JP2008286697A - Distributed optical fiber sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distributed optical fiber sensor capable of measuring precisely a strain and/or a temperature. <P>SOLUTION: In this distributed optical fiber sensor of the present invention for measuring the strain and/or the temperature, using a Brillouin scattering phenomenon, a main light pulse and a sub-light pulse having the maximum light intensity smaller than a light intensity of the main light pulse, and having energy smaller than energy in a fixed light pulse at the maximum light intensity from its leading-up to the leading-up of the main light pulse are made incident into a detecting optical fiber 15, prior to the main light pulse, and continuous light is made incident into the optical fiber 15. The strain and/or the temperature generated in the detecting optical fiber 15 are measured based on lights concerned in the Brillouin scattering phenomenon generated by interaction of the lights emitted from the detecting optical fiber 15. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a distributed optical fiber sensor that uses an optical fiber as a sensor and can measure strain and / or temperature with high accuracy in the longitudinal direction.

  Conventionally, as a technique for measuring strain and temperature, there is a method based on the Brillouin scattering phenomenon that occurs in an optical fiber. In this method, the optical fiber is used as a medium for detecting strain and / or temperature in the environment where the optical fiber is placed.

  The Brillouin scattering phenomenon is a phenomenon in which when two lights having different frequencies pass in an optical fiber, the power moves from high-frequency light to low-frequency light via an acoustic phonon in the optical fiber. The Brillouin frequency shift seen during this Brillouin scattering phenomenon is proportional to the speed of sound in the optical fiber, and the speed of sound depends on the strain and temperature of the optical fiber. For this reason, strain and / or temperature is measured by measuring the Brillouin frequency shift.

  FIG. 12 is a diagram illustrating a distributed optical fiber sensor according to the background art. FIG. 12A is a block diagram illustrating the configuration of this distributed optical fiber sensor, and FIGS. 12B and 12C are diagrams illustrating examples of optical pulses used in this distributed optical fiber sensor. is there. FIG. 13 is a diagram showing a Brillouin gain spectrum. The horizontal axis in FIG. 13 is the frequency, and the vertical axis is the amplitude of the acoustic phonon.

  12A, a distributed optical fiber sensor 500 according to the background art includes first and second light sources 501, 504, a detection optical fiber 502, an optical coupler 503, and a time domain detector 505. Configured.

  As shown in FIG. 12B, the first light source 501 generates an optical pulse having a rectangular light intensity, and emits the generated optical pulse. The light pulse emitted from the first light source 501 enters from one end of the detection optical fiber 502. The detection optical fiber 502 is an optical fiber for detecting strain and / or temperature in the environment in which it is placed, and is used as a sensor. The second light source 504 generates continuous light having a frequency lower than the frequency of the light pulse, and emits the generated continuous light (CW light). The continuous light emitted from the second light source 504 is incident from the other end of the detection optical fiber 502 via the optical coupler 503. In the detection optical fiber 502, the optical pulse and the continuous light cause a Brillouin scattering phenomenon, and the light related to the Brillouin scattering phenomenon is incident on the time domain detector 505 via the optical coupler 503. The time domain detector 505 measures the light intensity of light related to the Brillouin scattering phenomenon in the time domain. The distributed optical fiber sensor 500 measures the light intensity of the Brillouin scattering phenomenon for each frequency in the time domain while sequentially changing the frequency of the light pulse or continuous light, and in the longitudinal direction of the detection optical fiber 502. The Brillouin gain spectrum of each portion along the line is obtained, and the strain distribution and / or the temperature distribution along the detection optical fiber 502 are obtained.

  Note that by making the frequency of the continuous light higher than the frequency of the optical pulse, the distortion and / or temperature can be obtained in the same manner even if the Brillouin loss spectrum is used instead of the Brillouin gain spectrum. Hereinafter, the Brillouin gain spectrum or the Brillouin loss spectrum is abbreviated as “Brillouin loss / gain spectrum”.

  The spatial resolution of the distributed optical fiber sensor 500 is limited by the pulse width of an optical pulse used for measurement. For example, when the spatial resolution is 3 m, the pulse width of the optical pulse is 30 ns, and when the spatial resolution is 2 m, the pulse width of the optical pulse is 20 ns. Although the speed of light in the optical fiber is slightly different depending on the material of the optical fiber, in a general optical fiber that is usually used, about 28 ns is required for complete rise of the acoustic phonon. For this reason, as shown in FIG. 13, the Brillouin gain spectrum is a Lorentzain curve (curves a1 and a2 shown in FIG. 13) until the pulse width of the optical pulse is about 28 ns or more. However, when the optical pulse width is shortened, it becomes a broadband curve (curves b1, b2, and b3 shown in FIG. 13), and has a gentle shape that loses steepness near the center frequency. For this reason, it becomes difficult to obtain the center frequency, and the spatial resolution is usually about 2 to 3 m. Each curve a1, a2, b1, b2, b3 is a Brillouin gain spectrum when the pulse width of the optical pulse is 100 ns, 28 ns, 10 ns, 5 ns, 1 ns, respectively.

Therefore, the inventor of the present application instead of the light pulse shown in FIG. 12B, a staircase in which the light intensity is stepped so that the light intensity increases toward the inside as shown in FIG. 12C. Patent Document 1 proposes a technique for measuring strain and / or temperature distribution with high accuracy (for example, 200 με or less) and high spatial resolution (for example, 1 m or less) by using a shaped light pulse. Note that 100 με = 0.01%.
International Publication No. 2006/001071 Pamphlet

  By the way, in the distributed optical fiber sensor, higher accuracy is demanded, and the method proposed in Patent Document 1 has room for improvement in terms of higher accuracy.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a distributed optical fiber sensor capable of measuring strain and / or temperature with higher accuracy.

  As a result of various studies, the present inventor has found that the above object is achieved by the present invention described below. That is, according to one aspect of the present invention, in a distributed optical fiber sensor that measures strain and / or temperature using the Brillouin scattering phenomenon, the main light pulse and the maximum light intensity prior to the main light pulse are the main light pulse. An optical pulse light source that generates a sub-light pulse that is smaller than the light intensity of the light pulse and smaller than the energy in the constant light pulse at the maximum light intensity from the rise of the light to the rise of the main light pulse, and generates continuous light A continuous light source, and a sub optical pulse, the main light pulse, and the continuous light are incident, and a detection optical fiber in which a Brillouin scattering phenomenon occurs between the sub light pulse, the main light pulse, and the continuous light. And a Brillouin gain scan based on the light related to the Brillouin scattering phenomenon emitted from the detection optical fiber. A Brillouin time-domain detector that obtains a Kuttle or Brillouin loss spectrum and measures strain and / or temperature generated in the detection optical fiber based on the Brillouin gain spectrum or Brillouin loss spectrum obtained It is characterized by providing. A and / or B means at least one of A and B.

  FIG. 1 is a diagram for explaining the theoretical analysis of the Brillouin scattering phenomenon. FIG. 1 (A) shows a measurement system in theoretical analysis of the Brillouin scattering phenomenon, FIG. 1 (B) shows probe light, and FIG. 1 (C) shows pump light.

In FIG. 1, in this theoretical analysis, continuous light (CW) having a light intensity AL ² is incident as a probe light from one end of the detection optical fiber SOF, and an optical pulse OP having a light intensity (As + Cs) ^{2 with} a pulse width D. Prior to this light pulse OP, a constant light pulse forward light OPf from the rising edge to the rising edge of the light pulse OP at a light intensity Cs ² smaller than the light intensity AL ^{2 of the} light pulse OP is used as a pumping light. Incident from the other end of the fiber SOF. The light intensity As ² is a light intensity based on the light intensity Cs ² of the light pulse forward light OPf. The pulse width of the optical pulse forward light OPf is Tf. In this theoretical analysis, the Brillouin loss spectrum in such a measurement system is derived.

  In this theoretical analysis, the length of the detection optical fiber SOF is L, the position coordinate in the longitudinal direction of the detection optical fiber SOF is z (0 ≦ z ≦ L, and the origin is one end of the detection optical fiber SOF. If the time coordinate is t, the equation of Brillouin scattering when the detection optical fiber SOF is distorted is expressed by equations 1 to 3.

Here, vg is the group velocity of light in the detection optical fiber SOF (vg = c / n, c is the speed of light, n is the refractive index of the detection optical fiber SOF), and E _L is a field intensity of the pump light, E _S is the field strength of the Stokes light, E _a is a Γ × ρ / Λ. * Indicates conjugation. Γ is Γ _B / 2, ρ is the density of the detection optical fiber SOF, and Λ is (γ × q × q) / (16 × π × Ω). The gamma _B, a lifetime tau _B When Γ _{B =} 1 / _{τ B} of acoustic phonons, gamma, when called electrostrictive coupling constant (Electrostrietive Coupling Constant) and the dielectric constant ε γ = ρ (δε / a [Delta] [rho]), q is the wave number of the pump light and k _L and when the wave number of the Stokes light and k _S is _{q = k L + k S,} Ω is the Brillouin angular frequency shift in the case where distortion is not generated, When the angular frequency of the pump light is ω _L and the angular frequency of the Stokes light is ω _S , Ω = ω _L −ω _S , and Ω _B is a Brillouin angular frequency shift when a certain distortion occurs, When the angular frequency of light is ω _BL and the angular frequency of Stokes light is ω _BS , Ω _B = ω _BL −ω _BS . i is a complex unit, i × i = −1. β is κ × Λ / Γ, and κ is (γ × ω _L ) / (4 × ρ ₀ × n × c) ≈ (γ × ω _S ) / (4 × ρ ₀ × n × c). is there. ρ ₀ is an average value of the density of the detection optical fiber SOF. Β is g _SBS = 16 × π × β / (n × c) where g _SBS is a gain coefficient of stimulated Brillouin scattering (SBS), and g _SBS = 2.5 × 10 ⁻¹¹ m / W For example, “ALGaeta and RWBoyd,“ Stochastic dynamoics of stimulated Brillouin scattering in an optical fiber ”, Physical Review A, Vol. 44, no. 5, 1991, pp 3205-3209”.

  Expression 1 is an expression related to the pump light, Expression 2 is an expression related to the probe light, and Expression 3 is an expression related to the lifetime of the acoustic phonon. When these equations 1 to 3 are solved and Brillouin loss V (t, Ω) is obtained as an approximate solution, equations 4 to 11 are obtained.

