Search

JP-7855962-B2 - Optical fiber sensor and optical fiber sensing method

JP7855962B2JP 7855962 B2JP7855962 B2JP 7855962B2JP-7855962-B2

Inventors

  • 山城 直毅

Assignees

  • 沖電気工業株式会社

Dates

Publication Date
20260511
Application Date
20220728

Claims (8)

  1. A light source unit that generates light pulses as probe light, A light receiving unit that coherently detects the signal light, including the backscattered light generated in the optical fiber by the probe light, to generate a beat signal, The system comprises a calculation unit to which the beat signal is input, The aforementioned arithmetic unit, For each of the aforementioned optical pulses, an optical information acquisition means obtains from the beat signal the distribution of the signal light intensity I(x) and phase P(x) with respect to the distance x from the incident end of the optical fiber of the signal light, A position search range acquisition means that acquires a search range L S (x) for each position of the optical fiber with respect to the gauge length x GL from the distribution of the signal light intensity I (x), Accuracy degradation avoidance means for determining two points used to calculate the phase difference ΔP(x) at a distance x from the incident end of the optical fiber of the signal light, based on the gauge length x GL and the search range L S (x), An optical fiber sensor characterized by comprising a vibration information demodulation means for acquiring the phase difference ΔP(x) between two determined points and demodulating vibration information from the phase difference ΔP(x).
  2. Each of the aforementioned location search range acquisition means is: The optical fiber sensor according to claim 1, characterized in that it acquires, for each position of the optical fiber, the smallest search range in which the expected value of the number of intervals in which the phase error given by the signal component and noise component of the backscattered light is greater than or equal to a predetermined maximum phase error is less than 1.
  3. Each of the aforementioned location search range acquisition means is: The optical fiber sensor according to claim 1, characterized in that it acquires a search range that is shorter on the input end side of the optical fiber and longer on the termination side.
  4. The optical fiber sensor according to any one of claims 1 to 3, characterized in that, for each position x of the optical fiber, the input end position is determined as two points used to calculate the phase difference ΔP(x) when s is changed toward the input end from x-x GL to x-x GL -L S (x) and s is changed toward the terminal end from x+x GL to x+x GL +L S (x) for each position x of the optical fiber, the terminal position is determined as two points used to calculate the phase difference ΔP(x).
  5. The process of generating optical pulses as probe light, The process involves coherently detecting the signal light, which includes backscattered light generated in the optical fiber by the probe light, to generate a beat signal. For each of the aforementioned optical pulses, the process of obtaining the distribution of the signal light intensity I(x) and phase P(x) with respect to the distance x from the incident end of the optical fiber of the signal light from the beat signal, The process of obtaining the search range L S (x) for each position of the optical fiber with respect to the gauge length x GL from the distribution of the signal light intensity I (x), A process of determining two points for calculating the phase difference ΔP(x) at a distance x from the incident end of the optical fiber of the signal light, based on the gauge length x GL and the search range L S (x), An optical fiber sensing method characterized by comprising the steps of acquiring a phase difference ΔP(x) between two determined points and demodulating vibration information from the phase difference ΔP(x).
  6. In the process of obtaining the aforementioned search range L S (x), The optical fiber sensing method according to claim 5, characterized in that, for each position of the optical fiber, the minimum search range is obtained such that the expected value of the number of intervals in which the phase error given by the signal component and noise component of the backscattered light is greater than or equal to a predetermined maximum phase error is less than 1.
  7. In the process of obtaining the aforementioned search range L S (x), The optical fiber sensing method according to claim 5, characterized in that the search range obtained is shorter on the input end side of the optical fiber and longer on the termination side.
  8. In determining the two points for calculating the phase difference ΔP(x), The optical fiber sensing method according to any one of claims 5 to 7 , characterized in that, for each position x of the optical fiber, the incident end position where the minimum value of scattered light intensity for multiple light pulses is maximized when s is varied toward the incident end from x-x GL to x-x GL -L S (x), and the termination position where the minimum value of scattered light intensity for multiple light pulses is maximized when s is varied toward the termination side from x+x GL to x+x GL +L S (x), are determined as two points used to calculate the phase difference ΔP (x).

