JP5213125B2 - Distributed optical fiber sensor - Google Patents

Description

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

  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 power moves through an acoustic phonon in an optical fiber when light enters the optical fiber, and two lights having different frequencies are incident on the optical fiber. There is a stimulated Brillouin scattering phenomenon caused by the interaction of light, and a natural Brillouin scattering phenomenon caused by the interaction of this light with acoustic phonons caused by thermal noise 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 are measured by measuring the Brillouin frequency shift.

  Typical methods for measuring strain and temperature distribution using the Brillouin scattering phenomenon include BOTDA (Brillouin Optical Time Domain Analysis) and BOTDR (Brillouin Optical Time Domain Reflectometer). In BOTDA, the stimulated Brillouin scattering phenomenon is utilized, and two laser beams having different frequencies are incident on the detection optical fiber as pump light and probe light, and the end of the detection optical fiber where the pump light is incident The light intensity of the light that is emitted from the stimulated Brillouin scattering phenomenon is measured in the time domain. In this BOTDA, acoustic phonons are excited by the interaction of pump light and probe light. On the other hand, in BOTDR, one laser beam is incident as a pump beam from one end of a detection optical fiber, and light applied to a natural Brillouin scattering phenomenon emitted from the one end is detected by an optical bandpass filter. The light intensity of light applied to the natural Brillouin scattering phenomenon is measured in the time domain. In this BOTDR, acoustic phonons generated by thermal noise are used. In these BOTDA and BOTDR, such measurement is performed for each frequency while sequentially changing the frequency of the pump light or the frequency of the probe light in BOTDA, and at each part along the longitudinal direction of the optical fiber for detection. A Brillouin gain spectrum (or Brillouin loss spectrum in BOTDA) is obtained, and a strain distribution and / or a temperature distribution along the longitudinal direction of the detection optical fiber are measured based on the measurement result. For the pump light, a light pulse having a rectangular light intensity is usually used, and for the probe light in BOTDA, continuous light (CW light) is used.

  Here, in BOTDA, the Brillouin gain spectrum is detected by making the pump light frequency higher than the probe light frequency with respect to the probe light, while the probe light frequency is made higher than the pump light frequency. By raising it, the Brillouin loss spectrum is detected. In BOTDR, a Brillouin gain spectrum is detected. In BOTDA, strain and / or temperature are obtained using any of these Brillouin gain spectrum and Brillouin loss spectrum. In this specification, the Brillouin gain spectrum and the Brillouin loss spectrum are simply referred to as “Brillouin spectrum” in the BOTDA as appropriate.

  The spatial resolution of these BOTDA and BOTDR is limited by the pulse width of the optical pulse of the pump light used for measurement. 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, the Brillouin spectrum is a Lorentzain curve until the pulse width of the optical pulse is about 28 ns or more. If the optical pulse width is shortened, the Brillouin spectrum becomes a wide-band curve with a sharpness near the center frequency. The lost shape becomes a gentle shape. For this reason, it becomes difficult to obtain the center frequency, and the spatial resolution is usually about 2 to 3 m.

  Therefore, the inventor of the present application patented a method 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 configuring the optical pulse from two components. Proposed in Reference 1. The inventor of the present application calls this method PPP-BOTDA / BOTDR (Pulse Pre-Pumped BOTDA / BOTDR). Note that 100 με corresponds to 0.01% (100 με = 0.01%). The Brillouin frequency shift is about 500 MHz /% with respect to the distortion.

International Publication No. 2006/001071 Pamphlet

  By the way, in the method proposed in Patent Document 1, since the acoustic phonon is activated in advance by the sub light pulse, the pulse width of the main light pulse can be shortened, thereby enabling high spatial resolution. However, when the pulse width of the main light pulse is shortened, the average power is reduced, so that only a few km of strain and temperature can be detected by the detection optical fiber. Similarly, in BOTDR, when the pulse width of the main light pulse is shortened, the average power is reduced, so that the strain and temperature can be detected only about several kilometers by the detection optical fiber.

  The present invention has been made in view of the above-described circumstances, and the object thereof is to extend the measurable distance and measure farther, while allowing distortion and / or temperature to be measured with high spatial resolution. It is to provide a distributed optical fiber sensor.

  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 stimulated Brillouin scattering phenomenon, a main light pulse using a spread spectrum method and an unmodulated sub light pulse. An optical pulse light source that generates continuous light, a continuous light source that generates continuous light, and the sub light pulse and the main light pulse are incident so that the main light pulse is not incident temporally before the sub light pulse. The continuous light is incident and a detection optical fiber in which a stimulated Brillouin scattering phenomenon occurs between the sub light pulse and the main light pulse and the continuous light, and light emitted from the detection optical fiber is filtered. To detect the light related to the stimulated Brillouin scattering phenomenon, and to match the matching spectrum corresponding to the spread spectrum method. And a Brillouin gain spectrum or Brillouin loss spectrum based on the light applied to the stimulated Brillouin scattering phenomenon detected by the matched filter, and the obtained Brillouin gain spectrum or Brillouin loss spectrum is obtained. And a Brillouin time domain detector for measuring strain and / or temperature generated in the optical fiber for detection based on the above. Preferably, in the above-described distributed optical fiber sensor, the sub light pulse and the main light pulse are incident from one end of the detection optical fiber, and the continuous light is input to the other end of the detection optical fiber. The Brillouin time domain detector is used to determine a Brillouin gain spectrum or a Brillouin loss spectrum based on light related to the stimulated Brillouin scattering phenomenon emitted from one end of the detection optical fiber. Further, the strain and / or temperature generated in the detection optical fiber is measured based on the Brillouin gain spectrum or the Brillouin loss spectrum. Preferably, in the above-described distributed optical fiber sensor, the sub light pulse and the main light pulse are incident from one end of the detection optical fiber, and the continuous light is 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 subjected to the stimulated Brillouin scattering phenomenon emitted from one end of the detection optical fiber. Brillouin gain spectrum or Brillouin loss spectrum is obtained based on light, and strain and / or temperature generated in the detection optical fiber is measured based on the obtained Brillouin gain spectrum or Brillouin loss spectrum. It is to be. A and / or B means at least one of A and B.

  The distributed optical fiber sensor having such a configuration is a BOTDA, and can measure the distance and / or the temperature by extending the measurable distance while allowing the strain and / or temperature to be measured with high spatial resolution.

  According to another aspect of the present invention, in a distributed optical fiber sensor that measures strain and / or temperature using a Brillouin scattering phenomenon caused by natural scattering, a main light pulse using a spread spectrum method and non-modulation are used. A light pulse light source for generating a sub-light pulse, and a detection light in which the sub-light pulse and the main light pulse are incident, and the sub-light pulse and the main light pulse cause a natural Brillouin scattering phenomenon by sound waves due to thermal noise A fiber, a matched filter corresponding to the spread spectrum method for detecting light applied to the natural Brillouin scattering phenomenon by filtering light emitted from the detection optical fiber, and the natural filter detected by the matched filter Based on the Brillouin scattering phenomenon, the Brillouin gain spectrum Seeking Torr, characterized in that it comprises a Brillouin time domain detector that measures the strain and / or temperature generated in the detection optical fiber based on this the Brillouin gain spectrum obtained.

  The distributed optical fiber sensor having such a configuration is a BOTDR, and can measure the distance and / or temperature by extending the measurable distance while allowing the strain and / or temperature to be measured with high spatial resolution.

  The Brillouin frequency shift when the spread spectrum method is used for light incident on the detection optical fiber will be described below.

  The spread spectrum method or the pulse compression method is used to extend the measurable distance in the so-called radar field. This is because the spectrum of the pulse is diffused by using frequency modulation or phase modulation inside the pulse radiated to the space to detect the target, and the demodulation called pulse compression is applied to the reflected wave reflected by the target. By applying, the distance to the target is detected. Thereby, the energy of the pulse can be increased, and the measurable distance can be extended. Spread spectrum is generally deliberately increasing the bandwidth that is originally required to transmit a signal.

  When this spread spectrum method is applied to BOTDA and BOTDR, since the Brillouin frequency shift occurs through a non-linear process, when the spectrum of the optical pulse is broadened (spread), this firstly causes the acoustic phonon to be excited. As the spectrum spreads, secondly, the spectrum in the time-series signal of the reflected wave for each frequency also spreads, resulting in a double spread in the spectrum. For this reason, the spread spectrum code cannot simply be applied to BOTDA or BOTDR. Therefore, the inventor of the present application applies the spread spectrum method to BOTDA and BOTDR by configuring the light pulse from the main light pulse and the sub light pulse and using the spread spectrum method for the main light pulse, as will be analyzed below. Found that you can.

  In the following, the case of BOTDA will be described. Similarly, it is possible to analyze BOTDR by performing analysis.

  In BOTDA, pump light is incident from one end (z = 0) of a detection optical fiber, and probe light having a frequency different from that of the pump light is incident from the other end, and backscattering of excited acoustic phonons is performed. Is observed at the end point of z = 0. Brillouin gain spectrum (BGS) is an increase in the power of the probe light.

First, the pump light A _p (0, t) is an optical pulse having a shape in which a complex envelope is expressed by Equation 1.

Here, P _p is the power of the pump light, and f (t) is a function representing the amplitude of the pump light at time t, and is normalized so that the maximum of its absolute value is 1. .

  When the function is defined by Expression 2, the Fourier transform is expressed by Expression 3. In this case, the Brillouin gain spectrum V (t, ν) is a two-dimensional convolution and is expressed by Equation 4. The first term on the right side of Equation 4 is a time-varying Lorentz spectrum.

Here, the superscript * represents a complex conjugate, and i is a complex unit (i ² = −1). Further, γ is a gain coefficient, and ν _B (z) is a Brillouin frequency shift at the position z. G (ν) is a Lorentz spectrum, and _vg is a group velocity of pump light. The operator * represents convolution, and the superscripts t and ν represent two-dimensional convolution with respect to these variables. Note that the multiplication operator • is not shown.

  Here, ideally, the time-varying Lorentz spectrum itself of the first term on the right-hand side of Equation 4 is observed, but in reality, it is blurred by convolution with the point spread function ψ (t, ν). The observed Brillouin gain spectrum is observed. For this reason, the point spread function ψ (t, ν) needs to be a two-dimensional delta function or close thereto. Therefore, it is preferable that ψ (t, ν) ≈δ (t) δ (ν).

Here, the pump light is composed of the main light pulse f ₁ (t) and the sub light pulse f ₂ (t). That is, the amplitude f (t) of the pump light is expressed by Equation 5.

This sub light pulse functions to excite acoustic phonons for the main light pulse. The pulse width D _sub of the sub light pulse is made sufficiently longer than at least the lifetime of the acoustic phonon. The lifetime of acoustic phonons is usually about 5 ns.