Here, ζ is a position in the longitudinal direction of the detection optical fiber SOF, and s is time. c. c is a constant, and h (z, s) is Γ × e− ^{(Γ + i (ΩB (z) −Ω))} at time s at position z, where LL is the total length of the detection optical fiber SOF. , H ^c (ζ, s) = h (z, s) = h ((LL−ζ), s).

H _{1 in} Equation 5 represents a Brillouin loss spectrum based on an acoustic phonon excited by an optical pulse OP and continuous light. H _{2 in} Equation 6 represents a Brillouin loss spectrum based on acoustic phonons excited by the optical pulse forward light OPf and the continuous light and further excited by the optical pulse OP and the continuous light. H _{3 in} Equation 7 represents a Brillouin loss spectrum based on an acoustic phonon excited by an optical pulse OP and continuous light and further excited by an optical pulse forward light OPf and continuous light. H _{4 in} Equation 8 represents a Brillouin loss spectrum based on acoustic phonons excited by the optical pulse forward light OPf and continuous light. Comparing these H _{1 to} H ₄ , the light intensity (As + Cs) ² of the optical pulse OP, the pulse width Tf of the optical pulse forward light OPf, and the optical intensity Cs of the optical pulse forward light OPf so that H ₂ can be detected. By setting ² , it is understood that distortion and / or temperature can be detected with high accuracy and high spatial resolution using an optical pulse OP having a short pulse width D. The pulse width D of the optical pulse OP is appropriately set according to the desired spatial resolution and depends on the material of the optical fiber. For example, in order to obtain a spatial resolution of 50 cm, the pulse width is set to 5 ns, For example, in order to obtain a spatial resolution of 10 cm, the pulse width is set to 1 ns.

  In the present invention, the sub light pulse temporally preceding the main light pulse has the maximum light intensity of the sub light pulse smaller than the light intensity of the main light pulse, and from the rise to the rise of the main light pulse, When a constant light pulse with a maximum light intensity is considered, the energy of the sub light pulse is set to be smaller than the energy of the light pulse considered.

  Referring to FIG. 1C, the main light pulse corresponds to the light pulse OP, the maximum light intensity is smaller than the light intensity of the main light pulse, and the rise to the rise of the main light pulse. The light pulse constant at the maximum light intensity corresponds to the light pulse forward light OPf. Accordingly, the energy of the sub light pulse is set to be smaller than the energy of the light pulse forward light OPf.

  Such a sub-light pulse preferably has a time width shorter than the time from the rise to the rise of the main light pulse. Preferably, the light intensity of the sub light pulse decreases with time. Preferably, the light intensity of the sub light pulse increases with time. Also preferably, the sub-light pulse decreases after its light intensity increases with time.

By using such a sub-light pulse, the H ₄ component that is a noise component is reduced, and the influence on H ₂ is suppressed. At the same time, the peak width of the Brillouin loss / gain spectrum is narrowed, the measurement error of the center frequency is reduced, and the Brillouin frequency shift can be measured with higher accuracy. As a result, the strain and / or temperature can be measured with higher accuracy.

  In the distributed optical fiber sensor described above, the sub light pulse and the main light pulse are incident from one end of the detection optical fiber, and the continuous light is incident from the other end of the detection optical fiber. The Brillouin time domain detector obtains a Brillouin gain spectrum or a Brillouin loss spectrum based on light related to a Brillouin scattering phenomenon emitted from one end of the detection optical fiber, and determines the Brillouin gain The strain and / or temperature generated in the detection optical fiber is measured based on a spectrum or a Brillouin loss spectrum.

  According to this configuration, a distributed optical fiber sensor that performs Brillouin gain spectrum time domain analysis or Brillouin loss spectrum time domain analysis and detects strain and / or temperature based on the Brillouin frequency shift is provided.

  In the distributed optical fiber sensor described above, the sub light pulse and the main light pulse are incident from one end of the detection optical fiber, and the continuous light is incident from one end of the detection optical fiber. The detection optical fiber reflects the propagating continuous light at the other end, and the Brillouin time domain detector is based on the Brillouin scattering phenomenon emitted from one end of the detection optical fiber based on the Brillouin scattering phenomenon. A gain spectrum or a Brillouin loss spectrum is obtained, and strain and / or temperature generated in the detection optical fiber is measured based on the obtained Brillouin gain spectrum or Brillouin loss spectrum. To do.

  According to this configuration, a distributed optical fiber sensor that performs Brillouin gain spectrum time domain reflection analysis or Brillouin loss spectrum time domain reflection analysis to detect strain and / or temperature based on Brillouin frequency shift is provided. The

  Further, in these optical fiber sensors, the optical pulse light source and the continuous light source continuously emit light having a predetermined frequency with a narrow line width and a substantially constant light intensity. A light-emitting element; first and second temperature control units that respectively hold the temperatures of the first and second light-emitting elements substantially constant; and each of the lights emitted by the first and second light-emitting elements. First and second frequency control units that respectively hold the frequencies substantially constant; and first and second portions that emit part of the light emitted by the first and second light emitting elements, respectively, and cause a Brillouin scattering phenomenon. A reference optical fiber having a known relationship between the frequency difference in the second light and the light intensity of the light related to the Brillouin scattering phenomenon, and the light intensity of the light related to the Brillouin scattering phenomenon emitted from the reference optical fiber are known. Relationship Therefore, the frequency setting unit that controls the first frequency control unit and / or the second frequency control unit so that the frequency difference between the lights emitted from the first and second light emitting elements becomes a predetermined frequency difference. It is characterized by providing.

  According to this configuration, each frequency difference of each light emitted from each of the first and second light emitting elements is controlled to a predetermined frequency difference, so that the Brillouin frequency shift can be measured with higher accuracy. As a result, the strain and / or temperature can be measured with higher accuracy. According to this configuration, a separate reference optical fiber for frequency calibration is not required for the distributed optical fiber sensor, and the frequency can be calibrated within the distributed optical fiber device.

  In these distributed optical fiber sensors, the optical pulse light source includes a light emitting element that continuously emits light having a predetermined frequency with a narrow line width and a substantially constant first light intensity, and the light emitting element includes: An optical branching unit that splits the emitted light into two so that the optical intensities are different from each other, and a first optical intensity modulator that modulates the light intensity of the light that is branched by the optical branching unit and has a relatively large light intensity A second light intensity modulator that modulates the light intensity of the light having a smaller light intensity branched by the light branching unit, and each light modulated by the first and second light intensity modulators, respectively. The first optical intensity modulator generates the main optical pulse, and the second optical intensity modulator generates the sub optical pulse.

  According to this configuration, since the main light pulse and the sub light pulse are individually generated by the first light intensity modulator and the second light intensity modulator, the pulse width of the main light pulse can be accurately set, In addition, sub-light pulses with various light intensities can be generated. As a result, the strain and / or temperature can be measured with higher accuracy.

  In the above-described distributed optical fiber sensors, the detection optical fiber is fixed to a measurement object whose strain and / or temperature is to be measured.

  According to this configuration, the strain and / or temperature of the measurement object can be measured.

  In the distributed optical fiber sensor according to the present invention, the strain and / or temperature can be measured with higher accuracy.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

As will be described later, the distributed optical fiber sensor according to the embodiment of the present invention switches the optical switch to change the sub optical pulse and the main light from one end of the optical fiber for detection for detecting strain and / or temperature. Pulse light is incident as pump light and continuous light is incident as probe light from the other end of the detection optical fiber to receive light related to the Brillouin scattering phenomenon generated in the detection optical fiber, and the Brillouin gain spectrum is received. Distortion based on Brillouin frequency shift by performing time domain analysis (B ^Gain- OTDA, Brillouin Gain Optical Time Domain Analysis) or Brillouin ^Loss Spectrum time domain analysis (B ^Loss- OTDA, Brillouin Loss Optical Time Domain Analysis) And / or temperature distribution detection. Hereinafter, Brillouin gain spectrum time domain analysis or Brillouin loss spectrum time domain analysis is abbreviated as Brillouin gain / loss spectrum time domain analysis. In this Brillouin gain / loss spectrum time domain analysis, the light related to the Brillouin scattering phenomenon is light subjected to Brillouin amplification / attenuation.

Then, as will be described later, this distributed optical fiber sensor has a sub optical pulse and main light as pump light from one end of a detection optical fiber for detecting strain and / or temperature by switching an optical switch. A pulse and continuous light as probe light are incident, pump light subjected to the effect of the Brillouin scattering phenomenon is received by a detection optical fiber, and Brillouin gain spectrum time domain reflection analysis (B ^Gain -OTDR, Brillouin Gain) Optical time domain Reflectometer) or the Brillouin loss spectrum time domain reflection analysis (B ^loss -OTDR, by performing the Brillouin loss Optical time domain Reflectometer), and detects the strain and / or temperature based on the Brillouin frequency shift . Hereinafter, Brillouin gain spectrum time domain reflection analysis or Brillouin loss spectrum time domain reflection analysis is abbreviated as Brillouin gain / loss spectrum time domain reflection analysis. In this Brillouin gain / loss spectrum time domain reflection analysis, the light related to the Brillouin scattering phenomenon is Brillouin scattered light.

  FIG. 2 is a block diagram illustrating a configuration of the distributed optical fiber sensor in the embodiment. FIG. 3 is a block diagram showing a configuration of an optical pulse generation unit in the distributed optical fiber sensor.

  In FIG. 2, the distributed optical fiber sensor S includes a first light source 1, optical couplers 2, 5, 8, 21, 23, an optical pulse generator 3, optical switches 4, 22, and light intensity / polarization adjustment. Unit 6, optical circulators 7 and 12, optical connectors 9, 26, 27 and 28, a first automatic temperature controller (hereinafter abbreviated as “first ATC”) 10, and a first automatic frequency controller ( Hereinafter, abbreviated as “first AFC”.) 11, control processing unit 13, Brillouin time domain detector 14, detection optical fiber 15, temperature detection unit 16, reference optical fiber 17, and second An automatic temperature controller (hereinafter abbreviated as “second ATC”) 18, a second automatic frequency controller (hereinafter abbreviated as “second AFC”) 19, a second light source 20, and a light intensity adjuster 24 and a 1 × 2 optical switch 25.

