Fusion type optical fiber distributed multi-point disturbance detection demodulation system and fault positioning method

Abstract

The invention discloses a fusion type optical fiber distributed multi-point disturbance detection demodulation system and a multi-point fault positioning method. The fusion type optical fiber distributed multi-point disturbance detection demodulation system comprises two light sources, a one-way Mach-Zehnder optical fiber interferometer, a phase-sensitive optical time domain reflectometer and a data acquisition and processing module, when a plurality of abnormal vibration events act on the sensing optical fiber at the same time, a continuous laser signal emitted by the first laser enters the one-way Mach-Zehnder interferometer, and a photoelectric detector receives a continuous interference sensing optical signal in real time; a continuous laser signal emitted by the second laser is converted into a periodic pulse optical signal, the periodic pulse optical signal enters the phase-sensitive optical time domain reflectometer and the one-way Mach-Zehnder interferometer, and the pulse optical signal is received in real time by the photoelectric detector; the data acquisition and processing module adopts an improved phase generation carrier phase demodulation scheme to demodulate the phase change of a vibration signal applied to the sensing optical fiber so as to calculate amplitude-frequency information; and the obtained backward Rayleigh scattering light signals are utilized to calculate and demodulate position information of a plurality of fault events.

Description

Technical Field

[0001] The present invention belongs to the field of sensing and detection, and in particular relates to an optical fiber distributed multi-point precise detection and demodulation system and a fault location method based on the combination of forward signal light interference and backward scattered light interference. Background Art

[0002] Distributed fiber optic vibration sensing technology is a new type of sensing detection technology in recent years. In the process of sensing and detecting specific vibration events, it can simultaneously realize the sensing detection and transmission of signals based on a single fiber optic link. Compared with traditional electromagnetic vibration sensing detection technology, distributed fiber optic vibration sensing technology has many advantages such as high sensitivity, large monitoring range, high positioning accuracy and easy installation. At present, this technology has been widely used in perimeter security, health monitoring of large buildings, and safe detection of important resource transmission. With the deepening of the application of distributed fiber optic vibration sensing technology in the above-mentioned related fields, the synchronous detection of multi-point fault vibration information and high-frequency vibration information has become a key technical problem that needs to be solved in complex application environments. For example, when dangerous events such as cracks occur during the health quality detection of large buildings, the frequency response is generally as high as several megahertz. On the other hand, due to the distributed fiber optic vibration sensing system, its sensing signal is ultimately sensed and demodulated in the form of interference light. Therefore, the amplitude of the interference sensing light received by the detector is nonlinearly related to the magnitude of the stress event acting on the sensing optical fiber, which makes the system unable to accurately restore the amplitude-frequency information of the vibration event of the target to be measured, thereby affecting the sensing system's accurate perception and measurement of the vibration event of the target to be measured.

[0003] Distributed fiber optic vibration sensing systems can be divided into two types according to their sensing structure and sensing principle: forward light interferometer type and backscattered light interferometer type. The forward light interferometer type distributed fiber optic vibration sensing system realizes the sensing detection and transmission of forward signal light by constructing optical fiber interferometers such as Mach-Zehnder optical fiber interferometers, Michelson optical fiber interferometers and Sagnac optical fiber interferometers. This type of distributed fiber optic vibration sensing system has the advantages of simple sensing structure and fast response speed. In particular, its frequency response is mainly limited by the real-time data sampling rate of the demodulation terminal, so it also has the outstanding advantage of wide detection frequency response. However, since this type of distributed fiber optic vibration sensing system generally solves the specific disturbance position by estimating the time delay relationship of the signal, it cannot simultaneously detect multiple vibration events on the optical fiber link. On the other hand, the backscattered light interferometer type distributed fiber optic vibration sensing system mainly realizes the sensing detection and transmission of vibration events along the optical fiber through the backscattered light such as backscattered Rayleigh scattered light and backscattered Brillouin scattered light formed when ultra-narrow pulse light is transmitted in the sensing optical fiber. Therefore, this type of distributed optical fiber vibration sensing system can synchronously demodulate and detect multi-point vibration events on the optical fiber link. And its positioning spatial resolution is mainly limited by the width of the pulse light injected into the sensing optical fiber, so this type of distributed optical fiber vibration sensing system also has the advantage of high positioning accuracy. However, due to the constraint relationship between the pulse light injected into the sensing optical fiber and the maximum monitoring distance of the sensing optical fiber, this type of distributed optical fiber vibration sensing system cannot accurately analyze the frequency of high-frequency vibration events, that is, this type of sensing system has the disadvantage of low detection frequency response. For this reason, the traditional single-mechanism distributed optical fiber vibration sensing system cannot directly accurately sense and detect multi-point broadband vibration events in practical applications, thereby restricting the application prospects of distributed optical fiber vibration sensing systems in the field of vibration detection. In addition, since the interference signal light and the phase information introduced by the vibration event acting on the sensing optical fiber are in a nonlinear mapping relationship, the original interference signal light obtained by demodulation cannot accurately restore the amplitude-frequency information of the original vibration event, which seriously restricts the quantitative analysis of the sensing system in practical applications.

