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WO2024195025A1 - Procédé de traitement de signal dans un otdr de phase - Google Patents

Procédé de traitement de signal dans un otdr de phase Download PDF

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Publication number
WO2024195025A1
WO2024195025A1 PCT/JP2023/011104 JP2023011104W WO2024195025A1 WO 2024195025 A1 WO2024195025 A1 WO 2024195025A1 JP 2023011104 W JP2023011104 W JP 2023011104W WO 2024195025 A1 WO2024195025 A1 WO 2024195025A1
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Prior art keywords
optical
frequency
scattered light
signal processing
phase
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Japanese (ja)
Inventor
佳史 脇坂
央 高橋
貴大 石丸
大輔 飯田
優介 古敷谷
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NTT Inc
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Nippon Telegraph and Telephone Corp
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Priority to JP2025507994A priority Critical patent/JPWO2024195025A1/ja
Priority to PCT/JP2023/011104 priority patent/WO2024195025A1/fr
Publication of WO2024195025A1 publication Critical patent/WO2024195025A1/fr
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means

Definitions

  • the present invention relates to a phase OTDR (Optical Time Domain Reflectometer) that measures the phase of scattered light from each point in a measured optical fiber.
  • phase OTDR Optical Time Domain Reflectometer
  • DAS Distributed Acoustic Sensing
  • DAS-P (DAS-phase) is a method that measures the phase of scattered light from each point in the optical fiber under test and measures the change in phase over time.
  • DAS-P the phase changes linearly with respect to the change 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).
  • Prior Art 1 makes use of the fact that the points where the scattered light intensity is low change with different optical frequencies.
  • Step S01 Using measured data from multiple times, 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 frequency.
  • Step S02 Rotate each frequency vector at each time by the rotation angle, and then average the rotated vectors of different frequencies to calculate a frequency average vector. Calculate the angular change of the frequency average vector.
  • Step S03 Using the angle change, the phase difference between two points separated by the gauge length is calculated, and a phase unwrapping process is performed to calculate a vibration waveform.
  • step S01 the details of step S01 are as follows: where t is the sampling interval of vibration, M points of measurement data from measurement time 0 to (M-1)t (M is a natural number) are used, the scattered light vector of the reference optical frequency (let it be f 1 ) at each time mt (m is an integer from 0 to (M-1)) is r 1 (mt, z) (dependent on the distance z from the input end since it depends on the optical fiber position), and the scattered light vector of each other optical frequency f i (i is an integer from 2 to N, N represents the frequency multiplexing number) is r i (mt, z).
  • the reference optical frequency can be set arbitrarily.
  • Step S01-1 Calculate the angle ⁇ 1 (mt,z) of the scattered light vector r 1 (mt,z) of the reference light frequency at each time and each optical fiber point. If the scattered light vector r 1 (mt,z) is considered to be a complex vector on the complex plane, that is, a complex number, the angle ⁇ 1 (mt,z) can be calculated by arg[r 1 (mt,z)], where arg is an operator that gives the argument of a complex number.
  • Step S01-2 Rotate the scattered light vector r i (mt,z) of each optical frequency at each time and each optical fiber point by an angle - ⁇ 1 (mt,z) to obtain r i _rot (mz,t). If the scattered light vector r i (mt,z) is a complex vector on a complex plane, the rotated vector r i _rot (mz,t) can be calculated as exp[- ⁇ 1 (mt,z)] ⁇ r i (mt,z).
  • Step S01-3 After rotating the scattered light vector of each optical frequency at each optical fiber point, the vector r i _ rot (mt, z) is averaged over M points, where m is the measurement data used, from 0 to (M-1), to calculate the time-averaged vector r i _ avet (z). In actual calculations, vector summation may be used instead of the vector average over M points. Regardless of which method is used, the same results will be obtained in subsequent processing.
  • Step S01-4 Calculate the rotation angle ⁇ i (z) when rotating the scattered light vector of each optical frequency at each optical fiber point in step S02 as ⁇ arg[r i _ avet (z)] using the argument of the time-averaged vector. Since the value of +arg[r i _ avet (z)] is the difference in phase offset value, it is possible to correct the difference in phase offset by rotating by ⁇ arg[r i _ avet (z)].
