Fusion type optical fiber distributed multipoint disturbance detection demodulation system and fault positioning method

Abstract

The application discloses a fusion type optical fiber distributed multipoint disturbance detection demodulation system and a multipoint fault positioning method. The 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 multiple abnormal vibration events simultaneously act on a sensing optical fiber, a continuous laser signal emitted by a first laser enters the one-way Mach-Zehnder interferometer, and a continuous interference sensing optical signal is received by a photodetector in real time. A continuous laser signal emitted by a second laser enters the phase-sensitive optical time domain reflectometer and the one-way Mach-Zehnder interferometer after being converted into a periodic pulse optical signal, and a pulse optical signal is received by the photodetector in real time. A data acquisition and processing module adopts an improved phase generation carrier phase demodulation scheme to demodulate phase changes of vibration signals applied on the sensing optical fiber, so as to calculate amplitude-frequency information. Position information of multiple fault events is demodulated by using obtained backscattering Rayleigh scattering light signals.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of sensing and detection, and particularly relates to a distributed multi-point precision detection demodulation system and fault positioning method based on combination of forward signal light interference and backward scattering light interference. BACKGROUND

[0002] As a new type of sensing and detection technology in recent years, distributed optical fiber vibration sensing technology can realize simultaneous signal sensing and transmission based on a single fiber link in the specific vibration event sensing and detection process. Compared with traditional electromagnetic vibration sensing and detection technology, distributed optical fiber 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, large building health monitoring and important resource transmission safety detection fields. With the in-depth application of distributed optical fiber vibration sensing technology in the above related fields, 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 environment. For example, when a dangerous event such as a crack occurs in the health quality detection process of a large building, its frequency response is generally as high as several megahertz. On the other hand, since the sensing signal of the distributed optical fiber vibration sensing system is finally detected and demodulated in the form of interference light, the amplitude of the interference sensing light received by the detector is nonlinearly related to the size of the stress event acting on the sensing fiber, which makes the system unable to accurately restore the amplitude-frequency information of the target vibration event to be measured, thereby affecting the accurate sensing and measurement of the target vibration event to be measured by the sensing system.

[0003] The distributed optical fiber vibration sensing system can be divided into two types of forward optical interferometer and backward scattering optical interferometer according to its sensing structure and sensing principle. The forward optical interferometer type distributed optical fiber vibration sensing system realizes the sensing detection and transmission of the forward signal light by constructing a Mach-Zehnder fiber interferometer, a Michelson fiber interferometer and a Sagnac fiber interferometer. This type of distributed optical fiber vibration sensing system has the advantages of simple sensing structure, fast response speed, etc. Especially, 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 frequency response. However, since this type of distributed optical fiber vibration sensing system generally estimates the time delay relationship of the signal to solve the specific position of the disturbance, it cannot simultaneously detect multiple point vibration events on the optical fiber link. On the other hand, the backward scattering optical interferometer type distributed optical fiber vibration sensing system mainly realizes the sensing detection and transmission of the vibration events along the optical fiber by the backward scattering light such as backward Rayleigh scattering light and backward Brillouin scattering light formed by the transmission of ultra-narrow pulse light in the sensing optical fiber. Therefore, this type of distributed optical fiber vibration sensing system can simultaneously demodulate and detect multiple 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 high-frequency vibration events, that is, this type of sensing system has the disadvantage of low frequency response. Therefore, the traditional single-mechanism type distributed optical fiber vibration sensing system cannot directly accurately perceive and detect multiple wideband vibration events in actual applications, thereby restricting the application prospect of the distributed optical fiber vibration sensing system in the vibration detection field. In addition, since the phase information introduced by the vibration events acting on the sensing optical fiber and the interference signal light are in a nonlinear mapping relationship, the original vibration event amplitude-frequency information cannot be accurately restored from the original interference signal light obtained by demodulation, thereby seriously restricting the quantitative analysis of the sensing system in actual applications.

