CN116105848A - Method and device for improving quality of optical fiber sensing signal - Google Patents
Method and device for improving quality of optical fiber sensing signal Download PDFInfo
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Abstract
The invention provides a method and a device for improving the quality of optical fiber sensing signals, which are used for generating two paths of pulse light sources with phase differences, ensuring that the two paths of pulse light can not interfere with each other through the design of light paths, generating clockwise interference signals and anticlockwise interference signals at different positions, adopting a phase difference control technology of optical sequences without interference and a dynamic time delay adjustment technology for controlling the length of an optical fiber, and extracting effective interference signals through a time division multiplexing control algorithm after the acquisition of two paths of detection signals. The invention can be applied to vibration signal detection and vibration positioning under the conditions of single-ended detection, single-span optical fiber, middle and opposite ends without any amplification or relay, has the advantages of realizing vibration signal demodulation and signal analysis technology, improving the signal to noise ratio of detection signals, obviously improving the detection distance and detection precision of the sensor, obviously improving the detection distance, and breaking through the detection distance bottleneck of the optical fiber sensor based on the M-Z interference principle due to the problem of back Rayleigh scattering.
Description
Technical Field
The invention relates to the technical field of measurement and test, in particular to a method and a device for improving the quality of optical fiber sensing signals.
Background
The optical fiber sensor has the advantages of long detection distance, high response speed, high sensitivity, no electromagnetic wave radiation, no electromagnetic interference and the like, and is widely applied to various fields. The dual-M-Z interference optical fiber sensing system based on the M-Z (Mach-Zehnder) interference principle is mainly applied to vibration detection in the long-distance field due to the high sensitivity characteristic, and particularly has obvious advantages for monitoring and positioning vibration points of long-distance optical fiber vibration or disturbance of more than 100 km.
Scattering of light is a phenomenon in which a portion of light propagates away from the original direction as it passes through an inhomogeneous medium. When light is transmitted in the optical fiber, scattering occurs due to uneven refractive index distribution in the optical fiber, and three forms of Rayleigh scattering, brillouin scattering and Raman scattering are mainly adopted.
Rayleigh scattering is a scattering phenomenon generated by particles with dimensions far smaller than the wavelength of incident light, and the wavelength of the scattered light is equal to the wavelength of the incident light, and has no frequency change, so that the Rayleigh scattering is elastic scattering. Rayleigh scattering in an optical fiber is due to local fluctuations in refractive index caused by random fluctuations in optical fiber density during the manufacturing process of the optical fiber, so that light is scattered in all directions.
Brillouin scattering is inelastic scattering in which incident light interacts with the acoustic wave field of the fiber. The spontaneous Brillouin scattering and stimulated Brillouin scattering are classified. Stimulated brillouin scattering refers to the fact that when the pumping power of incident light entering an optical fiber exceeds a certain threshold, electrostriction effect generated in the optical fiber causes periodic deformation or elastic vibration along the optical fiber, namely coherent sound waves are generated in the optical fiber, the refractive index of the optical fiber is periodically modulated along the propagation direction of the sound waves, so that a refractive index grating moving at the sound speed is formed, the incident light is scattered, the frequency of scattered light moves downwards, when wave field phase matching is met, the sound wave field is greatly enhanced, the electrostriction sound wave field and the corresponding scattered light wave field in the optical fiber are enhanced by more than the respective loss, coherent amplification of the sound wave field and the scattered light field occurs, and most of transmitted light power is transmitted into backward scattered light.
Raman scattering is the scattering of light through a medium due to changes in frequency caused by interaction of incident light with molecular motion.
In the practical application of optical fiber sensing, detection distance, detection precision, response time and the like are key technical indexes, and due to scattering, the signal-to-noise ratio of an optical signal and the output power of an optical fiber are greatly limited, so that the effect of optical fiber sensing in application is affected. The pulse light source mode is adopted, so that the average injection light power can be reduced, the instantaneous injection light power is increased, the effective output light power of the optical fiber can be improved, and the influence of stimulated Brillouin scattering is reduced.
The degradation of the osnr due to rayleigh scattering in the optical fiber is a major problem to be solved in practical applications.
The prior art is a double M-Z interference optical fiber sensing system in a basic form, wherein C1, C2 and C3 are optical fiber couplers, PD1 and PD2 are photodetectors, A, B, C, D are four optical fibers, B, C is a sensing optical fiber, and A, D is a conducting optical fiber.
As can be seen from fig. 1, there are two light propagation paths, the first path is clockwise, namely, laser source→c1→c2→sensing fiber B, C →c3→conducting fiber d→pd2; the second path is anticlockwise, namely a laser source, C1, a conducting optical fiber A, C3, a sensing optical fiber B, C, C2 and PD1; the PD1 detection signal is affected by the backward Rayleigh scattering of the clockwise injected light, the signal to noise ratio of the PD1 detection signal is reduced, the long-distance application of optical fiber sensing is limited, and the detection precision is affected.
According to measurement and test verification, the intensity of the back Rayleigh scattered light received by the PD1 is about-35 dB of the incident light intensity of the light source, if the incident light is 0dBm, the influence caused by the back Rayleigh scattered light is-35 dBm, so that the detection signal in the anticlockwise direction is required to be larger than-35 dBm, and the PD1 detection signal has an optical signal to noise ratio of about 3dB so that the PD1 detection signal has effective detection capability, which is also a key problem to be solved by the invention.
