A multi-fiber parallel grating array, fiber optic distributed vibration sensing system and method

Abstract

This invention proposes a multi-fiber parallel-band grating array, an optical fiber distributed vibration sensing system and method, relating to the field of optical fiber sensing technology. The multi-fiber parallel-band grating array includes n optical fibers arranged side-by-side and maintaining a fixed relative position, where n is an integer greater than or equal to 2. Each optical fiber in the multi-fiber parallel-band grating array is inscribed with multiple gratings, and the multiple gratings in each optical fiber are arranged sequentially along the fiber axis to form a grating array. The axial spacing between any two adjacent gratings in the same optical fiber is 'a'. The grating arrays in different optical fibers are staggered along the fiber axis, and the axial positions of corresponding gratings in any two adjacent optical fibers are staggered by a preset distance, so that the gratings in the n optical fibers form an interleaved sampling structure in space. The preset distance is less than the axial spacing, so that the equivalent spatial sampling spacing of the multi-fiber parallel-band grating array is less than the spacing between any two adjacent gratings in a single optical fiber.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a multi-fiber parallel grating array, a fiber optic distributed vibration sensing system and method. Background Technology

[0002] High spatial resolution is a core requirement for achieving accurate vibration signal localization and precise scene monitoring. Traditional vibration sensing systems based on phase-sensitive optical time-domain reflectometry (Φ-OTDR) have long been limited in spatial resolution by the width of the detection pulse. This physical bottleneck stems from the technical principle of Φ-OTDR—spatial resolution is usually positively correlated with pulse width, meaning that the narrower the pulse, the higher the theoretical spatial resolution.

[0003] Chinese Patent CN119022973B discloses a heterogeneous parallel grating array and a distributed multi-parameter sensing system, belonging to the field of fiber optic sensing technology. The heterogeneous parallel grating array includes a prestressed grating array and a relaxed grating array. The prestressed grating array includes a first optical fiber and multiple prestressed broadband gratings and multiple prestressed narrowband gratings etched on the first optical fiber. The relaxed grating array includes a second optical fiber and multiple relaxed broadband gratings and multiple relaxed narrowband gratings etched on the second optical fiber. However, the above solution is still based on a weak grating array with limited spacing within a single optical cable. The spatial sampling interval and the probe pulse width are strongly coupled, making it difficult to further compress the equivalent sampling interval while ensuring the sensing distance, resulting in… The spatial resolution is insufficient. Therefore, this paper provides a multi-fiber parallel grating array, a fiber-optic distributed vibration sensing system and method, to improve the spatial resolution. Spatial resolution is essential. Summary of the Invention

[0004] In view of this, the present invention proposes a multi-fiber parallel grating array, fiber optic distributed vibration sensing system and method, which helps to improve... Spatial resolution.

[0005] The present invention provides a multi-fiber parallel grating array, comprising n optical fibers arranged in parallel and maintaining a fixed relative position, wherein n is an integer greater than or equal to 2; Each fiber in the multi-fiber parallel grating array is inscribed with multiple gratings. The multiple gratings in each fiber are arranged sequentially along the fiber axis to form a grating array, and the axial spacing between any two adjacent gratings in the same fiber is a. The grating arrays in different optical fibers are staggered along the fiber axis. The axial positions of corresponding gratings in any two adjacent optical fibers are staggered by a preset distance, so that the gratings in n optical fibers form an interleaved sampling structure in space. The preset distance is less than the axial spacing, so that the equivalent spatial sampling spacing of the multi-fiber parallel grating array is less than the spacing between any two adjacent gratings in a single optical fiber.

[0006] Based on the above technical solutions, preferably, a set of grating sensing equivalent measurement areas is formed between any two adjacent gratings on different optical fibers, and the grating sensing equivalent measurement areas on each optical fiber are uniformly numbered in spatial order to form equivalent measurement areas continuously distributed along the length of the optical fiber.

[0007] Based on the above technical solutions, preferably, the gratings inscribed in each optical fiber are weakly reflective fiber Bragg gratings, the axial misalignment distance of corresponding gratings in any two adjacent optical fibers is a / n, and the equivalent spatial sampling interval of the multi-fiber parallel grating array is a / n.

[0008] More preferably, the multi-fiber parallel band grating array includes a first fiber, a second fiber, a third fiber, ... and an nth fiber arranged in parallel, and the specific arrangement of the multi-fiber parallel band grating array is as follows: The first optical fiber is inscribed with the first grating at the starting position, and then the remaining gratings in the first optical fiber are inscribed sequentially at axial spacing a. The first grating in the second optical fiber is etched at position a / n, and then the remaining gratings in the second optical fiber are etched sequentially at axial spacing a. The first grating in the third optical fiber is etched at position 2a / n, and thereafter the remaining gratings in the third optical fiber are etched sequentially at axial spacing a. The first grating in the nth fiber is etched at position (n-1)×a / n, and thereafter the remaining gratings in the nth fiber are etched sequentially at axial spacing a.