  The first and second light sources 1 and 20 are held substantially constant at a predetermined temperature preset by the first and second ATCs 10 and 18, respectively, and at a predetermined frequency preset by the first and second AFCs 11 and 19, respectively. It is a light source device that generates and emits continuous light of a predetermined frequency by being held substantially constant. The output terminal (emission terminal) of the first light source 1 is optically connected to the input terminal (incident terminal) of the optical coupler 2. The output terminal (emission terminal) of the second light source 20 is optically connected to the input terminal (incident terminal) of the optical coupler 21.

  Such first and second light sources 1 and 20 are, for example, a light emitting element, a temperature detecting element such as a thermistor that is disposed in the vicinity of the light emitting element and detects the temperature of the light emitting element, and the rear of the light emitting element. For example, an optical coupler such as a half mirror that receives the back light emitted from the light and splits it into two, and one of the lights branched by the optical coupler is a periodic filter, a Fabry-Perot etalon filter (Fabry-perotetalon Filter) A first light receiving element that receives light via the optical coupler, a second light receiving element that receives the other light branched by the optical coupler, a temperature adjusting element, the light emitting element, the temperature detecting element, the optical coupler, and the first and second light receiving elements. And a substrate on which a Fabry-Perot etalon filter and a temperature adjustment element are disposed.

  A light-emitting element is an element that emits light of a predetermined frequency with a narrow line width and can change an oscillation wavelength (oscillation frequency) by changing an element temperature or a drive current. For example, a multi-quantum well structure DFB laser, A tunable semiconductor laser (frequency tunable semiconductor laser) such as a tunable wavelength distribution Bragg reflection laser. The temperature detection elements in the first and second light sources 1 and 20 output the detected temperatures to the first and second ATCs 10 and 18, respectively. The first and second light receiving elements in the first and second light sources 1 and 20 include photoelectric conversion elements such as photodiodes, for example, and output the respective light receiving outputs corresponding to the received light intensity to the first and second AFCs 11 and 19, respectively. To do. The temperature adjustment element is a component that adjusts the temperature of the substrate by generating heat and absorbing heat, and includes, for example, a thermoelectric conversion element such as a Peltier element or a Seebeck element.

  The first and second ATCs 10 and 18 respectively control the temperature adjusting elements based on the detected temperatures of the temperature detecting elements in the first and second light sources 1 and 20 according to the control of the control processing unit 13, respectively. This circuit automatically keeps the temperature of each substrate at a predetermined temperature substantially constant. Thereby, the temperature of each light emitting element in the first and second light sources 1 and 20 is automatically kept substantially constant at a predetermined temperature. For this reason, when the frequency of the light emitted from the light emitting element has temperature dependency, the temperature dependency is suppressed.

  The first and second AFCs 11 and 19 respectively control the light emitting elements based on the light reception outputs of the first and second light receiving elements in the first and second light sources 1 and 20 according to the control of the control processing unit 13, respectively. Thus, the frequency of the light emitted from each light emitting element is automatically kept substantially constant at a predetermined frequency.

  The optical coupler and Fabry-Perot etalon filter first and second light receiving elements and the first and second AFCs 11 and 19 in the first and second light sources 1 and 20 emit light from the light emitting elements in the first and second light sources 1 and 20, respectively. So-called wavelength lockers that substantially fix the wavelength (frequency) of the light to be transmitted are configured.

  The optical couplers 2, 5, 21, and 23 are optical components that distribute incident light incident from one input terminal into two light beams and emit the light beams to two output terminals, respectively. The optical coupler 8 emits incident light incident from one of the two input terminals from one output terminal and emits incident light incident from the other input terminal from the output terminal. It is an optical component. The optical couplers 2, 5, 21, 23, and 8 use, for example, a micro optical element type optical branch coupler such as a half mirror, an optical fiber type optical branch coupler of a molten fiber, an optical waveguide type optical branch coupler, or the like. be able to.

  One output terminal of the optical coupler 2 is optically connected to the input terminal of the optical pulse generator 3, and the other output terminal is optically connected to the first terminal of the optical circulator 12. One output terminal of the optical coupler 5 is optically connected to the input terminal of the light intensity / polarization adjusting unit 6, and the other output terminal is optically connected to the second input terminal of the Brillouin time domain detector 14. The One output terminal of the optical coupler 21 is optically connected to the input terminal of the optical switch 22, and the other output terminal is optically connected to the other end of the reference optical fiber 17 via the optical connector 28. . One output terminal of the optical coupler 23 is optically connected to the input terminal of the light intensity adjusting unit 24, and the other output terminal is optically connected to the fourth input terminal of the Brillouin time domain detector 14. One input terminal of the optical coupler 8 is optically connected to the second terminal of the optical circulator 7, and the other input terminal is optically connected to the other output terminal of the 1 × 2 optical switch 25. Is optically connected to one end of the detection optical fiber 15 via the optical connector 9.

  The light pulse generation unit 3 is a device that receives continuous light emitted from the first light source 1 and generates a main light pulse and a sub light pulse preceding the main light pulse from the continuous light. The maximum light intensity of the sub light pulse is smaller than the light intensity of the main light pulse. Then, assuming an optical pulse whose light intensity is constant at the maximum light intensity from the rise of the sub light pulse to the rise of the main light pulse, the energy of the sub light pulse is the energy of the assumed light pulse. Smaller than.

  Such an optical pulse generator 3 includes, for example, polarization maintaining optical couplers 31 and 36, first and second optical intensity modulators 32 and 34, and first and second driver circuits 33, as shown in FIG. , 35.

  The polarization maintaining optical couplers 31 and 36 are optical components such as a polarization maintaining beam splitter, for example. The polarization maintaining optical coupler 31 receives the continuous light emitted from the first light source 1 via the optical coupler 2 and branches the incident continuous light into two while maintaining the polarization direction. One output terminal of the polarization maintaining optical coupler 31 is optically connected to the input terminal of the first light intensity modulator 32, and the other output terminal is optically connected to the input terminal of the second light intensity modulator 34. Is done.

  The first and second light intensity modulators 32 and 34 are optical components that modulate the light intensity of incident light. For example, a Mach-Zehnder light modulator (hereinafter abbreviated as “MZ light modulator”) or a semiconductor is used. An electroabsorption optical modulator or the like. The output terminal of the first light intensity modulator 32 is optically connected to one input terminal of the polarization maintaining optical coupler 36, and the output terminal of the second light intensity modulator 34 is the other input of the polarization maintaining optical coupler 36. Optically connected to the terminal.

  In the MZ optical modulator, for example, an optical waveguide, a signal electrode, and a ground electrode are formed on a substrate having an electrooptic effect such as lithium niobate, lithium tantalate, lithium niobate / lithium tantalate, and the like. The optical waveguide is composed of two Y-branch waveguides, the middle part of which is divided into two to form first and second waveguide arms, and constitutes a Mach-Zehnder interferometer. The signal electrode is formed on each of the two waveguide arms, and the ground electrode is formed on the substrate so as to be parallel to the signal electrode at a predetermined interval. The light incident on the MZ light modulator propagates through the optical waveguide, branches into two at the first Y branch waveguide, propagates through each waveguide arm, and is multiplexed again at the second Y branch waveguide. Ejected from the waveguide. Here, by applying an electric signal to each signal electrode, the light intensity of the incident light is modulated and emitted.

  In addition to the electro-optic effect, the magneto-optic modulator utilizing the magneto-optic effect, the acousto-optic modulator utilizing the acousto-optic effect, the Franz-Keldysh effect and the quantum confined Stark effect (quantum) There are also electro-absorption optical modulators using -confined Stark effect).

  The first and second driver circuits 33 and 35 are circuits that are controlled by the control processing unit 13 and drive the first and second light intensity modulators 32 and 34, respectively. The first and second driver circuits 33 and 35 generate, for example, a DC voltage signal for turning off the first and second light intensity modulators 32 and 34 in a normal state, respectively. In order to turn on the first and second light intensity modulators 32 and 34, which are normally turned off, in order to generate a light pulse having a predetermined waveform and a direct current power supply circuit that outputs as a direct current output (DC output). A pulse generation circuit that generates a voltage pulse having a voltage waveform and outputs the generated voltage pulse as an AC output (AC output), and a timing generation circuit that controls the generation timing of the voltage pulse are configured.

  The first light intensity modulator 32 generates a main light pulse, for example, under the control of the first driver circuit 33, and the second light intensity modulator 34, for example, a sub light pulse, under the control of the second driver circuit 35. Is generated. The first driver circuit 33 outputs a voltage pulse having a waveform corresponding to the waveform of the main light pulse as an AC output at the generation timing of the main light pulse. The second driver circuit 33 outputs a voltage pulse having a waveform corresponding to the waveform of the sub light pulse as an AC output at the generation timing of the sub light pulse. As described above, the maximum light intensity of the sub light pulse is smaller than the light intensity of the main light pulse. For this reason, the polarization maintaining optical coupler 31 branches the incident light into two so that the light intensities are different from each other. For example, the polarization maintaining optical coupler 31 branches the incident light into two so that the light intensity ratio is 5: 5. Further, for example, the polarization maintaining optical coupler 31 branches the incident light into two so that the light intensity ratio is 8: 2. Further, for example, the polarization maintaining optical coupler 31 branches the incident light into two so that the ratio of the light intensity is 9: 1. The light that is branched by the polarization-maintaining optical coupler 31 and has a relatively large light intensity is incident on the first light intensity modulator 32, and the light that is branched by the polarization-maintaining optical coupler 31 and has a relatively small light intensity is , And enters the second light intensity modulator 34.

  The polarization maintaining optical coupler 36 receives the light emitted from the first and second light intensity modulators 32 and 34, and the light emitted from the first light intensity modulator 32 and the light emitted from the second light intensity modulator 34. The combined light is combined with each polarization direction being maintained. The output terminal of the polarization maintaining optical coupler 36 is the output terminal of the optical pulse generator 3 and is optically connected to the input terminal of the optical switch 4 at the subsequent stage.

  Note that, as indicated by a broken line in FIG. 3, the output terminal of the polarization maintaining optical coupler 36 has a sub light pulse and a main light so that the light intensity of the light pulse emitted from the light pulse generation unit 3 is a predetermined light intensity. An optical amplifier 37 that amplifies the optical pulse may be optically connected as necessary.

