Method and apparatus for detecting Brillouin phase shift and optical fiber temperature sensing method

Abstract

To overcome the difficulty of synchronizing optical frequencies of local oscillation light and probe light, while increasing an optical intensity of the local oscillation light, in detecting a Brillouin phase shift using a coherent light detection method.SOLUTION: Probe light, pilot light and pump light are generated from a first light source, and the probe light and the pilot light are inputted from one end of an optical fiber for a sensor, whereas the pump light is inputted from the other end, and light obtained from the other end is detected by local light generated from a second light source. After dividing a probe light electric signal corresponding to the probe light and a pilot light electric signal corresponding to the pilot light, the probe light is multiplied by a conjugate signal of the pilot light and a local light component is removed. Further, the probe light is multiplied by a down-convert signal generated from the pilot signal, thereby down-converting to a direct current component and calculating a Brillouin phase signal exp (jΔφb) in order to extract a phase component and obtain a Brillouin phase shift amount.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a Brillouin optical fiber sensor capable of measuring the wide-area distribution of temperature, strain, and vibration. Compared to the prior art, this invention realizes a Brillouin optical fiber sensor with high sensitivity by enabling the installation of a local emission with sufficient intensity in a coherent optical detector.

[0002] By using the digital processing method and logic of the present invention to stably compensate for the optical phase difference between probe light and local emission, the receiving sensitivity of the Brillouin optical fiber sensor is improved by more than 10 dB (more than 10 times), realizing a highly sensitive optical fiber sensor that enables vibration detection at a distance of 50 to 100 km. [Background technology]

[0003] Optical fiber sensors can detect temperature changes, tension (strain) changes, and vibrations, and are seeing increasing industrial applications such as soil monitoring in buildings, bridges, and disaster-prone areas, as well as vibration sensing in aircraft.

[0004] Among these, the Brillouin optical fiber sensor, which detects Brillouin scattered light generated in optical fibers, is an economical remote sensing technology that can detect temperature changes, tension (strain) changes, and vibrations over a wide area using optical fibers with the same specifications as communication optical fibers without requiring special processing of the optical fiber base material (Non-Patent Literature 1). By making the most of the features of this Brillouin optical fiber sensor, it is possible to realize distributed measurement type seismometers that extend over lengths of several tens to around 100 km.

[0005] The operating principle of the Brillouin optical fiber sensor, which detects temperature changes, tension (strain) changes, and vibrations, is as follows:

[0006] The pump light and probe light are propagated in reverse along the optical fiber. During this process, the probe light frequency is shifted from the pump light frequency to a Brillouin shift frequency Δf. bShifting the frequency band to a lower frequency (approximately 10.8 GHz to 11 GHz in the case of a quartz fiber) causes stimulated Brillouin scattering. During this process, the probe light experiences stimulated Brillouin gain, which increases the probe light amplitude, as well as an optical phase shift called Brillouin phase shift. The frequency band in which this stimulated Brillouin scattering occurs is known to be extremely narrow, around 50 MHz.

[0007] Brillouin optical fiber sensors exhibit a sharp frequency response characteristic due to the inductive Brillouin gain and Brillouin phase shift, resulting in a Brillouin shift frequency Δf b By detecting changes in these parameters, temperature changes, tension (strain) changes, or vibrations can be detected. In particular, the detection of Brillouin phase shift is considered advantageous for realizing stable temperature, strain, and vibration sensing in terms of ensuring stability against the depletion of pump light energy and the linearity of the Brillouin optical phase shift spectrum (Non-Patent Literature 2).

[0008] To ensure the stable operation of long-length Brillouin optical fiber sensors, such as distributed seismometers, securing probe light quality and improving the sensitivity of the optical detector are extremely important. Coherent optical detection is known to be advantageous as a means of improving the sensitivity of the optical detector, improving the receiving sensitivity by more than 6 dB compared to intensity detection (Non-Patent Literature 3).

[0009] Furthermore, the application of coherent photodetection is essential to detect the Brillouin optical phase and achieve the desired sensing operation. For these reasons, several studies have been reported on the detection of Brillouin optical phase shift using coherent photodetection (Non-Patent Literature 4). [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] https: / / doi.org / 10.1103 / PhysRevLett.96.110213 , Google Scholar Crossref , CAS 31. T.Horiguchi and M. Tateda, “Investigation of optical-fiber attenuation using stimulated Brillouin scattering between a plus and a continuous wave,” Opt. Lett.,vol. 14, no.8, pp. 101-1 408-410,April.1989.

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[0011] The detection of Brillouin phase shift using coherent photodetection has the following main challenges. (1) It is necessary to synchronize the optical frequency and optical phase of the local light emitted by the coherent optical detector with the probe light carrier component which has Brillouin phase shift information. (2) The local light emitted to be installed in the coherent photodetector must have sufficient light intensity.

[0012] To overcome these challenges, a Brillouin optical fiber sensor applying the self-heterodyne photodetection method has been proposed (Non-Patent Literature 4: Reprinted). In this method, the probe light and local light emission are generated from the same light source, and while the optical frequency of the local light emission is controlled to be different from the probe light frequency, the optical phases of both are synchronized, and both are propagated in parallel in the optical fiber sensor section to maintain this state. Therefore, although the problem (1) of the aforementioned coherent photodetection method can be solved, if the length of the optical fiber sensor section becomes long, the intensity of the local light emission is lost, making it impossible to meet the requirements of problem (2), and the receiving sensitivity remains at around -20 dBm.

[0013] Therefore, the present invention applies intradyne photodetection, a type of coherent photodetection method, rather than the conventional self-heterodyne method for detecting Brillouin phase shift. Although the application of intradyne photodetection to a Brillouin optical fiber sensor has been proposed in (Non-Patent Document 5), a technique for stably compensating for the optical phase difference between the probe light and the local emission has not been shown.

[0014] Furthermore, although electrical means to compensate for the slight optical phase shift of local light have been proposed (Non-Patent Document 6), they are insufficient for application to the intradyne photodetection method.

[0015] The present invention provides a means for realizing a Brillouin optical fiber sensor that applies an intradyne photodetection method, which can solve the problem. The present invention not only satisfies the requirements of problem (1), but also satisfies the requirements of problem (2) by enabling a local emission with sufficient intensity to be installed in the coherent photodetector, and improves the receiving sensitivity of the Brillouin optical fiber sensor by 10 dB or more by stably compensating the optical phase difference between the probe light and the local emission. [Means for solving the problem]

[0016] To solve the above problems, the present invention combines probe light and pilot light and inputs them to an optical fiber sensor, and uses pump light propagated in reverse to cause stimulated Brillouin scattering only in the probe light. Then, these probe light and pilot light are detected by a Brillouin scattering optical detection function. In the present invention, the Brillouin scattering optical detection function is the intradyne optical detection method. The present invention provides a method for detecting Brillouin phase shift and an optical fiber temperature sensing method (and apparatus) using the same.

[0017] More specifically, the Brillouin phase shift detection method according to the present invention is: Light from the first light source is used to generate probe light and pilot light using a probe light generation signal and a pilot light generation signal. The probe light and the pilot light are combined and input from one end of the optical fiber for the sensor. A light input step in which light from the first light source is input as pump light from the other end of the optical fiber for the sensor, A detection step to obtain a beat electrical signal by detecting the output light from the other end of the optical fiber for the sensor using local light generated from a second light source, A separation step of separating the beat electrical signal into a probe photoelectrical signal corresponding to the probe light and a pilot photoelectrical signal corresponding to the pilot light, A local light component removal step is performed to obtain a probe-pilot photoelectric signal from which the influence of the local light has been removed by multiplying the phase conjugate signal of the pilot photoelectric signal by the probe photoelectric signal. A down-converted signal is generated to convert the aforementioned probe pilot photoelectric signal to the baseband band. The system is characterized by having a phase component calculation step that involves multiplying the probe pilot photoelectric signal by the Brillouin phase signal to obtain a Brillouin phase signal, and then determining the Brillouin phase shift amount from the Brillouin phase signal. [Effects of the Invention]

[0018] The present invention eliminates the need to synchronize the optical frequency and phase of the local light emitted by the coherent optical detector with the probe light carrier component containing Brillouin phase shift information when detecting Brillouin phase shift in an optical fiber sensor. Furthermore, since the local light emitted by the coherent optical detector can be provided independently of the probe light, etc., it can be driven with sufficient light intensity.

