CN113721287A - Monitoring method and device based on sensing optical fiber - Google Patents
Monitoring method and device based on sensing optical fiber Download PDFInfo
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- G01V1/01—
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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
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
- G01K11/3206—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres at discrete locations in the fibre, e.g. using Bragg scattering
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
- G01K11/324—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres using Raman scattering
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/16—Receiving elements for seismic signals; Arrangements or adaptations of receiving elements
- G01V1/18—Receiving elements, e.g. seismometer, geophone or torque detectors, for localised single point measurements
Abstract
The invention discloses a monitoring method and a device based on a sensing optical fiber, wherein the monitoring method comprises the following steps: high-power laser pulses are applied to the sensing grating, and Rayleigh scattered light signals and Raman scattered light signals are generated simultaneously; delay modulating the generated Rayleigh scattering optical signal to generate a Rayleigh scattering interference optical signal; demodulating the Rayleigh scattering interference optical signal to obtain a vibration signal; and demodulating the Raman scattering optical signal to obtain a temperature signal. Compared with the prior art, the distributed Raman temperature sensing system has the advantages that the laid distributed Raman temperature sensing system is simply improved, the synchronous measurement of vibration is realized on the basis of the original temperature measurement, the signal-to-noise ratio of the system is high, the system is simple and reliable, and the cost is low.
Description
Technical Field
The invention relates to a full-distributed temperature self-compensation interference type optical fiber microseism sensing technology and a device thereof, which are used for distributed vibration and temperature sensing of microseism, vibration, acceleration or sound wave and seismic wave of various geological and engineering structures. The full-distributed detection positioning and the real-time correction of the temperature deviation of the micro-vibration, the dynamic strain deformation, the seismic waves and the sound waves of geological, geotechnical and various engineering structures can be realized.
Background
The distributed optical fiber Raman temperature sensing system is widely applied due to a series of advantages of simple technical scheme, sensitivity to temperature, strong anti-crosstalk capability and the like. In the fiber Raman sensing system, backward scattering signals comprise Raman scattering and Rayleigh scattering, the sensing mechanism is to detect the change of Raman scattering intensity to realize temperature sensing, and the Rayleigh scattering and Raman scattering intensity contrast is utilized to eliminate the sensing deviation caused by the jitter noise, loss and attenuation of signal intensity. Because the distributed optical fiber Raman sensing system has single function and can only realize temperature sensing, a plurality of optical fiber sensing systems can utilize the Raman temperature sensing technology to carry out temperature compensation at present, namely for other optical fiber sensing systems which are easily influenced by temperature crosstalk, the temperature can cause measurement deviation, so the Raman temperature sensing system can be adopted to cooperatively work to measure the temperature distribution of the sensing optical fiber and carry out temperature compensation or deviation elimination aiming at sensing data, but the technologies are still two independent sensing systems which are simply integrated and independently work, so the system is complex, high in cost and poor in implementability.
Disclosure of Invention
The invention aims to provide a monitoring method and a monitoring device based on an optical fiber sensor, which are used for distributed vibration temperature sensing of micro-vibration, acceleration or sound wave and seismic wave of various geological and engineering structures, can realize simultaneous measurement of distributed vibration and temperature, and have the advantages of high system signal-to-noise ratio, simplicity, reliability and low cost.
The technical solution of the invention is as follows:
a monitoring method based on sensing optical fibers is characterized by comprising the following steps:
high-power laser pulses are applied to the sensing grating, and Rayleigh scattered light signals and Raman scattered light signals are generated simultaneously;
delay modulating the generated Rayleigh scattering optical signal to generate a Rayleigh scattering interference optical signal;
demodulating the Rayleigh scattering interference optical signal to obtain a vibration signal; and demodulating the Raman scattering optical signal to obtain a temperature signal.
A sensing fiber based monitoring device comprising: the device comprises a pulse laser, a first optical fiber coupler, a delay optical fiber, a second optical fiber coupler, a wavelength division multiplexer, a sensing optical fiber, a first photoelectric detector, a second photoelectric detector, a data acquisition card, a temperature demodulation unit, a vibration demodulation unit and a display unit; the output end of the pulse laser is connected with the first input port of the first optical fiber coupler, the first output port of the first optical fiber coupler is sequentially connected with the delay optical fiber and the first input port of the second optical fiber coupler, the second output port of the first optical fiber coupler is directly connected with the second input port of the second optical fiber coupler, the output port of the second optical fiber coupler is connected with the first input port of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected with the sensing optical fiber, the second input port of the wavelength division multiplexer is connected with the input end of the first photoelectric detector, the second input port of the first optical fiber coupler is connected with the input end of the second photoelectric detector, the output ends of the first photoelectric detector and the second photoelectric detector are respectively connected with two input ports of a data acquisition card, one output port of the data acquisition card is connected with the temperature demodulation unit, and the other output port of the data acquisition card is connected with the microseismic demodulation unit, the output ends of the temperature demodulation unit and the microseismic demodulation unit are connected with the display unit; the pulse light emitted by the pulse laser is reflected by the sensing optical fiber to form Rayleigh scattering and Raman scattering, and the Rayleigh scattering is enabled by the delay optical fiber to generate distributed Rayleigh scattering interference for vibration monitoring.
