CN113483795A - 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 synthesizing the delayed second single pulse light and the first pulse light into double pulse light; inputting the double pulse light into a weak grating optical fiber array, generating a beat frequency pulse signal in the weak grating optical fiber array by the double pulse light, converting the beat frequency pulse signal into an electric signal, and acquiring an I signal and a Q signal of the electric signal; 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 grating sensing, in particular to a weak grating array distributed vibration sensing demodulation method and system.
Background
Phase-sensitive optical time domain reflectometer technology
It is a vibration sensing element and signal transmission medium using optical fibreThe optical fiber sensor has the advantages of small volume, light weight, high sensitivity, good environmental adaptability, intrinsic safety, electromagnetic interference resistance and the like, is suitable for flammable and explosive severe environments and can be applied to the fields of perimeter security, geological exploration, oil and gas leakage, power grid monitoring, hydrophone and the like.
For a signal acquisition and demodulation end of a distributed weak grating vibration sensing demodulation system, according to a vibration sensing mechanism of a fiber grating, a vibration signal is substantially modulated into an interference signal, and the demodulation of the vibration signal is actually phase demodulation; for the
In terms of a system, two methods of signal demodulation mainly exist, 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 a beat frequency signal is high, a complete waveform which can be acquired only by an ultrahigh-frequency acquisition card is needed, modulation of an I signal and a Q signal in heterodyne demodulation is performed in the upper computer, and real-time measurement is difficult to achieve.
Disclosure of Invention
In view of the above, it is necessary to provide a method and a system for demodulation of distributed vibration sensing of a weak grating array, so as to solve the problem of poor real-time performance of the conventional 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 synthesizing the delayed second single pulse light and the first pulse light into double pulse light;
inputting the double pulse light into a weak grating optical fiber array, generating a beat frequency pulse signal in the weak grating optical fiber array by the double pulse light, converting the beat frequency pulse signal into an electric signal, and acquiring an I signal and a Q signal of the electric signal;
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 dual pulse light comprises front pulse light and rear pulse light, and the pulse widths of the front pulse light and the rear pulse light are both TWWith a pulse repetition frequency of FpThe pulse delay of the rear pulse relative to the front pulse is Tp2lWherein, in the step (A),
v is the propagation speed of light in the weak grating array, L is the grating distance in the weak grating array, neIs the refractive index of the weak grating, S is the length of the weak grating array, and c is the speed of light.
Further, the generating of the beat frequency pulse signal in the weak grating fiber array by the dual pulse light specifically includes that after the back pulse is reflected by the ith grating, the back pulse and the front pulse are reflected by the (i + 1) th grating, and then meet each other at the ith grating to generate the beat frequency pulse signal, and the intensity of the beat frequency pulse signal is
Wherein E isi、RiThe light intensity amplitude of the reflected light of the ith grating and the reflectivity of the ith grating are respectively,
is the phase difference caused by the perturbation between the (i + 1) th and the (i) th gratings,
the phase difference is fixed for the adjacent grating, and delta omega is the angular frequency difference of the front detection light and the rear detection light corresponding to the acousto-optic modulator.
Further, acquiring the I signal and the Q signal of the electric signal specifically comprises,
and filtering direct-current components of the electric signals, and then respectively mixing the electric signals with sine signals and cosine signals to obtain sine mixing signals and cosine mixing signals, and filtering out double frequency components of the sine mixing signals and the cosine mixing signals to obtain I signals and Q signals of the electric signals.
Further, I signal of the electric signal
Q signal of electric 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 probe light and rear probe light, the first DDS signal generator and the acousto-optic modulator are used for respectively modulating the front probe light and the rear probe light into first single pulse light and second single pulse light, the delay 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 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 length of the delay fiber is twice of the adjacent grating spacing in the weak grating fiber array.
Further, the dual pulse light comprises front pulse light and rear pulse light, and the pulse widths of the front pulse light and the rear pulse light are both TWWith a pulse repetition frequency of FpThe pulse delay of the rear pulse relative to the front pulse is Tp2lWherein, in the step (A),
v is the propagation speed of light in the weak grating array, L is the grating distance in the weak grating array, neIs the refractive index of the weak grating, S is the length of the weak grating array, and c is the speed of light.