[0019] As a result, the receiving sensitivity of the Brillouin optical fiber sensor can be significantly improved. This effect makes it possible to develop distributed seismometers with lengths exceeding 100 km by increasing the length of the Brillouin optical fiber sensor, and even when the length of the Brillouin optical fiber sensor is short, the sampling rate for temperature, strain, and vibration measurements can be improved by more than 10 times. [Brief explanation of the drawing]

[0020] [Figure 1] This figure shows the overall configuration for implementing the Brillouin phase shift detection method and optical fiber temperature sensing method according to the present invention. [Figure 2] This figure shows the detailed configuration of the light source module in the second embodiment. [Figure 3] This diagram shows the configuration of the optical fiber sensor unit. [Figure 4] This diagram shows the frequency allocation of the pump light, probe light, pilot light, and local light. [Figure 5] This figure shows the configuration of the Brillouin scattering photodetector in the second embodiment. [Figure 6] This graph illustrates the relationship between the frequency difference between the pump and probe light, the stimulated Brillouin gain, and the Brillouin phase shift. [Figure 7] This graph illustrates the change in Brillouin phase shift when the frequency of the probe light is changed in the second embodiment. [Figure 8] This graph shows the relationship between the change in probe light frequency and the temperature of the sensor fiber. [Figure 9]This graph shows the relationship between the change in probe light gain and the temperature of the sensor fiber. [Figure 10] This is a lookup table plotting the relationship between Brillouin shift frequency and temperature. (a) shows the case for phase detection, and (b) shows the case for intensity detection. [Figure 11] This graph shows the received power of the probe light and the combined signal-to-noise ratio. [Figure 12] This figure illustrates the principle for measuring the Brillouin phase shift or stimulated Brillouin gain at any point in a sensor optical fiber. [Figure 13] This diagram shows the flow chart for temperature measurement. [Figure 14] This diagram shows the frequency allocation for pump light, probe light, pilot light, local light, and other frequencies. [Figure 15] This diagram shows the frequency allocation for pump light, probe light, pilot light, local light, and other frequencies. [Figure 16] This diagram shows the frequency allocation for pump light, probe light, pilot light, local light, and other frequencies. [Figure 17] This diagram shows the configuration of the light source module in the third embodiment. [Figure 18] This figure shows the configuration of the Brillouin scattering photodetector in the third embodiment. [Figure 19] This figure shows the configuration of the Brillouin scattering photodetector in the fourth embodiment. [Figure 20] This figure shows the hardware configuration for implementing the optical fiber temperature sensing method of the fifth embodiment. [Figure 21] This diagram shows the configuration of the light source module in the fifth embodiment. [Figure 22] This figure shows the configuration of the Brillouin scattering photodetector in the fifth embodiment. [Figure 23] This diagram shows the configuration of the light source module in the sixth embodiment. [Figure 24] This figure shows the waveform of the probe light used in the sixth embodiment. [Figure 25] This figure shows the configuration of the Brillouin scattering photodetector in the sixth embodiment. [Figure 26] The seventh embodiment is shown in the diagram illustrating the configuration of the Brillouin scattering photodetector. [Figure 27] The seventh embodiment is shown in the diagram illustrating the configuration of a complex multiplication circuit. [Modes for carrying out the invention]

[0021] The following describes the Brillouin phase shift detection method, the optical fiber (temperature) sensing method using the same, and the apparatus for realizing them, with reference to drawings. The following description illustrates one embodiment of the present invention and one example, and the present invention is not limited to the following description. The following description may be modified without departing from the spirit of the present invention.

[0022] (First embodiment) The Brillouin phase shift detection method according to the present invention will be explained with reference to Figure 1. The optical fiber (temperature) sensing device 1 that implements the Brillouin phase shift detection method includes a light source module 11, an optical fiber sensor 21, a Brillouin scattered light detection unit 31, and a control unit 50. Furthermore, since the optical fiber (temperature) sensing device 1 performs temperature detection, it can be said that it implements an optical fiber temperature sensing method.

[0023] The light source module 11 generates the pump light L1, probe light L3, and pilot light L4 from the same light source (first light source). These are stably generated by an electrical signal generator (not shown in Figure 1). The light source module 11 also generates and outputs a frequency offset signal S5 corresponding to the frequency difference between the probe light L3 and the pilot light L4.

[0024] The optical fiber sensor unit 21 includes a sensor optical fiber 215. The probe light L3 and the pilot light L4 are input from one end 212 of the optical fiber sensor unit 21, and the pump light L1 is input from the other end 211. Here, the one end 212 and the other end 211 are also referred to as the input port 212 and the input port 211, respectively.

[0025] The Brillouin scattered light detection unit 31 has an optical port 311 that receives the explored light L5 output from the other end 211 of the optical fiber sensor unit 21 and an electrical signal port 312 that receives the frequency offset signal S5 output from the light source module unit 11. Further, the Brillouin scattered light detection unit 31 has a local light emission unit 322 that generates a local light LO (a second light source different from the light source of the light source module unit 11) inside. Then, the explored light L5 input from the optical port 311 to the Brillouin scattered light detection unit 31 is detected by the local light LO.

[0026] The explored light L5 is interfered with the local light LO (E LO exp(j(ω LO t + φ LO ))) from the local light emission unit 322 built in the Brillouin scattered light detection unit 31, and is detected by a phase diversity differential square detector also built in the Brillouin scattered light detection unit 31. As a result, it is converted into the beat electrical signal S1 (complex amplitude electrical signal) of equation (1). <00,00428>

[0027]

Equation

[0028] In equation (1), B G is the square root of the induced Brillouin gain B G 2 , and the induced Brillouin gain B G 2 is expressed by equation (2). Also, the Brillouin phase shift Δφ b in equation (1) is expressed by equations (3) and (4).

[0029]

Equation

[0030] In equations (2), (3), and (4), z is the detection position on the sensor optical fiber 215, g0 is the gain coefficient, and Δω sbs The stimulated Brillouin scattering spectral width (reduced to angular frequency), ω b (z) is the Brillouin peak frequency (converted to angular frequency) at detection position z, ω pp is the pump optical angular frequency. Also, as can be seen from equation (2), the induced Brillouin gain B G 2 This depends on the detection position "z" on the sensor optical fiber 215. In the following description, the stimulated Brillouin gain B at a certain position on the sensor optical fiber 215 is... G 2 It is assumed that the detection position information can be calculated from the detection timing of the detected beat electrical signal S1 without further explanation.

[0031] Note that equations (2) and (3) represent the stimulated Brillouin gain B in an optical fiber. G 2 and Brillouin phase shift Δφ b This represents the phenomenon as a mathematical model, and the induced Brillouin gain B can be seen from equations (2) and (3). G 2 and Brillouin phase shift Δφ b It is not possible to calculate the induced Brillouin gain B for a single beat electrical signal S1. G 2 and Brillouin phase shift Δφ b The answer is calculated as follows.

[0032] First, the induced Brillouin gain B G 2 This can be obtained by comparing the beat electrical signal S1 with and without the pump light L1. The Brillouin phase shift can be determined by using the method to remove the effect of the local light LO, as shown below.

[0033] The first term of equation (1) is the complex amplitude electrical signal component for the probe light L3, and the second term is the complex amplitude electrical signal component for the pilot light L4. The angular frequencies of these electrical signals reflect the difference in optical frequency and optical phase with respect to the local light LO. These frequency and phase differences give the frequency (more precisely, angular frequency) (ω) of each complex amplitude electrical signal. pr -ω LO ), (ω pi -ω LO ) and phase (Δφ b +φ pr -φ LO ), (φ pi -φ LO ) is the result. Note that the Brillouin phase shift amount is Δφ b This manifests as a phase shift between the probe light L3 and the pilot light L4.

[0034] Next, the first and second terms of the beat electrical signal S1 in equation (1) are separated. The method of separation is not particularly limited. Specific examples include a method in which the polarization planes of the probe light L3 and the pilot light L4 are orthogonal, and a method of frequency separation using a frequency filter, which will be shown in the embodiments described later. The separated first and second terms are called the probe light electrical signal S2 and the pilot light electrical signal S3, and are expressed as in equations (5) and (6), respectively.

[0035]

number

[0036] Next, the phase conjugate signal of the pilot photoelectric signal S3 in equation (6) is multiplied by the probe photoelectric signal S2 in equation (5) to obtain the probe-pilot photoelectric signal S4. The probe-pilot photoelectric signal S4 can be written out as equation (7).

[0037]

number

[0038] Note that in equation (5), E *pi is E pi It is the phase conjugate signal of [the given signal].

[0039] As can be seen from equation (7), the electrical signal (complex amplitude electrical signal) corresponding to the explored light L5 is the power |E of the local light LO. LO | 2 While it is amplified by a certain amount, the components corresponding to the frequency difference and phase difference with the local optical LO that appeared in equations (1), (5), and (6) immediately after intradyne photodetection are completely removed. Specifically, ω LO Ya φ LO The entry has been removed.

[0040] In this embodiment, the probe-pilot photoelectric signal S4 is obtained by multiplying the phase-conjugate signal of the pilot photoelectric signal S3 by the probe photoelectric signal S2 of equation (5). However, the above operation can also be achieved by a configuration in which the probe-pilot photoelectric signal S4 is obtained by multiplying the phase-conjugate signals of the pilot photoelectric signal S3 and the probe photoelectric signal S2 of equation (5).

[0041] This solves problems (1) and (2) that the present invention aims to solve. Specifically, there is no need to synchronize the optical phase of the searched light L5 and the local light LO, and since the local light LO can be output from an independent light source inside the receiver, the light intensity can be freely set regardless of the searched light L5.

[0042] In equation (7), equation (8), which is the frequency difference component between the pilot light L4 and the probe light L3, is generated by the electrical signal generator of the light source module 11 (explained in Figure 2 and later) and is extremely stable. This frequency component signal is the frequency offset signal S5. To convert this component down to a DC component, we simply multiply equation (7) by equation (9), which is the complex conjugate of this component. Therefore, equation (9) is called the downconverted signal S6.

[0043] By multiplying the probe pilot photoelectric signal S4 and the downconvert signal S6, only the Brillouin phase shift information can be stably extracted, as shown in equation (10). Equation (10) is called the Brillouin phase signal S7.

[0044]

number

[0045] The Brillouin phase signal S7 of equation (10) is output from the Brillouin scattering optical detection unit 31 and input to the control unit 50. The control unit 50 can consist of a CPU, memory, input / output device, and display device. When the Brillouin phase signal S7 of equation (10) is input to the control unit 50, it converts the real and imaginary parts of the signal into the phase information of equation (10) (Brillouin phase shift amount Δφ) as shown in equation (11). b ) can be obtained.

[0046]

number

[0047] As described above, the present invention aims to detect the Brillouin phase shift Δφ b However, we focused on the fact that, due to the narrowband nature of the stimulated Brillouin scattering spectrum, it is superimposed only on the probe light L3 component. Then, a pilot light L4, which has a different frequency from the probe light L3, is passed through the optical fiber sensor section 21 together with the probe light L3. Because the pilot light L4, which is not affected by the Brillouin phase shift, coexists with the probe light L3, the influence of the local light LO can be removed from the detection signal using the local light LO, and the Brillouin phase shift Δφ can be stably controlled. b It detects the Brillouin phase shift Δφ. b The hardware that detects this constitutes a Brillouin phase shift detection device.