[0004] To sum up, designing a distributed optical fiber vibration sensing system with multi-point broadband detection and accurate demodulation of the amplitude and frequency information of vibration signals has important practical significance for improving its in-depth application in the field of vibration sensing detection. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and propose an optical fiber distributed multi-point precision detection and demodulation system and a multi-point fault location method based on the combination of forward signal light interference and backscattered light interference. The demodulation system is a fusion-type distributed optical fiber sensing system based on a forward light interferometer and a backscattered light interferometer such as a Mach-Zehnder interferometer. It continuously monitors phase changes based on forward signal light interference to obtain amplitude-frequency change information, and uses backscattered light interference to synchronously demodulate position information of multi-point vibration events, thereby realizing multi-point broadband precision perception detection and demodulation of the distributed optical fiber vibration sensing system, and providing a dual-mechanism fusion distributed optical fiber vibration sensing system based on the combination of forward signal interference light and backscattered interference light for more accurate analysis of vibration information applied to the sensing optical fiber. The improved phase generation carrier demodulation technology that can accurately restore the phase information introduced by the vibration event to be measured can effectively realize the accurate demodulation of the amplitude-frequency information of the vibration signal to be measured.

[0006] A fusion type optical fiber distributed multi-point disturbance detection and demodulation system based on the combination of forward signal light interference and backscattered light interference, comprising: a first laser, a second laser, an isolator, a unidirectional Mach-Zehnder fiber interferometer, a phase-sensitive optical time domain reflectometer (hereinafter referred to as OTDR) and a data acquisition and processing module;

[0007] The output end of the first laser is sequentially connected to the isolator, the first optical fiber coupler and the input end of the unidirectional Mach-Zehnder interferometer, and the output end of the unidirectional Mach-Zehnder interferometer is sequentially connected to the second optical fiber coupler, the photoelectric detector and the data acquisition and processing module;

[0008] The output end of the second laser is connected to the isolator and the input end of the OTDR in sequence, and the output end of the OTDR is connected to the photodetector and the data acquisition and processing module in sequence; the phase-sensitive optical time domain reflectometer can simultaneously synchronously locate multiple vibration events acting on the sensing optical fiber for subsequent demodulation;

[0009] The working process of the demodulation system includes: after the continuous laser signal output by the first laser is transmitted through the isolator, it is divided into two paths by the first optical fiber coupler and enters the unidirectional Mach-Zehnder interferometer for sensing detection, one of which enters the sensing optical fiber link of the unidirectional Mach-Zehnder interferometer through one port of the wavelength division multiplexer, and the other enters the reference optical fiber and performs high-frequency carrier modulation; after the continuous laser signal output by the second laser is transmitted through the isolator, it is converted into a periodic pulse optical signal by the acousto-optic modulator, and then enters the OTDR for power amplification and filtering, and then enters the sensing optical fiber link of the unidirectional Mach-Zehnder interferometer through the optical fiber circulator and the other port of the wavelength division multiplexer;

[0010] The continuous sensing light signal from the first laser generates interference at the second optical fiber coupler after high-frequency modulation and sensing detection by the reference optical fiber and the sensing optical fiber to form an interference sensing light signal, which is received in real time by the photodetector; the backward Rayleigh scattered light generated by the pulse light from the second laser along the sensing optical fiber link is again transmitted in reverse by the wavelength division multiplexer and the optical fiber circulator, and is received in real time by another channel of the photodetector;

[0011] The data acquisition and processing module acquires backward Rayleigh scattered light and interference sensing light signals, uses the sensing light signals to demodulate the phase change of the vibration signal applied to the sensing optical fiber to calculate the amplitude-frequency information; and uses the obtained backward Rayleigh scattered light signals to calculate and demodulate the corresponding specific fault disturbance position information.

[0012] Furthermore, the data acquisition and processing module includes a data acquisition card and an industrial computer, and the industrial computer also includes an improved phase generation carrier modulation subsystem that can accurately restore the amplitude and frequency information of the vibration signal to be measured, specifically including:

[0013] DC filter: used to filter out the DC component in the continuous interference sensing light signal with a central wavelength of λ1 emitted by the first laser, and provide effective AC components in the sensing signal light for subsequent demodulation schemes;

[0014] Primary carrier signal cosw0t: provides a high-frequency carrier signal for one AC component, so that it can be demodulated with the subsequent filter to restore the sinusoidal part containing the vibration signal to be measured;

[0015] Low-pass filter: used to obtain the product part containing the zero-order Bessel term and the cosine term of the vibration signal to be measured, and to obtain the product part containing the first-order Bessel term and the sine term of the vibration signal to be measured;

[0016] Differentiator: used to perform differential operation on the product part containing the first-order Bessel term and the sine term containing the vibration signal to be measured, so as to complete the conversion of trigonometric functions and effectively separate the phase information introduced by the vibration signal to be measured;

[0017] Multiplier: used to complete the product operation of the corresponding output items to obtain the expected product result;

[0018] Divider: used to complete the division operation of the corresponding output items to eliminate redundant items in the operation results;

[0019] Inverter: used to complete the inversion operation processing in the operation result;

[0020] Square root operator: used to complete the specific square root mathematical operation of the operation result;

[0021] Integrator: It is used to complete the integration operation of the operation results to achieve accurate demodulation and restoration of the vibration signal to be measured.

