Signal processing method for phase OTDR

Abstract

The purpose of the present disclosure is to be able to perform streaming processing of data, and prevent deterioration of the S / N ratio and vibration measurement accuracy without increasing memory size requirements for a computer, even during measurements over a long-time.　The signal processing device and signal processing method of the present disclosure are a signal processing device and a signal processing method that perform signal processing of measurement data of scattered light obtained by using an optical fiber to scatter a plurality of optical pulses with different optical frequencies, wherein the scattered light vector ri of scattered light at each optical frequency is calculated in a prescribed time range in which any point on the optical fiber can be measured, the scattered light vectors ri of the optical frequencies are averaged in the time range, the rotation angle αi for correcting the phase of each optical frequency is calculated using the time average vector ri_avet obtained by the averaging, and the phase of the scattered light vector ri of each optical frequency is rotated by the rotation angle αi, thereby the phase of the scattered light vector ri of each optical frequency is corrected.

Description

[Technical Field]

[0001] The present disclosure relates to a phase OTDR that measures the phase of scattered light from each point on an optical fiber under test. [Background technology]

[0002] As a means for measuring physical vibrations applied to an optical fiber in a distributed manner along the length of the optical fiber, a method called DAS (Distributed Acoustic Sensing) is known, in which pulsed test light is injected into the optical fiber under test and backscattered light due to Rayleigh scattering is detected (Non-Patent Document 1).

[0003] One DAS technique is phase OTDR (Optical Time Domain Reflectometry), which measures the phase of scattered light from each point in the optical fiber under test and observes the time change of the phase. Phase OTDR is also called DAS-P (DAS-phase). DAS-P allows the phase to change linearly with changes in the optical path length of the optical fiber due to vibration, and the rate of change can be considered to be approximately the same at each point along the optical fiber's length, making it possible to quantitatively measure vibration and faithfully reproduce the vibration waveform applied to the optical fiber under test (for example, Non-Patent Document 2).

[0004] In DAS-P, which uses optical pulses of a single optical frequency, interference between scattered lights within the pulse width creates points where the scattered light intensity is low, resulting in a deterioration of sensitivity. One method to prevent this deterioration in sensitivity is to perform optical frequency multiplexing and average signals at different optical frequencies (Non-Patent Document 3, Patent Document 1). This method utilizes the fact that the points where the scattered light intensity is low change with different optical frequencies.

[0005] In Non-Patent Document 3 and Patent Document 1, the following specific procedure is carried out as an efficient averaging method. Step S01: Using the measurement data, calculate the difference in phase offset value between the scattered light vector of the optical frequency component selected as the internal reference of the multiplexed optical frequency components and the scattered light vectors of the other optical frequency components. Using the calculated difference in phase offset value, calculate the rotation angle for correcting the phase offset of each optical frequency.

[0006] Step S02: Rotate the scattered light vector at each time by the rotation angle, and then average the rotated vectors of different optical frequencies to calculate a frequency average vector. Using the frequency average vectors at different times, calculate the angular change of the frequency average vector.

[0007] Step S03: Using the angle change, the phase difference between two points on the optical fiber that are separated by the gauge length is calculated, and phase unwrapping processing and the like are performed to calculate the vibration waveform generated in the section between the two points.

[0008] In particular, the details of step S01 are as follows: where the repetition interval of pulses of the same optical frequency is t, that is, the sampling interval of the vibration is t, and measurement data of M points from measurement time 0 to (M-1)t (M is a natural number) is used, and the scattered light vector of the reference optical frequency (let's say f1) at each time mt (m is an integer from 0 to (M-1)) is r1(mt,z) (depending on the fiber point and therefore on the distance z from the input end), and each other optical frequency f i (i is an integer between 2 and N, and N represents the number of optical frequencies multiplexed) is the scattered light vector of r i (mt,z) where M is conventionally set to include all measurement time points or the first few points.

[0009] Step S01-1: Calculate the angle θ1(mt,z) of the scattered light vector r1(mt,z) of the reference optical frequency at each time and each fiber point. If we consider the scattered light vector r1(mt,z) as a complex vector on the complex plane, i.e., a complex number, then the angle θ1(mt,z) can be calculated as arg[r1(mt,z)], where arg is an operator that gives the argument of a complex number.

