CN111157101A - Weak grating array distributed vibration sensing system and method - Google Patents

Abstract

The invention discloses a weak grating array distributed vibration sensing system and a method, belongs to the technical field of fiber grating sensing, and solves the problems that demodulation by using a double-arm interferometer in the prior art is easily interfered by an external environment, bottom noise is large, and frequency response bandwidth is narrow. A weak grating array distributed vibration sensing system comprises a narrow linewidth laser used for generating continuous light with a certain central wavelength; the acousto-optic modulator is used for modulating the continuous light into a corresponding double-pulse signal; the circulator is used for transmitting the double-pulse signal to the weak grating array; the weak grating array reflects the double-pulse signal to a circulator; the circulator is also used for transmitting the reflected double-pulse signal to the 3 x 3 coupler; the 3 x 3 coupler is used for enabling the reflected double-pulse signals to form interference and generating interference signals; and the photoelectric detector is used for acquiring the interference signal and converting the interference signal into an electric signal. The system bottom noise is reduced, and the signal-to-noise ratio and the frequency response range are improved.

Description

A weak grating array distributed vibration sensing system and method

technical field

The invention relates to the technical field of fiber grating sensing, in particular to a weak grating array distributed vibration sensing system and method.

Background technique

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, the vibration signal is essentially modulated into the interference signal, and the demodulation of the vibration signal is actually the phase Demodulation: At present, the commonly used phase demodulation methods in distributed sensing systems include quadrature (IQ) demodulation algorithm, phase carrier generation (PGC) detection method and 3×3 coupler demodulation algorithm;

For the signal demodulation of the distributed weak grating vibration sensing demodulation system, the commonly used interferometers are Mach-Zehnder interferometer, Sagnac interferometer and Michelson interferometer; the pulsed light is reflected back by the continuous weak grating and finally reaches the interferometer The interference occurs in the coupler after passing through two unequal length interference arms, so that the reflected light of the adjacent weak grating produces interference phenomenon; the interferometer with sensitive arms is easily disturbed by the external environment, such as chassis temperature, fan , external noise, vibration and other influences, resulting in a large noise floor of signal demodulation, thereby affecting the signal-to-noise ratio of the system. In addition, most of the existing vibration sensing systems have a narrow bandwidth for frequency response, and it is difficult to respond to low frequencies.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome at least one of the above-mentioned technical deficiencies, and to propose a weak grating array distributed vibration sensing system and method.

In one aspect, the present invention provides a weak grating array distributed vibration sensing system, comprising a narrow linewidth laser, an acousto-optic modulator, a circulator, a weak grating array, a 3×3 coupler and a photodetector;

The narrow linewidth laser is used to generate continuous light with a certain center wavelength and send it to the acousto-optic modulator; the acousto-optic modulator is used to modulate the continuous light into a corresponding double-pulse signal, and sending the double-pulse signal to a circulator; the circulator is configured to receive the double-pulse signal and transmit the double-pulse signal to a weak grating array, and the weak grating array reflects the double-pulse signal to the circulator; the circulator is also used to transmit the reflected double-pulse signal to the 3×3 coupler; the 3×3 coupler is used to cause the reflected double-pulse signal to form interference to generate interference signal; the photodetector is used for acquiring the interference signal and converting the interference signal into an electrical signal.

Further, the weak grating array distributed vibration sensing system also includes a data acquisition and FPGA processing unit, the data acquisition and FPGA processing unit is used to generate electrical pulses, so that the acousto-optic modulator modulates the continuous light. is a corresponding double-pulse signal; the data acquisition and FPGA processing unit is also used to collect and demodulate the electrical signal to form a demodulated signal.

Further, the weak grating array distributed vibration sensing system further includes an erbium-doped fiber amplifier for amplifying the double-pulse signal; the acousto-optic modulator amplifies the double-pulse signal. The transmitting to the circulator specifically includes that the acousto-optic modulator transmits the double-pulse signal to the erbium-doped fiber amplifier, and after being amplified by the erbium-doped fiber amplifier, the signal is transmitted to the circulator.