Further, the generating of the beat frequency pulse signal in the weak grating fiber array by the dual pulse light specifically includes that after the back pulse is reflected by the ith grating, the back pulse and the front pulse are reflected by the (i + 1) th grating, and then meet each other at the ith grating to generate the beat frequency pulse signal, and the intensity of the beat frequency pulse signal is
Wherein E isi、RiThe light intensity amplitude of the reflected light of the ith grating and the reflectivity of the ith grating are respectively,
is the phase difference caused by the perturbation between the (i + 1) th and the (i) th gratings,
the phase difference is fixed for the adjacent grating, and delta omega is the angular frequency difference of the front detection light and the rear detection light corresponding to the acousto-optic modulator.
Further, the signal obtaining 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 obtaining module obtains an I signal and a Q signal of the electrical signal, specifically includes,
the band-pass filter filters direct-current components of the electric signals to obtain direct-current-filtered electric signals, the second DDS signal generator is used for generating sine signals and cosine signals, the direct-current-filtered electric signals are respectively mixed with the sine signals and the cosine signals in the first multiplier and the second multiplier to obtain sine mixing signals and cosine mixing signals, and the first low-pass filter and the second low-pass filter respectively filter double-frequency components of the sine mixing signals and the cosine mixing signals to obtain I signals and Q signals of the electric signals.
Compared with the prior art, the invention has the beneficial effects that: dividing a beam of continuous light into front probe light and rear probe light, respectively modulating the front probe light and the rear probe light into first single pulse light and second single pulse light, delaying the second single pulse light, and synthesizing the delayed second single pulse light and the first pulse light into double pulse light; inputting the double pulse light into a weak grating optical fiber array, generating a beat frequency pulse signal in the weak grating optical fiber array by the double pulse light, converting the beat frequency pulse signal into an electric signal, and acquiring an I signal and a Q signal of the electric signal; acquiring an initial phase signal according to an I signal and a 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 weak grating array distributed vibration sensing demodulation method provided by the present invention;
fig. 2 is a schematic structural diagram of a distributed vibration sensing demodulation system of a weak grating array provided by the invention.
Detailed Description
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.
Example 1
The embodiment of the invention provides a weak grating array distributed vibration sensing demodulation method, which has a flow schematic diagram as shown in fig. 1 and comprises the following steps:
s1, dividing a beam of continuous light into front probe light and rear probe light, respectively modulating the front probe light and the rear probe light into first single pulse light and second single pulse light, delaying the second single pulse light, and synthesizing the delayed second single pulse light and 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 acquiring I signals and Q signals of the electric signals;
and 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 a specific embodiment, the front pulse width and the rear pulse width of the pilot frequency double-pulse light are respectively 40ns, the time delay between the front pulse and the rear pulse is 50ns, and the repetition frequency of the pilot frequency double-pulse light emission is 10 KHz; the front pulse frequency of the pilot frequency double-pulse light is f1+ f, rear pulse frequency f2+f；f1Frequency shift, f, of the acousto-optic modulator one2The frequency shift of the acousto-optic modulator II is shown, and f is the frequency shift of the narrow linewidth laser;
preferably, the dual pulse light includes a front pulse light and a rear pulse light, and the pulse widths of the front and rear pulse lights are both TWWith a pulse repetition frequency of FpThe pulse delay of the rear pulse relative to the front pulse is Tp2lWherein, in the step (A),
v is the propagation speed of light in the weak grating array, L is the grating distance in the weak grating array, neThe refractive index of the weak grating, S the length of the weak grating array and c the speed of light;
it should be noted that, due to the pulse delay, the reflected light of the back pulse from the ith weak grating meets the reflected light of the front pulse (light) from the (i + 1) th grating, so that the two reflected lights of the front and back pulses generate a beat frequency phenomenon at the ith weak grating, and a series of beat frequency pulse signals are generated by the series of reflected lights; if vibration is generated between two adjacent gratings, the transmission optical path difference of light between the two gratings is changed, so that the phase is changed, and the beat frequency intensity is changed;
preferably, the dual pulse light generates beat frequency pulse in the weak grating fiber arrayThe signal comprises that after the back pulse is reflected by the ith grating, the back pulse and the front pulse are reflected by the (i + 1) th grating and meet each other at the ith grating to generate a beat frequency pulse signal, and the intensity of the beat frequency pulse signal is
Wherein E isi、RiThe light intensity amplitude of the reflected light of the ith grating and the reflectivity of the ith grating are respectively,
is the phase difference caused by the perturbation between the (i + 1) th and the (i) th gratings,