The technical principle of the bidirectional M-Z interference optical fiber sensing system is that when external vibration occurs, the change of the optical phase caused by the vibration is distributed to propagate along two directions of the bidirectional M-Z interferometer, and the distance between the vibration position and the detector PD1 is assumed to be
The distance from the detector PD2 is then: />
The time for the vibration signal to pass from the vibration place to the detector PD1 is:
the time for the vibration signal to pass from the vibration place to the detector PD2 is:
the expression where the vibration occurrence position can be calculated is:
wherein the method comprises the steps of
、/>
For B, D fiber length, ">
Is the speed of light,/->
The refractive index of the optical fibers is equal to that of A, B, C, D optical fibers. As can be seen from the calculation formula, as long as the time difference between the transmission of the vibration signal to the two photodetectors is obtained>
The position where the vibration occurs can be obtained. The two paths of detection signals are subjected to cross-correlation operation, and the corresponding time delay at the position with the maximum cross-correlation coefficient is the time difference
Thereby obtaining a vibration generation position.
In addition, there are also prior art solutions employing dual laser sources. The scheme has the advantages of increasing the detection distance by adding a single-frequency narrow-linewidth laser source and using a wavelength division multiplexing device to filter the backward Rayleigh scattering interference, but has obvious defects, and firstly, the main hardware cost in the optical fiber sensing test system, the cost of the single-frequency narrow-linewidth laser and the cost of a plurality of matched optical modulation devices and optical amplification devices are increased, and the system structure is complicated, and the reliability and stability difficulties are increased; secondly, the system polarization state changes caused by two different light sources are inconsistent, so that the primary phase of interference signals in two directions in the system and the polarization-induced phase drift uncertainty are large, which are core problems causing obvious deterioration of positioning accuracy and are unfavorable for practical application.
Disclosure of Invention
The invention provides a method and a device for improving the quality of optical fiber sensing signals, which are used for eliminating adverse effects of back Rayleigh scattering and are a technical architecture of a double M-Z interference optical fiber sensing system with optical signal time division multiplexing clockwise and anticlockwise transmission. The invention generates two paths of pulse light sources with phase difference, can not interfere each other between the two paths of pulse light by light path design, can generate clockwise interference signals and anticlockwise interference signals at different positions, adopts a phase difference control technology of light sequences without interference and a dynamic time delay adjustment technology for controlling the length of optical fibers, extracts effective interference signals by a time division multiplexing control algorithm after the two paths of detection signals are acquired, can eliminate the influence of back Rayleigh scattered light on detection signals, and has the technology of detecting and positioning vibration signals with a repeater optical fiber link. The method and the device can be applied to vibration signal detection and vibration positioning under the conditions of single-end detection, single-span optical fiber, middle and opposite ends without amplification or relay, and have the advantages of realizing vibration signal demodulation and signal analysis technology, improving the signal-to-noise ratio of detection signals and obviously improving the detection distance and detection precision of the sensor. The detection distance of the optical fiber vibration detection system is obviously improved, and the detection distance bottleneck of the optical fiber sensor based on the M-Z interference principle due to the difficulty of back Rayleigh scattering is broken through.
The invention provides a method for improving the quality of optical fiber sensing signals, which comprises the following steps:
s1, carrying out light modulation and light amplification on a light source output by a laser source through a light modulation amplifying device to generate two paths of light sources, respectively outputting the two paths of light sources to an optical fiber coupler C1 and an optical fiber coupler C3, wherein transmission of clockwise interference signals enters a step S2, and transmission of anticlockwise interference signals enters a step S3;
s2, the transmission process of the clockwise interference signal is as follows: one path of light source output by the optical modulation amplification device generates interference at the optical fiber coupler C2 through the optical fiber A and the optical fiber B to form a clockwise interference signal, and then the clockwise interference signal is transmitted to the second photoelectric detector through the optical fiber D to form a clockwise interference signal, and the step S4 is performed;
s3, the transmission process of the anticlockwise interference signal is as follows: the other path of light source output by the optical modulation amplification device outputs two paths of signals after passing through the optical fiber coupler C2, reaches the optical fiber coupler C4 through the optical fiber C and the optical fiber D respectively, generates interference at the optical fiber coupler C4 to form a counterclockwise interference signal, and transmits the counterclockwise interference signal to the first photoelectric detector to form a counterclockwise interference signal;
s4, the industrial personal computer collects and synchronously extracts signals received by the first photoelectric detector and the second photoelectric detector, extracts a counterclockwise interference signal from the detection signal of the first photoelectric detector, extracts a clockwise interference signal from the detection signal of the second photoelectric detector, and obtains a vibration generation position by analyzing time difference, thereby improving the quality of the optical fiber sensing signal.
In the method for improving the quality of the optical fiber sensing signal, in the step S2, as a preferred mode, the transmission process of the clockwise interference signal is as follows: one path of light source output by the optical modulation amplification device is divided into two paths of light sources through an optical fiber coupler C1, one path of light source enters an optical fiber coupler C2 through an optical fiber A, the other path of light source enters the optical fiber coupler C2 through an optical fiber coupler C3 and an optical fiber B in sequence, the two paths of light sources generate interference at the optical fiber coupler C2 to form a clockwise interference signal, and the clockwise interference signal is transmitted to a second photoelectric detector through an optical fiber D and an optical fiber coupler C5 in sequence.