[0009] More preferably, the n optical fibers are fixed into a parallel structure by any one of the following methods: adhesive bonding, sleeve encapsulation, ribbon encapsulation, coating encapsulation, and composite material encapsulation, so as to maintain the stability of the relative spatial position between each optical fiber.

[0010] A second aspect of this application provides an optical fiber distributed vibration sensing system, which includes a narrow linewidth laser, a 1×2 beam splitter, a modulation gain module, a multi-channel coherent detection module, and the aforementioned multi-fiber parallel band grating array, wherein... The narrow linewidth laser is connected to the input end of the 1×2 beam splitter, and the narrow linewidth laser is used to output continuous light; The 1×2 beam splitter is connected to the modulation gain module and the multi-channel coherent detection module respectively. The 1×2 beam splitter is used to split the continuous light into a first continuous light and a second continuous light. The first continuous light is used as a probe light and input to the modulation gain module, and the second continuous light is used as a local oscillator light and directly input to the multi-channel coherent detection module. The modulation gain module is used to pulse modulate and amplify the power of the first continuous light to obtain pulse probe light, and inject the pulse probe light into multiple optical fibers in the multi-fiber array with gratings. The multi-channel coherent detection module is connected to the multi-fiber parallel grating array. The multi-fiber parallel grating array is used to receive pulse detection light from each channel and generate corresponding back-reflected light under external vibration. The multi-channel coherent detection module is used to perform coherent detection on the second continuous light and the back-reflected light from each channel, and to generate and output multi-channel interference signals, so as to synchronously acquire and demodulate the vibration information of each channel in the multi-fiber parallel grating array with high spatial resolution.

[0011] More preferably, the modulation gain module includes an acousto-optic modulator, an erbium-doped fiber amplifier, and a multi-channel optical interface connected in sequence, wherein, The acousto-optic modulator is connected to the first output terminal of the 1×2 beam splitter and the erbium-doped fiber amplifier, respectively. The acousto-optic modulator is used to modulate the first continuous light into a pulse probe light with a preset pulse width and repetition frequency under the action of an external TTL pulse drive signal. The erbium-doped fiber amplifier is connected to the multi-channel optical interface. The erbium-doped fiber amplifier is used to amplify the pulse power of the pulse probe light. The multi-channel optical interface is used to distribute the amplified pulse probe light according to the channels and inject it into the corresponding optical fiber in the multi-fiber grating array.

[0012] More preferably, the multi-channel coherent detection module includes multiple detection channels, each detection channel including a circulator, a 2×2 beam splitter, a photodetector, and a signal processing device connected in sequence. The first end of the circulator is connected to the first end of the circulator in the other detection channels, the third end of the circulator is connected to the multi-fiber parallel grating array, and the second end of the circulator is connected to the first input end of the 2×2 beam splitter. The second input terminal of the 2×2 beam splitter is connected to the second output terminal of the 1×2 beam splitter. The 2×2 beam splitter is used to combine the local oscillator light with the back-reflected light returned by the multi-fiber grating array and perform coherent interference. The first and second output terminals of the 2×2 beam splitter are both connected to the photodetector, which is used to perform photoelectric conversion on the interferometric optical signal to obtain a multi-channel interferometric electrical signal. The signal processing device is connected to the photodetector. The signal processing device is used to synchronously acquire the multi-channel interference electrical signals and output raw data for vibration event localization and demodulation.

[0013] More preferably, the multi-fiber parallel grating array is a four-fiber parallel grating array, and the multi-channel optical interface includes four optical interfaces.

[0014] A third aspect of this application provides a fiber optic distributed vibration sensing method, implemented according to the aforementioned fiber optic distributed vibration sensing system, the method comprising: A narrow linewidth laser outputs continuous light, which is then input into a 1×2 beam splitter. The 1×2 beam splitter splits the continuous light into a first continuous light and a second continuous light. The first continuous light is output as a probe light to a modulation gain module, and the second continuous light is output as a local oscillator light to a multi-channel coherent detection module. In the modulation gain module, the first continuous light is pulse-modulated and power-amplified to obtain pulse probe light, and the pulse probe light is injected into multiple optical fibers in a multi-fiber array with gratings. The multi-fiber parallel grating array receives pulsed probe light from each channel. Under external vibration, the gratings corresponding to each channel undergo refractive index and / or length changes, thereby forming back-reflected light carrying vibration information, and returning the back-reflected light to the multi-channel coherent detection module. In the multi-channel coherent detection module, the second continuous light, which serves as the local oscillator light, is coherently detected with the back-reflected light returned from each channel to obtain and output a multi-channel interference signal. The multi-channel interference signals are synchronously acquired and processed. Based on the misaligned distribution of multiple optical fibers in the multi-fiber parallel grating array, the interference signals of each channel are spatially registered and phase demodulated to obtain vibration information corresponding to each equivalent measurement area, so as to synchronously acquire and demodulate the vibration events of each channel in the multi-fiber parallel grating array with high spatial resolution.