the phase difference is fixed for adjacent gratings, delta omega is the angular frequency difference of the front detection light and the rear detection light corresponding to the acousto-optic modulator, and delta omega is 2 pi (f)1-f2)；
In one embodiment, the intensity of the back pulse light after being reflected by the ith grating is
The light intensity of the front pulse light after being reflected by the (i + 1) th grating and passing through the (i) th grating is
Wherein, ω is2、
Optical frequency, initial phase, omega, of the rear pulse1Is the frequency of the light of the pre-pulse,
is the phase difference caused by the perturbation between the (i + 1) th and the (i) th gratings,
fixing the phase difference for the adjacent gratings; e'R1And ER2Meet at the ith grating exactly at the same time, thereby generatingBeating frequency; the strength of the beat frequency pulse signal is
In the above formula, the former term is a direct current term, the cosine function in the second term varies with time, and the phase thereof is
The strength 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, specifically including,
and filtering direct-current components of the electric signals, and then respectively mixing the electric signals with sine signals and cosine signals to obtain sine mixing signals and cosine mixing signals, and filtering out double frequency components of the sine mixing signals and the cosine mixing signals to obtain I signals and Q signals of the electric signals.
Preferably, the I signal of the electrical signal
Q signal of electric signal
After data acquisition is carried out through an acquisition card, square sum of the I signal and the Q signal, root opening number and arc tangent calculation are carried out on an upper computer to obtain an initial amplitude signal and a phase signal, initial phase expansion is carried out on the initial phase signal, and a final phase signal is finally 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 narrow linewidth laser is connected with the first coupler through 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 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 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 a specific embodiment, a narrow-linewidth DFB laser generates continuous light with a certain central wavelength, a coupler divides a light source into 50:50, the continuous light respectively enters two acousto-optic modulators (AOMs), a DDS signal generator generates corresponding electric pulses to control the driving of the acousto-optic modulators and the acquisition triggering of an acquisition card, the two acousto-optic modulators (a first acousto-optic modulator and a second acousto-optic modulator) modulate the continuous light (front probe light and rear probe light) into corresponding single pulse light (signals), and a delay optical fiber is used for delaying the single pulse light generated by the second acousto-optic modulator;
in another embodiment, the central wavelength, the output optical 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 acousto-optic modulator is f1The frequency shift of the second acousto-optic modulator is f2(ii) a The double pulse comprises two pulse lights, namely a front pulse light and a rear pulse light;
preferably, the length of the delay fiber is twice of the adjacent grating spacing in the weak grating fiber array;
in a specific embodiment, the first coupler synthesizes the two single pulse lights into a double pulse light (signal), the double pulse light enters from a first port of the circulator after being pre-amplified by an erbium-doped fiber amplifier (EDFA), and then enters into a weak grating fiber array connected with a second port of the circulator in series, and the double pulse light is reflected by a continuous weak grating;
preferably, the dual pulse light includes a front pulse light and a rear pulse light, and the pulse widths of the front and rear pulse lights are both TWWith a pulse repetition frequency of FpThe pulse delay of the rear pulse relative to the front pulse is Tp2lWherein, in the step (A),
v is the propagation speed of light in the weak grating array, L is the grating distance in the weak grating array, neThe refractive index of the weak grating, S the length of the weak grating array and c the speed of light;
it should be noted that, due to the pulse delay, the reflected light of the back pulse from the ith weak grating meets the reflected light of the front pulse (light) from the (i + 1) th grating, so that the two reflected lights of the front and back pulses generate a beat frequency phenomenon at the ith weak grating, and a series of beat frequency pulse signals are generated by the series of reflected lights; if vibration is generated between two adjacent gratings, the transmission optical path difference of light between the two gratings is changed, so that the phase is changed, and the beat frequency intensity is changed;
preferably, the generating of the beat frequency pulse signal in the weak grating fiber array by the dual pulse light specifically includes that after the back pulse is reflected by the ith grating, the back pulse and the front pulse are reflected by the (i + 1) th grating, and then the back pulse and the front pulse meet each other at the ith grating to generate the beat frequency pulse signal, and the intensity of the beat frequency pulse signal is
Wherein E isi、RiRespectively the light intensity amplitude of the reflected light of the ith grating and the reflectivity of the ith grating，
Is the phase difference caused by the perturbation between the (i + 1) th and the (i) th gratings,
the phase difference is fixed for the adjacent grating, and delta omega is the angular frequency difference of the front detection light and the rear detection light corresponding to the acousto-optic modulator.
