Signal processing method in phase OTDR

Abstract

The purpose of the present disclosure is to enable streaming of data, and to prevent deterioration in signal-to-noise ratio and vibration measurement accuracy without increasing the memory size requirement of a computer even if measurement is performed for a long period of time. A signal processing device and a signal processing method according to the present disclosure are a signal processing method and a signal processing method for performing signal processing on measurement data of scattered light obtained by scattering a plurality of optical pulses having different optical frequencies in an optical fiber. Scattered light vectors ri of scattered light at each light frequency within a preset time range in which any location of the optical fiber can be measured are calculated, the scattered light vectors ri of each light frequency within the time range are averaged, and a time-average vector riave obtained by the averaging is used to calculate the scattered light vector riave of the scattered light at each light frequency within the time range. A rotation angle [alpha] i for correcting the phase of each light frequency is calculated, and the phase of the scattered light vector ri of each light frequency is corrected by rotating the phase of the scattered light vector ri of each light frequency by the rotation angle [alpha] i.

Description

Technical Field

[0001] The present disclosure relates to a phase OTDR that measures the phase of scattered light from various locations of an optical fiber being measured. Background Art

[0002] As a method 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 (Non-Patent Document 1), which injects pulsed test light into the optical fiber being measured and detects backscattered light caused by Rayleigh scattering.

[0003] As one of the DAS methods, there is a phase OTDR (Optical Time Domain Reflectometry), which measures the phase of scattered light from various locations of the measured optical fiber and observes the time change of the phase. Phase OTDR is also called DAS-P (DAS-phase). DAS-P changes the phase linearly with respect to the change in the optical path length of the optical fiber caused by vibration, and its rate of change can also be considered to be roughly the same at various locations in the length direction of the optical fiber. Therefore, it is possible to perform quantitative measurement of vibration and faithfully reproduce the vibration waveform applied to the measured optical fiber (for example, non-patent document 2).

[0004] In DAS-P using optical pulses of a single optical frequency, due to the interference effect of scattered light within the pulse width, there will be a location where the scattered light intensity is small, resulting in degradation of sensitivity. As a method to prevent degradation of sensitivity, there is a method of performing optical frequency multiplexing and averaging signals at different optical frequencies (Non-Patent Document 3, Patent Document 1). This method utilizes the property that the location where the scattered light intensity becomes small changes at different optical frequencies.

[0005] In Non-Patent Document 3 and Patent Document 1, the following steps are specifically performed as an efficient averaging method.

[0006] Step S01: Using the measurement data, the difference in phase shift values ​​between the scattered light vector of the optical frequency component selected as the internal reference of the multiplexed optical frequency component and the scattered light vectors of other optical frequency components is calculated. Using the calculated difference in phase shift values, the rotation angle for correcting the phase shift of each optical frequency is calculated.

[0007] Step S02: After rotating the scattered light vector at each moment by the rotation angle, the vectors after rotation at different light frequencies are averaged to calculate a frequency average vector. The frequency average vectors at different moments are used to calculate the angle change of the frequency average vector.

[0008] Step S03: Using the angle change, the phase difference between two locations on the optical fiber that are separated by a gauge length is calculated, and phase connection processing is performed to calculate the vibration waveform generated in the interval between the two locations.

[0009] In particular, the details of step S01 are to perform the following specific steps. In which, the repetition interval of the pulses of the same optical frequency is set to t, that is, the sampling interval of the vibration is set to t, and the measurement data of M points from the measurement time 0 to (M-1)t (M is a natural number) is used, and the scattered light vector of the reference optical frequency (set to f1) at each time mt (m is an integer from 0 to (M-1)) is set to r1(mt,z) (depending on the distance z from the incident end due to the location of the optical fiber), and the scattered light vector of each other optical frequency f i The scattered light vector is r (i is an integer from 2 to N, N represents the multiplexing number of optical frequencies). i (mt, z) Here, conventionally, M is set to include all points of the measurement time or the first few points.

