Optical sensing system

Abstract

A control terminal 40 according to the present disclosure is connected to: an optical sensing device 20 that inputs light to a plurality of optical fibers 50 and measures scattered light from the plurality of optical fibers 50; and an external optical switch 30 configured to select an optical fiber 50 to which light is input from among the plurality of optical fibers 50. The control terminal 40 outputs a switching instruction to the external optical switch 30 to select one or more optical fibers from among the plurality of optical fibers 50, and acquires data relating to the scattered light measured by the optical sensing device 20.

Description

Optical sensing system

[0001] This disclosure relates to an optical sensing system equipped with an external optical switch.

[0002] Conventionally, optical sensing has been known in which test light such as optical pulses or CW (continuous wave) is incident on an optical fiber, and the backscattered light from the optical fiber is received to measure the state of the optical fiber in a distributed manner.

[0003] In particular, there are plans to consider using the communication fiber optic network spread throughout cities as a sensor for measurement. In this case, there are plans to use an optical switch that switches between multiple optical fibers so that the test light is input to the target optical fiber.

[0004] For example, Non-Patent Document 1 discloses a system comprising an optical testing module (OTM), an external optical switch (FS), and a control terminal installed in a building. In Non-Patent Document 1, the optical testing module is controlled from the control terminal via a VPN (Virtual Private Network), and the optical switch is switched according to switching instructions from the optical testing module.

[0005] However, in the technology described in Non-Patent Document 1, an interface (IF) for communication with the external optical switch must be provided within the signal processing unit of the sensing device in order to switch the sensing network using an external optical switch. As a result, the expandability is reduced depending on the type and number of external optical switches.

[0006] NTT Access Service Systems Laboratories, Optical Line Testing System Using Fiber Selector for Small Buildings, [online], [Retrieved September 20, 2024], Internet, <URL: https: / / www.rd.ntt / as / times / 058 / 01 / 03.html>

[0007] To solve the aforementioned problems, this disclosure aims to provide an optical sensing system with excellent scalability.

[0008] To achieve the above objectives, the control terminal, optical sensing system, and optical sensing method disclosed herein employ a method in which a control terminal connected to an external optical switch outputs a switching instruction to the external optical switch to select one or more optical fibers from a plurality of optical fibers.

[0009] Specifically, the control terminal of this disclosure is connected to an optical sensing device that incident light into a plurality of optical fibers and measures the scattered light from the plurality of optical fibers, and is connected to an external optical switch configured to select the optical fiber into which the light is incident among the plurality of optical fibers. The control terminal outputs a switching instruction to the external optical switch to select one or more optical fibers from the plurality of optical fibers, and acquires data relating to the scattered light measured by the optical sensing device.

[0010] Furthermore, the scattered light data is digital data, and information regarding the switching of connection ports between the multiple optical fibers may be obtained from the external optical switch, and the information regarding the switching of connection ports may be added to the digital data and stored.

[0011] More specifically, the optical sensing system of this disclosure comprises the control terminal described above, an optical sensing device that incidents light onto a plurality of optical fibers and measures the scattered light from the plurality of optical fibers, and an external optical switch that receives a switching instruction from the control terminal and switches the connection ports between the plurality of optical fibers.

[0012] More specifically, the optical sensing method of the present disclosure is an optical sensing method performed by a control terminal connected to an external optical switch which is connected to an optical sensing device that incidents light into a plurality of optical fibers and measures scattered light from the plurality of optical fibers, and is configured to select an optical fiber into which the light is incident among the plurality of optical fibers, wherein the control terminal outputs a switching instruction to the external optical switch to select one or more optical fibers from the plurality of optical fibers, and acquires data relating to the scattered light measured by the optical sensing device.

[0013] The device described herein can also be implemented using a computer and a program, and the program can be recorded on a recording medium or provided over a network. The program described herein is a program that causes a computer to implement each function of the device described herein, and a program that causes a computer to execute each procedure of the method performed by the device described herein.

[0014] Furthermore, the above disclosures can be combined as much as possible.

[0015] This disclosure provides an optical sensing system with excellent scalability.

[0016] This is a block diagram illustrating the outline of the optical sensing system according to the first embodiment. This is a flowchart illustrating the processing of the control terminal. This is a block diagram illustrating the configuration of the optical sensing device. This is a block diagram illustrating the configuration of the calculation unit. This is a flowchart illustrating the phase measurement method. This is a diagram illustrating the uncertainty of the position pointed to by the vector due to noise. This is a diagram illustrating the difference in the vector with and without noise. This is a diagram illustrating the principle of the phase measurement method. This is a diagram illustrating the principle of the phase measurement method. This is a diagram illustrating the effect of the phase measurement method. This is a block diagram illustrating the configuration of the calculation unit. This is a flowchart illustrating the phase measurement method. This is a block diagram illustrating the configuration of the optical sensing device according to the second embodiment. This is a diagram illustrating an example of an optical pulse. This is a flowchart illustrating the details of the processing of block K in the calculation unit. This is a block diagram illustrating a related optical sensing system.

[0017] Embodiments of this disclosure will be described in detail below with reference to the drawings. However, this disclosure is not limited to the embodiments shown below. These examples are illustrative, and this disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In this specification and in the drawings, components with the same reference numerals refer to the same components.

[0018] (First Embodiment) The configuration of the optical sensing system 100 according to the first embodiment of the present disclosure will be described with reference to Figure 1. As shown in Figure 1, the optical sensing system 100 comprises an optical sensing device 20, an external optical switch 30, and a control terminal 40. The optical sensing system 100 performs switching control for the external optical switch 30 and file processing linked thereto using software processing on the control terminal 40 side.

[0019] The optical sensing device 20 is a device that measures and analyzes Rayleigh reflected light obtained from multiple optical fibers 50. The optical sensing device 20 comprises an optical transmitter 21, an optical receiver 22, a signal processing unit 23, and an optical switch 24. Specifically, the optical sensing device 20 incidents light onto multiple optical fibers 50 and measures the scattered light from the multiple optical fibers 50.

[0020] The optical transmitter 21 is equipped with a light source and is configured to emit light of a predetermined frequency into a plurality of optical fibers 50. The output light from the optical transmitter 21 is selectively distributed among the plurality of optical fibers by an optical switch 24 built into the optical sensing device 20. Note that the optical switch 24 is optional and not required. The optical receiver 22 is configured to receive scattered light reflected by the plurality of optical fibers 50.

[0021] The signal processing unit 23 performs A / D (analog-to-digital) conversion on the scattered light received by the optical receiver 22 and transfers the processed digital data to the control terminal 40 as temporally continuous digital data.

[0022] The external optical switch 30 has the function of selectively distributing the output light from the optical sensing device 20 among multiple optical fibers 50. Specifically, the external optical switch 30 switches the connection ports between the multiple optical fibers 50 in response to a switching instruction from the control terminal 40. If the optical sensing device 20 has a built-in optical switch 24, multiple external optical switches 30 are connected, with the number of external optical switches 30 being the maximum number of output ports of the optical switch 24.

[0023] The control terminal 40 has the function of controlling the optical sensing device 20 and the external optical switch 30. The control terminal 40 includes an optical switch switching setting unit 41, a file processing unit 42, a storage unit 43, and a visualization unit 44.

[0024] Specifically, the control terminal 40 is connected to an external optical switch 30 which is connected to an optical sensing device 20 that injects light into multiple optical fibers 50 and measures the scattered light from the multiple optical fibers 50, and is configured to select the optical fiber 50 into which light is injected among the multiple optical fibers 50. The control terminal 40 outputs a switching instruction to the external optical switch 30 to select one or more optical fibers from the multiple optical fibers 50, and acquires data on the scattered light measured by the optical sensing device 20.

