CN113483795B - Weak grating array distributed vibration sensing demodulation method and system - Google Patents
Weak grating array distributed vibration sensing demodulation method and system Download PDFInfo
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Abstract
The invention relates to a weak grating array distributed vibration sensing demodulation method and a system, wherein the method comprises the following steps: dividing a beam of continuous light into front detection light and rear detection light, respectively modulating the front detection light and the rear detection light into first single-pulse light and second single-pulse light, delaying the second single-pulse light, and combining the delayed second single-pulse light with the first pulse light into double-pulse light; inputting the double-pulse light into a weak grating optical fiber array, generating beat frequency pulse signals in the weak grating optical fiber array by the double-pulse light, converting the beat frequency pulse signals into electric signals, and obtaining I signals and Q signals of the electric signals; and acquiring an initial phase signal according to the I signal and the Q signal of the electric signal, and acquiring a final phase signal according to the initial phase signal. The weak grating array distributed vibration sensing demodulation method improves the real-time performance of I/Q signal demodulation.
Description
Technical Field
The invention relates to the technical field of fiber bragg grating sensing, in particular to a weak grating array distributed vibration sensing demodulation method and system.
Background
Phase-sensitive optical time domain reflectometer techniqueThe optical fiber sensor is a technology for using the optical fiber as a vibration sensing sensitive element and a transmission signal medium, has the advantages of small volume, light weight, high sensitivity, good environmental adaptability, intrinsic safety, electromagnetic interference resistance and the like, is suitable for severe environments such as inflammable and explosive environments and the like, and can be applied to the fields such as perimeter security, geological exploration, oil gas leakage, power grid monitoring, water hearing and the like.
For the signal acquisition and demodulation end of the distributed weak grating vibration sensing demodulation system, according to the vibration sensing mechanism of the fiber grating, vibration signals are substantially modulated into interference signals, and demodulation of the vibration signals is actually phase demodulation; for the followingIn the system, two signal demodulation methods are mainly two kinds, namely heterodyne coherent detection and homodyne coherent detection, heterodyne coherent detection generally uses local oscillator reference light and backward Rayleigh scattering signal light to perform beat frequency, a subsequent demodulation algorithm is performed in an upper computer after data acquisition, the frequency of beat frequency signals is higher, an ultrahigh frequency acquisition card is required to acquire complete waveforms, and I signal and Q signal modulation in heterodyne demodulation are performed in the upper computer, so that real-time measurement is difficult to realize.
Disclosure of Invention
In view of the foregoing, it is necessary to provide a method and a system for demodulating weak grating array distributed vibration sensor, which are used for solving the problem of poor real-time performance of the existing I/Q signal demodulation.
The invention provides a weak grating array distributed vibration sensing demodulation method, which comprises the following steps:
dividing a beam of continuous light into front detection light and rear detection light, respectively modulating the front detection light and the rear detection light into first single-pulse light and second single-pulse light, delaying the second single-pulse light, and combining the delayed second single-pulse light with the first pulse light into double-pulse light;
Inputting the double-pulse light into a weak grating optical fiber array, generating beat frequency pulse signals in the weak grating optical fiber array by the double-pulse light, converting the beat frequency pulse signals into electric signals, and obtaining I signals and Q signals of the electric signals;
And acquiring an initial phase signal according to the I signal and the Q signal of the electric signal, and acquiring a final phase signal according to the initial phase signal.
Further, the double pulse light includes a front pulse light and a rear pulse light, both of which have pulse widths of T W, a pulse repetition frequency of F p, and a pulse delay of T p2l of the rear pulse with respect to the front pulse,V is the propagation speed of light in the weak grating array, L is the grating distance in the weak grating array, n e is the refractive index of the weak grating, S is the length of the weak grating array, and c is the light speed.
Further, the double pulse light generates beat pulse signals in the weak grating fiber array, specifically comprises that the rear pulse is reflected by the ith grating and then is reflected by the (i+1) th grating with the front pulse, and then meets the ith grating to generate beat pulse signals, wherein the intensity of the beat pulse signals is thatWherein E i、Ri is the light intensity amplitude of the reflected light of the ith grating, the reflectivity of the ith grating,/>, respectivelyFor the phase difference caused by disturbance between the i+1 and i grating,/>The phase difference is fixed for the adjacent gratings, and delta omega is the angular frequency difference of the acousto-optic modulator corresponding to the front detection light and the rear detection light.
