Measuring device and its control method

Abstract

This enables the realization of an optical fiber characteristic measurement device with a simpler configuration. [Solution] The measuring device for measuring the characteristics of an optical fiber comprises a light source unit that emits frequency-modulated light, a first light generation unit that generates first light from the frequency-modulated light, an adjustment unit capable of adjusting the optical path length between the first light generation unit and the first end of the optical fiber, a second light generation unit that generates second light with a different frequency from the first light from the frequency-modulated light, a photodetection unit that converts scattered light, which is generated by injecting the first light generated by the first light generation unit into the first end of the optical fiber via the adjustment unit and injecting the second light generated by the second light generation unit into the second end of the optical fiber, into an electrical signal, and a calculation unit that calculates the frequency shift of the third light converted into an electrical signal relative to the second light, wherein the adjustment unit includes an optical switch that switches whether or not to connect a delay optical path having an optical path length corresponding to the interval of correlation peaks.

Description

[Technical Field]

[0001] This disclosure relates to a measuring device and a method for controlling the same. [Background technology]

[0002] A technology is known that uses an optical fiber as a sensor to measure the strain or temperature of the location where the optical fiber is laid, and is related to an optical fiber characteristic measuring device.

[0003] For example, Patent Documents 1 and 2 describe a Brillouin Gain Spectrum (BGS) measurement device equipped with two light sources. Each of the two light sources includes a semiconductor laser and a signal generator. Therefore, the BGS measurement device can have a desired difference (in the range of approximately 10 GHz to approximately 11 GHz) between the frequencies of the light emitted from the two semiconductor lasers. The modulation frequency and phase applied to the semiconductor lasers can also be adjusted for each semiconductor laser in the BGS measurement device. As a result, the BGS measurement device can shift the correlation peak position and measure the BGS without the need for optical frequency shifters such as delay optical fibers and SSB (Single Side Band) modulators. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2013-195224 [Patent Document 2] Japanese Patent Publication No. 2013-195225 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The above-described BGS measurement device requires precise setting and sweeping of the frequency difference between two semiconductor lasers (with an accuracy of several MHz or less) in order to accurately measure the peak frequency of the background gas (BFS: Brillouin Frequency Shift). Generally, the frequency of semiconductor lasers is unstable because it fluctuates with the drive current and temperature. The above-described BGS measurement device is equipped with a configuration such as an optical multiplexer to constantly monitor the frequency difference between the two semiconductor lasers and corrects the semiconductor lasers during BGS measurement to achieve the desired frequency difference. As a result, the above-described BGS measurement device has a complex configuration for controlling the semiconductor lasers, which increases manufacturing costs.

[0006] Thus, conventional optical fiber characteristic measurement devices had room for improvement in terms of their complexity of configuration and manufacturing cost.

[0007] The purpose of this disclosure is to realize an optical fiber characteristic measurement device with a simpler configuration. [Means for solving the problem]

[0008] A measuring device according to several embodiments is: (1) A measuring device for measuring the characteristics of an optical fiber, A light source unit that emits frequency-modulated light, A first light generation unit that generates first light from the frequency-modulated light, An adjustment unit connected to the first light generation unit and the first end of the optical fiber, which is capable of adjusting the optical path length between the first light generation unit and the first end of the optical fiber, A second light generation unit that generates a second light with a different frequency from the first light from the frequency-modulated light, A photodetector converts scattered light, which is a third light generated by the first light generation unit being incident on the first end of the optical fiber via the adjustment unit, and the second light generation unit being incident on the second end of the optical fiber, into an electrical signal. A calculation unit that calculates the frequency shift of the third light, which has been converted into an electrical signal, relative to the second light, comprising The adjustment unit includes an optical switch that switches the presence or absence of connection of a delay optical path having an optical path length corresponding to the interval between correlation peaks, which is a position where the optical frequency difference between the first light and the second light is constant.

[0009] Thus, since the measuring device includes an optical switch that switches the presence or absence of connection of a delay optical path having an optical path length corresponding to the interval between correlation peaks, when a zero-order correlation peak exists near a desired measurement position, the zero-order correlation peak can be moved away by switching the optical switch. Therefore, the measuring device can measure characteristics at an arbitrary position of an optical fiber with a simple configuration.

[0010] In one embodiment, (2) In the measuring device of (1), The characteristics of the optical fiber may be measured by a Brillouin optical correlation domain method.

[0011] Therefore, the measuring device can measure the distributions of strain and temperature of the optical fiber.

[0012] In one embodiment, (3) In the measuring device of (2), The measuring device may further include a conversion unit that converts the frequency shift into strain or temperature.

