Optical fiber sensor, optical fiber sensing method, and program

Abstract

To eliminate the excessive light source control in a temperature strain measuring coherent OTDR.SOLUTION: An optical fiber sensor comprises a pulse light generation unit that has a frequency variable light source and generates pulse light and reference light, and a scattered light information acquisition unit that receives input of the reference light and scattered light that is the pulse light scattered in an optical fiber. The scattered light information acquisition unit comprises a light receiving unit and an operation unit. The light receiving unit performs coherent detection of the reference light and the scattered light and sends an obtained electric signal to the operation unit. The operation unit comprises: pulse width and frequency step width selection means that selects a frequency step width δf satisfying δf≤1 / 2Tp for the pulse width Tp of the pulse light; and cross-correlation function calculation means that changes the frequency f of the frequency variable light source at the frequency step width δf, calculates the cross-correlation function R(Δf, x) of the intensity distribution S1(f, x) at a first time and the intensity distribution S2(f+Δf, x) at a second time, and acquires Δfmax where the cross-correlation function R(Δf, x) becomes maximum.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical fiber sensor and an optical fiber sensing method suitable for use in, for example, a temperature strain measurement type coherent OTDR, and a program that can be used therefor. [Background technology]

[0002] With the development of optical fiber communications, there has been active research into technologies that use optical fiber itself as a sensing medium. In particular, optical fiber sensing, which uses scattered light, enables long-distance distributed sensing, unlike electrical sensors that measure at points.

[0003] Strain (temperature) sensors that use optical fiber as a sensing medium are broadly classified into BOTDR (Brillouin Optical Time Domain Reflectometry) that uses Brillouin scattered light (see, for example, Patent Document 1), and temperature strain measurement type coherent OTDR (Optical Time Domain Reflectometry) that uses Rayleigh scattered light.

[0004] Among these, the temperature strain measurement type coherent OTDR has high strain (temperature) sensitivity due to the frequency shift of Rayleigh scattered light, and therefore generally allows for more accurate measurements than the BOTDR method. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2015 / 059969 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the temperature strain measurement type coherent OTDR, the frequency of the light source needs to be changed stepwise, and precise control of the light source is required.

[0007] The present invention has been made in view of the above circumstances, and aims to provide an optical fiber sensor and an optical fiber sensing method, as well as a program that can be used for these, that enable selection of an appropriate frequency step width for improving frequency resolution by upsampling based on the relationship between the pulse width and the frequency step width of the light source in a temperature strain measurement coherent OTDR, and that eliminates the need for excessive light source control. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the optical fiber sensor of the present invention is configured to include a pulsed light generating unit that has a frequency-tunable light source, branches continuous light generated by the frequency-tunable light source into two, generates pulsed light from one of the two branches, and uses the other branch as reference light, an optical fiber into which the pulsed light is input, and a scattered light information acquiring unit into which scattered light generated by scattering the pulsed light in the optical fiber and the reference light are input.

[0009] The scattered light information acquisition unit includes a light receiving unit and a calculation unit. The light receiving unit coherently detects the reference light and the scattered light, and sends the obtained electrical signal to the calculation unit.

[0010] The calculation unit calculates the pulse width T p For δf≦1 / 2T p a pulse width / frequency step width selection means for selecting a frequency step width Δf that satisfies the following: a pulse width / frequency step width selection means for selecting a frequency step width Δf that satisfies the following: a pulse width / frequency step width selection means for selecting a frequency step width Δf that satisfies the following following: a pulse width / frequency step width selection means for selecting a frequency step width Δf that satisfies the following following following; a pulse width / frequency step width selection means for selecting a frequency step width Δf that satisfies the following following following following; a pulse width / frequency step width selection means for selecting a frequency step width Δf that satisfies the following following following following; max and a cross-correlation function calculation means for obtaining the cross-correlation function.

[0011] According to a preferred embodiment of the optical fiber sensor of the present invention, the calculation unit further includes 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.

