Optical fiber sensor, optical fiber sensing method, and program

Abstract

In a wavelength-swept COTDR, the measurement performance is improved by compensating for the influence of the wavelength dispersion of the optical fiber. 【Solution means】The frequency f of the tunable light source i The position x in the longitudinal direction of the optical fiber in the reference distance coordinate system at regular intervals obtained by changing j , and the intensity distribution S(f i of the scattered light as a function of i , x j ), wavelength dispersion compensation means for compensating for the wavelength dispersion of the optical fiber, and the intensity distribution S(f i , x j ) of the scattered light obtained by the wavelength dispersion compensation means, the optical intensity distributions S1(f i , x), S2(f i + Δf, x) of the scattered light at the first time and the second time are acquired, and the cross-correlation function R(Δf, x) of the intensity distribution S1(f i , x) at the first time and the intensity distribution S2(f i + Δf, x) at the second time is calculated, and cross-correlation function calculation means for acquiring Δf at which the cross-correlation function R(Δf, x) becomes maximum.​​​​​​​​

Description

[Technical Field]

[0001] This invention relates to an optical fiber sensor and optical fiber sensing method suitable for use in, for example, a wavelength-swept COTDR, and a program that can be used with them. [Background technology]

[0002] 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 a single point.

[0003] Strain (temperature) sensors using optical fibers as a sensing medium are broadly classified into BOTDR (Brillouin Optical Time Domain Reflectometry), which uses Brillouin scattered light, and wavelength-swept COTDR (Coherent Optical Time Domain Reflectometry) (see, for example, Patent Document 1) or frequency-domain optical reflectometry (OFDR: Optical Frequency Domain Reflectometry), which uses Rayleigh scattered light.

[0004] Among these, wavelength-swept COTDRs and OFDRs have high distortion (temperature) sensitivity due to the frequency shift of Rayleigh scattered light, allowing for more accurate measurements compared to general BOTDR methods. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International release 2015 / 059969 [Overview of the project] [Problems that the invention aims to solve]

[0006] Here, since wavelength-swept COTDR is a technology that relies on wavelength sweeping of the light source, it is affected by the wavelength dispersion of the optical fiber, resulting in a deterioration of measurement accuracy. While wavelength dispersion compensation using auxiliary interferometers has been considered for OFDRs, it has not been considered for wavelength-swept COTDRs.

[0007] This is because the influence of chromatic dispersion on measurements has been limited to specific regions, such as when large distortions occur only over very short intervals during long-distance measurements, and therefore its effects have not been apparent until now. However, as the development of wavelength-swept COTDRs progresses, it has become necessary to consider the effects of chromatic dispersion.

[0008] This invention has been made in view of the above circumstances. The purpose of this invention is to provide an optical fiber sensor and an optical fiber sensing method, and a program that can be used therein, which improve measurement performance in a wavelength-swept COTDR by compensating for the effects of chromatic dispersion of the optical fiber. [Means for solving the problem]

[0009] To achieve the above-mentioned objectives, the optical fiber sensor of this invention comprises a pulse light generation unit having a frequency-variable light source, which splits the continuous light generated by the frequency-variable light source into two, generates pulse light from one of the two branches and uses the other as a reference light, an optical fiber to which the pulse light is input, scattered light obtained when the pulse light is scattered in the optical fiber, and a scattered light information acquisition unit to which the reference light is input.

[0010] The scattered light information acquisition unit comprises a light receiving unit and a calculation unit. The light receiving unit coherently detects the reference light and the scattered light and sends the resulting electrical signal to the calculation unit.

[0011] The calculation unit determines the frequency f of the variable frequency light source. i The longitudinal position x of the optical fiber in a reference distance coordinate system at regular intervals, obtained by changing the x j , and the frequency fi As a function of the intensity distribution S(f i , x j ), wavelength dispersion compensation means for compensating for the wavelength dispersion of the optical fiber, and the intensity distribution S(f i , x j ) of the scattered light obtained by the wavelength dispersion compensation means, the intensity distributions S1(f i , x) and S2(f i + Δf, x) of the scattered light at the first time and the second time are obtained, and the cross-correlation function R(Δf, x) between the intensity distribution S1(f i , x) at the first time and the intensity distribution S2(f i + Δf, x) at the second time is calculated, and cross-correlation function calculation means for obtaining Δf at which the cross-correlation function R(Δf, x) is maximized is provided.