[0022] Further, the Mach-Zehnder interferometer includes a sensing optical fiber, a reference optical fiber, a phase modulator (PZT), a wavelength division multiplexer (DWDM) and a second optical filter;

[0023] The OTDR includes an erbium-doped fiber amplifier (EDFA), a first optical filter, an optical fiber circulator and a Mach-Zehnder interferometer which are connected in sequence.

[0024] Wherein, the first laser is a narrow linewidth laser with a central wavelength of λ1, and the second laser is an ultra-narrow linewidth laser with a central wavelength of λ2;

[0025] The isolator is used to maintain unidirectional transmission of the continuous laser signal output by the first laser / the second laser;

[0026] The first optical fiber coupler and the second optical fiber coupler are 3dB optical fiber couplers;

[0027] The optical fiber circulator is a three-port optical fiber circulator, which is used to couple the power-amplified pulse light into one port of the wavelength division multiplexer, and simultaneously receive the back Rayleigh scattered light generated by the transmission pulse light in the sensing optical fiber;

[0028] The wavelength division multiplexer is used to couple the continuous light with a central wavelength of λ1 and the pulse light with a central wavelength of λ2 into the sensing optical fiber link for transmission.

[0029] Preferably, the central wavelength λ1 ranges from 1549.00 to 1550.22 nm, and the central wavelength λ2 ranges from 1549.7 to 1550.92 nm.

[0030] A multi-point fault location method using the optical fiber distributed multi-point precise detection and demodulation system comprises:

[0031] Step 1: When at least two abnormal vibration events act on the sensing optical fiber at the same time, the refractive index at the force-bearing position of the corresponding sensing optical fiber will change, and the continuous laser signal with a central wavelength of λ1 emitted by the first laser enters the unidirectional Mach-Zehnder interferometer, one way enters the sensing optical fiber, and the other way enters the reference optical fiber, so that the phase of the continuous interference light with a central wavelength of λ1 is synchronously modulated by the vibration force, and the photoelectric detector receives the continuous interference sensing light signal in real time;

[0032] At the same time, the continuous laser signal with a central wavelength of λ2 emitted by the second laser is converted into a periodic pulse light signal and then enters the phase-sensitive optical time-domain reflectometer and the one-way Mach-Zehnder interferometer in sequence. The backward Rayleigh scattered light with a central wavelength of λ2 generated along the sensing optical fiber modulates the vibration force, causing the amplitude of the interference signal near the corresponding position to change, and the pulse light signal is received in real time by the photoelectric detector.

[0033] Step 2: Since multiple abnormal vibration events will be uniformly reflected in the final interference signal when synchronously phase modulating the continuous interference sensor light signal with a central wavelength of λ1, the receiving end of the data acquisition and processing module synchronously collects and receives the corresponding interference vibration sensor light signal according to the time length; the improved phase generation carrier phase demodulation scheme is used at the processing end of the data acquisition and processing module to accurately demodulate the specific amplitude-frequency information of the vibration event;

[0034] At the same time, the collected multiple backward Rayleigh scattered interference lights are triggered and collected according to the pulse time entering the sensing optical fiber to obtain a complete backward Rayleigh scattering curve; then, the difference operation is used to process and according to the fixed time difference between the pulse light and the backward Rayleigh scattered light, the position information of multiple abnormal vibration events acting on the sensing optical fiber is demodulated in real time.

[0035] Furthermore, the improved phase generation carrier phase demodulation scheme specifically includes:

[0036] The collected interference sensing light signal enters the DC filter to perform DC filtering to eliminate the DC component in the interference sensing light signal;

[0037] Then the interference sensing light signal is divided into two paths, one is low-pass filtered in the reference optical fiber, and the other is low-pass filtered in the sensing optical fiber after being multiplied with the primary carrier signal cosw0t;

[0038] Perform differential operation on the signal containing the cosine term of the vibration signal to be measured and the signal containing the sine term of the vibration signal to be measured after filtering, so as to complete the trigonometric function conversion of the cosine term and the sine term of the vibration signal to be measured output by the filter, so that the original differential term containing the phase information introduced by the vibration signal to be measured directly appears in the trigonometric function term after conversion, so as to eliminate the trigonometric function term through mathematical operation in the subsequent process, so as to demodulate and obtain the original phase information introduced by the vibration signal;

[0039] The divider, multiplier, inverter and square root operator are used in turn to perform division, multiplication, inversion and square root operations on the corresponding output items, and the differential term of phase change is introduced into the interference vibration sensor light signal; then the integrator is used to output and restore the original time domain waveform signal of the accurate vibration signal.

[0040] Furthermore, a plurality of backward Rayleigh scattered interference lights entering the industrial computer are firstly processed by cumulative averaging to remove burr signals.