In the monitoring device, laser pulses emitted by the high-power pulse laser are divided into two paths after passing through the first optical fiber coupler, wherein one path enters the second optical fiber coupler after passing through the delay optical fiber, and the other path directly enters the second optical fiber coupler. And two paths of pulse light signals output from the second optical fiber coupler enter the sensing optical fiber after passing through the wavelength division multiplexer. Backward Rayleigh scattered light and raman backward scattered light generated by the sensing optical fiber return to the wavelength division multiplexer along the original path and are divided into two paths, wherein the raman backward scattered light directly enters the first photoelectric detector, the backward Rayleigh scattered light is divided into two paths after passing through the second optical fiber coupler, one path sequentially enters the second photoelectric detector after passing through the delay optical fiber and the first optical fiber coupler, and the other path directly enters the second photoelectric detector through the first optical fiber coupler and is converted into an electric signal after photoelectric conversion. The two-way data acquisition card synchronously acquires two paths of electric signals output by the first photoelectric detector and the first photoelectric detector, wherein one path of electric signals enters the temperature demodulation unit after passing through the Raman scattering intensity noise elimination unit to eliminate light source jitter and various loss noises, and the other path of electric signals enters the microseismic demodulation unit to be demodulated to obtain external temperature and vibration changes, and finally, the results are displayed on the display unit.
A sensing fiber based monitoring device comprising: the device comprises a pulse laser, a first optical fiber coupler, a delay optical fiber, a second optical fiber coupler, a sensing optical fiber, a wavelength division multiplexer, a first photoelectric detector, a second photoelectric detector, a data acquisition card, a vibration demodulation unit, a noise elimination unit and a display and storage unit; the output end of the pulse laser is connected with the first input port of the first optical fiber coupler, the first output port of the first optical fiber coupler is sequentially connected with the first input ports of the delay optical fiber and the second optical fiber coupler, the second output port of the first optical fiber coupler is directly connected with the second input port of the second optical fiber coupler, the output port of the second optical fiber coupler is connected with the sensing optical fiber, the first output port of the second optical fiber coupler is sequentially connected with the first input ports of the delay optical fiber and the first optical fiber coupler, the second output port of the second optical fiber coupler is directly connected with the second input port of the first optical fiber coupler, the output port of the first optical fiber coupler is connected with the input port of the wavelength division multiplexer, two output ports of the wavelength division multiplexer are respectively connected with the input ends of the first photoelectric detector and the second photoelectric detector, the output ends of the first photoelectric detector and the second photoelectric detector are connected with the input end of the data acquisition card, the output end of the data acquisition card is sequentially connected with the vibration demodulation unit, the noise elimination unit and the display and storage unit.
A sensing fiber based monitoring device comprising: the device comprises a pulse laser, a first optical fiber coupler, a time-delay optical fiber, a second optical fiber coupler, an optical fiber circulator, a sensing optical fiber, a third optical fiber coupler, a time-delay compensation optical fiber, a fourth optical fiber coupler, a wavelength division multiplexer, a first photoelectric detector, a second photoelectric detector, a data acquisition card, a vibration demodulation unit, a noise elimination unit and a display and storage unit; the output end of the pulse laser is connected with the first input port of the first optical fiber coupler, the first output port of the first optical fiber coupler is sequentially connected with the delay optical fiber and the first input port of the second optical fiber coupler, the second output port of the first optical fiber coupler is directly connected with the second input port of the second optical fiber coupler, the output port of the second optical fiber coupler is connected with the first port of the optical fiber circulator, the second port of the optical fiber circulator is connected with the sensing optical fiber, the third port of the optical fiber circulator is connected with the input end of the third optical coupler, the first output port of the third optical fiber coupler is sequentially connected with the delay compensation optical fiber and the first input port of the fourth optical fiber coupler, the second output port of the third optical fiber coupler is directly connected with the second input port of the fourth optical fiber coupler, the output port of the fourth optical fiber coupler is connected with the input port of the wavelength division multiplexer, and the two output ports of the wavelength division multiplexer are respectively connected with the input end of the first photoelectric detector and the input end of the second photoelectric detector, the output end of the first photoelectric detector and the output end of the second photoelectric detector are connected with the input end of a data acquisition card, and the output end of the data acquisition card is sequentially connected with a vibration demodulation unit, a noise elimination unit and a display and storage unit.
Compared with the prior art, the invention has the beneficial effects that:
the invention is based on the distributed Raman temperature sensing system, which is a simple improvement of the distributed Raman temperature sensing system, develops a new application, and realizes the synchronous measurement of vibration on the basis of the original temperature measurement. The high-power laser pulse is utilized to simultaneously generate Rayleigh scattering and Raman scattering, the optical fiber delay modulation design structure is adopted to enable the Rayleigh scattering to be used for power noise compensation of Raman scattering signals so as to realize temperature sensing, meanwhile, distributed Rayleigh scattering interference can be generated and applied to vibration sensing, and then, the optical fiber distributed microseismic sensing and the full-distributed real-time correction of vibration measurement deviation caused by temperature can be realized through the optical fiber sensing system based on the Raman scattering.
The invention simultaneously leads Rayleigh scattering and Raman scattering generated by the Raman sensing system to form interference, utilizes the Rayleigh scattering signal and the Raman scattering signal to lead the interference signal to have different coherent fading positions due to different wavelengths, and further can identify and eliminate the positioning fading noise by analyzing the two paths of interference signals.
Drawings
Fig. 1 is a schematic structural view of embodiment 1 of the present invention.
Fig. 2 is a schematic structural diagram of embodiment 2 of the present invention.
Fig. 3 is a schematic structural diagram of embodiment 3 of the present invention.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings, but the scope of the present invention should not be limited thereto.
