Dual-wavelength distributed weak grating array sensing system and method based on heterodyne detection

Abstract

This invention discloses a dual-wavelength distributed weak grating array sensing system based on heterodyne detection, comprising a first narrow-linewidth laser, a second narrow-linewidth laser, a 2×2 coupler, a first acousto-optic modulator, a second acousto-optic modulator, a pulse signal generator, a 2×1 coupler, an erbium-doped fiber amplifier, a circulator, a sensing fiber fused with the dual-wavelength weak grating array, a wavelength division multiplexer, a first photodetector, a second photodetector, a data acquisition card, and a data processor. This invention can nearly double the sensing distance while maintaining the same spatial resolution, or double the spatial resolution while maintaining the same sensing distance.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, specifically relating to a dual-wavelength distributed weak grating array sensing system and method based on heterodyne detection. Background Technology

[0002] With the practical application of optical fibers and the development of optical fiber communication technology, optical fiber sensing technology began to emerge. Optical fiber sensing technology uses light waves as a carrier and optical fiber itself as a transmission medium. When the environment along the optical fiber changes, it causes changes in parameters such as the phase, frequency, polarization state, and intensity of the optical signal. By detecting these parameters, information such as temperature, strain, vibration, and defects at any point along the optical fiber can be extracted, thereby achieving large-scale sensing.

[0003] The principle of distributed weak grating array sensing is as follows: each weak grating embedded in the optical fiber is equivalent to a "weak reflector". The probe pulse will be reflected at these "weak reflectors". By uniformly writing the weak grating into the optical fiber, a stable and intensity-controllable reflected light signal can be provided at a specified position in the optical fiber. These reflected light signals are superimposed with the reference light through interference. By demodulating the changes in the phase and power of the interference light, the disturbance signal applied to the optical fiber can be recovered.

[0004] Compared to spontaneous Rayleigh scattering signals in traditional fiber optic sensing systems, the reflected light signals obtained by distributed weak grating array sensing systems are more stable and have a higher signal-to-noise ratio. However, the energy loss of the reflected signal for the probe pulse is also higher than that of the scattered signal. When the probe pulse propagates in the weak grating array, some energy is lost with each reflected signal until the generated reflected signal is too weak to detect disturbances. This limits the sensing distance of the distributed weak grating array sensing system. Moreover, the spatial resolution of the distributed weak grating array sensing system is related to the grating spacing. To achieve a longer sensing distance, the grating density must be reduced, thereby reducing the spatial resolution of the sensing system. Therefore, improving the sensing distance while maintaining spatial resolution, or improving spatial resolution while keeping the sensing distance constant, is an urgent problem to be solved.

[0005] The invention disclosed in CN110806259A is a device for locating and detecting high-frequency disturbances in fiber optic sensing. While traditional optical time-domain reflectometry (OTDR) systems offer significant improvements in sensing distance, positioning accuracy, and frequency measurement range, they still cannot identify higher-frequency disturbance signals. This invention addresses the difficulty of frequency detection of high-frequency disturbance events using existing technologies by proposing a method combining coherent optical time-domain reflectometry (CODR) and interferometry to simultaneously locate the disturbance point and detect the high-frequency signal. A first laser and a second laser emit continuous light with wavelengths λ1 and λ2, respectively, which are simultaneously injected into the sensing fiber using wavelength division multiplexing (WDM). The interference of the two wavelengths carries both disturbance and frequency information. The interference signal at wavelength λ1 is orthogonally demodulated to obtain the amplitude information, and then variance processing is performed on the interference signal at wavelength λ1 to obtain the location information of the external disturbance. The interference signal at wavelength λ2 is phase-demodulated to obtain the frequency information of the external disturbance. The sensing fiber used in this invention contains a Bragg fiber grating with a single center wavelength. The frequency of the disturbance signal is detected by using the reflected light generated by the Bragg fiber grating through a Mach-Zehnder interferometer structure. The location and amplitude of the disturbance signal are measured by using the backscattered Rayleigh light in the sensing fiber through optical time-domain reflectometry. The purpose is to achieve the location and measurement of high-frequency signals. However, it cannot increase the sensing distance without changing the spatial resolution while ensuring a high signal-to-noise ratio of the interference signal, or increase the spatial resolution while keeping the sensing distance constant. Summary of the Invention