Further, the I signal and the Q signal of the electric signal are obtained, specifically comprising,
And filtering the direct current component of the electric signal, and then mixing the direct current component with a sine signal and a cosine signal respectively to obtain a sine mixing signal and a cosine mixing signal, and filtering double frequency components of the sine mixing signal and the cosine mixing signal to obtain an I signal and a Q signal of the electric signal.
Further, the I signal of the electrical signalQ Signal of Electrical Signal/>
The invention also provides a weak grating array distributed vibration sensing demodulation system, which comprises a narrow linewidth laser, a first coupler, a first DDS signal generator, an acousto-optic modulator, a delay optical fiber, a second coupler, a circulator, a photoelectric converter, a signal acquisition module and a signal processing module;
The narrow linewidth laser is used for generating a beam of continuous light, the first coupler is used for dividing the beam of continuous light into front detection light and rear detection light, the first DDS signal generator and the acousto-optic modulator are used for respectively modulating the front detection light and the rear detection light into first single-pulse light and second single-pulse light, the delay optical fiber is used for delaying the second single-pulse light, and the second coupler is used for synthesizing the delayed second single-pulse light and the first pulse light into double-pulse light;
the circulator is used for inputting the double-pulse light into the weak grating optical fiber array, the double-pulse light generates beat frequency pulse signals in the weak grating optical fiber array, the photoelectric converter is used for converting the beat frequency pulse signals into electric signals, and the signal acquisition module is used for acquiring I signals and Q signals of the electric signals;
the signal processing module is used for obtaining an initial phase signal according to the I signal and the Q signal of the electric signal and obtaining a final phase signal according to the initial phase signal.
Further, the length of the delay optical fiber is twice the distance between adjacent gratings in the weak grating optical fiber array.
Further, the double pulse light includes a front pulse light and a rear pulse light, both of which have pulse widths of T W, a pulse repetition frequency of F p, and a pulse delay of T p2l of the rear pulse with respect to the front pulse,V is the propagation speed of light in the weak grating array, L is the grating distance in the weak grating array, n e is the refractive index of the weak grating, S is the length of the weak grating array, and c is the light speed.
Further, the double pulse light generates beat pulse signals in the weak grating fiber array, specifically comprises that the rear pulse is reflected by the ith grating and then is reflected by the (i+1) th grating with the front pulse, and then meets the ith grating to generate beat pulse signals, wherein the intensity of the beat pulse signals is thatWherein E i、Ri is the light intensity amplitude of the reflected light of the ith grating, the reflectivity of the ith grating,/>, respectivelyFor the phase difference caused by disturbance between the i+1 and i grating,/>The phase difference is fixed for the adjacent gratings, and delta omega is the angular frequency difference of the acousto-optic modulator corresponding to the front detection light and the rear detection light.
Further, the signal acquisition module comprises a band-pass filter, a second DDS signal generator, a first multiplier, a second multiplier, a first low-pass filter and a second low-pass filter, the signal acquisition module acquires an I signal and a Q signal of the electric signal, and specifically comprises,
The band-pass filter filters direct current components from the electric signal to obtain a direct current-filtered electric signal, the second DDS signal generator is used for generating a sine signal and a cosine signal, the direct current-filtered electric signal is mixed with the sine signal and the cosine signal in the first multiplier and the second multiplier respectively to obtain a sine mixed signal and a cosine mixed signal, and the first low-pass filter and the second low-pass filter are used for filtering frequency doubling components of the sine mixed signal and the cosine mixed signal respectively to obtain an I signal and a Q signal of the electric signal.
Compared with the prior art, the invention has the beneficial effects that: the method comprises the steps of dividing a beam of continuous light into front detection light and rear detection light, respectively modulating the front detection light and the rear detection light into first single-pulse light and second single-pulse light, delaying the second single-pulse light, and combining the delayed second single-pulse light with the first pulse light into double-pulse light; inputting the double-pulse light into a weak grating optical fiber array, generating beat frequency pulse signals in the weak grating optical fiber array by the double-pulse light, converting the beat frequency pulse signals into electric signals, and obtaining I signals and Q signals of the electric signals; acquiring an initial phase signal according to the I signal and the Q signal of the electric signal, and acquiring a final phase signal according to the initial phase signal; the real-time performance of I/Q signal demodulation is improved.