  The main light pulse functions to pass the energy scattered by the acoustic phonon to the probe light. The main light pulse is divided into a plurality of cells with a predetermined time width in the time direction, and is broadened by using a spread spectrum system. Broadband is compared to the spectral linewidth (approximately 30-40 MHz) of acoustic phonons. The time width of this cell determines the spatial resolution of BOTDA, and this reciprocal is the width of the spectrum. For example, when the cell width (cell time width) is 0.1 ns, the spatial resolution is 1 cm and the spectrum width is 10 GHz. The pulse width D of the main light pulse determines the amount of energy given to the pump light in order to extend the measurable distance. Here, since the spatial resolution of BOTDA is determined by the cell width of the main optical pulse as described above, the pulse width D of the main optical pulse can be set independently of the spatial resolution of BOTDA. Therefore, the pulse width D of the main light pulse can be appropriately determined according to a desired measurable distance. For this reason, it becomes possible to extend measurable distance conventionally.

  When the pump light is composed of two components in this way, the Brillouin gain spectrum V (t, ν) is composed of three components, and Equations 6 and 7 (Equations 7-1 to 7-3) Represented by

  The point spread function ψ (t, ν) is expressed by Equation 8, and since the pump light is composed of the main light pulse and the sub light pulse, the point spread function ψ (t, ν) is It is represented by Equation 9 and Equation 10.

Here, in the spread spectrum method, a matched filter (matched filter) corresponding to the spread spectrum method is used for demodulation, and the impulse response h (t) of the matched filter is set to f ₁ (Dt) ( h (t) = f ₁ (D−t)). The matched filter, for example, inverts the signal used for spread spectrum (the code in the case of using a code sequence for spread spectrum) with respect to time and takes the convolution with the input of the matched filter.

The main light pulse uses a spread spectrum system, and the sub light pulse is unmodulated and its pulse width is sufficiently long. Therefore, the components ψ _1,2 (t, ν) can be approximated as in Equation 11 and is the preferred type.

Here, C _p is an amplitude ratio between the main light pulse and the sub light pulse.

  Therefore, the corresponding Brillouin gain spectrum is represented by Equation 12.

The other components V _1,1 (t, ν) and V _2,1 (t, ν) in the Brillouin gain spectrum V (t, ν) are spectrally spread by the pseudorandom numbers of the main light pulse. In some cases, the spectrum is flat. The other components V _2,2 (t, ν) are suppressed by the matched filter at the time of demodulation.

Further, the components V _1,1 (t, ν) and V _2,2 (t, ν) in the Brillouin gain spectrum V (t, ν) are composed of only the main light pulse or the sub light pulse. And can be extracted by measuring the Brillouin gain spectrum.

  From the above analysis, in the distributed optical fiber sensor having the above-described configuration, the light pulse incident on the detection optical fiber is composed of two components of the main light pulse using the spread spectrum method and the unmodulated sub light pulse. Thus, the spatial resolution and the measurable distance can be set independently, so that the measurable distance can be extended and further measured while the strain and / or temperature can be measured with a high spatial resolution.

  In the BOTDA distributed optical fiber sensor described above, preferably, the Brillouin time domain detector is configured such that the sub-light pulse, the main light pulse, and the continuous light are incident on the detection optical fiber. The first Brillouin gain spectrum or the first Brillouin loss spectrum obtained based on the light related to the first stimulated Brillouin scattering phenomenon emitted from the detection optical fiber, the main light pulse, and the continuous light; Is incident on the detection optical fiber, the second Brillouin gain spectrum or the second Brillouin loss spectrum obtained based on the light related to the second stimulated Brillouin scattering phenomenon emitted from the detection optical fiber. The spectrum and / or the sub-light pulse and the continuous light are transmitted to the detection optical fiber. The difference between the third Brillouin gain spectrum or the second Brillouin loss spectrum obtained based on the light related to the third stimulated Brillouin scattering phenomenon emitted from the detection optical fiber when the light is emitted is obtained. Then, based on the obtained difference, the strain and / or temperature generated in the detection optical fiber is measured.

  According to this configuration, when the Brillouin frequency shift is obtained, unnecessary components of the Brillouin spectrum can be suppressed, and the Brillouin frequency shift can be obtained more easily and with high accuracy. And / or the temperature can be determined more easily and with higher accuracy.

  In the above-described BOTDA distributed optical fiber sensor, preferably, the sub light pulse is incident on the detection optical fiber in advance of the main light pulse in time.

  According to this configuration, a distributed optical fiber sensor in which the sub light pulse is incident on the detection optical fiber in advance of the main light pulse in time is provided. The sub light pulse may be temporally separated from the main light pulse, may be temporally continuous with the main light pulse, and a part thereof overlaps with the main light pulse in time ( May overlap). When the sub light pulse is temporally separated from the main light pulse, the pulse width of the sub light pulse is preferably about 30 ns or more so that the acoustic phonon is sufficiently excited. The time interval with the pulse is preferably less than the life of the acoustic phonon. When the sub light pulse is overlapped with the main light pulse, both the pulse width of the sub light pulse and the pulse width of the main light pulse can be set to arbitrary lengths. Therefore, the energy of the pump light can be set to a desired value, and the measurable distance can be set appropriately. In this case, in order to sufficiently excite the acoustic phonon, it is preferable that the sub light pulse precedes the main light pulse by about 30 ns.

  In the above-described BOTDA distributed optical fiber sensor, it is preferable that the main light pulse and the sub light pulse have a portion overlapping in time.

  According to this configuration, a distributed optical fiber sensor having a portion (overlapped portion) overlapping the main light pulse and the sub light pulse in terms of time is provided. By overlapping the sub light pulse with the main light pulse, as described above, the pulse width of the sub light pulse can be set to an arbitrary length, and the measurable distance can be further extended. The part overlapped in time may be overlapped in part in the part, or may overlap so that they coincide completely in time.

  In the BOTDR distributed optical fiber sensor described above, preferably, the Brillouin time domain detector includes the detection optical fiber when the sub optical pulse and the main optical pulse are incident on the detection optical fiber. The first Brillouin gain spectrum obtained based on the light that is emitted from the first natural Brillouin scattering phenomenon, and when the main light pulse is incident on the detection optical fiber, The detection light when the second Brillouin gain spectrum obtained based on the emitted light related to the second natural Brillouin scattering phenomenon and / or the sub-light pulse is incident on the detection optical fiber. 3rd Briller determined based on the light applied to the 3rd natural Brillouin scattering phenomenon emitted from the fiber - a gain spectrum, determining a difference, to measure the strain and / or temperature generated in the detection optical fiber based on the difference obtained by this determined.

  According to this configuration, when the Brillouin frequency shift is obtained, unnecessary components of the Brillouin spectrum can be suppressed, and the Brillouin frequency shift can be obtained more easily and with high accuracy. And / or the temperature can be determined more easily and with higher accuracy.

  In the distributed optical fiber sensor according to the present invention, the strain and / or temperature can be measured with a high spatial resolution and further.

It is a block diagram which shows the structure of the distributed optical fiber sensor in embodiment. FIG. 2 is a block diagram illustrating a schematic configuration of the distributed optical fiber sensor when the distributed optical fiber sensor illustrated in FIG. 1 is operated in a first mode. It is a block diagram which shows schematic structure of the distributed optical fiber sensor at the time of operating the distributed optical fiber sensor shown in FIG. 1 in a 2nd aspect. It is a figure for demonstrating the structure and operation | movement of an optical pulse production | generation part. It is a figure for demonstrating the structure and matched filter of pump light (a sub light pulse and a main light pulse). FIG. 2 is a block diagram showing a configuration of a distributed optical fiber sensor when the distributed optical fiber sensor shown in FIG. 1 is configured as a BOTDR. It is a figure for demonstrating a narrow line | wire width optical band pass filter. It is a figure for demonstrating the method of calculating | requiring a Brillouin frequency shift by subtracting a component from the whole. It is a figure which shows the numerical experiment result of the distributed optical fiber sensor at the time of using the pump light of the structure shown to FIG. 5 (A). It is a figure for demonstrating the other structure of pump light (a sub light pulse and a main light pulse). It is a figure which shows the numerical experiment result of the distributed optical fiber sensor at the time of using the pump light of the structure shown to FIG. 10 (B). It is a figure for demonstrating the further another structure and matching filter of pump light (a sub light pulse and a main light pulse). It is a figure for demonstrating the structure and operation | movement of an optical pulse production | generation part for producing | generating the pump light of the structure shown to FIG. 12 (A). It is a figure which shows one calculation result of a point spread function. It is a block diagram which shows the structure of the signal processing part for remove | eliminating component V2, ₁ (t, (nu)) in Brillouin gain spectrum V (t, (nu)) and calculating | requiring Brillouin gain spectrum V (t, (nu)). is there. The figure which shows the numerical experiment result of the distributed optical fiber sensor in the case of using the pump light which has the part which the main light pulse and the sub light pulse overlapped in time, and giving distortion to a comparatively short section width It is. The figure which shows the numerical-experimental result of the distributed optical fiber sensor when using the pump light which has the part which the main light pulse and the sub light pulse overlapped in time, and giving distortion to a comparatively long section width It is.

  Hereinafter, an embodiment according to the present 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.

  FIG. 1 is a block diagram illustrating a configuration of a distributed optical fiber sensor according to an embodiment. FIG. 2 is a block diagram showing a schematic configuration of the distributed optical fiber sensor when the distributed optical fiber sensor shown in FIG. 1 is operated in the first mode. FIG. 3 is a block diagram showing a schematic configuration of the distributed optical fiber sensor when the distributed optical fiber sensor shown in FIG. 1 is operated in the second mode.

The distributed optical fiber sensor S (S1) shown in FIG. 1 according to the embodiment of the present invention is a BOTDA and operates as a first mode (both-end measurement) by switching an optical switch 25 as will be described later. 2, one of the detection optical fibers OF (15) for detecting strain and / or temperature using the sub light pulse and the main light pulse light generated by the light pulse light source LS _p as pump light. While entering from the other end, the continuous light generated by the continuous light source LS _CW enters as the probe light from the other end of the detection optical fiber OF (15) and is detected by the Brillouin time domain detector BD (14). It receives light related to the stimulated Brillouin scattering phenomenon generated in the optical fiber OF (15), and is received by the Brillouin time domain detector BD (14). By performing Riruan gain spectrum time domain analysis and ^{(B Gain} -OTDA) or the Brillouin loss spectrum time domain analysis ^{(B Loss} -OTDA), detects the strain distribution and / or temperature based on the Brillouin frequency shift Is. In the optical pulse light source LS _p , the laser light emitted from the laser light source LD is phase-modulated by the pseudo random number from the pseudo random number generator RG in the optical signal generator OSG, so that the main optical pulse using the spread spectrum system is generated. Generated. The pseudo random number generated by the pseudo random number generator RG is notified to the Brillouin time domain detector BD (14) for demodulation. In the Brillouin time domain detector BD (14), the light related to the stimulated Brillouin scattering phenomenon emitted from the detection optical fiber OF (15) is transmitted by the matched filter MF corresponding to the pseudo random number from the pseudo random number generator RG. By filtering and BOTDA signal processing by the signal processing unit SP, a strain and / or temperature distribution based on the Brillouin frequency shift is detected. Hereinafter, Brillouin gain spectrum time domain analysis or Brillouin loss spectrum time domain analysis is abbreviated as Brillouin spectrum time domain analysis as appropriate. In this Brillouin spectrum time domain analysis, the light applied to the stimulated Brillouin scattering phenomenon is light that has undergone Brillouin amplification or attenuation.