[0015] The multi-fiber parallel grating array, fiber optic distributed vibration sensing system and method provided by this invention have the following advantages over the prior art: (1) By arranging grating arrays axially staggered on multiple optical fibers, the equivalent spatial sampling spacing of the multi-fiber parallel grating array is smaller than the spacing between any two adjacent gratings in a single optical fiber. Without changing the single-fiber grating writing spacing a, higher spatial resolution distributed or quasi-distributed measurement can be achieved. In addition, within the same length range, the gratings of multiple optical fibers are spatially staggered, which is equivalent to superimposing multiple grating arrays, greatly increasing the effective sampling point density of the spatial segment and enhancing the ability to characterize the spatial distribution changes of the measured field. The conventional grating spacing a is maintained on a single optical fiber, avoiding the problems of increased process difficulty, reduced processing efficiency, and mutual coupling of gratings caused by writing ultra-small pitch gratings on a single fiber. Equivalent small-pitch sampling can be obtained through the multi-fiber staggered structural design, making the process easier and more stable. At the same time, due to the reduction of the equivalent spatial sampling spacing, the ability to capture local abrupt changes or fine-scale changes on the measured object is enhanced, which can reduce the loss of signal details and missed detection of risk points caused by too sparse sampling points, and improve the accuracy and reliability of the overall monitoring results.

[0016] (2) By staggering the first gratings of the first to n optical fibers respectively, and maintaining the axial spacing of a on each fiber, the multi-fiber system forms a uniform sampling structure with an equivalent spatial sampling step size of a / n, which greatly improves the spatial sampling resolution. Furthermore, the gratings of each fiber are still written with a spacing of a according to conventional processes, without the need to achieve an ultra-small spacing smaller than a on a single fiber. This avoids problems such as high processing difficulty, poor writing stability, and enhanced crosstalk between gratings. At the same time, the equivalent ultra-small spacing sampling is achieved by staggering the multi-fiber system. Since the first gratings of each fiber are staggered sequentially at a fixed interval of a / n, the multi-fiber parallel gratings form a strictly periodic and equally spaced staggered sampling grid in space. The overall positional relationship is simple and the regularity is clear. At the same time, after the equivalent sampling spacing is reduced to a / n, the small changes in temperature field, strain field, etc. along the axial direction can be more finely characterized, improving the detection rate of small-scale anomalies such as abrupt changes and local damage, thereby improving the accuracy and reliability of the overall monitoring system. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of the structure of a multi-fiber parallel grating array with 4 optical fibers provided by the present invention; Figure 2 This is a schematic diagram of the structure of a fiber optic distributed vibration sensing system provided by the present invention.

[0019] Explanation of reference numerals in the attached figures: 1. Multi-fiber parallel grating array; 2. Narrow linewidth laser; 3. 1×2 beam splitter; 4. Modulation gain module; 41. Acousto-optic modulator; 42. Erbium-doped fiber amplifier; 43. Multi-channel optical interface; 5. Multi-channel coherent detection module; 51. Detection channel; 511. Circulator; 512. 2×2 beam splitter; 513. Photodetector; 514. Signal processing device. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] The present invention provides a multi-fiber parallel grating array 1, comprising n optical fibers arranged in parallel and maintaining a fixed relative position, wherein n is an integer greater than or equal to 2; Each fiber in the multi-fiber parallel grating array 1 is inscribed with multiple gratings. The multiple gratings in each fiber are arranged sequentially along the fiber axis to form a grating array, and the axial spacing between any two adjacent gratings in the same fiber is a. The grating arrays in different optical fibers are staggered along the fiber axis. The axial positions of corresponding gratings in any two adjacent optical fibers are staggered by a preset distance, so that the gratings in n optical fibers form an interleaved sampling structure in space. The preset distance is less than the axial spacing, so that the equivalent spatial sampling spacing of the multi-fiber parallel grating array 1 is less than the spacing between any two adjacent gratings in a single optical fiber.

[0022] In this system, fiber segments between any two adjacent gratings on different optical fibers form a set of grating sensing equivalent measurement areas. The grating sensing equivalent measurement areas on each fiber are uniformly numbered according to their spatial position, forming a continuous distribution of equivalent measurement areas along the fiber length. The gratings etched in each fiber are weakly reflective fiber Bragg gratings. The axial misalignment distance between corresponding gratings in any two adjacent fibers is a / n, and the equivalent spatial sampling spacing of the multi-fiber parallel grating array 1 is a / n. Furthermore, the n optical fibers are fixed into a parallel structure using any one of the following methods: bonding, tubing encapsulation, ribbon encapsulation, coating encapsulation, or composite material encapsulation, to maintain the relative spatial stability between the fibers.

[0023] The tail of the multi-fiber parallel grating array, namely the last grating of the first fiber and all subsequent test areas, is solidified and encapsulated to achieve vibration separation from the preceding fiber.

[0024] Furthermore, the multi-fiber parallel band grating array 1 includes a first fiber, a second fiber, a third fiber, ... and an nth fiber arranged in parallel. The specific arrangement of the multi-fiber parallel band grating array 1 is as follows: The first grating in the first optical fiber is inscribed at the starting position, and then the remaining gratings in the first optical fiber are inscribed sequentially at axial spacing a. The first grating in the second optical fiber is etched at position a / n, and then the remaining gratings in the second optical fiber are etched sequentially at axial spacing a. The first grating in the third fiber is etched at position 2a / n, and then the remaining gratings in the third fiber are etched sequentially at axial spacing a. The first grating in the nth fiber is etched at position (n-1)×a / n, and the remaining gratings in the nth fiber are etched sequentially at axial spacing a.

