Optical fiber sensor and brillouin frequency shift measurement method

Abstract

To correct a measurement error of BFS by performing calculation of BFS on the basis of an extinction ratio of optical pulses.SOLUTION: An optical fiber sensor comprises: a light source section for generating probe light that is an optical pulse train; an optical coupler for branching probe light into two; an interference signal acquisition section for generating an interference signal by self-delay type heterodyne interference after rear Brillouin scattered light generated by an optical fiber measured by one probe light branched into two by an optical coupler is inputted; an extinction ratio measuring instrument for measuring an extinction ratio of the other probe light branched into two by the optical coupler; and signal processing means. The signal processing means includes: BFS calculation means for calculating a Brillouin frequency shift amount as a BFS measurement value from an interference signal; and extinction ratio correction means for correcting a BFS measurement value and obtaining a true BFS value on the basis of an extinction ratio measured by the extinction ratio measuring instrument.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical fiber sensor using Brillouin scattered light and a method for measuring the Brillouin frequency shift. [Background technology]

[0002] With the development of optical fiber communications, distributed optical fiber sensing, which uses the optical fiber itself as the sensing medium, has been actively researched. In particular, optical fiber sensing, which uses scattered light, is different from electrical sensors that measure at each point, in that it is possible to measure a long-distance distributed measurement, and therefore can measure the physical quantity of the entire object being measured.

[0003] A representative distributed optical fiber sensing technique that can measure long-distance distribution is Optical Time Domain Reflectometry (OTDR), which inputs an optical pulse from one end of an optical fiber and measures the light backscattered in the optical fiber over time. Backscattering in optical fibers includes Rayleigh scattering, Brillouin scattering, and Raman scattering. Among these, the one that measures natural Brillouin scattering is called BOTDR (Brillouin OTDR) (for example, see Non-Patent Document 1).

[0004] Brillouin scattering is observed at a frequency shift of about GHz to the Stokes side and anti-Stokes side with respect to the center frequency of the optical pulse input to the optical fiber, and the spectrum is called the Brillouin gain spectrum (BGS). The frequency shift and spectral linewidth of the BGS are called the Brillouin frequency shift (BFS) and the Brillouin linewidth, respectively. The BFS and the Brillouin linewidth vary depending on the material of the optical fiber and the wavelength of the input light. For example, in the case of a silica-based single-mode optical fiber, it has been reported that the magnitude of the BFS and the Brillouin linewidth at a wavelength of 1.55 μm are about 11 GHz and about 30 MHz, respectively. Also, according to Non-Patent Document 1, the magnitude of the BFS due to strain and temperature changes in a single-mode fiber are 0.049 MHz / με and 1.0 MHz / ℃, respectively, at a wavelength of 1.55 μm.

[0005] As described above, the BFS is dependent on strain and temperature. For this reason, the BOTDR is attracting attention for its potential applications in diagnosing deterioration of large structures such as bridges and tunnels, temperature monitoring in plants, and monitoring areas at risk of landslides.

[0006] In BOTDR, in order to measure the spectral waveform of the spontaneous Brillouin scattering light generated in the optical fiber, it is common to perform heterodyne detection with a separately prepared reference light. The intensity of the spontaneous Brillouin scattering light is two to three orders of magnitude smaller than the intensity of the Rayleigh scattering light. For this reason, heterodyne detection is also useful for improving the minimum light receiving sensitivity.

[0007] Here, because the natural Brillouin scattered light is very weak, even if heterodyne detection is applied, a sufficient signal-to-noise ratio (S / N) cannot be ensured. As a result, averaging processing is required to improve the S / N ratio. Conventional optical fiber strain measurement devices that perform BOTDR acquire three-dimensional information of time, amplitude, and frequency, but it is difficult to shorten the measurement time due to the averaging processing and acquisition of this three-dimensional information.

[0008] In response to this, the inventors of this application have developed a self-delayed heterodyne BOTDR (SDH-BOTDR: Self-delayed heterodyne BOTDR). An optical fiber distortion measuring device and an optical fiber distortion measuring method that utilize the above have been proposed (see, for example, Patent Document 1). In SDH-BOTDR, changes in BFS are observed as phase changes in the beat signal by comparing the phase of the received beat signal with that of a local oscillator signal. In this way, SDH-BOTDR can directly calculate the BFS without requiring frequency sweeping, thereby enabling high-speed and low-cost measurements.