[0010] Step S01-2: Scattered light vector r of each optical frequency at each time and fiber point i Rotate (mt,z) by the angle -θ1(mt,z), and i_rot (mz,t). The scattered light vector r i If (mt,z) is a complex vector on the complex plane, the vector r after rotation is i_rot (mz,t) is exp[-θ1(mt,z)]*r i It can be calculated as (mt,z).

[0011] Step S01-3: Vector r after rotating the scattered light vector of each optical frequency at each fiber point i_rot (mt,z) is averaged over M points, where m is the measurement data used, from 0 to (M-1), and the time-averaged vector r i_avet Calculate (z). +arg[r i_avet (z)] is the difference in the phase offset value. In actual calculations, vector sum can be used instead of vector average for M points. Whichever is used, the same results will be obtained in subsequent processing.

[0012] Step S01-4: Rotation angle α when rotating the scattered light vector of each optical frequency at each fiber point in step S02 i (z) is expressed as -arg[r i_avet (z)]. -arg[r i_avet (z)], it is possible to correct for the difference in phase offset.

[0013] The rotation angle α given in step S01-4 i Since time averaging is performed in steps S01-3, (z) is a value in which noise has been effectively reduced, and the rotation angle α i By calculating the optical frequency mean vector in step S02 using (z), the signal-to-noise ratio of the final vibration waveform can be improved and waveform distortion can be suppressed.

[0014] In step S01 of the conventional technique, the rotation angle of each optical frequency is calculated using measurement data at M points from measurement time 0 to (M-1)t (M is a natural number), and in step S02, the calculated rotation angle is used to perform frequency averaging on the measurement data at M points from measurement time 0 to (M-1)t (M is a natural number) and on measurement data at other times. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Japanese Patent Publication No. 2020-169904 [Non-patent literature]

[0016] [Non-Patent Document 1] Ali. Masoudi, TP Newson, “Contributed Review: Distributed optical fiber dynamic strain sensing.” Review of Scientific Instruments, vol.87, pp011501 (2016) [Non-patent document 2] K. Nishiguchi, C. Lee, M. Guzik-Arter, M. Yokoyama, and K. Masuda, "Prototype of a distributed acoustic wave sensor using optical fiber and its signal processing," IEICE Technical Report, 115(202), pp. 29-34 (2015) [Non-patent document 3] Yoshifumi Wakisaka, Daisuke Iida, Hiroyuki Oshida, and Nazuki Honda, “Fading Suppression of Φ-OTDR With the New Signal Processing Methodology of Complex Vectors Across Time and Frequency Domains,” J. Lightwave Technol. 39, 4279-4293 (2021) Summary of the Invention [Problem to be solved by the invention]

[0017] The optimal value of the rotation angle calculated by the method of step S01 of the conventional technique varies over time due to changes in optical characteristics such as the laser oscillation frequency, temperature changes in the optical fiber under test itself, application of large dynamic strain to the optical fiber under test, etc. Therefore, in long-term distributed vibration measurement, it is necessary to continuously update the optimal value of the rotation angle and perform the processes from step S02 onwards.

[0018] However, the conventional techniques described in Non-Patent Document 3 and Patent Document 1 do not disclose a method for performing the processes from step S02 onwards while continuously updating the optimum value of the rotation angle. Furthermore, when frequency averaging is performed on the measurement data used to calculate the rotation angle using the calculated rotation angle, streaming of the data is not possible, and it becomes necessary to hold the measurement data in the computer's memory until frequency averaging is complete.

[0019] The present disclosure aims to enable streaming processing of data, preventing degradation of the signal-to-noise ratio and vibration measurement accuracy even in long-term measurements without increasing the memory size requirements of the computer. [Means for solving the problem]

[0020] The present disclosure relates to a signal processing method that performs processing from step S02 onward while continuously updating the optimal value of the rotation angle. The present disclosure enables streaming processing of data, eliminating the need to store measurement data in computer memory until frequency averaging is complete.

[0021] Specifically, the measurement system of the present disclosure includes: a measuring device for measuring scattered light generated by scattering a plurality of optical pulses having different optical frequencies in an optical fiber; The measurement data of the scattered light measured by the measuring device is acquired, and the scattered light vector r of the scattered light at an arbitrary point of the optical fiber is calculated. i , and the calculated scattered light vector r ia signal processing device according to the present disclosure for calculating a phase change at an arbitrary point of the optical fiber using Equipped with.