The distributed optical fiber sensor S (S2) shown in FIG. 1 is a BOTDA and operates as a second mode (one-end measurement) by switching the optical switch 25 as will be described later. As shown, the sub optical pulse and the main optical pulse light generated by the optical pulse light source LS _p are used as pump light, and the continuous light generated by the continuous light source LS _CW is used as probe light, and the detection optical fiber OF ( 15) is incident on one end of the light beam, and receives light related to the stimulated Brillouin scattering phenomenon generated in the detection optical fiber OF (15) by the Brillouin time domain detector BD (14), and the Brillouin time domain detector BD (14) ) Brillouin gain spectrum time domain analysis (B ^Gain -OTDA) or Brillouin loss spectrum By performing inter-domain analysis (B ^Loss- OTDA), strain and / or temperature distribution is detected based on the Brillouin frequency shift. A spread spectrum system is used for the main light pulse.

  More specifically, such a distributed optical fiber sensor S (S1, S2) includes a first light source 1, optical couplers 2, 5, 8, 21, 23, and an optical pulse as shown in FIG. The generating unit 3, the optical switches 4 and 22, the light intensity / polarization adjusting unit 6, the optical circulators 7 and 12, the optical connectors 9, 26, 27, and 28, and a first automatic temperature control unit (hereinafter referred to as “first”). 1 ATC ”), a first automatic frequency control unit (hereinafter abbreviated as“ first AFC ”) 11, a control processing unit 13, a Brillouin time domain detector 14, and a detection optical fiber 15. A temperature detection unit 16, a reference optical fiber 17, a second automatic temperature control unit (hereinafter abbreviated as “second ATC”) 18, and a second automatic frequency control unit (hereinafter referred to as “second AFC”). Abbreviated) 19, second light source 20, light intensity adjustment unit 24, × constructed and a 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 adjusting 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 are provided with photoelectric conversion elements such as photodiodes, for example, and each light receiving output corresponding to each received light intensity is output 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 a thermoelectric conversion element such as a Peltier element or a Seebeck element, for example.

  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. As a result, 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.

  These optical couplers, Fabry-Perot etalon filters, first and second light receiving elements and first and second AFCs 11 and 19 in the first and second light sources 1 and 20 are 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 emitted light 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 optical pulse generator 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 as pump light from the continuous light. The main light pulse is an optical pulse using a spread spectrum method. Examples of the spread spectrum method include a frequency chirp method that changes the frequency, a phase modulation method that modulates the phase, and a hybrid method that combines the frequency chirp method and the phase modulation method. Examples of the frequency chirp method include a method of changing the frequency monotonously, for example, linearly. Examples of the phase modulation method include a method of modulating the phase using a PN sequence. The PN sequence is a pseudo-random number sequence, and examples of the PN sequence include an M sequence (maximal-length sequences) and a Gold sequence. The M series can be generated by a circuit including a plurality of shift registers and a logic circuit that feeds back a logical combination of each state in each of the plurality of stages to the shift register. Also, the Gold sequence is defined as M, Mj generated by n-order primitive polynomials F1 (x) and F2 (x), where 0 is -1 and 1 is +1. Can be generated by the product Mi · Mj. Also, a Golay code sequence can be used as a phase modulation type pseudo-random number sequence. This Golay code sequence has an excellent characteristic that the side lobe of the autocorrelation function is strictly zero. The sub light pulse is an unmodulated unmodulated light pulse, the maximum light intensity of which is less than or equal to the light intensity of the main light pulse, and the pulse width is sufficiently longer than the lifetime of the acoustic phonon. In the Brillouin spectrum time domain analysis (BOTDA) of the present embodiment, the optical pulse generator 3 detects the optical fiber 15 for detection earlier in time than the sub optical pulse in accordance with the Brillouin spectrum time domain analysis (BOTDA) of the present embodiment. The sub light pulse and the main light pulse are generated so as not to be incident on the light beam. The sub light pulse and the main light pulse as the pump light generated by the light pulse generator 3 will be described in detail later.

  The optical switches 4 and 22 are optical components that turn light on and off 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. This driver circuit is, for example, a DC power source that generates a DC voltage signal for turning off the light intensity modulator in a normal state, and a pulse generator that generates a voltage pulse for turning on the light intensity modulator that is normally turned off. And a timing generator for controlling the generation timing of the voltage pulse. 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 part 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 operating in the first mode of Brillouin spectrum time domain analysis (BOTDA) 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 end and operated in the second mode of Brillouin spectrum time domain analysis (BOTDA), the light incident from the input terminal is coupled to the optical coupler 8 and the optical connector. The 1 × 2 optical switch 25 is switched so as to be incident on one end of the detection optical fiber 15 via 9.

  The detection optical fiber 15 is an optical fiber for a sensor that detects strain and / or temperature, and a sub light pulse, a main light pulse, and continuous light are incident thereon. In BOTDA, the detection optical fiber 15 is affected by stimulated Brillouin scattering. Light is emitted. 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 used as an adhesive, a fixing member, or the like. Is fixed to the measurement object.

  The reference optical fiber 17 is an optical fiber used for adjusting the frequency of each light emitted from the first and second light sources 1 and 20, and the first and second light causing the stimulated Brillouin scattering phenomenon. The optical fiber is known in advance for the relationship between the frequency difference and the light intensity of light applied to the stimulated 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 (S1, S2) by inputting and outputting signals to and from the control processing unit 13. The Brillouin time domain detector 14 obtains the light intensity of the light related to the stimulated Brillouin scattering phenomenon emitted from the reference optical fiber 17 that is incident on the first input terminal via the optical connector 27 and the optical circulator 12. The 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 stimulated Brillouin scattering phenomenon received at a predetermined sampling interval. Accordingly, the Brillouin spectrum of each region portion of the detection optical fiber 15 in the longitudinal direction of the detection optical fiber 15 is obtained, and the Brillouin frequency shift of each region portion is obtained based on the obtained Brillouin spectrum of each region portion. Then, the strain distribution and / or the temperature distribution of the detection optical fiber 15 are detected based on the Brillouin frequency shift of each area portion thus obtained. Each incident light incident from the first, second, and 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 digitally converted by an analog / digital converter. And is used to obtain a Brillouin spectrum. The incident light incident from the third input terminal is directly detected by being converted into an electrical signal by the light receiving element as light related to the stimulated Brillouin scattering phenomenon, filtered by a matched filter, and then by an analog / digital converter. It is converted into a digital electrical signal and used to determine the Brillouin 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 / outputs a signal to / from the Brillouin time domain detector 14, so that the strain and / or temperature distribution of the detection optical fiber 15 in the longitudinal direction of the detection optical fiber 15 can be obtained with high spatial resolution. First and second light sources 1 and 20, first and second ATCs 10 and 18, first and second AFCs 11 and 19, optical pulse generator 3, optical switches 4 and 22, It is an electronic circuit that controls the polarization adjusting unit 6 and 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 stores in advance a relationship between the frequency difference between the first and second lights causing the stimulated Brillouin scattering phenomenon and the light intensity of the light applied to the stimulated Brillouin scattering phenomenon in the reference optical fiber 17. And the first and second light sources 1 and 20 based on the light intensity of the light related to the stimulated 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 by the second light emitting 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 adjusting unit 6, the light intensity adjusting unit 24, and the light intensity modulator are Patent Document 1 can be referred to.

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

  First, at the start of measurement, each frequency of each continuous light emitted from the first and second light sources 1 and 20 is adjusted (calibrated) using the reference optical fiber 17.

  More specifically, the control processing unit 13 controls the first ATC 10 and the first AFC 11 and the second ATC 18 and the second AFC 19 to cause the first and second light sources 1 and 20 to emit respective continuous lights at respective predetermined frequencies. These continuous lights are incident on the reference optical fiber 17 so as to face each other. The continuous light from the first light source 1 and the continuous light from the second light source 20 cause a stimulated Brillouin scattering phenomenon in the reference optical fiber 17, and the light related to the stimulated Brillouin scattering phenomenon is transmitted from the reference optical fiber 17. The light enters the Brillouin time domain detector 14 via the circulator 12. The Brillouin time domain detector 14 receives the light related to the stimulated Brillouin scattering phenomenon, detects the light intensity of the received light related to the stimulated Brillouin scattering phenomenon, and notifies the control processing unit 13 of the detected light intensity. . In the control processing unit 13, the relationship between the frequency difference between the first and second lights causing the stimulated Brillouin scattering phenomenon and the light intensity of the light applied to the stimulated Brillouin scattering phenomenon in the reference optical fiber 17 is stored in advance in the storage unit. When the control processing unit 13 receives this notification, the frequency setting unit sets a predetermined frequency 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. The reference light intensity Pa corresponding to the difference fa is obtained from the above relationship, and the first AFC 11 and the second AFC 19 are controlled so that the measured light intensity Pd detected by the Brillouin time domain detector 14 coincides with the reference light intensity Pa. As a result, the frequency difference between the lights emitted by 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.

  Here, the relationship between the frequency difference between the first and second lights causing the stimulated Brillouin scattering phenomenon and the light intensity of the light applied to the stimulated Brillouin scattering phenomenon in the reference optical fiber 17 generally has temperature dependence. ing. In the present embodiment, at the time of the adjustment, the control processing unit 13 detects the temperature of the reference optical fiber 17 by the temperature detection unit 16, and corrects the relationship in the reference optical fiber 17 according to the detected temperature. ing. For this reason, it is possible to execute the adjustment with higher accuracy.

  By operating in this way, each frequency of each continuous light emitted from the first and second light sources 1 and 20 is adjusted. Such adjustment may be performed every time the frequency is changed for sweeping when obtaining the Brillouin spectrum from the viewpoint of further improving the measurement accuracy, or from the viewpoint of shortening the measurement time. Strain and / or temperature may be performed for each measurement, or for the elapse of a predetermined period, and / or upon activation of the distributed optical fiber sensor S.

  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 and the second ATC 18 and the second AFC 19 to cause the first and second light sources 1 and 20 to emit the continuous lights at the predetermined frequencies, respectively. 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 to generate predetermined pump light (sub optical pulse and main optical pulse). More specifically, the control processing unit 13 generates pump light by operating the optical pulse generation unit 3 as follows, for example.

  FIG. 4 is a diagram for explaining the configuration and operation of the optical pulse generator. FIG. 5 is a diagram for explaining the configuration of the pump light (sub-light pulse and main light pulse) and the matched filter. FIG. 5 (A) shows the configuration of the pump light, and FIG. It is a figure which shows a matched filter.

  For example, as shown in FIG. 4, the optical pulse generator 3 has an LN intensity modulator 101 that modulates the light intensity of incident light and a direct current that constitutes a first drive circuit for driving the LN intensity modulator 101. A power source 102, a multiplier 103, a timing pulse generator 104, an LN phase modulator 111 that modulates the phase of incident light, and a DC power source 112 that constitutes a second drive circuit for driving the LN phase modulator 111, Multiplier 113, pseudorandom number generator 114, erbium-doped optical fiber amplifier (EDFA) 121, LN intensity modulator 131 that modulates the light intensity of incident light, and a third for driving this LN intensity modulator 131 A DC power supply 132, a multiplier 133, and a timing pulse generator 134 that constitute a drive circuit are provided.