[0006] Technical problem to be solved: The spatial resolution of traditional distributed weak grating array-based sensing systems is related to the grating spacing. To improve the spatial resolution, the grating density needs to be increased, which will shorten the sensing distance. Similarly, to extend the sensing distance, the grating density needs to be reduced, which will reduce the spatial resolution.

[0007] Technical solution:

[0008] A dual-wavelength distributed weak grating array sensing system based on heterodyne detection is disclosed. The dual-wavelength distributed weak grating array sensing system includes a first narrow linewidth laser, a second narrow linewidth laser, a 2×2 coupler, a first acousto-optic modulator, a second acousto-optic modulator, a pulse signal generator, a 2×1 coupler, an erbium-doped fiber amplifier, a circulator, a sensing fiber fused with the dual-wavelength weak grating array, a wavelength division multiplexer, a first photodetector, a second photodetector, a data acquisition card, and a data processor.

[0009] The first narrow-linewidth laser emits continuous light with a center wavelength of λ1, and the second narrow-linewidth laser emits continuous light with a center wavelength of λ2. The 2×2 coupler sends two continuous light beams with different center wavelengths into two branches, which exist simultaneously in both branches. The pulse signal generator sends a first pulse electrical signal and a second pulse electrical signal to control the first and second acousto-optic modulators to modulate the continuous light, respectively, and transmits a synchronization trigger signal to the data acquisition card. The first acousto-optic modulator outputs a first pulse light and a second pulse light superimposed together, and the second acousto-optic modulator outputs a third pulse light and a fourth pulse light superimposed together. The pulse widths of the first, second, third, and fourth pulse lights are the same. The frequency shift frequencies of the first and second acousto-optic modulators are different. The 2×1 coupler sends the first, second, third, and fourth pulse lights into the same branch, where they are amplified by the erbium-doped fiber amplifier. The amplified first pulse light... Light, a second pulse, a third pulse, and a fourth pulse enter a sensing fiber containing a fused dual-wavelength weak grating array through a circulator. The sensing fiber contains a first weak grating array with a center wavelength of λ1 and a second weak grating array with a center wavelength of λ2. The first and third pulses are reflected and superimposed on adjacent gratings of the first weak grating array. The second and fourth pulses are reflected and superimposed on adjacent gratings of the second weak grating array. A wavelength division multiplexer splits the superimposed light with center wavelengths of λ1 and λ2 into two paths. A first photodetector acquires the optical signal with a center wavelength of λ1 and converts it into an electrical signal, and a second photodetector acquires the optical signal with a center wavelength of λ2 and converts it into an electrical signal. A data acquisition card acquires and digitizes the electrical signals from the first and second photodetectors. A data processor performs disturbance localization and quantitative measurement on the two digitized electrical signals acquired by the data acquisition card.

[0010] The data processor demodulates the beat signal between adjacent gratings in each electrical signal. The demodulated vibration indicates that the vibration exists between the grating pairs. The processor observes the grating regions that generate disturbances in each data stream. When the positions of the grating pairs that generate disturbances in the first weak grating array and the second weak grating array overlap, the two gratings that overlap between the grating pairs in the first and second weak grating arrays are taken as the disturbance regions, and the disturbance positions are reduced to adjacent gratings with different center wavelengths.

[0011] Furthermore, the 2×2 coupler is replaced with an optical switch or modulator. The timing of the output light waves of the first narrow linewidth laser and the second narrow linewidth laser is controlled by the optical switch or modulator, so that the light waves with center wavelengths λ1 and λ2 are respectively incident on the system.