In the method for improving the quality of the optical fiber sensing signal, in the step S3, the transmission process of the anticlockwise interference signal is as follows: the other path of light source output by the optical modulation amplification device sequentially passes through the optical fiber coupler C3, the optical fiber B and the optical fiber coupler C2 and then outputs two paths of signals, one path of light source is output to the optical fiber coupler C4 through the optical fiber C, the other path of light source sequentially passes through the optical fiber D, the optical fiber coupler C5 and one branch output optical fiber of the optical fiber coupler C5 and is output to the optical fiber coupler C4, interference is generated at the optical fiber coupler C4 to form a anticlockwise interference signal, and the anticlockwise interference signal is transmitted to the first photoelectric detector to form the anticlockwise interference signal.
In the method for improving the quality of the optical fiber sensing signal, the optical source output by the optical modulation amplifying device is a two-path pulse optical source with a phase difference as an optimal mode.
The method for improving the quality of the optical fiber sensing signal, which is provided by the invention, is used as a preferable mode, and the method for generating the two paths of pulse light sources with phase differences is as follows: generating two paths of pulse sequences with phase difference through a pulse generating device, respectively driving two optical modulators to generate two paths of optical pulse sequences, and amplifying the optical pulses;
or is: the pulse generating device generates a pulse sequence, the optical modulator is driven to generate an optical pulse sequence, the optical pulse sequence is divided into two paths through the coupler, and optical fibers with different lengths are connected to delay two paths of optical signals, so that the two paths generate proper phase difference, and then the optical pulse is amplified.
The invention provides a device for improving the quality of optical fiber sensing signals, which comprises a clockwise MZ interferometer and a counterclockwise MZ interferometer, wherein one path of light source output by a laser source generates a clockwise interference signal through the clockwise MZ interferometer and enters a second photoelectric detector to form a clockwise interference signal, the other path of light source output by the laser source generates a counterclockwise interference signal through the counterclockwise MZ interferometer and enters a first photoelectric detector to form a counterclockwise interference signal, the clockwise interference signal and the counterclockwise interference signal can be respectively extracted by adjusting the phase difference of the clockwise interference signal and the counterclockwise interference signal, and then the vibration generation position is obtained by analyzing the time difference.
The device for improving the quality of the optical fiber sensing signal comprises an optical source, an optical modulation amplifying device, an optical fiber coupler C1 and an optical fiber coupler C3 which are connected with the output end of the optical modulation amplifying device in an optical mode, an optical fiber A connected with the output end of the optical fiber coupler C1, an optical fiber B connected with the output end of the optical fiber coupler C3, an optical fiber coupler C2 connected with the optical fiber A and the optical fiber B in an optical mode, an optical fiber C and an optical fiber D connected with the output end of the optical fiber coupler C2 in an optical mode, an optical fiber coupler C4 connected with the other end of the optical fiber C, a first photoelectric detector connected with the output end of the optical fiber C4, an optical fiber coupler C5 connected with the other end of the optical fiber D in an optical mode, and an industrial personal computer connected with the laser source, the first photoelectric detector and the second photoelectric detector;
one input branch of the optical fiber coupler C3 is also in optical fiber connection with the output end of the optical fiber coupler C1, one output branch of the optical fiber coupler C5 is also in optical fiber connection with the input end of the optical fiber coupler C4, and the optical fiber A, the optical fiber B, the optical fiber C and the optical fiber D are all sensing optical fibers;
the clockwise MZ interferometer comprises a laser source, an optical modulation amplifying device, an optical fiber coupler C1, an optical fiber coupler C2, an optical fiber coupler C3, one output branch of an optical fiber coupler C5, an optical fiber A, an optical fiber B, an optical fiber D and a second photoelectric detector;
the anticlockwise MZ interferometer comprises a laser source, an optical modulation amplifying device, a fiber coupler C2, a fiber coupler C3, a fiber coupler C4, one output branch of a fiber coupler C5, a fiber a, a fiber C, a fiber D and a first photodetector.
The invention relates to a device for improving the quality of optical fiber sensing signals, which is characterized in that, as a preferable mode, the propagation path of clockwise interference signals is as follows: the light source output by the laser source outputs two paths of light sources after passing through the optical modulation amplifying device, one path of light source outputs to the optical fiber coupler C1 and outputs two paths of signals, one path of signal enters the optical fiber coupler C2 through the optical fiber A, the other path of signal enters the optical fiber coupler C2 through the optical fiber coupler C3 and the optical fiber B in sequence, the two paths of signals interfere to obtain a clockwise interference signal, the clockwise interference signal is output to the second photoelectric detector through the optical fiber D and the optical fiber coupler C5, and the industrial personal computer analyzes the clockwise interference signal from the second photoelectric detector.
The device for improving the quality of the optical fiber sensing signal disclosed by the invention is characterized in that, as a preferable mode, the propagation path of the anticlockwise interference signal is as follows: the light source output by the laser source outputs two paths of light sources after passing through the optical modulation amplifying device, the other path of light source sequentially passes through the optical fiber coupler C3 and then enters the optical fiber coupler C2 by the optical fiber B, the optical fiber coupler C2 outputs two paths of signals, one path of signals enters the optical fiber coupler C4 by the optical fiber C, the other path of signals sequentially passes through the optical fiber D, the optical fiber coupler C5 and one branch output optical fiber of the optical fiber coupler C5 to reach the optical fiber coupler C4, the two paths of signals are interfered to obtain a anticlockwise interference signal, the anticlockwise interference signal is output to the first photoelectric detector from the optical fiber coupler C4, and the industrial personal computer analyzes the anticlockwise interference signal from the second photoelectric detector.