Further, the acousto-optic modulator modulates the continuous light into a corresponding double-pulse signal, which specifically includes that the acousto-optic modulator modulates the continuous light into a time delay of two rising edges before and after T _ps , and a pulse. A double-pulse signal with a pulse width of _Tw and a pulse repetition frequency of _Fp ,

F_p≤v/2L，v为光在弱光栅阵列中的传播速度，d为弱光栅阵列光栅距离，n_e为弱光栅阵列的折射率，L为弱光栅阵列的长度，c为光速。in,

F _p ≤ v/2L, v is the propagation speed of light in the weak grating array, d is the grating distance of the weak grating array, _ne is the refractive index of the weak grating array, L is the length of the weak grating array, and c is the speed of light.

Further, the 3×3 coupler causes the reflected double-pulse signal to form interference. When t=0, the double-pulse signal is input into the sensing fiber, and the interference intensity formed by the i-th and i+1 grating reflection signals is I(t ) interference signal;

Among them, E _i , R _i , τ _i , are the amplitude, reflectivity, and time of the i-th grating, respectively; φ(t) is the phase difference between the i+1-th grating and the i-th grating, and the σ polarization mismatch factor.

Further, the weak grating array distributed vibration sensing system also includes an interference signal with an interference intensity of I(t) formed by the i and i+1 grating reflection signals to obtain the currents of the three detectors.

And using the standard arctangent algorithm, the voltage of the electrical signal can be obtained,

Among them, D is the DC component, φ ₀ is the initial phase difference of adjacent weak grating arrays, and Δφ is the phase difference caused by the external environment.

On the other hand, the present invention also provides a weak grating array distributed vibration sensing method, comprising the following steps:

The continuous light with a certain central wavelength is modulated into a corresponding double-pulse signal, and the double-pulse signal is transmitted to the weak grating array; the weak grating array reflects the double-pulse signal, so that the reflected double-pulse signal forms interference , generating an interference signal; acquiring the interference signal, and converting the interference signal into an electrical signal.

Further, the weak grating array distributed vibration sensing method further includes collecting and demodulating the electrical signal; using an arctangent algorithm on the demodulated signal to obtain a phase change between two adjacent gratings.

Further, the method for distributed vibration sensing of the weak grating array further includes amplifying the double pulse signal before transmitting the double pulse signal to the weak grating array.

Further, modulating the continuous light into a corresponding double-pulse signal specifically includes: modulating the continuous light into a double-pulse signal with a time delay of T _ps , a pulse width of _Tw , and a pulse repetition frequency of F _p ,

F_p≤v/2L，v为光在弱光栅阵列中的传播速度，d为弱光栅阵列光栅距离，n_e为弱光栅阵列的折射率，L为弱光栅阵列的长度，c为光速。in,

F _p ≤ v/2L, v is the propagation speed of light in the weak grating array, d is the grating distance of the weak grating array, _ne is the refractive index of the weak grating array, L is the length of the weak grating array, and c is the speed of light.

Compared with the prior art, the beneficial effects of the present invention include: the narrow linewidth laser generates continuous light with a certain center wavelength and sends it to the acousto-optic modulator; the acousto-optic modulator modulates the continuous light is the corresponding double-pulse signal, and transmits the double-pulse signal to the circulator; the circulator receives the double-pulse signal, and transmits the double-pulse signal to the weak grating array, and the weak grating array transmits the double-pulse signal to the circulator. The pulse signal is reflected to the circulator; the circulator transmits the reflected double-pulse signal to the 3×3 coupler; the 3×3 coupler interferes the reflected double-pulse signal to generate an interference signal; The photodetector acquires the interference signal and converts the interference signal into an electrical signal; the conventional double-arm interferometer is not used to demodulate the phase difference between adjacent gratings, and the system will not be disturbed by the external environment, improving the The stability of the system is improved, the noise floor of the system is reduced, and the signal-to-noise ratio and frequency response range are improved.

Description of drawings

1 is a schematic structural diagram of the weak grating array distributed vibration sensing system according to Embodiment 1 of the present invention;

2 is a schematic diagram of the working principle of the weak grating array distributed vibration sensing system according to Embodiment 1 of the present invention;

传感系统的解调信号频谱图；Figure 3(a) is the Michelson-based structure under the applied disturbance described in Embodiment 1 of the present invention.