[0012] Furthermore, the grating spacing in the first weak grating array is equal, the grating spacing in the second weak grating array is equal, and the grating spacing in both the first and second weak grating arrays is L; the grating spacing between the grating in the first weak grating array and the grating spacing between the adjacent second weak grating array are L1 and L2, respectively.

[0013] Furthermore, the gratings in the first weak grating array and the gratings in the adjacent second weak grating array are spaced apart.

[0014] Furthermore, the pulse width of both the first and second pulse electrical signals generated by the pulse signal generator is t1, and the pulse interval is... t1 < t2; where c is the speed of light in a vacuum, n is the equivalent refractive index of the optical fiber, and L is the spacing between adjacent gratings with the same center wavelength in the grating array.

[0015] Furthermore, assuming that the electric field intensity of the first, second, third, and fourth pulses is all E0, and their angular frequencies are ω1, ω2, ω3, and ω4 respectively, where ω3-ω1 equals ω4-ω2, determined by the frequency shift difference between the first and second acousto-optic modulators, and the initial phase of the first and third pulses is... The initial phases of the second and fourth pulses are The spacing between the gratings in the first weak grating array and the second weak grating array is L, the reflectivity is r, and ΔL is the change in fiber length caused by external disturbance.

[0016] The reflected photoelectric fields of the four pulsed lights are respectively represented as follows:

[0017]

[0018]

[0019]

[0020]

[0021] The reflected light from the first pulse and the reflected light from the third pulse interfere with each other, and the resulting optical signal is represented as follows:

[0022]

[0023] in, It is a phase change caused by external disturbances;

[0024] The reflected light from the second pulse and the reflected light from the fourth pulse interfere with each other, and the resulting optical signal is represented as follows:

[0025]

[0026] in, It is a phase change caused by external disturbances.

[0027] This invention discloses a dual-wavelength distributed weak grating array sensing method based on heterodyne detection, wherein the dual-wavelength distributed weak grating array sensing method is executed based on the dual-wavelength distributed weak grating array sensing system based on heterodyne detection as described above.

[0028] The dual-wavelength distributed weak grating array sensing method includes the following steps:

[0029] Step 1: The 2×2 coupler injects the continuous light wave generated by the first narrow linewidth laser and the continuous light wave generated by the second narrow linewidth laser into the same two branches;

[0030] Step 2: The pulse signal generator sends a first pulse electrical signal to control the first acousto-optic modulator to modulate the continuous light generated by the first narrow linewidth laser and the second narrow linewidth laser into a first pulse light and a second pulse light. The pulse signal generator sends a second pulse electrical signal to control the second acousto-optic modulator to modulate the continuous light generated by the first narrow linewidth laser and the second narrow linewidth laser into a third pulse light and a fourth pulse light. The first pulse light and the second pulse light overlap, and the third pulse light and the fourth pulse light overlap. The pulse widths of the first pulse light, the second pulse light, the third pulse light, and the fourth pulse light are the same, and the pulse spacings of the first pulse light, the second pulse light, the third pulse light, and the fourth pulse light are the same.

[0031] Step 3: The 2×1 coupler sends the first, second, third, and fourth pulses into a branch and is amplified by the erbium-doped fiber amplifier. The amplified first, second, third, and fourth pulses then enter the sensing fiber of the fused dual-wavelength weak grating array through the circulator.

[0032] Step 4: The first and third pulses are reflected and superimposed on adjacent gratings of the first weak grating array only, and the second and fourth pulses are reflected and superimposed on adjacent gratings of the second weak grating array only.

[0033] Step 5: The wavelength division multiplexer splits the superimposed light of different center wavelengths into two paths, which are collected by the first photodetector and the second photodetector respectively and converted into electrical signals. The data acquisition card digitizes the collected electrical signals and transmits them to the data processor.