  The LN phase modulator 111 is formed by, for example, forming an optical waveguide, a signal electrode, and a ground electrode on a lithium niobate substrate having an electro-optic effect, and by applying a predetermined signal between the electrodes. The apparatus modulates the phase of incident light by directly using the phase change accompanying the refractive index change caused by the electro-optic effect. The LN intensity modulators 101 and 131 are devices that modulate the light intensity of incident light by configuring, for example, a Mach-Zehnder interferometer and changing this phase change accompanying a change in refractive index due to the electro-optic effect into an intensity change. The LN intensity modulators 101 and 131 and the LN phase modulator 111 have other electro-optic effects such as lithium tantalate, lithium niobate / lithium tantalate, and the like instead of the lithium niobate substrate. A substrate may be used.

  In the first drive circuit, the DC power supply 102 is a power supply circuit that generates a DC voltage to be applied to the signal electrode of the LN intensity modulator 101 in order to modulate the intensity, and the timing pulse generator 104 includes the LN intensity modulator 101. A pulse generation circuit that generates an operation timing pulse for operation, and a multiplier 103 multiplies the DC voltage input from the DC power supply 102 by the operation timing pulse input from the timing pulse generator 104, This is a circuit that outputs a DC voltage corresponding to the operation timing pulse to the LN intensity modulator 101.

  In the second drive circuit, the DC power supply 112 is a power supply circuit that generates a DC voltage to be applied to the signal electrode of the LN phase modulator 111 in order to perform phase modulation, and the pseudorandom number generator 114 has a spectrum of incident light. In order to operate the LN phase modulator 111 so as to perform modulation by the spread method, the pseudo random number generation circuit generates a pseudo random number at an operation timing. The multiplier 113 generates a DC voltage input from the DC power source 112 and a pseudo random number. This circuit multiplies the pseudo random number input from the device 114 and outputs a DC voltage corresponding to the pseudo random number to the LN intensity modulator 101.

  The EDFA 121 is an optical component that includes an optical fiber doped with erbium, and amplifies and emits incident light. The EDFA 121 amplifies incident light at a predetermined amplification factor set in advance so as to obtain a light intensity suitable for detecting distortion and / or temperature in the detection optical fiber 15. As a result, when a loss occurs during propagation from the first light source 1 to the detection optical fiber 15, this loss is also compensated, and measurement in a predetermined measurement range becomes possible.

  In the third drive circuit, the DC power supply 132 is a power supply circuit that generates a DC voltage to be applied to the signal electrode of the LN intensity modulator 131 so as to modulate the intensity of the LN intensity modulator 131 so as to perform on / off control. The timing pulse generator 134 is a pulse generation circuit that generates an operation timing pulse to operate the LN intensity modulator 131. The multiplier 133 is a DC voltage input from the DC power supply 132 and a timing pulse generator. This circuit multiplies the operation timing pulse input from 134 and outputs a DC voltage corresponding to the operation timing pulse to the LN intensity modulator 131.

  By operating such an optical pulse generator 3, for example, pump light having a configuration shown in FIG. 5A can be generated.

  The pump light shown in FIG. 5A is unmodulated with the main light pulse encoded by the spread spectrum method, and precedes in time without overlapping (without overlapping) the main light pulse. And sub-light pulses. The main light pulse is divided into a plurality of cells with a predetermined time width (cell width), and in the present embodiment, each cell is modulated (encoded) by an M-sequence binary code. The cell width is set according to the desired spatial resolution, and the pulse width of the main light pulse is set according to the desired measurement distance. Further, the sub light pulse has a pulse width that can completely raise the acoustic phonon, and in the example shown in FIG. 5A, the light intensity is the same as the light intensity of the main light pulse. The sub light pulse and the main light pulse are continuous in time in the example shown in FIG. 5A, but may be separated in time. In the case of temporal separation, it is preferable to set the time interval at which the main light pulse acts on the acoustic phonon before the acoustic phonon raised by the sub light pulse disappears. Usually, since the acoustic phonon has a lifetime of about 5 ns, the time interval between the sub light pulse and the main light pulse is preferably within about 5 ns.

  In order to generate the pump light having the configuration shown in FIG. 5A, in FIG. 4, first, the continuous light L1 emitted from the first light source 1 is transmitted through the optical coupler 2 to the LN of the optical pulse generator 3. The light enters the intensity modulator 101.

In the light pulse generation unit 3, at the generation timing of the pump light, the pulse width (D _{sub + D)} operation timing pulse is a timing pulse generator which corresponds to the pulse width D of the pulse width D _sub and main light pulse of the sub light pulse The voltage is output from 104 to the multiplier 103, multiplied by the DC voltage input from the DC power supply 102, and a DC voltage having a pulse width (D _sub + D) is applied to the signal electrode of the LN intensity modulator 101. As a result, the LN intensity modulator 101 is turned on for a time width (D _sub + D) corresponding to the pulse width (D _sub + D) according to the operation timing pulse, and the continuous light L1 is turned on by the LN intensity modulator 101. Thus, an optical pulse L2 having a pulse width (D _sub + D) is emitted.

  Then, in the optical pulse generation unit 3, the pseudo random number is multiplied from the pseudo random number generator 114 by the time timing of the cell width during the time width D corresponding to the pulse width D of the main optical pulse at the generation timing of the main optical pulse. The DC voltage is sequentially output to 113, multiplied by the DC voltage input from the DC power supply 112, and the DC voltage modulated with the M-sequence binary code from the generation timing of the main optical pulse is modulated with the time width D. The signals are sequentially applied to the signal electrodes of the phase modulator 111. That is, the DC voltage modulated by the M-sequence binary code is emitted from the LN phase modulator 111 when the DC voltage corresponding to the case where the M-sequence binary code is “+” is supplied to the LN phase modulator 111. The phase of light and the phase of light emitted from the LN phase modulator 111 are 180 degrees different from each other when a DC voltage corresponding to the case where the M-sequence binary code is “−” is supplied to the LN phase modulator 111. It is a correct voltage value. Thus, the optical pulse L2 is an optical pulse composed of an unmodulated portion (corresponding to the sub optical pulse) and a portion modulated by the M-sequence binary code (corresponding to the main optical pulse) by the LN phase modulator 111. Injected as L3.

  In the EDFA 121, the light pulse L3 is amplified until it reaches a predetermined light intensity, and is emitted as a light pulse L4.

Further, in the optical pulse generation unit 3, operation timing pulses having a pulse width (D _sub + D) corresponding to the pulse width D _sub of the sub optical pulse and the pulse width D of the main optical pulse are timing according to the generation timing of the pump light. The pulse generator 134 outputs to the multiplier 133 and is multiplied by the DC voltage input from the DC power supply 132, and a DC voltage having a pulse width (D _sub + D) is applied to the signal electrode of the LN intensity modulator 131. As a result, the optical pulse L4 is an LN intensity modulator 131 from which noise such as spontaneous emission light (ASE) associated with the optical pulse L4 is removed by the EDFA 121, and the sub-optical pulse that has a pulse width D _sub and is not modulated. And pump light L5 having the pulse width D and the main light pulse encoded by the spread spectrum method.

  Then, the control processing unit 13 turns on the optical switch 4 and the optical switch 22 according to the generation timing of the pump light (sub optical pulse, main optical pulse, and optical pulse L4) 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 pump light (sub light pulse and main light pulse).

  When the optical switch 4 is turned on, the pump light (sub optical pulse and main optical pulse) enters the optical coupler 5 and is branched into two. One of the branched pump lights is 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 adjusted randomly (randomly). 7, and enters one end of the detection optical fiber 15 through 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 pump light (sub light pulse and main light pulse), and notifies the control processing unit 13 of the frequency and light intensity of the pump light. Upon receiving this notification, the control processing unit 13 controls the first ATC 10, the first AFC 11, and the light intensity / polarization adjusting unit 6 as necessary so that an optimum measurement result can be obtained.

  On the other hand, when the optical switch 22 is turned on, continuous light (probe light) enters the optical coupler 23 and is branched into two. One of the branched probe lights (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. When the Brillouin spectrum time domain analysis (BOTDA) is executed in the first mode, the 1 × 2 optical switch 25 is configured such that light incident from the input terminal is connected to the other end of the detection optical fiber 15 via the optical connector 26. The probe light (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 spectrum time domain analysis (BOTDA) is executed in the second mode, the 1 × 2 optical switch 25 detects light incident from the input terminal via the optical coupler 8 and the optical connector 9. The probe light (continuous light) is switched to be incident on one end of the optical fiber 15, and 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 probe light (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 the probe light (continuous light), and notifies the control processing unit 13 of the frequency and light intensity of the probe light. Upon receiving this notification, the control processing unit 13 controls the second ATC 18, the second AFC 19 and the light intensity adjusting unit 24 as necessary so that an optimum measurement result can be obtained.

  In the Brillouin spectrum time domain analysis of the first aspect, pump light (sub-light pulse and main light pulse) incident on one end of the detection optical fiber 15 is incident from the other end of the detection optical fiber 15 and is detected. The detection optical fiber 15 propagates from one end to the other end while causing a probe light (continuous light) propagating 15 and a stimulated Brillouin scattering phenomenon. In the Brillouin spectrum time domain analysis of the second aspect, the pump light (sub light pulse and main light pulse) incident on one end of the detection optical fiber 15 is incident from one end of the detection optical fiber 15 and is detected. The probe light (continuous light) that is reflected at the other end of the light 15 and propagates through the detection optical fiber 15 is propagated from one end to the other end of the detection optical fiber 15 while causing a stimulated Brillouin scattering phenomenon. On / off timings of the optical switch 4 and the optical switch 22 are adjusted by the control processing unit 13 based on the interaction between the pump light and the probe light.

Light related to the stimulated Brillouin scattering phenomenon is emitted from one end of the detection optical fiber 15 and is incident on the Brillouin time domain detector 14 via the optical connector 9, the optical coupler 8, and the optical circulator 7. In the Brillouin time domain detector 14, the light related to the stimulated Brillouin scattering phenomenon is extracted by direct detection as described above, converted into an electric signal by the light receiving element, and filtered by the matched filter. For example, as shown in FIG. 5B, the matched filter is a phase modulation pattern (P ₁ P ₂ P ₃ ... Phase-modulated by an M-sequence binary code in the LN phase modulator 111 of the optical pulse generator _3. P _n-1 P _n ) is a filter of an antiphase modulation pattern (P _n P _n-1 ... P ₃ P ₂ P ₁ ) obtained by temporally inverting the P _n-1 P _n ). For example, when each cell of the main optical pulse is modulated with an M-sequence binary code with a phase modulation pattern of “+ − ++ − +... + −”, The matched filter temporally converts this phase modulation pattern. The reverse pattern of “− +... + − ++ − +” is inverted. By using such a matched filter, it is possible to accurately detect light related to the stimulated Brillouin scattering phenomenon caused by the spread spectrum encoded main light pulse. Based on the generation timing notified from the control processing unit 13, the Brillouin time domain detector 14 performs time domain analysis on the received light related to the stimulated Brillouin scattering phenomenon, and guides the detection optical fiber 15 in the longitudinal direction. The light intensity distribution of the Brillouin scattering phenomenon is measured.

