CN104568119A - Optical fiber vibration sensing system of single light source pulse and sensing method thereof - Google Patents

Abstract

The invention discloses an optical fiber vibration sensing system of a single light source pulse and a sensing method of the optical fiber vibration sensing system of the single light source pulse. Under the control of FPGA, a code is formed by an optical pulse, coded pulsed light is formed through a coupler, a sensing optical fiber is injected through an optical fiber circulator, interference is generated by backward propagation scattered light generated in the process of the propagation of the sensing optical fiber, the interference enters into the coupler through the optical fiber circulator to be interfered with local oscillating light, and beat frequency signals are generated; the beat frequency signals are converted into electrical signals by a photoelectric detector, difference frequency components are filtered through a band-pass filter circuit, the reduction of beat frequency is achieved through a frequency mixer, at last the signals are collected and amplified by a collection card, in an upper computer, the respective amplitude modulation and demodulation of each control frequency are achieved, and decoding and location processing are carried out. The optical fiber vibration sensing system of the single light source pulse has the advantages, peculiar to a distributed optical fiber detecting and monitoring system, of being distributed and subject to small external disturbance such as electromagnetism, the installation is convenient, and various vibration detecting and monitoring application, especially for long distance pipeline monitoring and perimeter security, can be met well.

Description

A kind of optical fiber vibration sensing system of single light source pulse code and method for sensing thereof

Technical field

The present invention relates to sensory field of optic fibre, particularly relate to a kind of optical fiber vibration sensing system and method for sensing thereof of single light source pulse code.

Background technology

Distributed optical fiber sensing system is highly sensitive due to it, and not by electromagnetic interference (EMI), sensing range is wide, the features such as cost is low, and be widely used in long distance oil-gas pipeline monitoring and circumference security protection, 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, is utilized the phase differential change caused by external disturbance in detection two sensing light path, and is positioned by the method that associated time delays is estimated, can carry out good perception to vibration.But because Time Delay Estimation Based itself determines the difficulty of time delay, make the method positioning precision not high, heavy to the accurate difficult judgment in oscillation point.

The Ruili scattering phenomenon occurred when distributed optical fiber sensing system based on optical time domain reflectometer (OTDR) technology utilizes light wave to transmit in a fiber, is detecting the intensity of Rayleigh scattering light dorsad to obtain the Dissipation change also accurate positioning optical waveguides trouble spot of optical fiber.Because this technology measures the intensity of Rayleigh scattering light, therefore its measurement sensistivity is lower and only can respond the change of quiescent dissipation.

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

Based on pulse modulated Φ-OTDR, effectively on the basis ensureing spatial resolution, improve distance sensing, but owing to keeping separate between each modulating pulse of needs, so need multiple light source to realize, its system complexity is higher, and cost is also higher.

Summary of the invention

The invention provides a kind of optical fiber vibration sensing system and method for sensing thereof of single light source pulse code, the present invention, not increasing on the basis of system complexity, passes through pulse code, successfully improve injection luminous energy, inhibit shot noise, improve distance sensing, described below:

A kind of optical fiber vibration sensing system of single light source pulse code, be made up of LASER Light Source, FPGA, acousto-optic modulator group, optical fiber circulator, coupling mechanism, photodetector, signal collection modulation device, bandwidth-limited circuit, frequency mixer, host computer and sensor fibre

LASER Light Source produces continuous light, the acousto-optic modulator group different via controlled frequency is converted to light pulse, under the control of FPGA, light pulse forms coding, coded pulse light is formed by coupling mechanism, sensor fibre is injected by optical fiber circulator, the scattered light of propagation dorsad produced in its communication process produces interferes, coupling mechanism is entered via optical fiber circulator, interference with local oscillator light, produce beat signal, photodetector is converted into electric signal, the electric signal formed is through bandwidth-limited circuit filtering difference frequency component, the reduction of beat frequency is realized again via frequency mixer, last by capture card collection and amplifying signal, in host computer, realize the respective demodulation of each controlled frequency, carry out again decoding and localization process.