[0048] (Second embodiment) This embodiment describes an optical fiber temperature sensing device 1 using the Brillouin phase shift detection method shown in the first embodiment. Furthermore, the relationships between equations (1) to (11) described in the first embodiment, including the following embodiments, can be used without further explanation. The general configuration of the optical fiber temperature sensing device 1 is the same as that shown in Figure 1. A more detailed configuration of each block described in the first embodiment is shown below. The optical fiber temperature sensing device 1 includes a Brillouin phase shift detection device (Brillouin phase shift detection method). The optical fiber temperature sensing device 1 also performs an optical fiber temperature sensing method.

[0049] Figure 2 shows the internal configuration of the light source module 11. This light source module 11 uses a light source 111 (first light source) to emit pump light L1, probe light L3, and pilot light L4, which are input to the optical fiber sensor 21. The light source 111 can be composed of a semiconductor laser diode or a solid-state laser such as a fiber ring laser. The laser light output from this light source 111 passes through an optical isolator 112 to prevent adverse effects of light reflection, and is then split into two at an optical demultiplexer 113. One is used as the pump light L1, and the other is used as the seed light L2 for the probe light L3 and pilot light L4.

[0050] First, the pump light L1 is input to the light intensity modulator 114 and pulsed. This light intensity modulator 114 is driven by an electrical signal generated by an electrical pulse generator 115. Here, the light intensity modulator 114 can use a lithium niobate optical waveguide or a KTN (potassium tantalate) crystal, etc.

[0051] The pulsed pump light L1 output from the light intensity modulator 114 is input to the polarization scrambler 116. The polarization scrambler 116 performs scrambling because the Brillouin scattered light intensity in the optical fiber of the optical fiber sensor unit 21 changes depending on the excitation light polarization state, with the aim of ensuring a stable Brillouin scattered light intensity as an average value.

[0052] Next, the pump light L1 output from the polarization scrambler 116 is amplified by the optical fiber amplifier 117 to become an optical pulse with a peak power of 100mW or more, and is input to the input port 211 (see Figure 1) of the optical fiber sensor unit 21 through the optical filter 118 that removes the spontaneous emission light from the optical fiber amplifier 117. The input of the pump light L1 to the input port 211 is controlled by the control unit 50. The input port 211 of the pump light L1 from the light source 111 is the pump light generation unit 502.

[0053] Meanwhile, the seed light L2, which is the source of the probe light L3 and pilot light L4 branched by the optical demultiplexer 113, is input to the vector optical modulator 121. This vector optical modulator 121 is an integrated unit of two optical IQ modulators 121a and 121b developed for communication applications, and the seed light L2 is split into two at the input side. In the first optical IQ modulator 121a, the frequency Δf generated by the electrical signal generator 124a is input. pr The electrical signal (probe light generation signal) is input, and the optical frequency of the input seed light L2 is calculated as Δf pr The probe light L3 is generated by shifting it.

[0054] Furthermore, the electrical signal generated by the electrical signal generator 124a is further divided into two; one signal is input to the Hilbert converter 142, and the resulting signal with a phase shift of π / 2 is input to the optical IQ modulator 121a.

[0055] Meanwhile, in the second optical IQ modulator 121b, the frequency Δf generated by the electrical signal generator 124b pi An electrical signal (pilot light generation signal) is input to shift the optical frequency of seed light L2 and generate pilot light L4. The electrical signal generated by the electrical signal generator 124b is further divided into two, and one signal is input to the Hilbert converter 142, resulting in a signal with a phase shift of π / 2, which is then input to the optical IQ modulator 121b.

[0056] The frequency Δf generated by electrical signal generators 124a and 124b pr And, frequency Δf piThe electrical signal is a generated signal for generating probe light L3 and pilot light L4, each with a different optical frequency, from the light source 111. The oscillation frequency of the electrical signal generator 124 is controlled by the control unit 50. The oscillation frequency Δf of the electrical signal generator 124a pr The electrical signal is the probe light generated signal, and the frequency Δf is the frequency at which the electrical signal generator 124b oscillates. pi The electrical signal is called the pilot light generation signal.

[0057] The outputs of optical IQ modulators 121a and 121b are combined as mutually orthogonal polarization components at the output side of the vector optical modulator 121 and output from the vector optical modulator 121. This output light is amplified to an optical power of approximately 1mW to 100mW by the optical fiber amplifier 122, and then input to the input port 212 of the optical fiber sensor unit 21 through an optical filter 123 that removes the spontaneous emission light from the optical fiber amplifier 122. The output light from the vector optical modulator 121 is called the probe pilot light. The section from the light source 111 to the input port 212 is called the probe pilot light generation unit 500.

[0058] The optical frequency difference between the pump light L1 and the probe light L3 generated in the above configuration is controlled to search for the Brillouin shift frequency (approximately 10.8 GHz to 11 GHz in the case of a quartz fiber) occurring in the sensor optical fiber 215 (see Figure 1). On the other hand, the optical frequency difference between the pump light L1 and the pilot light L4 is fixed, and the optical frequency difference between the probe light L3 and the pilot light L4 is set to a value of several tens of MHz to about 1000 MHz.

[0059] The optical frequency shift performed by the first optical IQ modulator 121a and the second optical IQ modulator 121b is the frequency Δf output from the electrical signal generators 124a and 124b. pr and Δf pi This is done using electrical signals. Here, a portion of these electrical signals is split by dividers 125a and 125b, and the split signals are input to the IQ coherent detector 126. The IQ coherent detector 126 outputs electrical signals for two channels.

[0060] These are frequency Δf pr- Δf pi This is a complex amplitude electrical signal, with the first channel corresponding to the real part of the complex amplitude electrical signal and the second channel corresponding to the imaginary part of the complex amplitude electrical signal, with a phase shift of π / 2 (rad) from the first channel. This is input as a frequency offset signal S5 (equation (5)) to the input ports 312a and 312b of the Brillouin scattering optical detection unit 31. The complex conjugate signal of this frequency offset signal S5 is called the downconverted signal S6.

[0061] Figure 3 shows the configuration diagram of the optical fiber sensor unit 21 (see Figure 1). Input ports 211 and 212 are connected to a single sensor optical fiber 215 via optical circulators 213 and 214, respectively. The sensor optical fiber 215 is either a quartz glass single-mode optical fiber or a quartz glass highly nonlinear optical fiber in which the nonlinear coefficient is enhanced by compressing the core diameter. Here, the length of the sensor optical fiber 215 can be selected from several meters to around 100 km depending on the application.

[0062] In this embodiment, since it is used in a wide-area distributed seismometer, the length of the sensor optical fiber 215 was selected to be 100 km. Since the optical fiber core is folded back at the halfway point, the length of the optical fiber sensor section 21 is 50 km.

[0063] The pump light L1 input from the input port 211 of the optical fiber sensor unit 21 is input to the sensor optical fiber 215 via the optical circulator 213 and reaches the optical circulator 214. Here, the output is output from the output port of the optical circulator 214 to the optical termination unit 217.

[0064] Meanwhile, the pair of probe light L3 and pilot light L4 input from input port 212 is input to the sensor optical fiber 215 via optical circulator 214 and reaches optical circulator 213. The probe light L3 and pilot light L4 that have propagated through the sensor optical fiber 215 are affected by Brillouin scattering and become explored light L5.

[0065] The detected light L5 is output from the output port of the optical circulator 213, passes through the optical filter 216, and is then input to the optical port 311 of the Brillouin scattering optical detection unit 31 (see Figure 1).

[0066] Therefore, the pump light L1 output from the light source module 11 (see Figure 1) and input to input port 211, and the pair of probe light L3 and pilot light L4 input to input port 212, propagate backward from each other. As these lights propagate through the sensor optical fiber 215, stimulated Brillouin scattering occurs between the pump light L1 and the probe light L3. In other words, the probe light L3 and the pilot light L4, which is the explored light L5, that reach the optical circulator 213 are affected by Brillouin scattering.

[0067] Figure 4 shows the optical frequency arrangement of the pump light L1, probe light L3, and pilot light L4 at this time. The optical frequencies of the local light LO, pilot light L4, probe light L3, and pump light L1 are f LO ,f pi ,f pr ,f pump The difference frequency between the pump light L1 and the probe light L3 is Δf. pr The difference frequency between the pump light L1 and the pilot light L4 is Δf pi The Brillouin shift frequency is the difference frequency with the pump light L1, and Δf B It is represented as follows.

[0068] The optical frequency f of the pump light L1 pump and the optical frequency f of probe light L3 pr The difference frequency Δf prThe frequency is set to a frequency close to the Brillouin shift frequency of the quartz glass fiber of the sensor optical fiber 215 (approximately 10.8 GHz to 11 GHz for quartz fibers). This causes a Brillouin interaction to occur between the pump light L1 and the probe light L3, resulting in Δf pr and Brillouin shift frequency Δf B When these two values ​​are equal, the energy transfer efficiency from the pump light L1 to the probe light L3 is maximized, and the gain of the probe light L3 (induced Brillouin gain B) is maximized. G 2 ) is maximized. Also, as will be described later, the phase difference Δφ that occurs between the probe light L3 and the pilot light L4 after they have propagated through the sensor optical fiber is maximized. b It becomes zero.