  • the rotation angle ⁇ i (z) given in step S01-4 is a value in which noise has been efficiently reduced due to the time averaging performed in steps up to S01-3.
  • step S01 of conventional technology 1 the rotation angle of each optical frequency is calculated using M points of measurement data 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 M points of measurement data from measurement time 0 to (M-1)t (M is a natural number) and on measurement data at other times.
  • the optimal value of the rotation angle calculated by the method of step S01 of conventional technology 1 varies over time due to changes over time in optical properties such as the laser oscillation frequency, changes in temperature of the optical fiber being measured itself, and application of large dynamic strain to the optical fiber being measured. Therefore, in long-term distributed vibration measurements, it is necessary to continuously update the optimal value of the rotation angle and perform the processes from step S02 onwards.
  • conventional technology 1 does not disclose a method for performing the processes from step S02 onwards while continuously updating the optimal value of the rotation angle. Furthermore, when frequency averaging is performed on the measurement data used to calculate the rotation angle at 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 completed.
  • Prior Application 1 PCT/JP2022/34477.
  • the processes from step S02 onwards are carried out while continuously updating the optimal value of the rotation angle.
  • the method described in Prior Application 1 will be referred to as Prior Application Invention 1.
  • Prior Application Invention 1 it is possible to respond to changes in the optimal value of the rotation angle, enabling streaming processing of data, and eliminating the need to hold measurement data in computer memory until frequency averaging is completed.
  • a window length Mt (M is a natural number corresponding to the number of data points) used in signal processing is set in advance, and the rotation angle is calculated using the measurement data contained within the window while moving the window, and this rotation angle is used to average the frequency vectors at the center of the window or at a time located a preset number of measurement data points behind.
  • Calculating the rotation angle while moving the window is a broad-sense moving average, and it is possible to obtain a rotation angle that changes smoothly without the discontinuous changes. By using a rotation angle that changes smoothly, discontinuous changes in the vibration waveform can be removed.
  • Prior Art 1 Prior Invention 1, and Prior Invention 2, when averaging vectors of different optical frequencies, an arbitrary optical frequency is used as a reference, and the scattered light vectors of an optical frequency different from the reference optical frequency are rotated, and then the vectors of the different optical frequencies are averaged.
  • Prior Invention 1 and Prior Invention 2 focus on the fact that the difference between the phase offset of a vector of an optical frequency different from the reference optical frequency and the phase offset of a vector of the reference optical frequency changes over time when large vibrations, temperature changes, etc. occur, and by updating the rotation angle in accordance with these changes, highly sensitive phase calculations are possible throughout the entire measurement time.
  • the vibration waveform finally obtained by updating the rotation angle in Prior Application Invention 1 and Prior Application Invention 2 has reduced phase noise and reduced effects of noise-induced phase connection errors compared to a vibration waveform obtained using a signal of only one of the selected reference optical frequency or any other optical frequency, even when large vibrations or temperature changes occur.
  • Vibration waveform distortion not caused by noise mainly includes vibration waveform distortion caused by interference between scattered light from Rayleigh scatterers randomly distributed in the optical fiber, and is difficult to remove by improving the device configuration, etc. Therefore, Prior Application Invention 1 and Prior Application Invention 2 have the problem of being unable to faithfully measure vibrations occurring in the optical fiber.
  • Patent Publication No. 2020-169904 (NTT, registered)
  • the purpose of this invention is to reduce vibration waveform distortion that is not caused by noise.
  • the phase OTDR system of the present invention comprises a measurement device that measures the phase of scattered light when a frequency-multiplexed optical pulse is reflected or scattered by an optical fiber, and a signal processing device that calculates the vibration waveform in the optical fiber using the phase measured by the measurement device.
  • the signal processing device of the present invention executes a signal processing method for generating a final vibration waveform from the signals of the different optical frequencies, suppressing vibration waveform distortion not caused by the noise.