[0025] In this embodiment, by staggering the first gratings of the first to nth optical fibers, while maintaining an axial spacing of 'a' on each fiber, the multi-fiber system forms a uniform sampling structure with an equivalent spatial sampling step size of 'a / n'. This significantly improves the spatial sampling resolution. Furthermore, the gratings on each fiber are still written at a spacing of 'a' using conventional processes, eliminating the need for ultra-small spacings smaller than 'a' on individual fibers. This avoids problems such as high processing difficulty, poor writing stability, and enhanced crosstalk between gratings. Simultaneously, the staggered arrangement of multiple fibers achieves equivalent ultra-small spacing sampling. Since the first gratings of each fiber are staggered sequentially at a fixed interval of 'a / n', the multi-fiber parallel gratings form a strictly periodic, equally spaced, staggered sampling grid in space. The overall positional relationship is simple and the pattern is clear. Moreover, with the equivalent sampling spacing reduced to 'a / n', the minute changes along the axial direction of the temperature field and strain field can be more precisely characterized, improving the detection rate of small-scale anomalies such as abrupt changes and local damage, thereby enhancing the accuracy and reliability of the overall monitoring system.

[0026] In one example, such as Figure 1 As shown, a fiber optic structure is constructed using four independent single-mode optical fibers, labeled fiber 1, fiber 2, fiber 3, and fiber 4. Through parallel arrangement and fixed encapsulation processes (such as adhesive bonding or tubing encapsulation), the four optical fibers maintain a stable relative position in space, thereby achieving multi-fiber synchronous sensing. Subsequently, gratings are inscribed in each optical fiber.

[0027] The grating arrays on the four optical fibers are arranged in a staggered spatial configuration, specifically as follows: Grating 1# is etched into fiber 1 at the starting position of 0 m, and then subsequent gratings 2#, 3#, etc. are etched in sequence at intervals of 4 x m. Grating 1# is etched into fiber 2 at the starting position X m, and then subsequent gratings 2#, 3#, etc. are etched in sequence at intervals of 4X m. Grating 1# is etched into fiber 3 at the starting position of 2×m, and then gratings 2#, 3#, etc. are etched in sequence at intervals of 4×m. Grating 1# is etched into fiber 4 at the starting position of 3×m, and then gratings 2#, 3#, etc. are etched in sequence at intervals of 4×m. Based on the above layout, let 0 to Xm be the equivalent test region 1, Xm to 2Xm be the equivalent test region 2, and so on.

[0028] For any region between two adjacent grating intervals, its vibration information can be obtained by subtracting the phases of corresponding intervals in adjacent optical fibers. Therefore, it is necessary to start from the equivalent measurement area at the end of the optical fiber and work backwards to deduce the phase of each region. For the end of the four optical fibers, i.e., the equivalent measurement area 4 N The portion after -4 is cured.

[0029] To achieve accurate positioning of the vibration phase in the equivalent test area, the first... Root fiber The first grating and the second The phase of the measurement area between +1 gratings is and define from the grating To the end grating The cumulative phase between the measurement areas is:

[0030] Equivalent test area number The corresponding fiber optic cable number and grating number are as follows:

[0031]

[0032] Define the cyclic fiber numbering and grating correction function:

[0033]

[0034] Then the equivalent test area The phase can be uniformly represented as:

[0035] in, Indicates the first The first in the root optical fiber The first grating and the second +1 phase value of the measurement area between gratings, Indicates from the first The first fiber Starting with the first grating, up to the second... Fiber end grating The cumulative phase between the measurement areas Indicates the first One equivalent test area, Indicates the first The fiber number corresponding to each equivalent measurement area Indicates the first The starting grating number corresponding to each equivalent measurement area This indicates the fiber number after cyclic correction. This indicates the starting raster number after cyclic correction. Indicates the first The final phase representation of each equivalent measurement area Indicates return -1 is the remainder when divided by 4. This can be understood as the cumulative phase of a grating in the current fiber to the end, minus the cumulative phase of the next segment (or the corresponding grating in the next segment of the fiber after a cycle) to the end.

[0036] Specifically, the four-fiber parallel grating array fiber consists of four independent fibers arranged side by side, labeled fiber 1, fiber 2, fiber 3, and fiber 4. Each fiber core is engraved with a periodically arranged grating array. The grating arrays on the four fibers are spatially staggered, arranged as follows: Fiber 1 has grating 1# engraved at the starting position of 0 m, followed by subsequent gratings 2#, 3#, etc., at 2 m intervals; Fiber 2 has grating 1# engraved at the starting position of 0.5 m, followed by subsequent gratings 2#, 3#, etc., at 2 m intervals; Fiber 3 has grating 1# engraved at the starting position of 1 m, followed by subsequent gratings 6#, etc., at 2 m intervals; Fiber 4 has the first grating 1# engraved at the starting position of 1.5 m, followed by subsequent gratings 2#, 3#, etc., at 2 m intervals. Through the above staggered arrangement, the grating arrays on the four optical fibers form an interlaced coverage in the spatial dimension, which shortens the equivalent sampling interval from 2m for a single optical fiber to 0.5m after the four optical fibers are interlaced, thus achieving a fourfold improvement in spatial resolution.

