A distributed optical fiber two-dimensional vector sensing system and method

Abstract

The application discloses a kind of distributed optical fiber two-dimensional vector sensing system and method, system uses acoustooptic modulator group, optical circulator group parallel inquiry multiple-core optical fiber multiple cores, heterodyne coherent detection utilizes local light to improve signal-to-noise ratio, accurately restores two-dimensional vector signal by the difference of core position and the direction angle relationship of two-dimensional sound wave in algorithm, the measurement vector angle range of the distributed optical fiber acoustic sensing system of the space division multiplexing two-dimensional sound wave is 0~360 Entire coverage, and vector sensing range is greater than 50 km far exceeds existing system, greatly improve the detection capability of distributed optical fiber acoustic sensing system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber communication and sensing technology, and more particularly, to a distributed optical fiber two-dimensional vector sensing system and method. BACKGROUND

[0002] Distributed optical fiber acoustic sensing technology is a technology that uses backscattered Rayleigh scattering light generated by light transmission in an optical fiber to realize distributed sensing by using the optical fiber as a continuous long-distance sensor. Compared with traditional single-point sensors, distributed optical fiber acoustic sensing technology can realize large-scale distributed array sensing, thereby providing higher-density sensing information and providing a low-cost and reliable sensing technical means for monitoring and analyzing various events. In distributed optical fiber acoustic sensing technology, Phase-sensitive Optical Time-Domain Reflectometry (phi-OTDR) based on phase sensitivity can realize large-scale sensing while restoring the acoustic signal waveform with high sensitivity, and therefore becomes the most suitable distributed acoustic sensing technology for dynamic acoustic signal. However, due to the one-dimensional distribution of the sensing array of ordinary single-core single-mode optical fibers, the distributed sensing system can only sense the content of the acoustic signal on a single channel and cannot sense complex signal information such as direction and polarization. The limitation of information dimensionality results in that the distributed acoustic sensing technology cannot realize high-dimensional signal sensing like a seafloor geophone, extract the direction of signal propagation, and have stronger analysis capability for complex events, such as restoring geological structure information through vector seismic wave signals. Therefore, a two-dimensional vector sensing distributed optical fiber acoustic sensing system is proposed, which can realize two-dimensional vector sensing on the entire optical fiber to improve the detection dimension of the traditional distributed optical fiber acoustic sensing system. However, the detection direction angle of the existing two-dimensional vector sensing distributed optical fiber acoustic sensing system is limited to 0~180°, and the detection range is less than 200 meters, which greatly limits the application of the technology. SUMMARY

[0003] One of the purposes of the present application is to provide a distributed optical fiber two-dimensional vector sensing system to solve the technical problem of the limited detection direction angle of the existing two-dimensional vector sensing distributed optical fiber acoustic sensing system. The second purpose of the present application is to provide a distributed optical fiber two-dimensional vector sensing method.

[0004] To solve the above technical problems, the technical solutions of the present application are as follows:

[0005] The first aspect of the present application provides a distributed optical fiber two-dimensional vector sensing system, which comprises a narrow linewidth continuous laser, a first optical fiber coupler, a second optical fiber coupler, an acoustic-optic modulator group, a signal transmitting device, an optical circulator group, a multi-core fiber fan-in device, a multi-core fiber, a third optical fiber coupler, a polarization diversity receiver, and a signal acquisition and processing device, wherein:

[0006] The laser outputted by the narrow linewidth continuous laser is divided into two paths by the first fiber coupler, one of which is inputted into the second fiber coupler, and then sequentially inputted into the multi-core fiber via the acousto-optic modulator group, the optical circulator group and the multi-core fiber fan-in device, and the other of which is inputted into the local oscillator input end of the polarization diversity receiver;

[0007] The signal transmitting device transmits electrical pulse signals to the acousto-optic modulator group;

[0008] The optical circulator group receives Rayleigh scattering signals transmitted by the multi-core fiber via the multi-core fiber fan-in device, and inputs the signals into the signal light input end of the polarization diversity receiver via the third fiber coupler;

[0009] The radio frequency signal output end of the polarization diversity receiver is connected to the signal collecting and processing device.