Described method for sensing comprises the following steps:

Host computer controls the different acousto-optic modulator group of N number of controlled frequency by FPGA, and making the short light pulse of N number of mutual time delay form code length at coupling mechanism place, N*1 road is N, and pulse width is the coded pulse light of N* τ, and injects sensor fibre via optical fiber circulator;

The Rayleigh scattering light of coded pulse light is interferenceed with the local oscillator light from LASER Light Source, forming frequency f _iand Δ f _ijbat ripple, be converted into corresponding electric signal via photodetector;

By choosing the controlled frequency of acousto-optic modulator group, the filter result of bandwidth-limited circuit and default sine wave being carried out mixing, obtains the bat ripple frequency after frequency reducing;

Host computer, by carrying out demodulation to the bat signal of the bat ripple frequency of frequency after frequency reducing, obtains the Rayleigh scattering signal of single encoded pulsed light;

By carrying out mobile Difference Calculation to the Rayleigh scattering signal of single encoded pulsed light, obtain the Vibration Condition that sensor fibre is along the line.

The beneficial effect of technical scheme provided by the invention is: the present invention, not increasing on the basis of system complexity, by pulse code, successfully improves injection luminous energy, inhibits shot noise, improve distance sensing; Improve the detectable minimum intensity of light of system further and Background suppression scattering by Heterodyne detect simultaneously, and on the basis of heterodyne detection, demodulation of the response of each coded pulse, make still can realize Code And Decode under same light source, further increase distance sensing and system sensitivity.This optical fiber vibration sensing system structure is simple, signal resolution is high, and noise level is low, highly sensitive, positioning precision is high, overcomes existing system complex structure, cost is high, simultaneously its signal resolution and spatial resolution restricts mutually, sensitivity is low, the problem of noise level restriction dynamic range.And this system have distributed specific to distribution type fiber-optic prison detection system, by features such as the external interference such as electromagnetism are little, and easy for installation, various vibration detection and monitoring and measuring application can well be met, the Monitoring Pinpelines of especially long distance and circumference security protection etc.

Accompanying drawing explanation

Fig. 1 is a kind of structural representation of optical fiber vibration sensing system of single light source pulse code;

Fig. 2 is a kind of process flow diagram of optical fiber vibration sensing method of single light source pulse code.

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

1, LASER Light Source; 2,1:99 coupling mechanism;

3, the first multicoupler; 4, the acousto-optic modulator group of different controlled frequency;

5, the second multicoupler; 6, optical fiber circulator;

7, sensor fibre; 8,1:1 coupling mechanism;

9, photodetector; 10, bandwidth-limited circuit;

11, frequency mixer; 12, signal generator;

13, low-pass filter circuit; 14, signal collection modulation module;

15, host computer; 16, FPGA.

Embodiment

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

Embodiment 1

A kind of optical fiber vibration sensing system of single light source pulse code, see Fig. 1, this optical fiber vibration sensing system is made up of acousto-optic modulator group 4, second multicoupler 5 of LASER Light Source 1,1:99 coupling mechanism 2, first multicoupler 3, different controlled frequency, optical fiber circulator 6, sensor fibre 7,1:1 coupling mechanism 8, photodetector 9, bandwidth-limited circuit 10, frequency mixer 11, signal generator 12, low-pass filter circuit 13, signal collection modulation module 14, host computer 15 and FPGA16.