[0012] According to a preferred embodiment of the optical fiber sensor of the present invention, the wavelength dispersion compensation means includes: the intensity distribution p(f i obtained by changing the frequency f j of the frequency-variable light source, and as a function of the frequency f i ), the intensity distribution p(f i , t j ) of the scattered light; a first means for obtaining the intensity distribution p(f j ), a second means for converting the time t g to the position x j in the reference distance coordinate system using the optical group velocity v of the optical fiber; a third means for obtaining the intensity distribution S(f j using the position x j ' in the distance coordinate system obtained by compensating for wavelength dispersion for each frequency; and a fourth means for interpolating the position x i , x j ] ') to obtain the intensity distribution S(f j ', x j ) of the scattered light at the position x i , x j ) in the reference distance coordinate system.

[0013] According to a further preferred embodiment of the optical fiber sensor of this invention, the third means uses x, which is a parameter D representing wavelength dispersion. j '=(1+2D×(f i -f1))x j According to the formula, the position x in the reference distance coordinate system j position x in the distance coordinate system j Convert to '.

[0014] According to a further preferred embodiment of the optical fiber sensor of this invention, the fourth means interpolates the position x in the distance coordinate system by cubic spline interpolation. j Interpolate the '.

[0015] According to a further preferred embodiment of the optical fiber sensor of this invention, the calculation unit further includes strain (temperature) information acquisition means for acquiring temperature changes or strain changes of the optical fiber between a first time and a second time from Δf acquired by the cross-correlation function calculation means.

[0016] Furthermore, the optical fiber sensing method of this invention performs the following steps at a first and second time point: splitting a continuous light into two, generating pulsed light from one of the two branches and using the other as a reference light; injecting the pulsed light into an optical fiber; and obtaining an electrical signal by coherently detecting the scattered light obtained from the pulsed light scattered in the optical fiber and the reference light, while changing the frequency of the continuous light. In addition, the longitudinal position x of the optical fiber in a reference distance coordinate system at regular intervals j , and the frequency f i The intensity distribution of scattered light S(f) as a function of i ,x j Regarding the above, the process of compensating for the wavelength dispersion of the optical fiber and the intensity distribution S(f) of the scattered light obtained by the wavelength dispersion compensation means. i ,x j ) From this, the intensity distribution of scattered light S1(f i ,x), S2(f i Obtain the intensity distribution S1(f +Δf,x) at the first time step. i(x), and the intensity distribution S2(f) at the second time step. i The method includes calculating the cross-correlation function R(Δf,x) of +Δf,x, and obtaining the Δf that maximizes the cross-correlation function R(Δf,x).

[0017] According to a preferred embodiment of the optical fiber sensing method of this invention, the process of compensating for wavelength dispersion involves the frequency f of the frequency tunable light source. i The time t obtained by changing j , and the frequency f i The intensity distribution of scattered light as a function of f i ,t j The first step is to obtain the time t j The optical group velocity v in the optical fiber g Using the position x in the aforementioned reference distance coordinate system j A second step is to convert to the position x in the reference distance coordinate system. j The position x in the distance coordinate system obtained by compensating for wavelength dispersion for each frequency. j Using ', the intensity distribution of scattered light S(f i ,x j The third step is to obtain ') and the position x in the distance coordinate system. j Interpolating ' to obtain the position x in the aforementioned reference distance coordinate system j Intensity distribution of scattered light S(f i ,x j The fourth step involves obtaining ).

[0018] According to a further preferred embodiment of the optical fiber sensing method of this invention, in the third step, x is used with a parameter D representing wavelength dispersion. j '=(1+2D×(f i -f1))x j According to the formula, the position x in the reference distance coordinate system j position x in the distance coordinate system j Convert to '.

[0019] According to a further preferred embodiment of the optical fiber sensing method of this invention, in the fourth step, the position x in the distance coordinate system is interpolated by cubic spline interpolation. j Interpolate the '.

[0020] A further preferred embodiment of the optical fiber sensing method of this invention further includes a step of obtaining the temperature change or strain change of the optical fiber between a first time and a second time from Δf obtained by the cross-correlation function calculation means.

[0021] Furthermore, the program of this invention comprises a pulse light generation unit having a frequency-variable light source, which splits the continuous light generated by the frequency-variable light source into two, generates pulse light from one of the two branches and uses the other as a reference light, an optical fiber to which the pulse light is input, scattered light obtained when the pulse light is scattered in the optical fiber, and a scattered light information acquisition unit to which the reference light is input, and the scattered light information acquisition unit of the optical fiber sensor has the frequency f of the frequency-variable light source i The longitudinal position x of the optical fiber in a reference distance coordinate system at regular intervals, obtained by changing the x j , and the frequency f i The intensity distribution of scattered light S(f) as a function of i ,x j Regarding the optical fiber, a wavelength dispersion compensation means for compensating for the wavelength dispersion of the optical fiber, and the intensity distribution S(f) of the scattered light obtained by the wavelength dispersion compensation means. i ,x j ) From this, the intensity distribution of scattered light S1(f i ,x), S2(f i Obtain the intensity distribution S1(f +Δf,x) at the first time step. i (x), and the intensity distribution S2(f) at the second time step. i This function calculates the cross-correlation function R(Δf,x) of +Δf,x, and uses it as a means to obtain the Δf that maximizes the cross-correlation function R(Δf,x).

