Analysis device and optical fiber sensing method

Abstract

The purpose of the present invention is to provide an analysis device and optical fiber sensing method for an optical fiber sensing device capable of suppressing the effects of displacement due to vibration under a small processing load without causing the deterioration of spatial resolution.　An analysis circuit 12 according to the present invention: measures the spectral shift Δν(xi, t) for each section #i of an optical fiber 13 by using a measuring device 11 (steps S01, S02, Si1, Si2); calculates, from the spectral shift, the optical frequency modulation amount f(xi, t) for each of the sections; calculates the cumulative value foffset(t) by accumulating the optical frequency modulation amounts of the sections located closer to a proximal end-side than the analysis position of the optical fiber 13 (step S03, step Si3); and corrects the analysis position xi on the basis of the cumulative value (step Sa1).

Description

[Technical Field]

[0001] The present disclosure relates to an analysis device for an optical fiber sensing device using OFDR (Optical Frequency Domain Reflectometry) and a sensing method thereof. [Background technology]

[0002] Fig. 1 is a diagram explaining the sensing principle using OFDR. OFDR uses frequency-swept light as the probe light. Then, the spectrum S(ν) (Fig. 1(B)) can be analyzed by Fourier transforming the waveform r(τ) (Fig. 1(A)) of the Rayleigh backscattered light corresponding to the probe light in the optical fiber (see, for example, Non-Patent Document 1).

[0003] The spectrum S(ν) of the backscattered light varies with the strain and temperature of the optical fiber (spectral shift). ref By detecting how much the optical fiber has moved at each measurement (spectral shift Δν), the amount of change in strain and temperature of the optical fiber can be calculated using the following equations.

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[0004] [Non-Patent Document 1] M. Froggatt and J. Moore, “High-spatial-resolution distributed strain measurement in optical fiber with Rayleigh scatter,” Appl. Opt., vol. 37, no. 10, pp. 1735-1740, 1998. [Non-patent document 2] Okamoto, Tatsuya, Daisuke Iida, and Hiroyuki Oshida. “Vibration-induced beat frequency offset compensation in distributed acoustic sensing based on optical frequency domain reflectometry”. Journal of Lightwave Technology 37.18 (2019): 4896-4901. [Non-patent document 3] Okamoto, Tatsuya, Daisuke Iida, and Hiroyuki Oshida. “Investigation of tolerance of OFDR-based DAS to vibration-induced beat frequency offset”., 2020 Optical Fiber Communications Conference and Exhibition (OFC). IEEE, 2020. Summary of the Invention [Problem to be solved by the invention]

[0005] Optical fiber sensing devices using OFDR have a fundamental problem in that optical frequency modulation caused by vibrations in front of the analysis position to be analyzed changes the distance to the analysis position, making it difficult to obtain a consistent optical spectrum and perform accurate vibration analysis.

[0006] Figure 2 illustrates the basic problem. Figure 2(A) shows the waveform r(τ) of Rayleigh backscattered light in response to a probe light beam from an optical fiber. Optical fibers typically vibrate. Therefore, the position of the waveform r(τ) to be analyzed fluctuates over time due to vibrations (frequency offset 21) of the optical fiber before the analysis position (the time interval from τ1 to τ2) (toward the probe light input end). This causes waveforms r(τ) that are not the subject of analysis to be included in the time interval from τ1 to τ2. In other words, because the waveform r(τ) to be analyzed changes over time, the optical spectral structure of the spectrum S(ν), which is the Fourier transform of the waveform r(τ), also changes, making it difficult to calculate the amount of spectral shift (amount of distortion) (Figure 2(B)).

[0007] To address this fundamental issue, Non-Patent Document 2 discloses a method for mitigating the effects of positional deviation due to an increase in the analysis length. This method utilizes the fact that if the sensor length (the section from time τ1 to τ2) is long enough relative to the frequency offset 21, positional deviation can be suppressed (the sensor has resistance to vibration). However, this method presents a new problem: if the analysis length is increased, the spatial resolution of strain analysis deteriorates.