  • a certain optical frequency is used as a reference, and the scattered light vectors of an optical frequency different from the reference optical frequency are rotated, and then the vectors of different optical frequencies are averaged, and the angular change in the average vector is used to calculate a vibration waveform, while switching between reference frequencies.
  • the present invention obtains vibration waveforms for the number of multiplexed optical frequencies, calculates the average of these vibration waveforms, and uses the averaged waveform to obtain the final vibration waveform.
  • the non-noise-induced vibration waveform distortion in the vibration waveform obtained based on each optical frequency reflects the vibration waveform distortion obtained using only the signal of each optical frequency. Therefore, the non-noise-induced vibration waveform distortion in the final vibration waveform obtained by averaging the vibration waveforms obtained using different reference optical frequencies is the average of the vibration waveform distortion obtained using only the signal of each optical frequency.
  • the vibration waveform distortions obtained using only the signal of each optical frequency are often independent of each other, and averaging them can suppress the vibration waveform distortion.
  • this invention it is possible to reduce vibration waveform distortion that is not caused by noise compared to prior art 1, while maintaining the characteristic of being able to measure large vibrations with higher sensitivity, compared to prior art 1 and prior art 2, which use the vibration waveform obtained using a single reference frequency as is. This makes it possible to measure vibrations occurring in optical fibers more faithfully.
  • the signal processing device of the present invention comprises: A signal processing device that calculates a vibration waveform in an optical fiber using a phase of scattered light obtained by reflecting or scattering a frequency-multiplexed optical pulse in the optical fiber, comprising: a functional unit that selects a reference optical frequency from among a plurality of frequency-multiplexed optical frequencies, rotates the phases of scattered light vectors of other optical frequencies among the scattered light vectors of the plurality of optical frequencies using the phase of the selected optical frequency as a reference, and then averages the scattered light vectors of the plurality of optical frequencies; Two or more of the plurality of optical frequencies are used as a reference to average the scattered light vectors of the plurality of optical frequencies.
  • the signal processing method of the present invention includes: A signal processing method executed by a signal processing device that calculates a vibration waveform in an optical fiber using a phase of scattered light resulting from reflection or scattering of a frequency-multiplexed optical pulse in the optical fiber, the method comprising: a step of selecting a reference optical frequency from among a plurality of frequency-multiplexed optical frequencies, rotating the phases of scattered light vectors of other optical frequencies among the scattered light vectors of the plurality of optical frequencies using the phase of the selected optical frequency as a reference, and then averaging the scattered light vectors of the plurality of optical frequencies; Two or more of the plurality of optical frequencies are used as a reference to average the scattered light vectors of the plurality of optical frequencies.
  • the optical fiber may be provided with a functional unit that calculates a vibration waveform in the optical fiber using the angular change of the averaged scattered light vector.
  • the functional unit may calculate a plurality of vibration waveforms with different standards and average the plurality of vibration waveforms.
  • all optical frequencies used in the averaging may be used as a reference.
  • the program of the present invention is a program for causing a computer to realize each function of the signal processing device of the present invention, and is a program for causing a computer to execute each procedure of the signal processing method executed by the signal processing device of the present invention.
  • FIG. 2 shows an example of the configuration of a processing unit in the prior art.
  • the processing procedure of the prior art is shown below.
  • the processing procedure of the prior art is shown below.
  • 1 illustrates an example of the configuration of a phase OTDR system according to an embodiment of the present invention.
  • 2 illustrates an example of a signal processing method according to an embodiment of the present invention.
  • 2 illustrates an example of a signal processing method according to an embodiment of the present invention.
  • Prior Application 1 In the method described in Prior Application 1, the processes from step S02 onwards are carried out while continuously updating the optimum value of the rotation angle.
  • Prior Application Invention 1 the method described in Prior Application 1 will be referred to as Prior Application Invention 1.
  • the rotation angle ⁇ i (z) of each optical frequency f i is calculated from the scattered light vector r i (kt, z) in the same manner as in the prior art 1.