[0022] According to a preferred embodiment of the program of this invention, the wavelength dispersion compensation means controls the frequency f of the frequency tunable light source.i obtained by changing, at time t j , and the frequency f i as a function of, the intensity distribution p(f i ,t j ) of scattered light, a first means for obtaining, the time t j using the group velocity v of light in the optical fiber g to convert the position x in the reference distance coordinate system j , a second means for converting to, a third means for obtaining the intensity distribution S(f j using the position x' in the distance coordinate system obtained by compensating for wavelength dispersion for each frequency j in the reference distance coordinate system, and a fourth means for interpolating the position x i ,x j ' in the distance coordinate system to obtain the intensity distribution S(f j ',x j ) of scattered light at the position x in the reference distance coordinate system i ,x j ) to function as.

[0023] According to a further preferred embodiment of the program of the present invention, in the third means, x j '=(1 + 2D×(f i -f1))x j using the formula of, the position x in the reference distance coordinate system j is converted to the position x j ' in the distance coordinate system.

[0024] According to a further preferred embodiment of the program of the present invention, in the fourth means, the position x j ' in the distance coordinate system is interpolated by cubic spline interpolation.

[0025] According to a further preferred embodiment of the program of the present invention, the scattered light information acquisition unit is further caused to function as a strain (temperature) information acquisition means for acquiring a temperature change or a strain change of the optical fiber between a first time and a second time from Δf acquired by the cross-correlation function calculation means.

Advantages of the Invention

[0026] According to the optical fiber sensor and optical fiber sensing method of this invention, and the program that can be used therewith, measurement performance is improved by compensating for the effects of chromatic dispersion of the optical fiber. [Brief explanation of the drawing]

[0027] [Figure 1] This is a schematic diagram of an optical fiber sensor used in a typical wavelength-swept COTDR. [Figure 2] This is a schematic diagram illustrating the principle of a typical wavelength-swept COTDR. [Figure 3] This diagram illustrates the effects of wavelength dispersion. [Figure 4] This is a schematic diagram of the optical fiber sensor used in the wavelength-swept COTDR of this invention. [Figure 5] This figure illustrates the results of applying the processing in the wavelength dispersion compensation means. [Figure 6] This figure shows the measurement results of the strain distribution. [Modes for carrying out the invention]

[0028] The embodiments of this invention will be described below with reference to the figures, but the shapes, sizes, and arrangements of each component are only shown in a general manner to the extent that the invention can be understood. Furthermore, preferred configuration examples of this invention will be described below, but these are merely examples. Therefore, this invention is not limited to the following embodiments, and many changes or modifications can be made to achieve the effects of this invention without departing from the scope of the configuration of this invention.

[0029] (Typical wavelength-swept COTDR) A typical wavelength-swept COTDR will be explained with reference to Figure 1. Figure 1 is a schematic diagram of an optical fiber sensor used in a typical wavelength-swept COTDR.

[0030] A typical wavelength-swept COTDR is used, for example, to measure strain and temperature. The optical fiber sensor is composed of a pulse light generation unit 10, a circulator 20, an optical fiber 30, and a scattered light information acquisition unit 40.

[0031] The pulsed light generation unit 10 is configured to include, for example, a frequency-variable light source 12, a brancher 13, an intensity modulator 14, a function generator 16, and an optical amplifier 18.

[0032] The variable frequency light source 12 generates continuous light at a frequency set by the scattered light information acquisition unit 40. The continuous light generated by the variable frequency light source 12 is sent to the branching switch 13.

[0033] The brancher 13 splits the continuous light sent from the frequency-variable light source 12 into two at a predetermined branching ratio. One of the two branches obtained by the brancher 13 is sent to the intensity modulator 14, and the other is sent to the scattered light information acquisition unit 40 as reference light.

