump light Pm to pass through (only the spectrum BSS of the Brillouin scattered light Br is intercepted). The optical receiver 70 detects the light after it has passed through the optical filter 90, and the data processing device 80 calculates the temperature or strain of the optical fiber 2 (sensing region SA) based on the light intensity detected by the optical receiver 70. By intercepting the Brillouin scattered light Br by the optical filter 90 in this way, the device configuration can be further simplified. Furthermore, when the pump light Pm has a wavelength of approximately 1.5 μm, the Brillouin gain spectrum (BGS) is generated approximately 11 GHz lower than the frequency components of the pump light Pm, while the Brillouin loss spectrum (BLS) is generated approximately 11 GHz higher. The spectral widths of the Brillouin gain spectrum (BGS) and the Brillouin loss spectrum (BLS) are generally below 100 MHz. The frequencies of these spectra shift approximately 1 MHz with a 1-degree temperature change, and approximately 10... -6 The optical filter 90 shifts by approximately 0.05 MHz due to strain changes. The transmission bandwidth (in the case of a transmission type) or reflection bandwidth (in the case of a reflection type) of the optical filter 90 used is preferably at least 0.1 nm or less. In the case of a transmission type, the transmitted light is detected by the optical receiver 70, and in the case of a reflection type, the reflected light is detected by the optical receiver 70. For example, a fiber diffraction grating (FBG) with a bandwidth of less than 0.1 nm can be used as such an optical filter.

[0032] Furthermore, the present invention is not limited to the embodiments described above and can be modified in various ways. The present invention includes configurations that are substantially the same as those described in the embodiments (e.g., configurations with the same function, method, and result, or configurations with the same purpose and effect). Additionally, the present invention includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. Furthermore, the present invention includes configurations that have the same effect as those described in the embodiments or that can achieve the same purpose. Additionally, the present invention includes configurations in which known techniques are added to the configurations described in the embodiments. Explanation of reference numerals in the attached figures

[0033] 1… Measuring device, 2… Optical fiber, 10… Laser source, 11, 12… Optical coupler, 20… Optical modulator, 30… Pulse signal generator, 40… Oscillator, 50… Optical circulator, 60… Optical frequency shifter, 70… Optical receiver, 80… Data processing device, 90… Optical filter.

Claims

1. A measuring device, characterized in that, Include: The branch section splits the light from the laser source into two beams; The optical modulation unit modulates the intensity of a branched-out light to generate pump light, which is a pulse light composed of two frequency components. The optical frequency shifting unit shifts the frequency of the branched-out light to generate probe light; The optical detection unit receives light after combining the light emitted from the one end of the optical fiber when the pump light is incident from the one end of the optical fiber to be measured with the probe light, and detects the beat signal between the Brillouin scattered light and the probe light generated in the frequency band between the two frequency components. as well as The processing unit measures the temperature or strain of the optical fiber based on the beat signal detected by the optical detection unit. The interval between the two frequency components is set such that the Brillouin gain spectrum generated on the low-frequency side of the higher frequency component overlaps with the Brillouin loss spectrum generated on the high-frequency side of the lower frequency component on the frequency axis.

2. A measuring device, characterized in that, Include: The optical modulation unit modulates the intensity of light from the laser source to generate pump light, which is a pulse light composed of two frequency components; The optical filter intercepts Brillouin scattered light generated in the frequency band between the two frequency components in the light emitted from the one end of the optical fiber when the pump light is incident from the one end of the optical fiber being measured. A light detection unit that detects the light intercepted by the light filtering unit; as well as The processing unit measures the temperature or strain of the optical fiber based on the light intensity detected by the light detection unit. The interval between the two frequency components is set such that the Brillouin gain spectrum generated on the low-frequency side of the higher frequency component overlaps with the Brillouin loss spectrum generated on the high-frequency side of the lower frequency component on the frequency axis.

3. The measuring device according to claim 1, wherein, The processing unit The temperature distribution or strain distribution of the optical fiber is determined based on the time change of the beat signal detected by the optical detection unit.

4. The measuring device according to claim 1 or 2, wherein, The optical modulation unit The pump light is generated by intensity modulation of a signal synthesized from a pulse signal generator and an intensity modulation signal from an oscillator.

5. The measuring apparatus according to claim 1 or 2, wherein, The optical modulation section is a Mach-Zehnder type optical modulator.

6. A method for determination, characterized in that, Include: The branching step splits the light from the laser source into two beams; The optical modulation step involves intensity modulation of one branch of light to generate pump light, which is a pulse light composed of two frequency components. The optical frequency shifting step shifts the frequency of the branched-out light to generate the probe light; The optical detection step involves receiving light after combining the light emitted from the one end of the optical fiber when the pump light is incident from the one end of the optical fiber being measured with the probe light, and detecting the beat signal between the Brillouin scattered light and the probe light generated in the frequency band between the two frequency components. as well as The processing step involves determining the temperature or strain of the optical fiber based on the beat signal detected by the optical detection step. The interval between the two frequency components is set such that the Brillouin gain spectrum generated on the low-frequency side of the higher frequency component overlaps with the Brillouin loss spectrum generated on the high-frequency side of the lower frequency component on the frequency axis.

7. A method for determination, characterized in that, Include: The light modulation step involves intensity modulation of the light from the laser source to generate pump light, which is a pulse of light composed of two frequency components. The optical filtering step involves intercepting the Brillouin scattered light generated in the frequency band between the two frequency components in the light emitted from the one end of the optical fiber when the pump light is incident from the one end of the optical fiber being measured. The light detection step detects the light extracted by the light filtering step. as well as The processing step involves determining the temperature or strain of the optical fiber based on the light intensity detected by the light detection step. The interval between the two frequency components is set such that the Brillouin gain spectrum generated on the low-frequency side of the higher frequency component overlaps with the Brillouin loss spectrum generated on the high-frequency side of the lower frequency component on the frequency axis.

Images