[0009] The inventors of this application have also proposed an optical fiber strain measuring device and an optical fiber strain measuring method that use a self-delayed homodyne type BOTDR as a self-delayed interferometer (see, for example, Patent Document 2). The self-delayed homodyne type BOTDR not only has a simpler configuration, but also improves the S / N ratio and spatial resolution. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2016-191659 A [Patent Document 2] JP 2019-060743 A [Non-patent literature]

[0011] [Non-Patent Document 1] T. Kurashima et al., “Brillouin Optical-fiber time domain reflectometry”, IEICE Trans. Commun., vol.E76-B, no.4, pp.382-390 (1993) Summary of the Invention [Problem to be solved by the invention]

[0012] In the conventional delayed self-heterodyne / homodyne BOTDR described above, the BFS is calculated from the phase change without observing the Brillouin frequency spectrum. In this delayed self-heterodyne / homodyne BOTDR, the extinction ratio of the optical pulse generated by the light source affects the BFS measurement value, and the fluctuation of the extinction ratio can be a cause of BFS measurement error. The extinction ratio of this optical pulse differs depending on the type and individual differences of the device, and also varies over time, so it is necessary to appropriately correct the BFS measurement error.

[0013] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an optical fiber sensor and a Brillouin frequency shift measurement method that can correct BFS measurement errors by calculating the BFS based on the extinction ratio of an optical pulse. [Means for solving the problem]

[0014] In order to achieve the above-mentioned object, the optical fiber sensor of the present invention is configured to include a light source unit that generates a probe light which is an optical pulse train, an optical coupler that branches the probe light into two, an interference signal acquisition unit that receives back Brillouin scattered light generated in an optical fiber to be measured by one of the probe lights branched by the optical coupler and generates an interference signal by self-delayed heterodyne interference, an extinction ratio measurement unit that measures the extinction ratio of the other probe light branched by the optical coupler, and a signal processing means.

[0015] The signal processing means includes a BFS calculation means for calculating the amount of Brillouin frequency shift (BFS) from the interference signal as a BFS measurement value, and an extinction ratio correction means for correcting the BFS measurement value based on the extinction ratio measured by the extinction ratio measurement device to obtain a true BFS value.

[0016] According to another preferred embodiment of the optical fiber sensor of the present invention, the sensor comprises a light source unit that generates a probe light which is an optical pulse train, an optical coupler that branches the probe light in two, a branching unit that branches in two back Brillouin scattered light generated in an optical fiber to be measured by one of the probe lights branched in two by the optical coupler, an interference signal acquiring unit that receives one of the scattered light branches at the branching unit and generates an interference signal by self-delayed homodyne interference, an intensity acquiring unit that receives the other scattered light branched in two by the branching unit and generates an intensity signal indicating the intensity of the scattered light, an extinction ratio measuring device that measures the extinction ratio of the other probe light branched in two by the optical coupler, and signal processing means.

[0017] The signal processing means includes a BFS calculation means that calculates the Brillouin frequency shift amount from the interference signal and the intensity signal as a BFS measurement value, and an extinction ratio correction means that corrects the BFS measurement value based on the extinction ratio measured by the extinction ratio measurement device to obtain a true BFS value.

[0018] In implementing the above-described optical fiber sensor, the signal processing means may further include a correction coefficient calculation means for calculating an extinction ratio correction coefficient from the relationship between the extinction ratio and the ratio of the BFS measurement value to the BFS true value, which is acquired in advance, and the extinction ratio correction means may be configured to obtain the BFS true value by dividing the BFS measurement value by the extinction ratio correction coefficient.

[0019] Moreover, the Brillouin frequency shift measurement method of the present invention includes the steps of generating a probe light which is an optical pulse train, branching the probe light into two, inputting back Brillouin scattered light generated in an optical fiber to be measured by one of the branched probe lights and generating an interference signal by self-delayed heterodyne interference, measuring the extinction ratio of the other of the branched probe lights, calculating the amount of Brillouin frequency shift from the interference signal as a BFS measurement value, and correcting the BFS measurement value based on the extinction ratio to obtain a true BFS value.