[0012] Furthermore, in the optical fiber sensing method of the present invention, Δf≦1 / 2T is satisfied for a preset pulse width Tp. p At the first time and the second time, the continuous light is split into two, and one of the two branches is split into a pulse with a pulse width T p The steps of generating an optical pulse of f and using the other as a reference light, inputting the pulsed light into an optical fiber, and coherently detecting the scattered light of the pulsed light in the optical fiber and the reference light to obtain an electrical signal are performed while changing the frequency of the continuous light by a selected frequency step width Δf. Furthermore, a cross-correlation function R(Δf, x) between the intensity distribution S1(f, x) of the scattered light at a first time and the intensity distribution S2(f+Δf, x) at a second time is calculated, and a cross-correlation function R(Δf, x) is selected at a frequency step width Δf at which the cross-correlation function R(Δf, x) is maximized. max The process includes obtaining the

[0013] The program of the present invention also provides a program for an optical fiber sensor including: a pulsed light generating unit that has a frequency-variable light source, splits continuous light generated by the frequency-variable light source into two, generates pulsed light from one of the two splits, and uses the other split as reference light; an optical fiber to which the pulsed light is input; and a scattered light information acquiring unit to which scattered light generated by scattering the pulsed light in the optical fiber and the reference light are input, the program comprising: a pulsed light generating unit that generates pulsed light from one of the two splits and uses the other split as reference light; p For δf≦1 / 2T pa pulse width / frequency step width selection means for selecting a frequency step width Δf that satisfies the following: a frequency f of the frequency variable light source is changed by the frequency step width Δf, intensity distributions S1(f, x) and S2(f, x) at a first time and a second time are acquired as a function of a position x in the longitudinal direction of the optical fiber and the frequency f; a cross-correlation function R(Δf, x) between the intensity distribution S1(f, x) at the first time and the intensity distribution S2(f+Δf, x) at the second time is calculated; and a cross-correlation function R(Δf, x) is selected at which the cross-correlation function R(Δf, x) is maximized. max The function is to function as a cross-correlation function calculation means for obtaining the cross-correlation function.

[0014] According to a preferred embodiment of the program of the present invention, the scattered light information acquisition unit is further made to function as strain (temperature) information acquisition means for acquiring a temperature change or strain change in the optical fiber between a first time and a second time from Δf acquired by the cross-correlation function calculation means. [Effects of the Invention]

[0015] According to the optical fiber sensor and optical fiber sensing method of the present invention, and the program that can be used therefor, excessive light source control is no longer necessary in a temperature strain measurement type coherent OTDR. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram for explaining an optical fiber sensor according to the present invention; [Figure 2] FIG. 1 is a schematic diagram for explaining the principle of a temperature strain measurement type coherent OTDR. [Figure 3] Graphs of the measured Rayleigh scattering intensity for each optical pulse width are shown. [Figure 4] FIG. 10 is a diagram showing the results of measuring temperature changes. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and positional relationship of each component are merely shown in a schematic manner to enable understanding of the present invention. Furthermore, preferred configuration examples of the present invention will be described below. However, the materials and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many modifications and variations that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention. Note that, although some hatching is applied in the plan view, it should be understood that this does not represent a cross section, but is added to facilitate understanding of the invention.

[0018] (composition) The optical fiber sensor of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic diagram for explaining the optical fiber sensor of the present invention.

[0019] The optical fiber sensor of the present invention is an optical fiber sensor that uses temperature and strain measurement coherent OTDR technology. The optical fiber sensor of the present invention is used, for example, to measure strain and temperature. The optical fiber sensor is configured with a pulsed light generating unit 10, a circulator 20, an optical fiber 30, and a scattered light information acquiring unit 40.

[0020] The pulsed light generating unit 10 includes, for example, a frequency-tunable light source 12, a branching unit 13, an intensity modulator 14, a function generator 16, and an optical amplifier 18.