[0022] The signal processing device of the present disclosure executes the signal processing method of the present disclosure, which is a signal processing method for performing signal processing of measurement data of scattered light obtained by scattering N optical pulses having different optical frequencies in an optical fiber, the method comprising the steps of: A scattered light vector r of scattered light at each optical frequency in a predetermined time range that can be measured at any point of the optical fiber i Calculate Scattered light vector r for each optical frequency i over the time range, The time-averaged vector r obtained by the averaging i_avet The rotation angle α for correcting the phase of each optical frequency is i Calculate Scattered light vector r for each optical frequency i The phase of is rotated by an angle α i By rotating the scattered light vector r i Correct the phase of

[0023] The time range may be the time range of any one of the blocks when the acquisition time of the measurement data is divided into a plurality of blocks. In this case, the signal processing device of the present disclosure calculates the scattered light vector r of each optical frequency for each block. i Here, the signal processing device of the present disclosure corrects the phase of the rotation angle α calculated in the previous block. i Using the scattered light vector r i The phase of the signal may be corrected.

[0024] The signal processing device of the present disclosure includes: AD conversion elements that individually convert the in-phase components of the scattered light into digital signals; an AD conversion function element that converts the orthogonal components of the scattered light into digital signals individually; The in-phase component I of the digital signal output from the AD conversion function element digital and the quadrature component Q digital , the signal Ii and signal Q i an optical frequency separation unit for separating the optical signal into The signal I output from the optical frequency separation unit i and signal Q i Using the scattered light vector r i , and the calculated scattered light vector r i over the time range, and the time-averaged vector r obtained by the averaging i_avet Using the rotation angle α i a rotation angle calculation unit that calculates The rotation angle α calculated by the rotation angle calculation unit i The scattered light vector r calculated by the rotation angle calculation unit is calculated using i a phase correction unit that corrects the phase of the Equipped with The processes in the AD conversion function element, the optical frequency separation unit, and the rotation angle calculation unit may be executable independently and in parallel.

[0025] The signal processing device of the present disclosure includes: Rotation angle α i The vector R after rotating i is frequency averaged, Frequency average vector R after frequency averaging avef Angle θ avef Calculate Angle θ avef The vibration waveform may be calculated using

[0026] The above disclosures can be combined as much as possible. [Effects of the Invention]

[0027] By using the present disclosure, it is possible to measure vibration waveforms while preventing degradation of the S / N ratio and vibration measurement accuracy, even in long-term distributed vibration measurements. Furthermore, the present disclosure is capable of streaming data while reducing the memory size requirements of the computer, making it theoretically applicable to real-time vibration waveform monitoring. Therefore, the present disclosure is capable of streaming data, preventing degradation of the S / N ratio and vibration measurement accuracy, even in long-term measurements, without increasing the memory size requirements of the computer. [Brief explanation of the drawings]

[0028] [Figure 1] 1 shows an example of the configuration of a measurement device according to the present disclosure. [Figure 2] 1 illustrates an example of a light pulse of the present disclosure. [Figure 3] The detailed processing of the signal processing unit 17d will be shown for the Kth block. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings indicate the same components.

[0030] An example configuration of a measurement system according to the present disclosure is shown in Figure 1. The measurement system according to the present disclosure includes a measurement device 31 that performs coherent detection using a 90-degree optical hybrid 7 in a receiving system, and a signal processing device 17 that executes the signal processing method according to the present disclosure.

[0031] The measuring device 31 measures scattered light from an optical fiber 6 under test using a plurality of optical pulses 4 with different optical frequencies. Continuous light with a single wavelength and optical frequency f0 is emitted from a CW light source 1, and is split into reference light and probe light by a coupler 2. The probe light is shaped into an optical pulse 4 as shown in Figure 2 by an optical modulator 3. The optical pulse 4 is a pulse having an ith optical frequency f i is f i =f0+Δf i (i is an integer) and the pulse width W is set to a value corresponding to the spatial resolution of the measurement in the longitudinal direction of the optical fiber, and the optical pulses are arranged in a sequence of i=1, 2, ..., N (N is an integer and represents the number of multiplexed optical frequencies). i is the modulation frequency given by the modulator 3, and is the shift amount from the laser frequency f0 of the CW light source 1. i is selected so that the scattered light intensity at each time and point is sufficiently separated so that it can be considered uncorrelated between different i. The pulse width W corresponds to the spatial resolution.