[0034] As the intensity modulator 14, for example, an acoustic-optical modulator (AOM) is used. The intensity modulator 14 generates optical pulses from the continuous light sent from the brancher 13, with pulse widths and pulse periods determined by electrical signals input from a function generator 16 or the like. The pulse width can be determined according to the desired spatial resolution. The pulse period can be set to an interval longer than the time it takes for the optical pulse to travel back and forth through the optical fiber 30. When an AOM is used as the intensity modulator 14, the frequency of the optical pulse changes from the frequency of the continuous light input to the intensity modulator 14 due to the optical Doppler effect. The optical pulses generated by the intensity modulator 14 are sent to the optical amplifier 18.

[0035] The optical amplifier 18 amplifies the optical pulse sent from the intensity modulator and sends it to the circulator 20. While it is common to insert an optical filter after the optical amplifier 18 to remove the amplified spontaneous emission (ASE) noise generated by the optical amplifier 14, a detailed explanation and illustration are omitted here.

[0036] In this manner, the pulsed light generation unit 10 generates light pulses, which are sent to the circulator 20. The pulsed light generation unit 10 also generates reference light, which is sent to the scattered light information acquisition unit 40.

[0037] The circulator 20 has a first to third port. Light input to the first port is output from the second port, light input to the second port is output from the third port, and light input to the third port is output from the first port.

[0038] In this example, the optical pulses sent from the pulsed light generation unit 10 are input to the first port of the circulator 20. The optical pulses input to the first port of the circulator 20 are output from the second port. The optical pulses output from the second port of the circulator 20 are sent to the optical fiber 30.

[0039] The optical fiber 30 is the object of measurement for strain and temperature. The optical pulse (input light) input to the optical fiber 30 is Rayleigh scattered as it propagates from the input end, which is the end of the optical fiber 30 on the circulator 20 side, to the other end, which is the termination. The backscattered light (hereinafter also simply referred to as scattered light) propagates in the opposite direction to the input light, from the scattering point towards the input end of the optical fiber, is output from the optical fiber 30, and is sent to the circulator 20.

[0040] The scattered light sent to the circulator 20 is input to the second port of the circulator 20. The scattered light input to the second port of the circulator 20 is output from the third port. The scattered light output from the third port of the circulator 20 is sent to the scattered light information acquisition unit 40.

[0041] The scattered light information acquisition unit 40 is configured to include a light receiving unit 50 and a calculation unit 60.

[0042] The light-receiving unit 50 generates an electrical signal by coherently detecting the scattered light generated in the optical fiber 30 using a reference light. The light-receiving unit 50 is composed of a coherent receiver 52, a photoelectric converter 54, and an analog-to-digital (AD) converter 56. The coherent receiver 52 performs coherent detection of the scattered light using the reference light. For example, a 90° optical hybrid coupler can be used as the coherent receiver 52.

[0043] When the modulation in the intensity modulator 14 involves a frequency shift, the detection in the coherent receiver 52 becomes heterodyne detection, and when the modulation in the intensity modulator 14 does not involve a frequency shift, it becomes homodyne detection. Alternatively, the scattered light received by the light receiving unit 50 may be amplified before being input to the coherent receiver 52.

[0044] The combined light obtained by coherent detection in the coherent receiver 52 is output from the coherent receiver 52 and sent to the photoelectric converter 54.

[0045] The photoelectric converter 54 is, for example, a PD (Photo Diode) and converts the multiplexed light generated by the coherent receiver 52 into an electrical signal. The electrical signal generated by the photoelectric converter 54 is sent to the AD converter 56.

[0046] The AD converter 56 converts the electrical signal generated by the photoelectric converter 54 from an analog signal to a digital signal. The digital signal obtained by the AD conversion in the AD converter 56 is sent to the arithmetic unit 60.

[0047] The arithmetic unit 60 can be configured in any suitable way, such as a commercially available personal computer (PC), and may include, for example, RAM (Random Access Memory) 62, ROM (Read Only Memory) 64, storage means 66, and a CPU (Central Processing Unit) 70, to perform digital signal processing.

[0048] Here, the CPU 70 is described as realizing predetermined functional means described later by reading and executing a program stored in the ROM 64, but it is not limited to this. The processing of each functional means is temporarily stored in the RAM 62, and the processing results of the arithmetic unit 60 and the intensity distribution S(f,x) at each time point are stored in the storage means 66.

[0049] Note that the input, output, and communication means provided by the PC are not shown in the diagrams or explanations.

[0050] Furthermore, the pulse light generation unit 10, circulator 20, optical fiber 30, and scattered light information acquisition unit 40 of the optical fiber sensor can be configured in any suitable conventional known configuration, except for the functional means realized by the scattered light information acquisition unit 40. Description of such a suitable conventional known configuration may be omitted.