Drawings
FIG. 1 is a schematic flow chart of a method for demodulating a weak grating array distributed vibration sensor;
fig. 2 is a schematic structural diagram of a weak grating array distributed vibration sensing demodulation system provided by the invention.
Detailed Description
The following detailed description of preferred embodiments of the application is made in connection with the accompanying drawings, which form a part hereof, and together with the description of the embodiments of the application, are used to explain the principles of the application and are not intended to limit the scope of the application.
Example 1
The embodiment of the invention provides a weak grating array distributed vibration sensing demodulation method, which is a flow diagram as shown in fig. 1, and comprises the following steps:
S1, dividing a beam of continuous light into front detection light and rear detection light, respectively modulating the front detection light and the rear detection light into first single-pulse light and second single-pulse light, delaying the second single-pulse light, and combining the delayed second single-pulse light with the first pulse light into double-pulse light;
s2, inputting the double-pulse light into a weak grating optical fiber array, generating beat frequency pulse signals in the weak grating optical fiber array by the double-pulse light, converting the beat frequency pulse signals into electric signals, and obtaining I signals and Q signals of the electric signals;
S3, acquiring an initial phase signal according to the I signal and the Q signal of the electric signal, and acquiring a final phase signal according to the initial phase signal.
In one embodiment, the front and back pulse width of the inter-frequency double-pulse light is 40ns respectively, the time delay between the front and back pulses is 50ns, and the repetition frequency of the inter-frequency double-pulse light emission is 10KHz; the front pulse frequency of the inter-frequency double-pulse light is f 1 +f, the rear pulse frequency is f 2+f;f1, the frequency shift of the first acousto-optic modulator is f 2, the frequency shift of the second acousto-optic modulator is f, and the frequency shift of the narrow linewidth laser is f;
Preferably, the double pulse light includes a front pulse light and a rear pulse light, the front and rear pulse lights each have a pulse width of T W, a pulse repetition frequency of F p, a pulse delay of T p2l of the rear pulse with respect to the front pulse, V is the propagation speed of light in the weak grating array, L is the grating distance in the weak grating array, n e is the refractive index of the weak grating, S is the length of the weak grating array, and c is the light speed;
It should be noted that, due to the pulse delay, the reflected light of the back pulse from the ith weak grating meets the (light of the) 1 st reflected light of the front pulse from the ith grating, so that the two reflected lights of the front pulse and the back pulse generate beat frequency phenomena at the ith weak grating, and a series of reflected lights generate a series of beat frequency pulse signals; if vibration is generated between two adjacent gratings, the transmission optical path difference of the light between the two gratings is changed, so that the phase is changed, and the beat frequency intensity is changed;
Preferably, the double pulse light generates beat pulse signals in the weak grating fiber array, specifically including that the back pulse is reflected by the ith grating and then is reflected by the (i+1) th grating with the front pulse, and then meets the ith grating to generate beat pulse signals, wherein the intensity of the beat pulse signals is that Wherein E i、Ri is the light intensity amplitude of the reflected light of the ith grating, the reflectivity of the ith grating,/>, respectivelyFor the phase difference caused by disturbance between the i+1 and i grating,/>For the adjacent gratings, the phase difference is fixed, delta omega is the angular frequency difference of the acousto-optic modulator corresponding to the front detection light and the rear detection light, and delta omega=2pi (f 1-f2);
In one embodiment, the intensity of the post-pulse light after being reflected by the ith grating is The light intensity of the front pulse light passing through the ith grating after being reflected by the (i+1) th grating is/>Wherein ω 2,/>The optical frequency and initial phase of the back pulse, omega 1 is the optical frequency of the front pulse,/>, respectivelyFor the phase difference caused by disturbance between the i+1 and i grating,/>Fixing a phase difference for adjacent gratings; e' R1 and E R2 meet at the ith grating exactly at the same time, thereby producing a beat frequency; the intensity of the beat pulse signal is
In the above formula, the former term is a direct current term, the cosine function in the second term changes with time, and the phase isThe intensity of the beat pulse signal after passing through the band-pass filter can be written as/>
Preferably, the I signal and the Q signal of the electrical signal are obtained, including in particular,
And filtering the direct current component of the electric signal, and then mixing the direct current component with a sine signal and a cosine signal respectively to obtain a sine mixing signal and a cosine mixing signal, and filtering double frequency components of the sine mixing signal and the cosine mixing signal to obtain an I signal and a Q signal of the electric signal.