[0020] According to another preferred embodiment of the Brillouin frequency shift measuring method of the present invention, the method includes the steps of: generating a probe light which is an optical pulse train; branching the probe light into two; branching back Brillouin scattered light generated in an optical fiber to be measured by one of the branched probe lights into two; inputting one of the branched scattered light and generating an interference signal by self-delayed homodyne interference; inputting the other branched scattered light and generating an intensity signal indicating the intensity of the scattered light; measuring the extinction ratio of the other of the branched probe lights; calculating the amount of Brillouin frequency shift from the interference signal and the intensity signal as a BFS measurement value; and correcting the BFS measurement value based on the extinction ratio to obtain a true BFS value. Equipped with.

[0021] When carrying out the above-mentioned Brillouin frequency shift measurement method, it is preferable to further include a process of calculating an extinction ratio correction coefficient from the relationship between the extinction ratio and the ratio of the BFS measurement value to the BFS true value, which is previously acquired, and in the process of acquiring the BFS true value, the BFS measurement value is divided by the extinction ratio correction coefficient to acquire the BFS true value. Effect of the Invention

[0022] According to the optical fiber sensor and Brillouin frequency shift measurement method of the present invention, the BFS is calculated based on the extinction ratio of the optical pulse, thereby preventing the extinction ratio of the optical pulse generated by the light source from affecting the BFS measurement value and preventing fluctuations in the extinction ratio from becoming a cause of BFS measurement errors. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic block diagram showing a configuration example of an optical fiber sensor. [Diagram 2] FIG. 2 is a schematic diagram of an optical pulse used in a BOTDR. [Diagram 3] FIG. 13 is a diagram showing a BFS distribution in a measured optical fiber. [Figure 4] FIG. 13 is a diagram showing the relationship between the BFS measurement value and the extinction ratio of an optical pulse. [Diagram 5]1 is a diagram showing the relationship between the extinction ratio of an optical pulse and the BFS measured value / BFS true value. [Figure 6] FIG. 1 is a schematic block diagram of an optical fiber sensor using delayed self-homodyne interference. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, the embodiments of the present invention will be described with reference to the drawings, but each drawing is merely a schematic illustration to the extent that the present invention can be understood. In addition, the following describes preferred configuration examples of the present invention, but these are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many changes or modifications can be made that can achieve the effects of the present invention without departing from the scope of the configuration of the present invention.

[0025] (Configuration example) The optical fiber sensor of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic block diagram showing a configuration example of the optical fiber sensor of the present invention. The optical fiber sensor of the present invention is a self-delay type BOTDR that utilizes self-delay heterodyne interference.

[0026] The measurement device comprises a light source unit 10, a circulator 20, an optical coupler 200, a pulse extinction ratio measuring device 210, an optical amplifier 30, an optical bandpass filter 32, a self-delayed heterodyne interferometer 40 as an interference signal acquiring unit, a signal processing unit 170 and a timing controller 90.

[0027] The light source unit 10 generates probe light and is configured to include a light source 12 that generates continuous light, and an optical pulse generator 14 that generates optical pulses from the continuous light.

[0028] Here, this measuring device measures the phase difference according to the frequency change. For this reason, the frequency fluctuation and frequency spectrum linewidth (hereinafter also simply referred to as linewidth) of the light source 12 must be sufficiently smaller than the Brillouin shift. For this reason, a frequency-stabilized narrow-linewidth light source is used as the light source 12. For example, when the distortion of the optical fiber to be measured (hereinafter also referred to as the measured optical fiber) 100 is 0.008%, the Brillouin shift corresponds to 4 MHz. For this reason, in order to measure a distortion of about 0.008%, the frequency fluctuation and linewidth of the light source 12 are sufficiently smaller than 4 MHz, and it is desirable that they are several tens of kHz or less. Note that narrow-linewidth lasers with frequency fluctuations and linewidths of about 10 kHz or less are generally available as ready-made products.

[0029] The optical pulse generator 14 is configured using any suitable conventionally known acousto-optical (AO) modulator or electro-optical (EO) modulator. The optical pulse generator 14 generates an optical pulse from continuous light in response to an electric pulse generated by a timing controller 90. The repetition period of this optical pulse is set to be longer than the time required for the optical pulse to travel round trip through the measured optical fiber 100. This optical pulse is output from the light source unit 10 as the probe light.