[0032] The optical modulator 3 is any device capable of generating optical pulses 4 with a pulse width W at an oscillation sampling interval t, and may be configured with multiple devices. For example, modulation using an LN modulator-based modulator such as an SSB (single sideband) modulator may be used, or a frequency-tunable AO modulator may be used, or intensity modulation using an SOA (semiconductor optical amplifier) ​​or the like may be performed to increase the extinction ratio in pulsing.

[0033] The optical pulse 4 is input to the optical fiber 6 under test via the circulator 5. The light scattered at each point along the length of the optical fiber 6 returns to the circulator 5 as backscattered light and is input to one input of the 90-degree optical hybrid 7. The reference light split by the coupler 2 is input to the other input of the 90-degree optical hybrid 7.

[0034] The internal configuration of the 90-degree optical hybrid 7 may be any configuration as long as it has the function of a 90-degree optical hybrid. Two of the four outputs of the 90-degree optical hybrid 7 are detected by a balance detector 13, and the analog in-phase component I analog The remaining two outputs of the 90-degree optical hybrid are detected by a balanced detector 14, which outputs an analog quadrature component Q analog As a result, the optical intensity of the in-phase component and the optical intensity of the quadrature component of the scattered light produced by scattering a plurality of optical pulses with different optical frequencies in the optical fiber are measured individually.

[0035] The electric signals 15 and 16 are sent to a signal processing device 17 having AD conversion function elements 17a and 17b capable of sampling the frequency band of the signals without aliasing. The signal processing device 17 converts the digitized in-phase components I output from the AD conversion function elements 17a and 17b into digital and the quadrature component Q digital Specifically, the signal processing unit 17c processes the in-phase component I digital and the quadrature component Q digital , each optical frequency f i Signal I of scattered light from light pulses (i=1,2,…,N) i and signal Q i Separate into.

[0036] That is, the signal processing unit 17c functions as an "optical frequency separating unit" and separates each optical frequency f0+f i In-phase component signal I obtained when an optical pulse of component I is input alone i and the quadrature component signal Q i is a superposition of in-phase components for all i digital and Q, which is a superposition of orthogonal components for all i digital The signal is separated by performing signal processing on the signals. digital and Q digital The center frequency is f0+Δf iOne possible solution is to pass the signal through a digital bandpass filter with a passband of 2 / W. For example, when using an FIR (Finite Impulse Response) filter, a delay occurs according to the filter characteristics, so to compensate for this delay, processing is also performed such as advancing the filtered signal by the amount of the delay.

[0037] If the filter characteristics of the digital band-pass filter are set to specifications that allow streaming of measurement data, taking into consideration the memory size of the computer used, the measurement data will be streamed up to the signal processing unit 17c. For example, when an FIR filter is used as the digital band-pass filter, if the number of filter taps is too large or the number of significant decimal points of the filter coefficients is too large, the memory and calculation speed of the computer used will not be suitable for streaming processing, so the number of filter taps and the number of significant decimal points of the filter coefficients are set according to the memory and calculation speed of the computer used to enable streaming processing.

[0038] The signal I acquired by the signal processing unit 17c i and signal Q i Based on this, signal processing units 17d, 17e, and 17f continue to perform phase calculations. The roles of each signal processing unit are as follows: The interval between incident optical pulses of the ith optical frequency, that is, the vibration sampling interval, is set to t, and vibration data is acquired at time kt using integer k. The interval between t1 and t1' in Figure 2 is t. Also, the distance from the incident end is set to z. By performing phase calculations for each distance z, the phase at each point in the optical fiber 6 under test can be calculated.

[0039] Signal processing unit 17d: Functions as a "rotation angle calculation unit." Specifically, signal I i (kt,z) and signal Q i (kt,z) is used to calculate the scattered light vector r of the scattered light at the i-th optical frequency in a predetermined time range in which the point of the optical fiber 6 to be measured can be measured. iCalculate (kt,z). The calculated scattered light vector r i The (kt,z) data is continuously streamed to the signal processing unit 17e.

[0040] Also, the scattered light vector r i (kt,z) to each optical frequency f i Rotation angle α i 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 time range. The rotation angle α calculated and updated for each block is i (z) is passed to the signal processing unit 17e. In this embodiment, the blocks are divided so that each block contains a predetermined number of optical pulses of the same frequency. Below, an example will be described in which the predetermined time range is a predetermined number of time points M, and the rotation angle is calculated and updated every measurement time Mt.