[0069] The optical frequency difference Δf between the pump light L1 and probe light L3 generated in the above configuration. pr This is controlled to search for the Brillouin shift frequency (approximately 10.8 GHz to 11 GHz in the case of a quartz fiber) that occurs in the sensor optical fiber 215 (see Figure 3). Meanwhile, the optical frequency difference Δf between the pump light L1 and the pilot light L4 is controlled. pi This is fixed and the optical frequency difference f between the probe light L3 and the pilot light L4 is fixed. pr -f pi ("Δf pi -Δf pr The same applies to the above.) The frequency is set to a value of approximately tens of MHz to 1000 MHz.

[0070] As a result, the probe light L3 is affected by stimulated Brillouin scattering, while the pilot light L4 is not. This causes the optical phases of the probe light L3 and the pilot light L4 to have a Brillouin phase shift Δφ. b Only the difference in phase occurs. In other words, the Brillouin phase shift Δφ is generated from the optical phase difference between the probe light L3 and the pilot light L4. b It can be detected.

[0071] Figure 5 shows the configuration of the Brillouin scattering optical detection unit 31 (see Figure 1). The probe light L3 and pilot light L4 mentioned above are input to the optical port 311 of the Brillouin scattering optical detection unit 31. In addition, the frequency offset signal S5, which is the output from the IQ coherent detector 126 (see Figure 2) of the light source module unit 11, is input to the electrical signal port 312.

[0072] The probe light L3 and pilot light L4 are input to the polarization / phase diversity optical detector 321 via the optical port 311. This polarization / phase diversity optical detector 321 has two optical input ports, and the local light LO output from the local oscillator light source, the laser diode 322, is input to the other optical input port. Here, the laser diode 322 is the local light emitter 322.

[0073] The polarization-phase diversity photodetector 321 outputs a beat electrical signal S1 (see equation (1)) for each polarization plane component of the input light (probe light L3 and pilot light L4: explored light L5), based on the optical frequency and optical phase of the local light LO, in accordance with the operating principle of this detector (Non-Patent Literature 3). The polarization-phase diversity photodetector 321 is a detection unit 506 that detects (explored light L5) using the local light LO generated from the local light emitter 322 (second light source) and obtains the beat electrical signal S1.

[0074] The polarization / phase diversity photodetector 321 has four output ports: 322a, 322b, 322c, and 322d. Ports 322a and 322b output beat electrical signals corresponding to the X-polarization components of the probe light L3 and pilot light L4, while ports 322c and 322d output beat electrical signals corresponding to the Y-polarization components of the probe light L3 and pilot light L4. These are called the X-polarization beat electrical signal S1X and the Y-polarization beat electrical signal S1Y, respectively.

[0075] Furthermore, in the pair of beat electrical signals (X-polarized beat electrical signals S1X) from output ports 322a and 322b, the signal phase is shifted by 90 degrees. Therefore, the combination of these two signals reproduces the complex amplitude of the probe light L3 and the pilot light L4. In other words, the polarization / phase diversity optical detector 321 also functions as a separation unit 508, separating the beat electrical signal S1 into the probe optical electrical signal S2 corresponding to the probe light L3 and the pilot optical electrical signal S3 corresponding to the pilot light L4.

[0076] The X-polarized beat electrical signal S1X is a complex amplitude electrical signal that reflects the frequency difference or optical phase difference between the probe light L3 or pilot light L4, with respect to the optical frequency and optical phase of the local light LO. That is, the electrical signal from the first channel (output port 322a) corresponds to the real part of the complex amplitude electrical signal, and the electrical signal from the second channel (output port 322b) corresponds to the imaginary part and is phase-shifted by π / 2 (rad) relative to the electrical signal of the first channel.

[0077] The same argument applies to the pair of Y-polarized beat electrical signals S1Y from output ports 322c and 322d. That is, the electrical signal from the first channel (output port 322c) corresponds to the real part of the complex amplitude electrical signal, and the electrical signal from the second channel (output port 322d) corresponds to the imaginary part and is phase-shifted by π / 2 (rad) relative to the electrical signal from the first channel.

[0078] The beat electrical signals S1 output from these four output ports are input to an analog-to-digital converter (ADC) 323, where they are converted from analog signals to digital signals, and then input to a digital polarization rotation compensation filter 324. The digital polarization rotation compensation filter 324 compensates for the polarization rotation generated in the optical fiber sensor section 21 (see Figure 1) of the probe light L3 and pilot light L4 by digital signal processing. The digital polarization rotation compensation filter 324 outputs the probe light electrical signal S2 and the pilot light electrical signal S3, which correspond to the probe light L3 and pilot light L4.

[0079] In this embodiment, since the polarization of the pilot light L4 and the probe light L3 are orthogonal, the probe optical electrical signal S2 and the pilot optical electrical signal S3 can be spatially separated. The probe optical electrical signal S2 is represented by the above-described equation (5), and the pilot optical electrical signal S3 is represented by equation (6). Equations (5) and (6) are reproduced below. Therefore, the separation unit 508 may be considered to be from the polarization-phase diversity optical detector 321 to the digital polarization rotation compensation filter 324.

[0080] [Number]

[0081] Each beat electrical signal is output from the digital polarization rotation compensation filter 324. Among them, the pilot optical electrical signal S3 is input to the digital phase conjugate arithmetic unit 325 and converted into a phase conjugate electrical signal. Here, the probe optical electrical signal S2 may be input to the digital phase conjugate arithmetic unit 325 and converted into a phase conjugate electrical signal.

[0082] Then, the probe optical electrical signal S2 and the pilot optical electrical signal S3 that has become a phase conjugate electrical signal are input to the next-stage digital complex multiplier 326. These signals each have an electrical signal frequency and phase corresponding to the difference in optical frequency and optical phase from the local light LO. This digital complex multiplier 326 stably eliminates the difference in optical frequency and optical phase from the local light LO from these signals. Specifically, ω LO and φ LO are eliminated by multiplying the conjugate signals of equations (5) and (6). This digital complex multiplier 326 is the local light component removal unit 510.

[0083] As a result, the output of the digital complex multiplier 326 is an electrical signal having a frequency f pr -f pi (in angular frequency, it is "ω pr -ω pi "), and its phase is the Brillouin phase shift Δφ bThe probe light L3 affected thereby and the optical phase difference (Δφ b +φ pr -φ pi ) of the pilot light L4. The output of the digital complex multiplier 326 becomes the probe pilot optoelectronic signal S4. This is expressed by equation (7). Equation (7) is reproduced below.

[0084]

Equation

[0085] Note that B G is the square root of the induced Brillouin gain B G 2 .

[0086] As described above, although the digital complex multiplier 326 removes the optical phase difference component from the local light LO, the frequency of the output complex amplitude probe pilot optoelectronic signal S4 is f pr -f pi (In terms of angular frequency, it is “ω pr -ω pi ”: see equation (7). It is equal to “Δf pr -Δf pi ”). Therefore, in order to detect the Brillouin phase shift Δφ b , it is necessary to convert it to a baseband band including a DC component.

[0087] Therefore, the complex amplitude frequency offset signal S5 input to the input ports 312a and 312b of the Brillouin scattered light detector 31 is used. The frequency of this signal is also Δf pr -Δf pi . The complex amplitude frequency offset signal S5 is digitized by the analog-to-digital converters (ADCs) 327 connected to the input ports 312a and 312b. Then, it is input to the digital phase conjugate arithmetic unit 328 to obtain a down-converted signal S6 which is a phase conjugate signal with respect to the frequency offset signal S5. The frequency offset signal S5 is expressed by equation (8), and the down-converted signal S6 which is a phase conjugate signal is expressed by equation (9). Equation (8) and equation (9) are reproduced below.

[0088]

number

[0089] Then, the complex amplitude probe pilot photoelectric signal S4 and the aforementioned down-converted signal S6 are input to the digital complex multiplier 329, and the frequency Δf pr -Δf pi The complex amplitude probe pilot photoelectric signal S4 is converted down to the baseband. As a result, the Brillouin phase signal S7 (equation (10)) can be obtained.

[0090]

number

[0091] Furthermore, the section from the IQ coherent detector 126 to the digital complex multiplier 329 in Figure 2 can be considered as the Brillouin phase signal calculation unit 512.

[0092] The Brillouin phase signal S7, which is the output of the digital complex multiplier 329, is sent to the control unit 50, and the Brillouin phase shift Δφ is obtained from equation (11). b The following is calculated. Note that the induced Brillouin gain B G 2 This can be obtained by comparing the beat electrical signal S1 when the pump light L1 is present with the beat electrical signal S1 when the pump light L1 is absent. Therefore, the control unit 50 can be said to be a Brillouin phase shift amount calculation unit 514 (see Figure 1).

[0093]

number

[0094] In this embodiment, the digital signal processing performed downstream of the analog-to-digital converter (ADC) 323 and the analog-to-digital converter (ADC) 327 is implemented and operated on an integrated circuit such as a Field Programmable Gate Array (FPGA) element.

[0095] Using the first embodiment of the present invention, the Brillouin shift frequency Δf B To detect it, the frequency Δf of the probe light generated signal output from the electrical signal generator 124a (see Figure 2) pr The setting value is changed sequentially in 1MHz steps, and the Brillouin phase signal S7(exp(jΔφ) b )) is calculated. Then, based on equation (11), the Brillouin phase shift Δφ b The induced Brillouin gain B is calculated separately. G 2 Calculate the Brillouin phase shift Δφ. b The value becomes zero or the induced Brillouin gain B G 2 The frequency f of probe light L3 that maximizes pr The Brillouin shift frequency Δf B We will seek it as follows.

