CN113654641B - Distributed optical fiber vibration sensing system and demodulation method - Google Patents
Distributed optical fiber vibration sensing system and demodulation method Download PDFInfo
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Abstract
The invention discloses a distributed optical fiber vibration sensing system and a demodulation method, wherein the system comprises the following steps: the system comprises a direct detection type phi-OTDR part, an interference part and a signal acquisition part; the direct detection type phi-OTDR part is used for positioning the vibration event, the interference part is used for improving the frequency response of the system, and the combination of the direct detection type phi-OTDR part and the interference part enables the system to have the vibration event positioning and the wide-frequency signal measuring capability. The demodulation algorithm improves the spatial positioning precision of the vibration event, and restores the frequency spectrum characteristic of the vibration signal with high fidelity, so that the recognition accuracy of the vibration event is higher. The invention fuses the direct detection type phi-OTDR structure and the interference structure, further improves the frequency response range of the sensing system on the basis of ensuring the high spatial resolution of the sensing system, and is more suitable for practical application.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a distributed optical fiber vibration sensing system and a demodulation method based on a fusion phi-OTDR technology and an interference technology.
Background
The phase sensitive optical time domain reflectometer (Φ -OTDR) is a late stage in the family of optical time domain reflectometers, which uses the coherent fading effect of the back rayleigh scattered light in the fiber to detect and locate the disturbance event applied to the fiber under test. As a full-distributed optical fiber sensing technology, the phi-OTDR has the advantages of long detection distance, low cost, continuous measurement, no blind area and the like shared by the full-distributed optical fiber sensor, has the characteristics of high sensitivity, high response speed and the like compared with other distributed optical fiber sensors, can accurately and quickly locate and identify faults and hidden dangers of an optical fiber detection area, and has wide application prospects in perimeter security, seismic wave detection, power transmission line monitoring, underwater cable monitoring, and safety and health monitoring and fault early warning of large-scale infrastructure such as bridges, tunnels, dams, oil gas pipelines and the like.
While phi-OTDR has high spatial resolution, its frequency response is mutually restricted with the measurement distance, and when the system covers a certain length of measurement distance, its frequency response becomes low, which results in that the spectral characteristics of part of the vibration event cannot be well restored. For example, in the case of pipeline leakage and rupture, equipment discharge, earthquake, bridge galloping and other faults, the frequency range of the generated vibration signal is very wide, the high frequency range can reach tens of kHz, the low frequency range can be as low as Hz to sub-Hz, and the frequency response of the sensing system is required to be high enough. Meanwhile, when the Nyquist sampling law is utilized for signal sampling, the signal is folded due to the narrow observation frequency band, and the misjudgment rate of the system is improved, so that the sensing system has high frequency response. In addition, in an actual phi-OTDR system, due to the phase difference of a modulating signal, a carrier signal and a triggering acquisition signal of a data acquisition card in the driving of an acousto-optic modulator, the acquired back Rayleigh scattering signal generates phase drift, and the signal to noise ratio of the whole system is further affected. Therefore, phase locking of these three signals is also an important means to improve the monitoring performance of the system.
The measuring principle of the interference technology (phase modulation) is that a signal to be measured is applied to a sensing arm of an interferometer, the detection signal in the sensing arm is subjected to phase change due to the elasto-optical effect, and the change of the signal to be measured can be monitored by demodulating the interfered signal through interference with a reference signal in a reference arm. The frequency response of the interference technique is determined by the detector bandwidth and the sampling frequency of the data acquisition card, so that in the case of sufficiently large both, the frequency response can theoretically be very high. Although the interference technology has very high frequency response and can restore the frequency spectrum characteristic of the vibration signal, the spatial resolution is very low, and accurate positioning of the vibration event is difficult to realize. The invention expects to realize the measurement of high spatial resolution, high frequency response and high signal to noise ratio by combining the phi-OTDR technology and the interference technology and combining the phase locking technology.