According to the device for improving the quality of the optical fiber sensing signal, as an optimal mode, the light source output by the laser source outputs two paths of pulse light sources with phase differences after passing through the optical modulation amplifying device, so that the clockwise interference signal and the anticlockwise interference signal have phase differences.
The invention can lead the optical signal to realize the brand new technology that the back Rayleigh scattering signal generated by the light source input signal can not enter the two optical detectors PD1 and PD2 under the brand new architecture of the optical fiber sensing optical path through the unique time division multiplexing signal processing mode and a series of control scheduling algorithms, thereby avoiding the influence of the back Rayleigh scattering on the useful signal, further greatly improving the signal-to-noise ratio of the optical detection signal and achieving the aim of obviously improving the detection distance.
The invention has the following advantages:
(1) The method and the device can be applied to vibration signal detection and vibration positioning under the conditions of single-end detection, single-span optical fiber, middle and opposite ends without any amplification or relay, and have the technology of realizing vibration signal demodulation and signal analysis;
(2) The invention has clear technical scheme principle, realizes Mach-Zehnder bidirectional interference detection technology with time division multiplexing as a core by means of accurate optical path and circuit design, eliminates adverse effects of back Rayleigh scattering, improves signal-to-noise ratio of detection signals, and remarkably improves detection distance and detection precision of a sensor. The detection distance of the optical fiber vibration detection system is obviously improved, and the detection distance bottleneck of the optical fiber sensor based on the M-Z interference principle due to the difficulty of back Rayleigh scattering is broken through.
(3) The method and the device can eliminate the influence of the back Rayleigh scattered light in the double-M-Z interference optical fiber sensing system on the detection signal, improve the signal-to-noise ratio of the detection signal, improve the quality of the detection signal, obviously improve the distance detection capability of the system, increase the detection distance of a single-ended detection, single-span optical fiber, middle and opposite ends under the condition of no power supply, no amplification or relay, and the detection distance of the system is obviously improved to more than 190km on the basis of the original detection distance, thereby breaking through the bottleneck of the maximum detection distance of the product (also the industry). Meanwhile, the device can be applied to an optical fiber link with a repeater to realize ultra-long-distance vibration monitoring.
Drawings
FIG. 1 is a schematic diagram of a basic form of a dual M-Z interferometric fiber optic sensing system;
FIG. 2 is a flow chart of a method of improving the quality of a fiber-optic sensing signal;
FIG. 3 is a schematic diagram of an apparatus for improving the quality of optical fiber sensing signals;
FIG. 4a is a schematic diagram a of a device for improving the quality of optical fiber sensing signals to generate a pulsed light source with phase difference;
FIG. 4b is a schematic diagram b of a pulsed light source with phase difference generated by a device for improving the quality of optical fiber sensing signals;
FIG. 4c is a schematic diagram c of a pulsed light source with phase difference generated by a device for improving the quality of optical fiber sensing signals;
FIG. 4d is a schematic diagram d of a pulsed light source with phase difference generated by a device for improving the quality of optical fiber sensing signals;
FIG. 5 is a schematic diagram of two pulses of light with a phase difference for a method and apparatus for improving the quality of a fiber-optic sensing signal.
Reference numerals:
1. a laser source; 2. An optical modulation amplifying device; 3. A first photodetector; 4. A second photodetector; 5. And the industrial personal computer.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments.
Example 1
As shown in fig. 2, a method for improving the quality of an optical fiber sensing signal comprises the following steps:
s1, carrying out optical modulation and optical amplification on a light source output by a laser source 1 through an optical modulation amplifying device 2 to generate two paths of light sources, respectively outputting the two paths of light sources to an optical fiber coupler C1 and an optical fiber coupler C3, wherein transmission of clockwise interference signals enters a step S2, and transmission of anticlockwise interference signals enters a step S3;
the light source output by the optical modulation amplifying device 2 is a two-path pulse light source with phase difference;
the method for generating the two paths of pulse light sources with the phase difference comprises the following steps: generating two paths of pulse sequences with phase difference through a pulse generating device, respectively driving two optical modulators to generate two paths of optical pulse sequences, and amplifying the optical pulses;
or is: generating a pulse sequence by a pulse generating device, driving an optical modulator to generate an optical pulse sequence, dividing the optical pulse sequence into two paths by a coupler, connecting optical fibers with different lengths to delay two paths of optical signals, so that the two paths generate proper phase difference, and amplifying the optical pulses;
s2, the transmission process of the clockwise interference signal is as follows: one path of light source output by the optical modulation amplification device 2 generates interference at the optical fiber coupler C2 through the optical fiber A and the optical fiber B respectively to form a clockwise interference signal, and then the clockwise interference signal is transmitted to the second photoelectric detector 4 through the optical fiber D to form a clockwise interference signal;
the transmission process of the clockwise interference signal is as follows: one path of light source output by the optical modulation amplification device 2 is divided into two paths of light sources through an optical fiber coupler C1, one path of light source enters an optical fiber coupler C2 through an optical fiber A, the other path of light source enters the optical fiber coupler C2 through an optical fiber coupler C3 and an optical fiber B in sequence, the two paths of light sources generate interference at the optical fiber coupler C2 to form a clockwise interference signal, and the clockwise interference signal is transmitted to a second photoelectric detector 4 through an optical fiber D and an optical fiber coupler C5 in sequence;