[0096] Figure 6 shows the frequency difference Δf between the pump light L1 and the probe light L3. pr Brillouin phase shift Δφ b and the induced Brillouin gain B G 2 This is an example of plotting the frequency difference Δf between the pump light L1 and the probe light L3. Refer to Figure 6, where the horizontal axis represents the frequency difference Δf between the pump light L1 and the probe light L3. pr The right vertical axis represents the induced Brillouin gain B. G 2 (dB), the left vertical axis is the Brillouin phase shift Δφ obtained by equation (11). b (rad)

[0097] As shown in Figure 6, the frequency difference Δf between the pump light L1 and the probe light L3 pr By calculating this at predetermined steps, the stimulated Brillouin gain of the probe light L3 is obtained. G 2 and Brillouin phase shift Δφ b It is possible to measure the induced Brillouin gain B G 2 and Brillouin phase shift Δφ bThe spectrum can be measured. Then, the stimulated Brillouin gain B G 2 The value that is maximized, or the Brillouin phase shift Δφ b The frequency at which is near 0 is the Brillouin shift frequency Δf B (Δω B It is calculated as follows:

[0098] Figure 7 shows an example of the output obtained from the output of the second embodiment. In both Figure 7(a) and Figure 7(b), the horizontal axis is time (sec), and the vertical axis is the Brillouin phase shift amount Δφ. b (rad). As the pump light L1 is input to the optical fiber sensor unit 21 (see Figure 1) at a repetition rate of 10 MHz, the Brillouin phase shift amount changes from positive to negative.

[0099] Furthermore, the frequency Δf of the probe light generated signal output from the electrical signal generator 124a pr (Δω pr ) Brillouin shift frequency Δf B (Δω B The amount of Brillouin phase shift Δφ that appears when the frequency is lower than ). b (Figure 7(a)) and the amount of Brillouin phase shift Δφ that appears when high frequency is used. b (Figure 7(b)) shows that the phases are inverted relative to each other.

[0100] Specifically, at the same time T1 and T2 in Figure 7, Figure 7(a) shows the Brillouin phase shift amount Δφ. b In Figure 7(b), the absolute value is maximized when the value is negative, whereas in Figure 7(b), the absolute value is maximized when the value is positive. Brillouin shift frequency Δf B The Brillouin phase shift amount Δφ b The method used to determine the induced Brillouin gain is called the phase detection method, and the induced Brillouin gain B G 2 The method used to determine this is called intensity detection.

[0101] Figure 8 shows the Brillouin phase shift amount Δφ b The vertical axis represents the frequency Δf of the probe light generated signal. prThis graph uses the horizontal axis as the graph. Figure 9 also shows the induced Brillouin gain B. G 2 With the vertical axis representing the frequency Δf of the probe light generated signal, pr A graph with the horizontal axis is also shown. A 3m length section of the sensor fiber 215, 3km from one end 211 (see Figure 1), was placed in a constant temperature bath, and measurements were taken while the temperature of the constant temperature bath was changed. As can be seen from these figures, the electrical signal frequency Δf is when the Brillouin phase shift is 0 (rad). pr It can be seen that the induced Brillouin gain is maximized. Also, in Figure 8, the electrical signal frequency Δf is 0 (rad). pr It can be seen that this shifts according to the ambient temperature of the optical fiber sensor unit 21.

[0102] Figure 10 shows the Brillouin shift frequency Δf of the optical fiber sensor unit 21 with respect to ambient temperature. B This shows the change. Figure 10(a) shows the Brillouin phase shift amount Δφ b The Brillouin shift frequency estimated from this, and the induced Brillouin gain B are shown in Figure 10(b). G 2 This is the Brillouin shift frequency estimated from the peak. In all figures, the horizontal axis is temperature (°C), and the vertical axis is the Brillouin shift frequency Δf. B It is (GHz).

[0103] The variances from the regression lines using the least squares method are 4.9 × 10⁻⁶ each. -6 and 6.9 × 10 -6 The Brillouin phase shift amount is Δφ. b The phase detection method using [the specified method] showed more stable detection. However, in both methods, the temperature changes linearly in accordance with the ambient temperature change of the optical fiber sensor unit 21, indicating that stable temperature sensing is achieved.

[0104] Figure 10 shows the relationship between Brillouin shift frequency and temperature. By maintaining this correspondence, if the Brillouin shift frequency is determined, the temperature can be measured. The relationship between Brillouin shift frequency and temperature is stored in the control unit 50 as a lookup table 518.

[0105] Figure 11 is a graph showing the relationship between the total received power of the pilot light L4 and probe light L3 and the signal-to-noise ratio of the detected probe light electrical signal S2. Referring to Figure 11, the horizontal axis represents the received power (dBm) of the probe light L3, and the vertical axis represents the signal-to-noise ratio of the probe light electrical signal S2. The black squares and white triangles in Figure 11 represent the results when the excitation power of the local light LO is 800mW and 200mW, respectively.

[0106] Assuming that a digital demodulation signal-to-noise ratio of 18 dB or higher is achievable, the Brillouin phase shift detection method according to the present invention allows for a large excitation power of the local optical fiber LO, so that even if the received power of the probe optical fiber L3 is -40 dBm, the signal-to-noise ratio of the probe optical electrical signal S2 can be demodulated to 18 dB or higher.

[0107] In conventional techniques, when local light is input to the sensor optical fiber together with probe light, and the amount of Brillouin phase shift is determined using the local light, the received power of the probe light is -22 dBm, resulting in a signal-to-noise ratio of 18 dB. Therefore, by using the Brillouin phase shift detection method according to the present invention, an improvement of approximately 18 dB compared to conventional methods is possible.

[0108] Thus, the sensor optical fiber 215 exhibits a Brillouin shift frequency Δf when the temperature changes. B Therefore, if you have a lookup table 518 like the one in Figure 10 beforehand, the Brillouin shift frequency Δf changes. B By calculating this, the temperature of the sensor optical fiber 215 can be determined. The lookup table 518 is used to determine the temperature and the Brillouin shift frequency Δf BThis may be a data sequence showing the relationship, or a mathematical formula showing that relationship. Lookup table 518 and Brillouin shift frequency Δf B The temperature is determined by the temperature estimation unit 520, which is performed by the control unit 50 (see Figure 1). Furthermore, the explored light L5, obtained a predetermined time after the pump light L1, which can be output in a pulsed manner, is input to the sensor optical fiber 215, is affected by the Brillouin scattering phenomenon at the point where the pump light L1 has traveled through the sensor optical fiber 215 for a predetermined time. Therefore, by sequentially changing the acquisition time of the explored light L5 from the time the pump light L1 is input, the temperature at any point in the sensor optical fiber 215 can be measured.

[0109] Figure 12 shows a conceptual diagram of such a temperature measurement method. Pump light L1 is input from the other end 211 of the sensor optical fiber 215, and probe light L3 and pilot light L4 are input from the one end 212. At time T=0, the pump light L1 input to the sensor optical fiber 215 is t b After seconds, distance D(t b Only the probe light L3 travels through the sensor optical fiber 215. At point A, it is affected by Brillouin scattering on the probe light L3, and the probe light L3 and pilot light L4 become explored light L5. In Figure 11, it is indicated as "L5(k)" that the explored light L5 was created by the k-th probe light L3.

[0110] The detected light L5 was detected at time t. b Then it reaches the other end 211 side. Therefore, after inputting the pump light L1, 2t b By detecting the detected light L5 after seconds, the distance D(t) from one end 212 is obtained. b Δφ of the Brillouin phase shift at the point ) b Alternatively, the induced Brillouin gain B G 2 This can be obtained. Next, the frequency of probe light L3 is changed (the k+1th probe light L3), pump light L1 is input, and then 2t b If the detected light L5 is detected a few seconds later, the Brillouin phase shift Δφ at the same location will be detected. b Alternatively, the induced Brillouin gain BG 2 You can obtain this.

[0111] By successively changing the frequency of the probe light L3, the graph in Figure 6 can be obtained, and the Brillouin phase shift amount Δφ can be determined. b The result is zero, or the induced Brillouin gain B G 2 The frequency at which this is maximized is the Brillouin shift frequency Δf B It can be calculated as follows: Brillouin shift frequency Δf B Once this is determined, the distance D(t) can be found using the previously stored lookup table 518. b The temperature at the location can be estimated.

[0112] Furthermore, the pump light L1 is input to the sensor optical fiber 215 and then 2t b+1 By detecting the detected light L5 after seconds, the distance D(t) from the other end 211 can be determined. b+1 The temperature at point B of ) can be estimated.

[0113] In this way, while changing the frequency of the probe light L3, the Brillouin phase shift amount Δφ b We successively calculate the Brillouin phase shift amount Δφ b The point at which the Brillouin shift frequency Δf becomes zero B The Brillouin shift frequency calculation unit 516 and the control unit 50 are responsible for determining this (see Figure 1).

[0114] Figure 13 illustrates the flow of processing performed by the control unit 50 when the optical fiber temperature sensing device 1 measures the temperature over the entire area of ​​the sensor optical fiber 215 by the operation shown in Figure 12.

[0115] Once processing starts (step S100), preprocessing is performed (step S102). Preprocessing includes the initialization of each variable (=1).

[0116] Next, the probe light L3 and pilot light L4 are input to the sensor optical fiber 215 (step S104). At this time, the frequency of the probe light L3 is Δf pr (k) is the value. "k" is a parameter, and by incrementing k, Δf is obtained in the example above. pr The frequency changes by 1MHz.

[0117] Then, the pump light L1 is input to the sensor optical fiber 215, and a waiting time T(m) is observed (step S106). "m" is a parameter, and as m is incremented, the waiting time increases. Since the speed at which the pump light L1 travels is known, this time can be converted into the distance from the other end 211 of the sensor optical fiber 215.

[0118] The explored light L5 after time T(m) has elapsed is detected by the Brillouin scattering light detection unit 31 (step S108) to obtain the Brillouin phase signal S7 expressed by equation (10). From the obtained Brillouin phase signal S7, the Brillouin phase shift amount Δφ is obtained by equation (11). b The following is calculated. In addition, the induced Brillouin gain B is calculated by comparing the beat electrical signal S1 when a separate pump light L1 is present with the beat electrical signal S1 when pump light L1 is absent. G 2 This is required (Step S110).