Example 1
A monitoring method based on a sensing optical fiber comprises the following steps:
high-power laser pulses are applied to the sensing grating, and Rayleigh scattered light signals and Raman scattered light signals are generated simultaneously;
delay modulating the generated Rayleigh scattering optical signal to generate a Rayleigh scattering interference optical signal;
demodulating the Rayleigh scattering interference optical signal to obtain a first vibration signal; and demodulating the Raman scattering optical signal to obtain a temperature signal.
The method for demodulating the Rayleigh scattering interference optical signal to obtain the first vibration signal comprises the following steps:
converting the Rayleigh scattering interference optical signal into an electric signal;
and demodulating the converted electric signal to obtain a first vibration signal.
The method for demodulating the Raman scattering optical signal to obtain the temperature signal comprises the following steps:
converting the Raman scattering optical signal into an electric signal;
eliminating Raman scattering intensity noise in the converted electric signal;
and demodulating the electric signal subjected to the elimination of the Raman scattering intensity noise to obtain a temperature signal.
The noise influence can be eliminated by the ratio of the first raman scattering light pulse intensity to the first rayleigh scattering light pulse intensity, and finally, accurate temperature information can be extracted by the temperature demodulation unit 11.
The monitoring device based on the sensing optical fiber of the invention is shown in figure 1 and comprises: the system comprises a pulse laser 1, a first optical fiber coupler 2, a delay optical fiber 3, a second optical fiber coupler 4, a wavelength division multiplexer 10, a sensing optical fiber 6, a first photoelectric detector 11, a second photoelectric detector 12, a data acquisition card 13, a temperature demodulation unit 17, a vibration demodulation unit 14 and a display unit 16; the output end of the pulse laser is connected with the first input port of the first optical fiber coupler, the first output port of the first optical fiber coupler is sequentially connected with the delay optical fiber and the first input port of the second optical fiber coupler, the second output port of the first optical fiber coupler is directly connected with the second input port of the second optical fiber coupler, the output port of the second optical fiber coupler is connected with the first input port of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected with the sensing optical fiber, the second input port of the wavelength division multiplexer is connected with the input end of the first photoelectric detector, the second input port of the first optical fiber coupler is connected with the input end of the second photoelectric detector, the output ends of the first photoelectric detector and the second photoelectric detector are respectively connected with two input ports of a data acquisition card, one output port of the data acquisition card is connected with the temperature demodulation unit, and the other output port of the data acquisition card is connected with the microseismic demodulation unit, the output ends of the temperature demodulation unit and the microseismic demodulation unit are connected with the display unit; the pulse light emitted by the pulse laser is reflected by the sensing optical fiber to form Rayleigh scattering and Raman scattering, and the Rayleigh scattering is enabled by the delay optical fiber to generate distributed Rayleigh scattering interference for vibration monitoring.
High-power laser pulse emitted by the high-power pulse laser 1 is divided into two paths after passing through the first optical fiber coupler 2, wherein one path of pulse light enters the second optical fiber coupler 4 after passing through the delay optical fiber 3, the other path of pulse light directly enters the second optical fiber coupler 4, and due to the existence of the delay optical fiber, an optical path difference exists between the two paths of light, so that a certain phase difference is formed. Two paths of pulse light signals with a certain phase difference output from the second optical fiber coupler 4 enter the sensing optical fiber 6 through the wavelength division multiplexer 10, two paths of high-power laser pulses are in the propagation process in the sensing optical fiber 6, when the pulses reach each point of the optical fiber, backward Rayleigh scattering light signals and Raman backward scattering light signals are generated, the two scattering light signals have different wavelengths, the two types of backward scattering light signals return to the wavelength division multiplexer 10 along the original path and are separated into two paths, the Raman backward scattering light enters the first photoelectric detector 11, the Raman backward scattering light signals have two pulses, Raman scattering is respectively generated by the two paths of pulse light signals with a certain phase difference, and Raman scattering pulses with weaker signals are generated by the pulses passing through the time delay optical fiber. Because the intensity of the Raman backward scattering optical signal is sensitive to temperature, the first photoelectric detector 11 detects the Raman scattering pulse with stronger signal to obtain the intensity change of the Raman scattering signal at each point along the optical fiber, and the temperature distribution of the outside along the optical fiber can be preliminarily obtained. The backward rayleigh scattered light signal returns along the original path and is divided into two paths by the second optical fiber coupler 4, wherein one path sequentially passes through the delay optical fiber 3 and the first optical fiber coupler 2 and then enters the second photoelectric detector 12, and the other path directly passes through the first optical fiber coupler 2 and then enters the second photoelectric detector 12, that is, for two paths of pulse light signals with a certain phase difference, which are incident into the sensing optical fiber 6, one rayleigh scattered light pulse correspondingly generated by each pulse can form two rayleigh scattered light pulses with a certain time delay difference, so that four rayleigh scattered light pulses with a certain time interval are formed by converging at the first optical fiber coupler 2. The intensity of the first Rayleigh scattering light pulse is the maximum, the interference is generated when the second Rayleigh scattering light pulse and the third Rayleigh scattering light pulse which have approximately equal optical path difference meet the coherence condition, when the optical fiber is disturbed by external micro-shock, the phase difference or the optical path difference between the two Rayleigh scattering light pulses changes, so that the interference signal changes correspondingly, and the external micro-shock information can be preliminarily obtained by detecting the interference change of the optical signal through the second photoelectric detector 12. In this embodiment, since the raman scattered light intensity is affected by temperature, various losses such as bending and connection of the optical fiber, and noise such as light source intensity jitter, and the rayleigh scattered light intensity is affected by only various losses such as bending and connection of the optical fiber, and noise such as light source intensity jitter, the raman scattered light intensity noise removing unit 18 obtains the ratio between the first raman scattered light pulse intensity and the first rayleigh scattered light pulse intensity to remove the noise, and finally, accurate temperature information can be extracted by the temperature demodulating unit 17. In addition, since the temperature will also affect the interference signal and the microseismic sensitivity, by calibrating the temperature influence trend on the microseismic sensing in advance, and after obtaining accurate temperature distribution information, the microseismic demodulation unit 14 can eliminate the temperature crosstalk by using the known temperature influence trend rule on one hand, and analyze the intensity, frequency and power spectrum of the microseismic disturbance signal after the temperature crosstalk is eliminated on the other hand, and finally display the temperature distribution and microseismic analysis results on the display unit 16.