[0010] Further, the acousto-optic modulator group comprises a plurality of acousto-optic modulators, the center frequencies of the plurality of acousto-optic modulators are different from each other, the optical input end of each acousto-optic modulator is connected to one of the output ends of the second fiber coupler, and the point input end of each acousto-optic modulator is connected to the signal transmitting device.

[0011] Further, the signal transmitting device transmits synchronous electrical pulse signals to the plurality of acousto-optic modulators.

[0012] Further, the optical circulator group comprises a plurality of optical circulators, wherein the first port of each optical circulator receives the output of one acousto-optic modulator, the second port of each optical circulator is connected to a different fiber core of the multi-core fiber via the multi-core fiber fan-in device, and the third port of each optical circulator is connected to one input end of the third fiber coupler.

[0013] Further, it further comprises a first erbium-doped fiber amplifier group and a second erbium-doped fiber amplifier group, wherein:

[0014] The first erbium-doped fiber amplifier group is arranged between the acousto-optic modulator group and the optical circulator group, and the second erbium-doped fiber amplifier group is arranged between the optical circulator group and the polarization diversity receiver.

[0015] Further, it further comprises a first optical filter group and a second optical filter group, wherein:

[0016] The first optical filter group is arranged between the first erbium-doped fiber amplifier group and the optical circulator group, and the second optical filter group is arranged between the second erbium-doped fiber amplifier group and the polarization diversity receiver.

[0017] A second aspect of the present invention provides a distributed optical fiber two-dimensional vector sensing method, the sensing method being applied to the aforementioned distributed optical fiber two-dimensional vector sensing system, the sensing method comprising:

[0018] The output signal of the polarization diversity receiver is sampled and processed by the signal acquisition and processing device to obtain the phase distribution along the line of different cores of the multi-core optical fiber.

[0019] Based on the phase distribution along the line of different cores of the multi-core optical fiber, the strain along the line of different cores of the multi-core optical fiber is obtained;

[0020] Based on the strain along different cores of the multi-core optical fiber, the distribution of the multi-core optical fiber cores, and the direction angle of the two-dimensional vector of the sound source to be determined, an equation is constructed for each core, and the equations corresponding to all cores are combined to obtain an overdetermined set of equations.

[0021] Solving the overdetermined system of equations yields the two-dimensional vector direction angle of the sound source.

[0022] Furthermore, the step of sampling and processing the output signal of the polarization diversity receiver through the signal acquisition and processing device to obtain the phase distribution along the line of different cores of the multi-core optical fiber includes:

[0023] The output signal of the polarization diversity receiver is sampled to obtain a sampled signal;

[0024] The sampled signal is digitally filtered to obtain the fiber core signals of different fiber cores;

[0025] For each fiber core signal, the complex amplitude of the fiber core signal is obtained through a phase-generated carrier algorithm;

[0026] After performing spatial difference operation, phase initialization, and spatial moving average on the complex amplitude of the fiber core signal, the preprocessed complex amplitude is obtained.

[0027] The phase of the preprocessed complex amplitude is taken to obtain the phase distribution along the line of different cores of the multi-core optical fiber.

[0028] Furthermore, digital filtering is performed on the sampled signal, including:

[0029] Digital bandpass filtering is performed using the frequency shifting frequencies of the multiple acousto-optic modulators as the center frequency to obtain fiber core signals for different fiber cores.

[0030] Furthermore, the distribution of the multi-core optical fiber cores includes the angle between each core and the line connecting the midpoint of the cross-section of the multi-core optical fiber.