[0119] Next, it is determined whether the sweep of probe light L3 is complete (step S112). If it is not complete (N branch in step S112), the frequency is incremented (step S114), and the process from step (S104) is repeated.

[0120] If the sweep of probe light L3 is complete (Y branch in step S112), the Brillouin phase shift amount Δφ at that distance is... b and the induced Brillouin gain B G 2 This yields the graph shown in Figure 6. Therefore, as explained in Figure 11, the Brillouin shift frequency Δφ can be obtained from the graph in Figure 6. b The following steps are performed: Determine the value and calculate the temperature from the lookup table in Figure 10 (Step S116).

[0121] Next, it is determined whether the time parameter m is at its final value (step S118). This determination is equivalent to determining whether or not the temperature measurement along the entire length of the sensor optical fiber 215 has been completed. If m is not at its final value (N branching in step S118), m is incremented and k is initialized (step S120). Then, the process from step S104 is repeated.

[0122] If m is the final value (Y-branch in step S118), the temperature measurement along the entire length of the sensor optical fiber 215 is completed, and the process stops (step S122). As described above, the optical fiber temperature sensing device 1 according to the present invention can measure the temperature at any desired position along the entire length of the sensor optical fiber 215.

[0123] In this embodiment, the pump light L1, probe light L3, and pilot light L4 are arranged as shown in Figure 4, but other arrangements are also possible. First, the relative magnitudes of the probe light L3 and pilot light L4 may be swapped. However, either light must have a Brillouin shift frequency (f) of the sensor optical fiber 215 of the optical fiber sensor unit 21. pump -Δf B It is necessary that the frequency be close to that of ).

[0124] Local optical LO is Brillouin shift frequency (f pump -Δf B ), it can be freely set as long as it is not in the vicinity of the probe light L3 and the pilot light L4. Examples of frequency configurations are shown in Figures 14 to 16.

[0125] Figure 14 shows the difference between the probe light L3 and pilot light L4 compared to Figure 4, with the local light LO and pump light L1 having a Brillouin shift frequency (f pump -Δf B This is the case when it is placed between ). Brillouin shift frequency (f pump -Δf B A pilot light L4 is placed near the ) element. In this case, the Brillouin phase shift is affected by the pilot light L4.

[0126] Figure 15 shows that the relative sizes of probe light L3 and pilot light L4 remain the same as in Figure 13, but the local light LO is set to the optical frequency f of probe light L3. pr Making it smaller. Brillouin shift frequency (f pump -Δf B Probe light L3 is positioned near (). The Brillouin phase shift is affected by probe light L3.

[0127] Figure 16 shows that the relative magnitudes of probe light L3 and pilot light L4 are the same as in Figure 4, and the local light LO is the same as the pump light L1 and the Brillouin shift frequency (f pump -Δf B This is the case when they are placed between ). The Brillouin phase shift is affected by the probe light L3. Even with these frequency arrangements, the Brillouin shift frequency can be obtained by a similar operation.

[0128] (Third embodiment) The configuration of the optical fiber temperature sensing device 1 in this embodiment is the same as that shown in Figure 1, but there are differences in the configuration of the light source module 11 and the Brillouin scattering optical detection unit 31.

[0129] Figure 17 shows the configuration of the light source module 11, and Figure 18 shows the configuration of the Brillouin scattering optical detection unit 31. The difference in the light source module 11 from the first embodiment is that the polarizations of the probe light L3 and the pilot light L4 are identical, rather than being orthogonal to each other.

[0130] Unlike the second embodiment, the vector optical modulator 121 provided inside the light source module 11 utilizes a single optical IQ modulator 121. Instead, a frequency Δf generated by the electrical signal generator 124 is placed before the electrical signal input port that is input to the optical IQ modulator 121. pr and frequency Δf piThe system is equipped with a frequency division multiplexing circuit 141 that frequency-division multiplexes the two generated signals. Of these signals, the complex amplitude electrical signal input to the Q channel side of the optical IQ modulator 121 is Hilbert-converted in the Hilbert converter 142.

[0131] The Hilbert converter 142 performs a Hilbert transform on the input signal, and the frequency Δf pr and frequency Δf pi It plays the role of simultaneously generating optical frequency shift spectral components corresponding to the two electrical signals. More specifically, it shifts the phase by π / 2 (rad).

[0132] On the other hand, referring to Figure 18, the difference in the second embodiment of the Brillouin scattering optical detection unit 31 lies in the stage after the digital polarization rotation compensation filter 324. In the second embodiment, since the polarizations of the probe light L3 and the pilot light L4 were orthogonal, the electrical signals corresponding to both were spatially separated at the output of the digital polarization rotation compensation filter 324. However, in this embodiment, since both lights have the same polarization, the electrical signals corresponding to both are not spatially separated at the output of the digital polarization rotation compensation filter 324. Therefore, the output of the digital polarization rotation compensation filter 324 is only the output for one polarization.

[0133] Therefore, in this embodiment, the output of the digital polarization rotation compensation filter 324 is split into two. One is connected to the high-pass digital filter 341, and its output yields an electrical signal corresponding to the probe light L3 (probe light electrical signal S2). The other is connected to the low-pass digital filter 342, and its output yields an electrical signal corresponding to the pilot light L4 (pilot light electrical signal S3). In this embodiment, the high-pass digital filter 341 and the low-pass digital filter 342 form the separation unit 508.

[0134] The subsequent digital signal processing is the same as in the second embodiment. The function of the digital polarization rotation compensation filter 324 used in this embodiment can be replaced by an optical polarization controller 320 located before the polarization / phase diversity photodetector 321. The optical polarization controller 320 can be composed of multiple waveplates.

[0135] This embodiment has the advantage of being able to reduce costs compared to the second embodiment, as the configuration of the vector optical modulator 121 (Figure 17) is simpler.

[0136] (Fourth embodiment) Figure 19 shows a fourth embodiment of the present invention, in which the configuration of the light source module 11 and the Brillouin scattering optical detection unit 31 is the same as in the second embodiment. However, in this embodiment, the digital signal processing in the Brillouin scattering optical detection unit 31 is implemented by software. In the third embodiment, the analog-to-digital converter (ADC) 323 built into the Brillouin scattering optical detection unit 31 converts the X-polarized beat electrical signal S1X and the Y-polarized beat electrical signal S1Y into digital signals.

[0137] Another analog-to-digital converter (ADC) 327 converts the generated signal output from the IQ coherent detector 126 (see Figure 1) in the light source module 11 into a digital signal. Digital signal processing is then performed downstream of these analog-to-digital converters to create a Brillouin phase shift Δφ in the baseband band, which includes a DC component. b A signal is being detected.

[0138] In contrast, the present invention implements the digital signal processing described in the second embodiment using software processing. This configuration uses a personal computer 301 incorporating an analog-to-digital converter (ADC) 323 and an analog-to-digital converter (ADC) 327. The software running on this personal computer 301 performs the digital signal processing described in the third embodiment, and the Brillouin phase shift amount Δφb is detected. This has an advantage in that the system can be constructed more economically compared to the first embodiment. The software-implemented functional parts are shown by the dashed lines in Figure 18.

[0139] This embodiment has the advantage of significantly reducing costs compared to the third embodiment, as the digital signal processing function is implemented in software. The personal computer 301 may be incorporated into the control unit 50.

[0140] (Fifth embodiment) Figure 20 shows the configuration of the optical fiber temperature sensing device 1 of this embodiment. In this embodiment, compared to the first to fourth embodiments, the frequency offset signal S5 from the light source module 11 is not supplied. The frequency offset signal S5 that has been removed compared to Figure 1 is shown by a dashed line.

[0141] Figure 21 shows the interior of the light source module 11. The IQ coherent detector 126 and the dividers 125a and 125b that split the electrical signals from the electrical signal generators 124a and 124b are omitted from the light source module 11. The omitted parts are represented by dashed lines.

[0142] Figure 22 shows the configuration of the Brillouin scattering optical detection unit 31. Since the frequency offset signal S5 is not received from the light source module unit 11, the Brillouin scattering optical detection unit 31 is equipped with a digital complex amplitude electrical signal generator 351 and a digital complex self-delay detection circuit 352. Also, the analog-to-digital converter (ADC) 327 (shown by a dashed line) is omitted.

[0143] The digital complex amplitude electrical signal generator 351 generates Δf pr -Δf pi While it is possible to emit the correct frequency, the reference phase of the Brillouin phase shift becomes unclear. Therefore, compensation for this is performed by the digital complex self-delay detection circuit 352.

[0144] The output of the digital complex self-delay detection circuit 352 is proportional to the relative phase difference signal with respect to the input signal. Therefore, even if a phase reference of θ (rad) exists, the relative phase difference becomes 0, and the Brillouin phase shift amount Δφ b This makes it possible to output only the phase variation associated with the above. In this embodiment, the digital complex amplitude electrical signal generator 351 to the digital complex self-delay detection circuit 352 can be considered as the Brillouin phase signal calculation unit 512.

[0145] This embodiment does not utilize the IQ coherent detector 126 (see Figure 2) and analog-to-digital converter (ADC) 327 (see Figure 5) in the light source module 11 of the second embodiment, and the digital polarization rotation compensation filter 324 (see Figure 5) is replaced with an optical polarization rotation compensator 371. This reduces the manufacturing cost of the circuit.

[0146] (Sixth embodiment) Figure 23 shows the light source module 11 of the sixth embodiment of the present invention. This embodiment is a modification of the fifth embodiment, and similar to the fifth embodiment, the IQ coherent detector 126 is omitted on the light source module 11 side. In this embodiment, the frequency Δf output from the electrical signal generator 124a pr The probe light generation signal is input to the multiplier 162. Here, by multiplying it with the Sinc function waveform pulse signal (Figure 24(a)) generated from the digital Sinc function pulse generator 161, which is newly added in this embodiment, a digital comb signal having a frequency spectrum as shown in Figure 24(b) is generated.