[0004] Based on the above analysis, it is of important practical significance to design a distributed optical fiber vibration sensing system with multiple point wideband detection and accurate demodulation of vibration signal amplitude-frequency information to improve its application in the field of vibration sensing and detection. SUMMARY

[0005] The purpose of the present application is to overcome the deficiencies in the prior art, and to provide a distributed multi-point precision detection demodulation system and a multi-point fault positioning method based on the combination of forward signal light interference and backward scattering light interference. The demodulation system is a fusion type distributed fiber sensing system based on a forward light interferometer such as a Mach-Zehnder interferometer and a backward scattering light interferometer. The amplitude-frequency change information is obtained by continuously monitoring the phase change based on forward signal light interference, and the position information is demodulated simultaneously by using backward scattering light interference to multi-point vibration events, so as to realize multi-point wide frequency precision sensing detection and demodulation of the distributed fiber vibration sensing system. A double-mechanism fusion distributed fiber vibration sensing system based on the combination of forward signal interference light and backward scattering interference light is provided for more accurate analysis of the vibration information applied to the sensing fiber. The improved phase generation carrier demodulation technology which can accurately restore the phase information of the measured vibration event can effectively realize the accurate demodulation of the amplitude-frequency information of the measured vibration signal.

[0006] A fusion type distributed multi-point disturbance detection demodulation system based on the combination of forward signal light interference and backward scattering light interference, comprising: a first laser, a second laser, an isolator, a one-way 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 connected to the input end of the one-way Mach-Zehnder interferometer in sequence through the isolator, the first fiber coupler and the second fiber coupler, and the output end of the one-way Mach-Zehnder interferometer is connected to the photodetector and the data acquisition and processing module in sequence.

[0008] The output end of the second laser is connected to the input end of the OTDR in sequence through the isolator, 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 locate the multi-point vibration events acting on the sensing fiber for subsequent demodulation.

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

[0010] The continuous sensing light signal from the first laser is modulated by the reference fiber and the sensing fiber, and after sensing detection, an interference sensing light signal is generated at the second fiber coupler, and is received by the photodetector in real time; the back Rayleigh scattering light generated by the pulsed light from the second laser along the sensing fiber link is transmitted reversely by the wavelength division multiplexer and the fiber ring, and is received by another channel of the photodetector in real time;

[0011] The data acquisition and processing module acquires the back Rayleigh scattering light and the interference sensing light signal, calculates the amplitude-frequency information by using the phase change of the vibration signal applied on the sensing fiber according to the sensing light signal demodulation, and calculates the specific fault disturbance position information according to the obtained back Rayleigh scattering light signal.

[0012] Further, the data acquisition and processing module comprises a data acquisition card and an industrial computer, and the industrial computer further comprises an improved phase generation carrier modulation subsystem which can accurately restore the amplitude-frequency information of the vibration signal to be measured, and specifically comprises:

[0013] A DC filter is used to filter out the DC component in the continuous interference sensing light signal with a center wavelength of λ1 emitted by the first laser, so as to provide the effective AC component in the sensing signal light for the subsequent demodulation scheme;

[0014] A first carrier signal cosw0t is used to provide a high-frequency carrier signal for the AC component, so that the subsequent filter demodulation can restore the sine part containing the vibration signal to be measured;

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

[0016] A differentiator is 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 the trigonometric function and effectively separate the phase information introduced by the vibration signal to be measured;

[0017] A multiplier is used to complete the multiplication operation of the corresponding output term, so as to obtain the expected product result;

[0018] A divider is used to complete the division operation of the corresponding output term, so as to eliminate the redundant terms in the operation result;

[0019] An inverter is used to complete the inversion operation processing of the operation result;

[0020] A root operation device is used to complete the specific root operation of the operation result;

[0021] Integrator: used to complete the integral operation of the operation result, to realize the accurate demodulation and restoration of the vibration signal to be measured.

[0022] Further, the Mach-Zehnder interferometer comprises 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 comprises an erbium-doped fiber amplifier (EDFA), a first optical filter, an optical fiber ring and a Mach-Zehnder interferometer connected in sequence.

[0024] The first laser is a narrow-linewidth laser with a center wavelength of λ1, and the second laser is an ultranarrow-linewidth laser with a center wavelength of λ2.