s3, the transmission process of the anticlockwise interference signal is as follows: the other path of light source output by the optical modulation amplification device 2 outputs two paths of signals after passing through the optical fiber coupler C2, respectively reaches the optical fiber coupler C4 through the optical fiber C and the optical fiber D, generates interference at the optical fiber coupler C4 to form a counterclockwise interference signal, and transmits the counterclockwise interference signal to the first photoelectric detector 3 to form a counterclockwise interference signal;
the transmission process of the anticlockwise interference signal is as follows: the other path of light source output by the optical modulation amplification device 2 sequentially passes through the optical fiber coupler C3, the optical fiber B and the optical fiber coupler C2 and then outputs two paths of signals, one path of signals is output to the optical fiber coupler C4 through the optical fiber C, the other path of signals is output to the optical fiber coupler C4 through one branch output optical fiber of the optical fiber D, the optical fiber coupler C5 and the optical fiber coupler C5 in sequence, interference is generated at the optical fiber coupler C4 to form a anticlockwise interference signal, and the anticlockwise interference signal is transmitted to the first photoelectric detector 3 to form an anticlockwise interference signal;
s4, the industrial personal computer 5 collects and synchronously extracts signals received by the first photoelectric detector 3 and the second photoelectric detector 4, extracts a counterclockwise interference signal from the detection signal of the first photoelectric detector 3, extracts a clockwise interference signal from the detection signal of the second photoelectric detector 4, and analyzes the time difference to obtain a vibration generation position, thereby improving the quality of the optical fiber sensing signal.
Example 2
As shown in fig. 3, a device for improving the quality of an optical fiber sensing signal comprises a clockwise MZ interferometer and a counterclockwise MZ interferometer, wherein one path of light source output by a laser source 1 generates a clockwise interference signal through the clockwise MZ interferometer and enters a second photoelectric detector 4 to form a clockwise interference signal, the other path of light source output by the laser source 1 generates a counterclockwise interference signal through the counterclockwise MZ interferometer and enters a first photoelectric detector 3 to form a counterclockwise interference signal, the clockwise interference signal and the counterclockwise interference signal can be respectively extracted by adjusting the phase difference of the clockwise interference signal and the counterclockwise interference signal, and then the vibration generating position is obtained by analyzing the time difference;
the device comprises a laser source 1, an optical modulation amplifying device 2, an optical fiber coupler C1 and an optical fiber coupler C3 which are connected with the output end of the optical modulation amplifying device 2, an optical fiber A connected with the output end of the optical fiber coupler C1, an optical fiber B connected with the output end of the optical fiber coupler C3, an optical fiber coupler C2 connected with the optical fibers A and B, an optical fiber C and an optical fiber D connected with the output end of the optical fiber coupler C2, an optical fiber coupler C4 connected with the other end of the optical fiber C, a first photoelectric detector 3 connected with the output end of the optical fiber coupler C4, an optical fiber coupler C5 connected with the other end of the optical fiber D, a second photoelectric detector 4 connected with one output end of the optical fiber coupler C5, and an industrial personal computer 5 connected with the laser source 1, the first photoelectric detector 3 and the second photoelectric detector 4;
one input branch of the optical fiber coupler C3 is also in optical fiber connection with the output end of the optical fiber coupler C1, one output branch of the optical fiber coupler C5 is also in optical fiber connection with the input end of the optical fiber coupler C4, and the optical fiber A, the optical fiber B, the optical fiber C and the optical fiber D are all sensing optical fibers;
the clockwise MZ interferometer comprises a laser source 1, an optical modulation amplifying device 2, an optical fiber coupler C1, an optical fiber coupler C2, an optical fiber coupler C3, one output branch of an optical fiber coupler C5, an optical fiber A, an optical fiber B, an optical fiber D and a second photoelectric detector 4;
the anticlockwise MZ interferometer comprises a laser source 1, an optical modulation amplifying device 2, an optical fiber coupler C3, an optical fiber coupler C4, one output branch of an optical fiber coupler C5, an optical fiber A, an optical fiber C, an optical fiber D and a first photoelectric detector 3;
the propagation path of the clockwise interference signal is: the light source output by the laser source 1 outputs two paths of light sources after passing through the optical modulation amplifying device 2, one path of light source outputs to the optical fiber coupler C1 and outputs two paths of signals, one path of signal enters the optical fiber coupler C2 through the optical fiber A, the other path of signal enters the optical fiber coupler C2 through the optical fiber coupler C3 and the optical fiber B in sequence, the two paths of signals interfere to obtain a clockwise interference signal, the clockwise interference signal is output to the second photoelectric detector 4 through the optical fiber D and the optical fiber coupler C5, and the industrial personal computer 5 analyzes the clockwise interference signal from the second photoelectric detector 4;
the propagation path of the interference signal in the counterclockwise direction is: the light source output by the laser source 1 outputs two paths of light sources after passing through the optical modulation amplifying device 2, the other path of light source sequentially passes through the optical fiber coupler C3 and then enters the optical fiber coupler C2 by passing through the optical fiber B, the optical fiber coupler C2 outputs two paths of signals, one path of signals enters the optical fiber coupler C4 by passing through the optical fiber C, the other path of signals sequentially passes through the optical fiber D, the optical fiber coupler C5 and one branch output optical fiber of the optical fiber coupler C5 to reach the optical fiber coupler C4, the two paths of signals are interfered to obtain a anticlockwise interference signal, the anticlockwise interference signal is output to the first photoelectric detector 3 from the optical fiber coupler C4, and the industrial personal computer 5 analyzes the anticlockwise interference signal from the second photoelectric detector 4;
the light source output by the laser source 1 passes through the optical modulation amplifying device 2 and then outputs two paths of pulse light sources with phase differences so that the clockwise interference signal and the anticlockwise interference signal have phase differences.