In recent years, many scholars have also studied intensively about the distributed optical fiber vibration sensing system integrating the Φ -OTDR technology and the interference technology, and the invention has certain disadvantages in comparison with the invention although the purposes of high spatial resolution and high frequency response are achieved. For example, the systems mentioned in papers "Zhao Z,Ming T,Liang W,et al.Distributed Vibration Sensor Based on Space-Division Multiplexed Reflectometer and Interferometer in Multicore Fiber[J].Journal of Lightwave Technology,2018,PP(24):1-1." and "Zhu T,He Q,Xiao X,et al.Modulated pulses based distributed vibration sensing with high frequency response and spatial resolution[J].Optics Express,2013,21(3):2953-2963." use multicore fiber and sensing fiber loop structures, respectively, which increase the complexity of the optical path. Patent 'Zhang Yixin, shan Yuanyuan, zhang Xuping, etc. A continuous distributed optical fiber vibration sensing device with broadband sensing capability and method thereof are disclosed in CN107436175A [ P ].2017 ] and paper' Shore Xiang Hui. A system based on interference and phi-OTDR composite distributed optical fiber vibration sensing technology [ D ]. Chongqing university, 2014 ] uses two lasers as core important devices of the system, which greatly increases the construction cost of the system, although the complexity of the optical path is not high. In 2017, the system of paper "A hybrid single-end-access MZI and Phi-OTDR vibration sensing system with high frequency response[J].Optics Communications:AJournal Devoted to the Rapid Publication of Short Contributions in the Field of Optics and Interaction of Light with Matter,2017,382:176-181." of the subject group has low complexity of optical path and uses only one laser, but an active device is arranged at the tail end of the sensing optical fiber, which makes it difficult to realize in practical application. And neither the papers nor the patents use a phase lock structure, the signal to noise ratio is poor.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a distributed optical fiber vibration sensing system and a demodulation method based on the fusion phi-OTDR technology and the interference technology, which only adopt one laser and do not contain active devices, and can improve the frequency response range and the signal to noise ratio on the basis of ensuring the high spatial resolution of the sensing system by combining the phase locking technology on the basis of simple structure.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
In a first aspect, an embodiment of the present invention provides a distributed optical fiber vibration sensing system, where the distributed optical fiber vibration sensing system includes a direct detection Φ -OTDR module, an interference module, and a signal acquisition module;
the direct detection type phi-OTDR module comprises a laser, a first coupler, a semiconductor optical amplifier modulation module, an erbium-doped optical fiber amplifier, a first circulator, a sensing optical fiber, an optical filter, a first photoelectric detector, a low-pass filter and a first low-noise amplifier; the interference module comprises a second coupler, an acousto-optic modulator, a second circulator, a sensing optical fiber, a Faraday rotator mirror, a third coupler, a second photoelectric detector, a band-pass filter and a second low-noise amplifier; the signal acquisition module comprises a clock generator and a data acquisition card; the clock generator is used for generating a synchronous clock signal and outputting the synchronous clock signal to a driving and data acquisition card of the acousto-optic modulator;
the laser is used for outputting continuous narrow linewidth laser to the first coupler, and the first coupler divides the narrow linewidth laser input by the laser into two paths: the first path is that part of signal light of the phi-OTDR system is input to the semiconductor optical amplifier modulation module, and the second path is that part of signal light of the interference system is input to the second coupler;
the semiconductor optical amplifier modulation module modulates the continuous signal light output by the first coupler into pulse light to be output to the erbium-doped optical fiber amplifier, so that the pulse light is amplified by the erbium-doped optical fiber amplifier and then is output to the 1 st port of the first circulator; the detection light input by the 1 st port of the first circulator is output from the 2 nd port of the first circulator to the sensing fiber to generate back scattered light; the back scattered light is output to a first photoelectric detector from a3 rd port of the first circulator, the first photoelectric detector converts the back scattered light into an electric signal, the electric signal is output to a low-pass filter for low-pass filtering and then is output to a first low-noise amplifier for amplification and then is output to an A port of a data acquisition card;
the second coupler divides the second path of narrow linewidth laser output by the first coupler into two paths: the first path is used as detection light to be input to the acousto-optic modulator, and the second path is used as local oscillation light to be input to the third coupler; the acousto-optic modulator carries out high-level modulation on the detection light input by the second coupler, outputs continuous detection light to the 1 st port of the second circulator, outputs the detection light from the 2 nd port of the second circulator to the sensing optical fiber, and outputs the detection light from the 3 rd port of the second optical fiber circulator to the third coupler after being reflected by the Faraday rotator; the third coupler outputs the reflected light input by the 3 rd port of the second circulator and the local oscillator light input by the second coupler to the second photoelectric detector, the second photoelectric detector converts the reflected light into an electric signal, the electric signal is output to the band-pass filter for band-pass filtering and then is output to the second low-noise amplifier for amplification and then is output to the B port of the data acquisition card;
The data acquisition card is used for taking a synchronous clock signal input by the clock generator as a trigger acquisition signal, performing analog-to-digital conversion on electric signals input by the first low noise amplifier and the second low noise amplifier, outputting two paths of digital signals to a computer end, and processing by using a demodulation algorithm embedded in the computer end; wherein, the A port of the data acquisition card corresponds to the A-path data, and the B port of the data acquisition card corresponds to the B-path data;
The demodulation algorithm carries out phase demodulation on the data of the path B, calculates short-time energy spectrum, compares the short-time energy spectrum with frequency spectrums in a database, if the frequency spectrum characteristics are matched, proves that the vibration generated at the position is to be monitored by the system, further positions vibration events by carrying out short-time variance calculation on the data of the path A, and if the data of the path A is not matched, continues to carry out short-time energy spectrum calculation on other data pieces until the vibration events to be monitored are found, and then the vibration events are positioned or are not existed.
Alternatively, the laser is a narrow linewidth laser.
Optionally, the first coupler is 90 of 1×2: 10 or 80:20, and the second coupler is 1 x2 50: 50.
Optionally, the first photodetector is an avalanche photodiode and the second photodetector is a balanced photodetector.