Example 2
A monitoring method based on a sensing optical fiber comprises the following steps:
high-power laser pulses are applied to the sensing grating, and Rayleigh scattered light signals and Raman scattered light signals are generated simultaneously;
delay modulating the generated Rayleigh scattering optical signal to generate a Rayleigh scattering interference optical signal; delay modulating the generated raman scattered light signal to produce a raman scattered interference light signal;
demodulating the Rayleigh scattering interference optical signal to obtain a first vibration signal; demodulating the Raman scattering interference optical signal to obtain a second vibration signal; and analyzing the second vibration signal and the first vibration signal, and identifying and eliminating the positioning fading noise.
The method for demodulating the Rayleigh scattering interference optical signal to obtain the first vibration signal comprises the following steps:
converting the Rayleigh scattering interference optical signal into an electric signal;
and demodulating the converted electric signal to obtain a first vibration signal.
The monitoring device based on the sensing optical fiber of the invention, as shown in fig. 2, comprises: the system comprises a pulse laser 1, a first optical fiber coupler 2, a delay optical fiber 3, a second optical fiber coupler 4, a sensing optical fiber 6, a wavelength division multiplexer 10, a first photoelectric detector 11, a second photoelectric detector 12, a data acquisition card 13, a vibration demodulation unit 14, a noise elimination unit 15 and a display and storage unit 16; the output end of the pulse laser is connected with the first input port of the first optical fiber coupler, the first output port of the first optical fiber coupler is sequentially connected with the first input ports of the delay optical fiber and the second optical fiber coupler, the second output port of the first optical fiber coupler is directly connected with the second input port of the second optical fiber coupler, the output port of the second optical fiber coupler is connected with the sensing optical fiber, the first output port of the second optical fiber coupler is sequentially connected with the first input ports of the delay optical fiber and the first optical fiber coupler, the second output port of the second optical fiber coupler is directly connected with the second input port of the first optical fiber coupler, the output port of the first optical fiber coupler is connected with the input port of the wavelength division multiplexer, two output ports of the wavelength division multiplexer are respectively connected with the input ends of the first photoelectric detector and the second photoelectric detector, the output ends of the first photoelectric detector and the second photoelectric detector are connected with the input end of the data acquisition card, the output end of the data acquisition card is sequentially connected with the vibration demodulation unit, the noise elimination unit and the display and storage unit.
High-power laser pulses emitted by a pulse laser 1 are divided into two paths after passing through a first optical fiber coupler 2, wherein one path of the pulse light enters a second optical fiber coupler 4 after forming a certain phase difference through a delay optical fiber 3, the other path of the pulse light directly enters the second optical fiber coupler 4, two paths of pulse light signals with a certain phase difference output from the second optical fiber coupler 4 sequentially enter a sensing optical fiber 6, backward Rayleigh scattering light signals and Raman backward scattering light signals with different wavelengths are generated when the pulses reach each point in the propagation process of the two paths of the high-power laser pulses in the sensing optical fiber 6, two types of backward scattering light are returned to the second optical fiber coupler 4 along the original path and divided into two paths, wherein one path of the pulse light passes through the delay optical fiber 3, the phase difference generated when the pulse light enters the delay optical fiber 3 is compensated and then enters the first optical fiber coupler 2, and the other path of the pulse light directly enters the first optical fiber coupler 2, in the two paths of pulse light signals output from the first optical fiber coupler 2, part of light meets the coherence condition and forms interference because the optical path difference is approximately equal, and after passing through the wavelength division multiplexer 10, backward Rayleigh scattering light and Raman backward scattering light are separated into two paths of output signals, wherein, the backward Rayleigh scattering light enters the first photoelectric detector, the Raman backward scattering light enters the second photoelectric detector, after the data acquisition card 13 synchronously acquires the electric signals output by the first photoelectric detector 11 and the second photoelectric detector 12, the collected data enter a vibration demodulation unit 14, the vibration demodulation unit 14 respectively extracts and analyzes the interference signals generated in the backward Rayleigh scattered light and the Raman backward scattered light, when the optical fiber is disturbed by external vibration, the interference state of the optical signal also changes correspondingly, and vibration information containing various noise disturbances can be preliminarily obtained by analyzing the interference states of the backward Rayleigh scattering light and the Raman backward scattering light. The related vibration information enters the noise eliminating unit 15, by utilizing the characteristic that the positions of generated coherent fading noise are different due to different wavelengths of backward Rayleigh scattering light and Raman backward scattering light, the fading noise and the real vibration can be identified by comparing backward Rayleigh scattering light with Raman backward scattering light signals, on the basis, the intensity fluctuation noise caused by various losses such as light source fluctuation, temperature change, optical fiber bending, connection and the like can be eliminated by comparing non-interference part optical signals with interference part optical signals, and finally, the final result is displayed and stored in the display and storage unit 16.