  Returning to FIG. 2, the optical switches 4 and 22 are optical components that turn on and off light between the input terminal and the output terminal according to the control of the control processing unit 13. When on, light is transmitted, and when off, light is blocked. In this embodiment, the optical switches 4 and 22 are light intensity modulators that modulate the light intensity of incident light, such as an MZ light modulator or a semiconductor electroabsorption optical modulator. The optical switches 4 and 22 include a driver circuit that is controlled by the control processing unit 13 and drives the light intensity modulator. The driver circuit includes, for example, a DC power supply circuit that generates a DC voltage signal for turning off the light intensity modulator in a normal state, and a pulse that generates a voltage pulse for turning on the light intensity modulator that is normally turned off. A generation circuit and a timing generation circuit for controlling the generation timing of the voltage pulse are provided. The output terminal of the optical switch 4 is optically connected to the input terminal of the optical coupler 5. The output terminal of the optical switch 22 is optically connected to the input terminal of the optical coupler 23.

  The light intensity / polarization adjusting unit 6 is a component that is controlled by the control processing unit 13 to adjust the light intensity of incident light and to randomly change the polarization plane of the incident light and emit the light. The output terminal of the light intensity / polarization adjustment unit 6 is optically connected to the first terminal of the optical circulator 7. For example, the light intensity / polarization adjustment unit 6 attenuates the light intensity of the incident light and emits it, and changes the amount of attenuation, and changes the polarization plane of the incident light at random. And a polarization controller that can be configured.

  The optical circulators 7 and 12 are first to third three-terminal optical circulators, and are irreversible optical components in which incident light and outgoing light have a cyclic relationship with their terminal numbers. That is, light incident on the first terminal is emitted from the second terminal and is not emitted from the third terminal, and light incident on the second terminal is emitted from the third terminal and from the first terminal. Light that is not emitted but is incident on the third terminal is emitted from the first terminal and is not emitted from the second terminal. The first terminal of the optical circulator 7 is optically connected to the output terminal of the light intensity / polarization adjusting unit 6, and the second terminal is optically connected to one input terminal of the optical coupler 8 as described above. The third terminal is optically connected to the third input terminal of the Brillouin time domain detector 14. As described above, the first terminal of the optical circulator 12 is optically connected to the other output terminal of the optical coupler 2, and the second terminal is optically connected to one end of the reference optical fiber 17 via the optical connector 27. The third terminal is optically connected to the first input terminal of the Brillouin time domain detector 14.

  The optical connectors 9, 26, 27, and 28 are optical components that optically connect optical fibers or optical components and optical fibers.

  The light intensity adjusting unit 24 is a component that is controlled by the control processing unit 13 to adjust the light intensity of incident light and emit the light. The output terminal of the light intensity adjusting unit 24 is optically connected to the input terminal of the optical switch 25. The light intensity adjusting unit 24 includes, for example, an optical variable attenuator that attenuates and emits light intensity of incident light, and an optical isolator that transmits light only in one direction from the input terminal to the output terminal. The incident light that has entered the light intensity adjusting unit 24 is emitted through an optical isolator after the light intensity is adjusted to a predetermined light intensity by an optical variable attenuator. This optical isolator plays a role of preventing the propagation of the reflected light generated at the connection portion of each optical component in the distributed optical fiber sensor S and the propagation of the sub light pulse and the main light pulse to the second light source 20.

  The 1 × 2 optical switch 25 is a 1-input 2-output optical switch that emits light incident from an input terminal from one of two output terminals by switching an optical path. An optical switch, an optical waveguide switch, or the like is used. As described above, one output terminal of the 1 × 2 optical switch 25 is optically connected to the other input terminal of the optical coupler 8, and the other output terminal is connected to the detection optical fiber 15 via the optical connector 26. Is optically connected to the other end. When the Brillouin gain / loss spectrum time domain analysis is executed manually or under the control of the control processing unit 13, the light incident from the input terminal is connected to the other end of the detection optical fiber 15 via the optical connector 26. When the 1 × 2 optical switch 25 is switched so as to be incident on the light and the Brillouin gain / loss spectrum time domain reflection analysis is performed, the light incident from the input terminal is the optical coupler 8 and the optical connector 9. The 1 × 2 optical switch 25 is switched so as to be incident on one end of the detection optical fiber 15 via.

  The detection optical fiber 15 is an optical fiber for a sensor that detects strain and / or temperature, and the sub light pulse, the main light pulse, and the continuous light are incident thereon, and light subjected to the Brillouin scattering phenomenon is emitted. The Here, when measuring distortion and / or temperature generated in a measurement object such as a structure such as a pipe, a bridge, a tunnel, a dam, a building, or the ground, the detection optical fiber 15 is an adhesive, a fixing member, or the like. Is fixed to the measurement object.

  The reference optical fiber 17 is an optical fiber that is used to adjust the frequency of each light emitted from the first and second light sources 1 and 20, and in the first and second light that causes the Brillouin scattering phenomenon. The optical fiber has a known relationship between the frequency difference and the light intensity of light related to the Brillouin scattering phenomenon.

  The temperature detection unit 16 is a circuit that detects the temperature of the reference optical fiber 17 and outputs the detected temperature to the control processing unit 13.

  The Brillouin time domain detector 14 controls each part of the distributed optical fiber sensor S by inputting / outputting signals to / from the control processing unit 13 and is incident on the first input terminal via the optical connector 27 and the optical circulator 12. Further, the light intensity of the light related to the Brillouin scattering phenomenon emitted from the reference optical fiber 17 is obtained, and the obtained light intensity is output to the control processing unit 13. The Brillouin time domain detector 14 controls each part of the distributed optical fiber sensor S by inputting / outputting signals to / from the control processing unit 13 and detects light related to the Brillouin scattering phenomenon received at a predetermined sampling interval. As a result, the Brillouin gain / loss spectrum of each region portion of the detection optical fiber 15 in the longitudinal direction of the detection optical fiber 15 is obtained, and based on the obtained Brillouin gain / loss spectrum of each region portion. The Brillouin frequency shift of each region portion is obtained, and the strain distribution and / or temperature distribution of the detection optical fiber 15 is detected based on the obtained Brillouin frequency shift of each region portion. Incident light incident from the first to fourth input terminals is converted into an electric signal corresponding to the amount of received light by a light receiving element that performs photoelectric conversion, and the electric signal is converted into a digital electric signal by an analog / digital converter. , Used to determine the Brillouin gain / loss spectrum. Further, if necessary, the electric signal is amplified by the amplifier circuit before being digitally converted. The Brillouin time domain detector 14 includes an optical switch, a spectrum analyzer, a computer, and the like.

  The control processing unit 13 inputs and outputs signals to and from the Brillouin time domain detector 14 to measure the strain and / or temperature distribution of the detection optical fiber 15 in the longitudinal direction of the detection optical fiber 15 with high spatial resolution. The first and second light sources 1 and 20, the first and second ATCs 10 and 18, the first and second AFCs 11 and 19, the optical pulse generator 3, the optical switches 4 and 22, the light intensity / polarization adjuster 6 and It is an electronic circuit that controls the light intensity adjusting unit 24. The control processing unit 13 includes, for example, a microprocessor, a working memory, and a memory that stores data necessary for measuring the strain and / or temperature distribution of the detection optical fiber 15 with high spatial resolution. Composed. The control processing unit 13 includes a storage unit that stores in advance the relationship between the frequency difference between the first and second light causing the Brillouin scattering phenomenon and the light intensity of the light related to the Brillouin scattering phenomenon in the reference optical fiber 17. First and second light emission in the first and second light sources 1 and 20 based on the light intensity of the light related to the Brillouin scattering phenomenon obtained by the Brillouin time domain detector 14 and the known relationship in the reference optical fiber 17. A frequency setting unit that controls the first AFC 11 and / or the second AFC 19 is functionally provided so that the frequency difference of each light emitted from the element becomes a predetermined frequency difference set in advance.

  The first and second light sources 1 and 20, the first and second ATCs 10 and 18, the first and second AFCs 11 and 19, the light intensity / polarization adjustment unit 6, the light intensity adjustment unit 24, and the light intensity modulator are Patent Document 1 can be referred to.

  Next, the operation of the distributed optical fiber sensor according to the embodiment will be described.

  First, adjustment (calibration) of the frequency of continuous light emitted from the first light source 1 and the frequency of continuous light emitted from the second light source 20 will be described.

  First, the control processing unit 13 controls the first ATC 10 and the first AFC 11 to cause the first light source 1 to emit continuous light of a predetermined frequency, emits the continuous light from the first light source 1, and causes the second ATC 18 and the second AFC 19 to be emitted. By controlling, the second light source 20 emits continuous light having a predetermined frequency, and the continuous light is emitted from the second light source 20.

  The continuous light emitted from the first light source 1 is incident on one end of the reference optical fiber 17 via the optical coupler 2, the optical circulator 12, and the optical connector 27, and the continuous light emitted from the second light source 20 is The light is incident on the other end of the reference optical fiber 17 via the optical coupler 21 and the optical connector 28. The continuous light from the first light source 1 incident on one end of the reference optical fiber 17 and the continuous light from the second light source 20 incident on the other end of the reference optical fiber 17 are Brillouin by the reference optical fiber 17. Causes a scattering phenomenon. The light related to the Brillouin scattering phenomenon generated thereby is emitted from one end of the reference optical fiber 17 and is incident on the Brillouin time domain detector 14 via the optical circulator 12.

  The Brillouin time domain detector 14 detects the light intensity of the light related to the received Brillouin scattering phenomenon and notifies the control processing unit 13 of the detected light intensity.

  Upon receiving this notification, the control processing unit 13 receives the frequency difference between the first and second lights causing the Brillouin scattering phenomenon and the Brillouin in the reference optical fiber 17 stored in advance in the storage unit by the frequency setting unit. The first and second light sources 1 and 20 in the first and second light sources 1 and 20 based on the relationship between the light intensity related to the scattering phenomenon and the light intensity related to the Brillouin scattering phenomenon obtained by the Brillouin time domain detector 14. The first AFC 11 and / or the second AFC 19 are controlled so that the frequency difference of each light emitted from the light emitting element becomes a predetermined frequency difference set in advance.

  FIG. 4 is a diagram for explaining the adjustment of the frequency of each light emitted from the first and second light sources. The horizontal axis in FIG. 4 is the relative frequency difference, and the vertical axis is the light intensity.