[0041] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0042] The light source of the optical fiber distributed multi-point precise detection and demodulation system and multi-point fault location method based on the combination of forward signal light interference and backscattered light interference of the present invention adopts narrow linewidth lasers and ultra-narrow linewidth lasers with different central wavelengths. The narrow linewidth laser is used to construct a unidirectional Mach-Zehnder fiber interferometer; the ultra-narrow linewidth laser is used to construct a phase-sensitive optical time domain reflectometer;

[0043] The constructed single Mach-Zehnder fiber interferometer and phase-sensitive optical time-domain reflectometer couple the sensing signal lights of the two into the same sensing optical fiber link through a dense wavelength division multiplexer, thus forming and establishing a dual-mechanism fusion optical fiber distributed vibration sensing system; when a vibration event acts on the optical fiber link, the amplitude and frequency information of the vibration signal to be measured can be demodulated through the unidirectional Mach-Zehnder fiber interferometer part, and the position information of the vibration signal to be measured can be synchronously analyzed through the phase-sensitive optical time-domain reflectometer part;

[0044] An improved phase generation carrier phase demodulation scheme is constructed to achieve multi-point broadband accurate sensing detection and demodulation of the distributed optical fiber vibration sensing system, which not only makes up for the shortcomings of the single-mechanism distributed optical fiber vibration sensing demodulation scheme, but also can realize multi-point broadband vibration detection of the vibration signal to be measured. In addition, compared with the traditional phase demodulation scheme of the vibration signal to be measured, the phase demodulation scheme of this design does not require high-frequency harmonic modulation and multi-channel signal coordinated detection, thereby optimizing the optical path demodulation structure, saving hardware design costs and realizing accurate measurement of the vibration signal to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The schematic diagram of the dual-mechanism fusion type optical fiber distributed multi-point broadband vibration sensing detection system of the present invention is shown;

[0046] Figure 2 The schematic diagram of the improved phase-generated carrier demodulation that can accurately demodulate and restore the phase information of the interference signal is shown.

[0047] In the figure:

[0048] 1: First laser 2: Second laser 3: Isolator

[0049] C1: First fiber coupler C2: Second fiber coupler 4: Acousto-optic modulator

[0050] 5: Erbium-doped fiber amplifier 6: First optical filter 7: Circulator

[0051] 8: Phase modulator 9: Wavelength division multiplexer 10: Second optical filter

[0052] 11: Sensing fiber 12: Reference fiber 14: Transmission fiber

[0053] 15: Photoelectric detector 16: Data acquisition card 17: Signal generator

[0054] 18: Industrial Computer DETAILED DESCRIPTION

[0055] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The described specific embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0056] like Figure 1 As shown, a fiber-optic distributed multi-point precision detection and demodulation system based on the combination of forward signal light interference and backscattered light interference includes: a first laser 1, a second laser 2, an isolator 3, an arbitrary signal generator (AFG) 17, a unidirectional Mach-Zehnder fiber interferometer, a phase-sensitive optical time domain reflectometer (hereinafter referred to as OTDR) and a data acquisition and processing module. The data acquisition and processing module includes a data acquisition card 16 and an industrial computer 18 connected in sequence. The demodulation system described in the present invention is based on the principle of forward signal light interference and backscattered light interference, and adopts dense wavelength division multiplexing technology to realize independent synchronous demodulation of vibration position information and frequency information on the optical fiber link. Moreover, in the sensing part based on the forward signal light interference mechanism, an improved phase generation carrier demodulation scheme is introduced by design to accurately restore the amplitude-frequency information of the vibration signal to be measured applied to the optical fiber link, thereby realizing the precise perception and measurement of multi-point broadband vibration signals.

[0057] Among them, the output end of the first laser 1 is connected to the isolator 3, the first fiber coupler C1 and the input end of the Mach-Zehnder interferometer in sequence, and the output end of the Mach-Zehnder interferometer is connected to the second fiber coupler C2, the photodetector 15, the data acquisition card 16 and the industrial computer 18 in sequence; the Mach-Zehnder interferometer includes a sensing fiber 11, a reference fiber 12, a phase modulator (PZT) 8, a wavelength division multiplexer (DWDM) 9 and a second optical filter 10.

[0058] The output end of the second laser 2 is sequentially connected to an isolator 3, an acousto-optic modulator (AOM) 4 and an input end of an OTDR, and the output end of the OTDR is sequentially connected to a photodetector 15, a data acquisition card 16 and an industrial computer 18. The OTDR includes an erbium-doped fiber amplifier (EDFA) 5, a first optical filter 6, an optical fiber circulator 7 and a Mach-Zehnder interferometer, which are sequentially connected.