[0041] In conventional methods, all measurement data is treated as one block, or the rotation angle is calculated using the first few points of measurement data and the rotation angle calculated for all data is used, but in this embodiment, the rotation angle is updated for each block as needed.

[0042] In other words, if k=0 is set as the first point of the measurement data and the calculation of the rotation angle starts from the first point, for example, the scattered light vector r i The measurement data for (kt,z) is the first block, and k from M to 2M-1 is the second block. K is used as a number symbol to distinguish the blocks. For example, in the above example, k from 0 to M-1 is the block K=1, and k from M to 2M-1 is the block K=2. The Kth block is the measurement data for k from M(K-1) to MK-1. To calculate the rotation angle for each block, the value changes depending on the block K, and the rotation angle is calculated as α i This is expressed as (z, K). The rotation angle for each block is calculated in the same way as in step S01 of the prior art.

[0043] FIG. 2 shows the detailed processing of the signal processing unit 17d for the Kth block. Step S17d-0: The signal processing unit 17d receives the signal I from 17c in ascending order of k as an input. i (kt,z) and signal Q i (kt,z) is streaming.

[0044] Process S17d-1: Signal I at time kt i (kt,z) and signal Q i (kt,z) to the scattered light vector r i Calculate (kt,z). For example, let j be the imaginary unit and calculate the following: (Number 1) r i (kt,z)=I i (kt,z)+jQ i (kt,z) (1) The calculated scattered light vector data is sequentially streamed to the signal processing unit 17e.

[0045] Process S17d-2: Let the reference optical frequency be f1. However, the reference optical frequency can be chosen arbitrarily and does not have to be f1. Calculate the angle θ1(kt,z) of the scattered light vector r1(kt,z) of the reference optical frequency at each fiber point at time kt. θ1(kt,z) can be expressed, for example, by the following equation: (Number 2) θ1(kt,z)=arg[r1(kt,z)] (2)

[0046] Process S17d-3: Scattered light vector r of each optical frequency at each fiber point at time kt i (kt,z) is rotated by the angle -θ1(kt,z), and r i_rot Let (kz,t). r i_rot (kz,t) can be expressed, for example, by the following equation: (Number 3) r i_rot (kz,t)=exp[-θ1(kt,z)]*r i (kt,z) (3)

[0047] Process S17d-4: If time kt is the first time M(K-1) of the Kth block, the time average vector r i_avet Prepare a new (z,K) and i_avet (z)=r i_rot (kz,t). If time kt is the second or later of the Kth block, the time average vector up to time (k-1)t is added to the r i_rot (kz,t) is added to update the time average vector. Time average vector r i_avet (z, K) is expressed by the following equation. (Number 4) r i_avet (z,K)=r i_rot (kz,t)+r i_avet (z,K) (4)

[0048] Process S17d-5: The time kt is the last time MK-1 of the Kth block, and the process S17d-4 is completed. i_avet Using (z, K), the rotation angle α of each optical frequency using the Kth block is i Calculate (z). α i (z) is expressed by the following equation. (Number 5) α i (z,K)=-arg[r i_avet (z,K)] (5) This makes it possible to obtain the difference in phase offset value of each optical frequency included in the block.

[0049] Process S17d-6: When the process S17d-5 is completed, the rotation angle α i (z) is passed to the signal processing unit 17e.

[0050] Signal processing unit 17e: Functions as a "phase correction unit" and executes the above-mentioned step S02. The signal processing unit 17e calculates the rotation angle α i (z) to obtain the scattered light vector r i For example, the signal processing unit 17e corrects the phase of each optical frequency fi Scattered light vector r i Rotation angle α i (z) Rotate and average the frequency average vector R avef Calculate.

[0051] However, unlike the conventional method, the rotation angle α i is updated for each block of time Mt, and therefore, in this disclosure, the rotation angle used when calculating the frequency average of the scattered light vectors belonging to a certain block K is the rotation angle calculated by signal processing unit 17d using the previous block K-1. That is, the detailed processing by signal processing unit 17e for the Kth block is as follows:

[0052] Process S17e-1: Scattered light vector r of each optical frequency at time kt i (kt,z) is the rotation angle α calculated in the (K-1)th block. i Rotate by (z,K-1) and use the rotated vector R i Calculate (kz,t). R i (kz,t) is expressed by the following equation. (Number 6) R i (kz,t)=exp(j·α i (z,K-1))·r i (kt,z) (6) Vector R i By calculating (kz,t), the scattered light vector r i This allows for correction of differences in phase offset between the two signals.