[0013] Therefore, the measuring device can obtain measurement values of strain and temperature of the optical fiber from the frequency shift.

[0014] In one embodiment, (4) In any one of the measuring devices of (1) to (3), The adjustment unit may include an optical path having an optical path length four times the minimum value of the interval between the correlation peaks as the delay optical path.

[0015] ​​​

[0016] In one embodiment, (5) In any one of the measuring devices (1) to (4), a control unit for controlling the frequency of the light emitted from the light source may be further provided.

[0017] Thus, by controlling the frequency of the light, the measuring device can change the correlation peak position other than the zero order and measure the characteristics at a desired position of the optical fiber.

[0018] A control method for a measuring device according to some embodiments is (6) A control method for a measuring device for measuring the characteristics of an optical fiber, comprising a light source unit, a first light generation unit, an adjustment unit, a second light generation unit, a light detection unit, and a calculation unit, wherein the light source unit emits frequency-modulated light, the first light generation unit generates first light from the frequency-modulated light, the adjustment unit is connected to the first light generation unit and the first end of the optical fiber, and adjusts the optical path length between the first light generation unit and the first end of the optical fiber, the second light generation unit generates second light having a frequency different from that of the first light from the frequency-modulated light, the light detection unit converts the third light, which is scattered light generated by making the first light generated by the first light generation unit enter the first end of the optical fiber via the adjustment unit and making the second light generated by the second light generation unit enter the second end of the optical fiber, into an electrical signal, the calculation unit calculates the frequency shift of the third light converted into an electrical signal with respect to the second light, and includes the adjustment unit adjusts the optical path length by a optical switch that switches the presence or absence of connection of a delay optical path having an optical path length corresponding to the interval between correlation peaks, which is a position where the optical frequency difference between the first light and the second light is constant.

[0019] Thus, since the measuring device is equipped with an optical switch that switches the connection of a delay optical path having an optical path length corresponding to the interval of correlation peaks, if a zero-order correlation peak exists near the desired measurement position, the zero-order correlation peak can be moved away by switching the optical switch. Therefore, the measuring device can measure the characteristics at any position in the optical fiber with a simple configuration.

[0020] In one embodiment, (7)(6) In the control method of the measuring device, The characteristics of the optical fiber may be measured using the Brillouin optical correlation domain method.

[0021] Therefore, the strain and temperature distribution of the optical fiber can be measured.

[0022] In one embodiment, (8)(7) In the control method of the measuring device, The conversion unit may convert the frequency shift into distortion or temperature.

[0023] Therefore, from the frequency shift, measurements of optical fiber strain and temperature can be obtained.

[0024] In one embodiment, In any of the control methods for measuring devices described in (9)(6) to (8), The adjustment unit may include, as the delay optical path, an optical path having an optical path length four times the minimum value of the interval between the correlation peaks.

[0025] Thus, by providing an optical path with a path length four times the minimum value of the interval between correlation peaks as the delay optical path, miniaturization is possible.

[0026] In one embodiment, In a control method for any of the measuring devices described in (10)(6) to (9), The control unit may control the frequency of the light emitted from the light source.

[0027] In this way, by controlling the frequency of light, the position of correlation peaks other than the 0th order can be changed, and the characteristics of the optical fiber at a desired position can be measured. [Effects of the Invention]

[0028] According to one embodiment of this disclosure, an optical fiber characteristic measurement device can be realized with a simpler configuration. [Brief explanation of the drawing]

[0029] [Figure 1] This figure shows an example configuration of a measurement system according to one embodiment. [Figure 2] This is a diagram illustrating the measurement of the Brillouin gain spectrum. [Figure 3] This figure illustrates the probe light and the correlation peaks generated by the probe light. [Figure 4] This figure shows an example of the configuration of the peak adjustment unit in Figure 1. [Figure 5] This figure illustrates the correlation peak shift using a measuring device according to one embodiment. [Figure 6] This figure illustrates the correlation peak shift using a measuring device according to one embodiment. [Figure 7] This diagram shows the configuration of the peak adjustment unit in the comparative example. [Figure 8] This figure illustrates the correlation peak shift caused by the measuring device in the comparative example. [Modes for carrying out the invention]

[0030] <Embodiment> Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, parts having the same configuration or function are denoted by the same reference numerals. In the description of this embodiment, redundant descriptions of the same parts may be omitted or simplified as appropriate.

[0031] Figure 1 is a diagram showing an example of the configuration of a measurement system 1 according to one embodiment. The measurement system 1 is The system includes a measuring device 10 and an optical fiber 50.