  Here, the degree of interaction between the pump light (sub light pulse and main light pulse) and the probe light (continuous light) related to the stimulated Brillouin scattering phenomenon depends on the relative relationship between the polarization planes of these lights. In the distributed optical fiber sensor S according to the present embodiment, since the polarization plane of the pump light randomly changes in the light intensity / polarization adjustment unit 6 for each measurement, the measurement is performed a plurality of times and the average value is adopted. Thus, this dependency can be substantially eliminated. For this reason, it is possible to obtain a light intensity distribution of light related to the stimulated Brillouin scattering phenomenon with high accuracy.

  The distribution of the light intensity of the light related to the stimulated Brillouin scattering phenomenon in the longitudinal direction of the detection optical fiber 15 is, for example, the frequency of the probe light (continuous light) emitted from the second light source 20. By sweeping in a predetermined frequency range at predetermined frequency intervals by control, measurement is performed with high accuracy and high spatial resolution at each frequency. As a result, a Brillouin 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 spectrum in the portion where the detection optical fiber 15 is not distorted as a reference, and the Brillouin in each region in the longitudinal direction of the detection optical fiber 15. By obtaining the frequency difference corresponding to the peak of the spectrum, the Brillouin frequency shift in each part of the detection optical fiber 15 in the longitudinal direction is obtained with high accuracy and high spatial resolution.

  Then, the Brillouin time domain detector 14 obtains the distortion 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.

  In the distributed optical fiber sensor S (S1, S2) having such a configuration, the pump light is composed of a main light pulse and a sub light pulse using a spread spectrum method, thereby obtaining a spatial resolution and a measurable distance. Since it can be set independently, the strain and / or temperature can be measured with high spatial resolution, and the measurable distance can be extended and measured further. Conventionally, the measurable distance has been several kilometers, but in this embodiment, about 100 km is possible.

  Note that the distributed optical fiber sensor S having the configuration shown in FIG. 1 can also constitute a BOTDR with a part of its constituent elements.

  FIG. 6 is a block diagram showing the configuration of the distributed optical fiber sensor when the distributed optical fiber sensor shown in FIG. 1 is configured as BOTDR. FIG. 7 is a diagram for explaining a narrow linewidth optical bandpass filter. FIG. 7A is a block diagram showing the configuration of a narrow linewidth optical bandpass filter, and FIGS. 7B to 7D are diagrams for explaining the operation of the narrowlinewidth optical bandpass filter. is there.

  In FIG. 6, the BOTDR distributed optical fiber sensor S (S3) includes a first light source 1, an optical pulse generator 3, an optical switch 4, an optical coupler 5, a light intensity / polarization adjuster 6, The optical circulator 7, the optical connector 9, the first ATC 10, the first AFC 11, the control processing unit 13, the Brillouin time domain detector 14, and the detection optical fiber 15 are configured. In FIG. 6, the optical coupler 2 interposed between the first light source 1 and the optical pulse generator 3 and the optical coupler 8 interposed between the optical circulator 7 and the optical connector 9 are shown in FIG. In the case where the distributed optical fiber sensor S is configured as BOTDR, it does not function substantially, so that illustration thereof is omitted in FIG.

  In the case of BOTDR, the Brillouin time domain detector 14 controls each part of the distributed optical fiber sensor S (S3) by inputting and outputting signals to and from the control processing unit 13, and receives natural Brillouin light received at a predetermined sampling interval. By detecting the light applied to the scattering phenomenon, the Brillouin gain spectrum of each region portion of the detection optical fiber 15 in the longitudinal direction of the detection optical fiber 15 is obtained, and the Brillouin gain · Based on the spectrum, 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. Each incident light incident from the second input terminal 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, and the Brillouin is converted. • Used to determine the gain spectrum. The incident light incident from the third input terminal is extracted by, for example, an optical bandpass filter (hereinafter abbreviated as “optical BPF”) shown in FIG. , Filtered by a matched filter, converted to a digital electrical signal by an analog / digital converter, and used to determine the Brillouin gain spectrum. Further, if necessary, the electric signal is amplified by the amplifier circuit before being digitally converted.

  The optical BPF optically connected to the third input terminal transmits an optical component having a narrow predetermined transmission frequency band, that is, light in a band excluding the predetermined frequency band while transmitting light having a narrow predetermined frequency band. It is an optical component that blocks Such an optical BPF 31 is, for example, as shown in FIG. 7A, a first Fabry-Perot etalon filter (hereinafter abbreviated as “EF”) 311 and a second EF 312 optically connected to the first EF 311. And is configured. As shown in FIG. 7B, the first EF 311 is set such that the full width at half maximum FWHM1 is a frequency width corresponding to a predetermined transmission frequency band in the optical BPF 31, and the center frequency fa1 of the transmission frequency band is set. Is set to coincide with the center frequency fa of the transmission frequency band in the optical BPF 31. As shown in FIG. 7C, the second EF 312 has an FSR (Free Spectral Range) 2 between the frequency of the optical pulse (sub optical pulse and main optical pulse) and the frequency of the natural Brillouin backscattered light. The full width at half maximum FWHM2 is set to be equal to or greater than the full width at half maximum FWHM1 of the first EF 311 so that the transmission frequency band includes the transmission frequency band of the first EF 311. , One of the center frequencies fa2 of the transmission frequency band is set to coincide with the center frequency fa of the transmission frequency band in the optical BPF 31. In the optical BPF 31 having such a configuration, light having a frequency corresponding to the predetermined transmission frequency band is transmitted by the first EF 311. That is, light of a frequency corresponding to the full width at half maximum FWHM1 is transmitted for each FSR1 of the first EF 311. The light transmitted through the first EF 311 is transmitted through the second EF 312, and only the light having a frequency corresponding to the transmission frequency band of the center frequency fa1 of the first EF 311 is transmitted. For this reason, the transmission frequency characteristic of the narrowband optical BPF 31 having such a configuration is obtained by combining the transmission frequency characteristic of the first EF 311 shown in FIG. 7B and the transmission frequency characteristic of the second EF 312 shown in FIG. 7C. As shown in FIG. 7D, the center frequency fa of the transmission frequency band is the frequency fa1 (= fa2), the full width at half maximum FWHM is the full width at half maximum FWHM1 of the first EF 311, and the FSR is the second EF 312. Of FSR2. Note that the first EF 311 and the second EF 312 may be optically connected in reverse.

  Further, in the case of BOTDR, the control processing unit 13 inputs and outputs signals to and from the Brillouin time domain detector 14, so that the strain and / or temperature of the detection optical fiber 15 in the longitudinal direction of the detection optical fiber 15 The first light source 1, the first ATC 10, the first AFC 11, the optical pulse generation unit 3, the optical switch 4, and the light intensity / polarization adjustment unit 6 are controlled so as to measure the distribution with a high spatial resolution to a longer distance.

In the BOTDR distributed optical fiber sensor S (S3) having such a configuration, the sub light pulse and the main light pulse light generated by the first light source 1 and the light pulse generation unit 3 are the optical switch 4, the optical coupler 5, The light is incident from one end of the detection optical fiber 15 through the light intensity / polarization adjusting unit 6, the optical circulator 7, and the optical connector 9. A spread spectrum system is used for the main light pulse. Light (natural Brillouin backscattered light) subjected to the effect of the natural Brillouin scattering phenomenon in the detection optical fiber 15 is emitted from one end of the detection optical fiber 15 and received by the Brillouin time domain detector 14. A Brillouin gain spectrum time domain reflection analysis (B ^Gain -OTDR) is then performed by the Brillouin time domain detector 14 to detect strain and / or temperature based on the Brillouin frequency shift. In addition, the light concerning a natural Brillouin scattering phenomenon is a natural Brillouin backscattered light.

  Even in the BOTDR distributed optical fiber sensor S (S3) having such a configuration, the spatial resolution and the measurable distance can be obtained by configuring the optical pulse by the main optical pulse and the sub optical pulse using the spread spectrum method. Since it can be set independently, the strain and / or temperature can be measured with high spatial resolution, and the measurable distance can be extended and measured further.

  FIG. 8 is a diagram for explaining a method for obtaining a Brillouin frequency shift by subtracting components from the whole. The horizontal axis in FIG. 8 is the frequency expressed in MHz, and the vertical axis is the Brillouin gain expressed in mW. FIG. 8A shows the first to third Brillouin spectra, and FIG. 8B shows the result of subtracting the second and third Brillouin spectra from the whole. 8A is the first Brillouin spectrum that is the entire Brillouin spectrum, and the broken line is the sum of the second Brillouin spectrum and the third Brillouin spectrum that are constituent elements.

  Note that, in the BOTDA distributed optical fiber sensor S according to the present embodiment, first, under the control of the control processing unit 13, the sub optical pulse as the pump light, the main optical pulse, and the probe light are applied to the detection optical fiber 15. In this case, the Brillouin time domain detector 14 obtains a first Brillouin spectrum based on the light related to the first stimulated Brillouin scattering phenomenon emitted from the detection optical fiber 15. Next, under the control of the control processing unit 13, the main optical pulse as the pump light and the continuous light as the probe light are made incident on the detection optical fiber 15, and the Brillouin time domain detector 14 in this case A second Brillouin spectrum is obtained based on the light related to the second stimulated Brillouin scattering phenomenon emitted from the optical fiber 15. Then, the Brillouin time domain detector 14 obtains a difference between the first Brillouin spectrum and the second Brillouin spectrum, and measures strain and / or temperature generated in the detection optical fiber 15 based on the obtained difference. Also good. Alternatively, under the control of the control processing unit 13, the sub optical pulse as the pump light and the continuous light as the probe light are incident on the detection optical fiber 15, and the Brillouin time domain detector 14 in this case A third Brillouin spectrum is obtained based on light related to the third stimulated Brillouin scattering phenomenon emitted from the detection optical fiber 15. Then, the Brillouin time domain detector 14 obtains a difference between the first Brillouin spectrum and the third Brillouin spectrum, and measures the strain and / or temperature generated in the detection optical fiber 15 based on the obtained difference. Also good. With this configuration, in BOTDA, when the Brillouin frequency shift is obtained, unnecessary components of the Brillouin spectrum can be suppressed, and the Brillouin frequency shift can be obtained more easily and with high accuracy. The strain and / or temperature generated in the fiber can be determined more easily and with higher accuracy.

  Alternatively, for example, in FIG. 8, first, the first Brillouin spectrum (solid line in FIG. 8A) is obtained by operating the distributed optical fiber sensor S (S1, S2) as described above. Next, the second and third Brillouin spectra are obtained by operating the distributed optical fiber sensor S (S1, S2) as described above. Next, the Brillouin time domain detector 14 determines the difference between the first Brillouin spectrum (solid line in FIG. 8A) and the sum of the second Brillouin spectrum and the third Brillouin spectrum (broken line in FIG. 8A) ( FIG. 8 (B)) is obtained. The Brillouin time domain detector 14 may measure strain and / or temperature generated in the detection optical fiber 15 based on the obtained difference. By configuring in this way, in BOTDA, when obtaining the Brillouin frequency shift, unnecessary components of the Brillouin spectrum can be suppressed, and the Brillouin frequency shift can be obtained more easily and with higher accuracy. The strain and / or temperature generated in the detection optical fiber can be determined more easily and with higher accuracy.