[0008] Furthermore, to address this fundamental issue, Non-Patent Document 3 discloses a method for correcting positional deviations using signal processing. This method involves signal processing that estimates the distance offset using the cross-correlation of the loss distribution waveforms of the vibration sensors and tracks the position of the vibration sensor to be analyzed. However, this method presents a new issue in that the signal load due to the cross-correlation is large.

[0009] Therefore, in order to solve the above-mentioned problems, the present invention aims to provide an analysis device for an optical fiber sensing device and an optical fiber sensing method that can suppress the effects of positional deviation due to vibration with a small processing load without degrading spatial resolution. [Means for solving the problem]

[0010] In order to achieve the above object, the optical fiber sensing device and method of the present invention calculate the amount of optical frequency modulation of each section of the optical fiber from the spectral shift of that section, and correct the positional deviation of the analysis position using the cumulative value of the optical frequency modulation of each section located before the analysis position.

[0011] Specifically, the analysis device for an optical fiber sensing device according to the present invention is an analysis device provided in an optical fiber sensing device using OFDR, calculating an amount of optical frequency modulation for each section of the optical fiber from the spectral shift measured for each section; accumulating the optical frequency modulation amounts of the sections located closer to the analysis position of the optical fiber to calculate an accumulated value; and correcting the analysis position based on the cumulative value; Do the following.

[0012] Further, an optical fiber sensing method according to the present invention is an optical fiber sensing method using OFDR, measuring the spectral shift for each section of optical fiber; calculating an amount of optical frequency modulation for each of the sections from the spectral shift; accumulating the optical frequency modulation amounts of the sections located closer to the analysis position of the optical fiber to calculate an accumulated value; and Correcting the analysis position based on the cumulative value. It is characterized by:

[0013] In the optical fiber sensing device, the cumulative amount of strain in each section is the amount of expansion and contraction of the optical fiber due to vibration, the optical fiber is divided into multiple sections to measure the amount of optical frequency modulation, and the positional deviation of the analysis position is corrected using the cumulative value of the amount of optical frequency modulation in each section located before the analysis position. Therefore, the present invention can provide an analysis device for an optical fiber sensing device and an optical fiber sensing method that can suppress the effects of positional deviation due to vibration with a small processing load without degrading spatial resolution.

[0014] Calculating the cumulative value may be accumulating the amount of optical frequency modulation from the section at the near end to the section immediately before the analysis position, or accumulating the amount of optical frequency modulation from any of the sections to the section immediately before the analysis position.

[0015] The present invention is a program for causing a computer to function as the analysis device.

[0016] The analysis device 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.

[0017] The above inventions can be combined as much as possible. [Effects of the Invention]

[0018] The present invention can provide an analyzer for an optical fiber sensing device and an optical fiber sensing method that can suppress the influence of positional deviation due to vibration with a small processing load without degrading spatial resolution. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram illustrating the sensing principle using OFDR. [Figure 2] FIG. 1 is a diagram illustrating a problem to be solved by the present invention. [Figure 3] 1 is a diagram illustrating an optical fiber sensing device according to the present invention. [Figure 4] 1A to 1C are diagrams illustrating an optical fiber sensing method according to the present invention. [Figure 5] 1A to 1C are diagrams illustrating the principle of an optical fiber sensing method according to the present invention. [Figure 6] 1A to 1C are diagrams illustrating the effects of the optical fiber sensing method according to the present invention. [Figure 7]1 is a diagram illustrating an optical fiber sensing device according to the present invention. [Figure 8] 1A to 1C are diagrams illustrating the effects of the optical fiber sensing method according to the present invention. [Figure 9] 1 is a diagram illustrating an optical fiber sensing device according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] The following description of the preferred embodiments of the present invention will be given with reference to the accompanying drawings. The preferred embodiments described below are examples of the present invention, and the present invention is not limited to the preferred embodiments. In this specification and the drawings, components having the same reference numerals are intended to represent the same components.

[0021] (Embodiment 1) 3 is a diagram illustrating an optical fiber sensing device 301 of this embodiment. The optical fiber sensing device 301 is a sensing system including a measurement device 11 and an analysis device 12. The measurement device 11 is an OFDR that inputs probe light whose frequency has been swept once into an optical fiber 13 and acquires the spectrum of Rayleigh backscattered light in the optical fiber 13. In this specification, of the two ends of the optical fiber 13, the end connected to the measuring device 11 may be referred to as the "near end" and the other end as the "far end."