[0032] The measuring device 10 is an optical fiber characteristic measuring device that uses an optical fiber 50 as a sensor to measure characteristics such as strain or temperature from changes in the physical quantities of the optical fiber 50. The measuring device 10 can also calculate the vibration of the optical fiber 50 from the temporal change in strain. By attaching or embedding the optical fiber 50 in a structure or the like and then measuring the changes in the physical quantities of the optical fiber 50, the measuring device 10 can determine the soundness (health condition) of the structure.

[0033] The measuring device 10 measures the characteristics of the optical fiber 50 using the Brillouin Optical Correlation Domain Analysis (BOCDA) method. The measuring device 10 measures the characteristics of the optical fiber 50 by injecting frequency-modulated probe light from one end of the optical fiber 50 while injecting frequency-modulated pump light from the other end. Here, at the correlation peak position, which is the position where the optical frequency difference between the probe light and the pump light is constant, the probe light gains due to stimulated Brillouin scattering.

[0034] Figure 2 illustrates the measurement of the Brillouin gain spectrum. The frequency difference between the pump light and the probe light is ν. B Sweep the frequency difference ν B When the level of the probe light relative to the optical fiber is measured as gain, a spectrum with the shape of a Lorentz function centered on the Brillouin frequency shift (BFS), a physical quantity of the optical fiber, is obtained. This spectrum is called the Brillouin gain spectrum (BGS).

[0035] BFS is known to depend on the material, strain, and temperature of the optical fiber 50, and in particular, to respond linearly to strain and temperature. Therefore, the measuring device 10 can detect the relative strain or temperature at the correlation peak position by measuring the BFS in the optical fiber 50. The measuring device 10 can measure the relative strain or temperature at the measurement position by moving the correlation peak to the desired position in the optical fiber 50 (optical fiber under test) and measuring the BFS. By repeating this process, the measuring device 10 can measure the strain distribution or temperature distribution along the longitudinal direction of the optical fiber 50 (optical fiber under test).

[0036] Although BFS depends on both strain and temperature, the measuring device 10 may use known quantities of strain and temperature to measure an unknown quantity based on the BFS value in order to separate these contributions. For example, when using an optical fiber 50 as a strain sensor, the measuring device 10 measures the BFS at the measurement position of the optical fiber 50 in a free, strain-free state. Next, the measuring device 10 measures the BFS at the same measurement position with the optical fiber 50 attached to the object to be measured. The measuring device 10 may measure the strain of the object by the difference between these BFS measurements.

[0037] As shown in Figure 1, the measuring device 10 comprises a light source unit 11, a pump light generation unit 12, a probe light generation unit 13, a light circulator 14, a peak adjustment unit 15, a light detection unit 16, a control unit 17, an amplifier 18, a BFS calculation unit 19, a setting unit 20, a measurement position list 21, a BFS distribution data generation unit 22, a conversion unit 23, a storage unit 24, a display unit 25, and a timing unit 26.

[0038] The light source unit 11 frequency modulates the laser light output from the semiconductor laser and emits it to the pump light generation unit 12 and the probe light generation unit 13. The light source unit 11 may include at least one of the following: a semiconductor laser, a temperature control circuit, a drive circuit, an optical pulse generation circuit, a frequency modulation circuit, a signal generator, a directional coupler (optical coupler), etc. This configuration is just one example, and the light source unit 11 may have any configuration capable of generating light.

[0039] The pump light generation unit 12, acting as a second light generation unit, amplifies the frequency-modulated light incident from the light source unit 11 and outputs pump light as the second light to the optical circulator 14. The pump light generation unit 12 may include at least one of the following: a polarization controller, an optical switch, an optical isolator, an optical amplifier, an optical frequency shifter, an optical attenuator, a signal generator, etc. The optical frequency shifter may be configured using an SSB modulator or the like. This configuration is just one example, and the pump light generation unit 12 may have any configuration capable of generating pump light. The pump light generation unit 12 is connected to the second end of the optical fiber 50 via the optical circulator 14.

[0040] The probe light generation unit 13, which acts as the first light generation unit, generates probe light as the first light from frequency-modulated light incident from the light source unit 11. The probe light generation unit 13 emits the generated probe light to the peak adjustment unit 15.

[0041] Probe light is light with a different frequency and amplitude from pump light. The probe light generation unit 13 generates probe light by shifting the frequency of the frequency-modulated light incident from the light source unit 11 and amplifying its amplitude. The probe light generation unit 13 can adjust the amount of shift when shifting the frequency of the frequency-modulated light incident from the light source unit 11.