Preferably, the signal obtaining 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 obtaining module obtains an I signal and a Q signal of the electrical signal, specifically includes,
the band-pass filter filters direct-current components of 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 respectively mixed with the sine signal and the cosine signal in a first multiplier and a second multiplier to obtain a sine mixing signal and a cosine mixing signal, and the first low-pass filter and the second low-pass filter respectively filter 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;
in one embodiment, the beat signal is converted into an electrical signal by a photoelectric converter after coming out of the third port of the circulator, and a direct current component is filtered out by a band-pass filter with a center frequency f1-f2(ii) a The beat frequency signal is respectively mixed with sine signal and cosine signal generated by DDS signal generator in the first multiplier and the second multiplier through the third coupler, the sine mixing signal and the cosine mixing signal are respectively passed through the first low-pass filter and the second low-pass filter, the double frequency component generated after mixing is filtered out to obtain I signal and Q signal of electric signal,
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 to 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 structural schematic diagram of 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: a second port of the first coupler 2 is connected to an input end of the first acousto-optic modulator 3, and an output end of the first acousto-optic modulator 3 is connected to a first port of the second coupler 4;
the third port of the first coupler 2 is connected to the input end of the second acousto-optic modulator 4; the output end of the second acousto-optic modulator 4 is connected with the input end of the delay optical fiber, and the output end of the delay optical fiber 6 is connected with a 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 a first port 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 a first port of the third coupler 13; the third coupler 13 comprises two outputs: port two of the third coupler 13 is connected to port one of the first multiplier 15; port three of the third coupler 7 is connected to port one of the second multiplier 16; port three of the first multiplier 15 is connected to the input terminal of the first low-pass filter 17; port three of the second multiplier 16 is connected to the input terminal of the second low-pass filter 18; the output ends 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 are 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 the drive of the acousto-optic modulator and sine signals and cosine signals used for frequency mixing, a first port of the DDS signal generator is connected to a second port of the first multiplier, a second port of the DDS signal generator is connected to a first port of the second multiplier, a third port of the DDS signal generator is connected to the input end of the drive of the acousto-optic modulator, and a 4 port of the DDS signal generator is connected to the input end of the acquisition card for acquisition and triggering; the optical amplifier EDFA is used for amplifying the generated pilot frequency double-pulse signals.
The invention discloses a weak grating array distributed vibration sensing demodulation method and a system, 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 synthesized into double pulse light; inputting the double pulse light into a weak grating optical fiber array, generating a beat frequency pulse signal in the weak grating optical fiber array by the double pulse light, converting the beat frequency pulse signal into an electric signal, and acquiring an I signal and a Q signal of the electric signal; acquiring an initial phase signal according to an I signal and a 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 heterofrequency dipulse replaces heterodyne of beat frequencies of the detection light and the local oscillator light, so that the influence of optical path difference on a demodulation signal is reduced, the frequency of the heterofrequency dipulse beat light is far less than that of beat light generated by beat frequencies of the detection photosynthetic light and the local oscillator light, and the requirement on the sampling rate 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, carries out I, Q signal modulation of electric signals by using sine signals and cosine signals generated by a DDS signal generator, namely I/Q signal modulation of an analog structure, lightens 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 when the upper computer modulates the I/Q signal of the digital signal is avoided, and the real-time performance of I/Q signal demodulation is further enhanced.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. A weak grating array distributed vibration sensing demodulation method is characterized by comprising 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 synthesizing the delayed second single pulse light and the first pulse light into double pulse light;
inputting the double pulse light into a weak grating optical fiber array, generating a beat frequency pulse signal in the weak grating optical fiber array by the double pulse light, converting the beat frequency pulse signal into an electric signal, and acquiring an I signal and a Q signal of the electric signal;
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.
