Optical fiber condition measuring device and optical fiber condition measuring method

Abstract

The present disclosure involves, on the basis of first beat frequencies ΔR1, ΔR1' and second beat frequencies ΔR2, ΔR2' between fixed Brillouin frequency shift amounts BFSR1, BFSR2 of respective first reference optical fiber 7 and second reference optical fiber 9 and Brillouin frequency shift amounts BFSM, BFSM' of a measurement-subject optical fiber M in a temperature steady state or in a strain or oscillation non-applied state and in a temperature non‐steady state or in a strain or oscillation applied state, determining the direction, to be either a positive direction or a negative direction, regarding a change ΔBFS in the Brillouin frequency shift amounts of the measurement-subject optical fiber M, the change being associated with a transition from the steady state or the non-applied state to the non‐steady state or the applied state.

Description

[Technical field]

[0001] The present disclosure relates to a technique for measuring the temperature, strain, or vibration of an optical fiber under test. [Background technology]

[0002] A technique for measuring the temperature, strain, or vibration of an optical fiber under test based on the amount of Brillouin frequency shift of the optical fiber under test is disclosed in Patent Document 1 and the like.

[0003] In a general technique, a change in the Brillouin frequency shift of the optical fiber under test from the steady state or the non-applied state of strain or vibration to the non-steady state or the applied state is detected based on the Brillouin frequency shift of the optical fiber under test in a steady state of temperature or a non-applied state of strain or vibration and a non-steady state of temperature or a non-applied state of strain or vibration. Here, since the Brillouin frequency shift of the optical fiber under test is on the order of 10 GHz, a wideband light receiving device is required, and the optical fiber state measurement device configuration becomes complicated.

[0004] In Patent Document 1, a change in the Brillouin frequency shift of the optical fiber under test from a steady state or the non-applied state of strain or vibration to the non-steady state or the applied state is detected based on a beat frequency between the Brillouin frequency shift of the optical fiber under test and a constant Brillouin frequency shift of a reference optical fiber in a steady state of temperature or a non-applied state of strain or vibration and a non-steady state of temperature or a non-applied state of strain or vibration. Here, since the beat frequency between two Brillouin frequency shift amounts is on the order of 100 MHz, a broadband light receiving device is not required, and the optical fiber state measurement device configuration is simplified. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Daisuke Iida, Fumihiko Ito, "Low-frequency temperature sensing using stimulated Brillouin scattering reference light", IEICE Technical Report, Institute of Electronics, Information and Communication Engineers, OFT2008-43, vol.108, no.245, pp.45-50, 2008. Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, the beat frequency between two Brillouin frequency shift amounts indicates the absolute value of the difference between the two Brillouin frequency shift amounts, and does not indicate the sign of the difference between the two Brillouin frequency shift amounts. Therefore, it is possible to detect the magnitude of change in the Brillouin frequency shift amount of the measured optical fiber from a steady state of temperature or a state in which no strain or vibration is applied to a non-steady state of temperature or a state in which strain or vibration is applied, but it is not possible to detect the direction of change in the Brillouin frequency shift amount of the measured optical fiber.

[0007] Therefore, in order to solve the above problems, an object of the present disclosure is to eliminate the need for a broadband light receiving device, simplify the device configuration for measuring the state of an optical fiber, and detect the direction and magnitude of change in the amount of Brillouin frequency shift of a measured optical fiber from a steady state of temperature or a state in which no strain or vibration is applied to a non-steady state of temperature or a state in which strain or vibration is applied. [Means for solving the problem]

[0008] In order to solve the above problem, the direction of change in the Brillouin frequency shift amount of the measured optical fiber from the steady state or the non-applied state of strain or vibration to the non-steady state or the applied state is determined to be "one of the positive and negative directions" based on "two or more" beat frequencies between the Brillouin frequency shift amount of the measured optical fiber and the constant Brillouin frequency shift amounts of "two or more" reference optical fibers in a steady state of temperature or a non-applied state of strain or vibration and a non-steady state of temperature or an applied state of strain or vibration.

[0009] Specifically, the present disclosure relates to an optical fiber condition measuring device for measuring the temperature, strain or vibration of an optical fiber under test, the device comprising: a first reference optical fiber and a second reference optical fiber having an optical fiber length longer than the optical fiber under test, having a constant Brillouin frequency shift amount different from that of the optical fiber under test in a steady state of temperature or in a state in which strain or vibration is not applied for the same incident wavelength, and having constant Brillouin frequency shift amounts different from each other for the same incident wavelength; a test light input unit that inputs a pulsed measurement test light into the optical fiber under test, and inputs continuous light or pulsed first reference test light and second reference test light having the same wavelength as the measurement test light into the first reference optical fiber and the second reference optical fiber; a beat frequency detection unit that combines the measurement Brillouin scattered light and the first reference Brillouin scattered light and detects a first beat frequency thereof, and combines the measurement Brillouin scattered light and the second reference Brillouin scattered light and detects a second beat frequency thereof; and a shift amount change detection unit that detects a direction of change, i.e., a sign of a Brillouin frequency shift amount of the measurement optical fiber from a steady state or an unapplied state to an unsteady state or an applied state, based on the first beat frequency and the second beat frequency in a steady state of temperature or a state in which strain or vibration is not applied of the measurement optical fiber and a unsteady state of temperature or a state in which strain or vibration is applied of the measurement optical fiber.