[0010] Step S01-1: Calculate the angle θ1(mt,z) of the scattered light vector r1(mt,z) of the reference optical frequency at each optical fiber location at each time. If the scattered light vector r1(mt,z) is considered as a complex vector on the complex plane, that is, a complex number, the angle θ1(mt,z) can be calculated by arg[r1(mt,z)]. Here, arg is an operator that gives the deflection angle of a complex number.

[0011] Step S01-2: The scattered light vector r of each optical frequency at each optical fiber location at each time i (mt, z) rotation angle -θ1(mt, z), set to r i_rot (mz, t). If the scattered light vector r i (mt, z) is set as a complex vector on the complex plane, then the rotated vector r can be calculated i_rot (mz, t) is exp[-θ1(mt, z)]*r i (mt, z).

[0012] Step S01-3: Rotate the scattered light vector of each optical frequency at each optical fiber point into the vector r i_rot (mt, z), the time average vector r is calculated by averaging M points where m is 0 to (M-1) as the measurement data used. i_avet (z). +arg[r i_avet The value of (z)] becomes the difference in phase shift value. In actual calculation, it is also possible to use vector sum instead of vector average of M points. No matter which one is used, the subsequent processing will get the same result.

[0013] Step S01-4: Using the deflection angle of the time-averaged vector, the rotation angle α of the scattered light vector of each optical frequency at each optical fiber point when rotating in step S02 is changed to i (z) is calculated as -arg[r i_avet (z)]. By rotating -arg[r i_avet (z)], the difference in phase shift can be corrected.

[0014] The rotation angle α given in step S01-4 i (z) is a value that effectively reduces noise by performing time averaging in the steps up to step S01-3. By using the rotation angle α i (z) Calculating the optical frequency average vector in step S02 can improve the signal-to-noise (SN) ratio of the final vibration waveform and suppress waveform distortion.

[0015] In step S01 of the above-mentioned prior art, the rotation angle of each optical frequency is calculated using the measurement data of M points from the measurement time 0 to (M-1)t (M is a natural number), and using the calculated rotation angle, in step S02, the measurement data of M points from the measurement time 0 to (M-1)t (M is a natural number) and the measurement data at other times are frequency averaged.

[0016] Prior art literature

[0017] Patent Literature

[0018] Patent Document 1: Japanese Patent Application Publication No. 2020-169904

[0019] Non-patent literature

[0020] Non-patent document 1: Ali.Masoudi, TPNewson, "Contributed Review: Distributed optical fiber dynamic strain sensing." Review of Scientific Instruments, vol.87, pp011501 (2016)

[0021] Non-patent document 2: Nishiguchi Kenichi, Lee Tetsukien, Guji Kuata, Yokoyama Mitsutoku, Masuda Shinzo, "Trial production of distributed acoustic wave sensor based on optical fiber and its signal processing", Journal of Information Science, 115(202), pp29-34 (2015)

[0022] Non-patent document 3: Yoshifumi Wakisaka, Daisuke Iida, Hiroyuki Oshida, and Nazuki Honda, "Fading Suppression ofΦ-OTDR With the New Signal ProcessingMethodology of Complex Vectors Across Time and Frequency Domains," J.LightwaveTechnol.39,4279-4293(2021) Summary of the invention

[0023] Problem that the invention aims to solve

[0024] The optimal value of the rotation angle calculated by the method of step S01 of the above-mentioned prior art will change with time due to the temporal change of optical characteristics such as the oscillation frequency of the laser, the temperature change of the measured optical fiber itself, the large dynamic strain applied to the measured optical fiber, etc. Therefore, in the long-term distributed vibration measurement, it is necessary to continuously update the optimal value of the rotation angle and perform the processing after step S02.