  • the prior art 1 divides the measurement data into blocks of M time points, and calculates and updates the rotation angle in units of blocks of measurement time Mt.
  • K is used as a number symbol to distinguish the blocks.
  • the Kth block is the measurement data where k is from M(K-1) to MK-1. Since the rotation angle is calculated for each block, the value changes according to the block K, and the rotation angle is expressed as ⁇ i (z, K).
  • the calculation method of the rotation angle for each block is performed in the same manner as in step S01 of the conventional technique 1.
  • Prior Invention 1 The key points of Prior Invention 1 regarding signal processing of the measurement data of the Kth block are explained below.
  • the key operations are performed by processing units 101 and 102 as shown in FIG. 1.
  • a flowchart of processing unit 101 is shown in FIG. 2.
  • the measurement data obtained in the processing prior to processing unit 101 is sent to processing unit 101.
  • Step S101-1 Calculate the scattered light vector r i (kt,z).
  • Step S101-2 Set the reference frequency to f1 .
  • the reference frequency is selected arbitrarily, so it does not have to be f1 .
  • Calculate the angle ⁇ 1 (kt,z) of the scattered light vector r1 (kt,z) of the reference light frequency at each optical fiber point at time kt. For example, calculate the following: ⁇ 1 (kt, z) arg[r 1 (kt, z)] (101)
  • Step S101-3 The scattered light vector r i (kt,z) of each optical frequency at each optical fiber point at time kt is rotated by an angle ⁇ 1 (kt,z) to obtain r i _rot (kt,z).
  • r i_rot (kt, z) exp[-j ⁇ 1 (kt, z)] ⁇ r i (kt, z) (102)
  • j is the imaginary unit.
  • Step S101-5 Using r i _ avet (z, K) obtained at the stage where step S101-4 is completed when time kt is the last time MK-1 of the Kth block, calculate the rotation angle ⁇ i (z, K) of each optical frequency using the Kth block.
  • step S101-5 is completed, ⁇ i (z, K) is passed to the processing unit 102.
  • Processing unit 102 rotates and averages the scattered light vector r i of each light frequency f i using the rotation angle calculated by processing unit 101 to calculate a frequency average vector.
  • rotation angle ⁇ i is updated for each block of time Mt, and therefore in the present invention, the rotation angle used when calculating the frequency average of the scattered light vector belonging to a certain block K is the rotation angle calculated by processing unit 101 in the previous block K-1. That is, detailed processing by processing unit 102 for the Kth block is as follows.
  • Step S102-1 Rotate the scattered light vector r i (kt, z) of each light frequency at time kt by the rotation angle ⁇ i (z, K ⁇ 1) calculated in the K ⁇ 1th block, and calculate the rotated vector R i (kt, z).
  • R i (kt, z) exp (j ⁇ i (z, K-1)) ⁇ r i (kt, z) (105)
  • Step S102-2 Calculate a vector obtained by averaging the frequency of the rotated vector R i (kt, z). Note that since the final result is the same whether it is vector averaging or vector synthesis (simple vector sum), in the actual calculation procedure, vector synthesis is performed to obtain the frequency average vector R avef (kt, z).
  • the calculation method is as follows.
  • Step S102-3 Calculate the angle ⁇ avef (kt,z) of the frequency average vector R avef (kt,z) and transfer it to the subsequent processing unit 103.
  • the rotation angle is not yet acquired, and the procedure of processing unit 102 cannot be performed. Therefore, the measurement time for the first Mt is treated as a pre-measurement, and processing after processing unit 102 is not performed.
  • the angular change ⁇ avef (kt,z) of the obtained frequency average vector is used to calculate the phase difference between two points separated by the gauge length, and phase unwrapping processing etc. are performed to calculate the vibration waveform.
  • a specific calculation method a method similar to the calculation method of the vibration waveform from the phase in a general phase OTDR can be used.
  • Processing unit 101 divides the measurement data into blocks of M time points, and calculates and updates the rotation angle in units of blocks of measurement time Mt, thereby dealing with changes over time in the optimal value due to changes over time in optical properties such as the laser oscillation frequency, changes in the temperature of the measured optical fiber itself, and the application of large dynamic strain to the measured optical fiber.