  As shown in FIG. 4, the relationship between the frequency difference between the first and second light causing the Brillouin scattering phenomenon and the light intensity of the light related to the Brillouin scattering phenomenon in the reference optical fiber 17 is substantially convex on the Lorentz curve. Curve C.

  First, the control processing unit 13 obtains a reference light intensity Pa corresponding to a predetermined frequency difference fa to be set for each light emitted by the first and second light emitting elements in the first and second light sources 1 and 20 from the above relationship. . Then, the control processing unit 13 controls the first AFC 11 and / or the second AFC 19 so that the measured light intensity Pd detected by the Brillouin time domain detector 14 matches the reference light intensity Pa.

  Alternatively, the control processing unit 13 obtains the frequency difference fd corresponding to the measured light intensity Pd detected by the Brillouin time domain detector 14 from the relationship. Then, the control processing unit 13 controls the first AFC 11 and / or the second AFC 19 so that the obtained frequency difference fd matches the predetermined frequency difference fa to be set.

  As a result, the frequency difference between the lights emitted from the first and second light emitting elements in the first and second light sources 1 and 20 is adjusted to a predetermined frequency difference fa to be set. In this embodiment, the light intensity Pd is given by a voltage value photoelectrically converted by the light receiving element, and the reference light intensity Pa is a voltage value corresponding to the reference light intensity Pa.

  The relationship between the frequency difference between the first and second light causing the Brillouin scattering phenomenon and the light intensity of the light related to the Brillouin scattering phenomenon in the reference optical fiber 17 has temperature dependence. In the present embodiment, when adjusting the frequency difference of each light emitted by the first and second light emitting elements in the first and second light sources 1 and 20 to the predetermined frequency difference fa, the control processing unit 13 includes the temperature detection unit. 16, the temperature of the reference optical fiber 17 is detected, and the relationship in the reference optical fiber 17 is corrected according to the detected temperature. For this reason, the frequency difference of each light which the 1st and 2nd light emitting element in the 1st and 2nd light sources 1 and 20 light-emit is adjusted with high precision to predetermined frequency difference fa.

  By operating in this way, the frequency of continuous light emitted from the first light source 1 and the frequency of continuous light emitted from the second light source 20 are adjusted.

  A distributed optical fiber sensor is usually composed of a detection optical fiber and a distributed optical fiber sensor main body. Conventionally, the frequency of continuous light emitted from the first light source 1 and the frequency of continuous light emitted from the second light source 20 are adjusted between the distributed optical fiber sensor body and the detection optical fiber (distributed type). The reference optical fiber is optically connected to the outside of the optical fiber sensor main body, and this reference optical fiber is used. In the distributed optical fiber sensor S of this embodiment, the distributed optical fiber sensor is used. This is performed by using a reference optical fiber 17 disposed inside the main body. For this reason, unlike the prior art, there is no need to optically connect a reference optical fiber to the outside of the distributed optical fiber sensor main body, and the complexity is eliminated. Since the reference optical fiber 17 is disposed inside the distributed optical fiber sensor main body, the temperature of the reference optical fiber 17 can be easily detected and emitted from the first light source 1 with higher accuracy. The frequency of the continuous light emitted and the frequency of the continuous light emitted from the second light source 20 can be adjusted.

  As will be described later, in order to obtain a Brillouin gain / loss spectrum, for example, the frequency of continuous light emitted from the second light source 20 is swept in a predetermined frequency range at predetermined frequency intervals under the control of the control processing unit 13. The For this reason, the adjustment of the frequency of the continuous light emitted from the first light source 1 and the frequency of the continuous light emitted from the second light source 20 changes the frequency for the sweep from the viewpoint of improving measurement accuracy. It may be executed whenever it is done.

  Further, the adjustment of the frequency of the continuous light emitted from the first light source 1 and the frequency of the continuous light emitted from the second light source 20 can be performed for the sweep if the adjustment is executed once with a certain frequency difference. Even if the frequency is changed, the changed frequency is changed to a predetermined frequency with high accuracy. Therefore, from the viewpoint of shortening the measurement time, the frequency may be executed every measurement or every elapse of a predetermined period. Alternatively, it may be executed when the distributed optical fiber sensor S is activated.

  Next, the strain and / or temperature measurement operation will be described.

  First, the control processing unit 13 controls the first ATC 10 and the first AFC 11 to cause the first light source 1 to emit continuous light of a predetermined frequency, emits the continuous light from the first light source 1, and causes the second ATC 18 and the second AFC 19 to be emitted. By controlling, the second light source 20 emits continuous light having a predetermined frequency, and the continuous light is emitted from the second light source 20. The continuous light emitted from the first light source 1 is incident on the optical pulse generator 3 via the optical coupler 2, and the continuous light emitted from the second light source 20 is incident on the optical switch 22 via the optical coupler 21. Is done.

  Next, the control processing unit 13 controls the optical pulse generation unit 3 so that the optical pulse generation unit 3 generates a sub optical pulse and a main optical pulse having a predetermined waveform, and the sub optical pulse and the main optical pulse are converted into the optical pulse. Injection from the generating unit 3. The sub light pulse and the main light pulse emitted from the light pulse generator 3 are incident on the optical switch 4.

  The control processing unit 13 turns on the optical switch 4 and the optical switch 22 according to the generation timing of the sub optical pulse and the main optical pulse in the optical pulse generation unit 3. The control processing unit 13 notifies the Brillouin time domain detector 14 of the generation timing of the sub light pulse and the main light pulse.

  When the optical switch 4 is turned on, the sub optical pulse and the main optical pulse are incident on the optical coupler 5 and branched into two. One of the branched sub-light pulses and the main light pulse are incident on the light intensity / polarization adjustment unit 6, the light intensity is adjusted by the light intensity / polarization adjustment unit 6, and the polarization direction is random (random). The light is adjusted and incident on one end of the detection optical fiber 15 via the optical circulator 7, the optical coupler 8, and the optical connector 9. On the other hand, the other sub optical pulse and the main optical pulse branched by the optical coupler 5 enter the Brillouin time domain detector 14.

  The Brillouin time domain detector 14 measures the spectrum of the sub light pulse and the main light pulse, and notifies the control processing unit 13 of the frequency and light intensity of the sub light pulse and the main light pulse. Upon receiving this notification, the control processing unit 13 controls the first ATC 10, the first AFC 11, and the light intensity / polarization adjustment unit 6 as necessary so that an optimum measurement result can be obtained.

  When the optical switch 22 is turned on, the continuous light is incident on the optical coupler 23 and branched into two. One branched continuous light is incident on the light intensity adjusting unit 24, the light intensity of which is adjusted by the light intensity adjusting unit 24, and incident on the 1 × 2 optical switch 25. In the 1 × 2 optical switch 25, when Brillouin gain / loss spectrum time domain analysis is performed, light incident from the input terminal enters the other end of the detection optical fiber 15 via the optical connector 26. The continuous light is incident on the other end of the detection optical fiber 15 via the optical connector 26. On the other hand, when the Brillouin gain / loss spectrum time domain reflection analysis is performed, the 1 × 2 optical switch 25 detects light incident from the input terminal via the optical coupler 8 and the optical connector 9. Switching is performed so as to be incident on one end of the fiber 15, and the continuous light is incident on one end of the detection optical fiber 15 via the optical coupler 8 and the optical connector 9. On the other hand, the other continuous light branched by the optical coupler 23 is incident on the Brillouin time domain detector 14.

  The Brillouin time domain detector 14 measures the spectrum of continuous light and notifies the control processing unit 13 of the frequency and light intensity of continuous light. Upon receiving this notification, the control processing unit 13 controls the second ATC 18, the second AFC 19, and the light intensity adjustment unit 24 as necessary so that an optimum measurement result can be obtained.

  In the Brillouin gain / loss spectrum time domain analysis, the sub optical pulse and the main optical pulse incident on one end of the detection optical fiber 15 are incident on the other end of the detection optical fiber 15 and propagate through the detection optical fiber 15. The detection optical fiber 15 propagates from one end to the other end while causing a continuous light and a Brillouin scattering phenomenon. In the Brillouin gain / loss spectrum time domain reflection analysis, the sub-light pulse and the main light pulse incident on one end of the detection optical fiber 15 are incident from one end of the detection optical fiber 15 and the detection optical fiber 15 It propagates from one end of the detection optical fiber 15 to the other end while causing a Brillouin scattering phenomenon and continuous light that is reflected at the other end and propagates through the detection optical fiber 15. In the Brillouin gain / loss spectrum time domain reflection analysis, the sub light pulse and the main light pulse are one end of the detection optical fiber 15 at the timing when the continuous light incident on one end of the detection optical fiber 15 is reflected by the other end. The timing at which the optical switch 4 is turned on is adjusted so as to be incident on the optical fiber, and the continuous light incident on one end of the detection optical fiber 15 and reflected on the other end is sub-pulsed and main light in the detection optical fiber 15. The timing at which the optical switch 22 is turned off is adjusted so as to cause the pulse and the Brillouin scattering phenomenon.

  The light related to the Brillouin scattering phenomenon is emitted from one end of the detection optical fiber 15 and is incident on the Brillouin time domain detector 14 through the optical connector 9, the optical coupler 8, and the optical circulator 7. The Brillouin time domain detector 14 performs time domain analysis on the received light related to the Brillouin scattering phenomenon based on the generation timing notified from the control processing unit 13, and Brillouin scattering in the longitudinal direction of the detection optical fiber 15. The distribution of light intensity of light related to the phenomenon is measured.

  Here, the degree of interaction between the sub light pulse and the main light pulse related to the Brillouin scattering phenomenon and the continuous light depends on the relative relationship between the polarization planes of these lights, but the distributed light according to the present embodiment. In the fiber sensor S, since the polarization planes of the sub light pulse and the main light pulse are randomly changed by the light intensity / polarization adjustment unit 6 for each measurement, this measurement can be performed by performing the measurement multiple times and adopting the average value. The sex can be substantially eliminated. Therefore, it is possible to obtain a light intensity distribution of light related to the Brillouin scattering phenomenon with high accuracy.