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

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

[0027] The optical fiber ring is a three-port optical fiber ring, which is used to couple the power-amplified pulsed light into one port of the wavelength division multiplexer, and simultaneously receive the backscattered Rayleigh light generated by the transmission pulsed light in the sensing optical fiber.

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

[0029] Preferably, the center wavelength λ1 is in the range of 1549.00-1550.22nm, and the center wavelength λ2 is in the range of 1549.7-1550.92nm.

[0030] A multi-point fault positioning method using the optical fiber distributed multi-point accurate detection demodulation system, comprising:

[0031] Step one: when at least two abnormal vibration events act on the sensing optical fiber at the same time, the refractive index at the position of the sensing optical fiber under stress will change, the continuous laser signal with a center wavelength of λ1 emitted by the first laser enters the unidirectional Mach-Zehnder interferometer, one way into the sensing optical fiber, and the other way into the reference optical fiber, so that the phase of the continuous interference sensing light with a center wavelength of λ1 is modulated synchronously by the vibration force, and the continuous interference sensing light signal is received in real time by the photodetector.

[0032] Meanwhile, the second laser emits a continuous laser signal with a center wavelength of λ2, which is converted into a periodic pulsed light signal and sequentially enters the phase-sensitive optical time domain reflectometer and the one-way Mach-Zehnder interferometer. The back Rayleigh scattering light with a center wavelength of λ2 generated along the sensing optical fiber changes in amplitude due to the modulation of the vibration acting force, and the pulsed light signal is received in real time by the photodetector;

[0033] Step two: Since multiple abnormal vibration events synchronously modulate the continuous interference sensing optical signal with a center wavelength of λ1, the corresponding interference vibration sensing optical signal received by the data acquisition and processing module is synchronously collected 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 amplitude-frequency information of the vibration event.

[0034] Meanwhile, the collected multiple back Rayleigh scattering interference lights are triggered and collected according to the pulse time entering the sensing optical fiber to obtain the complete back Rayleigh scattering curve. Then, the differential operation is performed, and the position information of the multiple abnormal vibration events acting on the sensing optical fiber is demodulated in real time according to the fixed time difference between the pulsed light and the back Rayleigh scattering light.

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

[0036] The collected interference sensing optical signal enters the direct current filter to perform direct current filtering to eliminate the direct current component in the interference sensing optical signal.

[0037] Then, the interference sensing optical signal is divided into two paths, one path is filtered through the low-pass filter in the reference optical fiber, and the other path is filtered through the low-pass filter after being multiplied by the first carrier signal cosw0t in the sensing optical fiber.

[0038] The signals containing the cosine term of the to-be-measured vibration signal and the signals containing the sine term of the to-be-measured vibration signal after filtering are differentiated to complete the trigonometric function conversion of the cosine term and the sine term of the to-be-measured vibration signal output by the filter, so that the original differential term containing the phase information introduced by the to-be-measured vibration signal directly appears in the converted trigonometric function term, so as to facilitate subsequent mathematical operation to eliminate the trigonometric function term, thereby demodulating the original phase information introduced by the vibration signal.

[0039] And the corresponding output term is subjected to division, multiplication, inversion and root operation by using the divider, multiplier, inverter and root operator in sequence, and the differential term of the phase change introduced by the interference vibration sensing optical signal; and then the integrator is used to output and restore the accurate original time domain waveform signal of the vibration signal.

[0040] Further, the multiple back Rayleigh scattering interference lights entering the industrial computer are first subjected to accumulation average processing to remove burr signals.

[0041] Compared with the prior art, the technical scheme of the present application has the beneficial effects that:

[0042] The light source of the optical fiber distributed multi-point precision detection demodulation system and multi-point fault positioning method based on the combination of forward signal light interference and back scattering light interference according to the present application adopts narrow linewidth lasers and ultra-narrow linewidth lasers with different central wavelengths, the narrow linewidth lasers are used to construct a one-way Mach-Zehnder optical fiber interferometer, and the ultra-narrow linewidth lasers are used to construct a phase-sensitive optical time domain reflectometer.