[0025] The optical switch switching setting unit 41 sends a port switching instruction directly to the external optical switch 30 so that the measurement is performed on the target optical fiber 50. The optical switch switching setting unit 41 also notifies the signal processing unit 23 of the measurement conditions. If the optical sensing device 20 is equipped with an optical switch 24, the measurement conditions may include a port switching instruction for the optical switch 24. The port switching instruction is performed based on an arbitrary optical switch switching setting. The optical switch switching setting may be set in advance by the user, or the setting may be updated in real time according to the situation.

[0026] The file processing unit 42 processes the digital data transmitted from the signal processing unit 23 of the optical sensing device 20 for a specified time period according to the optical switch switching setting, and then converts it into binary data. The storage unit 43 stores the binary data. The visualization unit 44 visualizes the optical sensing results based on the data stored in the storage unit 43.

[0027] Specifically, the file processing unit 42 of the control terminal 40 acquires information regarding the switching of connection ports between multiple optical fibers 50 from the external optical switch 30, and adds information regarding the switching of said connection ports to the digital data.

[0028] (Operation of the Optical Sensing System) The optical sensing system 100 in this embodiment operates as follows. The optical sensing device 20 does not retain any port information indicating which optical fiber was measured, and simply receives light and continuously transfers the processed digital data to the control terminal 40 over time. For example, assuming distributed vibration sensing as an optical sensing system using Rayleigh reflected light, optical pulses are continuously incident on the optical fiber from the optical transmitter 21 at regular intervals corresponding to the optical fiber length, and the amplitude and phase of each Rayleigh reflected light are calculated by the signal processing unit 23.

[0029] Meanwhile, the control terminal 40 processes according to the flowchart shown in Figure 2. The optical switch switching setting unit 41 of the control terminal 40 performs optical switch switching settings (step S01). Based on the optical switch switching settings, the optical switch switching setting unit 41 issues port switching instructions to both the optical sensing device 20 and the external optical switch 30 (step S02). At this time, the control terminal 40 receives information such as the port switching time and the destination port as a response.

[0030] Upon receiving the port switching instruction, the optical switch 24 and the external optical switch 30 perform the port switching. During this time, the signal processing unit 23 simply analyzes and transmits the continuously received signals without adding any port information to the data.

[0031] Meanwhile, the control terminal 40 receives digital data while temporarily buffering it based on the information received after issuing a port switching instruction, and extracts the digital data at arbitrary start and end times, converting it into binary data (step S03). At this time, by adding port information as a header, all saving and visualization of measurement results for each optical fiber is performed within the control terminal 40 (step S04).

[0032] (Comparison with related technologies) Next, the effects of the optical sensing system 100 will be explained in comparison with the related optical sensing system 100A shown in Figure 16. The related optical sensing system 100A comprises an optical sensing device 20A, an external optical switch 30A, and a control terminal 40A. The optical sensing device 20A comprises an optical transmitter 21A, an optical receiver 22A, a signal processing unit 23A, and an optical switch 24A. The control terminal 40A comprises an optical switch switching setting unit 41A, a storage unit 43A, and a visualization unit 44A. The optical switch 24A and the external optical switch 30A have the function of selectively distributing output light among multiple optical fibers 50A.

[0033] In the related optical sensing system 100A, a file processing unit 29A is provided in the signal processing unit 23A. Furthermore, in the related optical sensing system 100A, port switching instructions are given to the external optical switch 30A via the signal processing unit 23A.

[0034] The file processing unit 29A processes files and assigns port information according to the port switching times of the optical switch 24A and the external optical switch 30A. The processed data is then transferred to the control terminal 40 as binary data containing the port information.

[0035] In the related optical sensing system 100A, when expanding the sensing network with an external optical switch 30A, it is necessary to add a linkage interface (IF) to the signal processing unit 23A (mostly a hardware processing unit) within the optical sensing device 20A itself. Therefore, the expandability decreases depending on the type and number of external optical switches 30A.

[0036] In contrast, in this embodiment, switching control for the external optical switch 30 and file processing linked thereto are performed by software processing on the control terminal 40 side. Therefore, high expandability can be obtained when expanding the sensing network using various types and numbers of external optical switches 30 without modifying the optical sensing device 20.

[0037] (More detailed configuration and processing of the optical sensing device 20) Next, the more detailed configuration and processing of the optical sensing device 20 will be described with reference to Figures 3 to 12.

[0038] Figure 3 illustrates an optical sensing device 20 that performs vibration detection using DAS-P (Distributed Accusative Sensing-phase) according to this embodiment. This optical sensing device 20 uses a 90-degree optical hybrid in its receiving system to perform coherent detection and is equipped with a signal processing unit 23. For this reason, in the following description, the optical receiver 22 will be referred to as the 90-degree optical hybrid 22.

[0039] In DAS-P measurements, pulsed light is incident on the optical fiber under test, and the phase of the scattered light at time t when the pulsed light was incident is measured distributedly along the longitudinal direction of the optical fiber. That is, the phase θ(l,t) of the scattered light is measured with distance l from the incident end of the optical fiber. By repeatedly incidenting the optical fiber under test with pulsed light at time intervals T, the time change θ(l,nT) of the phase of the scattered light at time t = nT is measured for each point along the longitudinal direction of the optical fiber, where n is an integer. It is known that the magnitude of physical vibrations applied in the interval from distance l to distance l + δl at each time nT is proportional to the difference δθ(l,nT) between the phase θ(l + δl,nT) at distance l + δl and the phase θ(l,nT) at distance l. That is, with time zero as the reference, the following equation is satisfied.

[0040] Device configurations for detecting the phase of scattered light include direct detection, where the backscattered light from the optical fiber under test is directly detected using a photodiode or similar device, and coherent detection, where the phase is detected by combining it with a separately prepared reference light.

[0041] The mechanism for coherent detection and phase calculation can be further subdivided into two types: a software-based mechanism using Hilbert transforms and a hardware-based mechanism using a 90-degree optical hybrid. In both methods, the in-phase component I(l, nT) and the orthogonal component Q(l, nT) of the scattered light are obtained, and the phase is calculated using the following formula. However, the output value of the four-quadrant inverse tangent operator Arctan is in radians and is in the range (-π, π), and for any integer m, 2mπ + θ(l, nT) all have the same vector direction on the xy-plane, so the uncertainty is only 2mπ, which is the uncertainty of θ calculated above. ｃａｌ It exists in (l, nT).

[0042] Therefore, as a more accurate method for evaluating θ(l, nT), further signal processing such as phase unwrapping is performed. In general phase unwrapping, the phase after unwrapping is If so, let p be any integer, When it becomes greater than π radians, Select an appropriate integer q such that the result is less than or equal to π radians, and then the phase after unwrapping is Then, calculate the following equation. The calculation is performed as follows. Note that the superscript unwrap indicates the phase after unwrapping.

[0043] Based on the above overview of vibration detection in DAS-P, the configuration and processing of the optical sensing device 20 will be explained. The optical sensing device 20 measures scattered light from the optical fiber 50 to be measured as follows: From the light source 11, the frequency is f ０ A continuous beam of single wavelength light is emitted and split into a reference beam and a probe beam by the coupler 25. The probe beam is shaped into wavelength-multiplexed optical pulses, such as the optical pulse 60, by the optical modulator 26. The optical pulse 60 has a frequency of f ０ +f ｉ The configuration consists of a sequence of minute pulses 60a (where i is an integer) with a pulse width set to a value W corresponding to the spatial resolution of the measurement in the longitudinal direction of the optical fiber, i = 1, 2, ..., N (where N is an integer). ｉ The selection is made such that the intensity of scattered light at each time point and each location is sufficiently far apart that different values ​​of i can be considered uncorrelated.