High-power laser pulses emitted by the pulse laser 1 are divided into two paths after passing through the first optical fiber coupler 2, one path of the laser pulses enters the second optical fiber coupler 4 after passing through the delay optical fiber 3, the other path of the laser pulses directly enters the second optical fiber coupler 4, and due to the existence of the delay optical fiber 3, an optical path difference exists between the two paths of the laser pulses, so that a certain phase difference is formed. Two paths of pulse light signals with a certain phase difference output from the second optical fiber coupler 4 enter the sensing optical fiber 6, two paths of high-power laser pulses generate backward Rayleigh scattering light signals and Raman backward scattering light signals when reaching each point of the optical fiber in the propagation process of the sensing optical fiber 6, the two paths of high-power laser pulses have different wavelengths, the two paths of backward scattering light signals return to the second optical fiber coupler 4 along the original path and are separated into two paths, one path of backward scattering light signals sequentially passes through the delay optical fiber 3 and the first optical fiber coupler 2 and then enters the wavelength division multiplexer 10, the other path of backward scattering light signals directly passes through the first optical fiber coupler 2 and then enters the wavelength division multiplexer 10, namely, for the two paths of pulse light signals with a certain phase difference entering the sensing optical fiber 6, each pulse correspondingly generates a Rayleigh scattering reflection light pulse and a Raman scattering reflection light pulse, therefore, the two paths of pulse light signals finally form a pair of Rayleigh scattering reflected pulse light with a certain time delay difference and a pair of Raman scattering reflected pulse light with a certain time delay difference. Similarly, after each pulse reflected light returns, two reflected lights with a certain time delay difference are formed again, so that four rayleigh scattered light pulses with a certain time interval are formed by merging at the first fiber coupler 2. Similarly, four raman scattering light pulses with the same time interval are formed at the first optical fiber coupler 2 at the same time, and since part of the reflected light passes through the delay optical fiber 3, the optical path difference formed by part of the incident light passing through the delay optical fiber 3 can be effectively compensated and compensated, so that the propagation paths are approximately equal between the two rayleigh scattering light pulses of the pulse laser 1, the first optical fiber coupler 2, the delay optical fiber 3, the second optical fiber coupler 4, the sensing optical fiber 6, the second optical fiber coupler 4, the first optical fiber coupler 2, the wavelength division multiplexer 10, the pulse laser 1, the first optical fiber coupler 2, the second optical fiber coupler 4, the sensing optical fiber 6, the second optical fiber coupler 4, the delay optical fiber 3, the first optical fiber coupler 2, the wavelength division multiplexer 10 and between the two raman scattering light pulses, the coherence condition can be satisfied and thus interference can be formed at the first fiber coupler 2. Rayleigh scattered light signals and raman scattered light signals output by the first optical fiber coupler 2 are separated by a wavelength division multiplexer 10, then enter a first photoelectric detector 11 and a second photoelectric detector 12 respectively, are converted into electric signals respectively, are synchronously collected by a data acquisition card 13, and are identified and extracted from multiple groups of pulses by a vibration demodulation unit 14 for vibration sensing. When the optical fiber is disturbed by external vibration, the optical path difference is changed due to the deformation of the optical fiber, the phase difference between interference Rayleigh scattering optical signals and the phase difference between interference Raman scattering optical signals are changed, the state of the interference signals is correspondingly changed, and the external vibration information can be preliminarily obtained by analyzing the interference change of the Rayleigh scattering and Raman scattering optical signals. Because both the backward rayleigh scattered light and the raman backward scattered light signals can generate the influence of coherent fading noise, but the position where the coherent fading noise occurs is related to the signal wavelength, and the vibration is not influenced by the signal wavelength, the two interference signals can represent the same change characteristics by using the difference between the backward rayleigh scattered light and the raman backward scattered light wavelength if the two interference signals are true vibration, but the coherent fading noise in the two interference signals is randomly different in the distribution position of the optical fiber space, so that in the noise elimination unit 15, whether the signal abnormality at a certain space is caused by the true vibration or the coherent fading noise can be easily judged by comparing the two interference signals. In addition, for this scheme, rayleigh scattering and raman scattering signals are affected by system noise such as various losses of fiber bending, connection and the like, and light source intensity jitter and the like, and raman anti-stokes scattering light intensity is also affected by temperature change, but for the above noise, synchronous equal proportion change of interference signal pulse and non-interference signal intensity of the above two kinds of scattering can be caused, so in the noise elimination unit 15, the above system noise influence can be eliminated through comparing the rayleigh scattering interference signal pulse with the non-interference signal pulse intensity, and the ratio between the raman scattering interference light pulse and the non-interference raman scattering light pulse intensity, and finally, accurate vibration information can be obtained through analyzing the vibration signal intensity, frequency and power spectrum, and the final result is displayed and stored in the display and storage unit 16.