  The light intensity distribution of the light related to the Brillouin scattering phenomenon in the longitudinal direction of the detection optical fiber 15 is set to a predetermined frequency by controlling the frequency of continuous light emitted from the second light source 20 by controlling the control processing unit 13, for example. By sweeping in a predetermined frequency range at intervals, each frequency is measured with high accuracy and high spatial resolution. As a result, the Brillouin gain / loss spectrum in each region in the longitudinal direction of the detection optical fiber 15 can be obtained with high accuracy and high spatial resolution.

  Then, the Brillouin time domain detector 14 uses the frequency corresponding to the peak of the Brillouin gain / loss spectrum in the portion where the detection optical fiber 15 is not distorted as a reference in the longitudinal direction of the detection optical fiber 15. By obtaining the frequency difference corresponding to the Brillouin gain / loss spectrum peak in each region, the Brillouin frequency shift in each longitudinal portion of the detection optical fiber 15 is obtained with high accuracy and high spatial resolution.

  Then, the Brillouin time domain detector 14 obtains the strain and / or temperature in each region in the longitudinal direction of the detection optical fiber 15 with high accuracy and high spatial resolution from the Brillouin frequency shift of each region. The obtained strain and / or temperature distribution in each region in the longitudinal direction of the detection optical fiber 15 is presented to an output unit (not shown) such as a CRT display device, an XY plotter, or a printer.

  Next, an example of sub-light pulses and main light pulses used in the distributed optical fiber sensor according to the present embodiment will be described.

  FIG. 5 is a diagram illustrating waveforms of a sub light pulse and a main light pulse and a Brillouin gain spectrum according to the first aspect. FIG. 6 is a diagram illustrating AC outputs of the first and second driver circuits input to the first and second light intensity modulators. FIG. 7 is a diagram illustrating waveforms of a sub light pulse and a main light pulse and a Brillouin gain spectrum according to the second mode. FIG. 8 is a diagram illustrating waveforms of the sub light pulse and the main light pulse according to the third to fifth aspects. FIG. 9 and FIG. 10 are diagrams showing optical pulse waveforms and Brillouin gain spectra according to the first and second comparative examples. FIGS. 5A and 7A show waveforms of the sub light pulse and the main light pulse according to the first and second modes. FIGS. 9A and 10A show the waveforms of optical pulses according to the first and second comparative examples. 5 (A), FIG. 7 (A), FIG. 8 (A) to (C), FIG. 9 (A) and FIG. 10 (A), the horizontal axis represents time (time) expressed in units of ns. The vertical axis represents the light intensity. FIGS. 5B and 7B show Brillouin gain spectra according to the first and second aspects. FIGS. 9B and 10B show Brillouin gain spectra according to the first and second comparative examples. 5B, FIG. 7B, FIG. 9B, and FIG. 10B, the horizontal axis represents the frequency (Frequency) expressed in MHz, and the vertical axis represents a. u. It is a Brillouin gain represented by (arbitrary unit). Note that FIG. 5B, FIG. 7B, FIG. 9B, and FIG. 10B are simulation results. FIG. 6A shows the case of the first mode, and FIG. 6B shows the case of the second mode.

In the first mode, as shown in FIG. 5A, the main light pulse OPm has a first predetermined pulse width D1 and a rectangular shape having a first predetermined light intensity P1 (the light intensity P is between the first predetermined pulse widths D1). The sub-light pulse OPs has a rectangular shape of the second predetermined light intensity P2 with the second predetermined pulse width D2 (the light intensity P is between the second predetermined pulse widths D2). The light intensity P2 is constant). A predetermined time is provided between the sub light pulse OPs and the main light pulse OPm. Accordingly, the second predetermined pulse width D2 of the sub light pulse OPs is shorter than the time from the rise of the sub light pulse OPs to the rise of the main light pulse OPm. Since the sub light pulse OPs has such a waveform, even if the second predetermined light intensity P2 of the sub light pulse OPs is the same as the light intensity Cs ² of the light pulse forward light OPf shown in FIG. The energy is smaller than the energy of the light pulse forward light OPf.

  For example, the main light pulse OPm has a pulse width D1 of 1 ns and a light intensity P1 of 0.062, and the sub light pulse OPs has a pulse width D2 of 5 ns and a light intensity P2 of 0.005. A time of 7 ns is left between the sub light pulse OPs and the main light pulse OPm (from the fall of the sub light pulse OPs to the rise of the main light pulse OPm).

  In order to generate the sub optical pulse OPs and the main optical pulse OPm according to the first aspect, the optical pulse generator 3 operates as follows. As shown in FIG. 6A, first, the second driver circuit 35 determines that the light intensity P in the light emitted from the second light intensity modulator 34 is the second predetermined light intensity P2 (in the case of FIG. 5A). A rectangular voltage pulse having a voltage value of 0.005) is output as an AC output to the second light intensity modulator 34 at time t1 (0 ns in the case of FIG. 5A), and the second predetermined pulse width is output from time t1. This output is stopped at time t2 (5 ns in the case of FIG. 5A) when the time corresponding to D2 (5 ns in the case of FIG. 5A) has elapsed. Next, at time t3 (12 ns in the case of FIG. 5A) when the time corresponding to the predetermined time (7 ns in the case of FIG. 5A) has elapsed from the time t2, the first driver circuit 33 A rectangular voltage pulse having a voltage value at which the light intensity P in the light emitted from the one light intensity modulator 32 is the first predetermined light intensity P1 (0.062 in the case of FIG. 5A) is used as an AC output to obtain the first light intensity. This is output to the modulator 32, and at time t4 (13 ns in the case of FIG. 5A) when a time corresponding to the first predetermined pulse width D1 (1 ns in the case of FIG. 5A) has elapsed from the time t3. Stop output. As the optical pulse generator 3 operates in this manner, for example, the sub optical pulse OPs and the main optical pulse OPm having the waveform shown in FIG. 5A are generated. In order to synchronize between the first and second driver circuits 33 and 35, for example, the second driver circuit 35 notifies the first driver circuit 33 of the rising timing (time t1) of the rectangular voltage pulse. The same applies to the following second to fifth modes.

Here, the sub optical pulse OPs is light for generating acoustic phonons in the detection optical fiber 15 before the main optical pulse OPm generates acoustic phonons in the detection optical fiber 15. The time from the rise time of the optical pulse OPs to the rise time of the main light pulse OPm is appropriately set to a time within the duration of the acoustic phonon in the detection optical fiber 15, for example, 5 ns, 10 ns, 15 ns, 20 ns, etc. Is set. The pulse width D1 of the main light pulse OPm is appropriately set according to a desired spatial resolution, but is set to 10 ns or less in order to obtain a high spatial resolution of 1 m or less. The light intensity P2 of the sub light pulse OPs and the light intensity P1 of the main light pulse OPm define a ratio R = 10 × log (P1 / P2), and the simulation of H is performed to calculate H ₂ / (H _{1 with} respect to the ratio R. + H ₃ + H ₄ ) is determined, and the ratio R is set so that the value of H ₂ / (H ₁ + H ₃ + H ₄ ) is 0.5 or more. Since the strain and / or temperature can be detected with the highest accuracy and high spatial resolution, the ratio R is set to a value giving a peak of H ₂ / (H ₁ + H ₃ + H ₄ ), and the sub The light intensity P2 of the optical pulse OPs and the light intensity P1 of the main light pulse OPm are set. The same applies to the following second to fifth modes.

In the second mode, as shown in FIG. 7A, the main light pulse OPm has a rectangular shape having a first predetermined pulse width D1 and a first predetermined light intensity P1, and the sub light pulse OPs is a second predetermined pulse. The light intensity P rises at a second predetermined light intensity (maximum light intensity) P2 with a width D2, and the light intensity P gradually decreases with time, and the main light pulse OPm is almost immediately after the end of the sub light pulse OPs. Standing up. Since the sub light pulse OPs has such a waveform, even if the second predetermined light intensity P2 of the sub light pulse OPs is the same as the light intensity Cs ² of the light pulse forward light OPf shown in FIG. The energy is smaller than the energy of the light pulse forward light OPf.

  For example, the main light pulse OPm has a pulse width D1 of 1 ns and a light intensity P1 of 0.062, and the sub light pulse OPs has a pulse width D2 of 13 ns and a rising light intensity P2 of 0.005. is there.

  In order to generate the sub optical pulse OPs and the main optical pulse OPm according to the second mode, the optical pulse generator 3 operates as follows. As shown in FIG. 6B, first, the second driver circuit 35 generates a right triangular voltage pulse at time t1 (see FIG. 6) in which the light intensity P in the light emitted from the second light intensity modulator 34 is the right triangular shape. In the case of 7 (A), it is output to the second optical intensity modulator 34 as an AC output at 0 ns), and a time corresponding to the second predetermined pulse width D2 (13 ns in the case of FIG. 7A) from time t1. This output is stopped at the elapsed time t2 (13 ns in the case of FIG. 7A). Next, immediately (at time t3 (13 ns in the case of FIG. 7A)), the first driver circuit 33 determines that the light intensity P in the light emitted from the first light intensity modulator 32 is the first predetermined light intensity P1 ( A rectangular voltage pulse having a voltage value of 0.062 in the case of FIG. 7A is output as an AC output to the first light intensity modulator 32, and the first predetermined pulse width D1 (FIG. 7A) from time t3. ), The output is stopped at time t4 (14 ns in the case of FIG. 7A) at which time corresponding to 1 ns) has elapsed. The sub optical pulse OPs and the main optical pulse OPm having the waveform shown in FIG. 7A are generated.

In the third mode, as shown in FIG. 8A, the main light pulse OPm has a rectangular shape having a first predetermined pulse width D1 and a first predetermined light intensity P1, and the sub light pulse OPs is a second predetermined pulse. The light intensity P is a right triangle having a width D2 and gradually increases with time until reaching the second predetermined light intensity (maximum light intensity) P2, and the first light pulse OPm is almost immediately after the end of the second light pulse OPs. Standing up. Since the sub light pulse OPs has such a waveform, even if the second predetermined light intensity P2 of the sub light pulse OPs is the same as the light intensity Cs ² of the light pulse forward light OPf shown in FIG. The energy is smaller than the energy of the light pulse forward light OPf.

  For example, the main light pulse OPm has a pulse width D1 of 1 ns and a light intensity P1 of 0.062, and the sub light pulse OPs has a pulse width D2 of 13 ns and the falling light intensity P2 has a maximum light intensity. And 0.005.

