A distributed weak grating array sensing system and method based on direct detection

Abstract

The present invention discloses a distributed weak grating array sensing system and method based on direct detection. The steps of the method are: using an acousto-optic modulator to modulate the light wave output by the laser to form a double pulse light with a suitable pulse width and pulse spacing; then using a phase modulator to phase modulate the pre-pulse light in the double pulse light so that the three regions on the pre-pulse light have a phase difference; the double pulse light after amplitude modulation and phase modulation is amplified by an erbium-doped fiber amplifier and enters the grating array through a circulator; the double pulse light generates interference after the reflected light on the adjacent gratings is superimposed, and then the interference light enters the photoelectric detector through the circulator and collects data through an acquisition card; for the collected signal, the disturbance is located through the fluctuation of the reflected signal; three photocurrent signals with different phase differences are extracted from the reflected signal at the disturbance position, and phase separation is performed through DC removal, differentiation, integration and other processing to achieve quantitative measurement of the disturbance.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, in particular to a distributed weak grating array sensing system and method based on direct detection. Background Art

[0002] Since the emergence of fiber optic sensing technology in the 1970s, with the practical application of optical fiber and the development of optical communication technology, fiber optic sensing technology has developed rapidly. When light waves are transmitted in optical fibers, the polarization state, power, wavelength, phase and other parameters of the optical signal will change due to the influence of external environmental factors such as disturbance, temperature and strain. By detecting these parameters of light in the optical fiber, the change information of the environment around the optical fiber can be obtained, thus realizing sensing.

[0003] The principle of distributed weak grating array sensing is to treat the weak grating array embedded in the optical fiber as a group of "weak reflectors" to provide stable and intensity-controllable reflected light signals at the specified position of the optical fiber. These reflected light signals are used to replace the spontaneous Rayleigh scattering in the optical fiber. By demodulating the information of the phase, power and other changes of the interference light, the external disturbance signal can be finally obtained. Compared with the traditional optical fiber sensing system, the reflected light signal obtained by the distributed weak grating array sensing system is more stable and has a higher signal-to-noise ratio. The sensing system based on the distributed weak grating array is mainly divided into two structures: homodyne detection and heterodyne detection. Among them, heterodyne detection is mainly realized by self-heterodyne double pulses, and homodyne detection is mainly realized by 3×3 couplers. However, the former is limited by phase unwinding and cannot realize large strain measurement; the latter requires three photodetectors with completely consistent performance parameters, which is expensive, and it is difficult to ensure that the DC part and gain coefficient of the three photocurrent signals are consistent. Therefore, realizing low-cost and stable homodyne detection is a difficult problem that needs to be solved in grating array sensing. Summary of the invention

[0004] Purpose of the invention:

[0005] In traditional homodyne detection based on 3×3 couplers, it is difficult to keep the DC part and gain coefficient of the three photocurrent signals consistent, which will seriously affect the sensing and make the system very unstable. At the same time, it is necessary to have three photodetectors with completely consistent performance parameters such as frequency response characteristics and gain coefficient, which is costly.

[0006] The present invention adopts the following technical solutions to solve the above technical problems:

[0007] A distributed weak grating array sensing system based on direct detection, the system comprises a narrow linewidth laser, an acousto-optic modulator, a phase modulator, a first dual pulse signal generator, a second dual pulse signal generator, an erbium-doped fiber amplifier, a circulator, a sensing fiber fused with a weak grating array, a photodetector, a data acquisition card and a data processor; the narrow linewidth laser emits continuous light; the first dual pulse signal generator emits a first pulse electrical signal and a second pulse electrical signal to control the acousto-optic modulator to modulate the amplitude of the continuous light, and transmits a synchronous trigger signal to the second dual pulse signal generator at the same time, and the acousto-optic modulator outputs the first pulse light and the second pulse light to the phase modulator; the pulse width and pulse spacing of the first pulse light are consistent with those of the second pulse light, the second dual pulse signal generator emits a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to modulate the phase of the received pulse light to form a first pulse area, a second pulse area and a third pulse area connected end to end; the phase difference between the first pulse area, the second pulse area and the third pulse area is After the phase modulation is completed, the erbium-doped fiber amplifier amplifies the first pulse light and the second pulse light, and the amplified first pulse light and the second pulse light enter the sensing fiber integrated with the weak grating array through the circulator; the sensing fiber integrated with the weak grating array superimposes and interferes the reflected light of the first pulse light and the second pulse light on each grating; the photoelectric detector collects the optical signal in the sensing fiber integrated with the weak grating array and converts it into an electrical signal, and the data acquisition card digitizes the electrical signal of the photoelectric detector; the data processor performs disturbance positioning on the digitized electrical signal collected by the data acquisition card, extracts the photocurrent signals of the first pulse area, the second pulse area and the third pulse area from the reflection peak signal at the disturbance position, performs phase demodulation on the photocurrent signal, and realizes disturbance measurement.

