Sensing system, sensing method, and analysis device

Abstract

The purpose of the present invention is to provide a sensing system, a sensing method, and an analysis device using OFDR in which a strain / temperature sensing range is less likely to be limited by a frequency sweep width.　In the sensing method using OFDR, the sensing system according to the present invention sequentially updates a reference spectrum to an immediately-before-measured spectrum in each measurement by one frequency sweep of probe light to determine a spectral shift between an n-th measurement and (n-1)-th measurement, and integrates the spectral shift obtained in each measurement.

Description

[Technical field]

[0001] The present disclosure relates to a sensing system, a sensing method, and an analysis device thereof that use OFDR (Optical Frequency Domain Reflectometry). [Background technology]

[0002] Fig. 1 is a diagram explaining the sensing principle using OFDR. OFDR employs frequency swept light as a 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 with respect to the probe light of the optical fiber (see, for example, Non-Patent Document 1).

[0003] The spectrum of the backscattered light S(ν) varies with the strain and temperature of the optical fiber (spectral shift). Therefore, the reference spectrum S obtained in the reference measurement 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 equation (see, for example, Non-Patent Document 2).

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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] Y. Koyamada, M. Imahara, K. Kubota, and K. Hogari, “Fiber-optic distributed strain and temperature sensing with very high measurand resolution over long range using coherent OTDR,” IEEE J. Lightw. Technol., vol. 27, no. 9, pp. 1142-1146, 2009. Summary of the Invention [Problem to be solved by the invention]

[0005] The spectral shift Δν in FIG. 1(B) is calculated using cross-correlation, and therefore must be smaller than the frequency sweep width ΔF. [Number 2] |Δν|<ΔF Therefore, the sensing ranges of strain ε and temperature T are given by the following equations, respectively.

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[0006] As explained in FIG. 1B, in the conventional method for detecting the amount of spectrum shift, the cross-correlation between the spectrum obtained in the reference measurement and the spectrum obtained in each measurement is calculated. In other words, the part of the spectrum obtained in the reference measurement that is included in the frequency sweep width ΔF is called the reference spectrum S ref The reference spectrum S is included in the spectrum obtained in each measurement and is used as a standard. ref The same waveform part S' ref The amount of shift was obtained based on how much the value changed.

[0007] FIG. 2 is a diagram for explaining a problem with the conventional method for detecting the amount of spectrum shift. In the first measurement, the reference spectrum S ref Same waveform as S' ref A part of the spectrum is within the measurement band (frequency sweep width ΔF). Therefore, the cross-correlation between the reference spectrum and the spectrum obtained in the first measurement can be calculated, and the spectral shift Δν can be detected. On the other hand, in the second measurement, the reference spectrum S ref Same waveform as S' ref has shifted completely outside the measurement band (frequency sweep width ΔF). Therefore, the cross-correlation between the reference spectrum and the spectrum obtained in the second measurement cannot be calculated, and the spectral shift Δν cannot be detected.

[0008] In this way, the reference spectrum S obtained in the reference measurement ref Same waveform as S' ref If the frequency sweep width ΔF of the frequency band fluctuates outside the range of the frequency sweep width ΔF, the spectral shift Δν cannot be detected. In other words, conventional OFDR-based sensing has the problem that the strain / temperature sensing range is limited by the frequency sweep width ΔF.

[0009] Therefore, in order to solve the above problem, an object of the present invention is to provide a sensing system, a sensing method, and an analysis device using OFDR in which the strain / temperature sensing range is less likely to be limited by the frequency sweep width. [Means for solving the problem]

[0010] In order to achieve the above object, the sensing system according to the present invention uses as a reference spectrum not a reference measurement but a portion of the spectrum acquired in the immediately preceding measurement that is included in a frequency sweep width ΔF.