Optionally, the sensing optical fibers are multi-core optical fibers, no device is added at the tail end of one sensing optical fiber, and a Faraday rotator mirror is placed at the tail end of the other sensing optical fiber.
Optionally, the process of demodulating the B-path data in phase and calculating the short-time energy spectrum includes the following steps:
the B-path data is subjected to phase demodulation, wherein signal light of the interference part is continuous sinusoidal light, and the triggering acquisition signal frequency and the modulation signal frequency of the acousto-optic modulator of the data acquisition card are 4:1, the phase difference between adjacent sampling points is pi/2;
dividing the data of the B path into two paths of I and Q according to odd-even sampling points, obtaining phases by arctangent after tangent of the two paths, and uniformly cutting the unwound data into data sheets with the time length of T;
And carrying out short-time energy spectrum calculation on the data sheet.
In a second aspect, an embodiment of the present invention provides a demodulation method of a distributed optical fiber vibration sensing system, where the demodulation method includes the following steps:
S1, generating continuous light by using a laser, wherein the light is divided into two paths through a first coupler: one path is used as signal light of a direct detection type phi-OTDR part and is input to an SOA modulation module, and the other path is used as signal light of an interference part and is input to a second coupler;
S2, after signal light input to a direct detection type phi-OTDR part passes through an SOA modulation module, amplifying the signal light through an EDFA, inputting amplified detection pulse light through a1 st port of a first circulator, outputting the amplified detection pulse light into a sensing optical fiber through a2 nd port of the first circulator, returning a back Rayleigh scattering signal generated in the sensing optical fiber to the 2 nd port of the first circulator, outputting the back Rayleigh scattering signal through a 3 rd port of the first circulator, inputting the back Rayleigh scattering light output by the 3 rd port of the first circulator into an optical filter, inputting the light after passing through the optical filter into a first photoelectric detector, and converting the light into an electric signal through the first photoelectric detector;
the signal light input to the interference system part is divided into two paths through the second coupler, wherein one path is used as the detection light of the interference part, and the other path is used as the reference light of the interference part; the detection light path is modulated into continuous sine detection light through the acousto-optic modulator, the continuous sine detection light is injected from the 1 st port of the second circulator, the 2 nd port of the second circulator outputs the detection light to the sensing optical fiber, the Faraday rotator connected to the tail end of the sensing optical fiber reflects the detection light injected into the sensing optical fiber and injects the reflected light into the 2 nd port of the second circulator, the 3 rd port of the second circulator outputs the reflected light to the third coupler, and after the reflected light is coupled with the reference light path, the coupled light is output to the second photoelectric detector;
s3, sequentially inputting the electric signals output by the first photoelectric detector into a low-pass filter and a first low-noise amplifier for low-pass filtering and amplifying, and finally inputting the electric signals into an A port of a data acquisition card;
The electric signal output by the second photoelectric detector is sequentially input into a band-pass filter and a second low-noise amplifier for band-pass filtering and amplification, and finally is input into a port B of the data acquisition card;
s4, the clock generator generates a synchronous clock signal as a trigger acquisition signal of the data acquisition card and a modulation signal of the acousto-optic modulator;
S5, the data acquisition card acquires the data of the port A and the port B, performs analog-digital conversion, and outputs two paths of digital signals to the computer end; wherein, the A port of the data acquisition card corresponds to the A-path data, and the B port of the data acquisition card corresponds to the B-path data;
S6, carrying out phase demodulation on the data of the path B, calculating a short-time energy spectrum, comparing the short-time energy spectrum with a frequency spectrum in a database, if the frequency spectrum characteristics are matched, proving that the vibration generated at the position is to be monitored by the system, further carrying out short-time variance calculation on the data of the path A to locate a vibration event, and if the frequency spectrum characteristics are not matched, continuing to carry out short-time energy spectrum calculation on other data pieces until the vibration event to be monitored is found, and then locating or not having the vibration event.
The beneficial effects of the invention are as follows:
(1) The invention fuses the direct detection type phi-OTDR structure and the interference structure based on the phi-OTDR technology and the interference technology, and further improves the frequency response range of the sensing system on the basis of ensuring the high spatial resolution of the sensing system, so that the sensing system is more suitable for practical application.
(2) The synchronous clock signal generated by the clock generator is simultaneously transmitted to the driving of the acousto-optic modulator and the data acquisition card, so that the modulating signal, the carrier signal and the triggering acquisition signal of the data acquisition card in the driving of the acousto-optic modulator are locked, further, the phase drift of the back Rayleigh scattered light is avoided, and the signal to noise ratio of the system is improved.
(3) The data acquisition card is used for carrying out double-channel signal acquisition, and the acquired intermediate frequency signals realize high spatial positioning precision and high-fidelity vibration signal characteristic restoration through a demodulation algorithm.
Drawings
FIG. 1 is a schematic diagram of a distributed fiber vibration sensing system according to an embodiment of the present invention.
Fig. 2 is a flowchart of the demodulation algorithm of the present embodiment.
Fig. 3 is a schematic diagram of the spectral relationship of different vibration events according to the present embodiment.