[0044] There is no specific requirement for the type of optical modulator 26, as long as it can generate optical pulses 60, and there may be multiple modulators. For example, an SSB modulator or a frequency-variable AO modulator may be used, or intensity modulation using SOA or the like may be performed to increase the extinction ratio in pulse generation.

[0045] The optical pulse 60 is incident on the measured optical fiber 50 via the circulator 27. The light scattered at each point in the longitudinal direction of the optical fiber 50 returns to the circulator 27 as backscattered light and is incident on one input portion of the 90-degree optical hybrid 22. The reference light branched by the coupler 25 is incident on the other input portion of the 90-degree optical hybrid 22.

[0046] The internal configuration of the 90-degree optical hybrid 22 may be anything as long as it has the function of the 90-degree optical hybrid. A configuration example is shown in FIG. 3. The backscattered light is incident on a coupler 51 with a 50:50 splitting ratio, and the scattered light thus branched is incident on the input portions of a coupler 55 with a 50:50 splitting ratio and a coupler 54 with a 50:50 splitting ratio. The reference light is incident on a coupler 52 with a 50:50 splitting ratio. One of the branched reference lights is incident on the input portion of the coupler 54, and the other is phase-shifted by π / 2 by the phase shifter 53 and then incident on the input portion of the coupler 55.

[0047] The two outputs of the coupler 54 are detected by the balance detector 56, and an electrical signal 58 which is an analog in-phase component I ａｎａｌｏｇ is output. The two outputs of the coupler 55 are detected by the balance detector 57, and an electrical signal 59 which is an analog quadrature component Q ａｎａｌｏｇ is output.

[0048] The electrical signal 58 and the electrical signal 59 are sent to a signal processing unit 23 having an AD conversion functional element 23a and an AD conversion functional element 23b capable of sampling the frequency band of the signals without aliasing. In the signal processing unit 23, for the digitized in-phase component I ｄｉｇｉｔａｌ and quadrature component Q ｄｉｇｉｔａｌ signals output from the AD conversion functional element 23a and the AD conversion functional element 23b, signals due to the scattered light by the pulses of each frequency f ０ + f ｉ (i = 1, 2,..., N) constituting the optical pulse 60 are separated by the optical frequency separation unit 23c.

[0049] That is, the optical frequency separation unit 23c separates, for each frequency f ０ + f ｉCommon-phase component I obtained when a pulse of the component is injected alone ｉ ｍｅａｓｕｒｅ and orthogonal component Q ｉ ｍｅａｓｕｒｅ This is a superposition of in-phase components with respect to all i. ｄｉｇｉｔａｌ Q is a superposition of orthogonal components with respect to all i. ｄｉｇｉｔａｌ The signals are separated by performing signal processing. The specific signal processing method is as follows: ｄｉｇｉｔａｌ and Q ｄｉｇｉｔａｌ From, I ｉ ｍｅａｓｕｒｅ and Q ｉ ｍｅａｓｕｒｅ Any method is acceptable as long as it can accurately separate them. For example, I ｄｉｇｉｔａｌ and Q ｄｉｇｉｔａｌ The center frequency is f ０ +f ｉ And by passing each through a digital bandpass filter with a passband of 2 / W and then guaranteeing the phase delay, I ｉ ｍｅａｓｕｒｅ and Q ｉ ｍｅａｓｕｒｅ Methods for calculating this could be considered.

[0050] Furthermore, in the above method, the common-mode and quadrature components in the analog electrical signal state are converted to digital format using AD conversion and then separated into their respective frequency components. However, it is also possible to separate the common-mode and quadrature components in the analog electrical signal state into their respective frequency components using an analog electrical filter before performing AD conversion.

[0051] I obtained by the optical frequency separation unit 23c ｉ ｍｅａｓｕｒｅ and Q ｉ ｍｅａｓｕｒｅBased on this, the rotation angle calculation unit 23d performs a phase calculation. Figure 4 is a diagram illustrating the structure of the rotation angle calculation unit 23d. The rotation angle calculation unit 23d includes: an input unit 61 to which the in-phase and orthogonal components of scattered light generated by wavelength-multiplexed optical pulses 60 incident on the optical fiber 50 under test, measured by the optical sensing device 20, are input; a vector acquisition circuit 62 that acquires a two-dimensional vector composed of the in-phase and orthogonal components of the scattered light input to the input unit 61 at an arbitrary time and an arbitrary position of the optical fiber 50 under test, for each wavelength multiplexed in the optical pulse 60; a vector rotation circuit 63 that rotates the two-dimensional vectors for each wavelength at a reference time by a reference rotation amount for each wavelength so that each of the two-dimensional vectors acquired by the vector acquisition circuit 62 points in the reference direction, and rotates the two-dimensional vectors for each wavelength at a time different from the reference time, acquired by the vector acquisition circuit 62, by the reference rotation amount for each wavelength. The system includes a calculation circuit 64 which calculates a composite reference vector by averaging the two-dimensional vectors of each wavelength at the reference time when the vector rotation circuit 63 has rotated, calculates a composite vector by averaging the two-dimensional vectors of each wavelength at other times when the vector rotation circuit 63 has rotated, and calculates the amount of phase change of the scattered light from the angle between the composite reference vector and the composite vector.

[0052] Figure 5 is a diagram illustrating the phase measurement method performed by this vibration detection device. The phase measurement method comprises: a measurement procedure S11 for measuring the in-phase and orthogonal components of scattered light generated by wavelength-multiplexed optical pulses 60 incident on the optical fiber 50 under test; a vector acquisition procedure S12 for acquiring a two-dimensional vector composed of the in-phase and orthogonal components of the scattered light measured in measurement procedure S11 at an arbitrary time and an arbitrary position on the optical fiber 50 under test, for each wavelength multiplexed in the optical pulse 60; a vector rotation procedure S13 for rotating the two-dimensional vectors for each wavelength at a reference time by a reference rotation amount for each wavelength so that each of the two-dimensional vectors obtained in vector acquisition procedure S12 points in a reference direction, and rotating the two-dimensional vectors for each wavelength at other times different from the reference time obtained in vector acquisition procedure S12 by the reference rotation amount for each wavelength; The following calculation procedure S14 is performed: calculate a composite reference vector by averaging the two-dimensional vectors of each wavelength at the reference time that were rotated in the vector rotation procedure S13; calculate a composite vector by averaging the two-dimensional vectors of each wavelength at other times that were rotated in the vector rotation procedure S13; and calculate the amount of phase change of the scattered light from the angle between the composite reference vector and the composite vector.

[0053] First, the common-mode component I of a single frequency. ｉ ｍｅａｓｕｒｅ and orthogonal component Q ｉ ｍｅａｓｕｒｅ This section explains how to calculate the phase using [a specific method] and the effect of fading during phase calculation. It also describes the common-mode component I in the absence of noise. ｉ The measured value with noise added to (l, nT) is I ｉ ｍｅａｓｕｒｅ (l, nT) and the orthogonal component Q when there is no noise. ｉ Q is the measured value when noise is added to (l, nT). ｉ ｍｅａｓｕｒｅ (l, nT). In other words, the noise superimposed on the common-mode component and the orthogonal component is N Ｉ and N Ｑ Therefore, they can be expressed by the following equations.