[0010] The present disclosure also provides an optical fiber condition measuring method for measuring the temperature, strain or vibration of a test optical fiber, comprising the steps of: utilizing a first reference optical fiber and a second reference optical fiber having an optical fiber length longer than the test optical fiber, having a constant Brillouin frequency shift amount different from that of the test optical fiber in a steady state of temperature or in a state in which strain or vibration is not applied for the same incident wavelength, and having constant Brillouin frequency shift amounts different from each other for the same incident wavelength, and inputting a pulsed measurement test light into the test optical fiber, and inputting continuous light or pulsed first reference test light and second reference test light having the same wavelength as the measurement test light into the first reference optical fiber and the second reference optical fiber; a beat frequency detection step of multiplexing the measurement Brillouin scattered light and the first reference Brillouin scattered light and detecting a first beat frequency thereof and multiplexing the measurement Brillouin scattered light and the second reference Brillouin scattered light and detecting a second beat frequency thereof; and a shift amount change detection step of detecting a direction, i.e., a sign, of a change in the Brillouin frequency shift amount of the measurement optical fiber from a steady state or a non-applied state to an unsteady state or an applied state based on the first beat frequency and the second beat frequency in a steady state of temperature or a non-applied state of strain or vibration of the measurement optical fiber and an unsteady state of temperature or a applied state of strain or vibration of the measurement optical fiber.

[0011] These configurations make it possible to simplify the configuration of the optical fiber state measurement device while eliminating the need for a broadband light receiving device, and to detect the direction, or sign, of change in the Brillouin frequency shift amount of the measured optical fiber from a steady state of temperature or a state in which no strain or vibration is applied to a non-steady state of temperature or a state in which strain or vibration is applied.

[0012] The present disclosure also relates to an optical fiber condition measurement device, wherein the shift amount change detection unit detects a direction of change in the Brillouin frequency shift amount of the measured optical fiber from the steady state or the non-voltage applied state to the unsteady state or the applied state, based on a direction of change in the first beat frequency and a direction of change in the second beat frequency from the steady state or the non-voltage applied state to the unsteady state or the applied state.

[0013] According to this configuration, the direction, i.e., sign, of change in the amount of Brillouin frequency shift of the measured optical fiber can be easily detected based on the direction, i.e., sign (regardless of the magnitude, i.e., absolute value) of change in two or more types of beat frequencies from a steady state of temperature or a state in which no strain or vibration is applied to a non-steady state of temperature or a state in which strain or vibration is applied.

[0014] The present disclosure also relates to an optical fiber condition measurement device, wherein the shift amount change detection unit determines a direction of change in the Brillouin frequency shift amount of the measured optical fiber from the steady state or the non-voltage application state to the unsteady state or the voltage application state, based on a magnitude relationship between the first beat frequency and the second beat frequency in the unsteady state or the voltage application state, if the shift amount change detection unit cannot determine the direction of change in the Brillouin frequency shift amount of the measured optical fiber from the steady state or the non-voltage application state to the unsteady state or the voltage application state.

[0015] According to this configuration, if the direction of change, i.e., the sign, of the Brillouin frequency shift of the optical fiber under test cannot be determined using the direction of change, i.e., the sign, of the two or more beat frequencies, it is possible to reliably determine the direction of change, i.e., the sign, of the Brillouin frequency shift of the optical fiber under test based on the magnitude relationship between the two or more beat frequencies (regardless of the absolute value of each frequency) in a non-steady state of temperature or in a state where strain or vibration is applied.

[0016] The present disclosure also relates to an optical fiber condition measurement device, wherein the shift amount change detection unit detects a magnitude of change, i.e., an absolute value, of the Brillouin frequency shift amount of the measured optical fiber from the steady state or the non-voltage applied state to the unsteady state or the applied state, based on the first beat frequency and the second beat frequency in the steady state or the non-voltage applied state and the unsteady state or the applied state.

[0017] According to this configuration, a broadband light receiving device is not required, and the device configuration for measuring the state of an optical fiber can be simplified. It is possible to detect the magnitude of change, i.e., the absolute value, of the amount of Brillouin frequency shift of the optical fiber under test from a steady state of temperature or a state in which no strain or vibration is applied to a non-steady state of temperature or a state in which strain or vibration is applied.

[0018] The present disclosure also relates to an optical fiber condition measuring device, characterized in that the mutually different constant Brillouin frequency shift amounts of the first reference optical fiber and the second reference optical fiber are different from the Brillouin frequency shift amount of the measured optical fiber in the steady state or in the non-voltage-applied state by a Brillouin gain bandwidth or more.

[0019] According to this configuration, any beat frequency is unlikely to fall to the baseband frequency, so that it can be detected on the order of 100 MHz or 10 MHz. Also, it is possible to detect a wide range of change in the Brillouin frequency shift amount as the change in the Brillouin frequency shift amount of the optical fiber under test from a steady state of temperature or a state in which no strain or vibration is applied to a non-steady state of temperature or a state in which strain or vibration is applied.