[0025] However, in the prior art described in non-patent document 3 and patent document 1, there is no method for performing the processing after step S02 while continuously updating the optimal value of the rotation angle. In addition, when the measurement data used in the rotation angle calculation is frequency averaged with the calculated rotation angle, the data cannot be stream processed, and the measurement data needs to be saved in the computer memory before the frequency averaging is completed.

[0026] The present disclosure aims to enable streaming of data, even for long measurements, to prevent degradation of the signal-to-noise ratio and vibration measurement accuracy without increasing the memory size requirements of the computer.

[0027] Measures taken to solve the problem

[0028] The present disclosure relates to a signal processing method, which performs processing after step S02 while continuously updating the optimal value of the rotation angle. The present disclosure can stream data and does not need to save the measurement data in the computer memory before the frequency averaging is completed.

[0029] Specifically, the measurement system of the present disclosure has:

[0030] a measuring device for measuring scattered light after a plurality of light pulses having different optical frequencies are scattered in an optical fiber; and,

[0031] The signal processing device of the present disclosure acquires the measurement data of the scattered light measured by the measuring device, and calculates the scattered light vector r of the scattered light at any point of the optical fiber. i Calculate and use the calculated scattered light vector r i The phase change at any point on the optical fiber is calculated.

[0032] The signal processing device of the present invention executes the signal processing method of the present invention. The signal processing method of the present invention is a signal processing method for performing signal processing on measurement data of scattered light after N optical pulses with different optical frequencies are scattered in an optical fiber.

[0033] The scattered light vector r of the scattered light at each optical frequency within a preset time range at an arbitrary point of the optical fiber can be measured. i Perform calculations;

[0034] The scattered light vector r for each light frequency within the time range i To average;

[0035] The time average vector r obtained by the averaging is used. i_avet , for the rotation angle α used to correct the phase of each optical frequency i Perform calculations;

[0036] By dividing the scattered light vector r of each light frequency i The phase rotation angle α i , the scattered light vector r for each light frequency i The phase is corrected.

[0037] The time range may be the time range of any block 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 processes the scattered light vector r of each optical frequency for each block. i Here, the signal processing device of the present disclosure can use the rotation angle α calculated in the previous block i , for the scattered light vector r i The phase is corrected.

[0038] The signal processing device disclosed in the present invention comprises:

[0039] The AD conversion element converts the in-phase component of the scattered light into a digital signal alone;

[0040] AD conversion functional element, converting the orthogonal components of scattered light into digital signals separately;

[0041] The optical frequency separation unit separates the in-phase component I of the digital signal output from the AD conversion function element. digital and the orthogonal component Qdigital Separated into signals of each optical frequency I i and signal Q i ;

[0042] The rotation angle calculation unit uses the signal I output from the optical frequency separation unit. i and signal Q i Calculate the scattered light vector r i , within the time range, the calculated scattered light vector r i The time average vector r obtained by averaging is used i_avet Calculate the rotation angle α i ;and,

[0043] A phase correction unit uses the rotation angle α calculated by the rotation angle calculation unit. i , the scattered light vector r calculated by the rotation angle calculation unit i The phase of

[0044] The processing in the AD conversion function element, the optical frequency separation unit, and the rotation angle calculation unit may be executable independently and in parallel.

[0045] The signal processing device disclosed in the present invention can:

[0046] Rotated by angle α i Vector R i Perform frequency averaging;

[0047] The frequency average vector R after frequency averaging avef The angle θ avef Perform calculations;

[0048] Use angle θ avef Calculate the vibration waveform.

[0049] Furthermore, the above-mentioned disclosures can be combined as much as possible.

[0050] Effects of the Invention

[0051] By using the present disclosure, it is possible to measure vibration waveforms while preventing degradation of the signal-to-noise ratio and degradation of vibration measurement accuracy even in long-term distributed vibration measurements. In addition, the present disclosure is able to stream data while reducing the computer's memory size requirements, and in principle can be applied to real-time vibration waveform monitoring. Therefore, the present disclosure is able to stream data, and even in long-term measurements, it is possible to prevent degradation of the signal-to-noise ratio and vibration measurement accuracy without increasing the computer's memory size requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1A configuration example of a measuring device according to the present disclosure is shown.