[0051] This document describes a general optical fiber sensing method using a wavelength-swept COTDR, including the functions of each functional means.

[0052] Figure 2 is a schematic diagram illustrating the principle of a typical wavelength-swept COTDR. In a typical wavelength-swept COTDR, the intensity distribution of scattered light is measured at two time points: a first time point and a second time point.

[0053] Figure 2(A) shows the input light to optical fiber 30 and the scattering centers at the first time point. Here, the scattered light from each scattering center retains the phase of the input light.

[0054] Figure 2(B) shows the input light to the optical fiber 30 and the scattering center at the second time point. If distortion or temperature changes occur in the optical fiber 30 between the first and second time points, the position of the scattering center changes, and the relative phase of the scattered light changes.

[0055] Figure 2(C) shows the input light to optical fiber 30 and the scattering center at the second time point. The input light to optical fiber 30 at the second time point has a different frequency f (wavelength) than the input light at the first time point. As described above, if distortion or temperature changes occur between the first and second time points, the position of the scattering center changes and the relative phase of the scattered light changes. However, by changing the frequency f (wavelength) of the input light, the phase relationship can be restored to that of the first time point.

[0056] The cross-correlation function calculation means 74, acting as a functional means, reads out the intensity distribution S1(f,x) of scattered light at a first time and the intensity distribution S2(f,x) of scattered light at a second time, which are stored in the memory means 66. Then, the cross-correlation function calculation means 74 calculates the cross-correlation function R(Δf,x) of the intensity distribution S1(f,x) at the first time and the intensity distribution S2(f+Δf,x) at the second time using the following equation (1).

[0057] Here, position x, a variable in the intensity distribution of scattered light, represents the distance from the incident end of the optical fiber 30 being measured. Position x is obtained from the observation time t at the AD converter 56, and the group velocity v of light in the optical fiber 30. g Using this, x = v g It is converted using the formula t / 2.

[0058]

number

[0059] Here, the Δf at which R(Δf, x) is maximized is the desired frequency change Δf that can return the phase relationship at the second time to the phase relationship at the first time. max That is the case. Furthermore, the frequency change Δf max The method for obtaining this is not limited to this example. Other methods can be used as long as it is possible to calculate the amount of shift in f that makes the intensity distribution S1(f,x) at the first time point and the intensity distribution S2(f+Δf,x) at the second time point closest to each other.

[0060] The strain (temperature) information acquisition means 76 uses the Δf obtained by the cross-correlation function calculation means 74. max Using this, the strain (temperature) information, namely the strain change Δε and the temperature change ΔT, is obtained by the following equation (2). f0 is the frequency of the continuous light at the first time, generated by the frequency-tunable light source.

[0061]

number

[0062] (Wavelength-swept COTDR of this invention) In a wavelength-swept COTDR, the frequency of the input light is f i And at time t j The Rayleigh backscatter light observed is of the input light frequency f i The group velocity of light v in optical fiber 30 relative to the group velocity v g Therefore, position x = v g t j This is scattered light generated at / 2. Therefore, even though the intensity of Rayleigh scattered light observed at the same time is affected by the wavelength dispersion of the optical fiber 30, the frequency of the input light f i This causes the location of the scattered light to shift.

[0063] Refer to Figure 3 to explain the effect of chromatic dispersion. Figure 3 is a diagram illustrating the effect of chromatic dispersion, with time (Time [ns]) on the horizontal axis and Rayleigh scattered light intensity (Rayleigh Scattering [au]) on the vertical axis. Figure 3 shows the observed Fresnel reflection intensity at the end of the optical fiber 30 for three different incident frequencies: 194.1713 THz (Curve I), 194.6723 THz (Curve II), and 195.1713 THz (Curve III).

[0064] As shown in Figure 3, the timing at which reflected light from the end of the optical fiber 30 is observed depends on the frequency f of the input light due to the effect of wavelength dispersion. iThis varies depending on the method. Consequently, the position x of the intensity distribution S(f,x) of Rayleigh scattered light calculated using conventional methods shifts from the original scattered light generation position for each optical frequency f. As a result, in regions where the strain (temperature) change interval is short and this shift cannot be ignored, strain (temperature) measurement becomes impossible.

[0065] Therefore, the optical fiber sensor used in the wavelength-swept COTDR of this invention is equipped with wavelength dispersion compensation means in the calculation unit.