Description

This invention relates to an optical fiber sensor and an optical fiber sensing method. With the development of optical fiber communication, technologies that use optical fibers themselves as sensing media are being actively researched. In particular, optical fiber sensing, which utilizes scattered light, enables long-range distributed sensing, unlike electrical sensors that measure at specific points. Phase-sensitive time-domain reflectivity (φ-OTDR), known as a distributed optical fiber sensor utilizing Rayleigh scattered light, has attracted attention in a wide range of fields due to its broad measurement range and high measurement sensitivity (see, for example, Non-Patent Documents 1 or 2). However, in φ-OTDR, the Rayleigh scattered light intensity behaves randomly depending on the position on the optical fiber, and therefore the phase measurement accuracy also behaves randomly depending on the position (see, for example, Non-Patent Document 3). In particular, fading occurs at positions where the scattered light intensity is weak, resulting in distortion of the measured waveform (see, for example, Non-Patent Document 4). To address this problem, methods such as frequency multiplexing of probe light (see, for example, Non-Patent Document 5) and modulation of the optical phase of probe light (see, for example, Non-Patent Document 6) are known. Furthermore, in recent years, methods for suppressing the effects of fading solely through signal processing have been proposed, including methods using frequency domain analysis of fading (see, for example, Non-Patent Document 7), methods using nearest neighbor analysis (see, for example, Non-Patent Document 8), and methods using training data (see, for example, Non-Patent Document 9). Furthermore, the inventors of this application propose an adaptive gauge length method in which the optical phase at a certain position is substituted with the optical phase at the position with the highest intensity in its vicinity (see, for example, Patent Document 1 or 2, or Non-Patent Document 10). Japanese Patent Publication No. 2020-159915Japanese Patent Publication No. 2021-103107 Yuelan Lu, Tao Zhu, Liang Chen, and Xiaoyi Bao, "Distributed Vibration Sensor Based on Coherent Detection of Phase-OTDR," J. Lightwave Technol. 28, 3243-3249 (2010).Z. Pan, K. Liang, Q. Ye, H. Cai, R. Qu, and Z. Fang, "Phase-sensitive OTDR system based on digital coherent detection," in Optical Sensors and Biophotonics, J. Popp, D. Matthews, J. Tian, and C. Yang, eds., Vol. 8311 of Proceedings of SPIE (Optica Publishing Group, 2011), paper 83110S.A. K. Wojcik, “Signal statistics of phase dependent optical time domain reflectometry,” Ph.D. dissertation, Dept. Electr. Eng. Comput. Sci., Texas A&M University, College Station, TX, USA 2006. Available: <http://hdl.handle.net/1969.1/4873>.Healey, P, “Fading in heterodyne OTDR”, Electronics Letters 20(1), 30-32(1984).Y. Lu, X. Zhang, C. Liang, M. Chen, J. Wang, and Z. Meng, “Fading noise reduction in distributed vibration measurements utilizing multi-wavelength based on φ-OTDR”, in 26th International Conference on Optical Fiber Sensors, OSA Technical Digest(Optical Society of America, 2018), paper TuE21.X. Wang et al., "Interference-Fading-Free φ-OTDR Based on Differential Phase Shift Pulsing Technology," in IEEE Photonics Technology Letters, vol. 31, no. 1, pp. 39-42, 1 Jan.1, 2019.Yue Wu, Zinan Wang, Ji Xiong, Jialin Jiang, Shengtao Lin, and Yongxiang Chen, "Interference Fading Elimination With Single Rectangular Pulse in YO-OTDR," J. Lightwave Technol. 37, 3381-3387 (2019)Guojie Tu, Mengmeng Zhao, Zheng Tang, Kai Qian, and Benli Yu, "Fading Noise Suppression in φ-OTDR Based on Nearest Neighbor Analysis," J. Lightwave Technol. 38, 6691-6698 (2020).Fei Jiang, Zhenhai Zhang, Zixiao Lu, Honglang Li, Yahui Tian, Yixin Zhang, and Xuping Zhang, "High-fidelity acoustic signal enhancement for phase-OTDR using supervised learning," Opt. Express 29, 33467-33480 (2021)N. Yamashiro, Y. Kanda, H. Murai, and H. Sasaki, "Adaptive Gauge Length Method to Avoid Fading Effect for Phase-sensitive OTDR," in Optical Fiber Sensors Conference 2020 Special Edition, G. Cranch, A. Wang, M. Digonnet, and P. Dragic, eds., OSA Technical Digest (Optical Society of America, 2020), paper T2A.2. This is a schematic diagram illustrating the basic principles of fading suppression.This is a schematic diagram illustrating the optical fiber sensor of this invention.Figure (1) illustrates the operation of the optical fiber sensor of this invention.Figure (2) illustrates the operation of the optical fiber sensor of this invention.Figure (3) illustrates the operation of the optical fiber sensor of this invention. The embodiments of this invention will be described below with reference to the figures, but these are merely schematic representations to the extent that the invention can be understood. Furthermore, preferred configurations of this invention will be described below, but these are merely