[0034] Step Six: The data processor processes the two digital electrical signals acquired by the data acquisition card. It demodulates the beat signal between adjacent gratings in each electrical signal. If vibration is demodulated, it means that the vibration exists between the grating pairs. The grating regions that generate disturbances in each data channel are observed. When the positions of the grating pairs that generate disturbances in the first weak grating array and the second weak grating array overlap, the two gratings that overlap between the grating pairs in the first weak grating array and the second weak grating array are taken as the disturbance regions, thereby reducing the disturbance position to adjacent gratings with different center wavelengths.

[0035] Beneficial effects:

[0036] The present invention relates to a dual-wavelength distributed weak grating array sensing system and method based on heterodyne detection. The sensing system integrates a dual-wavelength weak grating array, in which the sensing fiber contains two sets of weak grating arrays with different center wavelengths. Each weak grating array reflects only the pulse light of its corresponding center wavelength and transmits the pulse light of the other center wavelength. The present invention can extend the sensing distance by nearly two times while keeping the spatial resolution unchanged, or increase the spatial resolution by two times while keeping the sensing distance unchanged. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the disturbance positioning principle using the solution of the present invention;

[0038] Figure 2 This is a schematic diagram of a traditional distributed weak grating array sensing system based on heterodyne detection;

[0039] Figure 3 This is a schematic diagram of the structure of the dual-wavelength distributed weak grating array sensing system based on heterodyne detection according to an embodiment of the present invention;

[0040] Figure 4 This is a schematic diagram of two time-domain signals acquired by the data acquisition card in an embodiment of the present invention;

[0041] Figure 5 This is a schematic diagram of the vibration results recovered by demodulation of adjacent beats corresponding to the disturbance positions in two time-domain signals acquired by the data acquisition card in this embodiment of the invention.

[0042] Figure 6 This is a schematic diagram of the demodulation results according to an embodiment of the present invention. Detailed Implementation

[0043] The following embodiments are provided to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0044] See Figure 3This embodiment proposes a dual-wavelength distributed weak grating array sensing system based on heterodyne detection. The sensing fiber used in this embodiment embeds two sets of weak grating arrays with different center wavelengths. The reflected light generated by the weak grating array is used to replace the back Rayleigh scattering light in the fiber for sensing, resulting in a higher signal-to-noise ratio of the generated interference signal. Through optical time-domain reflectometry, the reflected light generated by the two sets of weak grating arrays can be used simultaneously to locate and quantitatively measure the disturbance signal. The purpose of this embodiment is to increase the sensing distance without changing the spatial resolution while ensuring a high signal-to-noise ratio of the interference signal, or to increase the spatial resolution while keeping the sensing distance constant.

[0045] Specifically, the dual-wavelength distributed weak grating array sensing system of this embodiment includes the following devices:

[0046] Narrow linewidth laser 1: generates continuous light with a center wavelength of 1535nm.

[0047] Narrow linewidth laser 2: generates continuous light with a center wavelength of 1550nm.

[0048] 2×2 Coupler: Outputs continuous light generated by narrow linewidth laser 1 and narrow linewidth laser 2 to acousto-optic modulator 1 and acousto-optic modulator 2.

[0049] Acousto-optic modulator 1: By modulating the continuous light emitted by narrow linewidth laser 1 and narrow linewidth laser 2, pulse light with a specific period and a specific width is generated.

[0050] Acousto-optic modulator 2: By modulating the continuous light emitted by narrow linewidth laser 1 and narrow linewidth laser 2, pulse light with a specific period and a specific width is generated.

[0051] Pulse signal generator: generates two pulse electrical signals with a specific period, a specific width, and a specific pulse spacing, which drive acousto-optic modulator 1 and acousto-optic modulator 2 respectively.

[0052] 2×1 Coupler: Sends the pulsed light generated by the acousto-optic modulator into one branch.