[0054] The phase is determined by the signal processing unit 23 from the measured in-phase and orthogonal components. This is calculated as follows: Noise N Ｉ and N Ｑ Because such a vector exists, the vector (x, y) = (I) is found in the xy-plane where the in-phase component is the x-axis and the orthogonal component is the y-axis. ｉ ｍｅａｓｕｒｅ (l, nT), Q ｉ ｍｅａｓｕｒｅ An uncertainty arises in the position pointed to by (l, nT), and an uncertainty also arises in the phase, which is the direction pointed to by the vector. For example, in the absence of noise, the calculated phase value θ is obtained when no vibration is applied to the optical fiber. ｉ ｃａｌ (l, nT) remains constant over time for each l. However, in the presence of noise, even when no vibration is applied to the optical fiber, the calculated phase value θ ｉ ｃａｌ (l, nT) changes over time with respect to each l.

[0055] Figure 6 illustrates this situation. At a certain position l ０ Vector at (I ｉ ｍｅａｓｕｒｅ (l ０ ,nt), Q ｉ ｍｅａｓｕｒｅ (l ０ When plotting (x, y) on the xy plane, in the absence of noise, the vector 201 shows (x, y) = (I ｉ (l, nT), Q ｉ (l, nT) is always constant, and its angle 202 does not change over time. However, in reality, noise is present, so the vector composed of the in-phase and orthogonal components at each time is different from vector 201, as shown in vector 203, and its angle 204 is also different from angle 202. Therefore, the vector composed of actual measured values ​​varies around vector 201. The degree of variation can be evaluated using the standard deviation of the measured values ​​in each axis direction. For example, in the x-axis direction, the noise N represented by 205 can be evaluated from the variation of the x-component of the measured values. Ｉ The standard deviation σ(N) Ｉ There is only uncertainty.

[0056] In coherent detection, shot noise becomes dominant in order to sufficiently increase the intensity of the reference light, and the noise distribution can be approximated by a normal distribution. Also, since the light intensity incident on the two balance detectors 56 and 57 in Figure 1 can be considered to be about the same, the noise N Ｉ and N Ｑ The standard deviation of can also be considered to be of the same magnitude, and the uncertainty forms a circle centered on vector 201.

[0057] Even in device configurations where noise other than the shot noise of the reference light, such as thermal noise of the PD, cannot be ignored, for example, when direct detection is performed instead of coherent detection, the noise characteristics of the two balanced detectors 56 and 57 can be considered to be the same, so the uncertainty can be considered to be a circle centered on vector 201.

[0058] However, in device configurations that perform direct detection, if it is necessary to consider shot noise of scattered light, the degree of uncertainty will vary from point to point depending on the scattered light intensity. However, at points where the scattered light intensity is small, the uncertainty will be dominated by noise from the measuring instrument after the electrical stage, such as the thermal noise of the PD. Therefore, the effects of the fading phenomenon described below also apply to device configurations that perform direct detection.

[0059] Due to the fading phenomenon, there are points where the scattered light intensity decreases. At such points, the uncertainty during phase calculation increases, making it difficult to detect small vibrations. In particular, when the amplitude of scattered light in the absence of noise is small, as shown by vector 206 in Figure 7, where the signal-to-noise ratio is less than 1, the probability of the measured vector taking a significantly different value from vector 206 in the absence of noise increases, as shown by vector 207, leading to false detection of vibrations. Furthermore, in such cases, when performing the unwrapping process shown in the subsequent equation (3), the probability of selecting the wrong integer q increases, which can lead to false detection of particularly large vibrations.

[0060] It is known that the distribution D(P) of the variation in scattered light intensity P due to fading when experiments are conducted at a single wavelength satisfies the following equation, where is the average value of the scattered light intensity. As shown in this equation, the distribution D(P) of the variability in scattered light intensity P increases as the scattered light intensity P decreases. Therefore, when trying to reduce points with low scattered light intensity by increasing the pulse intensity of a single wavelength, a very large peak intensity is required, which has limitations when considering pulse distortion such as nonlinear effects.

[0061] Therefore, the rotation angle calculation unit 23d calculates the in-phase component I at N different frequencies i = 1, 2, ..., N, as described below. ｉ ｍｅａｓｕｒｅ and orthogonal component Q ｉ ｍｅａｓｕｒｅ Phase calculations are performed using this method to prevent an increase in phase uncertainty at points where the scattered light intensity due to fading is small.

[0062] [Measurement Procedure S11] Using the measurement system described in Figure 3, the in-phase and orthogonal components of the scattered light generated by the wavelength-multiplexed optical pulse 60 incident on the optical fiber 50 to be measured are measured.

[0063] [Vector acquisition procedure S12] A two-dimensional vector is acquired for each wavelength multiplexed in the optical pulse 60, which is composed of the in-phase component and the orthogonal component of the scattered light measured in measurement procedure S11, at an arbitrary time and at an arbitrary position in the optical fiber 50 under measurement.

[0064] [Vector rotation procedure S13] First, the vector of the measurement at time zero (I ｉ ｍｅａｓｕｒｅ (l, 0), Q ｉ ｍｅａｓｕｒｅ (l, 0)) from phase θ ｉ ｃａｌ Calculate (l, 0). Then, calculate the calculated phase value θ. ｉ ｃａｌ (l, 0) represents the amount of rotation in the opposite direction, and the vector at each time point (I ｉ ｍｅａｓｕｒｅ (l, nT), Q ｉ ｍｅａｓｕｒｅ By rotating (l, nT), the new vectors at each time point and each location are calculated as shown in equation (8).

[0065] [Calculation Procedure S14] Then, the newly calculated vectors for each wavelength are averaged by addition as in Equation (9) to calculate the vector directly used for phase calculation. Finally, the phase θ ｎｅｗ (l, nT), Q ｎｅｗ (l, nT)) is calculated from Equation (10) as follows. ｃａｌ (l, nT).

[0066] The vector (I ｎｅｗ (l, nT), Q ｎｅｗ (l, nT)) is used to calculate θ ｃａｌ (l, nT), which makes it possible to reduce the points where the scattered light intensity decreases due to fading. The principle is described below.

[0067] The θ values at N different frequencies of i = 1, 2, ···, N ｉ ｃａｌ (l, nT) take different values from each other. For example, taking N = 2 as an example, when there is no noise at time zero for i = 1 and i = 2, the vectors (I ｉ (l, 0), Q ｉ (l, 0)) are different in both direction and magnitude, like vector 301 and vector 302 in Figure 8. If the net expansion and contraction amount of the fiber in front of the point at a distance l from the incident end at time nT changes compared to time zero due to vibration, then the vectors (I ｉ (l, nT), Q ｉ (l, nT)) at time nT for i = 1 and i = 2 change as shown by vector 303 and vector 304 in Figure 8, respectively. The lengths of vector 303 and vector 304 change with respect to vector 301 and vector 302, respectively, and the amount of change is different for i = 1 and i = 2, but the directions of vector 303 and vector 304 change by the same amount with respect to vector 301 and vector 302, respectively.

[0068] In other words, angles 305 and 306 are identical, and this quantity corresponds to θ(l, nT) in equation (1). In the absence of noise, according to equation (8), vectors 301, 302, 303, and 304 are moved to vectors 307, 308, 309, and 310, respectively, as shown in Figure 9. In other words, the direction of all wavelength vectors is aligned at each time step.

