Optical fiber characteristics analysis device

Abstract

To make it possible to change a position at which Brillouin scattering can be measured using no variable delay line in a Brillouin optical correlation area reflectometer.SOLUTION: In an optical fiber characteristics analysis device that analyzes Brillouin scattering of optical fiber to be measured using a Brillouin optical correlation area reflectometer, signal light incident to the optical fiber to be measured is frequency-modulated by a noise wave having periodicity.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to optical fiber sensing technology that uses an optical fiber as a sensor. [Background technology]

[0002] The mainstream method for achieving position resolution in optical fiber sensing is OTDR (Optical Time Domain Reflectometry). With this method, an optical pulse is input and the return time of the backscattered light is analyzed, making it possible to determine the position at which the scattered light returned. In addition, by analyzing the Brillouin scattering of the returned scattered light, the temperature and strain of the optical fiber can be measured (see, for example, Non-Patent Documents 1 and 2).

[0003] On the other hand, in order to achieve high spatial resolution with OTDR, the optical pulse width needs to be narrowed, which generally reduces the energy available for measurement. To solve this problem, low-coherence Brillouin optical correlation-domain reflectometry has been proposed (see, for example, Non-Patent Document 3).

[0004] In this method, noise modulation is added to continuous light, one of which is used as the reference light and the other as the signal light, to measure the Brillouin scattering in the optical fiber under test. At this time, the noise pattern matches only at the equi-path points of the reference light and the scattered light returning from the optical fiber under test. In other words, the interference intensity corresponds to the scattered light at the equi-path points, so position resolution is possible. In addition, by providing a variable delay mechanism in the reference light path, the equi-path points can be changed, making it possible to perform distributed measurement. However, since the variable delay line can generally only be changed by about 1 to 10 m, there was a problem that the range of positions where Brillouin scattering can be measured is limited by the range of the variable delay line. It is possible to use a long variable delay line, but this is not practical because the device configuration becomes large and the cost increases as the variable range is expanded. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] K. Hotate, et. al., “Measurement of Brillouin Gain Spectrum Distribution along an Optical Fiber Using a Correlation-Based Technique-Proposal, Experiment and Simulation-”, IEICE Trans. Electron. E83-C, p.405-412 (2000). [Non-Patent Document 2] Y. Mizuno, et. al., “Proposal of Brillouin optical correlation-domain reflectometry (BOCDR)”, Opt. Express 16, p.12148-12153 (2008) [Non-Patent Document 3] Otsubo et al., "Proposal of a low-coherence Brillouin optical correlation domain reflectometer," 69th Spring Meeting of the Japan Society of Applied Physics, 22p-D215-4, 2022. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present disclosure is to make it possible to change the position at which Brillouin scattering can be measured in a Brillouin optical correlation domain reflectometer without using a variable delay line. [Means for solving the problem]

[0007] The present disclosure relates to an optical fiber characteristic analyzer that uses a Brillouin optical correlation domain reflectometer to analyze Brillouin scattering in an optical fiber under test, and in which signal light that has been frequency modulated with a periodic noise wave is input to the optical fiber under test.

[0008] The optical fiber characteristic analysis device executes an optical fiber characteristic analysis method. Specifically, the optical fiber characteristic analysis device splits the signal light into two, inputs one of the split signal lights into one end of the measured optical fiber, combines the other of the split signal lights with Brillouin scattered light emitted from the one end of the measured optical fiber, and detects the combined interference light.

[0009] The present disclosure can change the position of the correlation peak by changing the period of the noise wave that frequency-modulates the signal light, thereby making it possible to change the position at which Brillouin scattering can be measured in a Brillouin optical correlation domain reflectometer without using a variable delay line.