[0011] Specifically, the sensing system according to the present invention is a sensing system including a measurement device and an analysis device, The measuring device is The probe light with a single frequency sweep is input into the optical fiber, and measurements are repeatedly performed using OFDR (Optical Frequency Domain Reflectometry), which acquires the spectrum of the backscattered light. The analysis device includes: Calculating an individual spectrum shift, which is an amount of change in the spectrum obtained in the current measurement, using the spectrum obtained in the immediately preceding measurement as a reference spectrum; The individual spectral shifts in each measurement up to the current measurement are integrated to obtain the spectral shift at the time of the current measurement. It is characterized by:

[0012] Further, the sensing method according to the present invention comprises: A probe light with a single frequency sweep is input into an optical fiber, and measurements are repeatedly performed using OFDR to obtain the spectrum of the backscattered light. Calculating an individual spectrum shift, which is an amount of change in the spectrum obtained in the current measurement, using the spectrum obtained in the immediately preceding measurement as a reference spectrum; and Integrating the individual spectral shifts for each measurement up to a current measurement to obtain a spectral shift at a time of the current measurement. It is characterized by:

[0013] Furthermore, the present invention provides an analysis device that inputs a probe light whose frequency has been swept once into an optical fiber, repeats a measurement using OFDR to acquire a spectrum of backscattered light, and analyzes the spectrum obtained by the measurement, comprising: Calculating an individual spectrum shift, which is an amount of change in the spectrum obtained in the current measurement, using the spectrum obtained in the immediately preceding measurement as a reference spectrum; The individual spectral shifts in each measurement up to the current measurement are integrated to obtain the spectral shift at the time of the current measurement. It is characterized by:

[0014] In the present invention, in a sensing method using OFDR, the reference spectrum is successively updated to the spectrum measured immediately before for each measurement performed by one frequency sweep of the probe light, thereby determining the spectral shift between the nth measurement and the (n-1)th measurement, and the spectral shift determined in each measurement is integrated.

[0015] Since measurement is possible as long as the change in the spectral shift is smaller than the frequency sweep width of the probe light, the sensing range can be expanded by repeatedly performing spectrum measurements at high speed to satisfy this condition and successively updating the reference spectrum.

[0016] Therefore, the present invention can provide a sensing system, a sensing method, and an analysis device using OFDR in which the strain / temperature sensing range is less likely to be limited by the frequency sweep width.

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

[0018] The present invention can provide a sensing system, a sensing method, and an analysis device using OFDR in which the strain / temperature sensing range is less likely to be limited by the frequency sweep width. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram for explaining the sensing principle using OFDR. [Diagram 2] FIG. 1 is a diagram illustrating a problem to be solved by the present invention. [Diagram 3] FIG. 1 is a diagram illustrating a sensing system according to the present invention. [Figure 4] FIG. 2 is a diagram illustrating a sensing method according to the present invention. [Diagram 5] 1A to 1C are diagrams illustrating the sensing principle of a sensing system according to the present invention. [Figure 6] 1A to 1C are diagrams illustrating the effects of the sensing system according to the present invention. [Figure 7] 11 is a table illustrating the effects of the sensing system according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. Note that components with the same reference numerals in this specification and drawings indicate the same components.

[0021] FIG. 3 is a diagram illustrating the sensing system of this embodiment. This sensing system is a sensing system including a measurement device 11 and an analysis device 12. The measurement device 11 inputs the probe light, the frequency of which has been swept once, into the optical fiber 13, and repeatedly performs measurement using OFDR to obtain the spectrum of the backscattered light. The analysis device 12 includes: Calculating an individual spectrum shift, which is an amount of change in the spectrum obtained in the current measurement, using the spectrum obtained in the immediately preceding measurement as a reference spectrum; The individual spectral shifts for each measurement up to the current measurement are integrated to obtain the spectral shift at the time of the current measurement.

[0022] FIG. 4 is a flow chart illustrating the sensing method performed by the present sensing system. The probe light, the frequency of which has been swept once, is input to the optical fiber 13, and a measurement using OFDR for acquiring a spectrum of the backscattered light is repeatedly performed (step S11); Calculating an individual spectrum shift, which is the amount of change in the spectrum obtained in the current measurement, using the spectrum obtained in the immediately previous measurement as a reference spectrum (step S12); and Integrating the individual spectral shifts in each measurement up to the current measurement to obtain a spectral shift at the time of the current measurement (step S13). It is characterized by: It should be noted that step S01 corresponds to the reference measurement described with reference to FIG. 1, and is the 0th measurement.