[0022] The analysis device 12 obtains the spectral shift Δν from the time variation of the spectrum obtained by the measurement device 11. Then, the analysis device 12 divides the optical fiber 13 into a plurality of sections #i ("i" is the section number and is an integer from 0 to N) in the longitudinal direction, and calculates the spectral shift Δν(x i , t) to obtain the optical frequency modulation amount f(x i , t), and the cumulative value f of the optical frequency modulation amount of each section located before the analysis position is calculated. offset (t) is used to correct the positional deviation of the analysis position. The correction of the positional deviation of the analysis position performed by the analysis device 12 will be described in detail below.

[0023] FIG. 4 is a diagram illustrating the optical fiber sensing method performed by the analysis device 12. In FIG. The analysis device 12 Using the measuring device 11, the spectral shift Δν(x i , t) (steps S01, S02, Si1, Si2), The optical frequency modulation amount f(x i ,t), The optical frequency modulation amounts of the sections located closer to the analysis position of the optical fiber 13 are accumulated to obtain an accumulated value f offset Calculating (t) (step S03, step Si3), and The analysis position x based on the accumulated value i Correction of (Step Sa1) Do the following.

[0024] FIG. 5 is an image diagram for explaining the correction of the positional deviation of the analysis position in this optical fiber sensing method. The optical fiber 13 is divided into a plurality of sections #i (i is an integer from 0 to N) for consideration. x i is the length of section #i, t is the time, ε(x i , t) is the strain amount of the optical fiber 13 in section #i. i is set to be longer than the spatial resolution L of the strain that the measuring device 11 can detect.

[0025] This optical fiber sensing method calculates the strain amount ε(x i , t) to obtain the optical frequency modulation amount f(x i , t), and utilizes the fact that the amount of optical frequency modulation of the probe light propagating from the near end to section #i is given by the accumulation of the amount of optical frequency modulation from section #0 to #i. Note that this optical fiber sensing method calculates the amount of distortion ε by the spectral shift Δν(x i ,t).

[0026] [Step S01] The analysis device 12 acquires a spectrogram S(x0, t, v) from the light returning from section #0 (position at a distance x0 from the near end) among the backscattered light acquired by the measurement device 11, where v is the optical frequency. [Step S02] Then, the analysis device 12 analyzes the spectral shift Δν(x0,t) from the spectrogram S(x0,t,ν). Note that the method for analyzing the spectral shift Δν from the spectrogram S may be the method disclosed in Non-Patent Document 1. [Step S03] The analysis device 12 calculates the amount of optical frequency modulation f(x0, t) from Δν(x0, t) using the following equation: The relationship between the amount of distortion ε and the amount of phase change θ will be explained in Appendix A.

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[0027] After step Si3, in step Sc2, the section number is counted up by one, and the process returns to step Sa1. The vibration analysis position (distance x i-1 ) is corrected by equation (3).

[0028] [Example] Figure 7 is a diagram illustrating the experimental system. Optical fiber 13 was divided into two sections: optical fiber 13a at the near end and optical fiber 13b at the far end. Optical fiber 13a was 60 m long, and optical fiber 13b was 160 m long. A 30 Hz sinusoidal vibration was applied only to optical fiber 13a. The spatial resolution L of the measuring device 11 is 66 cm. Fig. 8 is a diagram illustrating the effects of the present invention. Fig. 8(A) shows the results of distortion measurement in the experimental system of Fig. 7, where no misalignment correction was performed by the analyzer 12 (Comparative Example). Fig. 8(B) shows the results of distortion measurement in the experimental system of Fig. 7, where misalignment correction was performed by the analyzer 12 (Example). In the comparative example, the strain ε can be measured correctly up to a distance of approximately 0 to 30 m, but measurement errors occur after that. This means the following: The spatial resolution of the measuring device 11 is strong enough to withstand the amount of accumulated frequency modulation when the probe light propagates up to a distance of approximately 0 to 30 m, but is insufficient to withstand the amount of accumulated frequency modulation at distances beyond that. Measurement errors occur frequently, particularly around the time when the positional deviation is at its maximum or the time when the sinusoidal distortion becomes zero. On the other hand, in the embodiment, the positional deviation is corrected in both the section of the optical fiber 13a and the section of the optical fiber 13b to which vibration is not applied, and the strain ε is measured correctly. (supplement) As shown in equation (A3), the strain ε causes a phase shift θ in the probe light. The time derivative of the phase shift θ is the optical frequency modulation amount f. In this experiment, a sinusoidal distortion was applied, so the optical frequency modulation amount (positional deviation amount) reaches its maximum when the distortion becomes zero (the time derivative of the sine wave reaches its maximum when it passes through the zero point). The experimental results certainly show this, with measurement errors occurring near the time when the distortion becomes zero. The amount of optical frequency modulation f due to the strain ε accumulates as the probe light propagates. Therefore, the strain ε can be measured correctly up to a distance of approximately 0 to 30 m, but beyond that, the accumulated value of the amount of optical frequency modulation exceeds the spatial resolution of the measurement device 11, causing measurement errors. (End of supplement)