[0031] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0032] Compared to existing technologies, the distributed fiber optic two-dimensional vector sensing system provided by this invention utilizes an acousto-optic modulator group and an optical circulator group to poll multiple cores of a multi-core optical fiber in parallel. Heterodyne coherent detection and polarization diversity reception improve the signal-to-noise ratio. Algorithmically, it accurately reconstructs the two-dimensional vector signal by analyzing the relationship between the core position differences and the directional angle of the two-dimensional sound wave. The spatially multiplexed distributed fiber optic acoustic sensing system provides full coverage of the measurement vector angle range of the two-dimensional sound wave from 0 to 360°, and its vector sensing range is greater than 50 km, far exceeding that of existing systems, significantly improving the detection capability of the distributed fiber optic acoustic sensing system. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of a distributed optical fiber two-dimensional vector sensing system provided in an embodiment of the present invention;

[0034] Figure 2 A flowchart illustrating a distributed optical fiber two-dimensional vector sensing method provided in an embodiment of the present invention;

[0035] Figure 3 This is a schematic diagram of the signal processing flow of a distributed optical fiber two-dimensional vector sensing method provided in an embodiment of the present invention;

[0036] Figure 4 This is an example diagram for calculating the two-dimensional vector direction angle provided in an embodiment of the present invention.

[0037] In the figure, 1 represents a narrow linewidth continuous laser, 2 represents the first fiber coupler, 3 represents the second fiber coupler, 4 represents an acousto-optic modulator group, 5 represents a signal transmitting device, 6 represents the first erbium-doped fiber amplifier group, 7 represents the first optical filter group, 8 represents the optical circulator group, 9 represents a multi-core fiber fan-in device, 10 represents the third fiber coupler, 11 represents the second erbium-doped fiber amplifier group, 12 represents the second optical filter group, 13 represents a polarization diversity receiver, 14 represents a signal acquisition and processing device, and 15 represents a multi-core fiber. Detailed Implementation

[0038] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent.

[0039] To better illustrate this embodiment, some parts in the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions;

[0040] It will be understood by those skilled in the art that certain well-known structures and their descriptions may be omitted in the accompanying drawings.

[0041] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0042] Example 1

[0043] This embodiment provides a distributed fiber optic two-dimensional vector sensing system, such as Figure 1 As shown, it includes a narrow-linewidth continuous-wave laser, a first fiber coupler, a second fiber coupler, an acousto-optic modulator group, a signal transmitting device, an optical circulator group, a multi-core fiber fan-in device, a multi-core fiber, a third fiber coupler, a polarization diversity receiver, and a signal acquisition and processing device, wherein:

[0044] The laser output from the narrow linewidth continuous laser is split into two paths by the first fiber coupler. One path is input to the second fiber coupler and then sequentially passes through the acousto-optic modulator group, the optical circulator group, and the multi-core fiber fan-in device before entering the multi-core fiber. The other path is input to the local oscillator input terminal of the polarization diversity receiver.

[0045] The signal transmitting device sends an electrical pulse signal to the acousto-optic modulator group;

[0046] The optical circulator group receives the Rayleigh scattering signal transmitted by the multi-core fiber through the multi-core fiber fan-in device, and inputs it to the signal optical input terminal of the polarization diversity receiver through the third fiber coupler.

[0047] The radio frequency signal output terminal of the polarization diversity receiver is connected to the signal acquisition and processing device.

[0048] In this embodiment, when a multi-core optical fiber is strained by an external vector acoustic wave, different cores respond differently to the same vector acoustic wave. By polling the multi-core optical fiber in parallel, the phase changes corresponding to different cores are demodulated to obtain the difference in the response of the cores to the vector acoustic wave. The calculation is then performed based on the geometric position of the core in the cross-section of the optical fiber, thereby achieving high-precision vector direction angle measurement of the acoustic wave and improving the detection signal dimension of distributed optical fiber acoustic wave sensing technology.

[0049] In a further embodiment, the acousto-optic modulator group includes a plurality of acousto-optic modulators, the optical input terminal of each acousto-optic modulator being connected to one of the output terminals of a second optical fiber coupler, and the electrical input terminal of each acousto-optic modulator being connected to the signal transmitting device.