[0147] This electrical signal is input to both the IQ channels of the optical IQ modulators 121a and 121b of the vector optical modulator 121. However, the Q channel is Hilbert-converted by the Hilbert converter 142a before being input to the optical IQ modulators 121a and 121b, respectively. This allows for the acquisition of a comb-shaped probe optical spectrum as shown in Figure 24(b).

[0148] In the second embodiment, the Brillouin shift frequency Δf B To detect, the probe light frequency f pr While sequentially moving the induced Brillouin gain B G 2 Or Brillouin phase shift amount Δφ b It was detecting [something]. In contrast, in this embodiment, since the probe light L3 always has a comb-shaped spectrum, the probe light frequency f pr No change is needed, and the probe optical frequency f pr The Brillouin shift frequency Δφ is shifted without sequential movement. b It will become possible to detect it.

[0149] Figure 25 shows the Brillouin scattering optical detection unit 31, which can accommodate additional functions on the transmitting side. As shown in this figure, a Fourier converter 353 is newly provided after the digital complex self-delay detection circuit 352 that was added in the fifth embodiment (see Figure 22).

[0150] The amplitude and phase changes corresponding to the comb-shaped spectral component in Figure 24(b) obtained from this output are detected, and the stimulated Brillouin gain B is obtained. G 2 Spectrum and Brillouin phase shift Δφ b Both spectra are measured in a single, simultaneous process.

[0151] Thus, in this embodiment, the frequency f of the probe light L3 pr Without sequentially changing the induced Brillouin gain B G 2 Spectrum and Brillouin phase shift amount Δφ b The spectrum, and by extension the Brillouin shift frequency Δf BThis enables detection of the optical fiber temperature sensing device 1. As a result, the measurement time of the optical fiber temperature sensing device 1 is dramatically improved. For example, when measuring in 1 MHz steps in an optical frequency width of 100 MHz, measurement becomes 100 times faster compared to the second to fifth embodiments.

[0152] (Seventh Embodiment) Figure 26 shows the configuration of the Brillouin scattering optical detection unit 31 of the seventh embodiment. The overall configuration as an optical fiber temperature sensing device 1 is the same as in Figure 1, and the light source module 11 is the same as in Figure 17. In this embodiment, the digital signal processing in the Brillouin scattering optical detection unit 31 is realized using analog electrical circuits. However, in this embodiment, an analog-to-digital converter is not used, and the digital polarization rotation compensation filter is replaced by an optical polarization rotation compensator 371.

[0153] The light source module 11 of this embodiment is realized with the configuration shown in Figure 17 of the third embodiment. That is, the probe light L3 and the pilot light L4 are frequency-division multiplexed and transmitted with the same polarization. Referring to Figure 26, the aforementioned probe light L3 and pilot light L4 are input to the optical port 311 of the Brillouin scattering optical detection unit 31, and the frequency offset signal S5, which is the output from the IQ coherent detector 126 of the light source module 11, is input to the electrical signal port 312.

[0154] The probe light L3 and pilot light L4 are input to the phase diversity optical detector 331 after the polarization rotation generated in the optical fiber sensor unit 21 is compensated by the optical polarization rotation compensator 371 via the optical port 311. In this embodiment, since the polarization rotation of the probe light L3 and pilot light L4 is compensated, unlike the third embodiment, a polarization diversity configuration is not employed in the optical detector, thereby reducing costs.

[0155] This phase diversity photodetector 331 has two optical input ports, and the local optical LO output from the laser diode 322, which is a local oscillator, is input to the other optical input port. This phase diversity photodetector 331 outputs a beat electrical signal S1 referenced to the optical frequency and optical phase of the local optical LO.

[0156] Here, the phase diversity photodetector 331 has two output ports, 332a and 332b. In the pair of 332a and 332b, the signal phase is shifted by 90 degrees. Therefore, the combination of these two signals reproduces the complex amplitude of the probe light L3 and the pilot light L4, and the beat electrical signal S1 becomes an electrical signal that reflects the frequency difference or optical phase difference between the probe light L3 or the pilot light L4, with respect to the optical frequency and optical phase of the local light LO.

[0157] The beat electrical signal S1 output from these two output ports is separated by a frequency filter into a probe optical electrical signal S2 corresponding to the probe light L3 and a pilot optical electrical signal S3 corresponding to the pilot light L4. In this embodiment, the probe optical electrical signal S2 is obtained from the output of the high-pass filter 343, and the pilot optical electrical signal S3 is obtained from the output of the low-pass filter 344.

[0158] Of these, the pilot photoelectric signal S3 is input to the polarity inversion circuit 345 on the circuit side corresponding to the imaginary part of the complex amplitude electrical signal of the two outputs, and a phase conjugate electrical signal is obtained. Here, the probe photoelectric signal S2 may also be input to the polarity inversion circuit 345 and converted into a phase conjugate electrical signal.

[0159] Then, the pilot photoelectric signal S3, which is the phase-conjugate electrical signal of the probe photoelectric signal S2, is input to the next stage complex multiplier circuit 386. These signals each have an electrical signal frequency and phase corresponding to the difference in optical frequency and optical phase with the local light LO. However, this complex multiplier circuit 386 stably cancels out the difference in optical frequency and optical phase with the local light LO from these signals. As a result, the output of the complex multiplier circuit 386 has a frequency Δf corresponding to the optical frequency difference between the pilot light L4 and the probe light L3. pr -Δf pi This becomes an electrical signal, and its phase is the optical phase difference between the probe light L3 and the pilot light L4, and its value is the Brillouin phase shift Δφ b The value will be...

[0160] Here, an example configuration of the complex multiplication circuit 386 is shown in Figure 27. This circuit realizes complex multiplication of complex amplitude electrical signals. That is, the operation X × Y(a + jb) × (c + jd) = (ac - bd) + j(bc + ad) is realized using analog multiplication circuits 361, 362, 363, 364, subtraction circuit 365, and addition circuit 366.

[0161] As mentioned above, although the complex multiplication circuit 386 removes the optical phase difference component with the local optical LO, the frequency of the output complex amplitude probe pilot photoelectric signal S4 is Δf pr -Δf pi Therefore, in order to detect the Brillouin phase shift, it is necessary to convert the signal to a baseband band that includes a DC component.

[0162] Therefore, the frequency offset signal S5 of complex amplitude input to the input ports 312a and 312b of the Brillouin scattering optical detection unit 31 is used. The frequency of this signal is also Δf pr -Δf pi This signal is then input to the polarity inversion circuit 387 connected to input ports 312a and 312b, and a down-converted signal S6, which is the phase conjugate of the frequency offset signal S5, is obtained.

[0163] Then, the complex amplitude probe pilot optoelectronic signal S4 and the aforementioned down-converted signal S6 are input into the complex multiplication circuit 388, and the frequency Δf pr -Δf pi of the complex amplitude probe pilot optoelectronic signal S4 is down-converted to the baseband. As a result, the Brillouin phase signal S7 is obtained, from which the Brillouin phase shift Δφ b can be calculated.

[0164] In this embodiment, an analog-to-digital converter is not used, and the digital polarization rotation compensation filter is also replaced by the optical polarization rotation compensator 371. Thereby, the manufacturing cost of the circuit can be reduced.

Industrial Applicability

[0165] In addition to industrial applications such as building, bridge, soil monitoring of disaster-prone locations, and aircraft vibration sensing, the present invention can be applied to social infrastructure such as wide-area distributed seismographs. [[ID=)18]]

Explanation of Signs

[0166] 1 Optical Fiber (Temperature) Sensing Device <00009C3>1 Optical Fiber Temperature Sensing Device 11 Light Source Module Unit 111 Light Source 112 Optical Isolator 113 Optical Demultiplexer 114 Optical Intensity Modulator 115 Electrical Pulse Generator 116 Polarization Scrambler 117 Optical Fiber Amplifier 122 Optical Fiber Amplifier 118 Optical Filter 123 Optical Filter 121 Vector Optical Modulator 121a Optical IQ Modulator 121b Optical IQ Modulator 124a Electrical Signal Generator 124b Electrical Signal Generator 125a 125b Divider 126 IQ Coherent Detector 141 Frequency Division Multiplexing Circuit 142 Hilbert converter 161 Digital Sinc Function Pulse Generator 162 Multipliers 21 Optical fiber sensor section 212 one end 211 Other end 211 input ports 212 input ports 213 214 Light Circulator 214 Light Circulator 215 Optical fiber for sensors 216 Light Filters 217 Optical termination section 31 Brillouin scattering optical detection section 301 Personal Computers 311 Optical Port 312 Electrical signal ports 312a 312b Input Ports 320 Optical Polarization Controller 321 Polarization and Phase Diversity Optical Detector 322a, 322b, 322c, 322d, 332a, 332b output ports 322 Local light-emitting section 322 Laser Diode 323 Analog-to-Digital Converter (ADC) 324 Digital Polarization Rotation Compensation Filter 325 Digital Phase Conjugate Unit 326 Digital Complex Multiplier 327 Analog-to-Digital Converter (ADC) 328 Digital Phase Conjugate Unit 329 Digital Complex Multiplier 331 Phase diversity optical detector 341 High-pass digital filter 342 Low-pass digital filter 343 High-pass filter 344 Low-pass filter 345 Polarity inversion circuit 351 Digital complex amplitude electrical signal generator 352 Digital complex self-delay detection circuit 353 Fourier transformer 361, 362, 363, 364 Analog multiplication circuit 365 Subtraction circuit 366 Addition circuit 371 Optical polarization rotation compensator 386 Complex multiplication circuit 387 Polarity inversion circuit 388 Complex multiplication circuit 50 Control unit 500 Probe pilot light generation unit 502 Pump light generation unit *508 Separation unit 506 Detection unit 510 Local light component removal unit 512 Brillouin phase signal calculation unit 514 Brillouin phase shift amount calculation unit 516 Brillouin shift frequency calculation unit<000M978>5*18 Look-up table 520 Temperature estimation unit L1 Pump light<00009M>L2 Seed light L3 Probe light<OOOOM83>L4 Pilot light L5 Explored light LO Local light S1 Beat electrical signal S1X X-polarized beat electrical signal S1Y Y-polarized beat electrical signal S2 Probe light electrical signal S3 Pilot light electrical signal S4 Probe pilot light electrical signal S5 Frequency offset signal S6 Down-convert signal S7 Brillouin phase signal Note: There seems to be a formatting issue in the original text where some tags might be misaligned or there are some unclear notations like <000M978> and <OOOOM83>. I've translated as accurately as possible based on the visible content. If these are errors in the original, it might affect the overall understanding and accuracy of the translation.