  • the rotation angle can be updated with sufficient precision. With such settings, there is no problem in using the rotation angle calculated by the processing unit 101 in block K-1 as the rotation angle used when the processing unit 102 calculates the frequency average of the scattered light vectors belonging to block K.
  • the processing unit 101 does not need to hold the data of the scattered light vector r i (kt, z) in the memory of the computer at the stage where r i _avet (z) is updated in steps S101-3 and S101-4.
  • the length of the measurement time Mt per block also affects the calculation accuracy of the rotation angle.
  • the measurement time Mt per block long enough to calculate the rotation angle with sufficient accuracy, and setting it small relative to the time scale of changes in optical properties over time, such as the laser oscillation frequency, changes in temperature of the measured optical fiber itself, and the application of large dynamic strain to the measured optical fiber, the calculation accuracy of the rotation angle can be ensured. Such settings are possible in many situations.
  • Non-Patent Document 3 it has been experimentally found that a sufficient rotation angle precision can be obtained by setting M to approximately 100 (Non-Patent Document 3), but even if the pulse transmission period t is 1 ms, Mt will be approximately 100 ms, which is considered to be sufficiently fine when the time scale of the change over time in optical properties such as the laser oscillation frequency, the temperature change of the measured optical fiber itself, and the application of large dynamic strain to the measured optical fiber is 1 s or more.
  • the processing unit 101 calculates the scattered light vector r i (kt,z) and continuously streams it to the processing unit 102.
  • the scattered light vector from time (k-W)t to (k+W)t is used to calculate the rotation angle ⁇ i (kt,z) of each optical frequency f i used for the frequency averaging at time kt.
  • the calculated rotation angle ⁇ i (kt,z) is continuously streamed to the processing unit 101.
  • Step S201-2 Set the reference frequency to f1 .
  • the reference frequency is selected arbitrarily and does not have to be f1 .
  • Calculate the angle ⁇ 1 (kt,z) of the scattered light vector r1 (kt,z) of the reference light frequency at each optical fiber point at time kt. For example, it can be calculated as follows. ⁇ 1 (kt, z) arg[r 1 (kt, z)] (2d2)
  • Step S201-3 The scattered light vector r i (kt,z) of each optical frequency at each optical fiber point at time kt is rotated by an angle ⁇ 1 (kt,z) to obtain r i _rot (kt,z).
  • r i_rot (kt, z) exp [-j ⁇ 1 (kt, z)] ⁇ r i (kt, z) (2d3)
  • Step S201-4 Calculate the time average vector r i _avet ((k-1-W)t,z) calculated using the data from time (k-2W-1)t to time (k-1)t, r i _rot ((k-2W-1)t,z) at time (k-2W-1)t, and r i _rot (kt,z) at time kt.
  • the calculation formula can be exemplified as follows.
  • r i_avet ((k-W)t, z) r i_avet ((k-W-1)t, z) -r i_rot ((k-2W-1)t,z)+r i_rot (kt,z) (2d4-1)
  • r i_avet (kt, z) r i_avet (Wt, z) (2d4-3)
  • the processing unit 102 rotates the scattered light vector r i of each light frequency f i using the rotation angle calculated by the processing unit 101, and then averages it to calculate a frequency average vector.
  • the rotation angle is not constant, but rather uses sequential values updated over time that are streamed from the processing unit 101.
  • a different value is used for each time, not for each block. An example of the implementation of the calculation procedure is described below.
  • Step S202-1 The scattered light vector r i (kt, z) streamed from the processing unit 101 in step S201-1 is rotated by the rotation angle ⁇ i (kt, z) streamed from the processing unit 101 in step S201-5 to calculate the rotated vector R i (kt, z).
  • the calculation method can be exemplified as follows.