[0066] The wavelength-swept COTDR of this invention will be explained with reference to Figure 4. Figure 4 is a schematic diagram of the optical fiber sensor used in the wavelength-swept COTDR of this invention. The wavelength-swept COTDR of this invention differs from the optical fiber sensor of a general wavelength-swept COTDR described with reference to Figure 1 in that the calculation unit is equipped with a wavelength dispersion compensation means 78. Other configurations are the same as those of a general wavelength-swept COTDR optical fiber sensor, so redundant explanations may be omitted here.

[0067] The wavelength dispersion compensation means 78 comprises the first to fourth means.

[0068] In the first step, the first means uses the input light frequency f i , time t j The scattered light intensity observed is p(f i ,t j )

[0069] Next, in the second step, the second means sets the position x in the reference distance coordinate system to the representative optical group velocity v of the optical fiber 30. g Using x j =v g t j Let's use / 2. Note that the method for determining the position x in the reference distance coordinate system is not limited to this example, and any suitable method can be used.

[0070] Next, in the third step, the third means converts the position x in the reference distance coordinate system to the position x' in the distance coordinate system. This conversion is, for example, x j '=(1+2D×(f i -f1))x j This is done using the formula. Then, the intensity of the scattered light at time t is p(f i ,t j ) is the scattered light intensity s(f) at position x'. i ,x j Let's leave it as ').

[0071] Here, D is a parameter representing chromatic dispersion. D is given, for example, by the delay when light with a wavelength interval of 1 nm is transmitted over a distance of 1 km.

[0072] Next, in the fourth step, the fourth means is S(f i ,x j Interpolating ') to S(f i ,x j This interpolation can be performed, for example, with cubic spline interpolation, but is not limited to this, and any suitable interpolation method can be used.

[0073] The position x' in the distance coordinate system obtained in the third step is not the position in a reference distance coordinate system with constant intervals, as a result of the wavelength dispersion compensation process. Therefore, interpolation in this fourth step converts it to the position x in a reference distance coordinate system with constant intervals.

[0074] The processing after the first to fourth steps in the wavelength dispersion compensation means 78 is the same as that of a general wavelength-swept COTDR. That is, the cross-correlation function calculation means 74 calculates Δf max After obtaining the above, the strain (temperature) information acquisition means 76 acquires the strain change amount Δε and the temperature change amount ΔT.

[0075] The effects of the wavelength-swept COTDR of this invention, which includes the wavelength dispersion compensation means 78, will be explained with reference to Figures 5 and 6.

[0076] Figure 5 illustrates the results of applying the processing in the wavelength dispersion compensation means 78, with time (Time [ns]) on the horizontal axis and Rayleigh scattering intensity (Rayleigh Scattering [au]) on the vertical axis. Similar to Figure 3, Figure 5 shows the observed Fresnel reflection intensity at the end of the optical fiber 30 for three different incident frequencies: 194.1713 THz (curve I), 194.6723 THz (curve II), and 195.1713 THz (curve III).

[0077] As shown in Figure 5, the processing by the wavelength dispersion compensation means 78 compensates for the Fresnel reflection from the end of the optical fiber 30, which had a positional shift in Figure 3, so that it is in the same position.

[0078] Figure 6 shows the measurement results of the strain distribution, with the horizontal axis representing the distance from the input end of the optical fiber 30 (Fiber Length [m]) and the vertical axis representing the strain (Strain [με]). Figure 6 shows the results when the wavelength dispersion compensation means 78 is applied (I) and when it is not applied (II). Figure 6 shows the results when strain is applied to a section of the optical fiber 30 under measurement, with a frequency sweep width of 1 THz and a frequency sweep step of 500 MHz.

[0079] As shown in Figure 6, under II, when the wavelength dispersion compensation means 78 is not applied, the strain change is not measured. In contrast, as shown in Figure 6, under I, when the wavelength dispersion compensation means 78 is applied, the strain change is measured.

[0080] Thus, with the wavelength-swept COTDR of this invention, measurement performance is improved, such as being able to measure strain changes even in events where large strains occur only in very short intervals, by performing wavelength dispersion compensation. [Explanation of Symbols]

[0081] 10. Pulsed light generation unit 12. Variable frequency light source 13. Turnout 14. Intensity modulator 16 Function Generator 18. Optical Amplifier 20 Circulators 30 optical fibers 40 Scattered light information acquisition section 50 Light receiving part 52 Coherent Receivers 54 Photoelectric Converter 56 AD Converter 60 Arithmetic section 62 RAM 64 ROM 66 Memory means 70 CPU 74. Means for calculating cross-correlation functions 76. Means for acquiring strain (temperature) information 78 Chromatic dispersion compensation means