  In order to generate the sub optical pulse OPs and the main optical pulse OPm according to the third aspect, the optical pulse generator 3 operates as follows. First, the second driver circuit 35 generates a right triangle voltage pulse at time t1 (in the case of FIG. 8A, 0 ns) in which the light intensity P in the light emitted from the second light intensity modulator 34 is the right triangle. An AC output is output to the second light intensity modulator 34, and a time t2 (FIG. 8A) when a time corresponding to the second predetermined pulse width D2 (13 ns in the case of FIG. 8A) elapses from the time t1. In this case, this output is stopped at 13 ns). Next, immediately (at time t3 (13 ns in the case of FIG. 8A)), the first driver circuit 33 determines that the light intensity P in the light emitted from the first light intensity modulator 32 is the first predetermined light intensity P1 ( A rectangular voltage pulse having a voltage value of 0.062 in the case of FIG. 8A is output as an AC output to the first light intensity modulator 32, and the first predetermined pulse width D1 (FIG. 8A from FIG. 8A) is output from time t3. ), The output is stopped at time t4 (14 ns in the case of FIG. 8A) when the time corresponding to 1 ns has elapsed. The sub optical pulse OPs and the main optical pulse OPm having the waveform shown in FIG. 8 (A) are generated.

In the fourth mode, as shown in FIG. 8B, the main light pulse OPm has a rectangular shape having a first predetermined pulse width D1 and a first predetermined light intensity P1, and the sub light pulse OPs is a second predetermined pulse. In the width D2, the light intensity P is an isosceles triangle shape that gradually increases to a second predetermined light intensity (maximum light intensity) P2 with time and then gradually decreases with time, and the main light pulse OPm is sub It rises almost immediately after the end of the optical pulse OPs. Since the sub light pulse OPs has such a waveform, even if the second predetermined light intensity P2 of the sub light pulse OPs is the same as the light intensity Cs ² of the light pulse forward light OPf shown in FIG. The energy is smaller than the energy of the light pulse forward light OPf.

  For example, the main light pulse OPm has a pulse width D1 of 1 ns and a light intensity P1 of 0.062, and the sub light pulse OPs has a pulse width D2 of 13 ns and the maximum light intensity P2 at the center of the pulse is 0. .005.

  In order to generate the sub optical pulse OPs and the main optical pulse OPm according to the fourth aspect, the optical pulse generator 3 operates as follows. First, the second driver circuit 35 generates an isosceles triangle voltage pulse in which the light intensity P in the light emitted from the second light intensity modulator 34 is the above isosceles triangle shape at time t1 (in the case of FIG. 8B, 0 ns). ) And output to the second light intensity modulator 34 as an AC output, and a time t2 (FIG. 8 (FIG. 8 (B)) when the time corresponding to the second predetermined pulse width D2 (14 ns in the case of FIG. 8 (B)) has elapsed from the time t1. In the case of B), this output is stopped at 14 ns). Next, immediately (at time t3 (14 ns in the case of FIG. 8B)), the first driver circuit 33 determines that the light intensity P in the light emitted from the first light intensity modulator 32 is the first predetermined light intensity P1 ( A rectangular voltage pulse having a voltage value of 0.062 in the case of FIG. 8B is output as an AC output to the first light intensity modulator 32, and the first predetermined pulse width D1 (FIG. 8B) from time t3. ), The output is stopped at time t4 when the time corresponding to 1 ns has elapsed (15 ns in the case of FIG. 8B). The sub optical pulse OPs and the main optical pulse OPm having the waveform shown in FIG. 8B are generated.

In the fifth mode, as shown in FIG. 8C, the main light pulse OPm has a rectangular shape with a first predetermined pulse width D1 and a first predetermined light intensity P1, and the sub light pulse OPs is a second predetermined pulse. The light intensity P is a Gaussian curve having a width D2 that gradually increases to a second predetermined light intensity (maximum light intensity) P2 over time and then gradually decreases over time. A predetermined time is provided between the sub light pulse OPs and the main light pulse OPm. Accordingly, the second predetermined pulse width D2 of the sub light pulse OPs is shorter than the time from the rise of the sub light pulse OPs to the rise of the main light pulse OPm. Since the sub light pulse OPs has such a waveform, even if the second predetermined light intensity P2 of the sub light pulse OPs is the same as the light intensity Cs ² of the light pulse forward light OPf shown in FIG. The energy is smaller than the energy of the light pulse forward light OPf.

  For example, the main light pulse OPm has a pulse width D1 of 1 ns and a light intensity P1 of 0.062, and the sub light pulse OPs has a pulse width D2 of 5 ns and a maximum light intensity P2 of 0.005. A time of 4.5 ns is left between the sub light pulse OPs and the main light pulse OPm (from the fall of the sub light pulse OPs to the rise of the main light pulse OPm).

  In order to generate the sub optical pulse OPs and the main optical pulse OPm according to the fifth aspect, the optical pulse generator 3 operates as follows. First, the second driver circuit 35 generates a voltage pulse having a Gaussian curve shape in which the light intensity P in the light emitted from the second light intensity modulator 34 has the Gaussian curve shape at time t1 (0 ns in the case of FIG. 8C). Is output to the second light intensity modulator 34 as an AC output, and the time t2 (FIG. 8C) when the time corresponding to the second predetermined pulse width D2 (5 ns in the case of FIG. 8C) has elapsed from the time t1. In this case, the output is stopped at 5 ns). Next, at a time t3 (9.5 ns in the case of FIG. 8C) when a time corresponding to the predetermined time (4.5 ns in the case of FIG. 8C) has elapsed from the time t2, the first driver circuit. 33 is a rectangular voltage pulse having a voltage value at which the light intensity P in the light emitted from the first light intensity modulator 32 becomes the first predetermined light intensity P1 (0.062 in the case of FIG. 8C) as an AC output. The signal is output to the first light intensity modulator 32, and the time corresponding to the first predetermined pulse width D1 (1 ns in the case of FIG. 8C) has elapsed from time t3 (in the case of time t4 (FIG. 8C)). This output is stopped at 10.5 ns). By operating the optical pulse generator 3 in this manner, for example, the sub optical pulse OPs and the main optical pulse OPm having the waveform shown in FIG. 8C are generated.

In the sub light pulse OPs and the main light pulse OPm according to the first to fifth aspects, the sub light pulse OPs temporally preceding the main light pulse OPm has a maximum light intensity P2 of the sub light pulse OPs of the main light pulse OPm. When a constant light pulse OPf is considered at the maximum light intensity P2 from the rise to the rise of the main light pulse OPm, the energy of the sub light pulse OPs is less than the light pulse OPf considered. Is set to be smaller than the energy at. Therefore, components of the H ₄ serving as a noise component is reduced, the influence of the H ₂ is suppressed. For this reason, the peak width of the Brillouin gain / loss spectrum is narrowed, the measurement error of the center frequency is reduced, and the Brillouin frequency shift can be measured with higher accuracy. As a result, the strain and / or temperature can be measured with higher accuracy.

  Here, as a first comparative example, as shown in FIG. 9A, first and second optical pulses OPw1 and OPw2 having the same pulse width and optical intensity are provided, and the first optical pulse OPw1 and the second optical pulse are provided. When a predetermined time is left between the first optical pulse OPw2 and the second optical pulse OPw1 and OPw2 in the case of FIG. 9A, the pulse width is 1 ns and the light intensity is 0. 0. 062 and the predetermined time is 5 ns), the Brillouin gain spectrum by the first and second optical pulses OPw1 and OPw2 and the continuous light is relatively large as shown in FIG. The profile has a plurality of peaks with high intensities, and the light intensity of the peak for obtaining the Brillouin frequency shift (the peak indicated by the arrow in FIG. 9B) has almost no difference from the intensities of the peaks on both sides of this peak. . For this reason, it is difficult for the distributed optical fiber sensor S to extract a peak for obtaining the Brillouin frequency shift.

  On the other hand, the Brillouin gain spectrum of the sub optical pulse OPs and the main optical pulse OPm and the continuous light according to the first to fifth aspects has a plurality of peaks, but the intensity of the peak for obtaining the Brillouin frequency shift is The profile is clearly larger than the intensity in the peaks on both sides of this peak. For example, the Brillouin gain spectrum in the case of the first mode is shown in FIG. 5B, and the Brillouin gain spectrum in the case of the second mode is shown in FIG. 7B. In each of these drawings, the peak for obtaining the Brillouin frequency shift is indicated by an arrow. For this reason, it becomes easier for the distributed optical fiber sensor S to extract a peak for obtaining the Brillouin frequency shift.

  As a second comparative example, as shown in FIG. 10A, in the case of the stepped light pulse disclosed in Patent Document 1 (in the case of FIG. 10A, the pulse width is 13 ns and the light intensity is Is a stepped light pulse having an optical pulse OP having a pulse width of 1 ns and a light intensity of 0.062 after the optical pulse forward light OPf having a value of 0.005, the stepped light pulse and the continuous light are The Brillouin gain spectrum has the profile shown in FIG. 10B, and the half width of the peak for obtaining the Brillouin frequency shift indicated by the arrow is the sub optical pulse OPs and the main optical pulse OPm according to the first to fifth aspects. Larger than the full width at half maximum of the peak for obtaining the Brillouin frequency shift in the Brillouin gain spectrum due to the continuous light. For this reason, distortion and / or temperature can be measured with higher accuracy in the Brillouin gain spectrum of the sub light pulse OPs and the main light pulse OPm and the continuous light according to the first to fifth aspects.

  The distributed optical fiber sensor S in the above embodiment measures the Brillouin gain / loss spectrum by fixing the frequency of the sub light pulse and the main light pulse and sweeping the frequency of the continuous light in a predetermined frequency range. To do. For this reason, the light-emitting element of the first light source 1 is not necessarily a frequency variable semiconductor laser, and may be a frequency fixed semiconductor laser.

  Further, in the distributed optical fiber sensor S in the above-described embodiment, the frequency of the sub light pulse and the main light pulse is fixed, and the frequency of the continuous light is swept in a predetermined frequency range to measure the Brillouin gain / loss spectrum. However, the Brillouin gain / loss spectrum may be measured by fixing the frequency of the continuous light and sweeping the frequencies of the sub light pulse and the main light pulse in a predetermined frequency range.