[0021] The frequency-tunable light source 12 generates continuous light having a frequency that is set according to the frequency step width Δf selected by the scattered light information acquisition unit 40. The continuous light generated by the frequency-tunable light source 12 is sent to a splitter 14.

[0022] Splitter 13 splits the continuous light sent from frequency-variable light source 12 into two at a predetermined splitting ratio. One of the two split by splitter 13 is sent to intensity modulator 14, and the other is sent to scattered light information acquisition unit 40 as reference light.

[0023] An acousto-optic modulator (AOM), for example, is used as the intensity modulator 14. The intensity modulator 14 generates optical pulses from the continuous light sent from the branching device 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 determined to be 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 pulses 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.

[0024] The optical amplifier 18 amplifies the optical pulses sent from the intensity modulator and sends them to the circulator 20. Note that an optical filter is often inserted after the optical amplifier 18 to remove amplified spontaneous emission (ASE) noise generated in the optical amplifier 14, but detailed explanation and illustration of this will be omitted here.

[0025] In this way, the pulsed light generating unit 10 generates an optical pulse, and the generated optical pulse is sent to the circulator 20. The pulsed light generating unit 10 also generates a reference light, and the generated reference light is sent to the scattered light information acquiring unit 40.

[0026] The circulator 20 has first to third ports, and 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.

[0027] In this example, the optical pulse sent from the pulsed light generating unit 10 is input to a first port of the circulator 20. The optical pulse input to the first port of the circulator 20 is output from a second port. The optical pulse output from the second port of the circulator 20 is sent to an optical fiber 30.

[0028] The optical fiber 30 is the object of measurement for strain and temperature. An optical pulse (input light) input into the optical fiber 30 to be measured undergoes Rayleigh scattering while propagating from the input end, which is the end on the circulator 20 side, toward the terminal end, which is the other end. The Rayleigh-scattered backscattered light (hereinafter also simply referred to as scattered light) propagates in the opposite direction to the input light, from the scattering point toward the input end of the optical fiber, and is output from the optical fiber 30 and sent to the circulator 20.

[0029] The scattered light sent to circulator 20 is input to the second port of circulator 20. The scattered light input to the second port of circulator 20 is output from the third port. The scattered light output from the third port of circulator 20 is sent to scattered light information acquisition unit 40.

[0030] The scattered light information acquisition section 40 is configured to include a light receiving section 50 and a calculation section 60.

[0031] The light receiving unit 50 coherently detects the scattered light generated in the optical fiber 30 using the reference light to generate an electrical signal. The light receiving unit 50 is configured with a coherent receiver 52, an opto-electric 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. An optical 90° hybrid coupler, for example, can be used as the coherent receiver 52.

[0032] When the modulation in the intensity modulator 14 is accompanied by a frequency shift, the detection in the coherent receiver 52 is heterodyne detection, and when the modulation in the intensity modulator 14 is not accompanied by a frequency shift, the detection is homodyne detection. Note that the scattered light received by the light receiving unit 50 may be configured to be input to the coherent receiver 52 after being amplified.

[0033] The combined light obtained by coherent detection in the coherent receiver 52 is output from the coherent receiver 52 and sent to an opto-electric converter 54 .

[0034] The photoelectric converter 54 is, for example, a photodiode (PD), and converts the multiplexed light generated by the coherent receiver 52 into an electric signal. The electric signal generated by the photoelectric converter 54 is sent to an AD converter 56.

[0035] 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 AD conversion in the AD converter 56 is sent to the calculation unit 60.

[0036] The calculation unit 60 may have any suitable configuration that performs digital signal processing, such as a commercially available personal computer (PC), and may include, for example, a RAM (Random Access Memory) 62, a ROM (Read Only Memory) 64, a storage means 66, and a CPU (Central Processing Unit) 70.

[0037] Here, the CPU 70 is assumed to realize predetermined functional means, which will be described later, by reading and executing a program stored in the ROM 64, but this is not limiting. The processing of each functional means is temporarily stored in the RAM 62, and the processing results of the calculation unit 60 and the intensity distribution S(f,x) at each time are stored in the storage means 66.