Spectrogram of the demodulated signal of the sensing system;

传感系统的解调信号波形图；Figure 3(b) is the Michelson-based structure under the applied disturbance described in Example 1 of the present invention.

The waveform diagram of the demodulation signal of the sensing system;

4 (a) and (b) are respectively the frequency domain and time domain signal diagrams after the demodulation of the electrical signal according to Embodiment 1 of the present invention;

FIG. 5 is a frequency response diagram of demodulation of 40 kHz and 0.1 Hz according to Embodiment 1 of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1

An embodiment of the present invention provides a weak grating array distributed vibration sensing system, the schematic diagram of which is shown in FIG. 1 , the system includes a narrow linewidth laser, an acousto-optic modulator, a circulator, a weak grating array, and 3 ×3 couplers and photodetectors;

The narrow linewidth laser is used to generate continuous light with a certain center wavelength and send it to the acousto-optic modulator; the acousto-optic modulator is used to modulate the continuous light into a corresponding double-pulse signal, and sending the double-pulse signal to a circulator; the circulator is configured to receive the double-pulse signal and transmit the double-pulse signal to a weak grating array, and the weak grating array reflects the double-pulse signal to the circulator; the circulator is also used to transmit the reflected double-pulse signal to the 3×3 coupler; the 3×3 coupler is used to cause the reflected double-pulse signal to form interference to generate interference signal; the photodetector is used for acquiring the interference signal and converting the interference signal into an electrical signal.

It should be noted that the optical fiber used in the embodiment of the present invention is an isotactic weak grating array with low reflectivity, the grating is a chirped grating, the 3dB bandwidth exceeds 3nm, the reflectivity is -50dB, and the grating array interval is 3m or 5m optional ;

Preferably, the weak grating array distributed vibration sensing system further includes a data acquisition and FPGA processing unit, the data acquisition and FPGA processing unit is used to generate electrical pulses, so that the acousto-optic modulator Modulated into a corresponding double-pulse signal; the data acquisition and FPGA processing unit is also used to collect and demodulate the electrical signal to form a demodulated signal.

Preferably, the weak grating array distributed vibration sensing system further comprises an erbium-doped fiber amplifier, which is used to amplify the double-pulse signal; the acousto-optic modulator amplifies the double-pulse signal. Sending the signal to the circulator specifically includes that the acousto-optic modulator sends the double-pulse signal to an erbium-doped fiber amplifier, and after being amplified by the erbium-doped fiber amplifier, the signal is sent to the circulator.

In a specific embodiment, a schematic diagram of the working principle of the weak grating array distributed vibration sensing system is shown in Figure 2; the narrow linewidth DFB laser generates continuous light with a certain center wavelength (eg, 1550.15nm), Data acquisition and FPGA processing unit (data acquisition card can be used for data acquisition) write control, data acquisition and FPGA processing unit generate corresponding electrical pulses according to the compiled program, and the corresponding electrical pulses are used to modulate the AOM acousto-optic modulator, The AOM acousto-optic modulator modulates the continuous laser light source (continuous light) into the corresponding double-pulse light (signal), which is pre-amplified by the EDFA (Erbium-Doped Fiber Amplifier) and then enters from the 1 port of the circulator, and then enters and 2 In the weak grating fiber array whose ports are connected in series, the double-pulse light is reflected back by the continuous weak grating, and reaches the 3×3 coupler after exiting from the 3 ports of the circulator. Due to the pulse delay, the post-pulse reflects light from the mth weak grating. The optical path of the reflected light from the m+1th weak grating is the same as that of the previous pulse, so that the reflected light of the adjacent weak grating will interfere, that is, the reflected light of the adjacent weak grating will interfere in the 3×3 coupler; A series of reflected light pulses will generate a series of interference pulse signals; if there is vibration between two adjacent gratings, the optical path difference of light transmission between the two gratings will change, resulting in phase changes, so The interference intensity will change; the interference signal (interference pulse signal) is converted into an electrical signal by three PD photodetectors; the electrical signal is collected and demodulated by the data acquisition and FPGA processing unit, and finally the signal is transmitted through PCIe. Enter the host computer for display and storage processing; the host computer PC is mainly used for human-computer interaction; at the same time, the host computer is also responsible for controlling the basic settings of FPGA acquisition.