[0023] Fig. 5 is a diagram for explaining an example of a spectrum acquired by this sensing method. The sensing principle of this sensing system will be explained using Fig. 5. First, as the 0th measurement, the measurement device 11 measures the spectrum S(ν) from the Rayleigh backscattered light for the probe light of the optical fiber 13 using OFDR as described in FIG. 1 (step S01a). The analysis device 12 extracts from the spectrum S(ν) a waveform included in the frequency sweep width ΔF as a reference spectrum S ref0 (Step S01b).

[0024] Next, as a first measurement, the measurement device 11 similarly uses OFDR to measure a spectrum S(ν) from Rayleigh backscattered light with respect to the probe light of the optical fiber 13 (step S11). The analysis device 12 extracts from the spectrum S(ν) a waveform included in the frequency sweep width ΔF as a reference spectrum S ref1 and updates the reference spectrum S as a new reference spectrum (step S12a). ref0 In the spectrum S(ν) of the first measurement, the amount by which it has moved (spectral shift Δν1) is calculated using a correlation function (step S12b).

[0025] This sensing system repeats steps S11 and S12 N times (N is an integer equal to or greater than 2). That is, the measurement device 11 repeats the above measurement N times, and the analysis device 12 obtains a reference spectrum S refn By successively updating, the spectral shift Δν n (n is an integer between 1 and N).

[0026] Here, as explained in FIG. 1(B), the spectral shift Δν n Since is calculated using cross-correlation, it must be smaller than the frequency sweep width ΔF. [Number 5] |Δν n |<ΔF This is the spectral shift Δν n In other words, in the case of conventional measurements where the shift amount becomes large from the reference measurement spectrum S(ν) and the spectral shift Δν cannot be calculated, this sensing system can calculate the shift amount by cross-correlation using the reference spectrum S(ν) from the previous measurement. ref(nー1) If the shift from is within the measurement band, the spectral shift Δν n It becomes possible to calculate

[0027] Then, the analyzer 12 finally calculates the spectral shift Δν n is integrated with respect to n to obtain the spectral shift Δν at time NΔt (step S13).

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[0028] In this way, even if the shift amount from the reference measurement spectrum S(ν) exceeds the measurement band, this sensing system uses the spectrum S(ν) of the immediately preceding measurement, where the shift amount is within the measurement band, and successively updates the reference spectrum, making it appear as if the measurement band (sensing range) has been expanded without substantially sacrificing the sensing speed.

[0029] (Other embodiments) The above-mentioned 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.

[0030] (Example) Figure 6 is a diagram explaining the results of comparing this sensing system with a conventional sensing system. The system configuration is shown in Figure 3, and the measurement conditions are as follows. -OFDR optical frequency sweep range: 2GHz Vibration applied to the measurement object 20: Sine wave (vibration frequency 10Hz, amplitude 13με) Spectral shift to distortion conversion factor: -151MHz / μe

[0031] Figure 6(A) shows a spectrum measured by a conventional sensing system. The horizontal axis is time (seconds) and the vertical axis is the swept optical frequency (GHz). Figure 6(B) shows a distortion waveform in which the spectrum in Figure 6(A) is cross-correlated (searching for correlation peaks) to calculate the spectral shift and then converted from the spectral shift to distortion. The horizontal axis is time (seconds) and the vertical axis is distortion (με).

[0032] Conventional sensing systems have a sensing range of only 6.5 με (= 2 GHz ÷ 151 MHz / με ÷ 2) in terms of vibration amplitude, and are therefore unable to measure vibrations with an amplitude of 12 με, which exceeds their measurement capabilities.

[0033] Figure 6(C) shows the spectrum (cross-correlation with the previously measured spectrum) measured by this sensing system. The horizontal axis is time (seconds) and the vertical axis is spectral shift (MHz). Figure 6(D) shows the time change of the spectral shift calculated by searching for a correlation peak in the spectrum of Figure 6(C). The horizontal axis is time (seconds) and the vertical axis is spectral shift (MHz). Figure 6(E) shows a distortion waveform obtained by integrating the time change of the spectral shift in Figure 6(D) and converting it from spectral shift to distortion. The horizontal axis is time (seconds) and the vertical axis is strain (με).