Fig. 4 is a vibration event localization schematic diagram of the present embodiment.
Detailed Description
The invention will now be described in further detail with reference to the accompanying drawings.
It should be noted that the terms like "upper", "lower", "left", "right", "front", "rear", and the like are also used for descriptive purposes only and are not intended to limit the scope of the invention in which the invention may be practiced, but rather the relative relationship of the terms may be altered or modified without materially altering the teachings of the invention.
Example 1
FIG. 1 is a schematic diagram of a distributed fiber vibration sensing system according to an embodiment of the present invention. Referring to fig. 1, the distributed optical fiber vibration sensing system includes a direct detection type Φ -OTDR module, an interference module, and a signal acquisition module.
The direct detection type phi-OTDR module comprises a laser, a first coupler, a Semiconductor Optical Amplifier (SOA) modulation module, an erbium-doped fiber amplifier (EDFA), a first circulator, a sensing fiber, an optical filter, a first photoelectric detector, a low-pass filter and a first low-noise amplifier.
The interference module comprises a second coupler, an acousto-optic modulator, a second circulator, a sensing optical fiber, a Faraday rotator mirror, a third coupler, a second photoelectric detector, a band-pass filter and a second low-noise amplifier.
The signal acquisition module comprises a clock generator and a data acquisition card; and the clock generator is used for generating a synchronous clock signal and outputting the synchronous clock signal to the driving and data acquisition card of the acousto-optic modulator.
And the laser is used for outputting continuous narrow linewidth laser to the first coupler.
The first coupler is used for dividing the narrow linewidth laser input by the laser into two paths: the first path is that part of signal light of the phi-OTDR system is input to the semiconductor optical amplifier modulation module, and the second path is that part of signal light of the interference system is input to the second coupler.
And the Semiconductor Optical Amplifier (SOA) modulation module is used for modulating the continuous signal light output by the first coupler into pulse light and outputting the pulse light to the erbium-doped fiber amplifier.
And the erbium-doped fiber amplifier (EDFA) is used for amplifying the pulse light output by the semiconductor optical amplifier modulation module and outputting the pulse light to the first circulator.
And the first circulator is used for outputting the detection light input by the 1 st port of the first circulator from the 2 nd port to the sensing optical fiber and outputting the back scattered light received by the 2 nd port from the 3 rd port of the first circulator to the first photoelectric detector.
And the sensing optical fiber is used for receiving back scattered light generated by the detection light input by the 2 nd port of the first circulator.
And the optical filter is used for filtering the back scattered light output by the 3 rd port of the first optical fiber circulator and outputting the back scattered light to the first photoelectric detector.
And the first photoelectric detector is used for converting the optical signal input by the optical filter into an electric signal and outputting the electric signal to the low-pass filter.
And the low-pass filter is used for carrying out low-pass filtering on the signal input by the first photoelectric detector and outputting the signal to the first low-noise amplifier.
And the first low-noise amplifier is used for amplifying the weak signal filtered by the low-pass filter and outputting the weak signal to the data acquisition card.
The second coupler is used for dividing the second path of narrow linewidth laser output by the first coupler into two paths: the first path is used as detection light to be input to the acousto-optic modulator, and the second path is used as local oscillation light to be input to the third coupler.
And the acousto-optic modulator is used for carrying out high-level modulation on the detection light input by the second coupler and outputting continuous detection light to the second circulator.
And the second circulator is used for outputting the detection light input by the 1 st port of the second optical fiber circulator from the 2 nd port to the sensing optical fiber and outputting the reflected light received by the 2 nd port from the 3 rd port of the second optical fiber circulator to the third coupler.
And the Faraday rotator mirror is used for reflecting the detection light input into the sensing optical fiber at the 2 nd port of the second circulator and outputting the detection light to the 2 nd port of the second optical fiber circulator.
And the third coupler is used for coupling the reflected light input by the 3 rd port of the second circulator and the local oscillation light input by the second coupler to the second photoelectric detector.
And the second photoelectric detector is used for converting the interference signal input by the third coupler into an electric signal and outputting the electric signal to the band-pass filter.
And the band-pass filter is used for band-pass filtering the interference electric signal input by the second photoelectric detector and outputting the interference electric signal to the second low-noise amplifier.
And the second low-noise amplifier is used for amplifying the weak signal filtered by the band-pass filter and outputting the weak signal to the data acquisition card.
And the clock generator is used for generating a synchronous clock signal and outputting the synchronous clock signal to the driving and data acquisition card of the acousto-optic modulator. In this embodiment, the phases of the modulated signal in the acousto-optic modulator drive, the carrier signal, and the trigger acquisition signal in the data acquisition card are locked.
The data acquisition card is used for taking the synchronous clock signal input by the clock generator as a trigger acquisition signal, carrying out analog-to-digital conversion on the electric signals input by the first low-noise amplifier and the second low-noise amplifier and acquiring data; the A port of the data acquisition card corresponds to the A-path data, and the B port of the data acquisition card corresponds to the B-path data.