[0037] In this embodiment, by axially staggering the arrangement of grating arrays on multiple optical fibers, the equivalent spatial sampling spacing of the multi-fiber parallel grating array 1 is smaller than the spacing between any two adjacent gratings in a single optical fiber. Without changing the single-fiber grating writing spacing 'a', higher spatial resolution distributed or quasi-distributed measurement is achieved. Furthermore, within the same length range, the gratings of multiple optical fibers are spatially staggered, equivalent to superimposing multiple grating arrays, significantly increasing the effective sampling point density of this spatial segment and enhancing the ability to characterize changes in the spatial distribution of the measured field. Maintaining a conventional grating spacing 'a' on a single optical fiber avoids the increased process difficulty, reduced processing efficiency, and grating coupling problems associated with writing ultra-small pitch gratings on a single fiber. Equivalent small-pitch sampling can be obtained through the multi-fiber staggered structural design, making the process easier and more stable to implement. Simultaneously, due to the reduced equivalent spatial sampling spacing, the ability to capture local abrupt changes or fine-scale variations on the measured object is enhanced, reducing signal detail loss and missed detection of risk points caused by sparse sampling points, thus improving the accuracy and reliability of the overall monitoring results.

[0038] Based on the aforementioned multi-fiber parallel band grating array 1, this application discloses an optical fiber distributed vibration sensing system, referencing... Figure 2 The fiber optic distributed vibration sensing system includes a narrow-linewidth laser 2, a 1×2 beam splitter 3, a modulation gain module 4, a multi-channel coherent detection module 5, and a multi-fiber parallel band grating array 1 as claimed in any one of claims 1-5, wherein... Narrow linewidth laser 2 is connected to the input of 1×2 beam splitter 3, and narrow linewidth laser 2 is used to output continuous light.

[0039] The 1×2 beam splitter 3 is connected to the modulation gain module 4 and the multi-channel coherent detection module 5 respectively. The 1×2 beam splitter 3 is used to split the continuous light into a first continuous light and a second continuous light. The first continuous light is used as the probe light and input to the modulation gain module 4, and the second continuous light is used as the local oscillator light and directly input to the multi-channel coherent detection module 5.

[0040] The modulation gain module 4 is used to pulse modulate and amplify the power of the first continuous light to obtain pulse probe light, and inject the pulse probe light into multiple optical fibers in the multi-fiber grating array 1.

[0041] The modulation gain module 4 includes an acousto-optic modulator 41, an erbium-doped fiber amplifier 42, and a multi-channel optical interface 43 connected in sequence. The acousto-optic modulator 41 is connected to the first output terminal of the 1×2 beam splitter 3 and the erbium-doped fiber amplifier 42 respectively. The acousto-optic modulator 41 is used to modulate the first continuous light into a pulse probe light with a preset pulse width and repetition frequency under the action of an external TTL pulse drive signal. Erbium-doped fiber amplifier 42 is connected to multi-channel optical interface 43. Erbium-doped fiber amplifier 42 is used to amplify the pulse power of pulse probe light. Multi-channel optical interface 43 is used to distribute the amplified pulse probe light according to the channel and inject it into the corresponding fiber in multi-fiber grating array 1.

[0042] The multi-channel coherent detection module 5 is connected to the multi-fiber parallel grating array 1. The multi-fiber parallel grating array 1 is used to receive the pulse detection light of each channel and generate the corresponding back reflection light under the action of external vibration. The multi-channel coherent detection module 5 is used to perform coherent detection on the second continuous light and the back reflection light of each channel, and to complete the generation and output of multi-channel interference signals, so as to synchronously acquire and demodulate the vibration information of each channel in the multi-fiber parallel grating array 1 with high spatial resolution.

[0043] The multi-channel coherent detection module 5 includes multiple detection channels 51. Each detection channel 51 includes a circulator 511, a 2×2 beam splitter 512, a photodetector 513, and a signal processing device 514 connected in sequence. The first end of the circulator 511 is connected to the first end of the circulator 511 in the other detection channels 51 respectively, the third end of the circulator 511 is connected to the multi-fiber parallel grating array 1, and the second end of the circulator 511 is connected to the first input end of the 2×2 beam splitter 512. The second input terminal of the 2×2 beam splitter 512 is connected to the second output terminal of the 1×2 beam splitter 3. The 2×2 beam splitter 512 is used to combine the local oscillator light with the back-reflected light returned by the multi-fiber grating array 1 and perform coherent interference. The first and second output terminals of the 2×2 beam splitter 512 are both connected to the photodetector 513, which is used to perform photoelectric conversion on the interferometric optical signal to obtain a multi-channel interference electrical signal. The signal processing device 514 is connected to the photodetector 513. The signal processing device 514 is used to synchronously acquire multi-channel interference electrical signals and output raw data for vibration event localization and demodulation.