[0020] The present disclosure also provides an optical fiber condition measuring device, characterized in that if the first beat frequency or the second beat frequency cannot be clearly measured in the unsteady state or the applied light state, the shift amount change detection unit utilizes a third reference optical fiber having a constant Brillouin frequency shift amount different from the Brillouin frequency shift amount in the steady state or the non-applied light state of the measured optical fiber and the different constant Brillouin frequency shift amounts of the first reference optical fiber and the second reference optical fiber.

[0021] According to this configuration, even if any beat frequency falls to the baseband frequency, the beat frequency replacing the beat frequency is unlikely to fall to the baseband frequency, so that it is possible to detect the Brillouin frequency shift in the order of 100 MHz or 10 MHz. Also, it is possible to detect a wide range of change in the Brillouin frequency shift amount as the change in the Brillouin frequency shift amount of the measured optical fiber from a steady state of temperature or a state in which no strain or vibration is applied to a non-steady state of temperature or a state in which strain or vibration is applied. Effect of the Invention

[0022] In this way, the present disclosure eliminates the need for a broadband light receiving device, simplifies the device configuration for measuring the state of an optical fiber, and makes it possible to detect the direction and magnitude of change in the amount of Brillouin frequency shift of the optical fiber under test from a steady state of temperature or a state in which no strain or vibration is applied to a non-steady state of temperature or a state in which strain or vibration is applied. [Brief description of the drawings]

[0023] [Figure 1] 1 is a diagram showing a configuration of an optical fiber state measuring device according to the present disclosure. [Diagram 2] FIG. 2 is a diagram showing a procedure of an optical fiber state measurement process according to the present disclosure. [Diagram 3] 5A to 5C are diagrams illustrating a specific example of an optical fiber state measurement process according to the first embodiment. [Figure 4] 5A to 5C are diagrams illustrating a specific example of an optical fiber state measurement process according to the first embodiment. [Diagram 5] 13A to 13C are diagrams illustrating a specific example of an optical fiber state measurement process according to the second embodiment. [Figure 6] 13A to 13C are diagrams illustrating a specific example of an optical fiber state measurement process according to the second embodiment. [Figure 7] FIG. 4 is a diagram showing the amount of Brillouin frequency shift in the first and second reference optical fibers. [Figure 8] FIG. 13 is a diagram showing the amount of Brillouin frequency shift in the third reference optical fiber. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present disclosure will be described with reference to the accompanying drawings. The embodiments described below are examples of the present disclosure, and the present disclosure is not limited to the following embodiments.

[0025] (Configuration of the optical fiber state measuring device of the present disclosure) The configuration of the optical fiber condition measuring device of the present disclosure is shown in Fig. 1. The procedure of the optical fiber condition measuring process of the present disclosure is shown in Fig. 2. The optical fiber condition measuring device D measures the temperature, strain, or vibration of the optical fiber M to be measured using BOTDR (Brillouin Optical Time Domain Reflectometry).

[0026] The optical fiber state measuring device D comprises a light source 1, a branching unit 2, a pulsating unit 3, a circulator 4, a branching unit 5, a circulator 6, a first reference optical fiber 7, a circulator 8, a second reference optical fiber 9, a branching unit 10, a combining unit 11, a first beat frequency detecting unit 12, a combining unit 13, a second beat frequency detecting unit 14, and a shift amount change detecting unit 15. The first beat frequency detecting unit 12, the second beat frequency detecting unit 14, and the shift amount change detecting unit 15 can be realized by installing the optical fiber state measuring program shown in Fig. 2 in a computer.

[0027] The first reference optical fiber 7 has an optical fiber length longer than the measured optical fiber M, and measures the Brillouin frequency shift BFS of the measured optical fiber M at a steady temperature state or in a state where no strain or vibration is applied, for the same incident wavelength λ. M A constant Brillouin frequency shift BFS R1 (≠ BFS below R2 The second reference optical fiber 9 has an optical fiber length longer than the measured optical fiber M, and for the same incident wavelength λ, measures the Brillouin frequency shift BFS of the measured optical fiber M in a steady state of temperature or in a state where no strain or vibration is applied. M A constant Brillouin frequency shift BFS R2 (≠ BFS above R1 ).

[0028] The Brillouin frequency shift of the optical fiber M under test is expressed as follows: M However, in a non-steady state of temperature or under strain or vibration, the BFS M The constant Brillouin frequency shift amount BFS of the first reference optical fiber 7 and the second reference optical fiber 9 changes to R1 , B.F.S. R2 may be set to a constant value by housing the first reference optical fiber 7 and the second reference optical fiber 9 in a thermostatic chamber capable of adjusting the temperature, or may be set to a constant value by making the materials, refractive index distribution in the cross section, or type of the first reference optical fiber 7 and the second reference optical fiber 9 different.

[0029] The light source 1, the branching unit 2, the pulsing unit 3, and the circulator 4 inject a pulsed measurement test light into the optical fiber M to be measured. The light source 1, the branching unit 2, the branching unit 5, and the circulator 6 inject a first reference test light, which is continuous light or a pulsed first reference test light having the same wavelength λ as the measurement test light, into the first reference optical fiber 7. The light source 1, the branching unit 2, the branching unit 5, and the circulator 8 inject a second reference test light, which is continuous light or a pulsed second reference test light having the same wavelength λ as the measurement test light, into the second reference optical fiber 9. By injecting continuous light as the first reference test light and the second reference test light, it is possible to obtain high-intensity Brillouin scattered light.