The computer end is embedded with a demodulation algorithm, and the demodulation algorithm comprises the following steps:
And carrying out phase demodulation on the data of the path B, calculating a short-time energy spectrum, comparing the short-time energy spectrum with a frequency spectrum in a database, if the frequency spectrum characteristics are matched, proving that the vibration generated at the position is to be monitored by the system, further carrying out short-time variance calculation on the data of the path A to locate a vibration event, and if the data of the path A are not matched, continuing to carry out short-time energy spectrum calculation on other data pieces until the vibration event to be monitored is found, and then locating or not existence of the vibration event.
In this embodiment, the direct detection Φ -OTDR portion locates the vibration event, and the interference portion improves the frequency response of the system, so that the system has the vibration event location and the measurement capability of the broadband signal. The demodulation algorithm improves the spatial positioning precision of the vibration event, and restores the frequency spectrum characteristic of the vibration signal with high fidelity, so that the recognition accuracy of the vibration event is higher.
Example two
Based on the distributed optical fiber vibration sensing system based on the fusion phi-OTDR technology and the interference technology, the embodiment also refers to a demodulation method, which comprises the following steps:
Step one, generating continuous light by using a laser, wherein the light is divided into two paths through a first coupler: one path is used as the signal light of the direct detection type phi-OTDR part and is input to the SOA modulation module, and the other path is used as the signal light of the interference part and is input to the second coupler.
Illustratively, the laser used is a narrow linewidth laser capable of generating continuous narrow linewidth laser light with high coherence. The SOA module has the functions of amplifying and modulating, and can modulate the signal light into pulse light while amplifying the signal light. The direct detection type Φ -OTDR system uses weak back rayleigh scattered light to realize the positioning of vibration, while the interference system uses reflected light, so that the signal light of the direct detection type Φ -OTDR system part is required to be strong, and therefore, in an actual system, the first coupler can be 1×2 90:10 or 80: 20.
And step two, the signal light input to the direct detection type phi-OTDR system part is amplified through an SOA modulation module, the amplified detection pulse light is input through a1 st port of the first circulator and is output to the sensing optical fiber through a2 nd port of the first circulator, the backward Rayleigh scattering signal generated in the sensing optical fiber is returned to the 2 nd port of the first circulator and is output through a3 rd port, the backward Rayleigh scattering light output by the 3 rd port of the first circulator is input to the optical filter, and the light after passing through the optical filter is input into the first photoelectric detector and is converted into an electric signal through the first photoelectric detector. The signal light input to the interference system part is divided into two paths by the second coupler, wherein one path is used as the detection light of the interference part, and the other path is used as the reference light of the interference part. The detection light path is modulated into continuous sine detection light through the acousto-optic modulator, the continuous sine detection light is injected from the 1 st port of the second circulator, the 2 nd port of the second circulator outputs the detection light to the sensing optical fiber, and the tail end of the sensing optical fiber is connected with the Lat rotary mirror. The Faraday rotator reflects the detection light injected into the sensing optical fiber, and injects the reflected light into the 2 nd port of the second circulator, the 3 rd port of the second circulator outputs the reflected light to the third coupler, and the reflected light is coupled with the reference optical path and then output to the second photoelectric detector.
In this embodiment, the SOA modulation module is used to amplify and modulate the continuous light into pulsed light, and the EDFA is used to re-amplify the signal. The optical filter can filter stray light outside the detection light wave band, so that the signal light entering the first photoelectric detector is purer. The first photodetector is an Avalanche Photodiode (APD), commonly used as a detector for a direct detection type fiber optic sensing system. The interference system partly uses the reflected light interference to perform measurement, so the intensity of the detection light path is not required to be strong, so in practical use, the second coupler is 1×2 of 50: 50. The interference uses continuous light as detection light, so that a high modulation level is applied to the driving of the acousto-optic modulator, the full-open state of the acousto-optic modulator is maintained, and the continuous sinusoidal detection light output can be ensured. The Faraday rotator mirror can reflect the detection light, and the reflected light interferes with the reference light to achieve the purpose of interferometry. The sensing optical fiber is a multi-core optical fiber, so that the tail end of one path of sensing optical fiber is not provided with a device, and the tail end of the other path of sensing optical fiber is provided with a Faraday rotary mirror. The second photodetector is a Balanced Photodetector (BPD), commonly used in coherent fiber optic sensing systems.
And thirdly, sequentially inputting the electric signals output by the first photoelectric detector into a low-pass filter and a first low-noise amplifier for low-pass filtering and amplifying, and finally inputting the electric signals into an A port of a data acquisition card. And the electric signal output by the second photoelectric detector is sequentially input into the band-pass filter and the second low-noise amplifier for band-pass filtering and amplification, and finally is input into the port B of the data acquisition card. Specifically, the low-pass filter is used for filtering high-frequency noise, and the band-pass filter is used for filtering invalid signals outside the pass band. The first low noise amplifier and the second low noise amplifier are used for amplifying the signal light while reducing the introduction of amplification noise.