[0030] The probe light output from the light source unit 10 is sent to the optical coupler 200. The optical coupler 200 splits the probe light into two, and sends one to the circulator 20 and the other to the extinction ratio measuring device 210. Any suitable conventional optical coupler can be used as the optical coupler 200. The splitting ratio in the optical coupler 200 can be set to any suitable value.

[0031] The probe light sent to the circulator 20 is incident on the measured optical fiber 100. Instead of the circulator 20, an optical coupler may be used.

[0032] The backscattered light from the optical fiber under test 100 is sent to an optical amplifier 30 constituted by, for example, an erbium-doped optical fiber amplifier (EDFA) via a circulator 20. The backscattered light amplified by the optical amplifier 30 is sent to an optical bandpass filter 32.

[0033] The optical bandpass filter 32 has a transmission band of about 10 GHz and transmits light that contains a component of natural Brillouin scattered light among backscattered light. The optical bandpass filter 32 includes an optical filter using, for example, a fiber Bragg grating (FBG). Optical filters may be provided in multiple stages so that the optical bandpass filter 32 exhibits desired transmission characteristics.

[0034] The light output from the optical bandpass filter 32 is sent to a self-delay heterodyne interferometer 40. The self-delay heterodyne interferometer 40 is configured to include a branching section 42, an optical frequency shifter section 43, a delay section 48, a multiplexing section 50, a coherent detection section 60, and a local electrical signal source 83.

[0035] The local electric signal source 83 has a frequency f AOM The device generates an electrical signal of

[0036] The branching section 42 receives the backward Brillouin scattered light generated in the measured optical fiber 100 by the probe light via the optical bandpass filter 32, and branches it into two, a first optical path and a second optical path.

[0037] In this configuration example, the optical frequency shifter unit 43 is provided in the first optical path. The optical frequency shifter unit 43 shifts the frequency f AOM The electrical signal of frequency f AOM gives a frequency shift of

[0038] In this configuration example, the second optical path is provided with a delay unit 48. The delay unit 48 imparts a delay of time τ to the light propagating through the second optical path.

[0039] The multiplexing section 50 multiplexes the light propagating through the first optical path and the second optical path to generate multiplexed light.

[0040] The coherent detection unit 60 performs heterodyne detection of the combined light to generate a beat signal. The coherent detection unit 60 includes, for example, a balanced photodiode (PD) 62, a FET amplifier 64, and an A / D 66.

[0041] The beat signal I generated by the coherent detection unit 60 12 are sent to a signal processing unit 170. The signal processing unit 170 includes an averaging processing means 172 and a digital signal processing means 180. The signal processing unit 170 can be configured, for example, with an FPGA (Field Programmable Gate Array). The signal processing unit may also be configured to be realized by executing software on a personal computer (PC) or the like, or an FPGA and a PC may be combined.

[0042] The interference signal I generated in the coherent detection unit 60 12 is very weak. Therefore, in order to improve the signal-to-noise ratio (S / N), it is necessary to perform averaging processing in the averaging processing means 172. This averaging processing is desirably performed by an FPGA for high speed.

[0043] The digital signal processing means 180 calculates the BFS using an I (In-Phase) signal and a Q (Quadrature-Phase) signal acquired by balanced detection in the coherent detection unit 60. The following formula (1) can generally be used to calculate the BFS.

[0044]

number

[0045] Here, τ is the delay time provided by the delay unit 48 of the self-delay heterodyne interferometer 40, and φ offset represents the phase offset.offset The BFS in the positive and negative directions is calculated with the frequency set to 0 MHz. After the BFS is calculated, the temperature and strain of the optical fiber are obtained using the temperature conversion coefficient and strain conversion coefficient of the optical fiber.

[0046] The extinction ratio measuring instrument 210 measures the extinction ratio of the probe light. Any suitable conventionally known technology can be used for the extinction ratio measuring instrument 210. Fig. 2 shows a schematic diagram of an optical pulse used in a BOTDR. In Fig. 2, the horizontal axis represents time t, and the vertical axis represents the peak intensity of the optical pulse. Here, the peak intensity of the optical pulse is normalized to 1.