[0053] Figure 2 An example of the light pulse of the present disclosure is shown.

[0054] Figure 3 The following shows the detailed processing of the signal processing unit 17d regarding the Kth block. DETAILED DESCRIPTION

[0055] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, the present disclosure is not limited to the embodiments shown below. These embodiments are merely examples, and the present disclosure can be implemented in various ways of changes and improvements based on the knowledge of those skilled in the art. In addition, in this specification and the accompanying drawings, the components with the same reference numerals represent the same components as each other.

[0056] Figure 1 The measurement system of the present disclosure includes a measurement device 31 that performs coherent detection using a 90-degree optical mixer 7 in a receiving system, and a signal processing device 17 that executes the signal processing method of the present disclosure.

[0057] The measuring device 31 uses a plurality of optical pulses 4 with different optical frequencies to measure the scattered light from the measured optical fiber 6. A single wavelength continuous light with an optical frequency of f0 is emitted from the CW light source 1 and is branched into reference light and probe light by the coupler 2. The probe light is shaped by the optical modulator 3 as follows: Figure 2 The light pulse 4 shown. The light pulse 4 is the i-th light frequency f i is set to 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 fiber length direction, i=1, 2, ..., N (N is an integer representing the multiplexing number of optical frequencies). Δf i is the modulation frequency given by the modulator 3, which is the offset relative to the laser frequency f0 of the CW light source 1. i , so that the intensity of scattered light at each point at each time is far enough away that different i can be regarded as unrelated to each other. The pulse width W corresponds to the spatial resolution.

[0058] The optical modulator 3 is an arbitrary device capable of generating an optical pulse 4 of a pulse width W at a vibrating sampling interval t, and may be composed of a plurality of devices. For example, modulation by a modulator based on an LN modulator such as an SSB (single side band) modulator may be used, or a frequency-variable AO modulator may be used. In order to increase the extinction ratio during pulsing, intensity modulation by a SOA (semiconductor optical amplifier) ​​or the like may be further performed.

[0059] The optical pulse 4 is incident on the measured optical fiber 6 via the circulator 5. The light scattered at each point in the length direction of the optical fiber 6 returns to the circulator 5 as backscattered light and is incident on one input end of the 90-degree optical mixer 7. The reference light branched by the coupler 2 is incident on the other input end of the 90-degree optical mixer 7.

[0060] The internal structure of the 90-degree optical mixer 7 may be anything as long as it has the function of a 90-degree optical mixer. Two of the four output ends of the 90-degree optical mixer 7 are detected by a balanced detector 13, and an analog in-phase component I is output. analog That is, the electrical signal 15. The remaining two output ends of the 90-degree optical mixer are detected by the balanced detector 14, which outputs the analog orthogonal component Q analog That is, the electrical signal 16. Thus, the light intensity of the in-phase component and the light intensity of the orthogonal component are measured for scattered light after a plurality of light pulses having different optical frequencies are scattered in the optical fiber.

[0061] The electrical signals 15 and 16 are sent to a signal processing device 17, which includes an AD conversion function element 17a and an AD conversion function element 17b capable of sampling without mixing up the frequency bands of the signals. The signal processing device 17 processes the digitized in-phase component I outputted from the AD conversion function element 17a and the AD conversion function element 17b. digital and the orthogonal component Q digital Specifically, the signal processing unit 17c converts the in-phase component I digital and the orthogonal component Q digital Separation: The light frequencies f constituting the light pulse 4 i The signal I of the scattered light caused by the light pulse (i=1, 2, ..., N) i and signal Q i .