[0042] The probe light generation unit 13 may include, for example, an optical frequency shifter and an optical amplifier. The optical frequency shifter shifts the frequency of the frequency-modulated light incident from the light source unit 11. The optical frequency shifter may be, for example, an SSB modulator. The optical amplifier amplifies the amplitude of the frequency-modulated light incident from the light source unit 11. The probe light generation unit 13 may further include at least one of the following: a polarization controller, an optical switch, an optical isolator, an optical attenuator, a signal generator, etc. Such a configuration is just an example, and the probe light generation unit 13 may have any configuration capable of generating probe light. The probe light is incident on the optical fiber 50 via the peak adjustment unit 15. The probe light generation unit 13 is connected to the first end of the optical fiber 50 via the peak adjustment unit 15.

[0043] The optical circulator 14 directs the pump light, which is incident from the pump light generation unit 12, into the optical fiber 50. As a result, the pump light is incident on one end of the optical fiber 50, and the probe light is incident on the other end of the optical fiber 50. This causes scattered light due to stimulated Brillouin scattering to be locally generated in the optical fiber 50.

[0044] The optical circulator 14 emits scattered light incident from the optical fiber 50 to the photodetector 16. The optical circulator 14 may also be equipped with a directional coupler (optical coupler).

[0045] The peak adjustment unit 15 adjusts the correlation peak position, which is the position where the optical frequency difference between the probe light and the pump light is constant, by delaying the probe light incident from the probe light generation unit 13. The peak adjustment unit 15 has any configuration to adjust the optical path length of the probe light. For example, the peak adjustment unit 15 may include a delay optical fiber and a phase adjuster. Alternatively, the peak adjustment unit 15 may include a spatial optical system.

[0046] The position of the correlation peak in the optical fiber 50 (optical fiber under test) can be moved by changing the modulation frequency applied to the semiconductor laser of the light source unit 11. However, as will be described later, the position of the zeroth-order correlation peak does not move even if the modulation frequency is changed. Therefore, the measuring device 10 is equipped with a peak adjustment unit 15 for adjusting the optical path length of the probe light so that there is no zeroth-order correlation peak in the measurement range of the optical fiber 50 (optical fiber under test).

[0047] The photodetector 16 converts the light incident from the light circulator 14 into an electrical signal. The photodetector 16 may include a photodiode for converting the incident light into an electrical signal. The photodiode may have any configuration, such as an avalanche photodiode, a PIN type photodiode, or a differential balanced photodiode incorporating two photodiodes with matched characteristics. The photodetector 16 may further include an optical attenuator, a trans-impedance amplifier circuit, etc. Such a configuration is just an example, and the photodetector 16 may have any configuration for converting the incident light into an electrical signal.

[0048] The control unit 17, based on commands from the setting unit 28, calculates each setting parameter so that the measuring device 10 can perform BFS distribution measurement according to the measurement conditions, and controls the light source unit 11, the pump light generation unit 12, the probe light generation unit 13, the photodetection unit 16, and the amplifier 18. The control unit 17 may also output drive signals to the pump light generation unit 12, the probe light generation unit 13, the photodetection unit 16, and the amplifier 18. The control unit 17 also performs processing to ensure that the measuring device 10 operates normally, such as starting and stopping the measurement. The relationship between the measurement position and the modulation frequency is calculated by the control unit 17.

[0049] The BFS calculation unit 19 analyzes the power spectrum of the Brillouin scattered light returning from each position of the optical fiber 50 and calculates the peak frequency (BFS). The BFS calculation unit 19 extracts the frequency of the Brillouin frequency shift at which the Brillouin gain peaks. Since the frequency of the Brillouin frequency shift at which the Brillouin gain peaks depends on the strain and temperature of the optical fiber 50, the BFS calculation unit 19 can measure the strain or temperature of the optical fiber 101 by extracting the frequency of the Brillouin frequency shift at which the Brillouin gain peaks. The BFS calculation unit 19 may also perform spectral analysis using a spectrum analyzer, oscilloscope, voltmeter, etc.

[0050] Furthermore, the location in the optical fiber 50 at which scattered light due to stimulated Brillouin scattering is generated depends on the modulation frequency of the frequency-modulated light emitted by the light source unit 11. Therefore, by sweeping and measuring the modulation frequency, the measuring device 10 can measure the strain or temperature distribution of the optical fiber 50.