[0047] Here, an ideal rectangular wave is assumed as the optical pulse contained in the probe light. The pulse width ΔT and the repetition period T rep are values ​​that determine the spatial resolution Δz and the fiber length L of the test optical fiber 100 that can be used for measurement, respectively. At this time, the duty ratio of the optical pulse is ΔT / T rep and this duty ratio corresponds to Δz / L.

[0048] Here, if the intensity during the time when the optical pulse is not output is m, the extinction ratio of the optical pulse is calculated as 10 × log(m) [dB].

[0049] Next, consider the case where the BFS distribution in the measured optical fiber 100 is given as shown in FIG. 3. FIG. 3 is a diagram showing the BFS distribution in the measured optical fiber 100. In FIG. 3, in the measured optical fiber 100 having a fiber length L, str ) where z str The BFS in the interval ω B2 , and the BFS in other intervals is ω B1 In this case, the BFS measured by the self-delay type BOTDR is calculated using the following equation (2).

[0050]

number

[0051] Here, v g is the speed of the light pulse propagating through the optical fiber. For simplicity, ω B1 =0, Δz< <z str Assuming this, the above equation (2) can be replaced with the following equations (3) and (4).

[0052]

number

[0053]

number

[0054] From the above equations (3) and (4), it can be seen that the BFS depends on the parameter m relating to the extinction ratio.

[0055] Fig. 4 is a diagram showing the relationship between the BFS measurement value and the extinction ratio of the optical pulse. In Fig. 4, the horizontal axis represents the distance [km] from the input end of the measured optical fiber 100, and the vertical axis represents the BFS [MHz].

[0056] Here, the fiber length L of the optical fiber 100 to be measured is 5 km, the spatial resolution Δz is 1 m, and the BFS change section z str The BFS distribution waveform is calculated when the distance from the entrance end is 10 m (4500 to 4510 m) and the BFS change amount is 100 MHz.

[0057] Fig. 4 shows the BFS true value (100 MHz) (indicated by A in Fig. 4), which is the BFS measurement value when the extinction ratio of the optical pulse is infinite, and the BFS measurement values ​​when the extinction ratio of the optical pulse is 50 dB (indicated by B in Fig. 4), 45 dB (indicated by C in Fig. 4), and 40 dB (indicated by D in Fig. 4). Fig. 4 shows that the error between the BFS measurement value and the BFS true value increases as the extinction ratio deteriorates. Thus, in BFS measurement using a self-delayed BOTDR, the extinction ratio of the optical pulse affects the BFS measurement value.

[0058] Figure 5 shows the extinction ratio and BFS measurement of the optical pulse. meas ) / BFS true value (BFS) normalized to 1. In Fig. 5, the horizontal axis shows the optical pulse extinction ratio [dB], and the vertical axis shows the normalized BFS measurement value / BFS true value (BFS meas / BFS).

[0059] This normalized BFS measurement value / BFS true value (BFS meas / BFS) and the extinction ratio correction factor C ER Then, the BFS measurement (BFS meas ) the BFS true value (BFS) can be calculated using the following equation (5).

[0060]

number

[0061] When the extinction ratio of the probe light generated by the light source unit 10 does not vary with time, the extinction ratio correction coefficient C ER However, when a device in which the bias voltage drifts, such as an LN intensity modulator, is used as the optical pulse generator 14, the extinction ratio changes with time. For this reason, the extinction ratio correction coefficient C ER It is better to update it over time rather than setting it as a fixed value.

[0062] The optical fiber sensor of the present invention includes an extinction ratio measuring device 210. The extinction ratio measuring device 210 measures the extinction ratio of an optical pulse from the probe light split into two by the optical coupler 200, and sends the measured extinction ratio to the signal processing unit 170.

[0063] Moreover, the digital signal processing means 180 of the signal processing unit 170 includes a phase calculation means 182 , a BFS calculation means 184 , an extinction ratio correction means 186 , a temperature / strain conversion means 188 , and a correction coefficient calculation means 190 .