Example 3
A monitoring method based on a sensing optical fiber comprises the following steps:
high-power laser pulses are applied to the sensing grating, and Rayleigh scattered light signals and Raman scattered light signals are generated simultaneously;
delay modulating the generated Rayleigh scattering optical signal to generate a Rayleigh scattering interference optical signal; delay modulating the generated raman scattered light signal to produce a raman scattered interference light signal;
demodulating the Rayleigh scattering interference optical signal to obtain a first vibration signal; demodulating the Raman scattering interference optical signal to obtain a second vibration signal; and analyzing the second vibration signal and the first vibration signal, and identifying and eliminating the positioning fading noise.
The method for demodulating the Rayleigh scattering interference optical signal to obtain the first vibration signal comprises the following steps:
converting the Rayleigh scattering interference optical signal into an electric signal;
and demodulating the converted electric signal to obtain a first vibration signal.
The invention relates to a monitoring device based on a sensing optical fiber, which is shown in figure 3 and comprises: the device comprises a pulse laser 1, a first optical fiber coupler 2, a delay optical fiber 3, a second optical fiber coupler 4, an optical fiber circulator 5, a sensing optical fiber 6, a third optical fiber coupler 7, a delay compensation optical fiber 8, a fourth optical fiber coupler 9, a wavelength division multiplexer 10, a first photoelectric detector 11, a second photoelectric detector 12, a data acquisition card 13, a vibration demodulation unit 14, a noise elimination unit 15 and a display and storage unit 16. The output end of the pulse laser is connected with the first input port of the first optical fiber coupler, the first output port of the first optical fiber coupler is sequentially connected with the delay optical fiber and the first input port of the second optical fiber coupler, the second output port of the first optical fiber coupler is directly connected with the second input port of the second optical fiber coupler, the output port of the second optical fiber coupler is connected with the first port of the optical fiber circulator, the second port of the optical fiber circulator is connected with the sensing optical fiber, the third port of the optical fiber circulator is connected with the input end of the third optical coupler, the first output port of the third optical fiber coupler is sequentially connected with the delay compensation optical fiber and the first input port of the fourth optical fiber coupler, the second output port of the third optical fiber coupler is directly connected with the second input port of the fourth optical fiber coupler, the output port of the fourth optical fiber coupler is connected with the input port of the wavelength division multiplexer, and the two output ports of the wavelength division multiplexer are respectively connected with the input end of the first photoelectric detector and the input end of the second photoelectric detector, the output end of the first photoelectric detector and the output end of the second photoelectric detector are connected with the input end of a data acquisition card, and the output end of the data acquisition card is sequentially connected with a vibration demodulation unit, a noise elimination unit and a display and storage unit.
High-power laser pulses emitted by a pulse laser 1 are divided into two paths after passing through a first optical fiber coupler 2, wherein one path of the pulse light enters a second optical fiber coupler 4 after forming a certain phase difference through a delay optical fiber 3, the other path of the pulse light directly enters the second optical fiber coupler 4, two paths of pulse light signals with a certain phase difference output from the second optical fiber coupler 4 sequentially enter a sensing optical fiber 6 through an optical fiber circulator 5, in the propagation process of the two paths of the high-power laser pulses in the sensing optical fiber 6, backward Rayleigh scattering light signals and Raman backward scattering light signals with different wavelengths are generated when the pulses reach each point, two types of backward scattering light are returned to the optical fiber circulator 5 along the original path and then are divided into two paths after passing through a third optical fiber coupler 7, wherein one path of the pulse light passes through a delay compensation optical fiber 8, the phase difference generated by the delay optical fiber 3 is compensated and then enters a fourth optical fiber coupler 9, the other path of pulse light directly enters a fourth optical fiber coupler 9, part of the light in two paths of pulse light signals output from the fourth optical fiber coupler 9 is approximately equal due to optical path difference, coherence conditions are met and interference is formed, after the light passes through a wavelength division multiplexer 10, backward Rayleigh scattering light and Raman backward scattering light are separated into two paths of output signals, wherein the backward Rayleigh scattering light enters a first photoelectric detector, the Raman backward scattering light enters a second photoelectric detector, a data acquisition card 13 synchronously acquires electric signals output by the first photoelectric detector 11 and the second photoelectric detector 12, the acquired data enter a vibration demodulation unit 14, the vibration demodulation unit 14 respectively extracts and analyzes signals interfering with the backward Rayleigh scattering light and the Raman backward scattering light, when the optical fiber is disturbed by external vibration, the interference state of the optical signals also changes correspondingly, and the interference state of the backward Rayleigh scattering light and the Raman backward scattering light can be preliminarily obtained by analyzing the interference states of the backward Rayleigh scattering light and Raman backward scattering light Vibration information of the noise disturbance. The related vibration information enters the noise eliminating unit 15, by utilizing the characteristic that the positions of generated coherent fading noise are different due to different wavelengths of backward Rayleigh scattering light and Raman backward scattering light, the fading noise and the real vibration can be identified by comparing backward Rayleigh scattering light with Raman backward scattering light signals, on the basis, the intensity fluctuation noise caused by various losses such as light source fluctuation, temperature change, optical fiber bending, connection and the like can be eliminated by comparing non-interference part optical signals with interference part optical signals, and finally, the final result is displayed and stored in the display and storage unit 16.