[0038] Note that illustration and description of input means, output means, communication means, etc. provided in the PC are omitted.

[0039] Furthermore, the pulsed light generating unit 10, circulator 20, optical fiber 30, and scattered light information acquiring unit 40 provided in the optical fiber sensor can have any suitable conventionally known configuration, except for the functional means realized by the scattered light information acquiring unit 40. Description of this suitable conventionally known configuration may be omitted.

[0040] (operation) The operation of the optical fiber sensor will now be described, including the function of each functional means.

[0041] Figure 2 is a schematic diagram illustrating the principle of a temperature strain measurement type coherent OTDR. A temperature strain measurement type coherent OTDR measures the intensity distribution of scattered light at two times, a first time and a second time, and extracts changes in strain and temperature based on the difference in the intensity distribution.

[0042] 2A shows the light input to the optical fiber 30 and the scattering centers at a first time instant. Here, the scattered light from each scattering center maintains the phase of the input light.

[0043] 2(B) shows the light input to the optical fiber 30 and the scattering center at a second time. If a change in strain or temperature occurs in the optical fiber 30 between the first time and the second time, the position of the scattering center changes, and the relative phase of the scattered light changes.

[0044] 2(C) shows the scattering center and the input light to the optical fiber 30 at the second time. The frequency (wavelength) is different from that of the input light at the first time. As described above, if a change in strain or temperature occurs between the first and second times, the position of the scattering center changes and the relative phase of the scattered light changes. However, by changing the frequency (wavelength) of the input light, the phase relationship can be restored to the same as that at the first time.

[0045] Cross-correlation function calculation means 74, which is a functional means, reads out the scattered light intensity distribution S1(f, x) at a first time and the scattered light intensity distribution S2(f, x) at a second time, which are stored in storage means 66. Then, cross-correlation function calculation means 74 calculates the cross-correlation function R(Δf, x) between 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):

[0046]

number

[0047] Here, 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 The frequency change Δf max The method for obtaining f is not limited to this example. Any other method may be used as long as it is possible to calculate the amount of deviation of f that makes the intensity distribution S1(f, x) at the first time and the intensity distribution S2(f+Δf, x) at the second time closest to each other.

[0048] The strain (temperature) information acquisition means 76 calculates the Δf max Using the above, the strain change amount Δε and the temperature change amount ΔT are obtained as strain (temperature) information by the following equation (2): f0 is the frequency of the continuous light generated by the frequency-variable light source at the first time instant.

[0049]

number

[0050] Here, there is a sampling theorem relationship between the pulse width of the incident pulsed light and the frequency step width of the light source, and if an inappropriate step width is selected, it will be impossible to measure temperature changes. Therefore, the optical fiber sensor of this invention is equipped with pulse width / frequency step width selection means 72.

[0051] In the temperature strain measurement type coherent OTDR, the complex electric field E(t) of the generated Rayleigh scattered light is expressed by the following equation (3).

[0052]

number

[0053] where f is the frequency of the light source, n is the refractive index, and n t is the refractive index at the scattering center of the light pulse that constitutes the Rayleigh scattered light at a certain time t. Also, r iis the scattering coefficient of Rayleigh scattered light. Here, we assume that the refractive index of the light pulse is uniform. The total phase T(t, n) of Rayleigh scattering at time t is given by the following equation (4).

[0054]

number

[0055] z i represents the position of the i-th Rayleigh scattering center. Therefore, the measured Rayleigh scattered light intensity distribution R(t) is given by the following equation (5).

[0056]

number

[0057] Consider the bandwidth of the signal S(f) when this Rayleigh scattering intensity distribution R(t) is considered as a function of the light source frequency f. By performing an inverse Fourier transform on S(f), the following equation (6) is obtained.