[0008] Preferably, the first double pulse signal generator generates a first pulse electrical signal and a second pulse electrical signal with a pulse width of t1 and a pulse interval of t1<t2, where c is the propagation speed of light in vacuum, n is the equivalent refractive index of the optical fiber, and L is the spacing between adjacent gratings in the grating array.

[0009] Preferably, the second dual pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal and transmits them to the phase modulator for phase modulation, and the pulse widths of the third pulse electrical signal and the fourth pulse electrical signal are both The pulse spacing is The amplitude of the third pulse electrical signal is The amplitude of the fourth pulse electrical signal is Where V π is the half-wave voltage of the phase modulator, and t1 is the pulse width of the first pulse electrical signal and the second pulse electrical signal generated by the first dual-pulse signal generator.

[0010] Preferably, the second dual pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to phase-modulate the received first pulse light, thereby forming a first pulse region, a second pulse region and a third pulse region connected end to end.

[0011] Preferably, the second dual pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to phase-modulate the received second pulse light to form a first pulse region, a second pulse region and a third pulse region connected end to end.

[0012] Preferably, the second dual pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to phase-modulate the received first pulse light and second pulse light to form a first pulse region, a second pulse region and a third pulse region connected end to end.

[0013] Preferably, the acousto-optic modulator and the erbium-doped fiber amplifier are replaced by a semiconductor optical amplifier.

[0014] A sensing method of a distributed weak grating array sensing system based on direct detection comprises the following steps:

[0015] Step 1: The first dual-pulse signal generator sends out the first pulse electrical signal and the second pulse electrical signal to control the acousto-optic modulator to amplitude-modulate the continuous light generated by the narrow linewidth laser into the first pulse light and the second pulse light, wherein the pulse width and pulse spacing of the first pulse light are consistent with those of the second pulse light;

[0016] Step 2: The second dual-pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to perform phase modulation processing on the pulse light, thereby forming a first pulse area, a second pulse area and a third pulse area connected end to end;

[0017] Step 3: Amplify the first pulse light and the second pulse light after phase modulation, and the amplified first pulse light and the second pulse light enter the sensing optical fiber integrated with the weak grating array through the circulator, and the photodetector detects the optical signal of the superposition interference of the reflected light of the first pulse light and the second pulse light on the adjacent gratings and converts the optical signal into an electrical signal, and the data acquisition card digitizes the collected electrical signal and transmits it to the data processor;

[0018] Step 4: Compare the collected reflected light digitized electrical signals and realize disturbance location by observing the fluctuation of the reflected peak signal;

[0019] Step 5: Extract the photocurrent signals of the first pulse region, the second pulse region and the third pulse region from the reflection peak signal at the disturbance position, perform phase demodulation on the photocurrent signal, and realize disturbance measurement.

[0020] Preferably, the first double pulse signal generator generates a first pulse electrical signal and a second pulse electrical signal with a pulse width of t1 and a pulse interval of t1<t2, where c is the propagation speed of light in vacuum, n is the equivalent refractive index of optical fiber, and L is the spacing between adjacent gratings in the grating array; the second dual-pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal and transmits them to the phase modulator for phase modulation, and the pulse widths of the third pulse electrical signal and the fourth pulse electrical signal are both The pulse spacing is The amplitude of the third pulse electrical signal is The amplitude of the fourth pulse electrical signal is Where V π is the half-wave voltage of the phase modulator.