Example 3
As shown in fig. 2, 3 and 4 a-4 d, a method and a device for improving the quality of optical fiber sensing signals;
the technical principle of the double M-Z interference optical fiber sensing system designed and developed by the invention is as follows:
in the system, C1, C2, C3, C4 and C5 are optical fiber couplers, PD1 and PD2 are photodetectors, A, B, C, D are four optical fibers, wherein A, B optical fibers form a clockwise optical fiber sensor, and C, D optical fibers form a counterclockwise optical fiber sensor.
The light source generates two paths of pulse light sources with phase difference after light modulation and light amplification. The first path of light is clockwise, namely, a light source respectively enters a clockwise optical fiber sensor formed by A, B optical fibers after passing through C1 and C3, and then is divided into two paths through C2, one path of signal is divided into two branches from C5 through a D optical fiber, one branch reaches PD2, and the other branch enters C4; the other path of clockwise interference signal split by C2 enters C4 through C optical fiber, interferes with the signal of the branch entering C4 after being split by C5, and reaches PD1. The signal received by the PD2 is the signal of the interference signal of the clockwise optical fiber sensor, which is transmitted through the D optical fiber after being split by the C2 and is further split by the C5 optical fiber, the signal received by the PD1 is the signal of the interference signal of the clockwise optical fiber sensor, which is transmitted through the C optical fiber and is further split by the C5 optical fiber after being split by the C4 optical fiber, and the clockwise MZ interferometer is composed of one branch of the C1 and the C3, the A, B optical fiber and the C2;
similarly, the second path is in a counterclockwise direction, namely, the light source enters the B optical fiber from C3, is divided into two paths by C2 and enters the counterclockwise optical fiber sensor formed by C, D optical fibers, the path passing through the D optical fiber is divided into two branches by C5, the signal of one branch reaches PD2, and the signal of the other branch reaches PD1 after interfering with the signal from the C optical fiber by C4. The signal reaching the PD2 is an optical signal of the light source after long-distance transmission, the PD1 signal is an interference signal of the anticlockwise optical fiber sensor, and the C2, one branch of the optical fiber C, D, C and the C4 form an anticlockwise MZ interferometer.
The time delay is adjusted by adjusting the length of the optical fiber, and the phase difference of the two paths of light sources is controlled by adjusting software and hardware, so that the two paths of light source signals do not generate mutual interference and interference exactly.
After the PD1 and PD2 signals are collected, the signals are synchronously extracted, the interference signals of the anticlockwise optical fiber sensor are extracted from the PD1 signals, and the interference signals of the clockwise optical fiber sensor are extracted from the PD2 signals. The two paths of interference signals completely accord with the principle of an M-Z interferometer, and a double M-Z interference optical fiber sensing system can be well realized. Meanwhile, the optical signals received by the two paths of detectors are physically separated from the optical signals injected into the optical fiber sensor by the light source, compared with the prior art, the optical signal detection device has the advantages that the optical signals can be enabled to enter the brand new technology that the back Rayleigh scattering signals generated by the light source input signals cannot enter the two optical detectors PD1 and PD2 under the brand new architecture of the optical fiber sensing light path through the unique time division multiplexing signal processing mode and a series of control scheduling algorithms, so that the influence of the back Rayleigh scattering on useful signals is avoided, the signal to noise ratio of the optical detection signals is greatly improved, and the aim of remarkably improving the detection distance is fulfilled.
The method for generating the pulse light source with phase difference in fig. 4a and 4b is to generate two pulse sequences with phase difference by a pulse generating device, drive two light modulators to generate two light pulse sequences, and then amplify the light pulses.
The method for generating the pulse light source with phase difference in fig. 4c and 4d is to generate a pulse sequence by a pulse generating device, drive an optical modulator to generate an optical pulse sequence, then divide the optical pulse sequence into two paths by a coupler, connect optical fibers with different lengths to delay the two paths of optical signals, so that the two paths generate proper phase difference, and amplify the optical pulse.
As shown in fig. 5, pulsed light
Through C1, two paths are divided, one path is transmitted to C2 through an A optical fiber, the other path is transmitted to C2 through a B optical fiber after being transmitted to C3, and the length of the A, B optical fiber is adjusted to enable the two paths to be>
And meanwhile, the C2 position is reached, and the light interference condition is satisfied.
By adjusting the pulse light injected with C3
、/>
The phase difference of (2) is such that the two are not simultaneously injected with C3, so that no interference is generated at C3, and the two are formed into +.>
、/>
Alternating pulse sequences, after transmission through the B-fiber, reach C2, due to +.>
And +.>
At the same time C2 is reached, so the pulsed light in fiber B +.>
And +.>
Two paths of pulse light do not meet the interference condition>
、/>
The signals do not interfere with each other and do not interfere with each other.
The same applies to the counterclockwise direction.