[0053] Process S17e-2: Vector R after rotation i Calculate the frequency-averaged vector of (kz,t). Note that the final result is the same whether it is vector averaging or vector synthesis (simple vector sum), so in the actual calculation procedure, vector synthesis is used to obtain the frequency-averaged vector R avef Let (kz,t). R avef (kz,t) is expressed by the following equation.

number

[0054] Process S17e-3: Frequency average vector R avef Angle θ of (kz,t) avef (kz,t) is calculated and passed to the signal processing unit 17f. avef (kz,t) is expressed by the following equation.

number

[0055] In the first block of K=1, since there is no data from the previous block, the rotation angle is not yet acquired, and the procedure of the signal processing unit 17e cannot be performed. Therefore, the measurement time of the first Mt is treated as a pre-measurement, and no processing is performed after the signal processing unit 17e. Alternatively, the scattered light vector r for the measurement time of the first Mt i It is also possible to store only (kt, z) separately in a computer and calculate the vibration waveform using conventional methods.

[0056] Signal processing unit 17f: Executes the above-mentioned step S03. The signal processing unit 17f converts the frequency average vector R obtained by the signal processing unit 17e into avef Angle θ avef Using (kz,t), the phase change at any point in the optical fiber 6 under test is calculated. For example, the signal processing unit 17f calculates the difference in phase between two points separated by the gauge length, performs phase unwrapping processing, etc., and calculates the vibration waveform. The specific calculation method is the same as the conventional method.

[0057] The present disclosure is characterized by the signal processing units 17d and 17e. The signal processing unit 17d processes the signal I obtained by measurement. i and Q i is divided into blocks of M time points, and the rotation angle α iBy calculating and updating, it is possible to deal with temporal changes in the optimum value due to changes over time in optical characteristics such as the oscillation frequency of the laser provided in the CW light source 1, changes in the temperature of the optical fiber 6 under test itself, and the application of large dynamic strain to the optical fiber 6 under test. By making the measurement time Mt per block small compared to the time scale of changes over time in optical characteristics such as the oscillation frequency of the laser provided in the CW light source 1, changes in the temperature of the optical fiber 6 under test itself, and the application of large dynamic strain to the optical fiber 6 under test, it becomes possible to update the rotation angle with sufficient precision.

[0058] With this setting, the scattered light vector r belonging to block K is detected by the signal processing unit 17e. i The rotation angle α used when calculating the frequency average of i The rotation angle α of the immediately preceding block K-1 calculated by the signal processing unit 17d is i In addition, there is no problem if the signal processing unit 17d uses the rotation angle α i to the signal processing unit 17e, so that the signal processing unit 17d outputs the scattered light vector r i_avet After updating (z), the scattered light vector r i There is no need to store the (kt, z) data in the memory of the signal processing device 17.

[0059] In this way, in the present disclosure, the AD conversion function elements 17a and 17b, the signal processing unit 17c functioning as an optical frequency separation unit, and the signal processing unit 17d functioning as a rotation angle calculation unit can perform streaming processing independently and in parallel. As a result, the present disclosure enables the signal processing unit 17e to process the scattered light vector r belonging to block K. i The rotation angle α used when calculating the frequency average of i In the prior art, the rotation angle calculated by the signal processing unit 17d in block K is used as the rotation angle itself, which requires the signal processing unit 17d to store all of the scattered light vector data belonging to block K in the computer memory, thereby reducing the computer memory required.

[0060] However, the length of the measurement time Mt per block is determined by the rotation angle α iThe measurement time Mt per block is calculated with sufficient accuracy by the rotation angle α i is taken as long as possible to calculate, and is taken small relative to the time scale of the change in optical characteristics such as the oscillation frequency of the laser provided in the CW light source 1, the temperature change of the optical fiber 6 under test itself, and the application of large dynamic strain to the optical fiber 6 under test. i This setting is possible in many situations. For example, if M is set to about 100, the rotation angle α i It has been experimentally found that an accuracy of 100 ms can be obtained (Non-Patent Document 3), and even if the optical pulse transmission period t is set to 1 ms, Mt is about 100 ms, which is considered to be sufficiently fine when the time scale is 1 s or more due to changes over time in optical characteristics such as the oscillation frequency of the laser provided in the CW light source 1, changes in the temperature of the optical fiber 6 under test itself, or the application of large dynamic strain to the optical fiber 6 under test.