And step four, the clock generator generates a synchronous clock signal as a trigger acquisition signal of the data acquisition card and a modulation signal of the acousto-optic modulator. Therefore, the phases of the modulating signals, the carrier signals and the triggering acquisition signals in the data acquisition card in the driving of the acousto-optic modulator can be locked, the occurrence of frequency drift of the back Rayleigh scattering signals is avoided, and the signal-to-noise ratio of the system is improved. And the triggering acquisition signal frequency of the data acquisition card is 4n times of the modulation signal frequency of the acousto-optic modulator, and n is a positive integer.
And fifthly, the data acquisition card acquires A, B paths of data, performs analog-to-digital conversion, and outputs two paths of digital signals to the computer end.
Step six, referring to fig. 2, the two paths of signals A, B are respectively processed by using a demodulation algorithm built in the computer end. Specifically, the phase demodulation is performed on the B-path signal, and because the signal light of the interference part is continuous sinusoidal light, and the trigger acquisition signal frequency of the data acquisition card and the modulation signal frequency of the acousto-optic modulator are 4:1, the phase difference between adjacent sampling points can be ensured to be pi/2, namely, the adjacent odd sampling points and even sampling points are equivalent to I and Q components in the traditional IQ demodulation, so that a B path signal is divided into two paths of I and Q according to the odd and even sampling points, the phases are obtained by arc tangent after tangent, data after unwrapping are uniformly cut into data sheets with the time length of T, short-time energy spectrum calculation is carried out on the data sheets, and whether vibration events occur or not can be observed from the energy spectrum, and the details are shown in fig. 3. If no vibration event occurs, the energy spectrum exhibits a uniform white noise state. If a vibration event occurs, the calculated energy spectrum is compared with the frequency spectrum in the database, and if the frequency spectrum characteristics are matched, the vibration occurring at the position is proved to be the vibration which the system wants to monitor, and then the vibration event is positioned by analyzing the A-path signal. In order to realize the positioning of the vibration signal, firstly, data segmentation is carried out on the A-path signal, data sheets with the time length of T are cut, the data sheets are two-dimensional data of space-time, then, variance in the time T is obtained for each position on a space axis of a certain data sheet, and the fluctuation condition of the signal amplitude is represented by the size of the variance. When no vibration event exists, the variance is smaller, the signal fluctuation condition is gentle, and when the vibration event exists somewhere, the variance is larger and exceeds the threshold value, so that the vibration event can be positioned. And after the vibration event is positioned, continuing to return to the B path, processing the rest data sheet, and judging whether other vibration events exist. If the spectrum characteristics of the B path are not matched, continuing to perform short-time energy spectrum calculation on the rest data slices of the B path until the vibration event to be monitored is found and the vibration event is positioned by the A path or does not exist. The time length T of the data slice in this embodiment is set to 0.1s, and T can be adjusted according to the actual situation and can be large or small. Fig. 4 is a vibration event localization schematic diagram of the present embodiment.
The embodiment combines the phi-OTDR technology and the interference technology, adopts a phase locking structure, and further improves the frequency response range and the signal to noise ratio of the sensing system on the basis of ensuring the high spatial resolution of the sensing system. The high spatial resolution ensures the accuracy of vibration event positioning; the high frequency response ensures that different events can be accurately distinguished even when multiple vibration events are present or when their spectra overlap (see fig. 3); the high signal-to-noise ratio ensures the quality of the intermediate frequency signal. The demodulation algorithm can accurately distinguish the vibration event to be monitored, restore the characteristics of the vibration signal with high fidelity, and accurately position the event.
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above examples, and all technical solutions belonging to the concept of the present invention belong to the protection scope of the present invention. It should be noted that modifications and adaptations to the invention without departing from the principles thereof are intended to be within the scope of the invention as set forth in the following claims.