The continuous light of narrow linewidth is produced by LASER Light Source 1, detection light and local oscillator light is produced via 1:99 coupling mechanism 2, detection light is divided into N way to detect light through the first multicoupler 3, each way detection light forms multiplex pulse light via acousto-optic modulator group 4, wherein acousto-optic modulator group 4 is write the programmed control break-make sequential of FGPA16 by host computer 15, produce corresponding time delay successively, and the encoder matrix S pulsed light of generation being met set, multiplex pulse light forms coded pulse light at the second multicoupler 5 place, coded pulse light injects sensor fibre 7 via optical fiber circulator 6, in communication process, the back-scattering light produced is contrary with the input coding pulsed light direction of propagation, the light pulse Rayleigh scattering light of encode internal produces interference effect, Rayleigh pulsed light between coding also produces disadvantageous interference, finally enter 1:1 coupling mechanism 8 back through optical fiber circulator 6, in 1:1 coupling mechanism 8, scattered light is interferenceed with local oscillator light, form the bat ripple of AOM controlled frequency and AOM controlled frequency difference frequency, electric signal is formed via photodetector 9, via bandwidth-limited circuit 10 filtering difference frequency signal, via the default sinusoidal wave mixed frequency that frequency mixer 11 and signal generator 12 produce, reduce beat frequency, signal quality is improved further via low-pass filter circuit 13, amplification and analog to digital conversion formation digital signal is carried out through signal collection modulation module 14, send in host computer 15 and complete demodulation, decoding and location, obtain the Vibration Condition that distributed sensor is along the line.

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

Embodiment 2

Based on a distributed optical fiber vibration sensing method for pulse code modulation (PCM) principle, Heterodyne detect principle, phase sensitive OTDR principle, see Fig. 1, the method comprises following process:

101: host computer 15 controls N number of controlled frequency different acousto-optic modulator group 4 (AOM) by FPGA16, making the short light pulse of N number of mutual time delay form code length at coupling mechanism 5 place, N*1 road is N, pulse width is the coded pulse light of N* τ, and injects sensor fibre 7 via optical fiber circulator 6;

In the scope needing detection vibration, lay a sensor fibre 7, utilize sensor fibre 7 as sensor and signal transmission medium, realize detection and the monitoring of vibration.Choose encoder matrix S, its size is N*N, selects every a line (length is N) of encoder matrix S for coding successively, then host computer 15 controls N number of controlled frequency difference by FPGA16 (controlled frequency is respectively f _i(i=1,2, N) acousto-optic modulator group 4), the respective the pulsewidth respectively continuous light wave from narrow linewidth light source being modulated into N number of mutual time delay is the short light pulse of τ, at coupling mechanism 5 place, a N*1 road, making the short light pulse of N number of mutual time delay form code length is N, and pulse width is the coded pulse light P of N* τ _i(i=1,2 ..., N), and inject sensor fibre 7 via optical fiber circulator 6.

102: the Rayleigh scattering light of coded pulse light is interferenceed with the local oscillator light from LASER Light Source 1, forming frequency f _iand Δ f _ijbat ripple, be converted into corresponding electric signal via photodetector 9;

When coded pulse light is propagated in sensor fibre 7, can form back rayleigh scattering, the Rayleigh scattering light of each short pulse is mutually interfered in respective pulsewidth τ, and also can produce the interference being unfavorable for detecting between each coding.Via optical fiber circulator 6, the 1:1 coupling mechanism 8 of all scattered lights before photodetector 9 is interferenceed with the local oscillator light from LASER Light Source 1, forming frequency f _i(i=1,2 ..., N) and Δ f _ij=f _i-f _j(i, j=1,2 ..., N) bat ripple, be converted into corresponding electric signal via on photodetector 9.

103: by choosing the controlled frequency of acousto-optic modulator group 4, the filter result of bandwidth-limited circuit 10 and default sine wave are carried out mixing, obtains the bat ripple frequency after frequency reducing;

That is, by choosing close AOM controlled frequency, its difference frequency is made to be less than its controlled frequency, i.e. f _i> Δ f _ij(i, j=1,2 ..., N), by bandwidth-limited circuit 10, make the bat ripple under its controlled frequency be selected out, by frequency mixer 11, by bandpass filtering result, (its frequency is f with the sinusoidal wave mixed frequency preset ₀), bat ripple frequency is down to tens of megahertz, i.e. f _i-f ₀(i=1,2 ..., N), via capture card with the speed collection of 100MHz.