[0059] Wherein, the first laser 1 is a narrow linewidth laser with a central wavelength of λ1, and the first light source emitted by it is a continuous laser signal used as the light source of a unidirectional Mach-Zehnder fiber interferometer; the second laser 2 is an ultra-narrow linewidth laser with a central wavelength of λ2, and the second light source emitted by it is a continuous laser signal used as the light source of a phase-sensitive optical time-domain reflectometer. The laser emitted by the first laser 1 enters the unidirectional Mach-Zehnder fiber interferometer after passing through the isolator 3, and the laser emitted by the second laser 2 enters the phase-sensitive optical time-domain reflectometer after passing through the isolator 3. The isolator 3 is used to maintain the unidirectional transmission of the continuous laser signal output by the first light source / the second light source. The arbitrary signal generator 17 is used to provide the demodulation system with various signal sources required, and the arbitrary signal generator 17 is connected to the acousto-optic modulator 4 and the data collector 16 respectively. The acousto-optic modulator (AOM) 4 modulates the continuous laser signal output by the second light source of the second laser 2 into a periodic pulse light under the modulation of an external trigger pulse. The erbium-doped fiber amplifier 5 is used to power amplify the pulse light signal output by the acousto-optic modulator 4. The first optical filter 6 is used to filter out and suppress the spontaneous radiation noise component carried by the pulse light signal during the power amplification process. The first fiber coupler C1 and the second fiber coupler C2 are 3dB fiber couplers, wherein the first fiber coupler C1 is used to divide the continuous light signal output by the first laser 1 into two optical signals for transmission, and the second fiber coupler C2 is used to combine the two optical signals with a central wavelength of λ1 for coupling interference, and the interference signal enters the transmission optical fiber for output. The fiber circulator 7 is a three-port fiber circulator, which is used to couple the power-amplified pulse light into one port of the wavelength division multiplexer 9, and at the same time receive the backward Rayleigh scattered light generated by the transmission pulse light in the sensing optical fiber. The wavelength division multiplexer 9 is a dense wavelength division multiplexer (DWDM), which is used to couple the continuous light with a central wavelength of λ1 and the pulse light with a central wavelength of λ2 into the sensing optical fiber link for transmission. The sensing optical fiber is an ordinary G.652D single-mode communication optical fiber, which is used to sense vibration events along the line and complete the transmission of the sensing signal. The phase modulator 8 is used to realize high-frequency modulation of the vibration signal to be measured in the Mach-Zehnder optical fiber interferometer under the action of an external high-frequency carrier signal. The photodetector 15 is used to simultaneously receive the interference sensing signal light output by the second optical fiber coupler C2 and the Rayleigh interference scattering sensing light transmitted in the reverse direction by the optical fiber circulator 7, and convert the two interference sensing light signals into corresponding sensing electrical signals. The second optical fiber coupler C2 is connected to the photodetector 15 through the transmission optical fiber 14. The photodetector 15 is an avalanche photodetector, and the data acquisition card 16 is used to perform analog-to-digital conversion on the sensing electrical signal and complete subsequent data acquisition and transmission. The industrial computer 17 finally demodulates and restores the position information and amplitude-frequency information of the vibration signal applied to the sensing optical fiber through signal processing and analysis.

[0060] Since the central wavelengths of the continuous laser and the pulsed laser transmitted simultaneously in the sensing optical fiber are different, they can respectively detect external vibration events simultaneously. Specifically, the optical path transmission process of the demodulation system includes:

[0061] The continuous laser light with a central wavelength of λ1 emitted by the first laser 1 enters the first fiber coupler C1 after passing through the isolator 3. The first fiber coupler C1 divides the signal light into two beams and enters the Mach-Zehnder interferometer for interference. One arm of the fiber is the reference fiber link, and the other arm is the sensing fiber link. The signal light on the reference fiber link enters the second fiber coupler C2 along the reference fiber 12 after being phase modulated by the phase modulator 8; the signal light on the sensing fiber link enters the wavelength division multiplexer 9; the continuous sensing light with a central wavelength of λ1 is subjected to high-frequency carrier modulation due to the phase modulation of the phase modulator 8 when it is transmitted in the reference fiber link, and the vibration event information acting on the sensing fiber link can be synchronously detected during the sensing transmission process. Finally, the two continuous sensing lights from the reference fiber and the sensing fiber interfere with each other at the second fiber coupler C2, and the interference output light is received and detected in real time by one port of the photodetector 15 after passing through the transmission fiber.

[0062] The laser light with a central wavelength of λ2 from the second laser 2 enters the acousto-optic modulator 4 through the isolator 3, and after modulation, the optical signal is converted into a periodic pulse light. Then, the pulse light signal enters the erbium-doped fiber amplifier 5 for power amplification and the second filter 10 for spontaneous radiation noise suppression, and then enters the fiber circulator 7 for transmission. Finally, the periodic pulse light with a central wavelength of λ2 enters the sensing fiber 11 through another port of the dense wavelength division multiplexer; in the wavelength division multiplexer 9, the signal light from the first laser and the pulse light from the OTDR are coupled together therein, and the pulse light from the OTDR is finally suppressed and attenuated by the second filter 10 after being transmitted through the sensing fiber 11, so as to prevent it from superimposing and affecting the continuous sensing light entering the second fiber coupler C2. Since the central bandwidth of the second filter 10 is set to λ1±0.2nm and the wavelength difference between λ1 and λ2 is greater than 0.2nm, the pulse light with a central wavelength of λ2 will be completely attenuated and suppressed at the second filter 10, so that it will not be further superimposed on the continuous light with a central wavelength of λ1 to produce an effect at the second fiber coupler C2. According to the principle of optical fiber Rayleigh scattering, when the pulse light from the OTDR is transmitted in the sensing optical fiber l1, it will generate continuous backward Rayleigh scattered light along the line and its central wavelength is still λ2; after the Rayleigh scattered light is reversely transmitted through the sensing optical fiber, it is transmitted again through the dense wavelength division multiplexer 9 and the 3-port optical fiber circulator 7, and then received and detected in real time by another path of the photodetector 15.

[0063] After the continuous sensing light and the backward Rayleigh scattered light enter the photoelectric detector 15, the two interference sensing light signals can be converted into corresponding sensing electrical signals, and then after analog-to-digital conversion and data acquisition by the data acquisition card 16, they are finally transmitted to the industrial computer 17 for demodulation processing.