[0069] As the average of vector 307 and vector 308 (I ｎｅｗ (l, 0), Q ｎｅｗ (l, 0)) is obtained as vector 311, and the average of vector 309 and vector 310 is (I ｎｅｗ (l, nT), Q ｎｅｗ (l, nT) is obtained as vector 312. The phase change between time 0 and nT is angle 313, which is the same as angles 305 and 306.

[0070] In actual measurements, noise introduces uncertainty into the directions of vectors 301, 302, 303, 304, 311, and 312, resulting in uncertainty in angles 305 and 306. However, by calculating angle 313 using the averaged vectors 311 and 312, the uncertainty can be reduced. There are two reasons for this.

[0071] One reason is that the probability distributions of intensity corresponding to the square of the amplitudes of vectors 307 and 308 independently follow equation (7). Therefore, the probability distribution of intensity corresponding to the square of the amplitude of vector 311 theoretically looks like distribution 402 in Figure 10, and even though the mean value itself is the same, it is possible to eliminate the point where the scattered light intensity becomes significantly smaller due to fading in the case of a single wavelength. For comparison, Figure 10 shows the probability distribution for the case of only one wavelength as distribution 401.

[0072] Another reason is that, in vector 311, by averaging vectors 307 and 308, the noise level becomes 1 / √2 of that of vectors 301 and 302. Therefore, even if the average length of vector 311 itself remains the same as that of vectors 301 and 302, the reduced noise level makes it possible to reduce the uncertainty during phase calculations. The same applies to vector 312.

[0073] Here, the effects of this proposal are specifically described for the case where N has two frequencies, but it is possible to generalize. First, as the number of multiplexing numbers N increases, the number of points where the scattered light intensity approaches zero decreases. This is shown in distribution 403 for the case of N=5 and in distribution 404 for the case of N=10. Also, since the magnitude of the noise level is multiplied by 1 / √N, even with the same average intensity, the uncertainty in phase calculation decreases as N increases.

[0074] Furthermore, the signal processing method described in this embodiment is simply θ ｉ ｃａｌ This is different from the method of averaging (l, nT) over different i, for example, the method of calculating the average of phase 305 and phase 306 when N=2. ｉ ｃａｌ In the method of averaging (l, nT) over different i, θ ｉ ｃａｌ Since (l, nT) itself is calculated at a single wavelength, the measured value differs significantly from the noise-free value in areas where the scattered light intensity due to fading is low. Therefore, it is not possible to reduce the occurrence of false vibration detections. Phase averaging can reduce the difference between the ideal phase value in the noise-free case and the measured value, but the frequency of such differences will increase because the points where the scattered light intensity itself is low differ for each wavelength. In other words, simply θ ｉ ｃａｌ Averaging (l, nT) over different i values ​​does not remove points with low scattered light intensity due to fading.

[0075] For explanatory purposes, the right-hand side of equation (9) is multiplied by 1 / N, but the phase value calculated in equation (10) does not change even if this multiplication is omitted, so it is not necessary to multiply by 1 / N in actual calculations.

[0076] (Modified Version) In the above embodiment, the rotation angle of the vector rotation in equation (8) is θ at time zero. ｉ ｃａｌ An example was given for the case where (l, 0). ｉ ｃａｌ The in-phase and orthogonal components used when calculating (l, 0) are (I ｉ ｍｅａｓｕｒｅ (l, 0), Q ｉ ｍｅａｓｕｒｅ (l, 0) is a vector that includes the effect of noise. Therefore, θ ｉ ｃａｌ (l, 0) is also affected by noise. If at time zero, θ ｉ ｃａｌ The value of (l, 0) is θ when there is no noise. ｉ If the value of (l, 0) differs significantly from the value of (l, 0), the effect of vector rotation in equation (8) may not be obtained.

[0077] This is explained in Figure 7. For example, suppose that at a certain point along the longitudinal direction of the fiber and at a certain frequency, the scattered light vector at time zero would be vector 206 if there were no noise, but becomes vector 207 due to noise. The operation of rotating the vector using equation (8) and then averaging the vectors using equation (9) has the effect of reducing the number of points where the vector length is close to zero (points affected by fading). However, in this example, since the rotation angle for that frequency is determined based on the angle of vector 207, this effect cannot be obtained for that frequency.

[0078] Furthermore, errors in the rotation angle can lead to situations where the magnitude of the vibration being measured cannot be correctly evaluated. This case is illustrated in Figure 8. For example, if vectors 301 and 303 (wavelength 1) and vectors 302 and 304 (wavelength 2) are unaffected by noise, the rotation angle required to align vectors with different wavelengths will not be zero. However, if, at the reference time zero, the directions of the wavelength 1 and wavelength 2 vectors happen to be the same due to the influence of noise, the method of Embodiment 1 will average the wavelength 2 vector with the wavelength 1 vector while keeping the rotation angle at zero, i.e., no rotation. In other words, the average vector obtained by averaging vector 301 and vector 302 (no rotation) is taken as the average vector at time zero, and the average vector obtained by averaging vector 303 and vector 304 (no rotation) is taken as the average vector at time nT. Therefore, the angular change of the average vector from time zero to time nT no longer coincides with the angular change from vector 301 to vector 303 or from vector 302 to vector 304, and the phase change cannot be correctly captured.

[0079] This modified example describes a method for reducing the frequency of the above-mentioned malfunctions. Figure 11 is a diagram illustrating the structure of the rotation angle calculation unit 23d of the vibration detection device in this embodiment.The rotation angle calculation unit 23d of this embodiment includes: an input unit 61 to which the in-phase and orthogonal components of scattered light generated by wavelength-multiplexed optical pulses incident on the optical fiber under test, as measured by a measuring instrument, are input; a vector acquisition circuit 62 to acquire a two-dimensional vector composed of the in-phase and orthogonal components of the scattered light input to the input unit 61 at an arbitrary time and at an arbitrary position of the optical fiber under test 50, for each wavelength multiplexed in the optical pulse; a first vector rotation circuit 63-1 to rotate the two-dimensional vectors acquired by the vector acquisition circuit 62 at each time of a reference wavelength by a reference rotation amount for each time so that each of the two-dimensional vectors points in the reference direction, and rotate the two-dimensional vectors acquired by the vector acquisition circuit 62 at each time of other wavelengths different from the reference wavelength by the reference rotation amount for each time; A first arithmetic circuit 64-1 calculates a first composite reference vector by averaging the two-dimensional vectors at each time point of the reference wavelength rotated by the first vector rotation circuit 63-1, calculates a first composite vector for each wavelength by averaging the two-dimensional vectors at each time point of the other wavelengths rotated by the first vector rotation circuit 63-1, and calculates a reference rotation amount for each wavelength from the angle formed by the first composite reference vector and the first composite vector; a second vector rotation circuit 63-2 rotates the two-dimensional vectors at each wavelength at the reference time by the reference rotation amount for each wavelength calculated by the first arithmetic circuit 64-1, and rotates the two-dimensional vectors at each wavelength at other times different from the reference time by the reference rotation amount for each wavelength calculated by the first arithmetic circuit 64-1, respectively. The system includes a second calculation circuit 64-2 that calculates a second composite reference vector by averaging the two-dimensional vectors of each wavelength at the reference time rotated by the second vector rotation circuit 63-2, calculates a second composite vector by averaging the two-dimensional vectors of each wavelength at other times rotated by the second vector rotation circuit 63-2, and calculates the amount of phase change of the scattered light from the angle between the second composite reference vector and the second composite vector.