[0051] The control unit 17 includes at least one processor, at least one dedicated circuit, or a combination thereof. The processor is a general-purpose processor such as a CPU (Central Processing Unit) or GPU (Graphics Processing Unit), or a dedicated processor specialized for a specific process. The dedicated circuit is, for example, an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0052] The amplifier 18 amplifies the scattered light, which has been converted into an electrical signal and supplied from the photodetector 16. The amplifier 18 outputs the amplified electrical signal of the scattered light to the BFS calculation unit 19. The amplifier 18 may be an electronic circuit including an operational amplifier, a resistor, a capacitor, etc. The amplifier 18 may further include a lock-in amplifier, a noise filter, etc. Such a configuration is just an example, and the amplifier 18 may be any configuration capable of amplifying an electrical signal based on scattered light.

[0053] The setting unit 20 accepts settings for various measurement conditions, such as spatial resolution, measurement distance range, measurement position step (distance sampling), measurement speed, and number of averaging cycles.

[0054] The measurement position list 21 stores a list of measurement positions set in the measurement condition setting unit in a memory or other storage device.

[0055] The BFS distribution data generation unit 22 associates the BFS calculated by the BFS calculation unit 19 with the corresponding measurement location.

[0056] The conversion unit 23 converts BFS into strain or temperature using a pre-set BFS-temperature dependence or BFS-strain dependence relationship. Through processing by the conversion unit 23, the measurement results of the BFS distribution can be expressed as a strain distribution or a temperature distribution.

[0057] The storage unit 24 stores various data such as Brillouin scattered light spectrum data for each measurement location, BFS, converted strain, converted temperature, measurement date and time, and measurement conditions. The storage unit 24 may be equipped with a storage device such as an HDD (Hard Disk Drive), SSD (Solid State Drive), or USB (Universal Serial Bus) memory.

[0058] The display unit 25 displays the measured strain distribution or temperature distribution measurement results on the measurement screen. The display unit 25 may be composed of, for example, a liquid crystal display and an organic EL display device.

[0059] The timing unit 26 measures the date and time of measurement. The timing unit 26 may be composed of any clock.

[0060] The optical fiber 50 is the optical fiber under test for measuring strain or temperature. The optical fiber 50 is composed of single-mode fiber, multimode fiber, multicore fiber, etc. The type of sheathing to protect the optical fiber 50 from damage may be appropriately selected depending on the environment in which the optical fiber 50 is laid.

[0061] Figure 3 illustrates the probe light and the correlation peaks generated by it. Figure 3 shows how the correlation peaks shift when the modulation frequency of the signal generator in the light source unit 11 is changed. Note that Figure 3 also shows an example of the correlation peak distribution when the optical path length is not adjusted by the peak adjustment unit 15. Changing the modulation frequency fm of the signal generator changes the interval dm of the correlation peaks, causing the correlation peaks to shift. In the example in Figure 3, changing the modulation frequency from fm0 to fm1 shows that the interval of the nth-order (n is an integer other than 0) correlation peaks changes from dm0 to dm1. However, the 0th-order correlation peak does not shift even when the modulation frequency is changed. When continuously measuring BFS along the optical fiber 50 (optical fiber under measurement) (distribution measurement), the displacement distance of the correlation peaks must be less than or equal to the spatial resolution of the measuring device 10. This is because if the displacement distance of the correlation peaks exceeds the spatial resolution, it becomes impossible to continuously measure the characteristics. Therefore, the minimum modulation frequency resolution that can be varied by the signal generator of the light source unit 11 must be an amount that can sufficiently reduce the displacement distance of the correlation peak with respect to the spatial resolution.

[0062] Next, the details of the procedure for calculating the measurement position performed by the control unit 17 will be explained. The interval dm of the correlation peaks is given by the speed of light c and the refractive index n of the optical fiber 50. ref It is known that, depending on the modulation frequency fm of the light source unit 11, it is given by the following equation. dm = c / (2 × fm × n) ref ) (Formula 1)

[0063] Therefore, for any correlation peak where the optical path difference between the pump light and the probe light is not zero (0th order correlation peak), from Equation (1), by adjusting the modulation frequency fm that modulates the light source unit 11, the correlation peak interval dm can be changed, and the correlation peak position can be moved (see FIG. 3).

[0064] The 0th order correlation peak where the optical path difference between the pump light and the probe light is zero exists at the midpoint of the series of optical paths from the probe light emission end, via the optical fiber 50, to the pump light emission end. That is, if the conditions shown in Equation (2) or Equation (3) are satisfied, there is no 0th order correlation peak in the optical fiber 50. L1 > L2 + L3 (Equation 2) L1 + L2 < L3 (Equation 3) Here, as shown in FIG. 3, L1 is the length (distance) of the optical fiber from the probe light emission end to the incident end (0 m position) of the probe light with respect to the optical fiber 50. L2 is the length (distance) of the optical fiber 50. L3 is the length (distance) of the optical fiber from the pump light emission end to the incident end of the pump light with respect to the optical fiber 50.