[0029] [effect] As explained in Figure 8, the optical fiber sensing method of the present invention requires less signal processing load (differentiation and addition) than conventional methods (cross-correlation), and can measure vibration distribution without degrading the spatial resolution of strain analysis.

[0030] In the above embodiment, the optical frequency modulation amount f(x) from the near-end section #0 to the section #N-1 immediately before the analysis position is i , t) and perform position correction. However, as explained in equation (2), the optical fiber sensing method according to the present invention can be implemented by accumulating the position of an arbitrary section (x i ~x j ) with respect to the frequency offset f offset Therefore, the optical frequency modulation amount f(x) can be calculated from the section at any point, not just the near end, to the section #N-1 immediately before the analysis position. i , t) can be accumulated to analyze the amount of misalignment. Therefore, the optical fiber sensing method according to the present invention can improve the accuracy of strain measurement as well as the convenience.

[0031] (Embodiment 2) The analysis device 12 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. 9 shows a block diagram of a system 100. The system 100 includes a computer 105 connected to a network 135.

[0032] Network 135 is a data communications network. Network 135 may be a private or public network and may include any or all of the following: (a) a personal area network, e.g., covering a room; (b) a local area network, e.g., covering a building; (c) a campus area network, e.g., covering a campus; (d) a metropolitan area network, e.g., covering a city; (e) a wide area network, e.g., covering an area spanning city, region, or country boundaries; or (f) the Internet. Communications are conducted over network 135 by electronic and optical signals.

[0033] Computer 105 includes a processor 110 and memory 115 connected to processor 110. Although computer 105 is depicted herein as a stand-alone device, it is not limited to such, but rather may be connected to other devices not shown in a distributed processing system.

[0034] Processor 110 is an electronic device made up of logic circuits that responds to and carries out instructions.

[0035] The memory 115 is a tangible computer-readable storage medium on which a computer program is encoded. In this regard, the memory 115 stores data and instructions, i.e., program code, that can be read and executed by the processor 110 to control its operation. The memory 115 can be implemented as a random access memory (RAM), a hard drive, a read-only memory (ROM), or a combination thereof. One component of the memory 115 is a program module 120.

[0036] The program modules 120 contain instructions for controlling the processor 110 to perform the processes described herein. Although operations are described herein as being performed by the computer 105 or a method or process or sub-process thereof, those operations are actually performed by the processor 110.

[0037] The term "module" is used herein to refer to a functional operation that may be embodied as either a stand-alone component or an integrated configuration of multiple subcomponents. Thus, program module 120 may be implemented as a single module or as multiple modules operating in coordination with one another. Furthermore, while program module 120 is described herein as being installed in memory 115 and thus implemented in software, it may be implemented in any of hardware (e.g., electronic circuitry), firmware, software, or a combination thereof.

[0038] Although program module 120 is shown as already loaded into memory 115, it may also be configured to reside on storage device 140 for later loading into memory 115. Storage device 140 is a tangible, computer-readable storage medium that stores program module 120. Examples of storage device 140 include compact discs, magnetic tape, read-only memory, optical storage media, a memory unit consisting of a hard drive or multiple parallel hard drives, and a universal serial bus (USB) flash drive. Alternatively, storage device 140 may be random access memory or another type of electronic storage device located in a remote storage system (not shown) and connected to computer 105 via network 135.