  The optical pulse generator 3 in the above-described embodiment splits the incident light into two, generates a sub optical pulse from the one incident light by the second light intensity modulator 34, and generates the first light from the other incident light. The main light pulse is generated by the light intensity modulator 32, and the sub light pulse and the main light pulse are combined. The sub voltage pulse having a shape corresponding to the sub light pulse and the main light pulse are supported. The main voltage pulse having the waveform to be electrically synthesized is input to the optical intensity modulator as the AC output from the electrically synthesized sub voltage pulse and the main voltage pulse. May be configured to generate.

  In the above-described embodiment, the distributed optical fiber sensor S is configured so that the Brillouin gain / loss spectrum time domain analysis and the Brillouin gain / loss spectrum time domain reflection analysis can be performed integrally. Even if the distributed optical fiber sensor capable of performing Brillouin gain / loss spectrum time domain analysis and the distributed optical fiber sensor capable of performing Brillouin gain / loss spectrum time domain reflection analysis are configured separately. good.

  In the above-described embodiment, in the Brillouin time domain detector, incident light incident from the third input terminal is received by a light receiving circuit including a light receiving element that performs photoelectric conversion. From the circuit configuration of the light receiving circuit, The continuous light incident on the detection optical fiber 15 may have its light intensity modulated as shown in FIG.

  FIG. 11 is a diagram for explaining the light intensity modulation of continuous light incident on the detection optical fiber. FIG. 11A shows a waveform of continuous light incident on the detection optical fiber, the horizontal axis is time, and the vertical axis is light intensity. FIG. 11B is a circuit diagram illustrating a configuration example of the light receiving circuit. FIG. 11C is a diagram showing the frequency characteristics of the light receiving circuit, the horizontal axis is the frequency, and the vertical axis is the output of the light receiving circuit.

  As shown in FIG. 11B, the light receiving circuit 40 includes, for example, a photoelectric conversion element photodiode 41, a resistance element 42, capacitors 43 and 45, an amplifier 44, and a high-pass filter (HPF) 46. Composed. The photodiode 41 is grounded via a current-voltage converting resistance element 42 connected in series, and a bias voltage Vcc is applied to the series-connected photodiode 41 and resistance element 42. An amplifier 44 is connected to a connection point between the photodiode 41 and the resistance element 42 via a capacitor 43 for cutting a DC component. A high pass filter 46 is connected to the amplifier 44 via a capacitor 43 for cutting a DC component. In such a light receiving circuit 40, when the photodiode 41 receives light related to the Brillouin scattering phenomenon, a photocurrent corresponding to the amount of received light flows through the resistance element 42, and current-voltage conversion is performed by the resistance element 42. The current-voltage converted voltage output is input to the amplifier 44 through the capacitor 43 and amplified by the amplifier 44. The output of the amplifier 44 is input to the high pass filter 46 through the capacitor 45, and a predetermined low frequency range set in advance is cut.

  Here, when the continuous light incident on the detection optical fiber 15 is received by a light receiving circuit including a photodiode 41, a resistor element 42, a capacitor 43, and an amplifier 44 without being modulated in light intensity, the light receiving circuit 11C gradually rises with a time constant determined by the resistance value R of the resistance element 42 and the capacitance C of the capacitor 43 in the low frequency region as shown in FIG. 11C, so that the measurement in the low frequency region is good. It may not be possible.

  Therefore, the continuous light incident on the detection optical fiber has a predetermined amplitude at a frequency corresponding to a time constant determined by the resistance value R of the resistance element 42 and the capacitance C of the capacitor 43, as shown in FIG. The light intensity is modulated. The light receiving circuit is configured as described above so that a low frequency component equal to or lower than this frequency is cut by the high pass filter 46.

  With this configuration, the light receiving circuit cuts the output of the region that gradually rises with a time constant determined by the resistance value R of the resistance element 42 and the capacitance C of the capacitor 43, as shown in FIG. Apparently, the output value can be obtained directly.

  In this embodiment, since the optical switch 22 includes a light intensity modulator, the continuous light emitted from the second light source 20 by the optical switch 22 has a light intensity with a predetermined amplitude centered on a predetermined light intensity. Modulated and incident on the detection optical fiber 15. For example, in the optical switch 22, the continuous light is subjected to light intensity modulation at 100 kHz, and the cutoff frequency of the high pass filter 46 is set to 100 kHz.

  In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Accordingly, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not limited to the scope of the claims. To be construed as inclusive.

It is a figure for demonstrating the theoretical analysis of a Brillouin scattering phenomenon. It is a block diagram which shows the structure of the distributed optical fiber sensor in embodiment. It is a block diagram which shows the structure of the optical pulse production | generation part in a distributed optical fiber sensor. It is a figure for demonstrating adjustment of the frequency of each light which a 1st and 2nd light source light-emits. It is a figure which shows the waveform of a sub optical pulse which concerns on a 1st aspect, and a main optical pulse, and a Brillouin gain spectrum. It is a figure which shows the AC output of the 1st and 2nd driver circuit input into a 1st and 2nd light intensity modulator. It is a figure which shows the waveform of the sub optical pulse which concerns on a 2nd aspect, and the main optical pulse, and a Brillouin gain spectrum. It is a figure which shows the waveform of the sub light pulse and main light pulse which concern on a 3rd thru | or 5th aspect. It is a figure which shows the waveform of the optical pulse which concerns on a 1st comparative example, and a Brillouin gain spectrum. It is a figure which shows the waveform of the optical pulse which concerns on a 2nd comparative example, and a Brillouin gain spectrum. It is a figure for demonstrating light intensity modulation of the continuous light which injects into the optical fiber for a detection. It is a figure which shows the distributed optical fiber sensor which concerns on background art. It is a figure which shows a Brillouin gain spectrum.

Explanation of symbols

DESCRIPTION OF SYMBOLS S Distributed type optical fiber sensor 3 Optical pulse generation part 13 Control processing part 14 Brillouin time domain detector 16 Temperature detection part 17 Reference optical fiber sensor 31, 36 Polarization-maintaining optical couplers 32, 34 First and second optical intensity modulators 33, 35 first and second driver circuits

Claims (10)

In a distributed optical fiber sensor that measures strain and / or temperature using the Brillouin scattering phenomenon,
Prior to the main light pulse, the maximum light intensity is smaller than the light intensity of the main light pulse, and the energy in the light pulse constant at the maximum light intensity from the rise to the rise of the main light pulse. An optical pulse light source that generates a small sub optical pulse, and
A continuous light source that generates continuous light;
An optical fiber for detection in which the sub light pulse and the main light pulse and the continuous light are incident, and a Brillouin scattering phenomenon occurs between the sub light pulse and the main light pulse and the continuous light;
A Brillouin gain spectrum or a Brillouin loss spectrum is obtained based on the light related to the Brillouin scattering phenomenon emitted from the detection optical fiber, and the Brillouin gain spectrum or the Brillouin loss spectrum is obtained based on the obtained Brillouin gain spectrum or the Brillouin loss spectrum. A distributed optical fiber sensor comprising: a Brillouin time domain detector that measures strain and / or temperature generated in a detection optical fiber. The sub light pulse and the main light pulse are incident from one end of the detection optical fiber,
The continuous light enters from the other end of the optical fiber for detection,
The Brillouin time domain detector obtains a Brillouin gain spectrum or a Brillouin loss spectrum based on light related to a Brillouin scattering phenomenon emitted from one end of the detection optical fiber, and determines the Brillouin gain spectrum obtained. The distributed optical fiber sensor according to claim 1, wherein strain and / or temperature generated in the detection optical fiber is measured based on a Brillouin loss spectrum. The sub light pulse and the main light pulse are incident from one end of the detection optical fiber,
The continuous light is incident from one end of the detection optical fiber,
The detection optical fiber reflects the continuous light propagating at the other end,
The Brillouin time domain detector obtains a Brillouin gain spectrum or a Brillouin loss spectrum based on light related to a Brillouin scattering phenomenon emitted from one end of the detection optical fiber, and determines the Brillouin gain spectrum obtained. The distributed optical fiber sensor according to claim 1, wherein strain and / or temperature generated in the detection optical fiber is measured based on a Brillouin loss spectrum. 4. The distributed light according to claim 1, wherein a pulse width of the sub light pulse is shorter than a time from a rising edge to a rising edge of the main light pulse. 5. Fiber sensor. 4. The distributed optical fiber sensor according to claim 1, wherein the light intensity of the sub light pulse decreases with time. The distributed optical fiber sensor according to any one of claims 1 to 3, wherein the light intensity of the sub light pulse increases with time. 4. The distributed optical fiber sensor according to claim 1, wherein the light intensity of the sub-light pulse increases with the passage of time and then decreases. The light pulse light source and the continuous light source are:
First and second light emitting elements that continuously emit light having a predetermined frequency with a narrow line width and a substantially constant light intensity;
First and second temperature controllers that respectively hold the temperatures of the first and second light emitting elements substantially constant;
First and second frequency control units for holding the frequencies of the lights emitted by the first and second light emitting elements substantially constant, respectively;
The relationship between the frequency difference between the first and second lights causing the Brillouin scattering phenomenon and the light intensity of the light related to the Brillouin scattering phenomenon when a part of each of the lights emitted from the first and second light emitting elements is respectively incident. A known reference optical fiber,
Based on the light intensity related to the Brillouin scattering phenomenon emitted from the reference optical fiber and the known relationship, the frequency difference between the lights emitted by the first and second light emitting elements becomes a predetermined frequency difference. The distributed light according to any one of claims 1 to 7, further comprising a frequency setting unit that controls the first frequency control unit and / or the second frequency control unit. Fiber sensor. The light pulse light source is
A light emitting element that continuously emits light having a predetermined frequency with a narrow line width and a substantially constant first light intensity;
A light branching portion that splits the light emitted from the light emitting element into two so that the light intensities are different from each other;
A first light intensity modulator that modulates the light intensity of the light that is branched at the light branching portion and has a relatively large light intensity;
A second light intensity modulator that modulates the light intensity of light that is branched at the light branching portion and whose light intensity is relatively small;
An optical multiplexing unit that multiplexes the lights modulated by the first and second light intensity modulators,
The first light intensity modulator generates the main light pulse;
The distributed optical fiber sensor according to any one of claims 1 to 8, wherein the second light intensity modulator generates the sub light pulse. The distributed optical fiber sensor according to any one of claims 1 to 9, wherein the detection optical fiber is fixed to an object to be measured for strain and / or temperature.

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