  Further, in the BOTDR distributed optical fiber sensor S according to the present embodiment, first, the sub optical pulse and the main optical pulse are incident on the detection optical fiber 15 under the control of the control processing unit 13, and the Brillouin time domain detector In this case, the first Brillouin gain spectrum is obtained based on the light related to the first natural Brillouin scattering phenomenon emitted from the detection optical fiber 15 in this case. Next, under the control of the control processing unit 13, the main light pulse is incident on the detection optical fiber 15, and the Brillouin time domain detector 14 in this case emits the second natural Brillouin scattering emitted from the detection optical fiber 15. A second Brillouin gain spectrum is obtained based on the light applied to the phenomenon. Then, the Brillouin time domain detector 14 calculates the difference between the first Brillouin gain spectrum and the second Brillouin gain spectrum, and based on the calculated difference, the distortion generated in the detection optical fiber 15 and / or Alternatively, the temperature may be measured. Alternatively, under the control of the control processing unit 13, the sub optical pulse is incident on the detection optical fiber 15, and the Brillouin time domain detector 14 is in this case emitted from the detection optical fiber 15. A third Brillouin gain spectrum is obtained based on the light associated with the Brillouin scattering phenomenon. Then, the Brillouin time domain detector 14 obtains a difference between the first Brillouin gain spectrum and the third Brillouin gain spectrum, and based on the obtained difference, the distortion generated in the detection optical fiber 15 and / or Alternatively, the temperature may be measured. By configuring in this way, when obtaining the Brillouin frequency shift in the BOTDR, unnecessary components of the Brillouin gain spectrum can be suppressed, and the Brillouin frequency shift can be obtained more easily and with high accuracy. The strain and / or temperature generated in the detection optical fiber can be obtained more easily and with higher accuracy.

  Alternatively, the second and third Brillouin gain spectra are determined, respectively, and the Brillouin time domain detector 14 determines the first Brillouin gain spectrum, the second Brillouin gain spectrum, and the third Brillouin gain spectrum. Alternatively, the difference and the sum may be measured, and the strain and / or temperature generated in the detection optical fiber 15 may be measured based on the obtained difference. With this configuration, when the Brillouin frequency shift is determined in BOTDR, unnecessary components of the Brillouin gain spectrum can be suppressed, and the Brillouin frequency shift can be determined more easily and with higher accuracy. As a result, the strain and / or temperature generated in the detection optical fiber can be determined more easily and with higher accuracy.

  A numerical experiment result (simulation result) in the distributed optical fiber sensor S using an optical pulse composed of such an unmodulated sub optical pulse and a main optical pulse using a spread spectrum system will be described. The result of the numerical experiment is, for example, that the difference between the first Brillouin spectrum and the sum of the second Brillouin spectrum and the third Brillouin spectrum in BOTDA is obtained, and the distortion and / or Or it is the result of measuring temperature.

  FIG. 9 is a diagram showing a numerical experiment result of the distributed optical fiber sensor when the pump light having the configuration shown in FIG. 5A is used. FIG. 9A shows the Brillouin gain spectrum and FIG. 9B shows the Brillouin frequency shift. In FIG. 9A, the x-axis is frequency (MHz), the y-axis is Brillouin gain (nW), and the z-axis is the distance (m) in the longitudinal direction of the detection optical fiber 15. The horizontal axis in FIG. 9B is the distance (m), and the vertical axis is the peak frequency (MHz). The solid line is the measured peak frequency and the dashed line is the Brillouin frequency shift.

  In this experiment, as shown in FIG. 5A, the pump light is composed of a sub-light pulse with a pulse width of 30 ns and a main light pulse with a pulse width of 12.7 ns following the sub-light pulse, The main optical pulse is divided into 127 cells having a cell width of 0.1 ns, and each cell is modulated (encoded) with an M-sequence binary code and subjected to spread spectrum encoding.

  As shown in Table 1, the detection optical fiber 15 includes a first section from z = 100 cm to z = 101 cm, a second section from z = 200 cm to z = 202 cm, and from z = 300 cm to z = 303 cm. The third section, each section of the fourth section from z = 400 cm to z = 404 cm, is given in advance a distortion of 80 MHz (= about 1600 με) in terms of Brillouin frequency shift.

  When the pump light partially using the spread spectrum method is incident on such a detection optical fiber 15 and measured, the Brillouin gain spectrum shown in FIG. 9A is obtained. As a result, FIG. The Brillouin frequency shift shown in (B) is obtained.

  As shown in FIG. 9, it is understood that a strain having a predetermined magnitude is measured at each strain position shown in Table 1, and the strain is obtained with high accuracy and high spatial resolution.

  As described above, distortion can be obtained with high accuracy and high spatial resolution even if the spread spectrum method is used for the main light pulse. As described above, by configuring the pump light with the main light pulse and the sub light pulse using the spread spectrum method, the spatial resolution and the measurable distance can be set independently, so that the distortion is reduced. While being able to measure with high spatial resolution, the measurable distance can be extended to measure farther.

  In the above-described embodiment, the pump light (sub light pulse and main light pulse) shown in FIG. 5 is used. However, the present invention is not limited to this. For example, the pump light shown in FIG. (Sub light pulse and main light pulse) may be used.

  FIG. 10 is a diagram for explaining another configuration of the pump light (sub light pulse and main light pulse). FIG. 10A shows another first configuration of the pump light, and FIG. ) Shows another second configuration of the pump light.

  In the pump light shown in FIG. 5A, the light intensity of the sub light pulse is the same level as the light intensity of the main light pulse. For example, as shown in FIG. The light intensity of the pulse may be smaller than the light intensity of the main light pulse. As described above, the sub-light pulse plays a role in raising the acoustic phonon in advance of the main light pulse in time, so that a large light intensity is not required unlike the main light pulse, and the light intensity of the main light pulse. Smaller than that.

  Each pump light shown in FIGS. 5A and 10A is configured such that the sub light pulse precedes the main light pulse in time without overlapping the main light pulse. As shown in FIG. 10B, the pump light may have a portion where the main light pulse and the sub light pulse overlap in time. In the pump light having such a configuration, from the viewpoint of starting the acoustic phonon by the sub light pulse temporally preceding the main light pulse, the portion of the sub light pulse that does not overlap the main light pulse is relative to the main light pulse. It is preferable that the time is preceded, and it is more preferable that the portion of the sub light pulse that does not overlap with the main light pulse is longer than the time for which the acoustic phonon is completely activated, for example, about 30 ns or more.

  Here, a numerical experiment result in the case where pump light composed of a main light pulse using such a spread spectrum system and a sub light pulse having a portion overlapping with the main light pulse is used in the distributed optical fiber sensor S. explain. Similar to the numerical experimental result shown in FIG. 9, for example, in BOTDA, the numerical experimental result is obtained by calculating a difference between the first Brillouin spectrum and the sum of the second Brillouin spectrum and the third Brillouin spectrum, and based on the obtained difference. This is a result of measuring strain and / or temperature generated in the detection optical fiber.

  FIG. 11 is a diagram illustrating a numerical experiment result of the distributed optical fiber sensor when the pump light having the configuration illustrated in FIG. 10B is used. FIG. 11A shows the Brillouin gain spectrum, and FIG. 11B shows the Brillouin frequency shift. Each axis in FIGS. 11A and 11B is the same as that in FIGS. 9A and 9B.

  In this experiment, as shown in FIG. 10B, the pump light overlaps with the sub light pulse having a pulse width of 132.3 ns and the sub light pulse with a time delay of 30 ns from the sub light pulse. The main optical pulse is divided into 1023 cells having a cell width of 0.1 ns, and each cell is modulated with an M-sequence binary code to be spread spectrum encoded. Has been.

  Similarly to the above, as shown in Table 1, the detection optical fiber 15 is preliminarily provided with 80 MHz distortion (= about 1600 με) in terms of Brillouin frequency shift in each of the first to fourth sections. ing.

  When the pump light having the configuration shown in FIG. 10B is incident on the detection optical fiber 15 and measured, the Brillouin gain spectrum shown in FIG. 11A is obtained. As a result, FIG. The Brillouin frequency shift shown in B) is obtained.

  As shown in FIG. 11, it is understood that a distortion having a predetermined magnitude is measured at each distortion position shown in Table 1, and the distortion is obtained with high accuracy and high spatial resolution.

  Thus, even when there is an overlapping portion between the sub light pulse and the main light pulse, distortion can be obtained with high accuracy and high spatial resolution. As described above, since the pump light is composed of the main light pulse and the sub light pulse using the spread spectrum method, the spatial resolution and the measurable distance can be set independently. Can be measured with a high spatial resolution, and the measurable distance can be extended to a greater distance.

  Furthermore, another aspect of pump light (sub light pulse and main light pulse) used in the distributed optical fiber sensor S of the present embodiment will be described.

  FIG. 12 is a diagram for explaining still another configuration of the pump light (sub-light pulse and main light pulse) and a matched filter. FIG. 12A shows the configuration of the pump light, and FIG. ) Is a diagram showing a matched filter. FIG. 13 is a diagram for explaining the configuration and operation of an optical pulse generator for generating pump light having the configuration shown in FIG.

  The pump light having the configuration shown in FIG. 10B is composed of a sub light pulse having a portion that temporally precedes the main light pulse and having a portion overlapping the main light pulse, and the main light pulse. However, as shown in FIG. 12 (A), the pump light does not have a portion that temporally precedes the main light pulse, and the sub light pulse overlapped so as to completely coincide with the main light pulse in time, The main light pulse may be included. In other words, the rising timing and the falling timing of the sub optical pulse coincide with the rising timing and the falling timing of the main optical pulse, respectively.

  Such pump light having the configuration shown in FIG. 12A can be generated from, for example, the optical pulse generator 3 having the configuration shown in FIG. In the optical pulse generator 3 having the configuration shown in FIG. 13, the configuration matches the configurations of the optical pulse generator 3 and the optical switch 4 shown in FIG. 4, and the operation thereof is the same as that of the optical pulse generator 3 shown in FIG. 4. It is different from the operation. For this reason, description of the structure is abbreviate | omitted here and the operation | movement is demonstrated.

  First, in order to generate pump light having the configuration shown in FIG. 12A, the LN intensity modulator 101 leaks (emits) a predetermined level of light (leakage light) in order to generate a sub-light pulse. ) So that it is on.

  The continuous light L11 (= L1) emitted from the first light source 1 is incident on the LN intensity modulator 101 of the optical pulse generator 3 via the optical coupler 2. When the continuous light L11 is incident, the LN intensity modulator 101 emits the leakage light.

  In the optical pulse generator 3, an operation timing pulse having a pulse width D corresponding to the pulse width D of the main optical pulse is output from the timing pulse generator 104 to the multiplier 103 and input from the DC power supply 102 at the generation timing of the pump light. The obtained DC voltage is multiplied, and a DC voltage having a pulse width D is applied to the signal electrode of the LN intensity modulator 101. Thus, the continuous light L11 is emitted by the LN intensity modulator 101 as an optical pulse L12 in which an optical pulse having a pulse width D is superimposed on leakage light.