[0030] The circulator 4 and the branching section 10 input pulsed measurement Brillouin scattered light from the measured optical fiber M. The circulator 6 inputs continuous light or pulsed first reference Brillouin scattered light from the first reference optical fiber 7. The circulator 8 inputs continuous light or pulsed second reference Brillouin scattered light from the second reference optical fiber 9. By inputting continuous light as the first reference Brillouin scattered light and the second reference Brillouin scattered light, a highly accurate Brillouin frequency shift amount can be obtained.

[0031] The multiplexing unit 11 and the first beat frequency detection unit 12 multiplex the measurement Brillouin scattered light and the first reference Brillouin scattered light, and detect a first beat frequency between the measurement Brillouin scattered light and the first reference Brillouin scattered light (step S1). The first beat frequency between the measurement Brillouin scattered light and the first reference Brillouin scattered light is expressed as follows: ΔR1=|BFS M -BFS R1 However, in a non-steady state of temperature or under strain or vibration, ΔR1'=|BFS M '-BFS R1 |is.

[0032] The multiplexing unit 13 and the second beat frequency detection unit 14 multiplex the measurement Brillouin scattered light and the second reference Brillouin scattered light, and detect the second beat frequency between the measurement Brillouin scattered light and the second reference Brillouin scattered light (step S1). The second beat frequency between the measurement Brillouin scattered light and the second reference Brillouin scattered light is expressed as follows: ΔR2=|BFS M -BFS R2 However, in a non-steady state of temperature or under strain or vibration, ΔR2'=|BFS M '-BFS R2 |is.

[0033] The first beat frequency detecting section 12 and the second beat frequency detecting section 14 may be capable of detecting the first beat frequency and the second beat frequency one or more times for one pulse of measurement Brillouin scattered light input with a delay time corresponding to a certain point of the measured optical fiber M.

[0034] The shift amount change detection unit 15 detects the direction, i.e., sign, of the change in the Brillouin frequency shift amount ΔBFS of the measured optical fiber M from the steady state or the non-applied state of application of strain or vibration to the non-steady state or the applied state based on the first beat frequency ΔR1, ΔR1' and the second beat frequency ΔR2, ΔR2' in the steady state of temperature or the non-applied state of strain or vibration and the non-steady state of temperature or the applied state of strain or vibration (step S2). The sign of the change in the Brillouin frequency shift amount ΔBFS of the measured optical fiber M is expressed as sgn(ΔBFS)=sgn(BFS M '-BFS M ) and will be described in detail in the first and second embodiments.

[0035] In this way, it is possible to eliminate the need for a broadband light receiving device, simplify the device configuration for measuring the optical fiber state, and detect the direction, i.e., sign, of the change ΔBFS in the Brillouin frequency shift amount of the measured optical fiber M from a steady state of temperature or a state in which no strain or vibration is applied to a non-steady state of temperature or a state in which strain or vibration is applied.

[0036] The shift amount change detection unit 15 detects the magnitude, i.e., absolute value, of the change ΔBFS in the Brillouin frequency shift of the measured optical fiber M from the steady state or the non-applied state of application of strain or vibration to the non-steady state or the applied state based on the first beat frequency ΔR1, ΔR1' and the second beat frequency ΔR2, ΔR2' in the steady state of temperature or the non-applied state of strain or vibration and the non-steady state of temperature or the applied state of strain or vibration (step S3). The absolute value of the change ΔBFS in the Brillouin frequency shift of the measured optical fiber M is expressed as |ΔBFS|=|BFS M '-BFS M This will be explained in detail in the first and second embodiments.

[0037] In this way, it is possible to eliminate the need for a broadband light receiving device, simplify the device configuration for measuring the optical fiber state, and detect the magnitude, i.e., absolute value, of the change ΔBFS in the Brillouin frequency shift amount of the measured optical fiber M from a steady state of temperature or a state in which no strain or vibration is applied to a non-steady state of temperature or a state in which strain or vibration is applied.

[0038] (Specific example of optical fiber state measurement process in the first embodiment) A specific example of the optical fiber state measurement process of the first embodiment is shown in Fig. 3 and Fig. 4. The pre-change state S11 is a steady temperature state or a state in which no strain or vibration is applied. The post-change states S12 to S17 are unsteady temperature states or states in which strain or vibration is applied.

[0039] In the pre-change state S11, BFS R1 <BFS M <BFS R2 holds. BFS M is BFS R1 and BFS R2 sgn(ΔBFS) indicates no shift, and |ΔBFS|=0, ΔR1-ΔR1'=0, and ΔR2-ΔR2'=0 hold.

[0040] In the post-change state S12, BFS M ' is BFS MStarting from the starting point, a downshift is performed with a shift amount smaller than ΔR1. sgn(ΔBFS) indicates a downshift, and |ΔBFS|=ΔR1-ΔR1'=ΔR2'-ΔR2, ΔR1-ΔR1'>0, ΔR2-ΔR2'<0 holds, and ΔR1+ΔR2=ΔR1'+ΔR2' also holds.

[0041] In the post-change state S13, BFS M ' is BFS M Starting from the starting point, it is upshifted by a shift amount smaller than ΔR2. sgn(ΔBFS) indicates an upshift, and |ΔBFS|=ΔR1'-ΔR1=ΔR2-ΔR2', ΔR1-ΔR1'<0, ΔR2-ΔR2'>0 holds, and ΔR1+ΔR2=ΔR1'+ΔR2' also holds.