Claims

1. A pulse light generation unit having a frequency-variable light source, which splits the continuous light generated by the frequency-variable light source into two, generates pulse light from one of the two branches, and uses the other as a reference light, The optical fiber into which the pulsed light is input, The optical fiber comprises scattered light obtained by scattering the pulsed light and a scattered light information acquisition unit to which the reference light is input. The scattered light information acquisition unit comprises a light receiving unit and a calculation unit. The light receiving unit coherently detects the reference light and the scattered light and sends the resulting electrical signal to the calculation unit. The aforementioned arithmetic unit, The frequency f of the aforementioned variable frequency light source ｉ The longitudinal position x of the optical fiber in a reference distance coordinate system at regular intervals, obtained by changing the x ｊ , and the frequency f ｉ The intensity distribution of scattered light S(f) as a function of ｉ , x ｊ Regarding the optical fiber, a wavelength dispersion compensation means for compensating for the wavelength dispersion of the optical fiber, The intensity distribution S(f ｉ , x ｊ ) of the scattered light obtained by the wavelength dispersion compensation means, the intensity distributions S １ (f ｉ , x), S ２ (f ｉ + Δf, x) at the first time and the second time are acquired, and the cross-correlation function R(Δf, x) between the intensity distribution S １ (f ｉ , x) at the first time and the intensity distribution S ２ (f ｉ + Δf, x) at the second time is calculated, and a cross-correlation function calculation means for obtaining Δf at which the cross-correlation function R(Δf, x) becomes maximum A fiber optic sensor equipped with the following features.

2. The wavelength dispersion compensation means is The frequency f of the aforementioned variable frequency light source ｉ The time t obtained by changing ｊ , and the frequency f ｉ The intensity distribution of scattered light p(f) as a function of ｉ ,t ｊ The first means of obtaining ) Said time t ｊ The optical group velocity v in the optical fiber ｇ Using the position x in the aforementioned reference distance coordinate system ｊ A second means of converting to, Position x in the aforementioned reference distance coordinate system ｊ The position x in the distance coordinate system obtained by compensating for wavelength dispersion for each frequency. ｊ Using ', the intensity distribution of scattered light S(f ｉ , x ｊ A third means of obtaining ') Position x in the aforementioned distance coordinate system ｊ Interpolating ' to obtain the position x in the aforementioned reference distance coordinate system ｊ Intensity distribution of scattered light S(f ｉ , x ｊ A fourth means to obtain ) The optical fiber sensor according to claim 1, comprising:

3. In the third method described above, x is obtained using the parameter D that represents wavelength dispersion. ｊ ' = (1 + 2D × (f ｉ -f １ )) x ｊ According to the formula, the position x in the reference distance coordinate system ｊ position x in the aforementioned distance coordinate system ｊ Convert to ' The optical fiber sensor according to claim 2.

4. In the fourth means described above, the position x in the distance coordinate system is determined by cubic spline interpolation. ｊ Interpolate ' The optical fiber sensor according to claim 3.

5. The aforementioned calculation unit further, From the Δf obtained by the cross-correlation function calculation means, strain (temperature) information acquisition means obtains the temperature change or strain change of the optical fiber between the first time and the second time. An optical fiber sensor according to any one of claims 1 to 4, comprising:

6. At the first time point and the second time point, The process involves splitting a continuous beam of light into two, generating pulsed light from one of the two branches, and using the other branch as a reference beam. The process of injecting the aforementioned pulsed light into the optical fiber, The process of obtaining an electrical signal by coherently detecting the scattered light obtained when the pulse light is scattered in the optical fiber and the reference light. This is done by changing the frequency of the continuous light. moreover, The longitudinal position x of the optical fiber in a reference distance coordinate system with fixed intervals ｊ , and the frequency f ｉ The intensity distribution of scattered light S(f) as a function of ｉ , x ｊ Regarding the above, the process of compensating for the wavelength dispersion of the optical fiber, The intensity distribution S(f) of scattered light obtained by the wavelength dispersion compensation means ｉ , x ｊ ) From this, the intensity distribution S of scattered light at the first time and the second time. １ (f ｉ ,x), S ２ (f ｉ The intensity distribution S at the first time step is obtained by obtaining +Δf,x). １ (f ｉ (x), and the intensity distribution S at the second time step. ２ (f ｉ The process of calculating the cross-correlation function R(Δf, x) of +Δf, x, and obtaining the Δf that maximizes the cross-correlation function R(Δf, x) and A fiber optic sensing method comprising [a specific feature / feature].