[0053] Erbium-doped fiber amplifier: amplifies the pulsed optical power at the output of a 2×1 coupler.

[0054] Circulator: Used to guide the amplified pulsed light into the sensing fiber of the fused dual-wavelength weak grating array, and to pass the returned superimposed light into the wavelength division multiplexer.

[0055] Sensing fiber integrating dual-wavelength weak grating arrays: Two sets of weak grating arrays 1 and 2, corresponding to the center wavelengths of narrow linewidth laser 1 and narrow linewidth laser 2 respectively, are embedded in the sensing fiber. Each grating of weak grating array 1 can only reflect pulse light corresponding to the center wavelength of narrow linewidth laser 1, and each grating of weak grating array 2 can only reflect pulse light corresponding to the center wavelength of narrow linewidth laser 2.

[0056] Wavelength division multiplexer: used to separate the interference light corresponding to narrow linewidth laser 1 and narrow linewidth laser 2.

[0057] Photodetector 1: Used to convert one optical signal output from the wavelength division multiplexer into an electrical signal and output it to the acquisition card.

[0058] Photodetector 2: Used to convert one optical signal output from the wavelength division multiplexer into an electrical signal and output it to the acquisition card.

[0059] Acquisition card: Used to digitize the acquired analog signals and output them to the processor.

[0060] Computer: Analyzes and processes the collected data to achieve disturbance measurement and further positioning along the sensing fiber of the fused dual-wavelength weak grating array.

[0061] A narrow-linewidth laser 1 generates continuous light at 1535 nm. This continuous light is then modulated into a first pulse and a second pulse by acousto-optic modulators 1 and 2, respectively, after passing through a 2×2 coupler. A narrow-linewidth laser 2 generates continuous light at 1550 nm. This continuous light is also modulated into a third and a fourth pulse by acousto-optic modulators 1 and 2, respectively, after passing through a 2×2 coupler. The first and second pulses are superimposed, as are the third and fourth pulses. The pulse widths of the first, second, third, and fourth pulses are equal. These four pulses are then amplified by an erbium-doped fiber amplifier after passing through a 2×1 coupler. The sensing fiber enters the fused dual-wavelength grating array through the circulator. The first and third pulses are reflected and superimposed at weak grating array 1, and the second and fourth pulses are reflected and superimposed at weak grating array 2. The four reflected beams are split into two interference beams by a wavelength division multiplexer after passing through the circulator. Photodetector 1 and photodetector 2 detect one interference beam respectively. The data acquisition card digitizes the acquired electrical signals and outputs them to the computer. The two digitized electrical signals are demodulated to achieve disturbance measurement. The grating region that generates disturbance in each data path is observed. When the positions of gratings with different center wavelengths that generate disturbance overlap, the disturbance position can be reduced to the area between the overlapping gratings.

[0062] The pulse signal generator outputs two pulse electrical signals with equal periods and pulse widths, and the pulse interval is equal to... c is the speed of light in a vacuum, n is the equivalent refractive index of the optical fiber, and L is the spacing between adjacent gratings in the same wavelength grating array.

[0063] The pulse signal generator provides a synchronization signal as the trigger signal for the data acquisition card.

[0064] Assuming the center wavelength of narrow-linewidth laser 1 is λ1 and the center wavelength of narrow-linewidth laser 2 is λ2, the electric field intensity of the first, second, third, and fourth pulses is E0, and their angular frequencies are ω1, ω2, ω3, and ω4, respectively, where ω3-ω1 equals ω4-ω2, determined by the frequency shift difference between acousto-optic modulator 1 and acousto-optic modulator 2. The initial phase of the first and third pulses is... The initial phases of the second and fourth pulses are The spacing between the gratings in weak grating array 1 and weak grating array 2 is L, the reflectivity is r, and ΔL is the change in fiber length caused by external disturbance.