[0065] The length (distance) L from the probe light emission end to the 0th order correlation peak position Z is given by Equation (4). L z = (L1 + L2 + L3) / 2 (Equation 4)

[0066] Note that Equations (2) to (4) assume that the refractive index of the optical fiber from the probe light emission end to the incident end (0 m position) of the probe light with respect to the optical fiber 50, the refractive index of the optical fiber 50, and the refractive index of the optical fiber from the pump light emission end to the incident end of the pump light with respect to the optical fiber 50 are all n ref and are the same.

[0067] The measurement position can be expressed by Equation (5) using the correlation peak interval dm, the order n of the correlation peak (n is a natural number), and L1, L Z as follows. Measurement position = dm × n - (L1 - L2) (Equation 5)

[0068] From equations (1) and (5), the measurement position is represented by equation (6) using the frequency fm, the speed of light c, and the refractive index n of the optical fiber 50. ref It is expressed by equation (6). Measurement position = c × n / (2 × fm × n ref ) - (L1 - L2) (Equation 6)

[0069] Based on equation (6), the measuring device 10 can set an arbitrary measurement position from the modulation frequency and the correlation peak order and measure the BFS. For example, by setting the modulation frequency to fm0 and the order to n, the measuring device 10 can measure the BFS at position A in FIG. 3. Similarly, by setting the modulation frequency to fm1 and the order to n, the measuring device 10 can measure the BFS at position B. Furthermore, by setting the modulation frequency fm and the correlation peak order n according to the measurement position, the measuring device 10 can also measure the distribution of the BFS in the optical fiber 50. Positions A and B are represented by the following equations (7) and (8). Position A = c × n / (2 × fm0 × n ref ) - (L1 - L2) (Equation 7) Position B = c × n / (2 × fm1 × n ref ) - (L1 - L2) (Equation 8)

[0070] In this way, the measuring device 10 can move the correlation peak to a desired position in the optical fiber 50 (the measured optical fiber) and measure the BFS, thereby measuring the relative strain, temperature, or vibration at that measurement position. Also, by repeating such a process, the measuring device 10 can measure the strain distribution or the temperature distribution along the longitudinal direction of the optical fiber 5 (the measured optical fiber).

[0071] However, as shown in Figure 3, if there is a zero-order correlation peak indicated at position Z in the optical fiber 50 (optical fiber under test), the measuring device 10 cannot measure the strain or temperature near the zero-order correlation peak position (in the range of less than ±dm). There are two possible reasons why measurement becomes impossible not only at the zero-order correlation peak position (position Z) but also in the vicinity of it. The first reason is that as the modulation frequency increases, dm becomes shorter, so the range of less than ±dm can be narrowed, but there is an upper limit to the range in which the modulation frequency can be varied, so there is a lower limit to the dm that can be set. The second reason is that as dm becomes shorter, multiple correlation peak positions will exist within the optical fiber 50 (optical fiber under test), making it difficult to separate the measured values ​​at each correlation peak position.

[0072] Therefore, the measuring device 10 according to this embodiment moves the zero-order correlation peak position by adjusting the length L1 with the peak adjustment unit 15. As a result, even if the zero-order correlation peak position exists within the optical fiber 50, the measuring device 10 can measure the BFS at any position in the optical fiber 50 by moving the zero-order correlation peak position with the peak adjustment unit 15.

[0073] As the peak adjustment unit 15, it is also conceivable to use an optical fiber having a length greater than or equal to the length of the optical fiber 50 (optical fiber under measurement), as shown in the comparative example described later with reference to Figures 7 and 8. With such a configuration, the position of the zero-order correlation peak that was located within the optical fiber 50 can be moved to the probe light generation side within the measuring device 10. However, the optical fiber 50 may have a length of several hundred meters or more, or even several kilometers or more, and accordingly, the length of the optical fiber in the peak adjustment unit 15 must also be several hundred meters or more, or even several kilometers or more. Thus, the configuration in the comparative example becomes larger and the manufacturing cost increases as the length (distance range) of the optical fiber 50 increases.

[0074] Therefore, the measuring device 10 according to this embodiment includes a peak adjustment unit 15 that allows switching via an optical switch between connecting a delay optical path of a certain length (approximately several tens of meters or more) instead of an optical fiber longer than the length of the optical fiber 50. When a zero-order correlation peak position exists near a desired measurement position within the optical fiber 50, the measuring device 10 moves the zero-order correlation peak position away from the measurement position by switching the optical switch. As a result, the measuring device 10 makes it possible to measure the BFS at any position in the optical fiber 50 and measure strain, temperature, or vibration with a configuration that is small in size and has low manufacturing costs.