In specific implementation, the central wavelength, output optical power, and 3dB linewidth of the continuous light of the narrow linewidth laser are 1550.15nm, 30mw, and 3kHz, respectively; the double pulse includes two optical pulses, which are respectively a pre-pulse and a post-pulse; The pulse width of a single pulse of the pulse signal is _Tw , and the pulse delay of the post-pulse relative to the pre-pulse is T _ps ,

Preferably, the acousto-optic modulator modulates the continuous light into a corresponding double-pulse signal, which specifically includes: the acousto-optic modulator modulates the continuous light into a time delay of two rising edges before and after T _ps , pulse A double-pulse signal with a pulse width of _Tw and a pulse repetition frequency of _Fp ,

F_p≤v/2L，v为光在弱光栅阵列中的传播速度，d为弱光栅阵列光栅距离，n_e为弱光栅阵列的折射率，L为弱光栅阵列的长度，c为光速。in,

F _p ≤ v/2L, v is the propagation speed of light in the weak grating array, d is the grating distance of the weak grating array, _ne is the refractive index of the weak grating array, L is the length of the weak grating array, and c is the speed of light.

In specific implementation, it is assumed that the light intensity before the post pulse reaches the 3×3 coupler after being reflected by the ith grating is,

Among them, E ₀ , R _m , ω, _ne , k, L _m , τ _m are the light intensity amplitude of the incident light, the reflectivity of the m-th grating, the optical frequency, the refractive index of the fiber, the wave number, and the i-th grating, respectively. The fiber distance of the grating and the transmission time of the reflected light to the coupler;

After the pre-pulse is transmitted, it passes through the i+1th grating and is reflected to reach the 3×3 coupler before the light intensity is,

E _i (t) and E _i+1 (t) arrive at the coupler just at the same time, causing interference in the PD, so the interference intensity of the interference signal is

In the above formula, the first two terms are both DC terms, and the cosine function in the third term changes with time, and its phase is φ(t), and its phase is φ ₀ (t) when there is no external disturbance. changes to φ ₁ (t), so φ(t)=φ ₁ (t)+φ ₀ (t), so the above formula can be written as,

I(t)∝D+I ₀ cos[φ(t)]

Therefore, since the output phase of the 3×3 coupler is 120° out of phase, after passing through the coupler and the three PDs, its intensity is,

The three-way signal in the coupler is collected by the photodetector, and the arc tangent algorithm is demodulated by the data acquisition and FPGA processing unit, and the relationship between the signal voltage V and the phase change can be obtained:

Among them, D is the DC component, φ ₀ is the initial phase difference of adjacent weak grating arrays, Δφ is the phase difference caused by the external environment, and the phase change of adjacent weak grating arrays can be obtained linearly through the voltage value, so as to realize the distributed phase Change demodulation: From the above formula, it can be seen that the signal voltage V has a linear relationship with the phase change. By measuring the voltage value, the phase change between adjacent gratings can be obtained, and fully distributed vibration monitoring can be realized by arranging the gratings.

In a specific implementation, the pulse period of the double-pulse signal is 90ns, the pulse width is 40ns, the interval between two pulses is 10ns, and the interval between two double-pulse light emission is 100us, and the photodetector is an avalanche diode (APD);

Preferably, the 3×3 coupler causes the reflected double-pulse signal to form interference to generate an interference signal. Specifically, the 3×3 coupler causes the reflected double-pulse signal to form interference, and when t=0, the double-pulse signal forms interference. The pulse signal is input into the sensing fiber (weak grating array), and the reflection signals of the i and i+1 gratings form an interference signal with an interference intensity of I(t);

Among them, E ₀ , R _m , ω, _ne , k ₀ , L _m , τ _m are the light intensity amplitude of the incident light, the reflectivity of the mth grating, the optical frequency, the refractive index of the fiber, the wavenumber, the mth The fiber distance of a grating and the transit time of the reflected light to the coupler.