[0062] That is, the signal processing unit 17c functions as an "optical frequency separation unit" by superimposing the in-phase components associated with all i on I. digital Q is formed by superposition of the orthogonal components associated with all i digital Signal processing is performed on each incident light frequency f0+f i In the case of a light pulse with a component, the in-phase component signal I is obtained. i and the orthogonal component signal Q i For separation. Specific signal processing methods, such as considering digital and Q digital Through the center frequency f0+Δf iA digital bandpass filter with a passband of 2 / W, etc. For example, when using an FIR (Finite Impulse Response) filter, a delay is generated according to the filter characteristics. Therefore, in order to compensate for the delay, the filtered signal is also processed by advancing the delayed time in the opposite direction.

[0063] If the filter characteristics of the digital bandpass filter are set to a specification that enables stream processing of the measurement data in consideration of the memory size of the computer used, etc., the measurement data is stream processed before the signal processing unit 17c. For example, when an FIR filter is used as a digital bandpass filter, if the number of taps of the filter is too large or the number of significant decimal points of the filter coefficient is too large, the memory and calculation speed of the computer used become unsuitable for stream processing, and therefore, the number of taps of the filter and the number of significant decimal points of the filter coefficient are set according to the memory and calculation speed of the computer used so that stream processing can be performed.

[0064] The signal processing units 17d, 17e, and 17f process the signals based on the signal I acquired by the signal processing unit 17c. i and signal Q i , perform continuous phase calculation. The role of each signal processing unit is as follows. Let the incident interval of the light pulse of the i-th light frequency, that is, the sampling interval of the vibration be t, and use the integer k to obtain the vibration data at the time kt. Figure 2 The interval between t1 and t1' is t. In addition, the distance from the incident end is z. By performing phase calculation for each distance z, the phase at each point in the measured optical fiber 6 can be calculated.

[0065] Signal processing unit 17d: functions as a "rotation angle calculation unit".

[0066] Specifically, using signal I i (kt, z) and signal Q i (kt, z), the scattered light vector r of the scattered light at the i-th optical frequency within a preset time range at which the position of the measured optical fiber 6 can be measured i (kt, z) is calculated. The calculated scattered light vector r i The (kt, z) data is continuously streamed to the signal processing unit 17e.

[0067] In addition, according to the scattered light vector r i (kt, z) calculate each optical frequency f i The rotation angle α i(z). 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 / updated in units of blocks of the time range. The rotation angle α calculated / updated for each block is i (z) is transmitted to the signal processing unit 17e. Here, in the present embodiment, a block is divided into a predetermined number of light pulses of the same frequency. The following is an example of calculating / updating the rotation angle for each measurement time Mt with a predetermined time range as the predetermined number of time points.

[0068] In the conventional method, all the measurement data are either processed as one block or the rotation angle is calculated using the first few measurement data and the calculated rotation angle is used for all the data. However, in the example of this embodiment, the rotation angle is updated at any time for each block.

[0069] That is, assuming that k=0 is the first point of the measurement data, and the rotation angle is calculated from the first point, then for example, k is the scattered light vector r from 0 to M-1. i The measurement data of (kt, z) becomes the first block, and k is M to 2M-1 becomes the second block. K is used as a symbol to distinguish the block number. For example, in the above example, k is 0 to M-1 for the block K=1, and k is m to 2M-1 for the block K=2. The Kth block is the measurement data of k is M(K-1) to MK-1. In order to calculate the rotation angle of each block, the value varies according to the block K, and the rotation angle is expressed as α i (z, K) The method of calculating the rotation angle in each block is performed in the same manner as step S01 in the conventional technique.

[0070] Figure 2 Detailed processing of the signal processing unit 17d regarding the Kth block is shown in FIG.

[0071] Processing S17d-0: As input to the signal processing unit 17d, signal I i (kt, z) and signal Q i (kt, z) is transmitted from 17c in the order of k from small to large.