[0075] Figure 4 shows an example configuration of the peak adjustment unit 15 in Figure 1. The peak adjustment unit 15 comprises two optical switches 151 (151a, 151b), an optical path 152, and a delay optical path 153.

[0076] The optical switches 151 (151a, 151b) switch the optical path connected between the probe light generation unit 13 and the optical fiber 50 between optical path 152 and delay optical path 153. In the example in Figure 4, the optical switches 151 (151a, 151b) are 1x2 switches, but any NxM switches such as 2x2 switches may also be used.

[0077] The optical path 152 has the shortest possible optical path length to guide the light incident from the probe light generation unit 13 to the optical fiber 50. The optical path 152 may be an optical fiber including a single-mode fiber such as a polarization-maintaining fiber.

[0078] The delay optical path 153 has the minimum optical path length required to enable BFS measurement at a desired position within the optical fiber 50. When the length L1 increases by d, the length (distance) L from the probe light emission end to the zero-order correlation peak position increases according to (Equation 4). Z It moves by d / 2. Therefore, the optical path length of the delay optical path 153 is, for example, the minimum value dm of the correlation peak interval dm. MIN Based on, 4 × dm MIN This may be considered as above. Here, dm MINThis is determined by (Equation 1) based on the range of possible values ​​for the modulation frequency fm of the light source unit 11. Therefore, the optical path length of the delay optical path 153 is determined by whether the modulation frequency fm that moves the correlation peak takes a value around 10 MHz, around 20 MHz, or around 5 MHz. For example, the optical path length of the delay optical path 153 is 4 × dm MIN Therefore, it would be around several tens of meters.

[0079] The delay optical path 153 can be implemented by any configuration having a constant optical path length. For example, the delay optical path 153 may be an optical fiber including a single-mode fiber such as a polarization-maintaining fiber. The delay optical path 153 may also be empty space. The delay optical path 153 may be made of a material with a higher refractive index than an optical fiber.

[0080] When measuring BFS along the entire length of the optical fiber 50, the measuring device 10 switches the optical switch 151 (151a, 151b) of the peak adjustment unit 15 once during each measurement, at the timing when measuring the range near the zeroth order that cannot be measured. Therefore, it is sufficient for the optical switch 151 (151a, 151b) to have a switching speed on the order of milliseconds.

[0081] Figures 5 and 6 illustrate the correlation peak shift in a measuring device 10 according to one embodiment. In the example of Figures 5 and 6, regardless of which state the optical switch 151 of the peak adjustment unit 15 is switched to, the optical path length in the peak adjustment unit 15 is shorter than the optical fiber 50, and the zero-order correlation peak position is located within the optical fiber 50.

[0082] Figure 5 shows the state in which the optical switches 151 (151a, 151b) of the peak adjustment unit 15 are not connected to the delay optical path 153 between the optical fiber 50 and the probe light generation unit 13. In Figure 5, in the AB section of the optical fiber 50, the zero-order correlation peak does not move even when the modulation frequency is changed. As a result, in the state shown in Figure 5, the measuring device 10 cannot measure the strain and temperature in the AB section. Therefore, when measuring the AB section, the measuring device 10 switches the optical switches 151 (151a, 151b) to connect to the delay optical path 153.

[0083] Figure 6 shows the state in which the optical switches 151 (151a, 151b) of the peak adjustment unit 15 connect the delay optical path 153 between the optical fiber 50 and the probe light generation unit 13. In the example in Figure 6, the optical path length of the delay optical path 153 is 4 × dm MIN That concludes the explanation. In Figure 6, when the modulation frequency of the light source 11 is fm0, the primary correlation peak is located at position A. The measuring device 10 can measure strain or temperature in the AB section by changing the modulation frequency fm and shifting the primary or secondary correlation peak.

[0084] Thus, according to the measuring device 10 of this embodiment, it is possible to measure strain or temperature at any position in the optical fiber 50, regardless of the length of the optical fiber 50, due to its compact size and low manufacturing cost.

[0085] (Comparative example) Figure 7 shows the configuration of the peak adjustment unit 15z in a comparative example. The peak adjustment unit 15z includes a delay optical fiber 159z having a length equal to or greater than the length of the optical fiber 50z.

[0086] Figure 8 illustrates the correlation peak shift in the measuring device 10z according to the comparative example. As shown in Figure 8, in the configuration of the comparative example, since the delay optical fiber 159z has a length greater than or equal to the length of the optical fiber 50z, the zero-order correlation peak is located outside the optical fiber 50. As a result, the measuring device 10z according to the comparative example can measure strain or temperature at any position in the optical fiber 50.