[0034] This sensing system was able to measure the time change of the spectral shift within a frequency sweep width of 2 GHz, and was able to correctly measure vibrations with an amplitude of 12 με.

[0035] (Effects of the Invention) As explained in Equation 2, the conventional sensing system calculates the spectral shift Δν using cross-correlation, and therefore cannot measure the spectral shift Δν unless it is smaller than the frequency sweep width ΔF. On the other hand, this sensing system calculates the amount of change in spectral shift d(Δν) / dt using cross-correlation as shown in the following equation, so it can be measured as long as the amount of change in spectral shift d(Δν) / dt is smaller than the frequency sweep width ΔF. In other words, this sensing system can measure spectral shifts as long as the change in the spectral shift is smaller than the frequency sweep width of the probe light. Therefore, the sensing range can be expanded by repeatedly measuring the spectrum at high speed to satisfy this condition and updating the reference spectrum.

[0036] Figure 7 is a table comparing the performance of the conventional sensing system and this sensing system. The sensing performance of OFDR is determined by the type of probe light source. If a wavelength-tunable light source is used, the repetition frequency of the probe light is a maximum of 10 Hz, and the frequency sweep width of the probe light is a maximum of 2 THz. In this case, the conventional sensing system has a measurement limit of a maximum strain of 13 mε and a maximum temperature change of 1500 K, and can only achieve slow sensing under extreme environments such as large strain / large temperature change. In addition, when an externally modulated light source with a repetition frequency of 100 Hz or more and a maximum frequency sweep width of 2 THz is used, the performance of the conventional sensing system is capable of high-speed sensing, but the measurement limit is a maximum strain of 66 με and a maximum temperature change of 7.5 K (small strain / small temperature change).

[0037] On the other hand, when the above-mentioned tunable light source is used in this sensing system, there is no measurement limit for strain or temperature change, and low-speed sensing is possible in extreme environments such as large strain / large temperature change. Also, when the above-mentioned externally modulated light source is used in this sensing system, there is no measurement limit for strain or temperature change, and high-speed sensing is possible in extreme environments such as large strain / large temperature change. [Explanation of symbols]

[0038] 11: Measuring device 12: Analysis device 13: Optical fiber 20: Measurement target

Claims

1. A sensing system including a measurement device and an analysis device, The measuring device is A probe light whose frequency has been swept once is input into an optical fiber, and measurements are repeatedly performed using OFDR (Optical Frequency Domain Reflectometry) to obtain the spectrum of the backscattered light; The analysis device includes: Calculating an individual spectrum shift, which is an amount of change in the spectrum obtained in the current measurement, using the spectrum obtained in the immediately preceding measurement as a reference spectrum; The individual spectral shifts in each measurement up to the current measurement are accumulated to obtain the spectral shift at the time of the current measurement. A sensing system comprising:

2. A probe light whose frequency has been swept once is input into an optical fiber, and a measurement is repeatedly performed using an OFDR to obtain a spectrum of the backscattered light; Calculating an individual spectrum shift, which is an amount of change in the spectrum obtained in the current measurement, using the spectrum obtained in the immediately preceding measurement as a reference spectrum; and The individual spectral shifts in each measurement up to the current measurement are accumulated to obtain a spectral shift at the time of the current measurement. A sensing method comprising:

3. 1. An analysis device that inputs a probe light having a frequency swept once into an optical fiber, repeats a measurement using an OFDR to acquire a spectrum of backscattered light, and analyzes the spectrum obtained by the measurement, comprising: Calculating an individual spectrum shift, which is an amount of change in the spectrum obtained in the current measurement, using the spectrum obtained in the immediately preceding measurement as a reference spectrum; The individual spectral shifts in each measurement up to the current measurement are accumulated to obtain the spectral shift at the time of the current measurement. An analytical device characterized by:

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