High-power laser pulses emitted by the pulse laser 1 are divided into two paths after passing through the first optical fiber coupler 2, one path of the laser pulses enters the second optical fiber coupler 4 after passing through the delay optical fiber 3, the other path of the laser pulses directly enters the second optical fiber coupler 4, and due to the existence of the delay optical fiber 3, an optical path difference exists between the two paths of the laser pulses, so that a certain phase difference is formed. Two paths of pulse light signals with a certain phase difference output from the second optical fiber coupler 4 enter the sensing optical fiber 6 through the optical fiber circulator 5, two paths of high-power laser pulses generate backward Rayleigh scattering light signals and Raman backward scattering light signals when reaching each point of the optical fiber, the two scattering light signals have different wavelengths, the two backward scattering light signals return to the optical fiber circulator 5 along the original path and are separated into two paths through the third optical fiber coupler 7, one path of the backward scattering light signals sequentially passes through the delay compensation optical fiber 8 and the fourth optical fiber coupler 9 and then enters the wavelength division multiplexer 10, and the other path of the backward scattering light signals directly passes through the fourth optical fiber coupler 9 and then enters the wavelength division multiplexer 10. For two paths of pulse light signals with a certain phase difference, which are incident into the sensing fiber 6, each pulse correspondingly generates a rayleigh scattering reflected light pulse and a raman scattering reflected light pulse, so that the two paths of pulse light signals finally form a pair of rayleigh scattering reflected light pulses with a certain time delay difference and a pair of raman scattering reflected light pulses with a certain time delay difference. After each reflected light pulse passes through the fourth optical fiber coupler 9, each reflected light pulse is divided into two paths again, that is, each backscattered light pulse finally forms two backscattered light pulses with a certain time delay difference, so that four rayleigh scattered light pulses with a certain time interval are formed by converging at the fourth optical fiber coupler 9. Similarly, four raman scattering light pulses with the same time interval are simultaneously formed at the fourth optical fiber coupler 9, and since part of the reflected light pulses passes through the delay compensation optical fiber 8, effective compensation can be performed on the optical path difference formed by part of the incident light passing through the delay optical fiber 3, so that the propagation path is approximately equal to the optical path difference between the two raman scattering light pulses of the first optical fiber coupler 2, the delay optical fiber 3, the second optical fiber coupler 4, the optical fiber circulator 5, the sensing optical fiber 6, the third optical fiber coupler 7, the fourth optical fiber coupler 9, the first optical fiber coupler 2, the second optical fiber coupler 4, the optical fiber circulator 5, the sensing optical fiber 6, the third optical fiber coupler 7, the delay compensation optical fiber 8 and the fourth optical fiber coupler 9 and between the two raman scattering light pulses, the coherence condition can be satisfied and thus interference can be formed at the fourth fiber coupler 9. Rayleigh scattered light signals and raman scattered light signals output by the fourth optical fiber coupler 9 are separated by the wavelength division multiplexer 10, enter the first photoelectric detector 11 and the second photoelectric detector 12 respectively, are converted into electric signals respectively, are synchronously collected by the data acquisition card 13, and are identified and extracted from the multiple groups of pulses by the vibration demodulation unit 14 for vibration sensing. When the optical fiber is disturbed by external vibration, the optical path difference is changed due to the deformation of the optical fiber, the phase difference between interference Rayleigh scattering optical signals and the phase difference between interference Raman scattering optical signals are changed, the state of the interference signals is correspondingly changed, and the external vibration information can be preliminarily obtained by analyzing the interference change of the Rayleigh scattering and Raman scattering optical signals. Because both the backward rayleigh scattered light and the raman backward scattered light signals can generate the influence of coherent fading noise, but the position where the coherent fading noise occurs is related to the signal wavelength, and the vibration is not influenced by the signal wavelength, the two interference signals can represent the same change characteristics by using the difference between the backward rayleigh scattered light and the raman backward scattered light wavelength if the two interference signals are true vibration, but the coherent fading noise in the two interference signals is randomly different in the distribution position of the optical fiber space, so that in the noise elimination unit 15, whether the signal abnormality at a certain space is caused by the true vibration or the coherent fading noise can be easily judged by comparing the two interference signals. In addition, for this scheme, rayleigh scattering and raman scattering signals are affected by system noise such as various losses of fiber bending, connection and the like, and light source intensity jitter and the like, and raman anti-stokes scattering light intensity is also affected by temperature change, but for the above noise, synchronous equal proportion change of interference signal pulse and non-interference signal intensity of the above two kinds of scattering can be caused, so in the noise elimination unit 15, the above system noise influence can be eliminated through comparing the rayleigh scattering interference signal pulse with the non-interference signal pulse intensity, and the ratio between the raman scattering interference light pulse and the non-interference raman scattering light pulse intensity, and finally, accurate vibration information can be obtained through analyzing the vibration signal intensity, frequency and power spectrum, and the final result is displayed and stored in the display and storage unit 16.
Claims (10)
1. A monitoring method based on sensing optical fibers is characterized by comprising the following steps:
high-power laser pulses are applied to the sensing grating, and Rayleigh scattered light signals and Raman scattered light signals are generated simultaneously;
delay modulating the generated Rayleigh scattering optical signal to generate a Rayleigh scattering interference optical signal;
demodulating the Rayleigh scattering interference optical signal to obtain a first vibration signal; and demodulating the Raman scattering optical signal to obtain a temperature signal.
2. The monitoring method according to claim 1, wherein the step of demodulating the rayleigh scattering interference optical signal to obtain the first vibration signal comprises:
converting the Rayleigh scattering interference optical signal into an electric signal;
and demodulating the converted electric signal to obtain a first vibration signal.
3. The monitoring method of claim 1, wherein the step of demodulating the raman scattered light signal to obtain a temperature signal comprises:
converting the Raman scattering optical signal into an electric signal;
eliminating Raman scattering intensity noise in the converted electric signal;
and demodulating the electric signal subjected to the elimination of the Raman scattering intensity noise to obtain a temperature signal.