[0043] The constructed one-way Mach-Zehnder optical fiber interferometer and the phase-sensitive optical time domain reflectometer are coupled into the same sensing optical fiber link through a dense wavelength division multiplexer, so as to form and establish a dual-mechanism fusion type optical fiber distributed vibration sensing system; when a vibration event acts on the optical fiber link, the amplitude-frequency information of the to-be-detected vibration signal can be demodulated through the one-way Mach-Zehnder optical fiber interferometer part, and the position information of the to-be-detected vibration signal 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 realize multi-point wideband precision sensing detection and demodulation of the distributed optical fiber vibration sensing system, which not only makes up for the shortcomings of the single-mechanism type distributed optical fiber vibration sensing demodulation scheme, but also can realize multi-point wideband vibration detection of the to-be-detected vibration signal. In addition, compared with the traditional to-be-detected vibration signal phase demodulation scheme, the phase demodulation scheme of the present design does not need high-frequency harmonic modulation and multi-channel signal coordinated detection, so as to optimize the optical path demodulation structure, save the hardware design cost and realize precise measurement of the to-be-detected vibration signal. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 A schematic diagram of the dual-mechanism fusion type optical fiber distributed multi-point wideband vibration sensing detection system according to the present application is shown.

[0046] Figure 2 An improved phase generation carrier demodulation schematic diagram capable of precisely demodulating and restoring the phase information of the interference signal is shown.

[0047] In the drawings:

[0048] 1: first laser 2: second laser 3: isolator

[0049] C1: first optical fiber coupler C2: second optical 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 with reference to the accompanying drawings and specific embodiments. The specific embodiments described are only used to illustrate 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 and 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 the input end of an OTDR. 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, a fiber circulator 7, and a Mach-Zehnder interferometer, which are sequentially connected.

[0059] The first laser 1 is a narrow linewidth laser with a center wavelength of λ1, which emits a first light source as a continuous laser signal for a unidirectional Mach-Zehnder fiber interferometer; the second laser 2 is an ultranarrow linewidth laser with a center wavelength of λ2, which emits a second light source as a continuous laser signal for a phase-sensitive optical time domain reflectometer. The laser emitted by the first laser 1 enters the unidirectional Mach-Zehnder fiber interferometer through the isolator 3, and the laser emitted by the second laser 2 enters the phase-sensitive optical time domain reflectometer through the isolator 3, and the isolator 3 is used to maintain the unidirectional transmission of the continuous laser signals output by the first light source / second light source. The arbitrary signal generator 17 is used to provide the required various types of signal sources for the demodulation system, and the arbitrary signal generator 17 is connected to the acousto-optic modulator 4 and the data acquisition card 16 respectively. The acousto-optic modulator (AOM) 4 modulates the continuous laser signal output by the second light source from the second laser 2 into periodic pulsed light under the modulation of an external trigger pulse. The erbium-doped fiber amplifier 5 is used to amplify the power of the pulsed light signal output by the acousto-optic modulator 4. The first optical filter 6 is used to filter out the spontaneous emission noise components carried by the pulsed light signal in 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 equal parts for transmission, and the second fiber coupler C2 is used to couple and interfere the two light signals with a center wavelength of λ1, and the interference signal enters the transmission fiber for output. The fiber circulator 7 is a three-port fiber circulator, which is used to couple the power-amplified pulsed light into one port of the wavelength division multiplexer 9, and simultaneously receive the backscattered Rayleigh scattering light generated by the transmission pulsed 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 center wavelength of λ1 and the pulsed light with a center wavelength of λ2 into the sensing optical fiber link for transmission. The sensing optical fiber is a common G.652D type single-mode communication optical fiber, which is used to sense the 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 measured vibration signal in the Mach-Zehnder fiber interferometer under the action of an external high-frequency carrier signal. The photodetector 15 is used to simultaneously receive the interference sensing light output by the second fiber coupler C2 and the Rayleigh interference scattering sensing light transmitted in the opposite direction by the fiber circulator 7, and convert the two kinds of interference sensing light signals into corresponding sensing electrical signals. The second fiber coupler C2 and the photodetector 15 are connected through the transmission 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 processes and analyzes the signals, and finally demodulates and restores the position information and amplitude-frequency information of the vibration signal applied to the sensing optical fiber.