[0064] According to the unidirectional Mach-Zehnder fiber interferometer, its frequency response is mainly limited by the real-time sampling rate of the demodulation end data acquisition card 16, so the photoelectric detector 15 receives a continuous interference sensing light signal with a central wavelength of λ1, which can be used for specific demodulation of the frequency information of the vibration signal. According to the phase-sensitive optical time-domain reflectometer, it has the ability to synchronously demodulate multi-point vibration position information, so the continuous back-Rayleigh scattered light signal with a central wavelength of λ2 received by the detector can be used for accurate demodulation of the vibration signal position information.

[0065] If the high-frequency carrier signal applied by the sensing part of the Mach-Zehnder fiber interferometer to the phase modulator 8 is Ccosw0t, the interference signal generated at the second fiber coupler C2 can be specifically expressed as:

[0066]

[0067] Wherein, A is the DC component of the sensing light signal received by the photodetector 15, and B is the interference intensity of the sensing light signal. is the phase information introduced by the vibration signal, C is the modulation depth, and w0 is the angular frequency of the modulation signal. The signal expressed by formula (1) is finally sent to the industrial computer 17 for specific analysis after analog-to-digital conversion and data acquisition.

[0068] The multi-point fault location method of the optical fiber distributed multi-point precise detection and demodulation system based on the combination of forward signal light interference and backscattered light interference includes:

[0069] Step 1: When multiple abnormal intrusion events occur simultaneously on the sensing optical fiber, the vibrations caused will cause the refractive index and other parameters at the corresponding sensing optical fiber to change, thereby causing the phase of the sensing signal to change accordingly. The continuous laser from the first laser 1 passes through the isolator 3, the first optical fiber coupler C1, and enters the Mach-Zehnder interferometer and the second optical fiber coupler C2. The interference sensing light signal is obtained through phase modulation, and then enters the industrial computer 18 through the transmission optical fiber 14, the photoelectric detector 15, and the data acquisition device 16 for demodulation of the amplitude-frequency information;

[0070] When an abnormal intrusion event occurs, the continuous laser from the second laser 2 passes through the isolator 3, the acousto-optic modulator 4, the phase-sensitive optical time-domain reflectometer, and the Mach-Zehnder interferometer, and the pulsed light signal enters the sensing optical fiber link. At the same time, the optical fiber circulator 7 receives the backward Rayleigh scattered light generated in the sensing optical fiber link, and after being received by the photoelectric detector, it enters the industrial computer 18 through the data acquisition device 16 to demodulate the position information.

[0071] Step 2: If Figure 2 As shown, the working process of the industrial computer 17 is as follows:

[0072] At the receiving end of the industrial computer, when multiple abnormal vibration events perform synchronous phase modulation on the continuous interference sensing light signal with a central wavelength of λ1, it will be uniformly reflected in its final interference signal. Therefore, it can be collected according to the time length, and then the proposed improved phase generation carrier phase demodulation scheme is further used at the processing end of the industrial computer to accurately demodulate the specific amplitude-frequency information of the vibration event; on the other hand, when multiple abnormal vibration events perform synchronous phase modulation on the Rayleigh scattered interference light with a central wavelength of λ2, the intensity of the corresponding interference signal will change accordingly along the specific position of the sensing optical fiber. Therefore, the backward Rayleigh scattered interference light signal can be triggered and collected according to the pulse time entering the sensing optical fiber to obtain a complete backward Rayleigh scattering curve. Subsequently, the cumulative average and difference algorithm is further used at the processing end of the industrial computer to demodulate the location information of multiple abnormal vibration events.

[0073] Specifically, the original interference signal is first filtered to remove its DC component, and then divided into two paths for transmission operation. The upper branch reference optical fiber link is filtered by a low-pass filter, and the lower branch sensing optical fiber link is multiplied by the first harmonic and filtered by a low-pass filter to obtain:

[0074]

[0075] Where J0(C) and J1(C) represent the first-order and second-order Bessel function terms respectively. After taking the derivatives of I0(t) and I1(t) in formula (2), we can get the following by cross division:

[0076]

[0077] By multiplying I2(t) and I3(t) in formula (3) and taking the inverse operation, we can obtain:

[0078]

[0079] Taking square root of I4(t) in formula (4) yields:

[0080]

[0081] Finally, after integrating I5(t) in formula (5), we can get:

[0082]

[0083] When the external vibration signal acts on the sensing optical fiber, the phase change of the interference sensing light signal is introduced. It can be specifically expressed as Where D0 is the amplitude of the vibration signal applied, w s is the angular frequency of the applied vibration signal. Therefore, it can be seen from formula (6) that the improved phase generation carrier demodulation scheme of the present invention can accurately demodulate the amplitude-frequency information of the vibration signal acting on the sensing optical fiber link.