[0039] System 100 further includes data source 150A and data source 150B, collectively referred to herein as data sources 150, that are communicatively connected to network 135. In practice, data sources 150 may include any number of data sources, i.e., one or more data sources. Data sources 150 may include unstructured data and may include social media.

[0040] The system 100 further includes a user device 130 operated by the user 101 and connected to the computer 105 via a network 135. The user device 130 includes an input device, such as a keyboard or a voice recognition subsystem, that allows the user 101 to communicate information and command selections to the processor 110. The user device 130 also includes an output device, such as a display device or a printer or a voice synthesizer. A cursor control, such as a mouse, trackball, or touch-sensitive screen, allows the user 101 to manipulate a cursor on the display device to communicate further information and command selections to the processor 110.

[0041] The processor 110 outputs the results 122 of the execution of the program modules 120 to the user device 130. Alternatively, the processor 110 can provide the output to a storage device 125, such as a database or memory, or via a network 135 to a remote device not shown.

[0042] 4 may be the program module 120. The system 100 may operate as the analysis device 12.

[0043] The terms "comprising" or "comprising" should be interpreted as specifying the presence of the stated features, integers, steps or components, but not excluding the presence of one or more other features, integers, steps or components or groups thereof. The terms "a" and "an" are indefinite articles and therefore do not exclude embodiments having a plurality thereof.

[0044] (Other embodiments) The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. In short, the present invention is not limited to the above-described embodiment, and the components can be modified and embodied in the implementation stage without departing from the spirit of the present invention.

[0045] Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in the above embodiments. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined.

[0046] [Appendix A] The relationship between the distortion amount ε, the spectrum shift Δ, and the phase change amount θ will be described. The distortion and temperature dependence of the spectral shift of Rayleigh backscattered light is given by:

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[0047] [Definition] The parameters used herein are as follows: x: Position in the longitudinal direction of the optical fiber (distance from the near end) t: time n: refractive index of optical fiber Δν: Spectral shift ν0: central optical frequency of the probe light c: Speed of light in a vacuum L: Spatial resolution of strain that can be detected by the measuring device k: wave number T: Temperature change of optical fiber f0: Vibration analysis position at t=0 γ: Frequency sweep speed of OFDR (measurement device) [Explanation of symbols]

[0048] 11: Measuring equipment 12:Analysis circuit 13: Optical fiber 100: System 101:User 105: Computer 110: Processor 115: Memory 120: Program module 122:Result 125: Storage device 130: User device 135: Network 140: Storage device 150: Data source 301: Optical fiber sensing device

Claims

1. An analysis device provided in an optical fiber sensing device using OFDR, calculating an amount of optical frequency modulation for each section of the optical fiber from the spectral shift measured for each section; accumulating the optical frequency modulation amounts of the sections located closer to the analysis position of the optical fiber to calculate an accumulated value; and correcting the analysis position based on the cumulative value; An analytical device that performs the following:

2. 2. The analyzer according to claim 1, wherein the calculation of the cumulative value is performed by accumulating the amount of optical frequency modulation from the section at the near end to the section immediately before the analysis position.

3. The analyzer according to claim 1 , wherein the calculation of the cumulative value is performed by accumulating the amount of optical frequency modulation from any one of the sections to the section immediately preceding the analysis position.

4. An optical fiber sensing method using OFDR, comprising: measuring the spectral shift for each section of optical fiber; calculating an amount of optical frequency modulation for each of the sections from the spectral shift; accumulating the optical frequency modulation amounts of the sections located closer to the analysis position of the optical fiber to calculate an accumulated value; and Correcting the analysis position based on the cumulative value. An optical fiber sensing method comprising:

5. 5. The optical fiber sensing method according to claim 4, wherein calculating the cumulative value comprises accumulating the amount of optical frequency modulation from the section at the near end to the section immediately before the analysis position.

6. 5. The optical fiber sensing method according to claim 4, wherein calculating the cumulative value comprises accumulating the amount of optical frequency modulation from any one of the sections to the section immediately preceding the analysis position.

7. A program for causing a computer to function as the analysis device according to any one of claims 1 to 3.

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