[0058]

number

[0059] Here, for simplicity, the scattering coefficient of Rayleigh scattered light r i is assumed to be constant. l ≦z i , z j ≦z m and z i -z j is the pulse width T of the input light pulse. p The distance x corresponds to half of p If we focus on the fact that the inverse Fourier transform of S(f) is determined by t x p / c≦t≦2n t x p Therefore, using an argument similar to the sampling theorem, it can be seen that the frequency step width Δf of the light source should satisfy the following equation (7):

[0060]

number

[0061] From the relationship in equation (7) above, it can be seen that shortening the pulse width allows for a larger frequency step width δf of the light source. Furthermore, if the condition in equation (7) above is met, it is suggested that interpolation will be possible in the subsequent signal processing.

[0062] Therefore, the pulse width / frequency step width selection means 72 selects the pulse width T p Then, the frequency step width Δf that satisfies the above formula (7) is selected by the cross-correlation function calculation means 74, and the frequency is changed by the frequency step width Δf to obtain Δf at which the cross-correlation function R(Δf, x) is maximized.

[0063] Figure 3 shows a graph of the Rayleigh scattering intensity measured for each optical pulse width. The horizontal axis shows time τ (unit: ns (nanoseconds)) and the vertical axis shows the Rayleigh scattering intensity (AU).

[0064] Here, the frequency step width was fixed at 100 MHz, and measurements were taken with pulse widths of 0.5 ns, 1.0 ns, 1.5 ns, 2.5 ns, and 5 ns. As shown in Figure 3, as the pulse width increases, the decrease in Rayleigh scattering intensity becomes more gradual, and the intensity increases up to a longer time τ. Since the time τ on the horizontal axis is proportional to the inverse of the frequency f, this corresponds to a broadening of the signal bandwidth.

[0065] The results of measuring the temperature change from 20 degrees to 25 degrees will be described with reference to Fig. 4. Fig. 4 is a diagram showing the results of measuring the temperature change. In Fig. 4, the horizontal axis represents the distance (unit: m) that input light propagates in the longitudinal direction of the optical fiber 30, and the vertical axis represents the temperature change (unit: degrees). Here, the thermostatic oven section is from 0 m to 45 m.

[0066] In Figures 4(A) and (B), the pulse width is 5 ns, and in Figures 4(C) and (D), the pulse width is 0.5 ns. Also, in Figures 4(A) and (C), the frequency step width is 100 MHz, and in Figures 4(B) and (D), the frequency step width is 600 MHz.

[0067] According to the above formula (7), when the pulse width is 5 ns, the frequency step width is 100 MHz or less, and when the pulse width is 0.5 ns, the frequency step width is 1000 MHz or less.

[0068] When the pulse width is 5 ns, the frequency width is 100 MHz, and in Figure 4(A), which satisfies the condition of 100 MHz or less given by equation (7) above, a temperature change of +5°C is measured correctly. On the other hand, when the pulse width is 5 ns, the frequency width is 600 MHz, and in Figure 4(B), which does not satisfy the condition of 100 MHz or less given by equation (7) above, a temperature change of +5°C is not measured correctly.

[0069] Furthermore, when the pulse width is 0.5 ns, the frequency width is 100 MHz in Figure 4(C) and 600 MHz in Figure 4(D), both of which satisfy the condition of 1000 MHz or less given by the above formula (7). In this case, a temperature change of +5°C is correctly measured in both Figures 4(C) and (D).

[0070] Thus, there is a sampling theorem relationship between the pulse width of the incident pulsed light and the frequency step width of the light source, and if an inappropriate step width is selected, it will be impossible to measure temperature changes. Also, if a frequency step width that satisfies the above constraints is selected, it will be possible to measure changes in strain (temperature) below the resolution determined by the frequency step width without degrading the information due to upsampling. [Explanation of symbols]

[0071] 10 Pulsed light generation unit 12 Frequency-tunable light source 13 Switch 14 Intensity Modulator 16 Function Generator 18 Optical Amplifier 20 Circulator 30 Optical Fiber 40 Scattered light information acquisition section 50 Light receiving part 52 Coherent Receiver 54 Photoelectric converter 56 AD converter 60 Arithmetic section 62 RAM 64 ROM 66 Memory means 70 CPU 72 Pulse width and frequency step width selection method 74 Cross-correlation function calculation means 76 Strain (temperature) information acquisition means