[0042] In the post-change state S14, BFS M ' is BFS M Starting from the starting point, a downshift is performed with a shift amount larger than ΔR1. sgn(ΔBFS) indicates a downshift, and |ΔBFS|=ΔR1+ΔR1'=ΔR2'-ΔR2, ΔR1-ΔR1'>0, ΔR2-ΔR2'<0 holds, and ΔR1+ΔR2=ΔR2'-ΔR1' also holds.

[0043] In the post-change state S15, BFS M ' is BFS M Starting from the starting point, it is upshifted by a shift amount larger than ΔR2. sgn(ΔBFS) indicates an upshift, and |ΔBFS|=ΔR1'-ΔR1=ΔR2+ΔR2', ΔR1-ΔR1'<0, ΔR2-ΔR2'>0 holds, and ΔR1+ΔR2=ΔR1'-ΔR2' also holds.

[0044] In the post-change state S16, BFS M ' is BFS M Starting from the starting point, a downshift is performed with a larger shift amount compared to the post-change state S14. sgn(ΔBFS) indicates a downshift, and |ΔBFS|=ΔR1+ΔR1'=ΔR2'-ΔR2, ΔR1-ΔR1'<0, ΔR2-ΔR2'<0 are satisfied, and ΔR1'<ΔR2' is also satisfied.

[0045] In the post-change state S17, BFS M ' is BFS M Starting from the changed state S15, an upshift occurs with a larger shift width compared to the changed state S15. sgn(ΔBFS) indicates an upshift, and |ΔBFS|=ΔR1'-ΔR1=ΔR2+ΔR2', ΔR1-ΔR1'<0, ΔR2-ΔR2'<0 holds, and ΔR1'>ΔR2' also holds.

[0046] The shift amount change detection unit 15 needs to detect unknown information sgn(ΔBFS) and |ΔBFS| based on known information ΔR1, ΔR1', ΔR2, and ΔR2'.

[0047] The shift amount change detection unit 15 can detect sgn(ΔBFS)=downshift based on ΔR1-ΔR1'>0 and ΔR2-ΔR2'<0, but cannot detect |ΔBFS| (see post-change state S12, S14). Therefore, the shift amount change detection unit 15 can detect |ΔBFS|=ΔR1-ΔR1'=ΔR2'-ΔR2 based on ΔR1+ΔR2=ΔR1'+ΔR2' (see post-change state S12). On the other hand, the shift amount change detection unit 15 can detect |ΔBFS|=ΔR1+ΔR1'=ΔR2'-ΔR2 based on ΔR1+ΔR2=ΔR2'-ΔR1' (see post-change state S14).

[0048] The shift amount change detection unit 15 can detect sgn(ΔBFS)=upshift based on ΔR1-ΔR1'<0, ΔR2-ΔR2'>0, but cannot detect |ΔBFS| (see post-change state S13, S15). Therefore, the shift amount change detection unit 15 can detect |ΔBFS|=ΔR1'-ΔR1=ΔR2-ΔR2' based on ΔR1+ΔR2=ΔR1'+ΔR2' (see post-change state S13). On the other hand, the shift amount change detection unit 15 can detect |ΔBFS|=ΔR1'-ΔR1=ΔR2+ΔR2' based on ΔR1+ΔR2=ΔR1'-ΔR2' (see post-change state S15).

[0049] The shift amount change detection unit 15 cannot detect sgn(ΔBFS) based on ΔR1-ΔR1'<0 and ΔR2-ΔR2'<0 (see post-change state S16, S17). Therefore, the shift amount change detection unit 15 can detect sgn(ΔBFS)=downshift, |ΔBFS|=ΔR1+ΔR1'=ΔR2'-ΔR2 based on ΔR1'<ΔR2' (see post-change state S16). On the other hand, the shift amount change detection unit 15 can detect sgn(ΔBFS)=upshift, |ΔBFS|=ΔR1'-ΔR1=ΔR2+ΔR2' based on ΔR1'>ΔR2' (see post-change state S17).

[0050] Note that the shift amount change detection section 15 may use either of the two types of detection values ​​as |ΔBFS|, or may use the average value of both to improve accuracy.

[0051] (Specific example of optical fiber state measurement process in the second embodiment) A specific example of the optical fiber state measurement process of the second embodiment is shown in Fig. 5 and Fig. 6. The pre-change state S21 is a steady temperature state or a state in which no strain or vibration is applied. The post-change states S22 to S26 are unsteady temperature states or states in which strain or vibration is applied.

[0052] In the pre-change state S21, BFS M <BFS R1 <BFS R2 holds. BFS R1 is BFS M and BFS R2 sgn(ΔBFS) indicates no shift, and |ΔBFS|=0, ΔR1-ΔR1'=0, and ΔR2-ΔR2'=0 hold.

[0053] In the post-change state S22, BFS M ' is BFS MStarting from the starting point, downshifting is performed by any shift amount (regardless of the magnitude relationship with ΔR1 and ΔR2). sgn(ΔBFS) indicates a downshift, and |ΔBFS|=ΔR1'-ΔR1=ΔR2'-ΔR2, ΔR1-ΔR1'<0, ΔR2-ΔR2'<0, and ΔR1'<ΔR2' are also true.

