CN107990970B - The method for eliminating the noise that declines in distribution type fiber-optic acoustic systems - Google Patents

The method for eliminating the noise that declines in distribution type fiber-optic acoustic systems Download PDF

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Publication number
CN107990970B
CN107990970B CN201711067989.8A CN201711067989A CN107990970B CN 107990970 B CN107990970 B CN 107990970B CN 201711067989 A CN201711067989 A CN 201711067989A CN 107990970 B CN107990970 B CN 107990970B
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reflectance curve
phase
polarization
module
state
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CN201711067989.8A
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CN107990970A (en
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何祖源
刘庆文
陈典
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上海交通大学
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01HMEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H9/00Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
    • G01H9/004Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors

Abstract

A method of eliminating the noise that declines in distribution type fiber-optic acoustic systems, by the way that in receiving end, the X state electric signal of the rayleigh backscattering light (RBS) to collected from chirped optical pulse and Y state electric signal are ranked up respectively in chronological order, and it is respectively divided into after subsignal by frequency range and matched filtering is carried out to each subsignal, then it handles to obtain the reflectance curve of phase rotation using polarization diversity, the elimination of interference fading and polarization decay is realized after superimposed.Present invention utilizes polarization diversity technologies to be superimposed two kinds of polarization state light signals, can directly eliminate interference fading, polarization decay, and then eliminate phase demodulating mistake, achievees the purpose that improve signal-to-noise ratio and accurate positionin.

Description

The method for eliminating the noise that declines in distribution type fiber-optic acoustic systems

Technical field

The present invention relates to a kind of technology in distributing optical fiber sensing field, specifically a kind of elimination distribution type fiber-optic sound The method of decline noise in wave system system.

Background technique

Distribution type fiber-optic sonic sensor (Distributed Fiber-optic Acoustic Sensor, DAS) is one It kind uses optical fiber as sensing probe, can detecte and position the strain signal of generation any position on optical fiber, and can be with Linearly obtain the sensor of strain signal waveform.When current most of DAS system structure is the light based on phase sensitive Domain reflectometer (Phase Sensitive Optical Time Domain Reflectometry,- OTDR).- OTDR knot There are many structure mutation, but basic principle is: emitting the light pulse of high coherence into sensor fibre, obtained using suitable demodulating algorithm On sensor fibre the strength information of the rayleigh backscattering light (Rayleigh Backscattering, RBS) of each reflection point and Phase information.- OTDR has certain advantage, for example system structure is simple and reliable, demodulating algorithm is simply easily realized, sensitivity It is high, can be detected with multiple spot etc..

Summary of the invention

The present invention will receive the influence of decline noise (Fading) for the existing DAS system based on Rayleigh scattering light, mention A kind of method for eliminating the noise that declines in distribution type fiber-optic acoustic systems out, is utilized polarization diversity technology for two kinds of polarization state lights Signal averaging, can directly eliminate interference fading, polarization decay, and then eliminate phase demodulating mistake, reach improve signal-to-noise ratio and The purpose of accurate positionin.

The present invention is achieved by the following technical solutions:

The present invention relates to it is a kind of elimination distribution type fiber-optic acoustic systems in decline noise method, by receiving end on time Between sequence the X state electric signal and Y state electric signal of the collected rayleigh backscattering light (RBS) from chirped optical pulse are distinguished It is ranked up, and is respectively divided into after subsignal by frequency range and matched filtering is carried out to each subsignal, then using at polarization diversity Reason obtains the reflectance curve of phase rotation, and the elimination of interference fading and polarization decay is realized after superimposed.

The polarization diversity processing refers to: with the X state of the rayleigh backscattering light of first chirped optical pulse and Y state electricity The reflectance curve of signal is conjugated phase as reference, with the reflectance curve of the rayleigh backscattering light of other chirped optical pulses Multiply, obtain the reflectance curve of phase rotation, averaged operation obtains after obtaining the reflectance curve of no interference fading and addition Eliminate the integrated reflectance curve of interference fading and polarization decay.

The reflectance curve further obtains the exact position of fibre strain by detecting its phase change, specifically Are as follows: integrated reflectance curve is obtained after being added all reflectance curves, its phase term obtain from after delay difference processing To differenced phase plot;Again to standard deviation is sought at the every bit on the differenced phase plot of each chirped optical pulse, when phase mark Quasi- difference is more than that threshold value is to determine that the optical fiber between corresponding points strains.

