CN104034409A - Distributed optical fiber vibration sensing method and system based on pulse code external modulation - Google Patents

Abstract

The invention discloses a distributed optical fiber vibration sensing method and a system thereof based on pulse code external modulation, wherein the method comprises the following steps: selecting a reverse echo curve obtained by continuously transmitting light pulses for K times, presetting average times and interval parameters, and obtaining a plurality of average curves; and combining the normalized average curves into a 2-dimensional signal matrix Y, selecting a range matrix to calculate local range, evaluating the vibration intensity of the sensing optical fiber according to each element in the range matrix, obtaining the vibration space position, and extracting the ith data of each curve in the echo curve after decoding and delaying to obtain a vibration time domain sampling signal. The system comprises: the photoelectric detector forms an electric signal, the signal acquisition conditioning device performs amplification and analog-to-digital conversion to form a digital signal, and the digital signal is sent to a computer to complete decoding, time delay, positioning and time domain extraction processing, so that the vibration condition along the distributed sensor is obtained. The invention meets various vibration detection and monitoring applications, in particular to long-distance pipeline monitoring and perimeter security protection.

Description

Distributed optical fiber vibration sensing method based on pulse code external modulation and system thereof

Technical field

The present invention relates to sensory field of optic fibre, relate in particular to a kind of distributed optical fiber vibration sensing method and system thereof based on pulse code external modulation.

Background technology

The features such as distributed optical fiber sensing system, because it is highly sensitive, is not subject to electromagnetic interference (EMI), and sensing range is wide, and cost is low, are widely used in long distance oil-gas pipeline monitoring and circumference security protection, and the fields such as building structure health monitoring, are the study hotspots of nearly many decades.

Mach-Zehnder/Sagnac interferometer Distributed optical fiber sensor system, utilizes the phase differential being caused by external disturbance in detection two sensing light paths to change, and positions by the method for relevant time delay estimation, can carry out good perception to vibration.But due to the difficulty of the definite time delay of Time Delay Estimation Based itself, make the method positioning precision not high, heavy to the accurate difficult judgment in oscillation point.

The Ruili scattering phenomenon occurring when distributed optical fiber sensing system based on optical time domain reflectometer (OTDR) technology utilizes light wave to transmit in optical fiber, changes and accurate positioning optical waveguides trouble spot in the loss that detects dorsad Rayleigh scattering light intensity and obtain optical fiber.Because this technology is that Rayleigh scattering light intensity is measured, therefore its to measure remolding sensitivity lower and only can respond the variation of quiescent dissipation.

Based on Φ-OTDR (phase sensitivity OTDR) technology of relevant Rayleigh scattering, by using long coherence light source, detect the relevant result of light pulse back light, its interference technique can effectively realize dynamic response, can realize high position precision and high-sensitivity detection, especially for the detection of faint disturbing signal simultaneously.Meanwhile, because spatial resolution is relevant with pulse length, for spatial resolution, the very narrow pulse of normal use, common is tens of extremely hundreds of nanoseconds, and therefore back light intensity is faint, and after long Distance Transmission, signal resolution is lower, limited dynamic range.

In sum, in existing technical scheme, the higher but station-keeping ability of the sensing accuracy of Mach-Zehnder/Sagnac interferometer Distributed optical fiber sensor system a little less than, and be easily disturbed; The precision of OTDR formula distributed sensing system location is high but system sensitivity is poor; Phase sensitive OTDR system is having good performance aspect positioning precision and system sensitivity, but its pulse width is narrow, a little less than back light signal, and signal resolution rate variance, narrow dynamic range, distance sensing is limited.

Summary of the invention

The invention provides a kind of distributed optical fiber vibration sensing method and system thereof based on pulse code external modulation, the present invention is ensureing, under the condition of positioning precision, to overcome the problem of existing prison detection system sensing sensitivity deficiency, described below:

Based on a distributed optical fiber vibration sensing method for pulse code external modulation, said method comprising the steps of:

Choose encoder matrix S, its size is N*N, forms scatter echo curve L at photodetector place _i; With scatter echo curve L _ifor row vector, consider ground unrest simultaneously, form echoed signal matrix L;

Echoed signal matrix L is decoded and obtained the Rayleigh scattering signal ω ' of single echo, obtain N desired signal r simultaneously _i(t);

Choose the common K bar backward echo curve that continuous K light emitted pulse obtains, default average time M, spacing parameter n, obtains many averaged curve; Every averaged curve of gained is carried out to standardization;

Averaged curve after standardization is combined into 2 dimensional signal matrix Y, chooses the local extreme difference computer capacity of big or small a × b matrix, according to the each element y in scope matrix _ijevaluate the oscillation intensity of sensor fibre, and obtain oscillation space position, extract the i point data of every curve in decoding delay back echo curve, obtain the time-domain sampling signal of vibration.