[0021] Preferably, the second dual-pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to modulate the phase of the received first pulse light, so as to form a first pulse area, a second pulse area and a third pulse area connected end to end; or the second dual-pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to modulate the phase of the received second pulse light, so as to form a first pulse area, a second pulse area and a third pulse area connected end to end; or the second dual-pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to modulate the phase of the received first pulse light and the second pulse light, so as to form a first pulse area, a second pulse area and a third pulse area connected end to end.

[0022] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0023] (1) The three photocurrent signals are generated by the superposition of the reflected light of the same two gratings, and their DC parts are consistent; the three photocurrent signals are obtained by the same photodetector, and their gain coefficients are consistent;

[0024] (2) Traditional homodyne detection based on 3×3 couplers requires three photodetectors with completely consistent performance parameters such as frequency response characteristics and gain coefficients, which is expensive. However, the above technical solution can realize distributed weak grating array sensing based on homodyne detection with a phase modulator and a dual-pulse signal generator, which is relatively low-cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a traditional distributed fiber optic sensing system based on homodyne detection;

[0026] Figure 2 A distributed weak grating array sensing system based on homodyne detection adopts the solution of the present invention;

[0027] Figure 3 It is a pulse reflection signal of a vibrating position grating in a device using the solution of the present invention;

[0028] Figure 4 In the device using the solution of the present invention, three mutually related signals are extracted from the pulse reflection signal of the vibrating position grating. Phase difference of the photocurrent signal.

[0029] Figure 5 It is traditionally based on Phase difference demodulation algorithm.

[0030] Figure 6 Is adopted Sinusoidal signal demodulated by the phase-modulated double-pulse weak grating array sensing system. DETAILED DESCRIPTION

[0031] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings:

[0032] A distributed weak grating array sensing system based on direct detection proposed in the present invention includes the following devices:

[0033] Laser: Select a narrow linewidth laser and generate continuous light which is output to the acousto-optic modulator through a coupler.

[0034] Acousto-optic modulator: By modulating the continuous light emitted by the laser, double pulse light with a specific period, specific width and specific pulse spacing is generated.

[0035] Phase modulator: By modulating the front pulse light in the double pulse light emitted by the acousto-optic modulator, three parts with phase differences are generated. Pre-pulse light.

[0036] Double pulse signal generator 1: Generates a double pulse electrical signal with a specific period, specific width, specific pulse interval and specific peak-to-peak value.

[0037] Double pulse signal generator 2: Generates a double pulse electrical signal with a specific period, specific width, specific pulse interval and specific peak-to-peak value.

[0038] Erbium-doped fiber amplifier: amplifies the power of amplitude-modulated and phase-modulated double-pulse light.

[0039] Circulator: It is used to guide the pulse light after power amplification into the sensing fiber fused with weak grating array, and transmit the interference light on each grating to the photodetector.

[0040] Sensing fiber fused with weak grating array: The reflected light of two pulses on each grating is superimposed to produce interference, sensing disturbance events in the system.

[0041] Photodetector: used to convert optical signals into electrical signals and output them to the acquisition card.

[0042] Acquisition card: used to digitize the acquired analog signals and output them to the processor.

[0043] Computer: Analyze and process the collected data to locate and measure disturbances along the sensing optical fiber fused with the weak grating array.

[0044] A narrow linewidth laser is used to generate continuous light, and the continuous light is amplitude modulated by an acousto-optic modulator into a first pulse light and a second pulse light, and the pulse width of the first pulse light is equal to the pulse width of the second pulse light; the first pulse light is phase modulated by a phase modulator into a first pulse area, a second pulse area and a third pulse area connected end to end, and the phase differences of the three pulse lights are different from each other. After the first pulse light and the second pulse light are compensated, they enter the sensing fiber of the fused grating array through the circulator. The photoelectric detector detects the optical signal of the superposition and interference of the reflected light on the adjacent gratings. The collected electrical signal is digitized by the data acquisition card and output to the computer. The time domain signals collected multiple times are displayed together, and the disturbance location is achieved by observing the fluctuation size of the reflection peak signal. Three phase differences are extracted from the reflection peak signal at the disturbance position. The three photocurrents are used for phase demodulation to achieve disturbance measurement.