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

[0061] The continuous laser with the central wavelength of λ1 emitted by the first laser 1 enters the first optical coupler C1 after the isolator 3. The first optical coupler C1 divides the signal light into two beams to enter 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 optical coupler C2 along the reference fiber 12 after phase modulation by the phase modulator 8. The signal light on the sensing fiber link enters the wavelength division multiplexer 9. The continuous sensing light with the central wavelength of λ1 is modulated by the phase modulator 8 during transmission in the reference fiber link, and the vibration event information acting on the sensing fiber link can be detected synchronously during the sensing transmission. Finally, the two continuous sensing lights from the reference fiber and the sensing fiber interfere at the second optical coupler C2, and the interference output light is detected in real time by one port of the photodetector 15 after transmission through the transmission fiber.

[0062] The laser with the central wavelength of λ2 from the second laser 2 enters the acousto-optic modulator 4 after the isolator 3. After modulation, the optical signal is converted into periodic pulse light, and then the pulse light signal enters the erbium-doped fiber amplifier 5 for power amplification and the second filter 10 for spontaneous emission noise suppression, and then enters the optical fiber ring 7 for transmission. Finally, the periodic pulse light with the central wavelength of λ2 enters the sensing fiber 11 through the other 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, and the pulse light from the OTDR is finally suppressed and attenuated by the second filter 10 to prevent it from superimposing and affecting the continuous sensing light entering the second optical 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 the central wavelength of λ2 will be completely attenuated and suppressed at the second filter 10, so it will not further superimpose on the continuous light with the central wavelength of λ1 at the second optical coupler C2. According to the principle of fiber Rayleigh scattering, the pulse light from the OTDR will produce continuous backscattered light along the line during transmission in the sensing fiber 11, and the central wavelength of the backscattered light is still λ2. The backscattered light is transmitted back through the sensing fiber, and then transmitted through the dense wavelength division multiplexer 9 and the 3-port optical fiber ring 7, and detected in real time by the other channel of the photodetector 15.

[0063] After the continuous sensing light and the back Rayleigh scattering light enter the photodetector 15, the two kinds of interference sensing light signals can be converted into corresponding sensing electric signals, and then the signals are subjected to analog-digital conversion and data collection by the data collection card 16, and finally transmitted to the industrial computer 17 for demodulation processing.

[0064] According to the frequency response of the single-mode Mach-Zehnder fiber interferometer, the frequency response is mainly limited by the real-time sampling rate of the data collection card 16 at the demodulation end, so the continuous interference sensing light signal with a central wavelength of λ1 received by the photodetector 15 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 of synchronous demodulation of multi-point vibration position information, so the continuous back Rayleigh scattering light signal with a central wavelength of λ2 received by the photodetector can be used for accurate demodulation of the position information of the vibration signal.

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

[0066]

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

[0068] The multi-point fault positioning method of the optical fiber distributed multi-point accurate detection and demodulation system based on the combination of forward signal light interference and back scattering light interference comprises:

[0069] Step one: when multiple abnormal intrusion events occur synchronously on the sensing optical fiber, the vibration caused thereby will cause the change of the refractive index and other parameters at the corresponding sensing optical fiber, thereby causing the corresponding change of the phase of the sensing signal. The continuous laser from the first laser 1 passes through the isolator 3, the first fiber coupler C1, enters the Mach-Zehnder interferometer, the second fiber coupler C2, obtains the interference sensing light signal through phase modulation, and enters the industrial computer 18 through the transmission fiber 14, the photodetector 15, and the data collector 16 for amplitude-frequency information demodulation processing;

[0070] At the same time of the abnormal intrusion event, 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 enters the sensing optical fiber link as a pulse light signal. At the same time, the optical fiber ring 7 receives the back Rayleigh scattering light generated in the sensing optical fiber link, and the light is received by the photodetector and enters the industrial computer 18 through the data collector 16 for position information demodulation processing.