The optical power of the fiber injection is limited by the stimulated brillouin threshold, which is about 8dBm; the minimum optical power input by the photodetector is about-55 dBm; the intensity of the injected pulse light back Rayleigh scattered light is about-42 db of the incident light intensity of the optical fiber; the optical fiber length was 160km and the fiber attenuation coefficient was 0.18db/km, i.e., the loss of the link was 28.8db.
For the basic form of dual M-Z interferometric fiber sensing system shown in FIG. 1, the optical power at the X0 point is 8dBm, the optical power at the X1 point is-20.8 dBm, and the optical power at the X2 point after passing through the optical fiber B, C and the two splitters in the counterclockwise direction (3 db attenuation is added) is-52.6 dBm; because of Rayleigh scattering, the injection optical power of the Y0 point cannot exceed-10.6 dBm (-52.6+42) in order to ensure the signal-to-noise ratio of the X2 point optical signal, the optical power of the Y1 point is-42.4 dBm after passing through the optical fiber B, C and two optical splitters in the clockwise direction (3 db attenuation is added), the optical power of the Y2 point is-71.2 dBm, and the optical device with the gain of 16.2db is amplified to meet the requirements of the detector.
In the basic form of the double M-Z interference optical fiber sensing system, the signal to noise ratio of the X2 point optical signal and the injection optical power of the Y0 point are mutually restricted due to the influence of Rayleigh scattering, so that the detection distance of the system is limited.
In the embodiment, the optical fiber length of the optical fiber is 190km, the optical fiber attenuation coefficient is 0.18db/km, namely the unidirectional loss of the link is 34.2db; in the double M-Z interference optical fiber sensing system, an optical device is added, and the loss of 6db is increased in the optical transmission process compared with that of a basic optical fiber sensing system.
The optical power of the X0 point is 8dBm, and the optical power of the Y2 point is 8-34.2-34.2-3-6= -69.4dBm; the optical power of the Y0 point is 8dBm, and the optical power of the X2 point is-69.4 dBm; and amplifying by an optical device with the gain of 15db to meet the requirements of the detector.
The double M-Z interference optical fiber sensing system can not only improve the amplitude of the detection signal, but also enable the detection signal not to be influenced by Rayleigh scattered light, and improve the signal-to-noise ratio of the signal.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.
Claims (10)
1. A method for improving the quality of an optical fiber sensing signal, which is characterized by comprising the following steps: the method comprises the following steps:
s1, a light source output by a laser source (1) is subjected to light modulation and light amplification by a light modulation amplifying device (2) to generate two paths of light sources, the two paths of light sources are respectively output to an optical fiber coupler C1 and an optical fiber coupler C3, transmission of clockwise interference signals enters a step S2, and transmission of anticlockwise interference signals enters a step S3;
s2, the transmission process of the clockwise interference signal is as follows: one path of light source output by the optical modulation amplification device (2) generates interference at the position of the optical fiber coupler C2 through the optical fiber A and the optical fiber B respectively to form a clockwise interference signal, and then the clockwise interference signal is transmitted to the second photoelectric detector (4) through the optical fiber D to form a clockwise interference signal;
s3, the transmission process of the anticlockwise interference signal is as follows: the other path of light source output by the optical modulation amplification device (2) outputs two paths of signals after passing through the optical fiber coupler C2, reaches the optical fiber coupler C4 through the optical fiber C and the optical fiber D respectively, generates interference at the optical fiber coupler C4 to form a counterclockwise interference signal, and transmits the counterclockwise interference signal to the first photoelectric detector (3) to form a counterclockwise interference signal;
s4, the industrial personal computer (5) collects and synchronously extracts signals received by the first photoelectric detector (3) and the second photoelectric detector (4), extracts the anticlockwise interference signal from the detection signal of the first photoelectric detector (3), extracts the clockwise interference signal from the detection signal of the second photoelectric detector (4), and obtains a vibration generation position through analyzing time difference.
2. A method of improving the quality of a fiber optic sensing signal according to claim 1, wherein: in step S2, the transmission process of the clockwise interference signal is as follows: one path of light source output by the optical modulation amplification device (2) is divided into two paths of light sources through the optical fiber coupler C1, one path of light source enters the optical fiber coupler C2 through the optical fiber A, the other path of light source sequentially passes through the optical fiber coupler C3 and the optical fiber B and enters the optical fiber coupler C2, the two paths of light sources generate interference at the optical fiber coupler C2 to form the clockwise interference signal, and the clockwise interference signal is transmitted to the second photoelectric detector (4) through the optical fiber D and the optical fiber coupler C5 in sequence.
3. A method of improving the quality of a fiber optic sensing signal according to claim 1, wherein: in step S3, the transmission process of the counter-clockwise interference signal is as follows: the other path of light source output by the optical modulation amplification device (2) sequentially passes through the optical fiber coupler C3, the optical fiber B and the optical fiber coupler C2 and then outputs two paths of signals, one path of light source is output to the optical fiber coupler C4 through the optical fiber C, the other path of light source is output to the optical fiber coupler C4 through one branch output optical fiber of the optical fiber D, the optical fiber coupler C5 and the optical fiber coupler C5, interference is generated at the position of the optical fiber coupler C4 to form the anticlockwise interference signal, and the anticlockwise interference signal is transmitted to the first photoelectric detector (3) to form the anticlockwise interference signal.
4. A method of improving the quality of a fiber optic sensing signal according to claim 1, wherein: the light source output by the optical modulation amplifying device (2) is a two-path pulse light source with a phase difference.