[0061] The device of the present disclosure can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network. The program of the present disclosure is a program for causing a computer to realize each functional unit of the device according to the present disclosure, and is a program for causing a computer to execute each step of a method executed by the device according to the present disclosure. [Explanation of symbols]

[0062] 1:CW light source 2: Coupler 3: Optical modulator 4: Light pulse 5: Circulator 6: Optical fiber under test 7:90 degree optical hybrid 13, 14: Balance detector 15, 16: Electrical signal 17: Signal processing device 17a, 17b: AD conversion function element 17c, 17d: signal processing section 31: Measuring equipment

Claims

1. Obtaining measurement data of scattered light from an optical fiber when multiple optical pulses with different optical frequencies are scattered, A scattered light vector r of scattered light at each optical frequency in a predetermined time range in which an arbitrary point of the optical fiber can be measured ｉ Calculate Scattered light vector r for each optical frequency ｉ over the time range, The time-averaged vector r obtained by the averaging ｉ＿ａｖｅｔ The rotation angle α for correcting the phase of each optical frequency is ｉ Calculate Scattered light vector r for each optical frequency ｉ The phase of is rotated by an angle α ｉ By rotating the scattered light vector r ｉ Correct the phase of Signal processing device.

2. the time range is the time range of any one of a plurality of blocks when the acquisition time of the measurement data is divided into a plurality of blocks, Scattered light vector r for each light frequency for each block ｉ Correct the phase of The signal processing device according to claim 1 .

3. The rotation angle α calculated in the previous block ｉ Using the scattered light vector r ｉ Correct the phase of The signal processing device according to claim 2 .

4. an AD conversion functional element that converts the in-phase component and quadrature component of the scattered light into digital signals separately; The in-phase component I of the digital signal output from the AD conversion function element ｄｉｇｉｔａｌ and the quadrature component Q ｄｉｇｉｔａｌ , the signal I ｉ and signal Q ｉ an optical frequency separation unit for separating the optical signal into The signal I output from the optical frequency separation unit ｉ and signal Q ｉ Using the scattered light vector r ｉ and the calculated scattered light vector r ｉ over the time range, and the time-averaged vector r obtained by the averaging ｉ＿ａｖｅｔ Using the rotation angle α ｉ a rotation angle calculation unit that calculates The rotation angle α calculated by the rotation angle calculation unit ｉ The scattered light vector r calculated by the rotation angle calculation unit is calculated using ｉ a phase correction unit that corrects the phase of the Equipped with The processes in the AD conversion function element, the optical frequency separation unit, and the rotation angle calculation unit can be executed independently and in parallel. The signal processing device according to claim 1 .

5. Rotation angle α ｉ Vector R after rotating ｉ is frequency averaged, Frequency average vector R after frequency averaging ａｖｅｆ Angle θ ａｖｅｆ Calculate Angle θ ａｖｅｆ Calculate the vibration waveform using The signal processing device according to claim 1 .

6. a measuring device for measuring scattered light generated by scattering a plurality of optical pulses having different optical frequencies in an optical fiber; The measurement data of the scattered light measured by the measuring device is acquired, and the scattered light vector r of the scattered light at an arbitrary point of the optical fiber is calculated. ｉ and the calculated scattered light vector r ｉ a signal processing device according to claim 1 , which calculates a phase change of A measurement system comprising:

7. A signal processing method for performing signal processing of measurement data of scattered light obtained by scattering a plurality of optical pulses with different optical frequencies in an optical fiber, the method comprising: A scattered light vector r of scattered light at each optical frequency in a predetermined time range in which an arbitrary point of the optical fiber can be measured ｉ Calculate Scattered light vector r for each optical frequency ｉ over the time range, The time-averaged vector r obtained by the averaging ｉ＿ａｖｅｔ The rotation angle α for correcting the phase of each optical frequency is ｉ Calculate Scattered light vector r for each optical frequency ｉ The phase of is rotated by an angle α ｉ By rotating the scattered light vector r ｉ Correct the phase of Signal processing methods.

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