[0080] Figure 12 is a diagram illustrating the phase measurement method performed by this vibration detection device. The phase measurement method comprises: a measurement procedure S11 for measuring the in-phase and orthogonal components of scattered light generated by wavelength-multiplexed optical pulses incident on the optical fiber under test; a vector acquisition procedure S12 for acquiring a two-dimensional vector composed of the in-phase and orthogonal components of the scattered light measured in measurement procedure S11 at an arbitrary time and at an arbitrary position on the optical fiber under test, for each wavelength multiplexed in the optical pulse; a first vector rotation procedure S23 for rotating the two-dimensional vectors acquired in vector acquisition procedure S12 at each time of a reference wavelength by a reference rotation amount for each time so that each of the two-dimensional vectors points in the reference direction, and rotating the two-dimensional vectors acquired in vector acquisition procedure S12 at each time of wavelengths other than the reference wavelength by the reference rotation amount for each time; A first calculation procedure S24 calculates a first composite reference vector by averaging the two-dimensional vectors at each time point of the reference wavelength rotated in the first vector rotation procedure S23, calculates a first composite vector for each wavelength by averaging the two-dimensional vectors at each time point of the other wavelengths rotated in the first vector rotation procedure S23, and calculates a reference rotation amount for each wavelength from the angle between the first composite reference vector and the first composite vector; a second vector rotation procedure S25 rotates the two-dimensional vectors at each wavelength of the reference time from the two-dimensional vectors acquired in the vector acquisition procedure S12 by the reference rotation amount for each wavelength calculated in the first calculation procedure S24, and rotates the two-dimensional vectors at each wavelength of other time points different from the reference time from the two-dimensional vectors acquired in the vector acquisition procedure S12 by the reference rotation amount for each wavelength calculated in the first calculation procedure S24; The second calculation procedure S26 is performed to calculate a second composite reference vector by averaging the two-dimensional vectors of each wavelength at the reference time that were rotated in the second vector rotation procedure S25, calculate a second composite vector by averaging the two-dimensional vectors of each wavelength at other times that were rotated in the second vector rotation procedure S25, and calculate the amount of phase change of the scattered light from the angle between the second composite reference vector and the second composite vector.

[0081] The input unit 61, the vector acquisition circuit 62, the measurement procedure S11, and the vector acquisition procedure S12 are the same as described in the above embodiment. First, the first vector rotation circuit 63-1 performs the following first vector rotation procedure S23. Using i=1 as the reference (reference wavelength), the following equation is calculated for all i.

[0082] Next, the first arithmetic circuit 63-1 performs the following first arithmetic procedure S24. The average of r'(l, nT) obtained in equation (11) is calculated using the following formula. M is the number of samples in the time direction. The r obtained in equation (12) ｉ Using ''(l), calculate the following equation.

[0083] In short, it works as follows: First, for a reference wavelength i=1, rotate the vector at each time point towards the I-axis. This rotation angle is θ. ｉ＝１ Let (t) be θ. ｉ＝１ (t) changes with time. Also, let At be the vector after rotation. Next, for the other wavelengths, let θ be the vector at each time. ｉ＝１ Rotates by (t). The vector for each wavelength after rotation is Bt ｉ Let's assume that the rotated vectors are then averaged over time for each wavelength. Let ΣAt be the time-averaged vector for the reference wavelength. Let ΣBt be the time-averaged vector for the other wavelengths. ｉ And then, ΣAt and ΣBt ｉ We find the angle between the two. This angle is θ in equation (13). ｉ (l) is θ ｉ '(l) exists for each other wavelength.

[0084] The second vector rotation procedure S25 performed by the second vector rotation circuit 63-2 and the second calculation procedure S26 performed by the second calculation circuit 64-2 are the same as the vector rotation procedure S13 and calculation procedure S14 described in Embodiment 1, respectively, except for the following point: When calculating equation (8), θ ｉ ｃａｌ Replace (l, 0) with θ in equation (13). ｉ Using (l), vector (I ｎｅｗ (l, nT), Qｎｅｗ Calculate (l, nT) and perform the phase calculation using equation (9).

[0085] The significance of this method is explained below. Even if vibration occurs, the angle between vectors of different frequencies does not change if there is no noise. For example, taking the case of two frequencies as an example, the angle between vectors 301 and 302 at the reference time and the angle between vectors 303 and 304 after time nT will be the same if there is no noise. Therefore, after rotating the vectors according to equation (11), the vectors are averaged using equation (12), and the angle between the averaged vector at the reference time and the averaged vector after time nT is the rotation angle θ. ｉ Let's set it to (l). This allows us to reduce the magnitude of the noise associated with each vector to 1 / √M. Therefore, by making M sufficiently large, we can reduce the effect of the noise.

[0086] The method of this embodiment differs from the method (hereinafter referred to as the comparison method) that calculates the rotation angle by determining the phase difference between vectors of different frequencies at each time and then averaging the phase differences for all time points. The method of this embodiment differs in that all wavelength vectors are rotated in advance by a rotation angle of wavelength 1. For example, in the case of two frequencies, the comparison method simply calculates the angle difference between vector 302 and vector 301, and the angle difference between vector 303 and vector 302, and calculates the rotation angle as the average value of these. In the comparison method, the probability of occurrence of a point where the calculated phase difference value at each time point differs significantly from the case without noise (measurement position of the fiber under test) does not change, so the effect of rotation according to equation (8) is insufficient.

[0087] For explanatory purposes, equation (12) multiplies the right-hand side by 1 / M, but the rotation angle calculated in equation (13) does not change even if this multiplication is omitted, so it is not necessary to multiply by 1 / M in actual calculations.

[0088] Compared to the method of the embodiment, the modified method increases computation time, but it can reduce the uncertainty in the final phase calculation compared to the embodiment.

[0089] It should be noted that the present invention is not limited to the above-described embodiments, and the components can be modified and implemented in practice without departing from the spirit of the invention.

[0090] [Note] The following describes the signal processing method of this embodiment. (1) This signal processing method is characterized by the following: In a device configuration in which a phase OTDR device exists for measuring the phase of scattered light scattered from an optical fiber under test, and the incident light in the device is wavelength-multiplexed, the scattered light at each wavelength is plotted on a two-dimensional plane with the in-phase component on the horizontal axis and the orthogonal component on the vertical axis to create a scattered light vector, the created scattered light vector is rotated at each point on the optical fiber under test for each wavelength to match its direction, a new vector is generated by adding and averaging the vectors whose directions have been matched, and the phase is calculated using the values ​​of the in-phase and orthogonal components of the generated new vector to perform a highly sensitive phase measurement.

[0091] (2): The signal processing method described in (1) above involves rotating the scattered light vectors at each point on the optical fiber under test for each wavelength, and calculating the amount of rotation for each wavelength from a vector generated by aligning the direction of the scattered light vectors at each point and time by rotating them, and then adding the vectors whose directions are aligned.

[0092] (3) The measuring device utilizing the above signal processing method comprises a laser light source that outputs continuous light, an element that splits the continuous light from the laser light source into reference light and probe light, an element that multiplexes the frequency of the probe light, an element that causes the probe light to be incident on the optical fiber to be measured, and an element that takes the backscattered light of the probe light from the optical fiber to be measured and the reference light as input and outputs the in-phase component and the orthogonal component of the backscattered light, and performs the above signal processing method using the output in-phase component and the orthogonal component.

[0093] Furthermore, the signal processing unit 23 includes a transmitting / receiving unit 29. The transmitting / receiving unit 29 transfers the signal-processed digital data to the control terminal 40 as temporally continuous digital data. In addition, if an optical switch 24 is provided inside the optical sensing device 20, the transmitting / receiving unit 29 is configured to receive port switching instructions from the control terminal 40.