[0010] The optical fiber characteristic analysis device comprises: A light source that outputs continuous light; an optical frequency modulation means for frequency-modulating the continuous light with a noise wave having periodicity; a first optical branching means for branching the signal light generated by frequency-modulating the continuous light into two; a second optical branching means for inputting one of the two branched signal lights into one end of the test optical fiber and outputting the Brillouin scattered light output from the one end of the test optical fiber to an optical detection means; an optical detection means for detecting interference light between the other of the two branched signal lights and the Brillouin scattered light output from the second optical branch means; a signal analysis means for analyzing the interference light detected by the optical detection means; Equipped with.

[0011] The repetition frequency of the noise wave is set to a value such that the interval between the correlation peaks of the Brillouin scattered light generated in the measured optical fiber by one of the signal lights branched into two by the first optical branching means and the other of the signal lights branched into two by the first optical branching means is longer than the fiber length of the measured optical fiber.

[0012] The optical fiber characteristic analysis device may sweep the measurement position in the longitudinal direction of the optical fiber under test by changing the repetition frequency of the noise wave.

[0013] The above disclosures may be combined to the greatest extent possible. Effect of the Invention

[0014] According to the present disclosure, in a Brillouin optical correlation domain reflectometer, it is possible to change the position at which Brillouin scattering can be measured without using a variable delay line. [Brief description of the drawings]

[0015] [Figure 1] 1 shows an example of the configuration of an optical fiber characteristic analysis device according to the present disclosure. [Diagram 2] FIG. 1 is an explanatory diagram of Brillouin scattering. [Diagram 3] This is an example of a periodic noise wave. [Figure 4] This is an example of the distance dm between correlation peaks caused by a noise wave with a repetition frequency fm. [Diagram 5] An example of the Brillouin measurement result is shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings are assumed to indicate the same components.

[0017] An example of the configuration of an optical fiber characteristic analyzer according to the present disclosure is shown in Fig. 1. The optical fiber characteristic analyzer 91 is a device that analyzes Brillouin scattering in a measured optical fiber 92 using a Brillouin optical correlation domain reflectometer, and includes, for example, a light source 11, a first optical branching means 12, a second optical branching means 13, an optical detection means 14, a signal analysis means 15, and an optical frequency modulation means 16. An optical circulator can be used as the second optical branching means 13.

[0018] The light source 11 generates continuous light, and the optical frequency modulation means 16 frequency-modulates the continuous light. As a result, frequency-modulated light is output from the light source 11. The light output from the light source 11 is branched into two. One of the two branches is input as signal light from the second optical branching means 13 to the measured optical fiber 92. As a result, the signal light is scattered and reflected in the measured optical fiber 92. The scattered and reflected backscattered light includes Brillouin scattered light.

[0019] The backscattered light in the measured optical fiber 92 is incident on the optical detection means 14 from the second optical branching means 13. Meanwhile, the other of the two branches is incident on the optical detection means 14 as reference light. The optical detection means 14 detects interference light between the backscattered light and the reference light. The signal analysis means 15 uses the interference light detected by the optical detection means 14 to analyze the Brillouin scattering in the measured optical fiber 92.

[0020] Brillouin scattering is a phenomenon in which incident light undergoes a frequency shift and is scattered by acoustic phonons. When Brillouin scattering occurs in a signal light with a frequency of f0, the frequency of the Brillouin scattered light becomes f0-f B The Brillouin frequency shift f B is the refractive index n of the optical fiber 92 to be measured, and the sound velocity v A Using the wavelength λ0 of the signal light propagating through the optical fiber 92 to be measured, it is expressed by the following equation. (Number 1) f B =2nν A / λ0(1)

[0021] The signal analysis means 15 analyzes the frequency f0-fB and the Brillouin frequency shift f based on the reference light frequency f0 B For example, the signal analysis means 15 calculates the signal intensity at a measurement point P E (Iso-optical path point) is detected and measurement point P E Brillouin frequency shift f B The Brillouin frequency shift f at each point in the longitudinal direction of the test optical fiber 92 is calculated. B By observing these, it is possible to measure the distribution of the temperature change ΔT and the strain ε in the longitudinal direction of the optical fiber 92 to be measured.