[0071] Step two: as shown in the figure, the working process of the industrial computer 17 is as follows: Figure 2

[0072] At the receiving end of the industrial computer, since multiple abnormal vibration events synchronously modulate the continuous interference sensing light signal with a center wavelength of λ1 in phase, it will be uniformly reflected in the final interference signal. Therefore, it can be collected according to the time length, and then further demodulated at the processing end of the industrial computer using the improved phase generation carrier phase demodulation scheme to obtain the specific amplitude-frequency information of the vibration event. On the other hand, since multiple abnormal vibration events synchronously modulate the Rayleigh scattering interference light with a center wavelength of λ2, the intensity of the corresponding interference signal will change along the specific position of the sensing optical fiber. Therefore, the back Rayleigh scattering interference light signal can be triggered and collected according to the pulse time entering the sensing optical fiber to obtain the complete back Rayleigh scattering curve. Then, at the processing end of the industrial computer, the position information of multiple abnormal vibration events is demodulated by using the cumulative average and difference algorithm.

[0073] Specifically, first, the original interference signal is filtered by a direct current filter to remove its direct current component, and then transmitted and operated in two ways. 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 a first harmonic and filtered by a low-pass filter to obtain:

[0074]

[0075] where J0(C) and J1(C) represent the first and second Bessel function terms, respectively. Deriving I0(t) and I1(t) in formula (2), and then cross dividing, we get:

[0076]

[0077] Multiplying I2(t) and I3(t) in formula (3) and taking the inverse operation, we get:

[0078]

[0079] Taking the square root operation of I4(t) in formula (4), we get:

[0080]

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

[0082]

[0083] Since the external vibration signal acts on the sensing optical fiber, it introduces phase changes in the interference sensing light signal which can be specifically represented as​ wherein D0 is the amplitude of the applied vibration signal, w s is the angular frequency of the applied vibration signal. For this, it can be known from formula (6) that the amplitude-frequency information of the vibration signal acting on the sensing optical fiber link can be accurately demodulated by the improved phase generation carrier demodulation scheme involved in the application.

[0084] At the same time, the phase-sensitive optical time domain reflectometer involved in the application can demodulate the vibration position information acting on the sensing optical fiber link. Specifically, after the backward continuous Rayleigh scattering sensing signal is analog-digital converted and data collected by the data acquisition card, it is sent to the industrial computer for first accumulation and average processing to eliminate the burr signal in the continuous sensing collection process to improve the overall signal-to-noise ratio of the sensing signal. According to the disturbance event acting on the optical fiber link, the refractive index at the corresponding point of the optical fiber 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 obtained backward Rayleigh scattering interference light curve signal is subjected to difference operation processing to demodulate the specific vibration information acting on the optical fiber in real time. According to the fact that the backward Rayleigh scattering light generated by the pulsed 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 pulsed light and the Rayleigh scattering light, i.e.:

[0085]

[0086] wherein x is the specific position of the disturbance event acting on the sensing optical fiber relative to the 3-port optical fiber circulator, c is the propagation speed of the optical wave signal in vacuum, and n is the inherent refractive index of the sensing optical fiber.

[0087] Since the phase-sensitive optical time domain reflectometer involved in the application can simultaneously position and analyze multiple-point vibration events acting on the sensing optical fiber, the dual-mechanism fusion type optical fiber distributed fiber disturbance sensing system designed by the application also has the function of positioning and detecting multiple-point vibration events.

[0088] Based on the above analysis, the distributed fiber sensing system designed by the application can realize accurate perception and detection of multiple-point wideband vibration events.

[0089] Although the preferred embodiments of the application have been described in detail above with reference to the accompanying drawings, the application is not limited to the above-described specific embodiments, which are merely illustrative and not restrictive. Those skilled in the art can make many forms under the inspiration of the application without departing from the purpose of the application and the scope protected by the claims, which all belong to the protection scope of the application.