[0084] At the same time, the phase-sensitive optical time-domain reflectometer involved in the present invention can demodulate the vibration position information acting on the sensing optical fiber link. Specifically, after the backward continuous Rayleigh scattering sensing signal is converted to a digital form and data is collected by the data acquisition card, it is sent to the industrial control computer and firstly subjected to cumulative averaging processing to eliminate the burr signal in the continuous sensing acquisition process to improve the overall signal-to-noise ratio of the sensing signal. When a disturbance event acts on the optical fiber link, the refractive index at the position of the corresponding optical fiber action point will change, thereby causing the interference signal amplitude at the corresponding position of the continuously received backward Rayleigh scattering interference light signal to also change. Accordingly, the continuously acquired backward Rayleigh scattering interference light curve signal is subjected to difference calculation processing to demodulate the specific vibration information acting on the optical fiber in real time. Since the backward Rayleigh scattering light generated by the pulse light signal is a function of the transmission time, the specific position information of the vibration event acting on the sensing optical fiber can be specifically analyzed according to the fixed time difference between the pulse light and the Rayleigh scattering light, that is:

[0085]

[0086] Where x is the specific position of the disturbance event on the sensing fiber relative to the three-port fiber circulator, c is the propagation speed of the light wave signal in a vacuum, and n is the intrinsic refractive index of the sensing fiber.

[0087] Since the phase-sensitive optical time domain reflectometer involved in the present invention can simultaneously perform synchronous positioning and analysis on multiple vibration events acting on the sensing optical fiber, the dual-mechanism fusion type optical fiber distributed optical fiber disturbance sensing system designed in the present invention also has the function of locating and detecting multiple vibration events.

[0088] Based on the above analysis, the distributed optical fiber sensing system designed in the present invention can realize the accurate perception and detection of multi-point broadband vibration events.

[0089] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, which are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which fall within the scope of protection of the present invention.

Claims

1. A fusion type optical fiber distributed multi-point disturbance detection and demodulation system, characterized in that include: A first laser (1), a second laser (2), an isolator (3), a unidirectional Mach-Zehnder fiber interferometer, a phase-sensitive optical time-domain reflectometer, and a data acquisition and processing module; The output end of the first laser (1) is sequentially connected to the isolator (3), the first optical fiber coupler (C1) and the input end of the unidirectional Mach-Zehnder interferometer, and the output end of the unidirectional Mach-Zehnder interferometer is sequentially connected to the second optical fiber coupler (C2), the photoelectric detector (15) and the data acquisition and processing module; The output end of the second laser (2) is sequentially connected to the isolator (3) and the input end of the phase-sensitive optical time-domain reflectometer, and the output end of the phase-sensitive optical time-domain reflectometer is sequentially connected to the photodetector (15) and the data acquisition and processing module; The phase-sensitive optical time-domain reflectometer can simultaneously locate multiple vibration events acting on the sensing optical fiber for subsequent demodulation; The working process of the demodulation system includes: after the continuous laser signal output by the first laser (1) is transmitted through the isolator (3), it is divided into two paths by the first optical fiber coupler (C1) and enters the unidirectional Mach-Zehnder interferometer for sensing detection, one path enters the sensing optical fiber link of the unidirectional Mach-Zehnder interferometer through one port of the wavelength division multiplexer (9), and the other path enters the reference optical fiber and performs high-frequency carrier modulation; after the continuous laser signal output by the second laser (2) is transmitted through the isolator (3), it is converted into a periodic pulse optical signal by the acousto-optic modulator (4), and then enters the phase-sensitive optical time domain reflectometer for power amplification and filtering, and then enters the sensing optical fiber link of the unidirectional Mach-Zehnder interferometer through the optical fiber circulator and the other port of the wavelength division multiplexer (9); The continuous sensing light signal from the first laser (1) is subjected to high-frequency modulation and sensing detection by the reference optical fiber (12) and the sensing optical fiber (11), and then generates interference at the second optical fiber coupler (C2) to form an interference sensing light signal, which is then received in real time by the photoelectric detector (15); the backward Rayleigh scattered light generated by the pulse light from the second laser (2) along the sensing optical fiber link is again transmitted in reverse by the wavelength division multiplexer (9) and the optical fiber circulator (7), and then is received in real time by another channel of the photoelectric detector (15); The data acquisition and processing module acquires backward Rayleigh scattered light and interference sensing light signals, uses the sensing light signals to demodulate the phase change of the vibration signal applied to the sensing optical fiber to calculate the amplitude-frequency information; and uses the obtained backward Rayleigh scattered light signals to calculate and demodulate the corresponding specific fault disturbance position information.

2. The fused optical fiber distributed multi-point disturbance detection and demodulation system according to claim 1 is characterized in that: The data acquisition and processing module comprises a data acquisition card (16) and an industrial computer (18), and the industrial computer (18) also comprises an improved phase generation carrier modulation subsystem capable of accurately restoring amplitude and frequency information of a vibration signal to be measured, specifically comprising: DC filter: used to filter out the DC component in the continuous interference sensing light signal with a central wavelength of λ1 emitted by the first laser, and provide effective AC components in the sensing signal light for subsequent demodulation schemes; Primary carrier signal cosw0t: provides a high-frequency carrier signal for one AC component, so that it can be demodulated with the subsequent filter to restore the sinusoidal part containing the vibration signal to be measured; Low-pass filter: used to obtain the product part containing the zero-order Bessel term and the cosine term of the vibration signal to be measured, and to obtain the product part containing the first-order Bessel term and the sine term of the vibration signal to be measured; Differentiator: used to perform differential operation on the product part containing the first-order Bessel term and the sine term containing the vibration signal to be measured, so as to complete the conversion of trigonometric functions and effectively separate the phase information introduced by the vibration signal to be measured; Multiplier: used to complete the product operation of the corresponding output items to obtain the expected product result; Divider: used to complete the division operation of the corresponding output items to eliminate redundant items in the operation results; Inverter: used to complete the inversion operation processing in the operation result; Square root operator: used to complete the specific square root mathematical operation of the operation result; Integrator: It is used to complete the integration operation of the operation results to achieve accurate demodulation and restoration of the vibration signal to be measured.