5. A method of improving the quality of a fiber optic sensing signal as defined in claim 4, wherein: the method for generating the two paths of pulse light sources with the phase difference comprises the following steps: generating two paths of pulse sequences with phase difference through a pulse generating device, respectively driving two optical modulators to generate two paths of optical pulse sequences, and amplifying the optical pulses;
or is: the pulse generating device generates a pulse sequence, the optical modulator is driven to generate an optical pulse sequence, the optical pulse sequence is divided into two paths through the coupler, and optical fibers with different lengths are connected to delay two paths of optical signals, so that the two paths generate proper phase difference, and then the optical pulse is amplified.
6. The utility model provides a device for improving optical fiber sensing signal quality which characterized in that: the device comprises a clockwise MZ interferometer and a counterclockwise MZ interferometer, wherein one light source output by a laser source (1) generates a clockwise interference signal through the clockwise MZ interferometer and enters a second photoelectric detector (4) to form a clockwise interference signal, the other light source output by the laser source (1) generates a counterclockwise interference signal through the counterclockwise MZ interferometer and enters a first photoelectric detector (3) to form a counterclockwise interference signal, and the clockwise interference signal and the counterclockwise interference signal can be respectively extracted by adjusting the phase difference of the clockwise interference signal and the counterclockwise interference signal, and then the vibration generation position is obtained by analyzing the time difference.
7. The apparatus for improving the quality of fiber optic sensing signals of claim 6, wherein: the optical fiber coupler comprises a laser source (1), an optical modulation amplifying device (2), an optical fiber coupler C1 and an optical fiber coupler C3 which are connected with the output end of the optical modulation amplifying device (2) in an optical mode, an optical fiber A connected with the output end of the optical fiber coupler C1, an optical fiber B connected with the output end of the optical fiber coupler C3, an optical fiber coupler C2 connected with the optical fiber A and the optical fiber B in an optical mode, an optical fiber C and an optical fiber D connected with the output end of the optical fiber coupler C2 in an optical mode, an optical fiber coupler C4 connected with the other end of the optical fiber C, a first photoelectric detector (3) connected with the output end of the optical fiber coupler C4 in an optical mode, an optical fiber coupler C5 connected with the other end of the optical fiber D in an optical mode, a second photoelectric detector (4) connected with one output end of the optical fiber coupler C5 and an industrial personal computer (5) connected with the laser source (1), the first photoelectric detector (3) and the second photoelectric detector (4) in an optical mode;
one input branch of the optical fiber coupler C3 is also in optical fiber connection with the output end of the optical fiber coupler C1, one output branch of the optical fiber coupler C5 is also in optical fiber connection with the input end of the optical fiber coupler C4, and the optical fiber A, the optical fiber B, the optical fiber C and the optical fiber D are all sensing optical fibers;
the clockwise MZ interferometer comprises the laser source (1), the optical modulation amplifying device (2), the optical fiber coupler C1, the optical fiber coupler C2, the optical fiber coupler C3, one output branch of the optical fiber coupler C5, the optical fiber a, the optical fiber B, the optical fiber D and the second photodetector (4);
the anticlockwise MZ interferometer comprises the laser source (1), the optical modulation amplifying device (2), the optical fiber coupler C2, the optical fiber coupler C3, the optical fiber coupler C4, one output branch of the optical fiber coupler C5, an optical fiber a, an optical fiber C, an optical fiber D and the first photodetector (3).
8. The apparatus for improving the quality of fiber optic sensing signals of claim 6, wherein: the propagation path of the clockwise interference signal is as follows: the light source output by the laser source (1) outputs two paths of light sources after passing through the optical modulation amplifying device (2), one path of light source outputs to the optical fiber coupler C1 and outputs two paths of signals, one path of signal enters the optical fiber coupler C2 through the optical fiber A, the other path of signal enters the optical fiber coupler C2 through the optical fiber coupler C3 and the optical fiber B in sequence, the two paths of signals interfere to obtain the clockwise interference signal, the clockwise interference signal is output to the second photoelectric detector (4) through the optical fiber D and the optical fiber coupler C5, and the industrial personal computer (5) analyzes the clockwise interference signal from the second photoelectric detector (4).
9. The apparatus for improving the quality of fiber optic sensing signals of claim 6, wherein: the propagation path of the counter-clockwise interference signal is as follows: the light source output by the laser source (1) outputs two paths of light sources after passing through the optical modulation amplifying device (2), the other path of light source sequentially passes through the optical fiber coupler C3 and then enters the optical fiber coupler C2 by passing through the optical fiber B, the optical fiber coupler C2 outputs two paths of signals, one path of signals enters the optical fiber coupler C4 by passing through the optical fiber C, the other path of signals sequentially passes through the optical fiber D, the optical fiber coupler C5 and one branch output optical fiber of the optical fiber coupler C5 to reach the optical fiber coupler C4, the two paths of signals interfere to obtain the anticlockwise interference signal, the anticlockwise interference signal is output from the optical fiber coupler C4 to the first photoelectric detector (3), and the industrial personal computer (5) analyzes the anticlockwise interference signal from the second photoelectric detector (4).
10. The apparatus for improving the quality of fiber optic sensing signals of claim 6, wherein: the light source output by the laser source (1) outputs two paths of pulse light sources with phase differences after passing through the optical modulation amplifying device (2) so that the clockwise interference signal and the anticlockwise interference signal have phase differences.
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