4. The monitoring method according to claim 3, wherein the noise effect is eliminated by a ratio between the first Raman scattering light pulse intensity and the first Rayleigh scattering light pulse intensity, and finally accurate temperature information can be extracted by the temperature demodulating unit 11.
5. The monitoring method of claim 1, further comprising:
delay modulating the generated raman scattered light signal to produce a raman scattered interference light signal;
demodulating the Raman scattering interference optical signal to obtain a second vibration signal;
and analyzing the second vibration signal and the first vibration signal, and identifying and eliminating the positioning fading noise.
6. A sensing fiber based monitoring device, comprising: the device comprises a pulse laser, a first optical fiber coupler, a delay optical fiber, a second optical fiber coupler, a wavelength division multiplexer, a sensing optical fiber, a first photoelectric detector, a second photoelectric detector, a data acquisition card, a temperature demodulation unit, a vibration demodulation unit and a display unit; the output end of the pulse laser is connected with the first input port of the first optical fiber coupler, the first output port of the first optical fiber coupler is sequentially connected with the delay optical fiber and the first input port of the second optical fiber coupler, the second output port of the first optical fiber coupler is directly connected with the second input port of the second optical fiber coupler, the output port of the second optical fiber coupler is connected with the first input port of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected with the sensing optical fiber, the second input port of the wavelength division multiplexer is connected with the input end of the first photoelectric detector, the second input port of the first optical fiber coupler is connected with the input end of the second photoelectric detector, the output ends of the first photoelectric detector and the second photoelectric detector are respectively connected with two input ports of a data acquisition card, one output port of the data acquisition card is connected with the temperature demodulation unit, and the other output port of the data acquisition card is connected with the microseismic demodulation unit, the output ends of the temperature demodulation unit and the microseismic demodulation unit are connected with the display unit; the pulse light emitted by the pulse laser is reflected by the sensing optical fiber to form Rayleigh scattering and Raman scattering, and the Rayleigh scattering is enabled by the delay optical fiber to generate distributed Rayleigh scattering interference for vibration monitoring.
7. The monitoring device according to claim 1, wherein a raman scattering intensity noise elimination unit is further disposed between the data acquisition card and the temperature demodulation unit.
8. The monitoring device of claim 1, wherein the first photodetector is an avalanche photodetector; the second photodetector is a high-speed photodetector.
9. A sensing fiber based monitoring device, comprising: the device comprises a pulse laser, a first optical fiber coupler, a delay optical fiber, a second optical fiber coupler, a sensing optical fiber, a wavelength division multiplexer, a first photoelectric detector, a second photoelectric detector, a data acquisition card, a vibration demodulation unit, a noise elimination unit and a display and storage unit; the output end of the pulse laser is connected with the first input port of the first optical fiber coupler, the first output port of the first optical fiber coupler is sequentially connected with the first input ports of the delay optical fiber and the second optical fiber coupler, the second output port of the first optical fiber coupler is directly connected with the second input port of the second optical fiber coupler, the output port of the second optical fiber coupler is connected with the sensing optical fiber, the first output port of the second optical fiber coupler is sequentially connected with the first input ports of the delay optical fiber and the first optical fiber coupler, the second output port of the second optical fiber coupler is directly connected with the second input port of the first optical fiber coupler, the output port of the first optical fiber coupler is connected with the input port of the wavelength division multiplexer, two output ports of the wavelength division multiplexer are respectively connected with the input ends of the first photoelectric detector and the second photoelectric detector, the output ends of the first photoelectric detector and the second photoelectric detector are connected with the input end of the data acquisition card, the output end of the data acquisition card is sequentially connected with the vibration demodulation unit, the noise elimination unit and the display and storage unit.
10. A sensing fiber based monitoring device, comprising: the device comprises a pulse laser, a first optical fiber coupler, a time-delay optical fiber, a second optical fiber coupler, an optical fiber circulator, a sensing optical fiber, a third optical fiber coupler, a time-delay compensation optical fiber, a fourth optical fiber coupler, a wavelength division multiplexer, a first photoelectric detector, a second photoelectric detector, a data acquisition card, a vibration demodulation unit, a noise elimination unit and a display and storage unit; the output end of the pulse laser is connected with the first input port of the first optical fiber coupler, the first output port of the first optical fiber coupler is sequentially connected with the delay optical fiber and the first input port of the second optical fiber coupler, the second output port of the first optical fiber coupler is directly connected with the second input port of the second optical fiber coupler, the output port of the second optical fiber coupler is connected with the first port of the optical fiber circulator, the second port of the optical fiber circulator is connected with the sensing optical fiber, the third port of the optical fiber circulator is connected with the input end of the third optical coupler, the first output port of the third optical fiber coupler is sequentially connected with the delay compensation optical fiber and the first input port of the fourth optical fiber coupler, the second output port of the third optical fiber coupler is directly connected with the second input port of the fourth optical fiber coupler, the output port of the fourth optical fiber coupler is connected with the input port of the wavelength division multiplexer, and the two output ports of the wavelength division multiplexer are respectively connected with the input end of the first photoelectric detector and the input end of the second photoelectric detector, the output end of the first photoelectric detector and the output end of the second photoelectric detector are connected with the input end of a data acquisition card, and the output end of the data acquisition card is sequentially connected with a vibration demodulation unit, a noise elimination unit and a display and storage unit.
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