[0054] In the post-change state S23, BFS M ' is BFS M Starting from , it is upshifted with a shift width smaller / smaller than ΔR1 / ΔR2. sgn(ΔBFS) indicates an upshift, and |ΔBFS|=ΔR1-ΔR1'=ΔR2-ΔR2', ΔR1-ΔR1'>0, ΔR2-ΔR2'>0 holds, and ΔR2-ΔR1=ΔR2'-ΔR1' also holds.

[0055] In the post-change state S24, BFS M ' is BFS M Starting from , it is upshifted by a shift amount larger / smaller than ΔR1 / ΔR2. sgn(ΔBFS) indicates an upshift, and |ΔBFS|=ΔR1+ΔR1'=ΔR2-ΔR2', ΔR1-ΔR1'>0, ΔR2-ΔR2'>0 holds, and ΔR2-ΔR1=ΔR1'+ΔR2' also holds.

[0056] In the post-change state S25, BFS M ' is BFS M Starting from , it is upshifted by a shift amount larger than ΔR1 / ΔR2. sgn(ΔBFS) indicates an upshift, and |ΔBFS|=ΔR1+ΔR1'=ΔR2+ΔR2', ΔR1-ΔR1'<0, ΔR2-ΔR2'>0 holds, and ΔR2-ΔR1=ΔR1'-ΔR2' also holds.

[0057] In the post-change state S26, BFS M ' is BFS MStarting from ΔR1 / ΔR2, it is upshifted by a shift amount larger than / even larger than ΔR1 / ΔR2. sgn(ΔBFS) indicates an upshift, and |ΔBFS|=ΔR1+ΔR1'=ΔR2+ΔR2', ΔR1-ΔR1'<0, ΔR2-ΔR2'<0 hold, and ΔR1'>ΔR2' also holds.

[0058] The shift amount change detection unit 15 needs to detect unknown information sgn(ΔBFS) and |ΔBFS| based on known information ΔR1, ΔR1', ΔR2, and ΔR2'.

[0059] The shift amount change detection unit 15 can detect sgn(ΔBFS)=upshift based on ΔR1-ΔR1'>0, ΔR2-ΔR2'>0, but cannot detect |ΔBFS| (see post-change state S23, S24). Therefore, the shift amount change detection unit 15 can detect |ΔBFS|=ΔR1-ΔR1'=ΔR2-ΔR2' based on ΔR2-ΔR1=ΔR2'-ΔR1' (see post-change state S23). On the other hand, the shift amount change detection unit 15 can detect |ΔBFS|=ΔR1+ΔR1'=ΔR2-ΔR2' based on ΔR2-ΔR1=ΔR1'+ΔR2' (see post-change state S24).

[0060] The shift amount change detection unit 15 can detect sgn(ΔBFS) = upshift based on ΔR1-ΔR1'<0, ΔR2-ΔR2'>0, and can detect |ΔBFS| = ΔR1 + ΔR1' = ΔR2 + ΔR2' (see post-change state S25).

[0061] The shift amount change detection unit 15 cannot detect sgn(ΔBFS) based on ΔR1-ΔR1'<0 and ΔR2-ΔR2'<0 (see post-change state S22, S26). Therefore, the shift amount change detection unit 15 can detect sgn(ΔBFS)=downshift, |ΔBFS|=ΔR1'-ΔR1=ΔR2'-ΔR2 based on ΔR1'<ΔR2' (see post-change state S22). On the other hand, the shift amount change detection unit 15 can detect sgn(ΔBFS)=upshift, |ΔBFS|=ΔR1+ΔR1'=ΔR2+ΔR2' based on ΔR1'>ΔR2' (see post-change state S26).

[0062] Note that the shift amount change detection section 15 may use either of the two types of detection values ​​as |ΔBFS|, or may use the average value of both to improve accuracy.

[0063] (Brillouin frequency shift of the reference optical fiber) In this way, the direction, i.e., sign, of the change in the Brillouin frequency shift amount ΔBFS of the measured optical fiber M can be easily detected based on the direction, i.e., sign (regardless of the magnitude, i.e., absolute value) of two or more types of beat frequency change from a steady state of temperature or a state in which no strain or vibration is applied to a non-steady state of temperature or a state in which strain or vibration is applied.

[0064] If the direction, i.e., sign, of the change in the Brillouin frequency shift amount ΔBFS of the measured optical fiber M cannot be determined using the direction, i.e., sign, of the change in the two or more beat frequencies, it is possible to reliably determine the direction, i.e., sign, of the change in the Brillouin frequency shift amount ΔBFS of the measured optical fiber M based on the magnitude relationship between the two or more beat frequencies (regardless of the absolute value of each frequency) in a non-steady state of temperature or in a state where strain or vibration is applied.

[0065] In order to properly detect the above two types of beat frequencies, a certain Brillouin frequency shift amount BFS of the first reference optical fiber 7 and the second reference optical fiber 9 is set. R1 , B.F.S. R2 is the Brillouin frequency shift BFS of the optical fiber M to be measured. MSet appropriately for.