[0064] The phase calculation means 182 obtains information on the phase that changes based on the BFS from the beat signal. The BFS calculation means 184 obtains the BFS from the phase information obtained by the phase calculation means 182. The phase calculation means 182 and the BFS calculation means 184 can be configured in the same manner as any suitable conventionally known self-delayed heterodyne BOTDR. The BFS calculated by the BFS calculation means 184 is sent to the extinction ratio correction means 186 as a BFS measurement value.

[0065] In addition, the correction coefficient calculation means 190 calculates the extinction ratio correction coefficient C based on the information of the extinction ratio measured by the extinction ratio measurement device 210. ER The extinction ratio correction coefficient C calculated by the correction coefficient calculation means 190 is calculated. ER is sent to the extinction ratio correction means 188. The extinction ratio correction coefficient C ER is calculated, for example, using the relationship between the optical pulse extinction ratio and the BFS measured value / BFS true value shown in FIG.

[0066] The extinction ratio correction means 186 calculates the BFS measurement value and the extinction ratio correction coefficient C ER The true BFS value is obtained, for example, from the above formula (5) using the above formula. The true BFS value is sent to a temperature / strain conversion means 188. The temperature / strain conversion means 188 obtains information on temperature and strain from the true BFS value obtained by the extinction ratio correction means 186. The temperature / strain conversion means 188, which obtains information on changes in temperature and strain of the optical fiber from the BFS, can be configured in the same manner as any suitable conventionally known self-delayed heterodyne BOTDR.

[0067] As described above, according to the optical fiber sensor of the present invention, even if the BFS measurement value deviates from the BFS true value due to fluctuations in the extinction ratio of the optical pulse, the extinction ratio of the optical pulse can be measured in real time, and the BFS measurement value can be corrected from this extinction ratio to obtain the BFS true value.

[0068] Here, an example has been described in which the interference signal acquisition unit includes a delayed self-heterodyne interferometer, but the interference signal acquisition unit may be configured to include a delayed self-homodyne interferometer instead of the delayed self-heterodyne interferometer.

[0069] An optical fiber sensor including a delayed self-homodyne interferometer in an interference signal acquisition section will be described with reference to Fig. 6. Fig. 6 is a schematic block diagram of an optical fiber sensor that utilizes delayed self-homodyne interference.

[0070] 1, the optical fiber sensor using delayed self-homodyne interference differs in that it includes a delayed self-homodyne interferometer instead of a delayed self-heterodyne interferometer, that it includes an intensity acquisition unit 51, and that it includes a branching unit 34. The branching unit 34 branches the backward Brillouin scattered light into two, and sends one to the delayed self-homodyne interferometer 41 and the other to the intensity acquisition unit 51.

[0071] The self-delay homodyne interferometer 41 does not have a frequency shifter, unlike the self-delay heterodyne interferometer 41. The self-delay homodyne interferometer 41 generates an interference signal by self-delay homodyne interference and sends it to the signal processing unit 170.

[0072] The intensity acquiring unit 51 also includes a delay unit 57, a PD 63, an amplifier 65, and an A / D 67. The intensity acquiring unit 51 generates an intensity signal including information on the intensity of the back Brillouin scattered light, and sends the intensity signal to the signal processing unit 170.

[0073] The BFS calculation means 184 calculates the Brillouin frequency shift amount from the interference signal and the intensity signal as a BFS measurement value. Note that in an optical fiber sensor equipped with a delayed self-homodyne interferometer, a configuration for acquiring the Brillouin frequency shift amount from the interference signal and the intensity signal is also conventionally known, and therefore a detailed description thereof will be omitted here.

[0074] In an optical fiber sensor using delayed self-homodyne interference, as in the optical fiber sensor using delayed self-heterodyne interference described above, even if the BFS measurement value deviates from the true BFS value due to fluctuations in the extinction ratio of the optical pulse, the extinction ratio of the optical pulse can be measured in real time, and the BFS measurement value can be corrected from this extinction ratio to obtain the true BFS value. [Explanation of symbols]