104: host computer 15, by carrying out demodulation to the bat signal of the bat ripple frequency of frequency after frequency reducing, obtains the Rayleigh scattering signal of single encoded pulsed light;

In host computer 15, by frequency at f _i-f ₀(i=1,2 ..., N) bat signal carry out demodulation, by demodulation scattered light echo sequence L _i(i=1,2 ..., N).With L _ifor row vector, form signal matrix $L=\left[\begin{array}{c}{L}_1\\ L_2\\ .\\ .\\ .\\ L_N\end{array}\right],$ Application decoder matrix obtains the Rayleigh scattering signal of individual pulse ${\mathrm{\ω}}^{\′}=\left[\begin{array}{c}{{\mathrm{\ϖ}}_1}^{\′}\\ {{\mathrm{\ω}}_2}^{\′}\\ .\\ .\\ .\\ {{\mathrm{\ω}}_N}^{\′}\end{array}\right]=S^{-1}\·\left[\begin{array}{c}{L}_1\\ L_2\\ .\\ .\\ .\\ L_N\end{array}\right],$ Here S ^-1for the inverse matrix of encoder matrix S, ω _i' be the Rayleigh scattering signal that obtains when i-th coded pulse acts solely on system in theory in the coding of N position.

105: by carrying out mobile Difference Calculation to the Rayleigh scattering signal of single encoded pulsed light, obtain the Vibration Condition that sensor fibre 7 is along the line.

When the sensor fibre 7 of this optical fiber sensing system is subject to vibration effect, the change of the scattered signal of response position can be caused, by carrying out mobile Difference Calculation to scattered signal, then can detect the Vibration Condition that sensor fibre 7 is along the line, realize distributed vibrating sensing.

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, not in order to limit the present invention, within the spirit and principles in the present invention all, any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (2)

1. the optical fiber vibration sensing system of a single light source pulse code, be made up of LASER Light Source, FPGA, acousto-optic modulator group, optical fiber circulator, coupling mechanism, photodetector, signal collection modulation device, bandwidth-limited circuit, frequency mixer, host computer and sensor fibre, it is characterized in that

LASER Light Source produces continuous light, the acousto-optic modulator group different via controlled frequency is converted to light pulse, under the control of FPGA, light pulse forms coding, coded pulse light is formed by coupling mechanism, sensor fibre is injected by optical fiber circulator, the scattered light of propagation dorsad produced in its communication process produces interferes, coupling mechanism is entered via optical fiber circulator, interference with local oscillator light, produce beat signal, photodetector is converted into electric signal, the electric signal formed is through bandwidth-limited circuit filtering difference frequency component, the reduction of beat frequency is realized again via frequency mixer, last by capture card collection and amplifying signal, in host computer, realize the respective demodulation of each controlled frequency, carry out again decoding and localization process.

2., for a method for sensing for the optical fiber vibration sensing system of a kind of single light source pulse code according to claim 1, it is characterized in that, described method for sensing comprises the following steps:

Host computer controls the different acousto-optic modulator group of N number of controlled frequency by FPGA, and making the short light pulse of N number of mutual time delay form code length at coupling mechanism place, N*1 road is N, and pulse width is the coded pulse light of N* τ, and injects sensor fibre via optical fiber circulator;

The Rayleigh scattering light of coded pulse light is interferenceed with the local oscillator light from LASER Light Source, forming frequency f _iand Δ f _ijbat ripple, be converted into corresponding electric signal via photodetector;

By choosing the controlled frequency of acousto-optic modulator group, the filter result of bandwidth-limited circuit and default sine wave being carried out mixing, obtains the bat ripple frequency after frequency reducing;

Host computer, by carrying out demodulation to the bat signal of the bat ripple frequency of frequency after frequency reducing, obtains the Rayleigh scattering signal of single encoded pulsed light;

By carrying out mobile Difference Calculation to the Rayleigh scattering signal of single encoded pulsed light, obtain the Vibration Condition that sensor fibre is along the line.