[0044] In one example, the multi-fiber parallel band grating array 1 is a four-fiber parallel band grating array, and the multi-channel optical interface 43 includes four optical interfaces. A fiber-optic distributed vibration sensing system is used as the demodulation end, and the multi-fiber parallel band grating array 1 is used as the sensing end. In this example, there are four fibers, and staggered parallel band grating arrays are inscribed along the length of each fiber to form an interlaced coverage of the test area in the spatial dimension.

[0045] Specifically, the continuous light output from the narrow-linewidth laser 2 is introduced into a 1×2 beam splitter 3, where it is split into a first continuous light and a second continuous light. The first continuous light is output as a probe light to the modulation gain module 4, and the second continuous light is output as a local oscillator light to the multi-channel coherent detection module 5. In the modulation gain module 4, the first continuous light is pulse-modulated and a preset frequency shift is introduced by an acousto-optic modulator 41. Then, the modulated light pulse is amplified by an erbium-doped fiber amplifier 42 to obtain a pulse probe light with sufficient peak power. The pulse probe light is then injected into multiple optical fibers in the multi-fiber array 1 through a multi-channel optical interface 43, so that the pulse probe light of each channel sequentially illuminates the grating array in each test area along the corresponding optical fiber.

[0046] In the multi-fiber parallel grating array 1, four optical fibers are fixed side by side. Each fiber core is engraved with a grating array arranged periodically along its length, with the same center wavelength. The gratings on each fiber are spatially staggered, with the spacing between adjacent gratings on the same fiber being 'a'. The starting positions of corresponding gratings on two adjacent fibers are staggered by 'a / 4', resulting in an interleaved sampling grid with a spacing of 'a / 4' in the spatial dimension. Under external vibration, the refractive index and / or length of the gratings in each measurement area change, modulating the phase and intensity of the pulsed probe light passing through that measurement area. This generates back-reflected light carrying vibration information in each channel, which then returns along each fiber to the multi-channel coherent detection module 5.

[0047] In the multi-channel coherent detection module 5, the second continuous light, which serves as the local oscillator, is heterodyne coherently detected with the backscattered light returned from each channel of the multi-fiber grating array 1 to obtain a multi-channel interference electrical signal containing beat frequency information. This multi-channel interference electrical signal is then sent to the signal processing device 514. In the signal processing device 514, the multi-channel interference electrical signal is synchronously acquired, and the phase information of the backscattered light from each channel is extracted using the digital orthogonal demodulation (IQ demodulation) method. Based on the staggered distribution of the multi-fiber grating array 1, the phase information of each channel is spatially registered, and the sampling points of the multiple optical fibers are mapped into an interleaved sampling grid with an equivalent spacing of a / n in the spatial dimension.

[0048] Furthermore, after spatial registration is completed, according to the preset adjacent channel phase difference algorithm in the signal processing device 514, for any two adjacent grating intervals, the vibration phase of the measurement area is obtained by calculating the difference in the cumulative phase of the corresponding intervals of the adjacent optical fibers; specifically, taking the first... Root fiber The first grating and the second The phase of the measurement area between +1 gratings is Defined from grating The cumulative phase of the measurement area between the fiber end grating and the fiber end grating is The corresponding fiber number and grating number are determined based on the survey area number. The final phase representation of the survey area is obtained by subtracting the cumulative phase of the corresponding segment of the adjacent or cyclic fiber from the cumulative phase of the current fiber segment. This allows for the precise location of vibration information in each measurement area.

[0049] Based on the aforementioned fiber optic distributed vibration sensing system, this application discloses a fiber optic distributed vibration sensing method, the method comprising: Step S1: The narrow linewidth laser 2 outputs continuous light and inputs the continuous light into the 1×2 beam splitter 3. The continuous light is then split into a first continuous light and a second continuous light by the 1×2 beam splitter 3. The first continuous light is output as a probe light to the modulation gain module 4, and the second continuous light is output as a local oscillator light to the multi-channel coherent detection module 5. Step S2: In the modulation gain module 4, the first continuous light is pulse-modulated and power-amplified to obtain pulse probe light, and the pulse probe light is injected into multiple optical fibers in the multi-fiber array 1. Step S3: The pulse probe light of each channel is received by the multi-fiber parallel grating array 1. Under the action of external vibration, the gratings corresponding to each channel will undergo changes in refractive index and / or length, thereby forming back-reflected light carrying vibration information, and the back-reflected light is returned to the multi-channel coherent detection module 5. Step S4: In the multi-channel coherent detection module 5, the second continuous light, which serves as the local oscillator light, is coherently detected with the back-reflected light returned from each channel to obtain and output the multi-channel interference signal. Step S5: Synchronously acquire and process the multi-channel interference signals. Based on the misaligned distribution of multiple optical fibers in the multi-fiber parallel grating array 1, spatially register and demodulate the interference signals of each channel to obtain vibration information corresponding to each equivalent measurement area, so as to synchronously acquire and demodulate the vibration events of each channel in the multi-fiber parallel grating array 1 with high spatial resolution.