[0075] 10 Light source section 12 light source 14 Optical Pulse Generator 20 Circulator 30 Optical Amplifier 32 Optical Bandpass Filter 34 Branch 40 Self-delayed heterodyne interferometer 41 Self-delayed homodyne interferometer 42 Branch 43 Frequency Shifter 48, 57 Delay section 50 Combiner 51 Strength acquisition section 60 Coherent detection section 61 Light receiving section 62 Balanced PD 63 PD 64, 65 FET amplifier 66, 67 A / D 90 Timing Controller 100 Optical fiber to be measured 170 Signal Processing Section 172 Averaging Processing Means 180 Digital signal processing means 182 Phase calculation means 184 BFS calculation method 186 Extinction ratio correction means 188 Temperature / Strain Conversion Method 190 Correction coefficient calculation means 200 Optical Coupler 210 Extinction ratio measuring device

Claims

1. a light source unit that generates a probe light that is an optical pulse train; an optical coupler that splits the probe light into two; an interference signal acquisition unit that receives back Brillouin scattered light generated in an optical fiber to be measured by one of the probe lights branched by the optical coupler and generates an interference signal by self-delayed heterodyne interference; an extinction ratio measuring device for measuring the extinction ratio of the other probe light branched into two by the optical coupler; Signal processing means; Equipped with The signal processing means a Brillouin frequency shift (BFS) calculation means for calculating a Brillouin frequency shift (BFS) amount from the interference signal as a BFS measurement value; an extinction ratio correction means for correcting the BFS measurement value based on the extinction ratio measured by the extinction ratio measuring device to obtain a true BFS value; An optical fiber sensor comprising:

2. a light source unit that generates a probe light that is an optical pulse train; an optical coupler that splits the probe light into two; a branching unit for branching back Brillouin scattered light generated in an optical fiber to be measured by one of the probe lights branched by the optical coupler into two; an interference signal acquisition unit that receives one of the scattered lights branched by the branch unit and generates an interference signal by self-delayed homodyne interference; an intensity acquisition unit that receives the other scattered light branched by the branch unit and generates an intensity signal indicating the intensity of the scattered light; an extinction ratio measuring device for measuring the extinction ratio of the other probe light branched into two by the optical coupler; Signal processing means; Equipped with The signal processing means a BFS calculation means for calculating a Brillouin frequency shift amount from the interference signal and the intensity signal as a BFS measurement value; an extinction ratio correction means for correcting the BFS measurement value based on the extinction ratio measured by the extinction ratio measuring device to obtain a true BFS value; An optical fiber sensor comprising:

3. The signal processing means further comprises: a correction coefficient calculation means for calculating an extinction ratio correction coefficient from a relationship between the extinction ratio and a ratio of a BFS measured value to a BFS true value, the relationship being acquired in advance; Equipped with The extinction ratio correction means obtains a true BFS value by dividing the BFS measurement value by an extinction ratio correction coefficient.

3. The optical fiber sensor according to claim 1 or 2.

4. generating a probe light which is a train of optical pulses; splitting the probe light into two beams; a step of inputting back Brillouin scattered light generated in an optical fiber to be measured by one of the two split probe lights and generating an interference signal by self-delayed heterodyne interference; measuring the extinction ratio of the other of the two branched probe lights; calculating a Brillouin frequency shift from the interference signal as a BFS measurement value; correcting the BFS measurement value based on the extinction ratio to obtain a true BFS value; A Brillouin frequency shift measurement method comprising:

5. generating a probe light which is a train of optical pulses; splitting the probe light into two beams; a step of splitting back Brillouin scattered light generated in an optical fiber to be measured into two by one of the split probe lights; a step of inputting one of the two split scattered lights and generating an interference signal by self-delayed homodyne interference; receiving the other of the two branched scattered light beams and generating an intensity signal indicative of the intensity of the scattered light beam; measuring the extinction ratio of the other of the two branched probe lights; calculating a Brillouin frequency shift from the interference signal and the intensity signal as a BFS measurement value; correcting the BFS measurement value based on the extinction ratio to obtain a true BFS value; A Brillouin frequency shift measurement method comprising:

6. moreover, A process of calculating an extinction ratio correction coefficient from a relationship between the extinction ratio and the ratio of the BFS measurement value to the BFS true value, which is previously obtained. Equipped with In the process of obtaining the true BFS value, the measured BFS value is divided by the extinction ratio correction coefficient to obtain the true BFS value.

6. The method for measuring the Brillouin frequency shift according to claim 4 or 5.

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