Claims

1. A fusion-type optical fiber distributed multipoint disturbance detection demodulation system, characterized by The application relates to a demodulation system for a fiber-optic vibration sensor, which comprises a first laser (1), a second laser (2), an isolator (3), a one-way Mach-Zehnder fiber-optic interferometer, a phase-sensitive optical time domain reflectometer and a data acquisition and processing module. The first laser (1) is a narrow-line-width laser with a center wavelength of lambda1, and the second laser (2) is an ultra-narrow-line-width laser with a center wavelength of lambda2; the first laser is used for constructing the one-way Mach-Zehnder fiber-optic interferometer; and the second laser is used for constructing the phase-sensitive optical time domain reflectometer. The output end of the first laser (1) is sequentially connected with the isolator (3), a first fiber-optic coupler (C1) and the input end of the one-way Mach-Zehnder interferometer; the output end of the one-way Mach-Zehnder interferometer is sequentially connected with a second fiber-optic coupler (C2), a photoelectric detector (15) and the data acquisition and processing module; the output end of the second laser (2) is sequentially connected with 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 with the photoelectric detector (15) and the data acquisition and processing module. The phase-sensitive optical time domain reflectometer can simultaneously and synchronously locate multiple vibration events acting on a sensing fiber for subsequent demodulation. The working process of the demodulation system comprises the following steps: continuous laser signals output by the first laser (1) are transmitted through the isolator (3), are divided into two paths by the first fiber-optic coupler (C1) and enter the one-way Mach-Zehnder interferometer for sensing detection; one path enters the sensing fiber link of the one-way Mach-Zehnder interferometer through one port of a wavelength division multiplexer (9), and the other path enters a reference fiber and is subjected to high-frequency carrier modulation; continuous laser signals output by the second laser (2) are transmitted through the isolator (3), are converted into periodic pulse light signals by an acousto-optic modulator (4), subsequently enter the phase-sensitive optical time domain reflectometer for power amplification and filtering, and then enter the sensing fiber link of the one-way Mach-Zehnder interferometer through a fiber-optic circulator and the other port of the wavelength division multiplexer (9); The continuous sensing light signals from the first laser (1) are subjected to high-frequency modulation and sensing detection through the reference fiber (12) and the sensing fiber (11), interference is generated at the second fiber-optic coupler (C2) to form interference sensing light signals, and the interference sensing light signals are received in real time by the photoelectric detector (15); the backward Rayleigh scattering light generated by the pulse light from the second laser (2) along the sensing fiber link is reversely transmitted through the wavelength division multiplexer (9) and the fiber-optic circulator (7), and is received in real time by the other channel of the photoelectric detector (15); The data acquisition and processing module collects the backward Rayleigh scattering light and the interference sensing light signals, demodulates the phase change of the vibration signals applied on the sensing fiber by using the sensing light signals to calculate the amplitude-frequency information, and calculates the specific fault disturbance position information corresponding to the backward Rayleigh scattering light signals to demodulate the specific fault disturbance position information; The data acquisition and processing module comprises a data acquisition card (16) and an industrial computer (18), the industrial computer (18) further comprises an improved phase generation carrier modulation subsystem which can accurately restore the amplitude-frequency information of the vibration signals to be measured, and specifically comprises: ​ ​ Direct current filter: used for filtering the direct current component in the continuous interference sensing light signal with central wavelength λ1 emitted by the first laser, providing the effective alternating current component in the sensing signal light for the subsequent demodulation scheme; First carrier signal cosw0t: providing a high-frequency carrier signal for one of the alternating current components, so that the subsequent filter demodulation restores the sine part containing the to-be-measured vibration signal; Low-pass filter: used for obtaining the product part containing the zero-order Bessel term and the to-be-measured vibration signal cosine term, and obtaining the product part containing the first-order Bessel term and the to-be-measured vibration signal sine term; Differentiator: used for differentiating the product part containing the first-order Bessel term and the to-be-measured vibration signal sine term, to complete the conversion of the trigonometric function and the effective separation of the to-be-measured vibration signal phase information introduced; Multiplier: used for completing the multiplication operation of the corresponding output term to obtain the expected product result; Divisor: used for completing the division operation of the corresponding output term to eliminate the redundant terms in the operation result; Inverter: used for completing the inversion operation processing in the operation result; Root operator: used for completing the specific root operation of the operation result; Integrator: used for completing the integration operation of the operation result to realize the accurate demodulation and restoration of the to-be-measured vibration signal; 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 optical fiber amplifier (5), a first optical filter (6), an optical fiber circulator (7), and the Mach-Zehnder interferometer connected in sequence; The isolator (3) is used to maintain the one-way 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 pulsed light into one port of the wavelength division multiplexer (9), and simultaneously receive the backscattered Rayleigh light generated by the transmission pulsed light in the sensing optical fiber; The wavelength division multiplexer (9) is used to couple the continuous light with central wavelength λ1 and the pulsed light with central wavelength λ2 into the sensing optical fiber link for transmission.