[0087] However, the measuring device 10z in the comparative example has a delay optical fiber 159z as the peak adjustment unit 15z, which has a length greater than or equal to the length of the optical fiber 50z, making it large and costly to manufacture. In contrast, the delay optical path 153 in the peak adjustment unit 15 of the measuring device 10 according to this embodiment only needs to be of a length corresponding to the correlation peak interval dm. Therefore, the measuring device 10 according to this embodiment can be manufactured in a small size and at low cost.

[0088] This disclosure is not limited to the embodiments described above. For example, multiple blocks shown in the block diagram may be merged, or a single block may be divided. Other modifications are possible without departing from the spirit of this disclosure. [Explanation of Symbols]

[0089] 1: Measurement System 10: Measuring device 10z: Measuring device (comparative example) 11: Light source part 12: Pump light generation unit 13: Probe light generation unit 14: Light Circulator 15: Peak adjustment section 15z: Peak adjustment section (comparative example) 151a, 151b: Optical switch 152: Light path 153: Delay optical path 159z: Optical fiber for delay (comparative example) 16: Light detection unit 17: Control Unit 18: Amplifier 19: BFS Calculation Unit 20: Settings Section 21: List of measurement locations 22: BFS Distribution Data Generation Unit 23: Conversion section 24: Preservation Department 25: Display section 26: Timekeeping section 50: Fiber optic 50z: Optical fiber (comparative example)

Claims

1. A measuring device for measuring the characteristics of optical fibers, A light source unit that emits frequency-modulated light, A first light generation unit that generates first light from the frequency-modulated light, An adjustment unit connected to the first light generation unit and the first end of the optical fiber, which is capable of adjusting the optical path length between the first light generation unit and the first end of the optical fiber, A second light generation unit that generates a second light with a different frequency from the first light from the frequency-modulated light, A photodetector converts scattered light, which is a third light generated by the first light generation unit being incident on the first end of the optical fiber via the adjustment unit, and the second light generation unit being incident on the second end of the optical fiber, into an electrical signal. A calculation unit that calculates the frequency shift of the third light, which has been converted into an electrical signal, relative to the second light, Equipped with, The adjustment unit includes an optical switch that switches whether or not to connect a delay optical path having an optical path length corresponding to the interval of correlation peaks, which is the position where the optical frequency difference between the first light and the second light is constant. Measuring device.

2. The measuring apparatus according to claim 1, which measures the characteristics of the optical fiber using the Brillouin optical correlation domain method.

3. The measuring device according to claim 2, further comprising a conversion unit that converts the frequency shift into distortion or temperature.

4. The measuring device according to any one of claims 1 to 3, wherein the adjustment unit includes an optical path having an optical path length four times the minimum value of the interval between correlation peaks as the delay optical path.

5. The measuring device according to any one of claims 1 to 3, further comprising a control unit for controlling the frequency of the light emitted from the light source.

6. A control method for a measuring device for measuring the characteristics of an optical fiber, comprising a light source unit, a first light generation unit, an adjustment unit, a second light generation unit, a light detection unit, and a calculation unit, The light source emits frequency-modulated light, The first light generation unit generates first light from the frequency-modulated light, The adjustment unit is connected to the first light generation unit and the first end of the optical fiber, and adjusts the optical path length between the first light generation unit and the first end of the optical fiber. The second light generation unit generates a second light having a different frequency from the first light from the frequency-modulated light, The light detection unit converts the scattered light, which is the third light generated by the first light generation unit being incident on the first end of the optical fiber via the adjustment unit, and the second light generation unit being incident on the second end of the optical fiber, into an electrical signal. The calculation unit calculates the frequency shift of the third light, which has been converted into an electrical signal, relative to the second light, Includes, The adjustment unit adjusts the optical path length by using an optical switch to switch between connecting or not connecting a delay optical path having an optical path length corresponding to the interval of correlation peaks, which is the position where the optical frequency difference between the first light and the second light is constant. A method for controlling a measuring device.

7. A control method for a measuring apparatus according to claim 6, wherein the characteristics of the optical fiber are measured using the Brillouin optical correlation domain method.

8. A control method for a measuring device according to claim 7, wherein the conversion unit converts the frequency shift into distortion or temperature.

9. The control method for a measuring device according to any one of claims 6 to 8, wherein the adjustment unit includes an optical path having an optical path length four times the minimum value of the interval between correlation peaks as the delay optical path.

10. A control method for a measuring device according to any one of claims 6 to 8, wherein the control unit controls the frequency of the light emitted from the light source.

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