[0050] In this embodiment, the acousto-optic modulator group includes multiple acousto-optic modulators, each with a different center frequency, to achieve frequency division multiplexing. The light of different frequencies modulated by the acousto-optic modulator group passes through the first erbium-doped fiber amplifier group, the first optical filter group, the optical circulator group, and the multi-core fiber fan-in device to connect to different cores of the multi-core fiber under test, thereby achieving parallel interrogation by space division multiplexing.

[0051] In a further embodiment, the signal transmitting device sends synchronized electrical pulse signals to the plurality of acousto-optic modulators.

[0052] In a further embodiment, the optical circulator group includes a plurality of optical circulators, wherein a first port of each optical circulator receives the output of an acousto-optic modulator, a second port of each optical circulator is connected to different cores of the multi-core optical fiber through the multi-core optical fiber fan-in device, and a third port of each optical circulator is connected to an input end of the third optical fiber coupler.

[0053] In a further embodiment, it also includes a first erbium-doped fiber amplifier group and a second erbium-doped fiber amplifier group, wherein:

[0054] The first erbium-doped fiber amplifier group is disposed between the acousto-optic modulator group and the optical circulator group, and the second erbium-doped fiber amplifier group is disposed between the optical circulator group and the polarization diversity receiver.

[0055] In a further embodiment, a first optical filter bank and a second optical filter bank are also included, wherein:

[0056] The first optical filter group is disposed between the first erbium-doped fiber amplifier group and the optical circulator group, and the second optical filter group is disposed between the second erbium-doped fiber amplifier group and the polarization diversity receiver.

[0057] Specifically, the working process of the distributed fiber optic two-dimensional vector sensing system provided in this embodiment is as follows:

[0058] The output light of the narrow-linewidth continuous-wave laser is split into two paths by a first fiber coupler. One path serves as the system's local oscillator input polarization diversity receiver; the other path is split into multiple continuous-wave inputs to an acousto-optic modulator group by a second fiber coupler. A signal transmitting device sends strictly synchronized electrical pulse signals to multiple acousto-optic modulators in the group. Because the center frequencies of the acousto-optic modulators are different, the multiple virtual beams are modulated into multiple strictly synchronized optical pulse signals with different frequencies. The detection signal is amplified by a first erbium-doped fiber amplifier group and filtered by a first optical filter group before entering the first ports of multiple optical circulators in the optical circulator group. The detection signal exits from the optical circulator... The outputs from the second ports of multiple optical circulators in the circulator group are fed into the multi-core fiber under test through a multi-core fiber fan-in device. The probe signal generates Rayleigh scattering signals that propagate backward along the multi-core fiber under test. These signals are then transmitted back through the multi-core fiber to the second ports of each optical circulator in the circulator group, and output from the third ports of each optical circulator in the circulator group. The signals are then combined through a third optical coupler, amplified by a second erbium-doped fiber amplifier, filtered by a second optical filter, and fed into a polarization diversity receiver. The signal light and the local oscillator light interfere with each other in the polarization diversity receiver and are converted into electrical signals, which are then acquired and processed by a signal acquisition and processing device.

[0059] Another embodiment of the present invention provides a distributed optical fiber two-dimensional vector sensing method, wherein the sensing method is applied to the aforementioned distributed optical fiber two-dimensional vector sensing system, such as... Figure 2 As shown, the sensing method includes:

[0060] The output signal of the polarization diversity receiver is sampled and processed by the signal acquisition and processing device to obtain the phase distribution along the line of different cores of the multi-core optical fiber.

[0061] Based on the phase distribution along the line of different cores of the multi-core optical fiber, the strain along the line of different cores of the multi-core optical fiber is obtained;

[0062] Based on the strain along different cores of the multi-core optical fiber, the distribution of the multi-core optical fiber cores, and the direction angle of the two-dimensional vector of the sound source to be determined, an equation is constructed for each core, and the equations corresponding to all cores are combined to obtain an overdetermined set of equations.

[0063] Solving the overdetermined system of equations yields the two-dimensional vector direction angle of the sound source.