[0066] The Brillouin frequency shift amounts of the first and second reference optical fibers are shown in FIG. 7. The constant Brillouin frequency shift amount BFS of the first reference optical fiber 7 and the second reference optical fiber 9 R1 , B.F.S. R2 is the Brillouin frequency shift amount BFS of the optical fiber M to be measured in the steady state or in the non-energized state. M is greater than the Brillouin gain bandwidth ΔBGS.

[0067] In the upper part of FIG. 7, in the first embodiment of FIGS. R1 <BFS M <BFS R2 Then, ΔR1=|BFS M -BFS R1 |>ΔBGS, ΔR2=|BFS M -BFS R2 In the lower part of FIG. 7, in the second embodiment of FIG. M <BFS R1 <BFS R2 Then, ΔR1=|BFS M -BFS R1 |>ΔBGS, ΔR2=|BFS M -BFS R2 |>2ΔBGS is set.

[0068] In this way, any beat frequency is unlikely to fall to the baseband frequency, and can be detected on the order of 100 MHz or 10 MHz. A wide range of change in the Brillouin frequency shift amount can be detected as the change ΔBFS in the Brillouin frequency shift amount of the measured optical fiber M from a steady state of temperature or a state in which no strain or vibration is applied to a non-steady state of temperature or a state in which strain or vibration is applied.

[0069] In order to reliably detect the two types of beat frequencies, a certain Brillouin frequency shift amount BFS of a third reference optical fiber (not shown in FIG. 1) is added. R3 will be newly added.

[0070] The Brillouin frequency shift amount of the third reference optical fiber is shown in Fig. 8. If the first beat frequency ΔR1' or the second beat frequency ΔR2' cannot be clearly measured in the non-steady state or in the applied state, the shift amount change detection unit 15 detects the Brillouin frequency shift amount BFS M and a constant Brillouin frequency shift amount BFS of the first reference optical fiber 7 and the second reference optical fiber 9. R1 , B.F.S. R2 BFS with a constant Brillouin frequency shift different from R3 A third reference optical fiber having a

[0071] In the upper part of FIG. 8, in the first embodiment of FIGS. M '-BFS R1 When |< 3 dB bandwidth of the Brillouin scattering spectrum, BFS R3 <BFS R1 , |BFS R3 -BFS R1 |>3 dB bandwidth of the Brillouin scattering spectrum, ΔR3'=|BFS M '-BFS R3 |>3 dB bandwidth of the Brillouin scattering spectrum. On the other hand, in the first embodiment of FIGS. M '-BFS R2 When |< 3 dB bandwidth of the Brillouin scattering spectrum, BFS R3 >BFS R2 , |BFS R3 -BFS R2 |>3 dB bandwidth of the Brillouin scattering spectrum, ΔR3'=|BFS M '-BFS R3 |>The 3 dB bandwidth of the Brillouin scattering spectrum can be used.

[0072] In the lower part of FIG. 8, in the second embodiment of FIGS. M '-BFS R1 When |< 3 dB bandwidth of the Brillouin scattering spectrum, BFSR3 <BFS R1 , |BFS R3 -BFS R1 |>3 dB bandwidth of the Brillouin scattering spectrum, ΔR3'=|BFS M '-BFS R3 |>3 dB bandwidth of the Brillouin scattering spectrum. On the other hand, in the second embodiment of FIGS. M '-BFS R2 When |< 3 dB bandwidth of the Brillouin scattering spectrum, BFS R3 >BFS R2 , |BFS R3 -BFS R2 |>3 dB bandwidth of the Brillouin scattering spectrum, ΔR3'=|BFS M '-BFS R3 |>The 3 dB bandwidth of the Brillouin scattering spectrum can be used.

[0073] In this way, even if any beat frequency falls to the baseband frequency, the beat frequency replacing that beat frequency is less likely to fall to the baseband frequency, and so it is possible to detect it on the order of 100 MHz or 10 MHz. And, it is possible to detect a wide range of change in the Brillouin frequency shift amount as the change amount ΔBFS of the Brillouin frequency shift amount of the measured optical fiber M from a steady state of temperature or a state in which no strain or vibration is applied to a non-steady state of temperature or a state in which strain or vibration is applied. [Industrial Applicability]

[0074] The optical fiber condition measuring device and optical fiber condition measuring method disclosed herein can eliminate the need for a broadband light receiving device when measuring temperature changes, strain changes, or vibration states of the optical fiber to be measured, and can simplify the device configuration for measuring the optical fiber condition.

[0075] In general, since the change in the Brillouin frequency shift amount is detected while sequentially changing the test light frequency, it is not possible to measure a phenomenon that changes rapidly, such as a vibration phenomenon. In the present disclosure, the change in the Brillouin frequency shift amount is detected only by monitoring the beat frequency, so that it is possible to measure a phenomenon that changes rapidly, such as a vibration phenomenon. [Explanation of symbols]

[0076] D: Optical fiber condition measuring device M: Optical fiber under test 1:Light source 2: Branching section 3: Pulse generator 4: Circulator 5: Branching section 6: Circulator 7: First reference optical fiber 8: Circulator 9: Second reference optical fiber 10: Branching section 11: Multiplexing section 12: First beat frequency detector 13: Multiplexing section 14: Second beat frequency detector 15: Shift amount change detection unit