2. The weak grating array distributed vibration sensing demodulation method according to claim 1, wherein the dual pulse light comprises a front pulse light and a rear pulse light, and the pulse widths of the front pulse light and the rear pulse light are both TWWith a pulse repetition frequency of FpThe pulse delay of the rear pulse relative to the front pulse is Tp2lWherein, in the step (A),
v is light in a weak grating arrayL is the grating distance in the weak grating array, neIs the refractive index of the weak grating, S is the length of the weak grating array, and c is the speed of light.
3. The distributed vibration sensing demodulation method for the weak grating array according to claim 2, wherein the dual pulse light generates beat frequency pulse signals in the weak grating fiber array, and specifically includes that after the back pulse is reflected by the ith grating, the back pulse and the front pulse are reflected by the (i + 1) th grating, and then meet with each other at the ith grating, so as to generate beat frequency pulse signals, and the intensity of the beat frequency pulse signals is
Wherein E isi、RiThe light intensity amplitude of the reflected light of the ith grating and the reflectivity of the ith grating are respectively,
is the phase difference caused by the perturbation between the (i + 1) th and the (i) th gratings,
the phase difference is fixed for the adjacent grating, and delta omega is the angular frequency difference of the front detection light and the rear detection light corresponding to the acousto-optic modulator.
4. The weak grating array distributed vibration sensing demodulation method according to claim 1, wherein obtaining I and Q signals of the electrical signal comprises,
and filtering direct-current components of the electric signals, and then respectively mixing the electric signals with sine signals and cosine signals to obtain sine mixing signals and cosine mixing signals, and filtering out double frequency components of the sine mixing signals and the cosine mixing signals to obtain I signals and Q signals of the electric signals.
5. The weak grating array distributed vibration sensing demodulation method of claim 4, wherein the I signal of the electrical signal
Q signal of electric signal
6. A weak grating array distributed vibration sensing demodulation system is characterized by comprising a narrow line width 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 probe light and rear probe light, the first DDS signal generator and the acousto-optic modulator are used for respectively modulating the front probe light and the rear probe light into first single pulse light and second single pulse light, the delay 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 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.
7. The distributed vibration sensing demodulation system of claim 6 wherein the length of the delay fiber is twice the pitch of adjacent gratings in the array of weak grating fibers.
8. The weak light according to claim 6The grid array distributed vibration sensing demodulation system is characterized in that the double pulse light comprises front pulse light and rear pulse light, and the pulse widths of the front pulse light and the rear pulse light are both TWWith a pulse repetition frequency of FpThe pulse delay of the rear pulse relative to the front pulse is Tp2lWherein, in the step (A),
v is the propagation speed of light in the weak grating array, L is the grating distance in the weak grating array, neIs the refractive index of the weak grating, S is the length of the weak grating array, and c is the speed of light.
9. The distributed vibration sensing demodulation system with the weak grating array according to claim 6, wherein the dual pulse light generates beat frequency pulse signals in the weak grating fiber array, and specifically comprises that after the back pulse is reflected by the ith grating, the back pulse and the front pulse are reflected by the (i + 1) th grating, and meet with each other at the ith grating, beat frequency pulse signals are generated, and the intensity of the beat frequency pulse signals is
Wherein E isi、RiThe light intensity amplitude of the reflected light of the ith grating and the reflectivity of the ith grating are respectively,
is the phase difference caused by the perturbation between the (i + 1) th and the (i) th gratings,
the phase difference is fixed for the adjacent grating, and delta omega is the angular frequency difference of the front detection light and the rear detection light corresponding to the acousto-optic modulator.
10. The distributed vibration sensing demodulation system of the weak grating array according to claim 6, wherein 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 the I signal and the Q signal of the electrical signal, and specifically comprises,
the band-pass filter filters direct-current components of the electric signals to obtain direct-current-filtered electric signals, the second DDS signal generator is used for generating sine signals and cosine signals, the direct-current-filtered electric signals are respectively mixed with the sine signals and the cosine signals in the first multiplier and the second multiplier to obtain sine mixing signals and cosine mixing signals, and the first low-pass filter and the second low-pass filter respectively filter double-frequency components of the sine mixing signals and the cosine mixing signals to obtain I signals and Q signals of the electric signals.
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