The present invention relates to a kind of de-noising units for realizing the above method, comprising: the sorting module that is sequentially connected, matched filtering Module, differential phase computing module and strain locating module, in which: sorting module is by the X state electric signal and Y state electricity after sequence Signal, which is divided into the subsignal of multiple frequency ranges and exports to matched filtering module, carries out frequency-division section matched filtering, matched filtering module It exports with handling to obtain integrated reflectance curve by polarization diversity after filtering to differential phase computing module, differential phase calculates Module extracts phase term from integrated reflectance curve and carries out obtaining phase difference curve, Ying Bianding from delay difference processing Position module to each point in the phase difference curve of each chirped optical pulse calculate standard deviation and judging obtain strain occur it is accurate Position.

Detailed description of the invention

Fig. 1 is distribution type fiber-optic acoustic save sensor systems figure;

Fig. 2 be signal generator output chirped pulse sequence when-frequency analysis figure.

Fig. 3 is the phase standard dygoram of embodiment output;

Fig. 4 is the strain waveform figure of embodiment output;

Fig. 5 is the strain signal power density spectrogram of embodiment output;

In figure: 1 being signal generating module, 2 be radio frequency signal amplifiers, 3 be laser, 4 be polarization-maintaining fiber coupler, 5 For acousto-optic modulator, 6 be erbium-doped fiber amplifier, 7 be optical fiber circulator, 8 be sensor fibre, 9 be optical splitter, 10 be polarization point Beam device, 11 be polarization beam apparatus, 12 be balance photodetector, 13 be balance photodetector, 14 be data collecting card, 15 be De-noising unit.

Specific embodiment

As shown in Figure 1, including: to be put as the signal generating module 1 and radiofrequency signal of signal generating module in the present embodiment Big device 2, the sound as the laser 3 and polarization-maintaining fiber coupler 4 of high coherent laser module, as chirped optical pulse generation module Optical modulator 5 and erbium-doped fiber amplifier 6, polarization-maintaining fiber coupler 4, optical fiber circulator 7, sensor fibre 8, as polarization diversity The optical splitter 9 of receiving module, balances photodetector 12 and balance photodetector 13 and as data at polarization beam apparatus 11 The data collecting card 14 and de-noising unit 15 of acquisition and processing module, in which: signal generating module generates mould to chirped optical pulse The chirped pulse sequence of block input power amplification, while trigger signal is sent to data acquisition and processing (DAP) module;High associated laser The height that laser 3 in module generates is relevant, the laser of frequency and power invariability is input to the first end of polarization-maintaining fiber coupler 4 The second port b output of mouth a, polarization-maintaining fiber coupler 4 detect light to chirped optical pulse generation module, polarization-maintaining fiber coupler 4 Third port c export local light to polarization diversity receiving module;The chirp of chirped optical pulse generation module output power amplification Light pulse sequence is inputted from the first port a of optical fiber circulator 7, is exported from second port b to sensor fibre 8;Sensor fibre 8 The RBS of generation enters polarization diversity receiving module from third port c into the second port b of optical fiber circulator 7;Polarization diversity The electric signal of X state and the electric signal of Y state of receiving module output switch to digital data transmission to de-noising list by data collecting card 14 Data processing is carried out in member 15.

The sensor fibre 8 is non-polarization-maintaining single-mode fiber, and overall length is 10 kilometers.

As shown in Fig. 2, the chirped pulse sequence that the signal generator 1 exports includes: the time intervals T such as multiple, phase With chirped frequency range delta F and same pulse width τpChirped pulse.

The time interval T of the chirped pulse sequence is 100 microseconds, and swept frequency range Δ F is 150~250MHz, pulse Width τpFor 2 microseconds.

The splitting ratio of the polarization-maintaining fiber coupler 4 is 90 to 10.

The bandwidth of the balance photodetector is AC-400MHz.

The sample rate of the data collecting card 14 is 1GSPS, and quantization resolution is 8 bits.

The present embodiment is related to the signal processing method of above system, comprising the following steps:

The X of the collected rayleigh backscattering light (RBS) from a chirped optical pulse of step 1, data collecting card 14 State electric signal { x (k);K=1 ..., 100000 } and Y state electric signal { y (k);K=1 ..., 100000 }, wherein k indicates length Unit, corresponding 10 kilometers of sensor fibres 8, the length of each length unit are 0.1 meter;When known totally 200 chirped light arteries and veins It when rushing, sorts in chronological order to all X state electric signals and Y state electric signal, it may be assumed that X state signal is { x (n, k);N=1 ..., 200;K=1 ..., 100000 }, Y state signal is { y (n, k);N=1 ..., 200;K=1 ..., 100000 };De-noising unit 15 three frequency ranges of generation are respectively the digital band-pass filter of 150-200MHz, 175-225MHz and 200-250MHz, will be each Electric signal is separated into three subsignals, it may be assumed that

{xl(n,k);N=1 ..., 200;K=1 ..., 100000;L=1,2,3 } and

{yl(n,k);N=1 ..., 200;K=1 ..., 100000;L=1,2,3 }.