[0065] The reflected photoelectric fields of the four pulsed lights can be represented as follows:

[0066]

[0067]

[0068]

[0069]

[0070] The reflected light from the first pulse and the reflected light from the third pulse interfere with each other, and the optical signal can be represented as:

[0071]

[0072] in, It is a phase change caused by external disturbances.

[0073] The reflected light from the second pulse and the reflected light from the fourth pulse interfere with each other, and the optical signal can be represented as:

[0074]

[0075] in, It is a phase change caused by external disturbances.

[0076] For demodulation of the beat signal of the two interfering beams, refer to Figure 1When a perturbation is applied between two gratings with different center wavelengths, the perturbation also exists between gratings with the same center wavelength. By demodulating the beat signals generated by the two gratings with the same center wavelength containing the perturbation, the vibration can be recovered. The positions of the gratings at this time can be located to obtain two sets of gratings with different center wavelengths. Their overlapping part is the perturbation region. Compared with a single-wavelength weak grating array, the spatial resolution is improved by 100%.

[0077] Figure 2 In traditional distributed weak grating array-based sensing systems, continuous light emitted from an extremely narrow-linewidth laser passes through a coupler and then enters two acousto-optic modulators, where it is modulated into two narrow-pulse beams. After passing through the coupler, the power is amplified by an erbium-doped fiber amplifier, and then passes through a circulator into the sensing fiber. The returning interference light is received by the detector. Since the grating spacing is the spatial resolution of the system, it is difficult to extend the sensing distance without reducing the spatial resolution, and it is also impossible to improve the spatial resolution without shortening the sensing distance. This proposed solution addresses these issues, and the following detailed explanation is based on experimental results:

[0078] Adopting such Figure 3 The experimental setup shown uses narrow-linewidth lasers with center wavelengths of 1535 nm and 1550 nm to emit continuous light, which simultaneously enters an acousto-optic modulator with modulation frequencies of 200 MHz and -60 MHz, modulating to obtain four pulses with a pulse width of 60 ns. Two pulses modulated by the same acousto-optic modulator overlap, and the pulse spacing between the pulses modulated by the two acousto-optic modulators is 100 ns. The four pulses are amplified by an erbium-doped fiber amplifier and then sent to a dual-wavelength grating array for sensing by a circulator. The spacing between the gratings of the same wavelength is 10 m, and the spacing between the gratings of different wavelengths is 5 m. The returned superimposed light is split into two interference beams by a wavelength division multiplexer after passing through the circulator. These beams are received by two detectors, collected by a data acquisition card, and sent to a computer for disturbance localization and measurement.

[0079] Figure 4 The image shows two imaging signals received by two detectors and acquired by a data acquisition card. There is a certain time delay between them, which is caused by the distribution of the dual-wavelength weak grating array. The magnitude of the time delay is related to the grating spacing of different center wavelengths.

[0080] A sinusoidal signal with a frequency of 200Hz and a voltage of 10V is applied near the grating at a distance of 2000 meters. Figure 5 This represents the demodulation results of two adjacent beats in the two beat signals. Each beat signal corresponds exactly to two pairs of adjacent gratings with different center wavelengths, such as... Figure 6 The two shots indicated by the black arrows in the middle, Figure 6It also shows that the demodulation results of each signal can only reduce the disturbance to a range of 10m. By combining the two signals, the disturbance can be reduced to a range of 5m, and the final vibration location is consistent with the actual location.

[0081] The dual-wavelength distributed weak grating array sensing system and method based on heterodyne detection in this embodiment, compared with the traditional scheme, uses a specially made dual-wavelength weak grating array. Through its unique staggered arrangement of gratings with different center wavelengths, it can form two interference beams for sensing, and perform two measurements and positioning on the same disturbance. This achieves a doubling of spatial resolution while keeping the sensing distance unchanged, and also extends the sensing distance by nearly two times while keeping the spatial resolution unchanged.