[0072] Processing S17d-1: Based on the signal I at time kt i (kt, z) and signal Q i (kt, z) calculates the scattered light vector r i (kt, z). For example, let the imaginary unit be j, and calculate the following.

[0073] (Mathematical formula 1)

[0074] r i (kt, z) = I i(kt,z)+jQ i (kt, z) (1)

[0075] The calculated scattered light vector data is sequentially streamed to the signal processing unit 17e.

[0076] Process S17d-2:

[0077] The reference optical frequency is set to f1. However, since the reference optical frequency can be arbitrarily selected, it may not be f1. The angle θ1(kt,z) of the scattered light vector r1(kt,z) of the reference optical frequency at each optical fiber point at time kt is calculated. θ1(kt,z) can be expressed, for example, by the following formula.

[0078] (Mathematical formula 2)

[0079] θ1(kt,z)=arg[r1(kt,z)] (2)

[0080] Process S17d-3:

[0081] Let the scattered light vector r of each optical frequency at each optical fiber point at time kt be i (kt, z) rotates by an angle -θ1(kt, z), set to r i_rot (kz, t). i_rot (kz, t) can be expressed by the following formula, for example.

[0082] (Mathematical formula 3)

[0083] r i_rot (kz, t)=exp[-θ1(kt, z)]*r i (kt,z) (3)

[0084] Process S17d-4:

[0085] When time kt is the first time M(K-1) of the Kth block, the new preparation time average vector r i_avet (z, K), let r i_avet (z) = r i_rot (kz, t). When time kt is the second or later of the Kth block, r at time kt is i_rot (kz, t) is added to the time average vector up to time (k-1)t to update it to a new time average vector. i_avet (z, K) is represented by the following formula.

[0086] (Mathematical formula 4)

[0087] r i_avet (z, K) = r i_rot (kz,t)+ri_avet (x,K) (4)

[0088] Process S17d-5:

[0089] The r obtained in the stage ending at the time kt which is the last time MK-1 of the Kth block and ends at the processing S17d-4 is used. i_avet (z, K), the rotation angle α of each optical frequency using the Kth block i (z) is calculated. i (z) is represented by the following formula.

[0090] (Mathematical formula 5)

[0091] α i (z, K) = -arg[r i_avet (z,K)] (5)

[0092] This makes it possible to obtain the difference in phase shift value of each optical frequency included in the block.

[0093] Process S17d-6:

[0094] At the end of processing S17d-5, the rotation angle α i (z) is transmitted to the signal processing unit 17e.

[0095] The signal processing unit 17e: functions as a "phase correction unit" and executes the above-mentioned step S02.

[0096] The signal processing unit 17e uses the rotation angle α calculated by the signal processing unit 17d. i (z), corrected scattered light vector r i For example, the signal processing unit 17e converts each optical frequency f included in the K block into i The scattered light vector r i Rotated by angle α i (z) and calculate the frequency average vector R avef .

[0097] However, unlike the previous method, the rotation angle α i The rotation angle used in calculating the frequency average of the scattered light vectors belonging to a certain block K is updated for each block of time Mt, and therefore, in the present disclosure, the rotation angle calculated by the signal processing unit 17d using the previous block K-1 is used. That is, the detailed processing of the signal processing unit 17e for the Kth block is as follows.

[0098] Processing S17e-1: The scattered light vector r of each light frequency at time kt is i (kt, z) is rotated by the rotation angle α calculated in the K-1th blocki (z, K-1), calculate the rotated vector R i (kz, t). i (kz, t) is expressed by the following formula.

[0099] (Mathematical formula 6)

[0100] R i (kz, t) = exp(j·α i (z,K-1))·r i (kt,z) (6)

[0101] By calculating the vector R i (kz, t), can be used to calculate the scattered light vector r of each optical frequency i The difference in phase shift is corrected.