Described echoed signal matrix L is:

L=[L ₁l ₂l _n] ^t=S[ω ₁ω ₂ω _n] ^t+ [e ₁e ₂e _n] ^t, wherein ω _ifor pulse P _idesirable scatter echo curve, e _ifor ground unrest, i=1,2 ..., N.

The Rayleigh scattering signal ω ' of described single echo is:

ω'＝[ω′ ₁?ω' ₂?…?ω' _N] ^T＝S ^-1·[L ₁?L ₂?…?L _N] ^T；

Described N desired signal r _i(t) be:

R _i(t)=ω ' _i(t+ (i-1) τ), its spatial resolution remains c is the light velocity in vacuum, n _cfor optical fibre refractivity, τ is pulse width.

A kind of distributed optical fiber vibration sensing system based on pulse code external modulation, comprise: LASER Light Source group, acousto-optic/electrooptic modulator and driver bank thereof, FPGA, multi-path light coupling mechanism, optical fiber circulator, photodetector, signal collection modulation device, computing machine and sensor fibre

Produce continuous light by described LASER Light Source group, via extremely driver bank formation pulsed light of described acousto-optic/electrooptic modulator, wherein said acousto-optic/electrooptic modulator extremely driver bank is write the programmed control break-make sequential of described FGPA by described computing machine, produce successively corresponding time delay, and make the pulsed light producing meet the encoder matrix S setting, multiplex pulse light forms coded pulse light at described multi-path light coupling mechanism place, coded pulse light injects described sensor fibre via described optical fiber circulator, in communication process, the back-scattering light producing is contrary with the input coding pulsed light direction of propagation, the light pulse Rayleigh scattering light of encoding inner produces interference effect, finally oppositely enter described photodetector by described optical fiber circulator and form electric signal, amplify and analog to digital conversion formation digital signal by described signal collection modulation device, send in described computing machine and complete decoding, time delay, location and the processing of extraction time domain, obtain distributed sensor Vibration Condition along the line.

The beneficial effect of technical scheme provided by the invention is: the present invention has overcome existing system signal resolution and spatial resolution restricts mutually, sensitivity is low, the problem of noise level restriction dynamic range.And this system have distribution type fiber-optic prison detection system peculiar distributed, be subject to the features such as the external interference such as electromagnetism are little, and easy for installation, can well meet various vibration detection and monitoring and measuring application, the pipeline monitoring of especially long distance and circumference security protection etc.

Brief description of the drawings

Fig. 1 is a kind of process flow diagram of the distributed optical fiber vibration sensing method based on pulse code external modulation;

Fig. 2 is a kind of structural representation of the distributed optical fiber vibration sensing system based on pulse code external modulation.

In accompanying drawing, the list of parts of each label representative is as follows:

1: LASER Light Source group; 2: light/electrooptic modulator and driver bank thereof;

3:FPGA; 4: multicoupler;

5: optical fiber circulator; 6: photodetector;

7: signal collection modulation module; 8: computing machine;

9: sensor fibre.

Embodiment

For making the object, technical solutions and advantages of the present invention clearer, below embodiment of the present invention is described further in detail.

In order to overcome the mutual restricting relation of distributed optical fiber sensing system signal resolution and spatial resolution, in the situation that keeping spatial resolution constant, the present invention carries out outer coded modulation by acousto-optic modulator (AOM) to the input pulse of distributed optical fiber sensing system, increase pulse width, improve input luminous energy, and then improve the energy of back light, reduces the ground unrest of system by decode procedure, the signal resolution of raising system simultaneously.Conventional pulse code mode has pseudo random sequence code, Gray code, Simplex coding (S coding) etc.

101: choose encoder matrix S, its size is N*N, form scatter echo curve L at photodetector place _i,