[0094] (Second Embodiment) The configuration and processing of the optical sensing device 70 according to the second embodiment of the present disclosure will be described with reference to Figures 13 to 15. As shown in Figure 13, the signal processing unit 23 of the optical sensing device 70 includes a calculation unit 23e and a calculation unit 23f.

[0095] In this embodiment, the signal I acquired by the optical frequency separation unit 23c ｉ and signal Q ｉ Based on this, the rotation angle calculation unit 23d, the calculation unit 23e, and the calculation unit 23f continue to perform phase calculations. The roles of each signal processing unit are as follows. Assume that vibration data is acquired at time kt using an integer k, where t is the incidence interval of the i-th optical frequency optical pulse, i.e., the vibration sampling interval. The interval between t1 and t1' in Figure 14 is t. Also, let z be the distance from the incident end. By performing phase calculations at distances of z, the phase at each point in the optical fiber 50 under test can be calculated.

[0096] Specifically, the rotation angle calculation unit 23d receives signal I ｉ (kt, z) and signal Q ｉ Using (kt, z), the scattered light vector r of the scattered light at the i-th optical frequency within a predetermined time range within which the point of measurement of the optical fiber 50 under test can be measured is determined. ｉ Calculate (kt, z). The calculated scattered light vector r ｉ The (kt, z) data is continuously streamed to the calculation unit 23e.

[0097] Also, the scattered light vector r ｉ (kt, z) to each optical frequency f ｉ Rotation angle α ｉ(z) is calculated. However, unlike the conventional method, the measurement data is divided into blocks of a predetermined time range on the time axis, and the rotation angle is calculated and updated for each block of the said time range. The rotation angle α calculated and updated for each block. ｉ (z) is passed to the calculation unit 23e. In this embodiment, the data is divided into blocks such that a predetermined number of light pulses of the same frequency are included in each block. Below, an example is described in which the predetermined time range is a predetermined number of time points M, and the rotation angle is calculated and updated at each measurement time Mt.

[0098] In conventional methods, all measurement data is treated as a single block, or the rotation angle is calculated using the first few measurement points and then used for all data. However, in this embodiment, the rotation angle is updated block by block as it occurs.

[0099] In other words, if we assume that k=0 is the first point of measurement data, and start calculating the rotation angle from the first point, then for example, the scattered light vector r from k0 to M-1 ｉ The measurement data for (kt, z) forms the first block, and the data for k from M to 2M-1 forms the second block. The symbol K is used as a number to distinguish the blocks. For example, in the above example, k from 0 to M-1 is block K=1, and k from M to 2M-1 is block K=2. The Kth block contains the measurement data for k from M(K-1) to MK-1. The value changes according to block K in order to calculate the rotation angle for each block, and the rotation angle is α ｉ This is denoted as (z, K). The method for calculating the rotation angle in each block is the same as in the first embodiment.

[0100] The detailed processing of the rotation angle calculation unit 23d for block K is shown in Figure 15. Processing S23d-0: The input to the rotation angle calculation unit 23d is the signal I from the optical frequency separation unit 23c, in order of increasing k. ｉ (kt, z) and signal Q ｉ (kt, z) is being streamed.

[0101] Process S23d-1: Signal I at time kt ｉ (kt, z) and signal Q ｉFrom (kt, z), the scattered light vector r ｉ We will calculate (kt, z). For example, let the imaginary unit be j and calculate the following: (Math 14) r ｉ (kt, z) = I ｉ (kt, z) + jQ ｉ (kt, z) (14) The calculated scattered light vector data is sequentially streamed to the calculation unit 23e.

[0102] Processing S23d-2: Set the reference optical frequency to f １ Let's assume that the reference optical frequency can be chosen arbitrarily, so f １ It doesn't have to be that way. The scattered light vector r of the reference light frequency at each fiber point at time kt. １ angle θ of (kt, z) １ Calculate (kt, z). θ １ (kt, z) can be expressed, for example, by the following equation: (Mathematics 15) θ １ (kt,z)=arg[r １ (kt, z)] (15)

[0103] Processing S23d-3: Scattered light vectors r of each optical frequency at each fiber point at time kt. ｉ (kt, z) as angle -θ １ Rotate by (kt, z), r ｉ＿ｒｏｔ Let (kz, t). ｉ＿ｒｏｔ (kz, t) can be expressed, for example, by the following equation: (Mathematics 16) r ｉ＿ｒｏｔ (kz, t)=exp[-θ １ (kt, z) * r ｉ (kt,z) (16)

[0104] Process S23d-4: If time kt is the first time M(K-1) of the K block, the time average vector r ｉ＿ａｖｅｔ Prepare a new (z, K), r ｉ＿ａｖｅｔ (z) = r ｉ＿ｒｏｔ Let (kz, t). If time kt is the second or later of the K block, the time-averaged vector up to time (k-1)t is given by r at time kt. ｉ＿ｒｏｔ The time-averaged vector is updated by adding (kz, t). ｉ＿ａｖｅｔ (z, K) is expressed by the following equation: (Equation 17) rｉ＿ａｖｅｔ (z, K) = r ｉ＿ｒｏｔ (kz, t) + r ｉ＿ａｖｅｔ (z, K) (17)

[0105] Process S23d-5: The value obtained when process S23d-4 is completed, where time kt is the last time MK-1 of the K block. ｉ＿ａｖｅｔ Using (z, K), the rotation angle α for each optical frequency using block K. ｉ Calculate (z). α ｉ (z) is expressed by the following equation: (Mathematics 18) α ｉ (z, K)=-arg[r ｉ＿ａｖｅｔ (z, K) (18) This allows us to obtain the difference in phase offset values ​​of each optical frequency contained in the block.

[0106] Process S23d-6: When process S23d-5 is completed, the rotation angle α ｉ (z) is passed to the signal processing unit 17e.

[0107] Calculation unit 23e: Functions as a "phase correction unit". The calculation unit 23e calculates the rotation angle α calculated by the rotation angle calculation unit 23d. ｉ Using (z), the scattered light vector r ｉ The phase is corrected. For example, the calculation unit 23e calculates each optical frequency f included in the K block. ｉ The scattered light vector r ｉ Rotation angle α ｉ (z) Rotate and average, then obtain the frequency-averaged vector R ａｖｅｆ Calculate.

[0108] However, unlike the conventional method, the rotation angle α ｉ Since it is updated for each time block Mt, in this disclosure, the rotation angle used when calculating the frequency average of scattered light vectors belonging to a certain block K is the rotation angle calculated in the rotation angle calculation unit 23d using the previous block K-1. That is, the detailed processing of the calculation unit 23e for the Kth block is as follows.

[0109] Processing S23e-1: Scattered light vectors r of each light frequency at time kt ｉ (kt, z) is the rotation angle α calculated in the K-1th block.ｉ Rotate by (z, K-1), and the resulting vector R ｉ Calculate (kz, t). R ｉ (kz, t) is expressed by the following equation. (Equation 19) R ｉ (kz, t)=exp(j・α ｉ (z, K-1))・r ｉ (kt, z) (19) Vector R ｉ By calculating (kz, t), the scattered light vector r for each optical frequency can be obtained. ｉ The difference in phase offset can be corrected.

[0110] Process S23e-2: Rotated vector R ｉ The frequency-averaged vector of (kz, t) is calculated. Note that the final result is the same whether vector averaging or vector addition (simple vector summation), so in the actual calculation procedure, vector addition is performed to obtain the frequency-averaged vector R. ａｖｅｆ Let (kz, t). R ａｖｅｆ (kz, t) is expressed by the following equation.