Matched filtering module in step 2, de-noising unit 15 generates the matched filter { h of above-mentioned each subsignall (k);K=1 ..., 2000;L=1,2,3 }, matched filtering is done to each subsignal, obtains the reflectance curve of sensor fibre 8, That is:

Wherein: i is index, and * indicates conjugate operation.

Step 3, take first chirped optical pulse rayleigh backscattering light (RBS) X state reflectance curve { RXl(1, k);K=1 ..., 100000;L=1,2,3 } and Y state reflectance curve { RYl(1,k);K=1 ..., 100000;L=1,2, 3 } as reference, with other reflectance curve conjugate multiplications, the reflectance curve of phase rotation is obtained, it may be assumed that

With

{RYl' (n, k)=RYl(n,k)×RYl *(1,k);N=1 ..., 200;K=1 ..., 100000;L=1,2, 3}。

Step 4 does average calculating operation to the reflectance curve for the phase RZ that previous step obtains, and obtains no interference fading Reflectance curve, it may be assumed that

With

Step 5, being directly added without interference fading reflectance curve without interference fading reflectance curve and Y state to X state, Obtain the integrated reflectance curve of no interference fading and no polarization decline, it may be assumed that

R (n, k)=RX " (n, k)+RY " (n, k);N=1 ..., 200;K=1 ..., 100000;}.

Step 6, by the phase term of integrated reflectance curve, i.e. phase curve { φ (n, k)=angle [R (n, k)];N= 1,…,200;K=1 ..., 100000 }, postpone 50 length unit k, the phase curve of delay front and back done into calculus of differences, is obtained To differenced phase plot, it may be assumed that

{ Δ φ (n, k)=φ (n, k)-φ (n, k-50);N=1 ..., 200;K=1 ..., 100000 }.

Step 7, to standard deviation is sought at each point of all 200 differenced phase plots, obtain a phase standard difference curve,As shown in Figure 3;From k in the phase standard difference curve =97630 to k=97730 standard deviation is greater than 0.05rad, then determines that this section of optical fiber strains, actual range z= 9763 meters are arrived at z=9773m, and strain waveform is as shown in Figure 4.

Distribution type fiber-optic sonic sensor of the present embodiment based on no interference fading proposed by the present invention and polarization decay, from Fig. 3 can be seen that all decline points are eliminated, and the strain of sensor fibre end is accurately positioned, the strain waveform of extraction such as Fig. 4 With shown in Fig. 5, there is the extraordinary linearity and signal-to-noise ratio.

Above-mentioned specific implementation can by those skilled in the art under the premise of without departing substantially from the principle of the invention and objective with difference Mode carry out local directed complete set to it, protection scope of the present invention is subject to claims and not by above-mentioned specific implementation institute Limit, each implementation within its scope is by the constraint of the present invention.

Claims (7)