Claims

1. An optical fiber condition measuring device for measuring a temperature, a strain, or a vibration of an optical fiber to be measured, a first reference optical fiber and a second reference optical fiber, each having a longer optical fiber length than the optical fiber under test, each having a constant Brillouin frequency shift amount different from that of the optical fiber under test in a steady temperature state or in a state in which no strain or vibration is applied, for the same incident wavelength, and each having a constant Brillouin frequency shift amount different from that of the optical fiber under test in a steady temperature state or in a state in which no strain or vibration is applied, for the same incident wavelength; a test light input section that inputs a pulsed measurement test light into the measured optical fiber, and inputs a first reference test light and a second reference test light, which are continuous light or pulsed and have the same wavelength as the measurement test light, into the first reference optical fiber and the second reference optical fiber; a scattered light input section that inputs a pulsed measurement Brillouin scattered light from the measured optical fiber, and inputs continuous light or a pulsed first reference Brillouin scattered light and a second reference Brillouin scattered light from the first reference optical fiber and the second reference optical fiber; a beat frequency detection unit that combines the measurement Brillouin scattered light and the first reference Brillouin scattered light to detect a first beat frequency thereof, and combines the measurement Brillouin scattered light and the second reference Brillouin scattered light to detect a second beat frequency thereof; a shift amount change detection unit that detects a direction, i.e., a sign, of a change in a Brillouin frequency shift amount of the test optical fiber from a steady state or a strain or vibration non-applied state to an unsteady state or an applied state based on the first beat frequency and the second beat frequency in a steady state of temperature of the test optical fiber or a strain or vibration non-applied state and an unsteady state of temperature of the test optical fiber or a strain or vibration applied state; An optical fiber state measuring device comprising:

2. the shift amount change detection unit detects a direction of change in the Brillouin frequency shift amount of the measured optical fiber from the steady state or the non-voltage application state to the unsteady state or the application state based on a direction of change in the first beat frequency and a direction of change in the second beat frequency from the steady state or the non-voltage application state to the unsteady state or the application state.

2. The optical fiber state measuring device according to claim 1 .

3. The shift amount change detection unit determines a direction of change in the Brillouin frequency shift amount of the optical fiber under test from the steady state or the non-voltage application state to the unsteady state or the voltage application state, based on a magnitude relationship between the first beat frequency and the second beat frequency in the unsteady state or the voltage application state, if the shift amount change detection unit cannot determine the direction of change in the Brillouin frequency shift amount of the optical fiber under test.

3. The optical fiber condition measuring device according to claim 2 .

4. The shift amount change detection unit detects a magnitude of change, i.e., an absolute value, of the Brillouin frequency shift amount of the measured optical fiber from the steady state or the non-voltage application state to the unsteady state or the application state based on the first beat frequency and the second beat frequency in the steady state or the non-voltage application state and the unsteady state or the application state.

4. The optical fiber state measuring device according to claim 1, wherein the optical fiber state measuring device is a fiber-optic optical fiber.

5. The different constant Brillouin frequency shift amounts of the first reference optical fiber and the second reference optical fiber are separated from the Brillouin frequency shift amount of the test optical fiber in the steady state or in the non-energized state by a distance equal to or greater than the Brillouin gain bandwidth.

5. The optical fiber state measuring device according to claim 1, wherein the optical fiber state measuring device is a fiber-optic optical fiber.

6. If the first beat frequency or the second beat frequency cannot be clearly measured in the unsteady state or the applied state, the shift amount change detection unit detects the Brillouin frequency shift amount of the measured optical fiber in the steady state or the non-applied state, and uses a third reference optical fiber having a constant Brillouin frequency shift amount different from the constant Brillouin frequency shift amounts of the first reference optical fiber and the second reference optical fiber.

6. The optical fiber state measuring device according to claim 1, wherein the optical fiber state measuring device is a fiber-optic optical fiber.

7. An optical fiber condition measurement method for measuring a temperature, a strain, or a vibration of a test optical fiber, comprising the steps of: Using a first reference optical fiber and a second reference optical fiber having a longer optical fiber length than the test optical fiber, a constant Brillouin frequency shift amount different from that of the test optical fiber in a steady temperature state or in a state in which no strain or vibration is applied for the same incident wavelength, and a constant Brillouin frequency shift amount different from each other for the same incident wavelength, a test light input step of inputting a pulsed measurement test light into the measured optical fiber, and inputting a first reference test light and a second reference test light, which are continuous light or pulsed and have the same wavelength as the measurement test light, into the first reference optical fiber and the second reference optical fiber; a scattered light input step of inputting a pulsed measurement Brillouin scattered light from the measured optical fiber, and inputting continuous light or a pulsed first reference Brillouin scattered light and a second reference Brillouin scattered light from the first reference optical fiber and the second reference optical fiber; a beat frequency detection step of multiplexing the measurement Brillouin scattered light and the first reference Brillouin scattered light to detect a first beat frequency thereof, and multiplexing the measurement Brillouin scattered light and the second reference Brillouin scattered light to detect a second beat frequency thereof; a shift amount change detection step of detecting a direction or sign of a change in a Brillouin frequency shift amount of the test optical fiber from a steady state or a strain or vibration non-applied state to an unsteady state or an applied state based on the first beat frequency and the second beat frequency in a steady state of temperature of the test optical fiber or a strain or vibration non-applied state and an unsteady state of temperature of the test optical fiber or a strain or vibration applied state; 4. An optical fiber condition measuring method comprising the steps of:

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