[0082] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A dual-wavelength distributed weak grating array sensing system based on heterodyne detection, characterized in that, The dual-wavelength distributed weak grating array sensing system includes a first narrow-linewidth laser, a second narrow-linewidth laser, a 2×2 coupler, a first acousto-optic modulator, a second acousto-optic modulator, a pulse signal generator, a 2×1 coupler, an erbium-doped fiber amplifier, a circulator, a sensing fiber optic cable for fusing the dual-wavelength weak grating array, a wavelength division multiplexer, a first photodetector, a second photodetector, a data acquisition card, and a data processor. The first narrow linewidth laser emits continuous light with a center wavelength of and the second narrow linewidth laser emits continuous light with a center wavelength of ; the 2x2 coupler sends the two continuous lights with different center wavelengths into two branches and exists in both branches simultaneously; The pulse signal generator emits a first pulse electrical signal and a second pulse electrical signal to control the first and second acousto-optic modulators to modulate continuous light, respectively, and simultaneously transmits a synchronization trigger signal to the data acquisition card. The first acousto-optic modulator outputs a first pulse light and a second pulse light superimposed together, and the second acousto-optic modulator outputs a third pulse light and a fourth pulse light superimposed together. The pulse widths of the first, second, third, and fourth pulse lights are the same. The frequency shift frequencies of the first and second acousto-optic modulators are different. The 2×1 coupler sends the first, second, third, and fourth pulse lights into the same branch, where they are amplified by the erbium-doped fiber amplifier. The amplified first, second, third, and fourth pulse lights then enter the sensing fiber of the fused dual-wavelength weak grating array through a circulator. The sensing fiber of the fused dual-wavelength weak grating array contains a center wavelength of... The first weak grating array and the center wavelength is The second weak grating array; the first pulse light and the third pulse light are reflected and superimposed on adjacent gratings of the first weak grating array only; the second pulse light and the fourth pulse light are reflected and superimposed on adjacent gratings of the second weak grating array only; the wavelength division multiplexer divides the wavelength of the light into two pulses with a center wavelength of 10 ... and The superimposed light is split into two paths; the first photodetector collects the center wavelength. The optical signal is converted into an electrical signal, and the second photodetector collects the center wavelength. The optical signal is converted into an electrical signal; the data acquisition card acquires the electrical signals from the first and second photodetectors and digitizes them; the data processor performs disturbance positioning and quantitative measurement on the two digitized electrical signals acquired by the data acquisition card. The data processor demodulates the beat signal between adjacent gratings in each electrical signal. The demodulated vibration indicates that the vibration exists between adjacent gratings. The processor observes the grating region that generates the disturbance in each data stream. When the position of the grating pair that generates the disturbance in the first weak grating array overlaps with the position of the grating pair that generates the disturbance in the second weak grating array, the two gratings that overlap between the grating pairs in the first weak grating array and the grating pairs in the second weak grating array are taken as the disturbance region, and the disturbance position is reduced to the adjacent gratings with different center wavelengths.

2. The dual-wavelength distributed weak grating array sensing system based on heterodyne detection according to claim 1, characterized in that, Replace the 2×2 coupler with an optical switch or modulator, and control the timing of the output light waves from the first narrow-linewidth laser and the second narrow-linewidth laser using the optical switch or modulator, so that the center wavelength is... and The light waves are respectively incident on the system.

3. The dual-wavelength distributed weak grating array sensing system based on heterodyne detection according to claim 1, characterized in that, The grating spacing in the first weak grating array is equal, the grating spacing in the second weak grating array is equal, and the grating spacing in both the first and second weak grating arrays is [missing information]. The gratings in the first weak grating array and the gratings in the adjacent second weak grating array are spaced apart as follows: and .

4. The dual-wavelength distributed weak grating array sensing system based on heterodyne detection according to claim 3, characterized in that, The gratings in the first weak grating array and the gratings in the adjacent second weak grating array are spaced apart. .