Preferably, the weak grating array distributed vibration sensing system further comprises an interference signal with an interference intensity of I(t) formed by the reflection signals of the ith and i+1 gratings to obtain the currents of the three detectors

And using the standard arctangent algorithm, the voltage of the electrical signal can be obtained,

Among them, D is the DC component, φ ₀ is the initial phase difference of adjacent weak grating arrays, and Δφ is the phase difference caused by the external environment. It can be seen from the above formula that the signal voltage V has a linear relationship with the phase change. By measuring the voltage value, the phase change between adjacent gratings can be obtained. By arranging the gratings, fully distributed vibration monitoring is realized.

传感系统为例，分别对基于Michelson结构的

传感系统和本系统的光路都施加300Hz扰动和20Hz传感信号；In the technical solution of the embodiment of the present invention, there is no double-arm interference structure in the optical path, so the optical path in the system will not be disturbed by the external environment;

Take the sensing system as an example, respectively for the Michelson structure-based

Both the sensing system and the optical path of the system apply 300Hz disturbance and 20Hz sensing signal;

传感系统的解调信号频谱图；即是施加扰动下基于Michelson双臂结构，单脉冲调制使用3×3耦合器方式解调相位信号的频率信号，显示频谱图在20Hz和300Hz处有两个峰值；图3(b)是施加扰动下基于Michelson结构的

传感系统的解调信号波形图，即图3(a)相应的时域信号；图3(b)中解调信号的波形图存在很多毛刺，显然传感信号受到了外界环境的影响，存在明显的噪声，从而影响系统的信噪比；图4(a)、(b)分别是利用本发明技术方案得到的电信号解调后的频域和时域信号图；图4(a)、图4(b)显示解调信号中不存在扰动信号，解调信号中的毛刺不明显，所以本发明系统可以避免振动对光路的干扰，提高系统的稳定性与可靠性，系统的信噪比也明显提升；图5是本发明系统解调40kHz和0.1Hz的频率响应图(左图对应40kHz频率响应，右图对应0.1Hz频率响应)，对本发明所述系统的传感器通过PZT施加震动信号，可以实现0.1Hz～40kHz的频率响应，系统的信噪比可达到42dB。可以看到，系统具有很宽的频率响应范围，仅仅受限于光纤的长度与采集卡的采样率影响。Fig. 3(a) is based on the Michelson structure under the applied perturbation

The spectrum diagram of the demodulated signal of the sensing system; that is, based on the Michelson double-arm structure under the applied disturbance, the single pulse modulation uses a 3×3 coupler to demodulate the frequency signal of the phase signal, and the spectrum diagram shows that there are two frequency signals at 20Hz and 300Hz. peak; Figure 3(b) is based on the Michelson structure under applied perturbation

The waveform diagram of the demodulation signal of the sensing system, that is, the corresponding time domain signal in Figure 3(a); the waveform diagram of the demodulation signal in Figure 3(b) has many burrs. Obviously, the sensing signal is affected by the external environment, and there are Obvious noise, thereby affecting the signal-to-noise ratio of the system; Figure 4 (a), (b) are the frequency domain and time domain signal diagrams of the demodulated electrical signal obtained by using the technical solution of the present invention; Figure 4 (a), Fig. 4(b) shows that there is no disturbance signal in the demodulated signal, and the burr in the demodulated signal is not obvious, so the system of the present invention can avoid the interference of vibration on the optical path, improve the stability and reliability of the system, and the signal-to-noise ratio of the system. Fig. 5 is the frequency response diagram of the demodulation system of the present invention at 40kHz and 0.1Hz (the left picture corresponds to the 40kHz frequency response, and the right picture corresponds to the 0.1Hz frequency response). The sensor of the present invention is applied with a vibration signal through PZT, The frequency response of 0.1Hz to 40kHz can be achieved, and the signal-to-noise ratio of the system can reach 42dB. It can be seen that the system has a wide frequency response range, which is only limited by the length of the optical fiber and the sampling rate of the acquisition card.