3. The fused optical fiber distributed multi-point disturbance detection and demodulation system according to claim 1 is characterized in that: The Mach-Zehnder interferometer comprises a sensing optical fiber (11), a reference optical fiber (12), a phase modulator (8), a wavelength division multiplexer (9) and a second optical filter (10); The phase-sensitive optical time-domain reflectometer comprises an erbium-doped fiber amplifier (5), a first optical filter (6), an optical fiber circulator (7) and the Mach-Zehnder interferometer which are connected in sequence; The first laser (1) is a narrow linewidth laser with a central wavelength of λ1, and the second laser (2) is an ultra-narrow linewidth laser with a central wavelength of λ2; The isolator (3) is used to maintain unidirectional transmission of the continuous laser signal output by the first laser / the second laser; The first optical fiber coupler (C1) and the second optical fiber coupler (C2) are 3dB optical fiber couplers; The optical fiber circulator (7) is a three-port optical fiber circulator, which is used to couple the power-amplified pulse light into one port of the wavelength division multiplexer (9), and simultaneously receive the back Rayleigh scattered light generated by the transmission pulse light in the sensing optical fiber; The wavelength division multiplexer (9) is used to couple continuous light with a central wavelength of λ1 and pulse light with a central wavelength of λ2 into a sensing optical fiber link for transmission.

4. A multi-point fault location method using the optical fiber distributed multi-point disturbance detection and demodulation system of claim 1, comprising: Step 1: When at least two abnormal vibration events act on the sensing optical fiber at the same time, the refractive index at the corresponding force-bearing position of the sensing optical fiber will change, and the continuous laser signal with a central wavelength of λ1 emitted by the first laser (1) enters the unidirectional Mach-Zehnder interferometer, one path enters the sensing optical fiber, and the other path enters the reference optical fiber, so that the phase of the continuous interference light with a central wavelength of λ1 is synchronously modulated by the vibration force, and the photoelectric detector (15) receives the continuous interference sensing light signal in real time; At the same time, the second laser (2) emits a continuous laser signal with a central wavelength of λ2, which is converted into a periodic pulse light signal and then enters a phase-sensitive optical time domain reflectometer and a one-way Mach-Zehnder interferometer. The backward Rayleigh scattered light with a central wavelength of λ2 generated along the sensing optical fiber modulates the vibration force, causing the amplitude of the interference signal near the corresponding position to change. The photoelectric detector (15) receives the pulse light signal in real time. Step 2: The receiving end of the data acquisition and processing module synchronously collects the corresponding interference vibration sensing light signal received according to the time length; the processing end of the data acquisition and processing module adopts an improved phase generation carrier phase demodulation scheme to accurately demodulate the specific amplitude and frequency information of the vibration event; At the same time, the collected multiple backward Rayleigh scattered interference lights are triggered and collected according to the pulse time entering the sensing optical fiber to obtain a complete backward Rayleigh scattering curve; Then, a differential operation is used to demodulate the position information of multiple abnormal vibration events acting on the sensing optical fiber in real time based on the fixed time difference between the pulse light and the backward Rayleigh scattered light.

5. The multi-point fault location method according to claim 4, characterized in that: The improved phase generation carrier phase demodulation scheme specifically includes: The collected interference sensing light signal enters the DC filter to perform DC filtering to eliminate the DC component in the interference sensing light signal; Then the interference sensing light signal is divided into two paths, one is low-pass filtered in the reference optical fiber, and the other is low-pass filtered in the sensing optical fiber after being multiplied with the primary carrier signal cosw0t; Perform differential operation on the signal containing the cosine term of the vibration signal to be measured and the signal containing the sine term of the vibration signal to be measured after filtering, so as to complete the trigonometric function conversion of the cosine term and the sine term of the vibration signal to be measured output by the filter, so that the original differential term containing the phase information introduced by the vibration signal to be measured directly appears in the trigonometric function term after conversion, so as to eliminate the trigonometric function term through mathematical operation in the subsequent process, so as to demodulate and obtain the original phase information introduced by the vibration signal; The divider, multiplier, inverter and square root operator are used in turn to perform division, multiplication, inversion and square root operations on the corresponding output items, and the differential term of phase change is introduced into the interference vibration sensor light signal; then the integrator is used to output and restore the original time domain waveform signal of the accurate vibration signal.

6. The multi-point fault location method according to claim 5, characterized in that: The multiple backward Rayleigh scattered interference lights entering the industrial computer are firstly processed by cumulative averaging to remove the burr signal.

7. The multi-point fault location method according to claim 5, characterized in that: The central wavelength λ1 ranges from 1549.00 to 1550.22 nm, and the central wavelength λ2 ranges from 1549.7 to 1550.92 nm.

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