[0064] In this embodiment, based on the approximate linear correlation between the strain of different fiber cores and the distance to the sound source, multi-core optical fibers are polled in parallel. The strain difference relationship between the fiber cores varies with the angular distribution of the sound source on the fiber cross-sectional plane. Figure 4 As shown, the distance difference between the sound sources in the fiber core is the difference in bending radius between different fiber cores. The bending length of the fiber core caused by sound wave modulation can be expressed in arc length. With bending radius The diffusion angle of sound waves Relationship The strain and radian length measured by the aforementioned spatially multiplexed distributed fiber optic acoustic sensing system are obtained. The relationship is linear, assuming the sound wave diffusion angle If fixed, it can be determined through the dependent variable. Relationship mapping bending radius The lines connecting each fiber core to the midpoint, and the lines connecting each corresponding fiber core, have an included angle. The included angle The relationship between the bending radii of different fiber cores can be expressed geometrically. For example in Where is the cross-sectional diameter of the optical fiber, and the amplitude of strain measured for each fiber core is . The actual direction angle of the two-dimensional vector of the sound source to be determined is... The included angle of the corresponding connecting lines of the multi-core optical fiber cores The amplitude of the dependent variable is The required direction angle This can form n equations. The number of 'n' is determined by the number of cores in the multi-core optical fiber used for parallel interrogation in the aforementioned space-division multiplexed distributed optical fiber acoustic sensing system. This overdetermined system of equations can be solved using the least squares method to obtain the two-dimensional vector direction angle. .

[0065] In a further embodiment, the output signal of the polarization diversity receiver is sampled and processed by the signal acquisition and processing device to obtain the phase distribution along the line of different cores of the multi-core optical fiber, such as... Figure 3 As shown, it includes:

[0066] The output signal of the polarization diversity receiver is sampled to obtain a sampled signal;

[0067] The sampled signal is digitally filtered to obtain the fiber core signals of different fiber cores;

[0068] For each fiber core signal, the complex amplitude of the fiber core signal is obtained through a phase-generated carrier algorithm;

[0069] After performing spatial difference operation, phase initialization, and spatial moving average on the complex amplitude of the fiber core signal, the preprocessed complex amplitude is obtained.

[0070] The phase distribution along the line of different cores of the multi-core optical fiber is obtained by dephase the preprocessed complex amplitude.

[0071] In a further embodiment, after obtaining the phase distribution along the line of different cores of the multi-core optical fiber, data on the change of strain along the optical fiber over time can be obtained based on the linear relationship between the phase and the strain on the optical fiber.

[0072] In a further embodiment, digital filtering of the sampled signal includes:

[0073] Digital bandpass filtering is performed using the frequency shifting frequencies of the multiple acousto-optic modulators as the center frequency to obtain fiber core signals for different fiber cores.

[0074] In a further embodiment, the distribution of the multi-core optical fiber cores includes the angle between each core and the line connecting the midpoint of the cross-section of the multi-core optical fiber.

[0075] In a further embodiment, the phase-generating carrier algorithm multiplies the signal component by two mutually orthogonal cosine signals with frequencies equal to and equal to its center frequency, respectively, as the real and imaginary parts, to obtain the complex amplitude of the signal component.

[0076] The same or similar labels correspond to the same or similar parts;

[0077] The terms used to describe positional relationships in the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent.