[0045] The period, pulse width, pulse spacing and specific peak-to-peak value of the double pulse electrical signal emitted by the double pulse signal generator 1 can be adjusted so that the power of the two pulse signals emitted is equal and the pulse spacing is equal to

[0046] The period, pulse width, pulse spacing and specific peak-to-peak value of the double pulse electrical signal emitted by the double pulse signal generator 2 can be adjusted so that the amplitude of the emitted front pulse is The post pulse amplitude is Where V π is the half-wave voltage of the phase modulator, and the modulation effect of the half-wave voltage is equivalent to π.

[0047] The double-pulse signal generator 1 provides a synchronization signal as a trigger signal for the double-pulse signal generator 2 .

[0048] Assume that the double pulse is modulated by an acousto-optic modulator and a phase modulator, the three parts of the light field distribution of the front pulse are E1, E2, E3, the light field distribution of the rear pulse is E4, the angular frequency of the pulse light is ω, and the initial phase is The electric field amplitude is E r1 ; The light field distribution of the subsequent pulse is E5, the angular frequency of the pulse light is ω, and the initial phase is The electric field amplitude is Er2 ; It is the phase change caused by external disturbance.

[0049] The electric fields of the reflected light of the three different phase parts on the front pulse are expressed as:

[0050]

[0051]

[0052] The electric field of the reflected light of the post-pulse is expressed as:

[0053]

[0054] The reflected light of the front pulse and the reflected light of the rear pulse are superimposed and interfere with each other. The optical signal is divided into three parts:

[0055]

[0056] in,

[0057] Add the three photocurrent signals I1(t), I2(t), and I3(t), and divide the sum by 3 to get the DC term:

[0058]

[0059] I1(t), I2(t), I3(t) minus D, we get:

[0060]

[0061] Differentiate a, b, c:

[0062]

[0063] Then multiply a, b, c by the difference after the other two differentials to get:

[0064]

[0065] Adding a(ef), b(fd), and c(de), we get:

[0066]

[0067] In order to eliminate E r1 2 E r2 2 The impact brought by this is to find the sum of squares of I1(t), I2(t), and I3(t), and we get:

[0068]

[0069] N divided by M eliminates E r1 2 E r2 2 ,have to:

[0070]

[0071] Finally, after integration, we get:

[0072]

[0073] In this demodulation process, the gain coefficients and DC parts of E1(t), E2(t), and E3(t) have the greatest impact. If they are inconsistent, the correctness of the demodulation result will be seriously affected. The technical solution of the present invention uses the reflected light of the grating instead of the scattered light for sensing, without a 3×3 coupler and other optical splitting devices. The same photodetector is used to receive three photocurrents, and the consistency of the gain coefficients and DC parts of E1(t), E2(t), and E3(t) is fully guaranteed.

[0074] refer to Figure 1 The traditional distributed fiber optic sensing system based on homodyne detection shown in the figure is a continuous light emitted by an extremely narrow linewidth laser that enters the acousto-optic modulator to modulate a narrow pulse light. After being amplified by the erbium-doped fiber amplifier, it enters the sensing fiber through a circulator, and the returned scattered light enters the 3×3 coupler. Detector 1, detector 2, and detector 3 are three photoelectric detectors with the same performance parameters. What they detect are three phase differences that differ from each other. The photocurrent signal.

[0075] However, in practice, it is difficult to ensure the consistency of the coupling of the three ports of the 3×3 coupler, and it is even more difficult to ensure the consistency of the photoelectric conversion efficiency of the three photodetectors. Therefore, the stability of the traditional distributed optical fiber sensing system based on homodyne detection has always been insufficient. At the same time, the three photodetectors with consistent performance parameters also bring about a huge cost increase. The above situation is solved by adopting this solution, which is explained in detail below based on the experimental introduction:

[0076] Use Figure 2 The experimental device shown in the figure is that a narrow line width laser emits a continuous laser into an acousto-optic modulator with a modulation frequency of 150MHz, and modulates to obtain two pulses of light with a pulse width of 300ns and a pulse interval of 500ns; a dual pulse signal generator 1 gives a dual pulse electrical signal to the acousto-optic modulator to achieve amplitude modulation; the amplitude modulated dual pulses enter the phase modulator, and the modulation obtains the phase difference between the three parts. The dual pulse signal generator 1 sends a synchronization signal to the dual pulse signal generator 2 as a trigger signal. The dual pulse signal generator 2 sends two pulse electrical signals with a pulse width of 100ns and pulse peak-to-peak values ​​of 3.3V and 6.6V respectively to the phase modulator to achieve phase modulation. The phase-modulated dual pulses enter the erbium-doped fiber amplifier for amplification and are sent to the grating array by the circulator for sensing. The returned interference light is received by the detector through the circulator, collected by the data acquisition card, and sent to the computer for disturbance positioning and measurement.

[0077] The vibration source at 3000 meters near the grating applies a sine signal with a frequency of 250Hz and a voltage of 10V. By observing the amplitude fluctuation of the reflection peak, the position of the disturbance can be located. Figure 3 As shown in the figure, it can be clearly seen from the reflection peaks at the disturbance position that the three regions have obvious boundaries. This is because they are This is caused by the phase difference, which is consistent with the expected effect of phase modulation using a phase modulator.

[0078] like Figure 4 As shown, the phase differences between the three regions can be extracted The photocurrent signals of the three photocurrent signals can be clearly seen from the envelope that there is a certain phase difference between them. Figure 5 The 3×3 coupler demodulation algorithm shown in the figure can finally obtain a sinusoidal signal with a period of 8.8, as shown in Figure 6 , a total of 0.035 seconds of signal was collected, with a cycle number of 8.8, that is, the frequency of the externally applied signal was 251 Hz, which is consistent with the actual applied frequency information of the experiment.

[0079] Compared with the traditional scheme, the system and method of this scheme uses one photodetector and one phase modulator to replace the three photodetectors that originally required to have completely consistent performance parameters, thereby reducing costs; at the same time, the reflected light of the grating is used instead of the scattered light for sensing, and a dual-pulse structure is used to receive three photocurrent signals with the same photodetector, so the consistency of the gain coefficient and the DC part is fully guaranteed, and the stability is improved.

[0080] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A distributed weak grating array sensing system based on direct detection, characterized in that: The system comprises a narrow linewidth laser, an acousto-optic modulator, a phase modulator, a first dual-pulse signal generator, a second dual-pulse signal generator, an erbium-doped fiber amplifier, a circulator, a sensing fiber fused with a weak grating array, a photodetector, a data acquisition card and a data processor; the narrow linewidth laser emits continuous light; the first dual-pulse signal generator emits a first pulse electrical signal and a second pulse electrical signal to control the acousto-optic modulator to modulate the amplitude of the continuous light, and transmits a synchronous trigger signal to the second dual-pulse signal generator at the same time, and the acousto-optic modulator outputs the first pulse light and the second pulse light to the phase modulator; the pulse width and pulse spacing of the first pulse light are consistent with those of the second pulse light, and the second dual-pulse signal generator emits a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to modulate the phase of the received pulse light to form a first pulse area, a second pulse area and a third pulse area connected end to end; The phase difference between the first pulse region, the second pulse region and the third pulse region is After the phase modulation is completed, the erbium-doped fiber amplifier amplifies the first pulse light and the second pulse light, and the amplified first pulse light and the second pulse light enter the sensing fiber integrated with the weak grating array through the circulator; the sensing fiber integrated with the weak grating array superimposes and interferes the reflected light of the first pulse light and the second pulse light on each grating; the photoelectric detector collects the optical signal in the sensing fiber integrated with the weak grating array and converts it into an electrical signal, and the data acquisition card digitizes the electrical signal of the photoelectric detector; the data processor performs disturbance positioning on the digitized electrical signal collected by the data acquisition card, extracts the photocurrent signals of the first pulse area, the second pulse area and the third pulse area from the reflection peak signal at the disturbance position, performs phase demodulation on the photocurrent signal, and realizes disturbance measurement.