1. it is a kind of eliminate distribution type fiber-optic acoustic systems in decline noise method, which is characterized in that by receiving end on time Between sequence the X state electric signal and Y state electric signal of the collected rayleigh backscattering light from chirped optical pulse are carried out respectively Sequence, and be respectively divided into after subsignal by frequency range and matched filtering is carried out to each subsignal, then handled using polarization diversity To the reflectance curve of phase rotation, the elimination of interference fading and polarization decay is realized after superimposed;
The polarization diversity processing refers to: with the X state of the rayleigh backscattering light of first chirped optical pulse and Y state electric signal Reflectance curve as reference, the reflectance curve conjugate multiplication with the rayleigh backscattering light of other chirped optical pulses obtains To the reflectance curve of phase rotation, averaged operation is eliminated after obtaining the reflectance curve of no interference fading and addition The integrated reflectance curve of interference fading and polarization decay;
The matched filtering refers to: doing matched filtering to each subsignal by the matched filter of each subsignal, obtains The reflectance curve of sensor fibre;
The reflectance curve of the phase rotation, the X of the rayleigh backscattering light (RBS) by taking first chirped optical pulse State reflectance curve and Y state reflectance curve are obtained as reference with other reflectance curve conjugate multiplications;
The elimination of the realization interference fading and polarization decay refers to: being averaged to the reflectance curve of obtained phase RZ Operation obtains the reflectance curve of no interference fading, to X state without interference fading reflectance curve and Y state without interference fading Reflectance curve is directly added, and obtains the integrated reflectance curve of no interference fading and no polarization decline.
2. according to the method described in claim 1, it is characterized in that, the reflectance curve, further by detect its phase Variation obtains the exact position of fibre strain, specifically: integrated reflectance curve is obtained after being added all reflectance curves, it will Its phase term carries out obtaining differenced phase plot from after delay difference processing;Again to the differenced phase plot of each chirped optical pulse On every bit at seek standard deviation, when phase standard difference be more than threshold value be determine corresponding points between optical fiber strain.
3. according to the method described in claim 1, it is characterized in that, the reflectance curve specifically:
Wherein: i is index, and * indicates conjugate operation, { xl(n,k);N=1 ..., 200;K=1 ..., 100000;L=1, 2,3 } and { yl(n,k);N=1 ..., 200;K=1 ..., 100000;L=1,2,3 } it is subsignal, { x (n, k);N= 1,...,200;K=1 ..., 100000 } and { y (n, k);N=1 ..., 200;K=1 ..., 100000 } it is respectively X state and Y State signal, k indicate length unit.
4. according to the method described in claim 1, it is characterized in that, the described polarization diversity processing, comprising the following steps:
1. by the X state reflectance curve of the rayleigh backscattering light of first chirped optical pulse and Y state reflectance curve and other Reflectance curve conjugate multiplication obtains the reflectance curve of phase rotation, it may be assumed that
With
{RYl' (n, k)=RYl(n,k)×RYl *(1,k);N=1 ..., 200;K=1 ..., 100000;L=1,2,3 };
2. doing average calculating operation to the reflectance curve of obtained phase RZ, the reflectance curve of no interference fading is obtained, it may be assumed that
With
3. obtaining X state being directly added without interference fading reflectance curve without interference fading reflectance curve and Y state without dry Relate to the integrated reflectance curve of decline and no polarization decline, it may be assumed that R (n, k)=RX " (n, k)+RY " (n, k);N=1 ..., 200;K=1 ..., 100000;}.
5. according to the method described in claim 2, it is characterized in that, the phase change, by by all reflectance curve phases The phase term of integrated reflectance curve, i.e. phase curve { φ (n, k)=angle [R (n, k)] are extracted after adding;N=1 ..., 200; K=1 ..., 100000 }, postpone 50 length unit k, the phase curve of delay front and back done into calculus of differences, obtains differential phase Curve, it may be assumed that { Δ φ (n, k)=φ (n, k)-φ (n, k-50);N=1 ..., 200;K=1 ..., 100000 };To all 200 Standard deviation is sought at each point of differenced phase plot, obtains phase standard difference curve
6. a kind of de-noising unit for realizing any of the above-described claim the method characterized by comprising the row being sequentially connected Sequence module, matched filtering module, differential phase computing module and strain locating module, in which: sorting module is by the X after sequence State electric signal and Y state electric signal, which are divided into the subsignal of multiple frequency ranges and export to matched filtering module, carries out frequency-division section matching filter Wave, by polarization diversity handles to obtain integrated reflectance curve after matched filtering module matched filtering and exports to differential phase and calculate Module, differential phase computing module extract phase term from integrated reflectance curve and carry out obtaining phase from delay difference processing Potential difference component curve, strain locating module calculate standard deviation to each point in the phase difference curve of each chirped optical pulse and judge It obtains strain and exact position occurs.
7. a kind of detection system comprising de-noising unit described in claim 6 characterized by comprising mould occurs as signal The signal generating module and radio frequency signal amplifiers of block, as the laser and polarization-maintaining fiber coupler of high coherent laser module, As the acousto-optic modulator and erbium-doped fiber amplifier of chirped optical pulse generation module, polarization-maintaining fiber coupler, optical fiber circulator, Sensor fibre, as the optical splitter of polarization diversity receiving module, polarization beam apparatus, balance photodetector and balance photodetection Device and data collecting card and de-noising unit as data acquisition and processing (DAP) module, in which: signal generating module is to chirped light The chirped pulse sequence of pulse generation module input power amplification, while trigger signal is sent to data acquisition and processing (DAP) module; The height that laser in high associated laser module generates is relevant, the laser of frequency and power invariability is input to polarization-maintaining fiber coupler First port, the second port output detection light of polarization-maintaining fiber coupler is to chirped optical pulse generation module, polarization maintaining optical fibre coupling The third port of clutch exports local light to polarization diversity receiving module;The Zhou of chirped optical pulse generation module output power amplification Light pulse sequence of singing is exported from second port to sensor fibre from the input of the first port of optical fiber circulator;Sensor fibre generates RBS enter polarization diversity receiving module from third port into the second port of optical fiber circulator;Polarization diversity receives mould The electric signal of the X state of block output and the electric signal of Y state switch to digital data transmission into de-noising unit by data collecting card and carry out Data processing.
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