[0022] In Non-Patent Document 3, signal light is generated by frequency modulating the continuous light generated by the light source 11 with a continuous noise wave. Any method capable of generating pseudo-noise can be adopted for modulation into a noise wave, and for example, it can be performed by modulating the continuous light using optical frequency modulation means 16 so that the optical band is 1 GHz or more. When signal light frequency-modulated with a noise wave is used, the side lobes of the spectrum of the light detected by the optical detection means 14 are reduced, so that highly accurate Brillouin spectrum analysis can be performed in the signal analysis means 15. However, in Non-Patent Document 3, as shown in FIG. 2, at measurement point P E was only one point determined by the optical path length of the reference light.

[0023] Measurement point P E can be detected using the optical correlation domain method. The position of the correlation peak obtained using the optical correlation domain method represents the position where the reference light and the scattered light interfere most, and the amplitude of the correlation peak represents the interference intensity. When attempting to detect interference light using the optical correlation domain method, the inventors have found that by imparting periodicity to the noise wave, the interval d at which the correlation peaks of the signal light and the reference light are equal can be obtained. m For example, when the noise wave to be frequency-modulated in the optical frequency modulation means 16 has a periodicity as shown in FIG. 3, the correlation peaks are generated at equal intervals d as shown in FIG. m occurs in.

[0024] Therefore, the optical fiber characteristic analysis device 91 executes the optical fiber characteristic analysis method of the present disclosure. Specifically, the optical fiber characteristic analysis device 91 inputs a signal light, frequency-modulated by a noise wave having periodicity, into the optical fiber 92 to be measured. In this embodiment, the optical frequency modulation means 16 modulates the continuous light generated by the light source 11 with a repetition frequency f m In this example, the first optical branching means 12 branches the signal light into two, one of the two branched signal lights is incident on one end of the test optical fiber 92, and the other of the two branched signal lights is multiplexed with the Brillouin scattered light emitted from the one end of the test optical fiber 92. The optical detection means 14 detects the interference light after the multiplexing.

[0025] The optical fiber characteristic analysis device 91 of the present disclosure includes: A light source 11 that outputs continuous light; an optical frequency modulation means for frequency-modulating the continuous light with a periodic noise wave; a first optical branching means for branching the signal light generated by frequency-modulating the continuous light into two; a second optical branching means for inputting one of the two branched signal lights into one end of the test optical fiber and outputting the Brillouin scattered light output from the one end of the test optical fiber to an optical detection means; an optical detection means for detecting an interference light between the other of the two branched signal lights and the Brillouin scattered light output from the second optical branch means; a signal analysis means for analyzing the interference light detected by the optical detection means; Equipped with.

[0026] Here, the repetition frequency of the noise wave is f m Depending on the interval d m The distance between the correlation peaks d also changes. m is expressed by the following equation. (Number 2) d m =c / 2nf m (2) Here, c is the speed of light in a vacuum, and n is the refractive index of the optical fiber 92 to be measured.

[0027] The signal analysis means 15 calculates the correlation peak interval d by using the formula (2). m is longer than the fiber length of the optical fiber 92 to be measured. m Calculate the variable range of the repetition frequency f m By setting an arbitrary value in this variable range to the optical frequency modulation means 16, m The interval d is determined by m Measurement point P E can be controlled.

[0028] In the present disclosure, the optical frequency modulation means 16 modulates the noise wave with a repetition frequency f m For example, the optical frequency modulation means 16 may change the repetition frequency f m In the variable range of f m This allows the interval d m Since is swept, the measurement position in the longitudinal direction of the test optical fiber 92 can be swept.

[0029] In addition, the spatial resolution can be changed by changing the voltage amplitude of the noise wave, so the signal analyzing means 15 may control the voltage amplitude of the noise wave of the optical frequency modulating means 16 in accordance with the spatial resolution.