  • R i (kt, z) exp(j ⁇ i (kt, z)) ⁇ r i (kt, z) (2e1)
  • Step S202-2 Calculate a vector obtained by averaging the frequency of the rotated vector R i (kt,z). Note that since the final result is the same whether it is vector averaging or vector synthesis (simple vector sum), in the actual calculation procedure, vector synthesis is performed to obtain the frequency average vector R avef (kt,z).
  • the calculation method can be exemplified as follows.
  • Step S2-3 Calculate the argument ⁇ avef (kt,z) of the frequency average vector R avef (kt,z) and transfer it to the downstream processing unit 103.
  • the processing unit 103 uses the angular change ⁇ avef (kt,z) of the frequency average vector obtained by the processing unit 102 to calculate the phase difference between two points separated by the gauge length, and performs phase unwrapping processing, etc. to calculate a vibration waveform.
  • a specific calculation method a calculation method similar to that of a general DAS-P can be used.
  • streaming processing is possible if the memory capacity of the signal processing unit can hold all the necessary information, such as scattered light vectors, contained in the window length Mt. Even if the memory capacity is not sufficient to hold the necessary information, the same final result can be obtained by performing offline processing on all or part of the above steps.
  • the processing unit 101 streams the rotation angle ⁇ i ((k-W)t, z) calculated using the measurement data from time (k-2W)t to time kt to the processing unit 102, and the processing unit 102 performs frequency averaging at time (k-W)t. Therefore, the processing unit 102 needs to hold the data from time (k-W)t to time kt. Therefore, in cases where the processing units 101 and 102 cannot share data in memory, the amount of memory held by the processing unit 102 increases.
  • the rotation angle ⁇ i ((k-W)t,z) can be used for the frequency average at time (k-W+Delay)t after time (k-W)t (the variable Delay is an integer reflecting the amount of delay).
  • the rotation angle calculated using the measurement data within the range of a time window having a window length of 2W+1 can be used for the frequency average at a time after the center time of the time window.
  • the greater the time difference amount Delay the greater the difference between the optimal rotation angle ⁇ i ((k-W+Delay)t,z) at time (k-W+Delay)t and the rotation angle ⁇ i ((k-W)t,z) to be used. Therefore, it is desirable to keep it to a minimum value determined by memory capacity, etc.
  • the measurement system of the present invention comprises a measurement device and a signal processing device 17.
  • the measurement device is a phase OTDR that measures the phase of scattered light from each point of the optical fiber to be measured.
  • the phase OTDR of this embodiment measures the phase at a plurality of different optical frequencies using optical frequency multiplexing.
  • the phase OTDR outputs an in-phase component and a quadrature component, and the signal processing device 17 uses these to calculate a scattered light vector signal representing the phase, and calculates a vibration waveform using the scattered light vector signal.
  • the measurement system has the following configuration.
  • a continuous wave light with a frequency of f0 is emitted from a CW light source 1, and is branched into a reference light and a probe light by a coupler 2.
  • the probe light is shaped into an optical pulse 4 by an optical modulator 3.
  • f is selected so that the intensity of the scattered light at each time and each point is sufficiently separated to be considered uncorrelated between different i.
  • the pulse width P corresponds to the spatial resolution.
  • optical modulator 3 There is no specific designation for the type of optical modulator 3 as long as it can generate optical pulses 4, and there may be more than one type.
  • an SSB modulator or a frequency-tunable AO modulator may be used, and intensity modulation may be performed using an SOA (semiconductor optical amplifier) or the like to increase the extinction ratio in pulsing.
  • SOA semiconductor optical amplifier
  • the pulsed probe light 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 optical 90-degree hybrid 7.
  • the reference light branched by the coupler 2 is input to the other input of the optical 90-degree hybrid 7.
  • the internal configuration of the optical 90-degree hybrid may be anything as long as it has the function of an optical 90-degree hybrid.
  • Two of the four outputs of the optical 90-degree hybrid are detected by a balanced detector 13 to obtain an analog in-phase component I analog , which is an electrical signal 15.
  • the remaining two outputs of the optical 90-degree hybrid are detected by a balanced detector 14 to obtain an analog quadrature component Q analog, which is an electrical signal 16.