, choose as required the encoder matrix of N*N (the present invention recommends N>3) $S=\left[\begin{array}{cccc}{S}_{11}& S_{12}& \·\·\·& S_{1N}\\ S_{21}& S_{22}& \·\·\·& S_{2N}\\ \·\·\·& \·\·\·& \·\·\·& \·\·\·\\ S_{N1}& S_{N2}& \·\·\·& S_{\mathrm{NN}}\end{array}\right],$ Its inverse matrix is $S^{-1}=\left[\begin{array}{cccc}{S_{11}}^{\′}& {S_{12}}^{\′}& \·\·\·& {S_{1N}}^{\′}\\ {S_{21}}^{\′}& {S_{22}}^{\′}& \·\·\·& {S_{2N}}^{\′}\\ \·\·\·& \·\·\·& \·\·\·& \·\·\·\\ {S_{N1}}^{\′}& {S_{N2}}^{\′}& \·\·\·& {S_{\mathrm{NN}}}^{\′}\end{array}\right],$ Every a line S of S _i(i=1,2 ..., N) and be a pulse code.Individual pulse light P ₁(t) pulse width is τ, and scatter echo curve is ω ₁(t), N light source forms N the pulse P of time delay τ successively by N acousto-optic modulator AOM successively ₂(t)=S _i1p ₁(t-1 τ), P ₃(t)=S _i2p ₁(t-2 τ) ..., P _n(t)=S _iNp ₁(t-(N-1) τ), at N*1 coupling mechanism place, the pulse that 1 pulsewidth of pulse shaping that N pulsewidth is τ is N* τ, its actual scatter echo curve is L _i(i=1,2 ..., N).

102: realize coding N time according to encoder matrix S, with scatter echo curve L _ifor row vector, consider ground unrest simultaneously, form signal matrix L;

Through N coding, coded pulse echo curve forms signal matrix L:

L＝[L ₁?L ₂?…?L _N] ^T＝S·[ω ₁?ω ₂?…?ω _N] ^T+[e ₁?e ₂?…?e _N] ^T，

Wherein ω _i(i=1,2 ..., N) and be pulse P _i(i=1,2 ..., N) desirable scatter echo curve, e _i(i=1,2 ..., N) and be ground unrest.

103: echoed signal matrix L is decoded and obtained the Rayleigh scattering signal ω ' of single echo, obtain N desired signal r simultaneously _i(t);

Be ω '=[ω ' ₁ω ' ₂ω ' _n] ^t=S ^-1[L ₁l ₂l _n] ^t, wherein, ω ' ₁ω ' ₂ω ' _nrepresent that time delay is 0, τ, 2 τ ..., (N-1) the Rayleigh scattering echo curve of τ, carries out corresponding delay disposal simultaneously and obtains N desired signal r _i(t)=ω ' _i(t+ (i-1) τ), its spatial resolution remains c is the light velocity in vacuum, n _cfor optical fibre refractivity.

In above-mentioned testing process, realize in the situation that reducing System spatial resolution, improve signal resolution, reduce system noise.Use N light source to realize the coding to light pulse, make light impulse length improve N doubly, thereby make light echo energy improve N doubly, increased signal resolution; Use corresponding decoding matrix to decode at receiving end, restoring system spatial resolution reduces system background noise simultaneously, overall Hoisting System signal to noise ratio (S/N ratio), and then promote detection sensitivity and detection range.

104: choose the common K bar backward echo curve that continuous K light emitted pulse obtains, choose average time M, spacing parameter n, is total to obtain T=int ((K-M)/n)+1 averaged curve;

Choose that continuous K time (the present invention recommends K>100, and being the integral multiple of N) (every curve comprises n sampled point to the common K bar backward echo curve that obtains of light emitted pulse altogether, n=fs/f, wherein fs is sample frequency, f is light pulse repetition rate), i.e. r=[r ₁, r ₂, r ₃..., r _i..., r _k] ^t, wherein r _ithe signal curve that the i time light pulse obtaining after corresponding demodulation latencies obtains.

Choose average time M (M < K, the present invention recommends M > 20), spacing parameter n (the present invention recommends n=5), K article of curve adopted: the 1st article to M article average, n article averages to M-n+1 article ... altogether T=int ((K-M)/n)+1 averaged curve, that is:

$R_i=\frac{1}{M}\stackrel{j=(i-1)n+M}{\underset{j=(i-1)n+1}{\mathrm{\&Sigma;}}}{r}_i,j\&Element;[1,T]$

Wherein R _ibe i article of moving average curve obtained, int () is downward rounding operation.

105: every averaged curve of gained is carried out to standardization;

Aforesaid operations process implementation the location of vibration event and time-domain signal extract.Use modified moving average algorithm for further stabilization signal, reduce noise level, use standardization to remove the impact of background light intensity propagation attenuation on signal fluctuation amplitude, use mobile local two-dimentional extreme difference quick and precisely to locate vibration occurrence positions.

Establish x _ijbe the value of j sampled point of i article of averaged curve, the standardized method that uses can be expressed as:

$z_{\mathrm{ij}}=(x_{\mathrm{ij}}-{\stackrel{\&OverBar;}{x}}_i)/{\mathrm{\&sigma;}}_i,i\&Element;(1,T),j\&Element;(1,n)$

Wherein, z _ijfor the value of each sampled point in the each averaged curve after standardization, be the mean value of i article of averaged curve, σ _iit is the standard deviation of i article of averaged curve.