[0030] 5 shows an example of the Brillouin measurement result. The horizontal axis indicates the position in the longitudinal direction of the optical fiber 92 under test, and the vertical axis indicates the Brillouin frequency shift f B The optical frequency modulation means 16 is used to modulate the noise wave repetition frequency f m By changing the interval d m By changing the distance, distortion detection was performed in the section from 0 m to 15 m and in the section from 12 m to 15 m, which is about 3 m, in the signal analysis means 15. As a result, distortion detection with spatial resolution was successful in both sections.

[0031] By using BOCDR, the optical fiber characteristic analysis device 91 of the present disclosure can realize analysis of the characteristics of the measured optical fiber 92 with high spatial resolution. Therefore, the optical fiber characteristic analysis device 91 of the present disclosure can measure the temperature and strain in the longitudinal direction of the measured optical fiber 92 with high spatial resolution.

[0032] Here, the optical fiber characteristic analysis device 91 of the present disclosure uses a repetition frequency f m The optical signal is frequency-modulated with pseudo noise having a periodicity of f = 1 / f, and one of the signals is input to one end of the optical fiber 92 under test, and the other is multiplexed with the Brillouin scattered light output from the one end of the optical fiber 92 under test. The interference light after multiplexing is detected, and the repetition frequency f m By varying the delay line, the measurement position in the longitudinal direction of the measured optical fiber 92 is swept. Therefore, the optical fiber characteristic analyzer 91 of the present disclosure can sweep the measurement position without using a variable delay line, and can perform distribution measurement with high spatial resolution.

[0033] The signal analysis means 15 included in the optical fiber characteristic analysis device 91 of the present disclosure can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network. [Explanation of symbols]

[0034] 11:Light source 12: First optical branching means 13: second optical branching means 14: Light detection means 15: Signal analysis means 16: Optical frequency modulation means 91: Optical fiber characteristic analyzer 92: Optical fiber under test

Claims

1. An optical fiber characteristic analyzer for analyzing Brillouin scattering of an optical fiber under test using a Brillouin optical correlation domain reflectometer, comprising: A signal light frequency-modulated by a periodic noise wave is input to the optical fiber to be measured. Optical fiber characteristic analysis device.

2. Sweeping the measurement position in the longitudinal direction of the optical fiber to be measured by changing the repetition frequency of the noise wave.

2. The optical fiber characteristic analyzer according to claim 1.

3. a first optical branching means for branching the signal light into two, a repetition frequency of the noise wave is set to a value such that an interval between correlation peaks between Brillouin scattered light generated in the measured optical fiber by one of the signal lights branched into two by the first optical branching means and the other of the signal lights branched into two by the first optical branching means is longer than a fiber length of the measured optical fiber.

2. The optical fiber characteristic analyzer according to claim 1.

4. A light source that outputs continuous light; an optical frequency modulation means for frequency-modulating the continuous light with a noise wave having periodicity; a first optical branching unit for branching the signal light generated by frequency-modulating the continuous light into two; a second optical branching means for inputting one of the two branched signal lights into one end of the test optical fiber and outputting the Brillouin scattered light output from the one end of the test optical fiber to an optical detection means; an optical detection means for detecting an interference light between the other of the two branched signal lights and the Brillouin scattered light output from the second optical branch means; a signal analysis means for analyzing the interference light detected by the optical detection means; The optical fiber characteristic analyzer according to claim 1 ,

5. An optical fiber characteristic analysis method executed by an optical fiber characteristic analysis device that analyzes Brillouin scattering of a test optical fiber using a Brillouin optical correlation domain reflectometer, comprising: A signal light frequency-modulated by a periodic noise wave is input to the optical fiber to be measured. Optical fiber characterization methods.

6. The signal light is split into two, One of the two branched signal lights is input to one end of the optical fiber to be measured; the other of the two branched signal lights is multiplexed with the Brillouin scattered light emitted from the one end of the test optical fiber; Detect the interference light after combining. The optical fiber characteristic analysis method according to claim 5 .

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