[0078] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A distributed fiber optic two-dimensional vector sensing system, characterized in that, It includes a narrow-linewidth continuous-wave laser, a first fiber coupler, a second fiber coupler, an acousto-optic modulator group, a signal transmitting device, an optical circulator group, a multi-core fiber fan-in device, a multi-core fiber, a third fiber coupler, a polarization diversity receiver, and a signal acquisition and processing device, wherein: The laser output from the narrow linewidth continuous laser is split into two paths by the first fiber coupler. One path is input to the second fiber coupler and then sequentially passes through the acousto-optic modulator group, the optical circulator group, and the multi-core fiber fan-in device into the multi-core fiber. The other path is input to the local oscillator input terminal of the polarization diversity receiver. The multi-core fiber includes at least three fiber cores. The signal transmitting device sends an electrical pulse signal to the acousto-optic modulator group; The optical circulator group receives the Rayleigh scattering signal transmitted by the multi-core fiber through the multi-core fiber fan-in device, and inputs it to the signal optical input terminal of the polarization diversity receiver through the third fiber coupler. The radio frequency signal output terminal of the polarization diversity receiver is connected to the signal acquisition and processing device, which is configured to obtain the two-dimensional vector direction angle of the sound source based on the strain of the multi-core optical fiber. The acousto-optic modulator group includes multiple acousto-optic modulators, each with a different center frequency. The optical input terminal of each acousto-optic modulator is connected to one of the output terminals of a second fiber optic coupler, and the electrical input terminal of each acousto-optic modulator is connected to the signal transmitting device. The optical circulator group includes multiple optical circulators, wherein the first port of each optical circulator receives the output of an acousto-optic modulator, the second port of each optical circulator is connected to different cores of the multi-core optical fiber through the multi-core optical fiber fan-in device, and the third port of each optical circulator is connected to one input end of the third optical fiber coupler.

2. The distributed fiber optic two-dimensional vector sensing system according to claim 1, characterized in that, The signal transmitting device sends synchronized electrical pulse signals to the plurality of acousto-optic modulators.

3. The distributed fiber optic two-dimensional vector sensing system according to claim 1 or 2, characterized in that, It also includes a first erbium-doped fiber amplifier group and a second erbium-doped fiber amplifier group, wherein: The first erbium-doped fiber amplifier group is disposed between the acousto-optic modulator group and the optical circulator group, and the second erbium-doped fiber amplifier group is disposed between the optical circulator group and the polarization diversity receiver.

4. The distributed fiber optic two-dimensional vector sensing system according to claim 3, characterized in that, It also includes a first optical filter bank and a second optical filter bank, wherein: The first optical filter group is disposed between the first erbium-doped fiber amplifier group and the optical circulator group, and the second optical filter group is disposed between the second erbium-doped fiber amplifier group and the polarization diversity receiver.

5. A distributed optical fiber two-dimensional vector sensing method, characterized in that, The sensing method is applied to the distributed fiber optic two-dimensional vector sensing system according to any one of claims 1 to 4, and the sensing method includes: The output signal of the polarization diversity receiver is sampled and processed by the signal acquisition and processing device to obtain the phase distribution along the line of different cores of the multi-core optical fiber. Based on the phase distribution along the line of different cores of the multi-core optical fiber, the strain along the line of different cores of the multi-core optical fiber is obtained; Based on the strain along different cores of the multi-core optical fiber, the distribution of the multi-core optical fiber cores, and the direction angle of the two-dimensional vector of the sound source to be determined, an equation is constructed for each core, and the equations corresponding to all cores are combined to obtain an overdetermined set of equations. Solving the overdetermined system of equations yields the two-dimensional vector direction angle of the sound source. The distribution of the multi-core optical fiber cores includes the angle between each core and the line connecting the midpoint of the cross-section of the multi-core optical fiber.

6. The distributed optical fiber two-dimensional vector sensing method according to claim 5, characterized in that, The step of sampling and processing the output signal of the polarization diversity receiver through the signal acquisition and processing device to obtain the phase distribution along the line of different cores of the multi-core optical fiber includes: The output signal of the polarization diversity receiver is sampled to obtain a sampled signal; The sampled signal is digitally filtered to obtain the fiber core signals of different fiber cores; For each fiber core signal, the complex amplitude of the fiber core signal is obtained through a phase-generated carrier algorithm; After performing spatial difference operation, phase initialization, and spatial moving average on the complex amplitude of the fiber core signal, the preprocessed complex amplitude is obtained. The phase distribution along the line of different cores of the multi-core optical fiber is obtained by dephase the preprocessed complex amplitude.

7. The distributed optical fiber two-dimensional vector sensing method according to claim 6, characterized in that, Digital filtering of the sampled signal includes: Digital bandpass filtering is performed using the frequency shifting frequencies of the multiple acousto-optic modulators as the center frequency to obtain fiber core signals for different fiber cores.

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