106: by the 2 dimensional signal matrix Y that to be combined into a size be T × n of the T bar averaged curve after standardization, choose the local extreme difference computer capacity of big or small a × b matrix, according to the each element y in scope matrix _ijevaluate the oscillation intensity of sensor fibre, and obtain oscillation space position, extract the i point data of every curve in decoding delay back echo curve, can obtain the time-domain sampling signal of vibration.

Wherein, the 2 dimensional signal matrix Y that the T bar averaged curve after standardization is combined into a size is T × n.Choose the local extreme difference computer capacity matrix of big or small a × b (recommendation 3*9 of the present invention).Centered by each element of signal matrix, calculate respectively each local pole difference taking a × b as size successively, extreme difference is calculated as y _ij=max (Y _ij)-min (Y _ij), i ∈ (1, T), and j ∈ (1, n).

Wherein y _ijbe that a matrix Y is capable by its i, centered by the element of j row, size is the element in the matrix of a × b.By y _ijas to the sensor fibre along the line evaluation on space i point and time j point, this value is larger, shows that vibration is stronger.According to formula A=(n _cci)/(2f) can determine oscillation space position.Extract decoding delay back echo curve r=[r ₁, r ₂, r ₃..., r _i..., r _k] ^tin the i point data of every curve, i.e. the i column data of matrix r, can obtain the time-domain sampling signal of vibration.

A kind of distributed optical fiber vibration sensing system based on pulse code external modulation, referring to Fig. 2, comprise: LASER Light Source group 1, acousto-optic/electrooptic modulator and driver bank 2 thereof, FPGA3, multi-path light coupling mechanism 4, optical fiber circulator 5, photodetector 6, signal collection modulation device 7, computing machine 8 and sensor fibre 9

Produce continuous light by LASER Light Source group 1, via acousto-optic/electrooptic modulator extremely driver bank 2 form pulsed light, wherein acousto-optic/electrooptic modulator extremely driver bank 2 write the programmed control break-make sequential of FGPA3 by computing machine 8, produce successively corresponding time delay, and make the pulsed light producing meet the encoder matrix S setting, multiplex pulse light forms coded pulse light at multi-path light coupling mechanism 4 places, coded pulse light injects sensor fibre 9 via optical fiber circulator 5, in communication process, the back-scattering light producing is contrary with the input coding pulsed light direction of propagation, the light pulse Rayleigh scattering light of encoding inner produces interference effect, the only light intensity stack of Rayleigh pulsed light between coding, finally oppositely enter photodetector 6 by optical fiber circulator 5 and form electric signal, amplify and analog to digital conversion formation digital signal by signal collection modulation device 7, send in computing machine 8 and complete decoding, time delay, location and the processing of extraction time domain, obtain distributed sensor Vibration Condition along the line.

The principle of work of this distributed optical fiber vibration sensing system is: choose encoder matrix S, its size is N*N, every a line (length is N) of selecting successively encoder matrix S is coding, computing machine 8 is controlled N acousto-optic/electrooptic modulator (AOM) and driver bank 2 thereof by FPGA3, utilize the long coherence light source of N identical wavelength, the short light pulse that the pulsewidth separately that forms N mutual time delay is τ, at coupling mechanism 4 places, Yi Ge N*1 road, making the short light pulse formation code length of N mutual time delay is N, and pulse width is the coded pulse light P of N τ _i(i=1,2 ..., N), and inject sensor fibre 9 via optical fiber circulator 5.When coded pulse light is propagated in sensor fibre 9, can form Rayleigh scattering dorsad, the Rayleigh scattering light of each short pulse is mutually interfered in pulsewidth τ separately, again can be by the electrical signal of computing machine 8 acquisition process via optical fiber circulator 5 final being converted on photodetector 6, along with coded pulse is along the propagation of sensor fibre 9, form scattered light echo sequence L at photodetector 6 places _i(i=1,2 ..., N).Realize coding N time according to encoder matrix S, with L _ifor row vector, form signal matrix L=[L ₁l ₂l _n] ^t.In the time that sensor fibre 9 is subject to vibration effect, can cause the variation of the interference light signal of output, computing machine 8 obtains the Rayleigh scattering signal ω ' of low noise single echo by decoding program.

Wherein, sensor fibre 9 will be to vibration signal sensitivity, can be single-mode fiber, can be also multimode optical fiber; Sensor fibre 9 both can make sensor and use, and also can be used as the link of data communication.