Preferably, the I signal of the electrical signalQ signal of electrical signal
After data acquisition is carried out through an acquisition card, square sum root opening number and arc tangent calculation are carried out on an I signal and a Q signal by an upper computer to obtain an initial amplitude signal and a phase signal, then initial phase expansion is carried out on the initial phase signal, and finally a final phase signal is obtained;
Example 2
The embodiment of the invention provides a weak grating array distributed vibration sensing demodulation system, which comprises a narrow linewidth laser, a first coupler, a first DDS signal generator, an acousto-optic modulator, a delay optical fiber, a second coupler, a circulator, a photoelectric converter, a signal acquisition module and a signal processing module, wherein the first coupler is connected with the first DDS signal generator;
the narrow linewidth laser is used for generating a beam of continuous light, and the first coupler is used for dividing the beam of continuous light into front detection light and rear detection light;
the first DDS signal generator and the acousto-optic modulator are used for respectively modulating the front detection light and the rear detection light into first single-pulse light and second single-pulse light, and the delay optical fiber is used for delaying the second single-pulse light;
The second coupler is used for combining the delayed second single-pulse light with the first pulse light into double-pulse light;
the circulator is used for inputting the double-pulse light into the weak grating optical fiber array, the double-pulse light generates beat frequency pulse signals in the weak grating optical fiber array, the photoelectric converter is used for converting the beat frequency pulse signals into electric signals, and the signal acquisition module is used for acquiring I signals and Q signals of the electric signals;
the signal processing module is used for obtaining an initial phase signal according to the I signal and the Q signal of the electric signal and obtaining a final phase signal according to the initial phase signal.
In a specific embodiment, a narrow linewidth DFB laser generates continuous light with a certain central wavelength, a light source is divided into 50:50 by a coupler and respectively enters two acousto-optic modulators (AOMs), corresponding electric pulses are generated by a DDS signal generator to control the driving of the acousto-optic modulators and the acquisition triggering of an acquisition card, the two acousto-optic modulators (a first acoustic modulator and a second acoustic modulator) modulate the continuous light (front detection light and rear detection light) into corresponding single-pulse light (signals), and a delay optical fiber delays the single-pulse light generated by the second acoustic modulator;
In another embodiment, the center wavelength, the output light power and the 3dB linewidth of the continuous light of the narrow linewidth laser are 1550.12nm, 30mw and 3kHz respectively; the frequency shift of the first acoustic-optic modulator is f 1, and the frequency shift of the second acoustic-optic modulator is f 2; the double pulse comprises two pulse lights, namely front pulse light and rear pulse light;
Preferably, the length of the delay optical fiber is twice the distance between adjacent gratings in the weak grating optical fiber array;
In one embodiment, the first coupler combines two single pulse lights into a double pulse light (signal), the double pulse light enters from a port one of the circulator after being preamplified by an erbium-doped fiber amplifier (EDFA), and then enters into a weak grating fiber array connected in series with a port two of the circulator, and the double pulse light is reflected back by a continuous weak grating;
Preferably, the double pulse light includes a front pulse light and a rear pulse light, the front and rear pulse lights each have a pulse width of T W, a pulse repetition frequency of F p, a pulse delay of T p2l of the rear pulse with respect to the front pulse, V is the propagation speed of light in the weak grating array, L is the grating distance in the weak grating array, n e is the refractive index of the weak grating, S is the length of the weak grating array, and c is the light speed;
It should be noted that, due to the pulse delay, the reflected light of the back pulse from the ith weak grating meets the (light of the) 1 st reflected light of the front pulse from the ith grating, so that the two reflected lights of the front pulse and the back pulse generate beat frequency phenomena at the ith weak grating, and a series of reflected lights generate a series of beat frequency pulse signals; if vibration is generated between two adjacent gratings, the transmission optical path difference of the light between the two gratings is changed, so that the phase is changed, and the beat frequency intensity is changed;
Preferably, the double pulse light generates beat pulse signals in the weak grating fiber array, specifically including that the back pulse is reflected by the ith grating and then is reflected by the (i+1) th grating with the front pulse, and then meets the ith grating to generate beat pulse signals, wherein the intensity of the beat pulse signals is that Wherein E i、Ri is the light intensity amplitude of the reflected light of the ith grating, the reflectivity of the ith grating,/>, respectivelyFor the phase difference caused by disturbance between the i+1 and i grating,/>The phase difference is fixed for the adjacent gratings, and delta omega is the angular frequency difference of the acousto-optic modulator corresponding to the front detection light and the rear detection light.