Claims (7)
1. The distributed optical fiber vibration sensing system is characterized by comprising a direct detection type phi-OTDR module, an interference module and a signal acquisition module;
the direct detection type phi-OTDR module comprises a laser, a first coupler, a semiconductor optical amplifier modulation module, an erbium-doped optical fiber amplifier, a first circulator, a sensing optical fiber, an optical filter, a first photoelectric detector, a low-pass filter and a first low-noise amplifier; the interference module comprises a second coupler, an acousto-optic modulator, a second circulator, a sensing optical fiber, a Faraday rotator mirror, a third coupler, a second photoelectric detector, a band-pass filter and a second low-noise amplifier; the signal acquisition module comprises a clock generator and a data acquisition card; the clock generator is used for generating a synchronous clock signal and outputting the synchronous clock signal to a driving and data acquisition card of the acousto-optic modulator;
the laser is used for outputting continuous narrow linewidth laser to the first coupler, and the first coupler divides the narrow linewidth laser input by the laser into two paths: the first path is that part of signal light of the phi-OTDR system is input to the semiconductor optical amplifier modulation module, and the second path is that part of signal light of the interference system is input to the second coupler;
the semiconductor optical amplifier modulation module modulates the continuous signal light output by the first coupler into pulse light to be output to the erbium-doped optical fiber amplifier, so that the pulse light is amplified by the erbium-doped optical fiber amplifier and then is output to the 1 st port of the first circulator; the detection light input by the 1 st port of the first circulator is output from the 2 nd port of the first circulator to the sensing fiber to generate back scattered light; the back scattered light is output to a first photoelectric detector from a3 rd port of the first circulator, the first photoelectric detector converts the back scattered light into an electric signal, the electric signal is output to a low-pass filter for low-pass filtering and then is output to a first low-noise amplifier for amplification and then is output to an A port of a data acquisition card;
the second coupler divides the second path of narrow linewidth laser output by the first coupler into two paths: the first path is used as detection light to be input to the acousto-optic modulator, and the second path is used as local oscillation light to be input to the third coupler; the acousto-optic modulator carries out high-level modulation on the detection light input by the second coupler, outputs continuous detection light to the 1 st port of the second circulator, outputs the detection light from the 2 nd port of the second circulator to the sensing optical fiber, and outputs the detection light from the 3 rd port of the second optical fiber circulator to the third coupler after being reflected by the Faraday rotator; the third coupler outputs the reflected light input by the 3 rd port of the second circulator and the local oscillator light input by the second coupler to the second photoelectric detector, the second photoelectric detector converts the reflected light into an electric signal, the electric signal is output to the band-pass filter for band-pass filtering and then is output to the second low-noise amplifier for amplification and then is output to the B port of the data acquisition card;
The data acquisition card is used for taking a synchronous clock signal input by the clock generator as a trigger acquisition signal, performing analog-to-digital conversion on electric signals input by the first low noise amplifier and the second low noise amplifier, outputting two paths of digital signals to a computer end, and processing by using a demodulation algorithm embedded in the computer end; wherein, the A port of the data acquisition card corresponds to the A-path data, and the B port of the data acquisition card corresponds to the B-path data;
The demodulation algorithm carries out phase demodulation on the data of the path B, calculates short-time energy spectrum, compares the short-time energy spectrum with frequency spectrums in a database, if the frequency spectrum characteristics are matched, proves that the vibration generated at the position is to be monitored by the system, further positions vibration events by carrying out short-time variance calculation on the data of the path A, and if the data of the path A is not matched, continues to carry out short-time energy spectrum calculation on other data pieces until the vibration events to be monitored are found, and then the vibration events are positioned or are not existed.
2. The distributed fiber optic vibration sensing system according to claim 1 wherein the laser is a narrow linewidth laser.
3. The distributed fiber optic vibration sensing system according to claim 1 wherein the first coupler is 1 x 2 90:10 or 80:20, and the second coupler is 1 x 2 50: 50.
4. The distributed fiber optic vibration sensing system according to claim 1 wherein the first photodetector is an avalanche photodiode and the second photodetector is a balanced photodetector.
5. The distributed optical fiber vibration sensing system according to claim 1, wherein the sensing optical fiber is a multi-core optical fiber, the tail end of one sensing optical fiber is not provided with a device, and the tail end of the other sensing optical fiber is provided with a faraday rotator.
6. The distributed optical fiber vibration sensing system according to claim 1, wherein the process of phase demodulating the B-path data and calculating the short-time energy spectrum comprises the steps of:
the B-path data is subjected to phase demodulation, wherein signal light of the interference part is continuous sinusoidal light, and the triggering acquisition signal frequency and the modulation signal frequency of the acousto-optic modulator of the data acquisition card are 4:1, the phase difference between adjacent sampling points is pi/2;
dividing the data of the B path into two paths of I and Q according to odd-even sampling points, obtaining phases by arctangent after tangent of the two paths, and uniformly cutting the unwound data into data sheets with the time length of T;
And carrying out short-time energy spectrum calculation on the data sheet.