5. The dual-wavelength distributed weak grating array sensing system based on heterodyne detection according to claim 1, characterized in that, The pulse signal generator generates first and second pulse electrical signals with pulse widths of both... The pulse interval is , < Where c is the speed of light in a vacuum, and n is the equivalent refractive index of the optical fiber. The spacing between adjacent gratings with the same center wavelength in a grating array.

6. The dual-wavelength distributed weak grating array sensing system based on heterodyne detection according to claim 1, characterized in that, Assume that the electric field strengths of the first, second, third, and fourth pulses are all... The angular frequencies are respectively , , and ,in equal The initial phase of the first pulse light and the third pulse light is determined by the frequency shift difference between the first and second acousto-optic modulators. The initial phase of the second pulse and the fourth pulse is The spacing between the gratings in the first weak grating array and the second weak grating array is... The reflectivity is , The change in fiber length is caused by external disturbances; The reflected photoelectric fields of the four pulsed lights are respectively represented as follows: ； ； ； ； The reflected light from the first pulse and the reflected light from the third pulse interfere with each other, and the resulting optical signal is represented as follows: ； in, It is a phase change caused by external disturbances; The reflected light from the second pulse and the reflected light from the fourth pulse interfere with each other, and the resulting optical signal is represented as follows: ； in, It is a phase change caused by external disturbances.

7. A dual-wavelength distributed weak grating array sensing method based on heterodyne detection, characterized in that, The dual-wavelength distributed weak grating array sensing method is performed based on the dual-wavelength distributed weak grating array sensing system based on heterodyne detection as described in any one of claims 1-6; The dual-wavelength distributed weak grating array sensing method includes the following steps: Step 1: The 2×2 coupler injects the continuous light wave generated by the first narrow linewidth laser and the continuous light wave generated by the second narrow linewidth laser into the same two branches; Step 2: The pulse signal generator sends a first pulse electrical signal to control the first acousto-optic modulator to modulate the continuous light generated by the first narrow linewidth laser and the second narrow linewidth laser into a first pulse light and a second pulse light. The pulse signal generator sends a second pulse electrical signal to control the second acousto-optic modulator to modulate the continuous light generated by the first narrow linewidth laser and the second narrow linewidth laser into a third pulse light and a fourth pulse light. The first pulse light and the second pulse light overlap, and the third pulse light and the fourth pulse light overlap. The pulse widths of the first pulse light, the second pulse light, the third pulse light, and the fourth pulse light are the same, and the pulse spacings of the first pulse light, the second pulse light, the third pulse light, and the fourth pulse light are the same. Step 3: The 2×1 coupler sends the first, second, third, and fourth pulses into a branch and is amplified by the erbium-doped fiber amplifier. The amplified first, second, third, and fourth pulses then enter the sensing fiber of the fused dual-wavelength weak grating array through the circulator. Step 4: The first and third pulses are reflected and superimposed on adjacent gratings of the first weak grating array only, and the second and fourth pulses are reflected and superimposed on adjacent gratings of the second weak grating array only. Step 5: The wavelength division multiplexer splits the superimposed light of different center wavelengths into two paths, which are collected by the first photodetector and the second photodetector respectively and converted into electrical signals. The data acquisition card digitizes the collected electrical signals and transmits them to the data processor. Step Six: The data processor processes the two digital electrical signals acquired by the data acquisition card. It demodulates the beat signal between adjacent gratings in each electrical signal. If vibration is demodulated, it means that the vibration exists between the grating pairs. The grating regions that generate disturbances in each data channel are observed. When the positions of the grating pairs that generate disturbances in the first weak grating array and the second weak grating array overlap, the two gratings that overlap between the grating pairs in the first weak grating array and the second weak grating array are taken as the disturbance regions, thereby reducing the disturbance position to adjacent gratings with different center wavelengths.

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