Preferably, the signal acquisition module includes a band-pass filter, a second DDS signal generator, a first multiplier, a second multiplier, a first low-pass filter, and a second low-pass filter, and the signal acquisition module acquires an I signal and a Q signal of the electrical signal, specifically including,
The band-pass filter filters direct current components from the electric signal to obtain a direct current-filtered electric signal, the second DDS signal generator is used for generating a sine signal and a cosine signal, the direct current-filtered electric signal is mixed with the sine signal and the cosine signal in the first multiplier and the second multiplier respectively to obtain a sine mixed signal and a cosine mixed signal, and the first low-pass filter and the second low-pass filter are used for filtering frequency doubling components of the sine mixed signal and the cosine mixed signal respectively to obtain an I signal and a Q signal of the electric signal;
In one embodiment, the beat frequency signal is converted into an electric signal through a photoelectric converter after coming out of a port III of the circulator, and the direct current component is filtered through a band-pass filter, wherein the center frequency of the band-pass filter is f 1-f2; the beat frequency signal is mixed with sine signals and cosine signals generated by the DDS signal generator in a first multiplier and a second multiplier respectively through a third coupler, the sine mixed signals and the cosine mixed signals are filtered through a first low-pass filter and a second low-pass filter respectively, frequency doubling components generated after mixing are filtered to obtain I signals and Q signals of the electric signals,
The I signal and the Q signal are acquired and subsequently demodulated through a signal processing module (a data acquisition and FPGA processing unit), and finally the signals are transmitted into an upper computer through PCIe for display and storage processing; the upper computer is mainly used for man-machine interaction; meanwhile, the upper computer is also responsible for controlling basic setting of FPGA acquisition;
In another embodiment, a weak grating array distributed vibration sensing demodulation system is shown in fig. 2, and includes a narrow linewidth laser 1, a first coupler 2, a first acousto-optic modulator 3, a second acousto-optic modulator 4, an acousto-optic modulator driver 5, a delay fiber 6, a second coupler 7, an erbium-doped fiber amplifier 8, a circulator 9, a weak grating array 10, a photodetector 11, a band-pass filter 12, a third coupler 13, a DDS signal generator 14, a first multiplier 15, a second multiplier 16, a first low-pass filter 17, a second low-pass filter 18, a data acquisition card 19, and an upper computer 20;
The narrow linewidth laser 1 is used for generating continuous light with a certain central wavelength and is connected with a first port of the first coupler 2; the first coupler 2 comprises two outputs: the second port of the first coupler 2 is connected to the input end of the first acousto-optic modulator 3, and the output end of the first acousto-optic modulator 3 is connected to the first port of the second coupler 4;
Port three of the first coupler 2 is connected to the input of the second acoustic optical modulator 4; the output end of the second acoustic optical modulator 4 is connected with the input end of the delay optical fiber, and the output end of the delay optical fiber 6 and the second port of the second coupler 4; the third port of the second coupler 4 is connected with the input end of the erbium-doped fiber amplifier 8;
The output end of the erbium-doped fiber amplifier 8 is connected with the port I of the circulator 9; the second port of the circulator is connected with the input end of the weak grating array 10; the third port of the circulator 9 is connected with the input end of the photoelectric detector 11; the output end of the photoelectric detector 11 is connected with the input end of the band-pass filter 12;
the output end of the band-pass filter 12 is connected with the port I of the third coupler 13; the third coupler 13 comprises two outputs: the second port of the third coupler 13 is connected to the first port of the first multiplier 15; the third port of the third coupler 7 is connected to the first port of the second multiplier 16; the third port of the first multiplier 15 is connected to the input of the first low-pass filter 17; port three of the second multiplier 16 is connected to the input of the second low-pass filter 18; the outputs of the first low-pass filter 17 and the second low-pass filter 18 are connected to a data acquisition card 19 for data acquisition, and the data acquisition card is processed by an upper computer 20 to obtain phase information to be demodulated, so that distributed sensing is realized;
The DDS signal generator is used for generating pulse signals required by driving the acousto-optic modulator and sine signals and cosine signals used for mixing, a port I of the DDS signal generator is connected with a port II of the first multiplier, a port II of the DDS signal generator is connected with a port I of the second multiplier, a port III of the DDS signal generator is connected with an input end of driving the acousto-optic modulator, and a port 4 of the DDS signal generator is connected with an input end of acquisition triggering of the acquisition card; the optical amplifier EDFA is used for amplifying the generated inter-frequency double pulse signal.