  Then, in the optical pulse generation unit 3, the pseudo random number is multiplied from the pseudo random number generator 114 by the time timing of the cell width during the time width D corresponding to the pulse width D of the main optical pulse at the generation timing of the main optical pulse. The DC voltage is sequentially output to 113, multiplied by the DC voltage input from the DC power supply 112, and the DC voltage modulated with the M-sequence binary code from the generation timing of the main optical pulse is modulated with the time width D. The signals are sequentially applied to the signal electrodes of the phase modulator 111. As a result, the optical pulse L12 is emitted as an optical pulse L13 in which a portion (corresponding to the main optical pulse) modulated by the M-sequence binary code is superimposed on the leakage light by the LN phase modulator 111.

  In the EDFA 121, the light pulse L13 is amplified until it reaches a predetermined light intensity, and is emitted as a light pulse L14.

Furthermore, in the light pulse generation unit 3, according to the generation timing of the pump light, the operation timing of the pulse width D _sub corresponding to the pulse width D _sub of the sub light pulse ₍₌ pulse width D of the main light pulse) _{(= D)} The pulse is output from the timing pulse generator 134 to the multiplier 133, multiplied by the DC voltage input from the DC power supply 132, and the DC voltage having the pulse width D _sub (= D) is applied to the signal electrode of the LN intensity modulator 131. Is done. As a result, the LN intensity modulator 131 removes noise such as spontaneous emission light accompanying the optical pulse L14 by the EDFA 121, and the light pulse L14 is light caused by leakage light before and after the optical pulse L14 (in the EDFA 121). Amplified leakage light) is removed, and the sub-light pulse having the pulse width D _sub (= D) and unmodulated and the main light pulse having the pulse width D (= D _sub ) and spread spectrum encoded Thus, the main light pulse is superimposed on the sub light pulse in time and is emitted as the pump light L15 that overlaps.

Here, as shown in FIGS. 10B and 12A, when using pump light having a portion where the main light pulse and the sub light pulse overlap in time, the distributed optical fiber sensor S is used. (S1, S2) is the current component V ₂ when a plurality of Brillouin frequency shifts corresponding to the components V _{2, 1} (t, ν) in the Brillouin gain spectrum V (t, ν) are obtained as time series data. ₁ (t, ν) is estimated by using a predetermined function formula based on the past Brillouin frequency shift corresponding to the component V _{2 , 1} (t, ν), and the first Brillouin spectrum is The estimation result _{ circumflex over (V) _{} 2, 1} (t, ν) may be further subtracted from the result of subtracting the second Brillouin spectrum and the third Brillouin spectrum. With this configuration, it is possible to measure the strain and / or temperature generated in the detection optical fiber 15 with higher accuracy.

  In the case of using pump light having a portion where the main light pulse and the sub light pulse overlap with each other in time, more accurately, the Brillouin gain spectrum V (t, ν) is composed of four components, It is represented by Formula 13 and Formula 14 (Formula 14-1 to Formula 14-4).

  Expressions 14-1, 14-2, and 14-4 are the same as Expressions 7-1, 7-2, and 7-3, respectively.

The point spread function ψ (t, ν) is expressed by the above-described equation 8, and the pump light is composed of the main light pulse and the sub light pulse, so this point spread function ψ (t, ν) Is represented by Equation 9 and Equation 10 above. FIG. 14 shows a calculation example of the point spread function ψ (t, ν). 14A shows the point spread function ψ _1,1 (t, ν), FIG. 14B shows the point spread function ψ _1,2 (t, ν), and FIG. , _Shows the point spread function ψ _2,1 (t, ν), and FIG. 14D shows the point spread function ψ _2,2 (t, ν).

When the pump light composed of the main light pulse and the sub light pulse and the continuous probe light are incident on the detection optical fiber 15, V _1,1 (t, ν) is emitted from the detection optical fiber 15. Among the light related to the stimulated Brillouin scattering phenomenon, the main light pulse is scattered by the phonons excited by the main light pulse and the probe light, and V _1,2 (t, ν) Of the light related to the stimulated Brillouin scattering phenomenon emitted from the detection optical fiber 15, this is a component generated by the main light pulse being scattered by the phonons excited by the sub light pulse and the probe light, and V _2,1 ( t, v) is the phono excited by the main light pulse and the probe light among the light related to the stimulated Brillouin scattering phenomenon emitted from the detection optical fiber 15 in the above case. In a component caused the sub light pulse is scattered _and, V _{2,2 (t,} ν), of the light pertaining to the stimulated Brillouin scattering phenomenon that is output from the detection optical fiber 15, the sub light pulse and the probe This is a component generated by scattering a sub-light pulse on a phonon excited by light.

The V _1,1 (t, ν) causes the main light pulse as the pump light and the continuous light as the probe light to enter the detection optical fiber 15, and in this case, is emitted from the detection optical fiber 15. V _2,2 (t, ν) is incident on the detection optical fiber 15 as a sub-light pulse as pump light and continuous light as probe light. In this case, it is based on the light related to the stimulated Brillouin scattering phenomenon emitted from the detection optical fiber 15.

For example, when the width of the distortion section is relatively short and there is no other distortion, the components in the Brillouin gain spectrum V (t, ν) are described as described in the section “Means for solving the problem”. V _2,1 (t, ν) is a flat spectrum because the main light pulse is spectrally spread by a pseudo-random number, and as shown in FIG. 11, distortion is required with high accuracy and high spatial resolution. More generally, this component V _2,1 (t, v) needs to be taken into account in order to determine the strain and / or temperature with high accuracy and high spatial resolution. This component V _2,1 (t, ν) is considered as follows, and the distributed optical fiber sensor S (S1, S2) has a portion in which the main light pulse and the sub light pulse overlap in time. When pump light is used, more generally, distortion and / or temperature can be obtained with high accuracy and high spatial resolution.

The point spread function ψ _2,1 (t, ν) in this component V ₂ , ₁ (t, ν) is expressed as shown in Equation 15, and the integral with respect to s among them is when t <0. , Expressed as Equation 16. Here, when t <0, t− | τ | <0 is always satisfied. Therefore, when the main light pulse is subjected to spectrum spreading (pulse compression), the integral value represented by Expression 16 is 0. It becomes. Therefore, in this case, the point spread function ψ _2,1 (t, ν) is approximated to 0. This can also be understood from FIG.

The fact that this point spread function ψ _2,1 (t, ν) has a non-zero value only in the range of t ≧ 0 indicates that Equation 17 satisfies ν _B (v _g s / 2) and s ≦ t. Means ν _B (v _g s / 2), s> t. From this, the components V _{2, 1} (t, ν) in the Brillouin gain spectrum V (t, ν) are Brillouin frequency shifts ν _B (s) up to the time t at time t, t−D ≦ It is possible to estimate from s ≦ t. That is, the estimated value of the component V _{2, 1} (t, ν) in the Brillouin gain spectrum V (t, ν) at time t is expressed as in Equation 18, where the main light pulse and the sub light pulse are timed. The Brillouin gain spectrum V (t, ν) in the case of using pump light having overlapping portions is expressed as shown in Equation 19, and the component V ₂ in the Brillouin gain spectrum V (t, ν) ₁ (t, v) can be substantially eliminated.

In the above formula, the estimated value of the component V _2,1 (t, ν) is represented by “V” in which a sign “^” representing an estimated value is overlapped.

  The processing represented by the above-described equations 18 and 19 is realized by, for example, the following signal processing unit.

FIG. 15 shows the configuration of a signal processing unit for obtaining the Brillouin gain spectrum V (t, ν) by removing the components V _{2, 1} (t, ν) in the Brillouin gain spectrum V (t, ν). FIG. The subscript n in FIG. 15 represents that the variable is a value at the time t _n when the time is discretized and t _n = nΔt (n = 1, 2, 3,...). . The time step width Δt is set to be approximately equal to or less than the cell width when the main optical pulse is subjected to frequency spreading.

For example, as illustrated in FIG. 15, the signal processing unit 41 includes a subtraction unit 411, a Brillouin frequency shift estimation unit (BFS estimation unit) 412, a Brillouin frequency shift estimation value storage unit (BFS estimation value storage unit) 413, and , V _2,1 component estimation unit 414. The signal processing unit 41 is further mounted on, for example, the Brillouin time domain detector 14 and is used when pump light having a portion where the main light pulse and the sub light pulse overlap in time is used. The signal processing unit 41 may be configured in hardware or may be configured in software. When configured in software, the signal processing unit 41 is functionally realized on a microcomputer mounted on the Brillouin time domain detector 14.

The subtracting unit 411 subtracts the output signal V _{2, 1} (t _n−1 , ν) from the V _{2, 1} component estimating unit 414 from the input signal Y _n (ν), and the subtraction result X _n (ν) Is a circuit that outputs. This input signal Y _n (ν) is a signal obtained by subtracting the second Brillouin spectrum and the third Brillouin spectrum from the first Brillouin spectrum. That is, the input signal Y _n (ν) is expressed as shown in Equation 20 when the observation noise (disturbance noise) is ζ (ν).

The subtraction result X _n (ν) output from the subtraction unit 411 is the component V _2,1 (t, ν) in the Brillouin gain spectrum V (t, ν) if there is no observation noise ζ (ν) or estimation error. ) That is, the subtraction result X _n (ν) output from the subtraction unit 411 includes the component V _2,1 (t in the Brillouin gain spectrum V (t, ν) including the observation noise ζ (ν) and the estimation error. , Ν).

The BFS estimation unit 412 obtains a Brillouin frequency shift (BFS) from the peak value of the subtraction result X _n (ν) by treating the subtraction result X _n (ν) output from the subtraction unit 411 as a Brillouin gain spectrum. , it is an estimated value ^ [nu _{B, n} Brillouin frequency shift of Brillouin frequency shift thus determined at discrete time t _n. Here, for the convenience of description, the sign “^” representing an estimated value is described before “ν”. However, in the formula, “^” is overlapped with “ν”. It is written. The same applies hereinafter. In this estimation, by allowing fitting a parabola to the subtraction result X _{n (ν)} or logarithmic near the peak of the result of subtraction X _{n (ν),} it is possible to relatively accurately estimate. The estimation results ^ ν _{B, 1} , ^ ν _{B, 2} , ^ ν _{B, 3} ,..., ^ Ν _{B, n} of the BFS estimation unit 412 are output from the signal processing unit 41 and BFS estimation values The data is output to the storage unit 413.

The BFS estimated value storage unit 413 stores the estimation results ^ ν _{B, 1} , ^ ν _{B, 2} , ^ ν _{B, 3} ,..., ^ Ν _{B, n} output from the BFS estimating unit 412. is there. BFS estimation value storage unit 413, an estimate of all the Brillouin frequency shift to which they store _{^ ν B, 1, ^ ν} B, 2, ^ ν B, 3, ···, a ^ ν _{B, n} V _{The result} is output to the 2- and _1- component estimation unit 414.