2. A distributed weak grating array sensing system based on direct detection according to claim 1, characterized in that: The first double pulse signal generator generates a first pulse electrical signal and a second pulse electrical signal with a pulse width of t1 and a pulse interval of t1<t2, where c is the propagation speed of light in vacuum, n is the equivalent refractive index of the optical fiber, and L is the spacing between adjacent gratings in the grating array.

3. A distributed weak grating array sensing system based on direct detection according to claim 1, characterized in that: The second dual pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal and transmits them to the phase modulator for phase modulation. The pulse widths of the third pulse electrical signal and the fourth pulse electrical signal are both The pulse spacing is The amplitude of the third pulse electrical signal is The amplitude of the fourth pulse electrical signal is Where V π is the half-wave voltage of the phase modulator, and t1 is the pulse width of the first pulse electrical signal and the second pulse electrical signal generated by the first dual-pulse signal generator.

4. A distributed weak grating array sensing system based on direct detection according to claim 1, characterized in that: The second dual pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to phase-modulate the received first pulse light, thereby forming a first pulse region, a second pulse region and a third pulse region connected end to end.

5. A distributed weak grating array sensing system based on direct detection according to claim 1, characterized in that: The second dual pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to phase-modulate the received second pulse light, thereby forming a first pulse region, a second pulse region and a third pulse region connected end to end.

6. A distributed weak grating array sensing system based on direct detection according to claim 1, characterized in that: The second dual pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to phase-modulate the received first pulse light and second pulse light to form a first pulse region, a second pulse region and a third pulse region connected end to end.

7. A distributed weak grating array sensing system based on direct detection according to claim 1, characterized in that: The acousto-optic modulator and erbium-doped fiber amplifier are replaced with semiconductor optical amplifiers.

8. A sensing method based on the distributed weak grating array sensing system based on direct detection according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: The first dual-pulse signal generator sends out the first pulse electrical signal and the second pulse electrical signal to control the acousto-optic modulator to amplitude-modulate the continuous light generated by the narrow linewidth laser into the first pulse light and the second pulse light, wherein the pulse width and pulse spacing of the first pulse light are consistent with those of the second pulse light; Step 2: The second dual-pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to perform phase modulation processing on the pulse light, thereby forming a first pulse area, a second pulse area and a third pulse area connected end to end; Step 3: Amplify the first pulse light and the second pulse light after phase modulation, and the amplified first pulse light and the second pulse light enter the sensing optical fiber integrated with the weak grating array through the circulator, and the photodetector detects the optical signal of the superposition interference of the reflected light of the first pulse light and the second pulse light on the adjacent gratings and converts the optical signal into an electrical signal, and the data acquisition card digitizes the collected electrical signal and transmits it to the data processor; Step 4: Compare the collected reflected light digitized electrical signals and realize disturbance location by observing the fluctuation of the reflected peak signal; Step 5: Extract the photocurrent signals of the first pulse region, the second pulse region and the third pulse region from the reflection peak signal at the disturbance position, perform phase demodulation on the photocurrent signal, and realize disturbance measurement.

9. The sensing method according to claim 8, characterized in that: The first double pulse signal generator generates a first pulse electrical signal and a second pulse electrical signal with a pulse width of t1 and a pulse interval of t1<t2, where c is the propagation speed of light in vacuum, n is the equivalent refractive index of optical fiber, and L is the spacing between adjacent gratings in the grating array; the second dual-pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal and transmits them to the phase modulator for phase modulation, and the pulse widths of the third pulse electrical signal and the fourth pulse electrical signal are both The pulse spacing is The amplitude of the third pulse electrical signal is The amplitude of the fourth pulse electrical signal is Where V π is the half-wave voltage of the phase modulator.

10. The sensing method according to claim 8, characterized in that: The second dual pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to phase-modulate the received first pulse light, thereby forming a first pulse region, a second pulse region and a third pulse region connected end to end; Or the second dual pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to phase-modulate the received second pulse light to form a first pulse region, a second pulse region and a third pulse region connected end to end; Alternatively, the second dual pulse signal generator sends out a third pulse electrical signal and a fourth pulse electrical signal to control the phase modulator to phase-modulate the received first pulse light and second pulse light to form a first pulse region, a second pulse region and a third pulse region connected end to end.

Images