The invention discloses a method and a system for distributed vibration sensing demodulation of a weak grating array, wherein a beam of continuous light is divided into front detection light and rear detection light, the front detection light and the rear detection light are respectively modulated into first single-pulse light and second single-pulse light, the second single-pulse light is delayed, and the delayed second single-pulse light and the first pulse light are combined into double-pulse light; inputting the double-pulse light into a weak grating optical fiber array, generating beat frequency pulse signals in the weak grating optical fiber array by the double-pulse light, converting the beat frequency pulse signals into electric signals, and obtaining I signals and Q signals of the electric signals; acquiring an initial phase signal according to the I signal and the Q signal of the electric signal, and acquiring a final phase signal according to the initial phase signal; the real-time performance of I/Q signal demodulation is improved; the heterodyne of the beat frequency of the detection light and the local oscillation light is replaced by the different-frequency double pulses, so that the influence of the optical path difference on the demodulation signal is reduced, the frequency of the beat frequency light of the different-frequency double pulses is far smaller than that of the beat frequency light generated by the detection light and the local oscillation light, and the sampling rate requirement of the acquisition card is greatly reduced;
The weak grating array distributed vibration sensing demodulation system adopted by the technical scheme of the invention can obtain stable vibration signal intensity, frequency and phase change, uses sine signals and cosine signals generated by the DDS signal generator to carry out I, Q signal modulation of electric signals, namely I/Q signal modulation of an analog structure, reduces the operation burden of an upper computer, improves the data processing efficiency, further reduces the requirement on the sampling rate of a collection card, and greatly reduces the system cost; the problem that a large amount of data is generated by modulating the I/Q signal of the digital signal by the upper computer is avoided, so that the real-time performance of I/Q signal demodulation is further enhanced.
The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present invention are intended to be included in the scope of the present invention.
Claims (9)
1. The weak grating array distributed vibration sensing demodulation method is characterized by comprising the following steps of:
dividing a beam of continuous light into front detection light and rear detection light, respectively modulating the front detection light and the rear detection light into first single-pulse light and second single-pulse light, delaying the second single-pulse light, and combining the delayed second single-pulse light with the first pulse light into double-pulse light;
Inputting the double-pulse light into a weak grating optical fiber array, generating beat frequency pulse signals in the weak grating optical fiber array by the double-pulse light, converting the beat frequency pulse signals into electric signals, and obtaining I signals and Q signals of the electric signals;
acquiring an initial phase signal according to the I signal and the Q signal of the electric signal, and acquiring a final phase signal according to the initial phase signal;
Wherein the double pulse light generates beat frequency pulse signals in the weak grating fiber array, and concretely comprises that the back pulse is reflected by the ith grating and then is reflected by the (i+1) th grating with the front pulse, and then meets the ith grating to generate beat frequency pulse signals, wherein the intensity of the beat frequency pulse signals is that Wherein/>、/>Respectively, the light intensity amplitude of the reflected light of the ith grating, the reflectivity of the ith grating,/>For the phase difference caused by disturbance between the i+1 and i grating,/>Fixing the phase difference for adjacent gratings,/>The angular frequency difference of the acousto-optic modulator corresponds to the front probe light and the rear probe light.