  • the electric signal 15 and the electric signal 16 are sent to a signal processing device 17 equipped with an AD conversion function element 17a and an AD conversion function element 17b capable of sampling the frequency band of the signal without aliasing.
  • Signal processing units 17d, 17e, 17f, and 17g continue to perform phase calculations.
  • the roles of each signal processing unit are as follows.
  • the pulse incidence interval, i.e., the vibration sampling rate, is set to t, and vibration data is acquired at time kt using an integer k.
  • the distance from the incidence end is set to z.
  • the signal processor 17d calculates the scattered light vector r i (kt,z) from I i (kt,z) and Q i (kt,z), and continuously streams the calculated scattered light vector r i (kt,z) data to the signal processor 17e.
  • the calculated rotation angle ⁇ i,x (kt,z) is continuously streamed to the signal processing unit 17d. However, for (i,x), calculations are performed for all possible combinations of the multiplexed optical frequencies.
  • the setting of the window length Mt is the same as that of the prior invention 2.
  • Step S17d-4 Using the time-average vector r i _rot,x (kt,z) when the reference optical frequency is f x , calculated using data from time (k-2W-1)t to time (k-1)t, r i _rot , x ((k-2W-1)t,z) at time (k-2W-1)t, and r i _rot,x (kt,z) at time kt, calculate the time-average vector r i _avet,x ((k-W)t,z) when the reference optical frequency is f x .
  • the calculation formula can be exemplified as follows.
  • r i_avet,x ((k-W)t,z) r i_avet,x ((k-W-1)t,z) -r i_rot,x ((k-2W-1)t,z)+r i_rot,x (kt,z) (d4-1)
  • a preliminary measurement is performed, or the time-averaged vector is calculated using the conventional technique 1.
  • Step S17d-5 From the time-averaged vector r i_avet,x ((k ⁇ W)t,z), the rotation angle ⁇ i,x ((k ⁇ W)t,z) of each optical frequency f i when each optical frequency f x is the reference optical frequency is calculated for all possible (i, x), and streamed to the signal processing unit 17e.
  • FIG. 6 shows a flowchart summarizing the main points of the signal processing units 17e to 17g.
  • Step S17e The signal processing unit 17e rotates the scattered light vector r i of each optical frequency f i using the rotation angle ⁇ i calculated by the signal processing unit 17d, and averages them to calculate a frequency average vector. Calculation is performed for all possible cases of the reference optical frequency f x . Specifically, the following steps are included.
  • Step S17e-1 The scattered light vector r i (kt,z) streamed from the signal processing unit 17d in step S17d-1 is rotated by the rotation angle ⁇ i,x (kt,z) streamed from the signal processing unit 17d in step S17d-5 to calculate the rotated vector R i,x (kt,z) when the reference light circumference is f x .
  • the calculation method can be exemplified as follows.
  • R i,x (kt, z) exp(j ⁇ i,x (kt, z)) ⁇ r i (kt, z) (e1)
  • Step S17e-2 Calculate a vector obtained by averaging the frequency of the rotated vector R i,x (kt,z). Note that since the final result is the same whether it is vector averaging or vector synthesis (simple vector sum), in the actual calculation procedure, vector synthesis is performed to obtain the frequency average vector R avef,x (kt,z).
  • the calculation method can be exemplified as follows.
  • Step S17e-3 Calculate the argument ⁇ avef,x (kt,z) of the frequency average vector R avef,x (kt,z) when the reference optical frequency is f x , and transfer it to the signal processing unit 17f.
  • Step S17f The signal processing unit 17f uses the angle change ⁇ avef,x (kt,z) of the reference optical frequency f x to calculate the phase difference between two points separated by the gauge length, and performs phase unwrapping and other processes to calculate the vibration waveform ⁇ x (kt,z).
  • a specific calculation method can be the same as the calculation method for the vibration waveform from the phase in a general phase OTDR.
  • the vibration waveform ⁇ x (kt,z) is streamed to the signal processing unit 17g. Calculation is performed for all possible f x .