Claims

1. a pulsed light generating unit having a frequency variable light source, branching continuous light generated by the frequency variable light source into two beams, generating pulsed light from one of the two beams, and using the other beam as a reference beam; an optical fiber into which the pulsed light is input; a scattered light information acquisition unit to which scattered light obtained by scattering the pulsed light in the optical fiber and the reference light are input, the scattered light information acquisition unit includes a light receiving unit and a calculation unit, the light receiving unit coherently detects the reference light and the scattered light, and sends the obtained electrical signal to a calculation unit; The calculation unit The pulse width T of the pulsed light ｐ For δf≦1 / 2T ｐ a pulse width / frequency step width selection means for selecting a frequency step width δf that satisfies the following: The frequency f of the frequency variable light source is changed by the frequency step width δf, and the intensity distribution S at the first time and the second time is calculated as a function of the position x in the longitudinal direction of the optical fiber and the frequency f. １ (f, x), S ２ (f, x) is obtained, and the intensity distribution S １ (f, x) and the intensity distribution S at the second time ２ a cross-correlation function calculation means for calculating a cross-correlation function R(Δf, x) of (f, x) and obtaining Δf at which the cross-correlation function R(Δf, x) is maximized; Equipped with Fiber optic sensors.

2. The calculation unit further a strain (temperature) information acquiring 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 calculating means; Equipped with 2. The optical fiber sensor according to claim 1.

3. For a preset pulse width Tp, δf≦1 / 2T ｐ The process of selecting a frequency step width δf that satisfies Equipped with At the first time and the second time, Continuous light is split into two, and one of the two splits emits a pulse with a pulse width of T ｐ a process of generating a light pulse of the same wavelength and using the other light as a reference light; a step of injecting the pulsed light into an optical fiber; a step of obtaining an electrical signal by coherently detecting scattered light resulting from scattering of the pulsed light in the optical fiber and the reference light; is performed by varying the frequency of the continuous light by a selected frequency step width δf; moreover, The intensity distribution S of the scattered light at the first time １ (f, x) and the intensity distribution S at the second time ２ A process of calculating the cross-correlation function R(Δf, x) of (f, x) and obtaining Δf at which the cross-correlation function R(Δf, x) is maximized. Equipped with Fiber optic sensing methods.

4. moreover, a step of obtaining a temperature change or a strain change of the optical fiber between a first time and a second time from Δf obtained by the cross-correlation function calculation means. Equipped with The optical fiber sensing method according to claim 3 .

5. a pulsed light generating unit having a frequency variable light source, branching continuous light generated by the frequency variable light source into two beams, generating pulsed light from one of the two beams, and using the other beam as a reference beam; an optical fiber into which the pulsed light is input; a scattered light information acquisition unit to which scattered light resulting from scattering of the pulsed light in the optical fiber and the reference light are input; The scattered light information acquisition unit of the optical fiber sensor includes: The pulse width T of the pulsed light ｐ For δf≦1 / 2T ｐ a pulse width / frequency step width selection means for selecting a frequency step width δf that satisfies The frequency f of the frequency variable light source is changed by the frequency step width δf, and the intensity distribution S at the first time and the second time is calculated as a function of the position x in the longitudinal direction of the optical fiber and the frequency f. １ (f, x), S ２ (f, x) is obtained, and the intensity distribution S １ (f, x) and the intensity distribution S at the second time ２ Cross-correlation function calculation means for calculating the cross-correlation function R(Δf, x) of (f, x) and obtaining Δf at which the cross-correlation function R(Δf, x) is maximized A program to function as a

6. The scattered light information acquisition unit further comprises: a strain (temperature) information acquiring 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 calculating means; The program according to claim 5, for causing the program to function as:

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