7. A demodulation method based on a distributed fibre optic vibration sensing system according to one of claims 1-6, characterized in that the demodulation method comprises the steps of:
S1, generating continuous light by using a laser, wherein the light is divided into two paths through a first coupler: one path is used as signal light of a direct detection type phi-OTDR part and is input to an SOA modulation module, and the other path is used as signal light of an interference part and is input to a second coupler;
S2, after signal light input to a direct detection type phi-OTDR part passes through an SOA modulation module, amplifying the signal light through an EDFA, inputting amplified detection pulse light through a1 st port of a first circulator, outputting the amplified detection pulse light into a sensing optical fiber through a2 nd port of the first circulator, returning a back Rayleigh scattering signal generated in the sensing optical fiber to the 2 nd port of the first circulator, outputting the back Rayleigh scattering signal through a 3 rd port of the first circulator, inputting the back Rayleigh scattering light output by the 3 rd port of the first circulator into an optical filter, inputting the light after passing through the optical filter into a first photoelectric detector, and converting the light into an electric signal through the first photoelectric detector;
the signal light input to the interference system part is divided into two paths through the second coupler, wherein one path is used as the detection light of the interference part, and the other path is used as the reference light of the interference part; the detection light path is modulated into continuous sine detection light through the acousto-optic modulator, the continuous sine detection light is injected from the 1 st port of the second circulator, the 2 nd port of the second circulator outputs the detection light to the sensing optical fiber, the Faraday rotator connected to the tail end of the sensing optical fiber reflects the detection light injected into the sensing optical fiber and injects the reflected light into the 2 nd port of the second circulator, the 3 rd port of the second circulator outputs the reflected light to the third coupler, and after the reflected light is coupled with the reference light path, the coupled light is output to the second photoelectric detector;
s3, sequentially inputting the electric signals output by the first photoelectric detector into a low-pass filter and a first low-noise amplifier for low-pass filtering and amplifying, and finally inputting the electric signals into an A port of a data acquisition card;
The electric signal output by the second photoelectric detector is sequentially input into a band-pass filter and a second low-noise amplifier for band-pass filtering and amplification, and finally is input into a port B of the data acquisition card;
s4, the clock generator generates a synchronous clock signal as a trigger acquisition signal of the data acquisition card and a modulation signal of the acousto-optic modulator;
S5, the data acquisition card acquires the data of the port A and the port B, performs analog-digital conversion, and outputs two paths of digital signals to the computer end; wherein, the A port of the data acquisition card corresponds to the A-path data, and the B port of the data acquisition card corresponds to the B-path data;
S6, carrying out phase demodulation on the data of the path B, calculating a short-time energy spectrum, comparing the short-time energy spectrum with a frequency spectrum in a database, if the frequency spectrum characteristics are matched, proving that the vibration generated at the position is to be monitored by the system, further carrying out short-time variance calculation on the data of the path A to locate a vibration event, and if the frequency spectrum characteristics are not matched, continuing to carry out short-time energy spectrum calculation on other data pieces until the vibration event to be monitored is found, and then locating or not having the vibration event.
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Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2014183412A1 (en) * | 2013-05-17 | 2014-11-20 | 国家电网公司 | Multi-parameter distributed optical fiber sensing apparatus |
| CN105606196A (en) * | 2016-01-25 | 2016-05-25 | 西南交通大学 | High-frequency vibration measurement distributed fiber sensing system based on frequency division multiplexing technology |
| CN106482822A (en) * | 2016-12-07 | 2017-03-08 | 吉林大学 | A kind of phase sensitive optical time domain reflection system of the detection that is concerned with based on double homologous heterodyne |
| WO2017067255A1 (en) * | 2015-10-20 | 2017-04-27 | 中兴通讯股份有限公司 | Processing method and device for use in coherent phase-sensitive optical time-domain reflectometer |
| CN107664541A (en) * | 2017-09-18 | 2018-02-06 | 南京大学 | A kind of distributed optical fiber vibration and Temperature fusion sensor-based system and method |
| CN107976248A (en) * | 2016-10-25 | 2018-05-01 | 北京大学 | It can realize the distributed optical fiber sensing system and its measuring method of all phase demodulation |
| CN110487308A (en) * | 2019-08-27 | 2019-11-22 | 南京大学 | A kind of high-performance coherent detection type Φ-OTDR realization system and method based on PGC demodulation |
| CN112833929A (en) * | 2021-01-06 | 2021-05-25 | 中国地质大学（武汉） | Disturbance monitoring system of heterodyne phi-OTDR technology based on local optical frequency shift |
-
2021
- 2021-08-13 CN CN202110931428.8A patent/CN113654641B/en active Active
Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2014183412A1 (en) * | 2013-05-17 | 2014-11-20 | 国家电网公司 | Multi-parameter distributed optical fiber sensing apparatus |
| WO2017067255A1 (en) * | 2015-10-20 | 2017-04-27 | 中兴通讯股份有限公司 | Processing method and device for use in coherent phase-sensitive optical time-domain reflectometer |
| CN105606196A (en) * | 2016-01-25 | 2016-05-25 | 西南交通大学 | High-frequency vibration measurement distributed fiber sensing system based on frequency division multiplexing technology |
| CN107976248A (en) * | 2016-10-25 | 2018-05-01 | 北京大学 | It can realize the distributed optical fiber sensing system and its measuring method of all phase demodulation |
| CN106482822A (en) * | 2016-12-07 | 2017-03-08 | 吉林大学 | A kind of phase sensitive optical time domain reflection system of the detection that is concerned with based on double homologous heterodyne |
| CN107664541A (en) * | 2017-09-18 | 2018-02-06 | 南京大学 | A kind of distributed optical fiber vibration and Temperature fusion sensor-based system and method |
| CN110487308A (en) * | 2019-08-27 | 2019-11-22 | 南京大学 | A kind of high-performance coherent detection type Φ-OTDR realization system and method based on PGC demodulation |
| CN112833929A (en) * | 2021-01-06 | 2021-05-25 | 中国地质大学（武汉） | Disturbance monitoring system of heterodyne phi-OTDR technology based on local optical frequency shift |
Non-Patent Citations (1)
| Title |
|---|
| 基于双光束干涉的相位敏感光时域反射计;安阳;封皓;张景川;冯欣;曾周末;靳世久;光学学报;20131231;33(7);全文 * |
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