  • Step S17g The signal processing unit 17g averages the vibration waveform ⁇ x (kt, z) with respect to x to calculate the final vibration waveform ⁇ (kt, z).
  • the waveform distortion of the vibration waveform ⁇ (kt,z) with respect to the actual vibration waveform is statistically suppressed compared to the waveform distortion of each vibration waveform ⁇ x (kt,z). Therefore, by using the vibration waveform ⁇ (kt,z), it is possible to perform measurement that is more faithful to the actual vibration waveform than the prior art 1 and prior art 2.
  • data can be processed by streaming, and it is possible to prevent 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. Even in the event of large vibrations or temperature changes, it is possible to reduce both the effects of phase noise and phase uncoupling errors associated with phase noise, as well as vibration waveform distortion that is not caused by noise, such as vibration waveform distortion caused by interference between scattered light from Rayleigh scatterers randomly distributed in the optical fiber.
  • the vibration waveforms that have been subjected to the phase unwrapping process are averaged in the processing by the signal processing units 17f and 17g.
  • the order of the specific calculation steps can be changed as long as the essence of the present invention is not compromised, for example, by carrying out averaging before carrying out the phase unwrapping process and then carrying out the phase unwrapping process.
  • the present invention is implemented based on Prior Invention 2.
  • the present invention is not limited to being based on Prior Invention 2, and can be widely applied to cases where Prior Invention 1 or other methods of averaging optical frequency multiplexed signals in a vector state are used as the basis.
  • the signal processing 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 over a network.
  • the program of the present disclosure is a program for realizing a computer as each functional unit of the device of the present disclosure, and is a program for causing a computer to execute each step of the method executed by the device of the present disclosure.
  • CW light source 2 Coupler 3: Optical modulator 4: Optical pulse 5: Circulator 6: Optical fiber to be measured 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, 17e, 17f, 17g: Signal processing unit 31: Measuring device

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)

Abstract

La présente invention concerne un dispositif de traitement de signal pour calculer une forme d'onde de vibration à l'aide des phases de lumière diffusée dans laquelle une impulsion de lumière multiplexée en fréquence est réfléchie ou diffusée par une fibre optique. Le dispositif de traitement de signal comprend une unité fonctionnelle pour sélectionner une fréquence optique à référencer parmi une pluralité de fréquences optiques qui sont multiplexées en fréquence, et moyenner des intensités de lumière diffusée de la pluralité de fréquences optiques après rotation d'une phase d'une autre fréquence optique parmi la pluralité de fréquences optiques sur la base de la phase de la fréquence optique, deux fréquences optiques ou plus parmi la pluralité de fréquences optiques étant utilisées en tant que référence pour moyenner les intensités de lumière diffusée de la pluralité de fréquences optiques.
PCT/JP2023/011104 2023-03-22 2023-03-22 Procédé de traitement de signal dans un otdr de phase Pending WO2024195025A1 (fr)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120067118A1 (en) * 2010-09-01 2012-03-22 Schlumberger Technology Corporation Distributed fiber optic sensor system with improved linearity
JP2020169904A (ja) * 2019-04-03 2020-10-15 日本電信電話株式会社 位相測定方法及び信号処理装置
WO2021075015A1 (fr) * 2019-10-17 2021-04-22 日本電信電話株式会社 Procédé et dispositif de test d'impulsion optique
JP7173313B2 (ja) * 2019-05-21 2022-11-16 日本電信電話株式会社 位相測定方法及び信号処理装置

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120067118A1 (en) * 2010-09-01 2012-03-22 Schlumberger Technology Corporation Distributed fiber optic sensor system with improved linearity
JP2020169904A (ja) * 2019-04-03 2020-10-15 日本電信電話株式会社 位相測定方法及び信号処理装置
JP7173313B2 (ja) * 2019-05-21 2022-11-16 日本電信電話株式会社 位相測定方法及び信号処理装置
WO2021075015A1 (fr) * 2019-10-17 2021-04-22 日本電信電話株式会社 Procédé et dispositif de test d'impulsion optique

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