Claims

1. Probe light and pilot light are generated from the output light of the first light source using the probe light generation signal and pilot light generation signal. The probe light and the pilot light are combined and input from one end of the optical fiber for the sensor. A light input step in which light from the first light source is input as pump light from the other end of the optical fiber for the sensor, A detection step to obtain a beat electrical signal by detecting the output light from the other end of the optical fiber for the sensor using local light generated from a second light source, A separation step of separating the beat electrical signal into a probe photoelectrical signal corresponding to the probe light and a pilot photoelectrical signal corresponding to the pilot light, A local light component removal step is performed to obtain a probe-pilot photoelectric signal from which the influence of the local light has been removed by multiplying the phase conjugate signal of the pilot photoelectric signal by the probe photoelectric signal. A down-converted signal is generated to convert the aforementioned probe pilot photoelectric signal to the baseband band. A method for detecting a Brillouin phase shift, comprising a phase component calculation step of multiplying the probe pilot photoelectric signal by the Brillouin phase signal to obtain a Brillouin phase signal and determining the amount of Brillouin phase shift from the Brillouin phase signal.

2. The aforementioned optical input process is, The process involves polarizing the probe light and the pilot light separately, combining them, and inputting them from one end of the sensor optical fiber, and inputting the pump light from the other end of the sensor optical fiber. The separation step is, A method for detecting a Brillouin phase shift according to claim 1, which comprises the step of separating the beat electrical signal into the probe photoelectric signal and the pilot photoelectric signal for each polarization of the beat electrical signal.

3. The aforementioned optical input process is, The process involves combining the probe light and the pilot light with the same polarization and inputting them from one end of the sensor optical fiber, and inputting the pump light from the other end of the sensor optical fiber. The separation step is, A method for detecting a Brillouin phase shift according to claim 1, which includes the step of separating the beat electrical signal into the probe optical electrical signal and the pilot optical electrical signal based on differences in frequency.

4. The phase component calculation step is as follows: A method for detecting a Brillouin phase shift according to claim 2 or 3, comprising the steps of: generating a downconvert signal for converting the probe pilot photoelectric signal to a baseband band from the probe light generation signal and the pilot light generation signal; multiplying the downconvert signal by the probe pilot photoelectric signal to obtain a Brillouin phase signal; and determining the amount of Brillouin phase shift from the Brillouin phase signal.

5. The phase component calculation step is as follows: A method for detecting a Brillouin phase shift according to claim 2 or 3, comprising the steps of: generating a downconvert signal for converting the probe pilot photoelectric signal to a baseband band from a signal other than the probe light generation signal and the pilot light generation signal; multiplying the downconvert signal by the probe pilot photoelectric signal to obtain a Brillouin phase signal; and determining the amount of Brillouin phase shift from the Brillouin phase signal.

6. Probe light and pilot light are generated from the output light of the first light source using the probe light generation signal and pilot light generation signal. The probe light and the pilot light are combined and input from one end of the optical fiber for the sensor. A light input step in which light from the first light source is input as pump light from the other end of the optical fiber for the sensor, A detection step to obtain a beat electrical signal by detecting the output light from the other end of the optical fiber for the sensor using local light generated from a second light source, A separation step of separating the beat electrical signal into a probe photoelectrical signal corresponding to the probe light and a pilot photoelectrical signal corresponding to the pilot light, A local light component removal step is performed by multiplying the conjugate signal of the pilot photoelectric signal by the probe photoelectric signal to obtain a probe-pilot photoelectric signal from which the influence of the local light has been removed. A down-converted signal is generated to convert the aforementioned probe pilot photoelectric signal to the baseband band. A phase component calculation step involves multiplying the probe pilot photoelectric signal by the Brillouin phase signal to obtain a Brillouin phase signal, and then determining the Brillouin phase shift amount from the Brillouin phase signal. A repeating process that repeats the phase component calculation process from the optical input process while changing the optical frequency of the probe light, A Brillouin shift frequency acquisition step to determine the Brillouin shift frequency at which the Brillouin phase shift amount becomes zero or the induced Brillouin gain is maximized, An optical fiber temperature sensing method comprising a lookup table representing the relationship between a pre-prepared temperature and the Brillouin shift frequency, and a step of determining the temperature from the Brillouin shift frequency.

7. The aforementioned optical input process is, The process involves polarizing the probe light and the pilot light separately, combining them, and inputting them from one end of the sensor optical fiber, and inputting the pump light from the other end of the sensor optical fiber. The separation step is, The optical fiber temperature sensing method according to claim 6, which includes the step of separating the beat electrical signal into the probe optical electrical signal and the pilot optical electrical signal for each polarization.

8. The aforementioned optical input process is, The process involves combining the probe light and the pilot light with the same polarization and inputting them from one end of the sensor optical fiber, and inputting the pump light from the other end of the sensor optical fiber. The separation step is, The optical fiber temperature sensing method according to claim 6, which includes the step of separating the beat electrical signal into the probe optical electrical signal and the pilot optical electrical signal based on differences in frequency.

9. The phase component calculation step is as follows: The optical fiber temperature sensing method according to claim 7 or 8, comprising the steps of generating a downconvert signal from the probe light generation signal and the pilot light generation signal for converting the probe pilot photoelectric signal to a baseband band, multiplying the downconvert signal by the probe pilot photoelectric signal to obtain a Brillouin phase signal, and determining the amount of Brillouin phase shift from the Brillouin phase signal.

10. The phase component calculation step is as follows: The optical fiber temperature sensing method according to claim 7 or 8, comprising the steps of generating a downconvert signal for converting the probe pilot photoelectric signal to a baseband bandwidth from sources other than the probe light generation signal and the pilot light generation signal, multiplying the downconvert signal by the probe pilot photoelectric signal to obtain a Brillouin phase signal, and determining the amount of Brillouin phase shift from the Brillouin phase signal.

11. A Brillouin phase shift detection device for detecting the Brillouin phase shift of an optical fiber for a sensor, A probe pilot light generation unit generates probe light and pilot light using a probe light generation signal and a pilot light generation signal from the output light of a first light source, combines the probe light and the pilot light to form a probe pilot light which is input from one end of the optical fiber for the sensor, The system includes a pump light generation unit that generates pump light from the first light source and inputs it from the other end of the optical fiber for the sensor. Light source module section, A detection unit that detects the output light from the other end of the optical fiber for the sensor using local light generated from a second light source to obtain a beat electrical signal, A separation unit that separates the beat electrical signal into a probe optical electrical signal corresponding to the probe light and a pilot optical electrical signal corresponding to the pilot light, A local light component removal unit obtains a probe-pilot photoelectric signal from which the influence of the local light has been removed by multiplying the phase-conjugate signal of the pilot photoelectric signal by the probe photoelectric signal, A Brillouin phase signal calculation unit generates a down-convert signal for converting the probe pilot photoelectric signal to the baseband band, multiplies it by the probe pilot photoelectric signal to obtain a Brillouin phase signal, A Brillouin phase shift detection device having a Brillouin phase shift amount calculation unit that calculates the amount of Brillouin phase shift from the Brillouin phase signal.

12. An optical fiber temperature sensing device for measuring the temperature of an optical fiber used as a sensor, A probe-pilot light generation unit generates probe light and pilot light using a probe light generation signal and a pilot light generation signal from the output light of a first light source, combines the probe light and the pilot light, and inputs them from one end of the optical fiber for the sensor. The system includes a pump light generation unit that generates pump light from the first light source and inputs it from the other end of the optical fiber for the sensor. Light source module section, A detection unit that detects the output light from the other end of the optical fiber for the sensor using local light generated from a second light source to obtain a beat electrical signal, A separation unit that separates the beat electrical signal into a probe optical electrical signal corresponding to the probe light and a pilot optical electrical signal corresponding to the pilot light, A local light component removal unit obtains a probe-pilot photoelectric signal from which the influence of the local light has been removed by multiplying the phase-conjugate signal of the pilot photoelectric signal by the probe photoelectric signal, A Brillouin phase signal calculation unit generates a down-convert signal for converting the probe pilot photoelectric signal to the baseband band, multiplies it by the probe pilot photoelectric signal to obtain a Brillouin phase signal, A Brillouin phase shift amount calculation unit that calculates the Brillouin phase shift amount from the Brillouin phase signal, A Brillouin shift frequency calculation unit that determines the Brillouin phase shift amount while changing the frequency of the probe light and determines the Brillouin shift frequency at which the Brillouin phase shift amount becomes zero or the induced Brillouin gain is maximized, A lookup table showing the correspondence between the Brillouin shift frequency and temperature, An optical fiber temperature sensing device having a lookup table and a temperature estimation unit that calculates temperature from the Brillunshift frequency.

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