2. The method for distributed vibration sensing demodulation of a weak grating array according to claim 1, wherein the double pulse light includes a front pulse light and a rear pulse light, and pulse widths of the front and rear pulse lights are respectivelyPulse repetition frequency is/>The pulse delay of the post pulse relative to the pre pulse is/>Wherein/>、/>、/>V is the propagation speed of light in the weak grating array, L is the grating distance in the weak grating array,/>The refractive index of the weak grating is S, the length of the weak grating array is S, and the light speed is c.
3. The method for distributed vibration sensing demodulation of a weak grating array according to claim 1 wherein the obtaining of the I and Q signals of the electrical signal comprises,
And filtering the direct current component of the electric signal, and then mixing the direct current component with a sine signal and a cosine signal respectively to obtain a sine mixing signal and a cosine mixing signal, and filtering double frequency components of the sine mixing signal and the cosine mixing signal to obtain an I signal and a Q signal of the electric signal.
4. The method of claim 3, wherein the I signal of the electrical signalQ Signal of electric Signal/>。
5. The weak grating array distributed vibration sensing demodulation system is characterized by comprising a narrow linewidth laser, a first coupler, a first DDS signal generator, an acousto-optic modulator, a delay optical fiber, a second coupler, a circulator, a photoelectric converter, a signal acquisition module and a signal processing module;
The narrow linewidth laser is used for generating a beam of continuous light, the first coupler is used for dividing the beam of continuous light into front detection light and rear detection light, the first DDS signal generator and the acousto-optic modulator are used for respectively modulating the front detection light and the rear detection light into first single-pulse light and second single-pulse light, the delay optical fiber is used for delaying the second single-pulse light, and the second coupler is used for synthesizing the delayed second single-pulse light and the first pulse light into double-pulse light;
the circulator is used for inputting the double-pulse light into the weak grating optical fiber array, the double-pulse light generates beat frequency pulse signals in the weak grating optical fiber array, the photoelectric converter is used for converting the beat frequency pulse signals into electric signals, and the signal acquisition module is used for acquiring I signals and Q signals of the electric signals;
the signal processing module is used for obtaining an initial phase signal according to the I signal and the Q signal of the electric signal and obtaining a final phase signal according to the initial phase signal.
6. The system of claim 5, wherein the delay fiber has a length twice the pitch of adjacent gratings in the array.
7. The weak grating array distributed vibration sensing demodulation system of claim 5, wherein the double pulse light comprises a front pulse light and a back pulse light, the pulse width of the front pulse light and the pulse width of the back pulse light are respectivelyPulse repetition frequency is/>The pulse delay of the post pulse relative to the pre pulse is/>Wherein/>、/>、/>V is the propagation speed of light in the weak grating array, L is the grating distance in the weak grating array,/>The refractive index of the weak grating is S, the length of the weak grating array is S, and the light speed is c.
8. The system of claim 5, wherein the dual pulse light generates beat pulse signals in the weak grating fiber array, and specifically comprises that the back pulse is reflected by the ith grating and then reflected by the (i+1) th grating, and then meets the ith grating to generate beat pulse signals with the intensity ofWherein/>、/>Respectively, the light intensity amplitude of the reflected light of the ith grating, the reflectivity of the ith grating,/>For the phase difference caused by disturbance between the i+1 and i grating,/>Fixing the phase difference for adjacent gratings,/>The angular frequency difference of the acousto-optic modulator corresponds to the front probe light and the rear probe light.
9. The system of claim 5, wherein the signal acquisition module comprises a bandpass filter, a second DDS signal generator, a first multiplier, a second multiplier, a first low-pass filter, and a second low-pass filter, the signal acquisition module acquires I and Q signals of the electrical signal, and the method comprises,
The band-pass filter filters direct current components from the electric signal to obtain a direct current-filtered electric signal, the second DDS signal generator is used for generating a sine signal and a cosine signal, the direct current-filtered electric signal is mixed with the sine signal and the cosine signal in the first multiplier and the second multiplier respectively to obtain a sine mixed signal and a cosine mixed signal, and the first low-pass filter and the second low-pass filter are used for filtering frequency doubling components of the sine mixed signal and the cosine mixed signal respectively to obtain an I signal and a Q signal of the electric signal.
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