[0050] In this embodiment, by injecting pulsed probe light into multiple optical fibers in the multi-fiber parallel grating array 1, and performing parallel coherent detection and synchronous acquisition of the back-reflected light from each channel in the multi-channel coherent detection module 5, synchronous monitoring of multi-channel vibration events is achieved, ensuring the temporal consistency and comparability of vibration information at each measurement point. Combining the aforementioned misaligned arrangement and equivalent small-pitch sampling structure of the multi-fiber parallel grating array 1, spatial registration and phase demodulation are performed according to the grating misalignment relationship during signal processing. This allows the multi-channel interference signal to be reconstructed into a vibration distribution with an equivalent sampling spacing much smaller than the single-fiber grating spacing, achieving high spatial resolution vibration demodulation and precise positioning along the fiber axis. A narrow-linewidth laser 2 outputs highly coherent continuous light, and interference signals are obtained through coherent detection of the local oscillator light and the back-reflected light. Compared to direct power detection, this significantly improves the detection sensitivity of phase changes and the system signal-to-noise ratio, enhancing the ability to sense weak vibrations. Pulse probe light is generated through pulse modulation and power amplification. While ensuring sufficient echo power, phase demodulation allows for the detection of small-signal micro-vibrations and the identification of large-amplitude vibration events, expanding the system's dynamic range and applicable operating conditions. In the signal processing stage, the known misaligned distribution of the multi-fiber parallel-band grating array 1 is used to spatially register the interference signals of each channel, effectively eliminating spatial misalignment between different channels. This achieves accurate mapping of vibration information corresponding to each equivalent measurement area and reconstruction of continuous spatial distribution. Multiple optical fibers are arranged in parallel in space with fixed relative positions. Different channels collaboratively sense vibration events within the same or adjacent areas. Through joint processing of multi-channel interference signals, cross-verification and multi-source fusion of abnormal vibrations can be achieved, improving the reliability of monitoring results and the ability to suppress environmental noise.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-fiber parallel grating array, characterized in that, It includes n optical fibers arranged side by side and maintaining a fixed relative position, where n is an integer greater than or equal to 2; Each fiber in the multi-fiber parallel grating array (1) is inscribed with multiple gratings. The multiple gratings in each fiber are arranged sequentially along the fiber axis to form a grating array, and the axial spacing between any two adjacent gratings in the same fiber is a. The grating arrays in different optical fibers are staggered along the fiber axis. The axial positions of the corresponding gratings in any two adjacent optical fibers are staggered by a preset distance, so that the gratings in n optical fibers form an interleaved sampling structure in space. The preset distance is less than the axial spacing, so that the equivalent spatial sampling spacing of the multi-fiber parallel grating array (1) is less than the spacing between any two adjacent gratings in a single optical fiber.

2. The multi-fiber parallel grating array as described in claim 1, characterized in that, A set of grating sensing equivalent measurement areas is formed between any two adjacent gratings on different optical fibers. The grating sensing equivalent measurement areas on each optical fiber are uniformly numbered according to their spatial position, forming equivalent measurement areas that are continuously distributed along the length of the optical fiber.

3. The multi-fiber parallel grating array as described in claim 1, characterized in that, The gratings inscribed in each optical fiber are weakly reflective fiber Bragg gratings. The axial misalignment distance of the corresponding gratings in any two adjacent optical fibers is a / n, and the equivalent spatial sampling spacing of the multi-fiber parallel grating array (1) is a / n.

4. A multi-fiber parallel grating array as described in claim 3, characterized in that, The multi-fiber parallel band grating array (1) includes a first fiber, a second fiber, a third fiber, ... and an nth fiber arranged in parallel. The specific arrangement of the multi-fiber parallel band grating array (1) is as follows: The first optical fiber is inscribed with the first grating at the starting position, and then the remaining gratings in the first optical fiber are inscribed sequentially at axial spacing a. The first grating in the second optical fiber is etched at position a / n, and then the remaining gratings in the second optical fiber are etched sequentially at axial spacing a. The first grating in the third optical fiber is etched at position 2a / n, and thereafter the remaining gratings in the third optical fiber are etched sequentially at axial spacing a. The first grating in the nth fiber is etched at position (n-1)×a / n, and thereafter the remaining gratings in the nth fiber are etched sequentially at axial spacing a.

5. The multi-fiber parallel grating array (1) as described in claim 1, characterized in that, The n optical fibers are fixed into a parallel structure by any one of the following methods: adhesive bonding, sleeve encapsulation, ribbon encapsulation, coating encapsulation, and composite material encapsulation, so as to maintain the stability of the relative spatial position between each optical fiber.