[0102] Process S17e-2: Calculate the rotated vector R i (kz, t) is the vector after frequency averaging. In addition, since the final result will not change regardless of vector averaging or vector synthesis (simple vector sum), in the actual calculation process, vector synthesis is performed and is set as the frequency average vector R avef (kz, t). avef (kz, t) is expressed by the following formula.

[0103] [Formula 7]

[0104]

[0105] Process S17e-3: Frequency average vector R avef The angle θ of (kz, t) avef (kz, t) is calculated and transmitted to the signal processing unit 17f. avef (kz, t) is expressed by the following formula.

[0106] [Mathematical formula 8]

[0107] θ avef (kz, t) = arg[R avef (kz, t)] (8)

[0108] In addition, in the first block of K=1, since there is no data of the previous block, the rotation angle is not obtained, and the steps of the signal processing unit 17e cannot be executed. Therefore, the measurement time of the first Mt is used as a prediction, and the subsequent processing of the signal processing unit 17e is not executed. Alternatively, only the scattered light vector r at the measurement time of the first Mt can be used. i (kt, z) is separately stored in a computer and calculated to a vibration waveform by a conventional method.

[0109] Signal processing unit 17f: executes the above-mentioned step S03.

[0110] The signal processing unit 17f uses the frequency average vector R obtained by the signal processing unit 17e. avef The angle θ avef (kz, t), calculates the phase change of the measured optical fiber 6 at any point. For example, the signal processing unit 17f calculates the phase difference between two points of the gauge length, performs phase connection processing, etc., and calculates the vibration waveform. The specific calculation method is the same as the conventional method.

[0111] The present disclosure is characterized by the signal processing units 17d and 17e. In the signal processing unit 17d, the measured signal I i and Q i Divide into blocks of time points M, and calculate / update the rotation angle α in units of blocks of measuring time Mt i , thereby corresponding to the temporal change of the optimal value caused by the temporal change of the optical characteristics such as the oscillation frequency of the laser light source 1, the temperature change of the measured optical fiber 6 itself, the large dynamic strain applied to the measured optical fiber 6, etc. By making the measurement time Mt of each block shorter than the time scale of the temporal change of the optical characteristics such as the oscillation frequency of the laser light source 1, the temperature change of the measured optical fiber 6 itself, and the large dynamic strain applied to the measured optical fiber 6, the rotation angle can be updated with sufficient precision.

[0112] With such a setting, even if the rotation angle α of the previous block K-1 calculated in the signal processing unit 17d is used, i , as the scattered light vector r belonging to block K is calculated in the signal processing unit 17e i The rotation angle α used for frequency averaging i In addition, the signal processing unit 17d rotates the previous block K-1 by an angle α i The signal processing unit 17e outputs the scattered light vector r, which is then updated in the signal processing unit 17d. i_avet (z) stage, the scattered light vector r i The data of (kt, z) is stored in the memory of the signal processing device 17.

[0113] As described above, in the present disclosure, the processing in 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 be independently and parallelly executed. i The rotation angle α used when averaging the frequenciesi Compared with the prior art in which the rotation angle calculated by the signal processing unit 17d is used in block K and the signal processing unit 17d needs to keep all the data of the scattered light vector belonging to block K in the computer's memory, the present invention can reduce the computer's memory.

[0114] However, the length of the measurement time Mt of each block is also related to the rotation angle α i By making the measurement time Mt of each block take a larger value, the rotation angle α can be calculated with sufficient accuracy. i By making the measurement time Mt of each block smaller relative to the temporal change of the optical characteristics such as the oscillation frequency of the laser light source 1, the temperature change of the measured optical fiber 6 itself, and the time scale of the large dynamic strain applied to the measured optical fiber 6, the rotation angle α can also be ensured. i In many cases, such a setting is possible. For example, as an experimental experience, if M is set to about 100, a sufficient rotation angle α can be obtained. i The accuracy of Mt is (non-patent document 3), but even if the transmission period t of the light pulse is set to 1 ms, Mt is about 100 ms, which is considered to be sufficiently precise when the time scale of the optical characteristics such as the oscillation frequency of the laser possessed by the CW light source 1, the temperature change of the measured optical fiber 6 itself, and the large dynamic strain applied to the measured optical fiber 6 is more than 1 s.