Example 2

The present invention also provides a distributed vibration sensing method for a weak grating array, comprising the following steps:

The continuous light with a certain central wavelength is modulated into a corresponding double-pulse signal, and the double-pulse signal is transmitted to the weak grating array; the weak grating array reflects the double-pulse signal, so that the reflected double-pulse signal forms interference , generating an interference signal; acquiring the interference signal, and converting the interference signal into an electrical signal.

Preferably, the weak grating array distributed vibration sensing method further includes collecting and demodulating the electrical signal to form a demodulated signal; using an arctangent algorithm on the demodulated signal to obtain the difference between two adjacent gratings phase change between.

Preferably, the method for distributed vibration sensing of the weak grating array further comprises amplifying the double pulse signal before transmitting the double pulse signal to the weak grating array.

Preferably, modulating the continuous light into a corresponding double-pulse signal specifically includes: modulating the continuous light into a double-pulse signal with a time delay of T _ps , a pulse width of _Tw , and a pulse repetition frequency of F _p ,

F_p≤v/2L，v为光在弱光栅阵列中的传播速度，d为弱光栅阵列光栅距离，n_e为弱光栅阵列的折射率，L为弱光栅阵列的长度，c为光速。in,

F _p ≤ v/2L, v is the propagation speed of light in the weak grating array, d is the grating distance of the weak grating array, _ne is the refractive index of the weak grating array, L is the length of the weak grating array, and c is the speed of light.

Preferably, the interference of the reflected double-pulse signal to generate the interference signal specifically includes: causing the reflected double-pulse signal to interfere, and the interference intensity is I(t), which is the interference signal,

Among them, E _i , R _i , τ _i are the amplitude, reflectivity, and time of the ith grating, respectively; φ(t) is the phase difference between the i+1th grating and the ith grating, and the σ polarization mismatch factor.

It should be noted that, the parts not repeatedly described in Embodiment 1 and Embodiment 2 can be used for reference from each other.

The invention discloses a weak grating array distributed vibration sensing system and method. The narrow linewidth laser generates continuous light with a certain center wavelength and sends it to the acousto-optic modulator; The continuous light is modulated into a corresponding double-pulse signal, and the double-pulse signal is transmitted to the circulator; the circulator receives the double-pulse signal, and transmits the double-pulse signal to the weak grating array, the weak grating array The double pulse signal is reflected to the circulator; the circulator transmits the reflected double pulse signal to the 3×3 coupler; the 3×3 coupler interferes with the reflected double pulse signal to generate interference signal; the photodetector acquires the interference signal and converts the interference signal into an electrical signal; the conventional double-arm interferometer is not used to demodulate the phase difference between adjacent gratings, and the system will not be affected by the outside world Environmental interference improves the stability of the system, reduces the noise floor of the system, and improves the signal-to-noise ratio and frequency response range;

It should be noted that, in order to reduce the complexity of the phase demodulation algorithm, improve the demodulation accuracy of the signal and the demodulation signal-to-noise ratio, the present invention adopts the arctangent demodulation algorithm during demodulation. Compared with other demodulation algorithms, the The operation of the forward and reverse tangent replaces the integral operation, avoiding the influence of noise self-excitation caused by the integral operation; the technical scheme of the present invention does not require double-arm interference, and uses direct detection, so that the demodulation will not be disturbed by the external environment and reduce the noise floor of the system , the signal-to-noise ratio of the system is improved, and the system of the present invention has an ultra-wide frequency response range, which is only limited by the length of the optical fiber, the minimum response frequency can reach 0.1Hz, the system structure is simple, and all components are conventional The device reduces the complexity of the system, greatly reduces the system cost, and is more suitable for engineering applications.