[0111] Processing S23e-3: Frequency-averaged vector R ａｖｅｆ angle θ of (kz, t) ａｖｅｆ The (kz, t) is calculated and passed to the calculation unit 23f. ａｖｅｆ (kz, t) is expressed by the following equation.

[0112] Furthermore, in the first block where K=1, the rotation angle is not acquired because there is no data from the previous blocks, and the procedure of the calculation unit 23e cannot be performed. Therefore, the measurement time of the first Mt is treated as a pre-measurement, and processing from the calculation unit 23e onward is not performed. Alternatively, the scattered light vector r for the measurement time of the first Mt is... ｉ It is also possible to store only (kt, z) separately in the computer and calculate the vibration waveform using conventional methods.

[0113] Calculation unit 23f: Executes the procedure S03 described above. The calculation unit 23f calculates the frequency average vector R obtained by the calculation unit 23e. ａｖｅｆ angle θ ａｖｅｆThe phase change at any point in the optical fiber 6 under measurement is calculated using (kHz, t). For example, the calculation unit 23f calculates the phase difference between two points separated by the gauge length, performs phase connection processing, and calculates the vibration waveform. The specific calculation method is the same as the conventional method.

[0114] The distinguishing feature of this disclosure lies in the rotation angle calculation units 23d and 23e. The rotation angle calculation unit 23d calculates the signal I obtained from the measurement. ｉ and Q ｉ The time is divided into blocks of M time points, and the rotation angle α is measured in units of Mt blocks. ｉ By calculating and updating this, the system can accommodate temporal changes in the optimal value due to temporal changes in the optical properties of the laser equipped in the CW light source 11, such as the oscillation frequency, temperature changes of the optical fiber 50 under test itself, and the application of large dynamic strain to the optical fiber 50 under test. By setting the measurement time Mt per block to a small time scale relative to the temporal changes in the optical properties of the laser equipped in the light source 11, such as the oscillation frequency, temperature changes of the optical fiber 50 under test itself, and the application of large dynamic strain to the optical fiber 50 under test, the system can update the rotation angle with sufficient precision.

[0115] With this setting, the scattered light vector r belonging to block K is calculated in the calculation unit 23e. ｉ The rotation angle α used when calculating the frequency average ｉ The rotation angle α of the block K-1 immediately before the calculation was performed by the rotation angle calculation unit 23d. ｉ Using this will also resolve the issue. In addition, the rotation angle calculation unit 23d calculates the rotation angle α of the previous block K-1. ｉ By outputting this to the calculation unit 23e, the rotation angle calculation unit 23d calculates the scattered light vector r ｉ＿ａｖｅｔ When (z) is updated, the scattered light vector r ｉ This eliminates the need to store the (kt, z) data in the memory of the signal processing unit 23.

[0116] Thus, the present disclosure enables the processing in the AD conversion functional elements 23a and 23b, the optical frequency separation unit 23c, and the rotation angle calculation unit 23d, which functions as a rotation angle calculation unit, to be performed independently and in parallel as streaming processing. As a result, the present disclosure enables the processing of the scattered light vector r belonging to block K in the calculation unit 23e. ｉ The rotation angle α used when calculating the frequency average ｉ In contrast to conventional techniques that use the rotation angle itself calculated by the rotation angle calculation unit 23d in block K, which require the rotation angle calculation unit 23d to store all the scattered light vector data belonging to block K in the computer's memory, this method reduces the amount of memory required by the computer.

[0117] However, the length of the measurement time Mt per block is the rotation angle α ｉ This also relates to the calculation accuracy. The measurement time Mt per block is calculated with sufficient precision for the rotation angle α. ｉ The rotation angle α is set to be as long as possible for calculation purposes, and small for the time scale of the temporal changes in optical characteristics such as the oscillation frequency of the laser provided in the light source 11, the temperature changes of the optical fiber 50 under test itself, and the time scale of large dynamic strains applied to the optical fiber 50 under test. ｉ This also ensures calculation accuracy. Such settings are possible in many situations. For example, if M is set to around 100, a sufficient rotation angle α can be obtained. ｉ Experimental findings have shown that this level of accuracy can be achieved. Even if the transmission period t of the optical pulse is 1 ms, Mt will be around 100 ms. This is considered sufficiently fine when the time scale of the optical characteristics such as the oscillation frequency of the laser in the light source 11, the temperature change of the optical fiber 50 under measurement itself, and the application of large dynamic strain to the optical fiber 50 under measurement is 1 s or longer.

[0118] Furthermore, similar to the first embodiment, the signal processing unit 23 includes a transmitting / receiving unit 29. The transmitting / receiving unit 29 transfers the signal-processed digital data to the control terminal 40 as temporally continuous digital data. In addition, if an optical switch 24 is provided inside the optical sensing device 20, the transmitting / receiving unit 29 is configured to receive port switching instructions from the control terminal 40.

[0119] The device described herein can also be implemented using a computer and a program, and the program can be recorded on a recording medium or provided over a network. The program described herein is a program that causes a computer to implement each function of the device described herein, and a program that causes a computer to execute each procedure of the method performed by the device described herein.

[0120] The optical sensing system disclosed herein can be applied to the information and communication industry.

[0121] 11: Light source 20: Optical sensing device 21: Optical transmitter 22: Optical receiver 23: Signal processing unit 23a, 23b: AD conversion element 23c: Optical frequency separation unit 23d: Rotation angle calculation unit 23e, 23f: Calculation unit 24: Optical switch 25: Coupler 26: Optical modulator 27: Circulator 29: Transceiver unit 30: External optical switch 40: Control terminal 41: Optical switch switching setting unit 42: File processing unit 43: Storage unit 44: Visualization unit 50: Optical fiber 51, 52: Coupler 53: Phase shifter 54, 55: Coupler 56, 57: Balance detector 58: Analog common-phase component electrical signal 59: Analog quadrature component electrical signal 60: Optical pulse 60a: Micro-pulse 61: Input unit 62: Vector acquisition circuit 63: Vector rotation circuit 64: Arithmetic circuit 63-1: First vector rotation circuit 64-1: First arithmetic circuit 63-2: Second vector rotation circuit 64-2: Second arithmetic circuit 70: Optical sensing device 100: Optical sensing system

Claims

1. A control terminal connected to an optical sensing device that incident light onto multiple optical fibers and measures the scattered light from the multiple optical fibers, and connected to an external optical switch configured to select the optical fiber from which the light is incident among the multiple optical fibers; the control terminal outputs a switching instruction to the external optical switch to select one or more optical fibers from the multiple optical fibers, and acquires data on the scattered light measured by the optical sensing device.

2. The control terminal according to claim 1, wherein the data relating to the scattered light is digital data, information regarding the switching of connection ports between the plurality of optical fibers is obtained from the external optical switch, and the information regarding the switching of connection ports is added to the digital data and stored.

3. An optical sensing system comprising: a control terminal according to claim 1 or 2; an optical sensing device that incidents light onto a plurality of optical fibers and measures scattered light from the plurality of optical fibers; and an external optical switch that receives a switching instruction from the control terminal and switches the connection ports between the plurality of optical fibers.

4. An optical sensing method performed by a control terminal connected to an external optical switch, which is connected to an optical sensing device that incident light onto multiple optical fibers and measures scattered light from the multiple optical fibers, and is configured to select an optical fiber from which the light is incident among the multiple optical fibers, the control terminal outputs a switching instruction to the external optical switch to select one or more optical fibers from the multiple optical fibers, and acquires data relating to the scattered light measured by the optical sensing device.

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