The V _{2, 1} component estimation unit 414 estimates the Brillouin frequency shift estimated at a time before the discrete time t _n stored in the BFS estimated value storage unit 413 ^ ν _{B, 1} , ^ ν _{B, 2} , ^ ν _{B, 3} ,..., ^ Ν _{B, n} are used to estimate the component V _2,1 (t, ν) in the Brillouin gain spectrum V (t, ν). V _2,1 component estimated value ^ V _2,1 (t _n , ν) is output to the subtracting unit 411. The V _2,1 component estimated value _{ circumflex over (V) _{} 2, 1} (t _n , ν) output to the subtraction unit 411 is one step with respect to the next input signal Y _n (ν) input to the subtraction unit 411. There is a time delay (Z ⁻¹ ) of (= Δt), which is V _2,1 component estimated value ^ V _2,1 (t _n−1 , ν) at discrete time t _n−1 . More specifically, the V ₂ , ₁ component estimation unit 414 calculates the component V _2,1 (t, v) in the Brillouin gain spectrum V (t, ν) by calculating the equation 21 obtained by discretizing the equation 18. Estimate value ν V _2,1 (t, ν) of ν) is obtained.

When this V _2,1 component estimated value ^ V _2,1 (t _n−1 , ν) is used, the subtraction result X _n (ν) of the subtracting unit 411 is expressed as in Expression 22.

  With this configuration, the distributed optical fiber sensor S (S1, S2) can detect with higher accuracy when using pump light having a portion where the main light pulse and the sub light pulse overlap in time. It is possible to measure the strain and / or temperature generated in the optical fiber 15 for use.

  FIG. 16 shows a numerical experiment of the distributed optical fiber sensor in the case where pump light having a portion where the main light pulse and the sub light pulse overlap in time is used and distortion is given to a relatively short section width. It is a figure which shows a result. 16A and 16B show the results when the signal processing by the signal processing unit 41 shown in FIG. 15 is not executed, and FIGS. 16C and 16D show the signal processing shown in FIG. The result when the signal processing by the part 41 is performed is shown. FIGS. 16A and 16C show the estimated value of the Brillouin frequency shift, the horizontal axis is the distance expressed in m units, and the vertical axis is the Brillouin frequency shift value expressed in MHz units. FIGS. 16B and 16D show the estimation error, the horizontal axis is a distance expressed in m units, and the vertical axis is an error value expressed in MHz units. CRB is a theoretical performance limit called the so-called Kramer-Lao limit, and the better the estimated value, the more the error approaches this limit.

  In the experiment shown in FIG. 16, as shown in Table 1, the detection optical fiber 15 has a first section from z = 100 cm to z = 101 cm, z = 200 cm, as in FIG. Corresponds to a Brillouin frequency shift of 80 MHz for each of the second section from z to 202 cm, the third section from z = 300 cm to z = 303 cm, and the fourth section from z = 400 cm to z = 404 cm. Distortion is given and no distortion is given elsewhere (Brillouin frequency shift is 0).

  As can be seen from a comparison between FIGS. 16A and 16B and FIGS. 16C and 16D, the signal processing unit is used in the second section having a section width of 2 cm and the third section having a section width of 3 cm. The estimated value which is better when the signal processing by 41 is executed is obtained, and these estimation errors are substantially close to the theoretical limit.

  FIG. 17 shows a numerical experiment of the distributed optical fiber sensor in the case where pump light having a portion where the main light pulse and the sub light pulse overlap in time is used and distortion is given to a relatively long section width. It is a figure which shows a result. FIGS. 17A and 17B show the results when the signal processing by the signal processing unit 41 shown in FIG. 15 is not executed, and FIGS. 17C and 17D show the signal processing shown in FIG. The result when the signal processing by the part 41 is performed is shown. FIGS. 17A and 17C show estimated values of Brillouin frequency shift, the horizontal axis is a distance expressed in m units, and the vertical axis is a Brillouin frequency shift value expressed in MHz units. FIGS. 17B and 17D show the estimation error, the horizontal axis is a distance expressed in m units, and the vertical axis is an error value expressed in MHz units.

  In the experiment shown in FIG. 17, the detection optical fiber 15 is given distortion corresponding to the Brillouin frequency shift of 10 MHz in the 11th section from z = 60 cm to z = 80 cm, and from z = 140 cm to z = 160 cm. A strain corresponding to a Brillouin frequency shift of 20 MHz is given to the 12th section, and a strain corresponding to a Brillouin frequency shift of 30 MHz is given to the 13th section from z = 220 cm to z = 240 cm, and z = 300 cm to z = 320 cm. The distortion corresponding to the Brillouin frequency shift of 40 MHz is given to the 14th section until, and the distortion corresponding to the Brillouin frequency shift of 50 MHz is given to the 15th section from z = 380 cm to z = 400 cm. No distortion (Brillouin frequency shift is 0) ).

  In the case of such a relatively long section width (20 cm in the example shown in FIG. 17), it can be understood by comparing FIGS. 17 (A) and 17 (B) with FIGS. 16 (C) and (D). If the signal processing by the signal processing unit 41 is not executed, the estimated value includes a relatively large error. However, when the signal processing by the signal processing unit 41 is executed, there is almost no estimation error. A good estimate is obtained.

  The optical pulses (sub optical pulse and main optical pulse) having the configurations shown in FIGS. 5A, 10A, 10B, and 12A are the BOTDR distributed light described above. The fiber sensor S (S3) can be used in the same manner as the BOTDA distributed optical fiber sensor S (S1, S2). Note that, as described above, since BOTDR uses acoustic phonons excited by thermal noise, the sub light pulse does not necessarily precede the main light pulse in terms of time. Of course, the sub light pulse may precede the main light pulse in terms of time.

  The BOTDA distributed optical fiber sensor S (S1, S2) in the above-described embodiment fixes the frequency of the pump light (sub light pulse and main light pulse) and sets the frequency of the probe light (continuous light) to a predetermined frequency. The Brillouin spectrum is measured by sweeping in a range. 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.

  In the BOTDA distributed optical fiber sensor S (S1, S2) in the above-described embodiment, the frequency of the pump light (sub light pulse and main light pulse) is fixed, and the frequency of the probe light (continuous light) is predetermined. Although the Brillouin spectrum is measured by sweeping in the frequency range, the Brillouin spectrum may be measured by fixing the frequency of the probe light and sweeping the frequency of the pump light in a predetermined frequency range.

  In the above-described embodiment, the distributed optical fiber sensor S (S1, S2, S3) is configured so that Brillouin spectrum time domain analysis (BOTDA) and Brillouin spectrum time domain reflection analysis (BOTDR) can be executed integrally. However, the distributed optical fiber sensors S1 and S2 capable of performing Brillouin spectrum time domain analysis and the distributed optical fiber sensor S3 capable of performing Brillouin spectral time domain reflection analysis may be configured separately.

  In the distributed optical fiber sensor S (S1, S2, S3) of this embodiment, the cell width can be set to an arbitrary width (seconds). In the experiment, the cell width is set to 0.1 ns (nanoseconds), but can be set to a shorter value such as a picosecond order. Therefore, the distributed optical fiber sensor S according to the present embodiment can realize an ultra-high resolution on the order of millimeters, and can also be applied to measure distortion of an optical component, for example, distortion of an optical waveguide. is there.

  In order to express the present invention, the present invention has been appropriately and fully described above 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.

S, S1, S2, S3 Distributed optical fiber sensor 3 Optical pulse generator 13 Control processor 14 Brillouin time domain detector 111 LN phase modulator 114 Pseudo random number generator

Claims (8)

In a distributed optical fiber sensor that measures strain and / or temperature using the stimulated Brillouin scattering phenomenon,
An optical pulse light source that generates a main optical pulse using a spread spectrum method and an unmodulated sub optical pulse;
A continuous light source that generates continuous light;
The sub light pulse and the main light pulse are incident so that the main light pulse is not temporally incident before the sub light pulse, the continuous light is incident, the sub light pulse and the main light pulse, An optical fiber for detection in which a stimulated Brillouin scattering phenomenon occurs with the continuous light;
A matched filter corresponding to the spread spectrum method, detecting light applied to the stimulated Brillouin scattering phenomenon by filtering light emitted from the detection optical fiber;
A Brillouin gain spectrum or a Brillouin loss spectrum is obtained based on light applied to the stimulated Brillouin scattering phenomenon detected by the matched filter, and based on the obtained Brillouin gain spectrum or Brillouin loss spectrum. A distributed optical fiber sensor comprising: a Brillouin time domain detector for measuring strain and / or temperature generated in the 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 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 applied to the stimulated Brillouin scattering phenomenon emitted from one end of the detection optical fiber, 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 gain spectrum or 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 calculates a Brillouin gain spectrum or a Brillouin loss spectrum based on light related to the stimulated Brillouin scattering phenomenon emitted from one end of the detection optical fiber, and determines the Brillouin gain 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 spectrum or a Brillouin loss spectrum. The Brillouin time domain detector detects a first stimulated Brillouin scattering phenomenon emitted from the detection optical fiber when the sub-light pulse, the main light pulse, and the continuous light are incident on the detection optical fiber. The detection light when the first Brillouin gain spectrum or the first Brillouin loss spectrum obtained based on the light, the main light pulse, and the continuous light are incident on the detection optical fiber. The second Brillouin gain spectrum or the second Brillouin loss spectrum obtained based on the light related to the second stimulated Brillouin scattering phenomenon emitted from the fiber, and / or the sub-light pulse and the continuous light. Third guided Brillouin emitted from the detection optical fiber when incident on the detection optical fiber The difference between the third Brillouin gain spectrum or the second Brillouin loss spectrum obtained based on the light applied to the disturbance phenomenon is obtained, and the distortion generated in the detection optical fiber based on the obtained difference and The distributed optical fiber sensor according to any one of claims 1 to 3, wherein temperature is measured. 5. The distributed type according to claim 1, wherein the sub light pulse is incident on the optical fiber for detection prior to the main light pulse in time. Optical fiber sensor. The distributed optical fiber sensor according to any one of claims 1 to 5, wherein the main light pulse and the sub light pulse have a temporally overlapping portion. In a distributed optical fiber sensor that measures strain and / or temperature using the Brillouin scattering phenomenon due to natural scattering,
An optical pulse light source that generates a main optical pulse using a spread spectrum method and an unmodulated sub optical pulse;
An optical fiber for detection in which the sub light pulse and the main light pulse are incident, and the sub light pulse and the main light pulse cause a natural Brillouin scattering phenomenon by sound waves due to thermal noise;
A matched filter corresponding to the spread spectrum method for detecting light applied to the natural Brillouin scattering phenomenon by filtering light emitted from the detection optical fiber;
A Brillouin gain spectrum is obtained based on the light applied to the natural Brillouin scattering phenomenon detected by the matched filter, and the distortion generated in the detection optical fiber based on the obtained Brillouin gain spectrum and / or A distributed optical fiber sensor comprising a Brillouin time domain detector for measuring temperature. The Brillouin time-domain detector is based on light applied to a first natural Brillouin scattering phenomenon emitted from the detection optical fiber when the sub light pulse and the main light pulse are incident on the detection optical fiber. Obtained based on the obtained first Brillouin gain spectrum and light related to the second natural Brillouin scattering phenomenon emitted from the detection optical fiber when the main light pulse is incident on the detection optical fiber. Based on the second Brillouin gain spectrum and / or light related to the third natural Brillouin scattering phenomenon emitted from the detection optical fiber when the sub-light pulse is incident on the detection optical fiber. The difference between the third Brillouin gain spectrum and the obtained third Brillouin gain spectrum is obtained, and the detection is performed based on the obtained difference. Distributed optical fiber sensor according to claim 7, characterized in that to measure strain and / or temperature generated in the optical fiber.