7. The process for compensating for the aforementioned wavelength dispersion is as follows: The frequency f of the aforementioned variable frequency light source ｉ The time t obtained by changing ｊ , and the frequency f ｉ The intensity distribution of scattered light p(f) as a function of ｉ ,t ｊ The first step is to obtain ) and Said time t ｊ The optical group velocity v in the optical fiber ｇ Using the position x in the aforementioned reference distance coordinate system ｊ The second step is to convert to, Position x in the aforementioned reference distance coordinate system ｊ The position x in the distance coordinate system obtained by compensating for wavelength dispersion for each frequency. ｊ Using ', the intensity distribution of scattered light S(f ｉ , x ｊ The third step to obtaining ') Position x in the aforementioned distance coordinate system ｊ Interpolating ' to obtain the position x in the aforementioned reference distance coordinate system ｊ Intensity distribution of scattered light S(f ｉ , x ｊ The fourth step to obtain ) The optical fiber sensing method according to claim 6, comprising:

8. In the third step described above, x is calculated using the parameter D that represents wavelength dispersion. ｊ ' = (1 + 2D × (f ｉ -f １ )) x ｊ According to the formula, the position x in the reference distance coordinate system ｊ position x in the aforementioned distance coordinate system ｊ Convert to ' The optical fiber sensing method according to claim 7.

9. In the fourth step, the position x in the distance coordinate system is determined by cubic spline interpolation. ｊ Interpolate ' The optical fiber sensing method according to claim 8.

10. moreover, The process of obtaining the temperature change or strain change of the optical fiber between the first time and the second time from Δf obtained by the cross-correlation function calculation means. The optical fiber sensing method according to any one of claims 6 to 9, comprising:

11. A pulse light generation unit having a frequency-variable light source, which splits the continuous light generated by the frequency-variable light source into two, generates pulse light from one of the two branches, and uses the other as a reference light, The optical fiber into which the pulsed light is input, The optical fiber contains scattered light obtained when the pulsed light is scattered, and a scattered light information acquisition unit receives the reference light. The scattered light information acquisition unit of the optical fiber sensor, which is equipped with the following: The frequency f of the aforementioned variable frequency light source ｉ The longitudinal position x of the optical fiber in a reference distance coordinate system at regular intervals, obtained by changing the x ｊ , and the frequency f ｉ The intensity distribution of scattered light S(f) as a function of ｉ , x ｊ Regarding the optical fiber, a wavelength dispersion compensation means for compensating for the wavelength dispersion of the optical fiber, The intensity distribution S(f ｉ , x ｊ ) of the scattered light obtained by the wavelength dispersion compensation means, the intensity distributions S １ (f ｉ , x), S ２ (f ｉ + Δf, x) at the first time and the second time are acquired, and the cross-correlation function R(Δf, x) between the intensity distribution S １ (f ｉ Id=16]], x) at the first time and the intensity distribution S ２ (fId=19]] ｉ + Δf, x) at the second time is calculated, and the cross-correlation function calculation means for obtaining Δf at which the cross-correlation function R(Δf, x) becomes maximum A program designed to function as such.

12. The wavelength dispersion compensation means is The frequency f of the aforementioned variable frequency light source ｉ The time t obtained by changing ｊ , and the frequency f ｉ The intensity distribution of scattered light p(f) as a function of ｉ ,t ｊ The first means of obtaining ) the time t ｊ using the optical group velocity v in the optical fiber ｇ to convert to the position x in the reference distance coordinate system ｊ a second means for conversion Position x in the aforementioned reference distance coordinate system ｊ frequency f ｉ The position x in the distance coordinate system obtained by compensating for wavelength dispersion for each point ｊ Using ', the intensity distribution of scattered light S(f ｉ , x ｊ A third means to obtain ') Position x in the aforementioned distance coordinate system ｊ Interpolating ' to obtain the position x in the aforementioned reference distance coordinate system ｊ Intensity distribution of scattered light S(f ｉ , x ｊ ) to function as a fourth means of obtaining The program according to claim 11.

13. In the third method described above, x is obtained using the parameter D that represents wavelength dispersion. ｊ ' = (1 + 2D × (f ｉ -f １ )) x ｊ According to the formula, the position x in the reference distance coordinate system ｊ position x in the aforementioned distance coordinate system ｊ Convert to ' The program according to claim 12.

14. In the fourth means described above, the position x in the distance coordinate system is determined by cubic spline interpolation. ｊ Interpolate ' The program according to claim 13.

15. The scattered light information acquisition unit is further, From the Δf obtained by the cross-correlation function calculation means, strain (temperature) information acquisition means obtains the temperature change or strain change of the optical fiber between the first time and the second time. A program according to any one of claims 11 to 14 for functioning as such.

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