The specific embodiments of the present invention described above do not limit the protection scope of the present invention. Any other corresponding changes and modifications made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (10)

1. A distributed vibration sensing system of a weak grating array is characterized by comprising a narrow line width laser, an acousto-optic modulator, a circulator, a weak grating array, a 3 x 3 coupler and a photoelectric detector;

the narrow linewidth laser is used for generating continuous light with a certain central wavelength and sending the continuous light to the acousto-optic modulator; the acousto-optic modulator is used for modulating the continuous light into a corresponding double-pulse signal and transmitting the double-pulse signal to the circulator; the circulator is used for receiving the double-pulse signal and transmitting the double-pulse signal to the weak grating array, and the weak grating array reflects the double-pulse signal to the circulator; the circulator is also used for transmitting the reflected double-pulse signal to the 3 x 3 coupler; the 3 × 3 coupler is used for enabling the reflected double-pulse signals to form interference and generating interference signals; and the photoelectric detector is used for acquiring the interference signal and converting the interference signal into an electric signal.

2. The distributed vibration sensing system of claim 1, further comprising a data acquisition and FPGA processing unit for generating electrical pulses to cause the acousto-optic modulator to modulate said continuous light into a corresponding double pulse signal; the data acquisition and FPGA processing unit is also used for acquiring and demodulating the electric signals to form demodulated signals.

3. The distributed vibration sensing system of claim 1, further comprising an erbium doped fiber amplifier for amplifying the double pulse signal; the acousto-optic modulator transmits the double-pulse signal to the circulator, and concretely comprises the steps that the acousto-optic modulator transmits the double-pulse signal to an erbium-doped fiber amplifier, and the double-pulse signal is amplified by the erbium-doped fiber amplifier and then transmitted to the circulator.

4. The distributed vibration sensing system according to claim 1, wherein the acousto-optic modulator modulates the continuous light into a corresponding double pulse signal, specifically comprising the acousto-optic modulator modulating the continuous light into two leading and trailing rising edges with a time delay of T_psPulse width of T_wA pulse repetition frequency of F_pThe double-pulse signal of (2) is,

wherein,

F_pv is less than or equal to v/2L, v is the propagation speed of light in the weak grating array, d is the grating distance of the weak grating array, n_eIs the refractive index of the weak grating array, L is the length of the weak grating array, and c is the speed of light.

5. The distributed vibration sensing system of claim 4, wherein the 3 × 3 coupler causes the reflected double-pulse signals to form interference to generate interference signals, and specifically includes that the 3 × 3 coupler causes the reflected double-pulse signals to form interference, when t is 0, the double-pulse signals are input into the sensing fiber, and the i-th and i + 1-th grating reflection signals form interference signals with interference intensity i (t);

wherein E is_i,R_i,τ_iRespectively the amplitude, reflectivity and time of the ith grating; phi (t) is the phase difference between the i +1 th and i-th gratings, sigma polarization mismatch factor.

6. The distributed vibration sensing system of claim 5, further comprising a means for obtaining the currents of three detectors according to the interference signal with interference intensity I (t) formed by the i and i +1 grating reflection signals

And using a standard arctangent algorithm, the voltage of the electrical signal can be obtained,

wherein D is a DC component, phi₀Is the initial phase difference of adjacent weak grating arrays, and delta phi is the phase difference caused by the external environment.

7. A distributed vibration sensing method of a weak grating array is characterized by comprising the following steps:

modulating continuous light with a certain central wavelength into a corresponding double-pulse signal, and transmitting the double-pulse signal to a weak grating array; the weak grating array reflects the double-pulse signals to enable the reflected double-pulse signals to form interference and generate interference signals; and acquiring the interference signal and converting the interference signal into an electric signal.

8. The distributed vibration sensing method of a weak grating array according to claim 7, further comprising collecting and demodulating the electrical signal to form a demodulated signal; and obtaining the phase change between two adjacent gratings by using an arc tangent algorithm on the demodulated signal.

9. The weak grating array distributed vibration sensing method of claim 7, further comprising amplifying the dipulse signal prior to transmitting the dipulse signal to the weak grating array.

10. The distributed vibration sensing method of a weak grating array according to claim 7, wherein modulating the continuous light into a corresponding double pulse signal specifically comprises modulating the continuous light into a time delay of T_psPulse width of T_wA pulse repetition frequency of F_pThe double-pulse signal of (2) is,

wherein,

F_pv is less than or equal to v/2L, v is the propagation speed of light in the weak grating array, d is the grating distance of the weak grating array, n_eIs the refractive index of the weak grating array, L is the length of the weak grating array, and c is the speed of light.

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