Coded system can be pseudo random sequence code, Gray code or Simplex coding (S coding), can be also other coded systems with decoding decrease of noise functions.

LASER Light Source 1 is multiple narrow-linewidth laser light sources, and to realize each inner being concerned with of coding in coded pulse, between each coding, irrelevant only light intensity superposes, and is conducive to obtain the signal of Rayleigh scattering.

Acousto-optic/electrooptic modulator and driver bank 2 thereof require have high modulation speed and high extinction ratio, and light pulse is narrower, and the spatial resolution of system is just higher; Higher extinction ratio, the light signal that system obtains is with regard to fewer optical noise that comprises, and the performance of system is better.

When specific implementation, photodetector 6 is based semiconductor avalanche photodide photodetector, can detect extremely faint light signal, and has the high speed of response.

Signal collection modulation device 7 comprises the unit such as amplification, collection and digital signal processing, is circuit structure commonly known in the art, and the embodiment of the present invention does not repeat this.

The embodiment of the present invention to the model of each device except do specified otherwise, the model of other devices does not limit, and all can as long as can complete the device of above-mentioned functions.

It will be appreciated by those skilled in the art that accompanying drawing is the schematic diagram of a preferred embodiment, the invention described above embodiment sequence number, just to describing, does not represent the quality of embodiment.

The foregoing is only preferred embodiment of the present invention, in order to limit the present invention, within the spirit and principles in the present invention not all, any amendment of doing, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.

Claims (4)

1. the distributed optical fiber vibration sensing method based on pulse code external modulation, is characterized in that, said method comprising the steps of:

Choose encoder matrix S, its size is N*N, forms scatter echo curve L at photodetector place _i; With scatter echo curve L _ifor row vector, consider ground unrest simultaneously, form echoed signal matrix L;

Echoed signal matrix L is decoded and obtained the Rayleigh scattering signal ω ' of single echo, obtain N desired signal r simultaneously _i(t);

Choose the common K bar backward echo curve that continuous K light emitted pulse obtains, default average time M, spacing parameter n, obtains many averaged curve; Every averaged curve of gained is carried out to standardization;

Averaged curve after standardization is combined into 2 dimensional signal matrix Y, chooses the local extreme difference computer capacity of big or small a × b matrix, according to the each element y in scope matrix _ijevaluate the oscillation intensity of sensor fibre, and obtain oscillation space position, extract the i point data of every curve in decoding delay back echo curve, obtain the time-domain sampling signal of vibration.

2. a kind of distributed optical fiber vibration sensing method based on pulse code external modulation according to claim 1, is characterized in that, described echoed signal matrix L is:

L=[L ₁l ₂l _n] ^t=S[ω ₁ω ₂ω _n] ^t+ [e ₁e ₂e _n] ^t, wherein ω _ifor pulse P _idesirable scatter echo curve, e _ifor ground unrest, i=1,2 ..., N.

3. a kind of distributed optical fiber vibration sensing method based on pulse code external modulation according to claim 1, is characterized in that, the Rayleigh scattering signal ω ' of described single echo is:

ω'＝[ω′ ₁?ω' ₂?…?ω' _N] ^T＝S ^-1·[L ₁?L ₂?…?L _N] ^T；

Described N desired signal r _i(t) be:

R _i(t)=ω ' _i(t+ (i-1) τ), its spatial resolution remains c is the light velocity in vacuum, n _cfor optical fibre refractivity, τ is pulse width.

4. the distributed optical fiber vibration sensing system based on pulse code external modulation, comprise: LASER Light Source group, acousto-optic/electrooptic modulator and driver bank thereof, FPGA, multi-path light coupling mechanism, optical fiber circulator, photodetector, signal collection modulation device, computing machine and sensor fibre, it is characterized in that

Produce continuous light by described LASER Light Source group, via extremely driver bank formation pulsed light of described acousto-optic/electrooptic modulator, wherein said acousto-optic/electrooptic modulator extremely driver bank is write the programmed control break-make sequential of described FGPA by described computing machine, produce successively corresponding time delay, and make the pulsed light producing meet the encoder matrix S setting, multiplex pulse light forms coded pulse light at described multi-path light coupling mechanism place, coded pulse light injects described sensor fibre via described optical fiber circulator, in communication process, the back-scattering light producing is contrary with the input coding pulsed light direction of propagation, the light pulse Rayleigh scattering light of encoding inner produces interference effect, finally oppositely enter described photodetector by described optical fiber circulator and form electric signal, amplify and analog to digital conversion formation digital signal by described signal collection modulation device, send in described computing machine and complete decoding, time delay, location and the processing of extraction time domain, obtain distributed sensor Vibration Condition along the line.