[0115] The device of the present disclosure can be implemented by a computer and a program, and the program can be recorded in a recording medium or provided through a network. The program of the present disclosure is a program for enabling a computer to implement each functional unit of the device of the present disclosure, and is a program for enabling a computer to execute each step of the method executed by the device of the present disclosure.

[0116] Description of Reference Numerals

[0117] 1: CW light source

[0118] 2: Coupler

[0119] 3: Optical modulator

[0120] 4: Light Pulse

[0121] 5: Circulator

[0122] 6: Measured optical fiber

[0123] 7: 90 degree optical mixer

[0124] 13, 14: Balanced detector

[0125] 15, 16: Electrical signal

[0126] 17: Signal processing device

[0127] 17a, 17b: AD conversion function element

[0128] 17c, 17d: Signal processing unit

[0129] 31: Measuring device.

Claims

1. Signal processing device, Acquiring measurement data of scattered light after a plurality of light pulses with different optical frequencies are scattered in an optical fiber; The scattered light vector r of the scattered light at each optical frequency within a preset time range at an arbitrary point of the optical fiber can be measured. i Perform calculations; The scattered light vector r for each light frequency within the time range i To average; The time average vector r obtained by the averaging is used. i_avet , for the rotation angle α used to correct the phase of each optical frequency i Perform calculations; By dividing the scattered light vector r of each light frequency i The phase rotation angle α i , the scattered light vector r for each light frequency i The phase is corrected.

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

3. The signal processing device according to claim 2, using the rotation angle α calculated in the previous block i , for the scattered light vector r i The phase is corrected.

4. The signal processing device according to claim 1, comprising: AD conversion functional element, converting the in-phase component and the orthogonal component of the scattered light into digital signals respectively; The optical frequency separation unit separates the in-phase component I of the digital signal output from the AD conversion function element. digital and the orthogonal component Q digital Separated into signals of each optical frequency I i and signal Q i ; The rotation angle calculation unit uses the signal I output from the optical frequency separation unit. i and signal Q i Calculate the scattered light vector r i , within the time range, the calculated scattered light vector r i The time average vector r obtained by averaging is used i_avet Calculate the rotation angle α i ; and, A phase correction unit uses the rotation angle α calculated by the rotation angle calculation unit. i , the scattered light vector r calculated by the rotation angle calculation unit i The phase of The processing in the AD conversion function element, the optical frequency separation unit, and the rotation angle calculation unit can be executed independently and in parallel.

5. The signal processing device according to claim 1, Rotated by angle α i Vector R i Perform frequency averaging; The frequency average vector R after frequency averaging avef The angle θ avef Perform calculations; Use angle θ avef Calculate the vibration waveform.

6. Measurement system, with: a measuring device for measuring scattered light after a plurality of light pulses having different optical frequencies are scattered in an optical fiber; and, The signal processing device according to any one of claims 1 to 5, wherein 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 any point of the optical fiber is i Calculate and calculate the scattered light vector r i The phase change is calculated.

7. A signal processing method for processing the measurement data of scattered light after a plurality of light pulses with different optical frequencies are scattered in an optical fiber, comprising: The scattered light vector r of the scattered light at each optical frequency within a preset time range at an arbitrary point of the optical fiber can be measured. i Perform calculations; The scattered light vector r for each light frequency within the time range i To average; The time average vector r obtained by the averaging is used. i_avet , for the rotation angle α used to correct the phase of each optical frequency i Perform calculations; By dividing the scattered light vector r of each light frequency i The phase rotation angle α i , the scattered light vector r for each light frequency i The phase is corrected.

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