6. A fiber optic distributed vibration sensing system, characterized in that, The fiber-optic distributed vibration sensing system includes a narrow-linewidth laser (2), a 1×2 beam splitter (3), a modulation gain module (4), a multi-channel coherent detection module (5), and a multi-fiber parallel band grating array (1) as described in any one of claims 1-5, wherein, The narrow linewidth laser (2) is connected to the input end of the 1×2 beam splitter (3), and the narrow linewidth laser (2) is used to output continuous light; The 1×2 beam splitter (3) is connected to the modulation gain module (4) and the multi-channel coherent detection module (5) respectively. The 1×2 beam splitter (3) is used to split the continuous light into a first continuous light and a second continuous light. The first continuous light is input into the modulation gain module (4) as a probe light, and the second continuous light is directly input into the multi-channel coherent detection module (5) as a local oscillator light. The modulation gain module (4) is used to pulse modulate and power amplify the first continuous light to obtain pulse probe light, and inject the pulse probe light into multiple optical fibers in the multi-fiber grating array (1); The multi-channel coherent detection module (5) is connected to the multi-fiber parallel grating array (1). The multi-fiber parallel grating array (1) is used to receive pulse detection light from each channel and generate corresponding back reflection light under external vibration. The multi-channel coherent detection module (5) is used to perform coherent detection on the second continuous light and the back reflection light of each channel, and to complete the generation and output of multi-channel interference signals, so as to synchronously acquire and demodulate the vibration information of each channel in the multi-fiber parallel grating array (1).

7. The fiber optic distributed vibration sensing system as described in claim 6, characterized in that, The modulation gain module (4) includes an acousto-optic modulator (41), an erbium-doped fiber amplifier (42), and a multi-channel optical interface (43) connected in sequence. The acousto-optic modulator (41) is connected to the first output terminal of the 1×2 beam splitter (3) and the erbium-doped fiber amplifier (42) respectively. The acousto-optic modulator (41) is used to modulate the first continuous light into a pulse probe light with a preset pulse width and repetition frequency under the action of an external TTL pulse drive signal. The erbium-doped fiber amplifier (42) is connected to the multi-channel optical interface (43). The erbium-doped fiber amplifier (42) is used to amplify the pulse power of the pulse probe light. The multi-channel optical interface (43) is used to distribute the amplified pulse probe light according to the channel and inject it into the corresponding fiber in the multi-fiber grating array (1).

8. The fiber optic distributed vibration sensing system as described in claim 6, characterized in that, The multi-channel coherent detection module (5) includes multiple detection channels (51), each detection channel (51) including a circulator (511), a 2×2 beam splitter (512), a photodetector (513), and a signal processing device (514) connected in sequence. The first end of the circulator (511) is connected to the first end of the circulator (511) in the other detection channels (51), the third end of the circulator (511) is connected to the multi-fiber parallel grating array (1), and the second end of the circulator (511) is connected to the first input end of the 2×2 beam splitter (512). The second input terminal of the 2×2 beam splitter (512) is connected to the second output terminal of the 1×2 beam splitter (3). The 2×2 beam splitter (512) is used to combine the local oscillator light with the back-reflected light returned by the multi-fiber grating array (1) and perform coherent interference. The first and second output terminals of the 2×2 beam splitter (512) are both connected to the photodetector (513), which is used to perform photoelectric conversion on the interferometric optical signal to obtain a multi-channel interferometric electrical signal. The signal processing device (514) is connected to the photodetector (513). The signal processing device (514) is used to synchronously acquire the multi-channel interference electrical signal and output raw data for vibration event localization and demodulation.

9. The fiber optic distributed vibration sensing system as described in claim 7, characterized in that, The multi-fiber parallel grating array (1) is a four-fiber parallel grating array, and the multi-channel optical interface (43) includes four optical interfaces.

10. A fiber optic distributed vibration sensing method, implemented according to the fiber optic distributed vibration sensing system described in claim 6, characterized in that, The method includes: A continuous light is output from a narrow linewidth laser (2), and the continuous light is input to a 1×2 beam splitter (3). The continuous light is then split into a first continuous light and a second continuous light by the 1×2 beam splitter (3). The first continuous light is output as a probe light to the modulation gain module (4), and the second continuous light is output as a local oscillator light to the multi-channel coherent detection module (5). In the modulation gain module (4), the first continuous light is pulse-modulated and power-amplified to obtain pulse probe light, and the pulse probe light is injected into multiple optical fibers in the multi-fiber array (1); The multi-fiber parallel grating array (1) receives pulsed probe light from each channel. Under the action of external vibration, the gratings corresponding to each channel undergo refractive index and / or length changes, thereby forming back-reflected light carrying vibration information, and returning the back-reflected light to the multi-channel coherent detection module (5). In the multi-channel coherent detection module (5), the second continuous light, which serves as the local oscillator light, is coherently detected with the back-reflected light returned from each channel to obtain and output a multi-channel interference signal; The multi-channel interference signals are synchronously acquired and processed. Based on the misaligned distribution of multiple optical fibers in the multi-fiber parallel grating array (1), the interference signals of each channel are spatially registered and phase demodulated to obtain vibration information corresponding to each equivalent measurement area, so as to synchronously acquire and demodulate the vibration events of each channel in the multi-fiber parallel grating array (1).

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