2. A multi-point fault positioning method using the optical fiber distributed multi-point disturbance detection and demodulation system of claim 1, comprising: Step one: when at least two abnormal vibration events act on the sensing optical fiber at the same time, the refractive index at the position where the sensing optical fiber is stressed will change, the continuous laser signal with central wavelength λ1 emitted by the first laser (1) enters the one-way Mach-Zehnder interferometer, one way into the sensing optical fiber, and the other way into the reference optical fiber, so that the phase of the continuous interference light with central wavelength λ1 is modulated synchronously by the vibration force, and the continuous interference sensing light signal is received in real time by the photodetector (15). Meanwhile, the second laser (2) emits a continuous laser signal with a center wavelength of λ2 into the phase-sensitive optical time domain reflectometer and the one-way Mach-Zehnder interferometer after being converted into a periodic pulsed light signal, and the back Rayleigh scattering light with a center wavelength of λ2 generated along the sensing optical fiber changes the amplitude of the interference signal near the corresponding position due to the modulation of the vibration acting force, and the pulsed light signal is received in real time by the photodetector (15); Step two: the receiving end of the data acquisition and processing module synchronously acquires the received corresponding interference vibration sensing optical signal according to the time length; and 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 amplitude-frequency information of the vibration event; Meanwhile, the collected multiple back Rayleigh scattering interference lights are triggered and collected according to the pulse time entering the sensing optical fiber to obtain the complete back Rayleigh scattering curve; Then, the differential operation processing is performed according to the fixed time difference between the pulsed light and the back Rayleigh scattering light, so as to demodulate the position information of the abnormal vibration events acting on the sensing optical fiber in real time; wherein the improved phase generation carrier phase demodulation scheme specifically includes: The collected interference sensing optical signal enters the direct current filter to perform direct current filtering to eliminate the direct current component in the interference sensing optical signal; Then, the interference sensing optical signal is divided into two paths, one path is filtered through the low-pass filter in the reference optical fiber, and the other path is filtered through the low-pass filter after being multiplied by the first carrier signal cosw0t in the sensing optical fiber; The differential operation is performed on the filtered signals containing the cosine term of the to-be-measured vibration signal and the signals containing the sine term of the to-be-measured vibration signal to complete the trigonometric function conversion of the cosine term and the sine term of the to-be-measured vibration signal output by the filter, so that the original differential term containing the phase information introduced by the to-be-measured vibration signal directly appears in the converted trigonometric function term, so as to facilitate subsequent mathematical operation to eliminate the trigonometric function term, thereby demodulating the original phase information introduced by the vibration signal; And the corresponding output terms are sequentially subjected to division, multiplication, inversion and root operation by using the divider, multiplier, inverter and root operator, and the differential term of the phase change introduced by the interference vibration sensing optical signal; and then the integrator is used to output and restore the accurate original time domain waveform signal of the vibration signal.

3. The method of claim 2, wherein, The multiple back Rayleigh scattering interference lights entering the industrial computer are first subjected to accumulation and average processing to remove the burr signal.

4. The method of claim 2, wherein, The center wavelength λ1 is in the range of 1549.00-1550.22 nm, and the center wavelength λ2 is in the range of 1549.7-1550.92 nm.

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