Distributed optical fiber two-dimensional vector sensing system and method

Abstract

The invention discloses a distributed optical fiber two-dimensional vector sensing system and method, the system uses an acousto-optic modulator group and an optical circulator group to ask a plurality of fiber cores of a multi-core optical fiber in parallel, heterodyne coherent detection uses local oscillator light to improve the signal-to-noise ratio, and through the relation between the fiber core position difference and the direction angle of a two-dimensional sound wave in the aspect of algorithm, the two-dimensional sound wave direction angle is obtained. According to the space division multiplexing distributed optical fiber acoustic sensing system, a two-dimensional vector signal is accurately restored, the measurement vector angle range of the space division multiplexing distributed optical fiber acoustic sensing system for two-dimensional sound waves is 0-360 degrees, the vector sensing range is larger than 50 km and far exceeds that of an existing system, and the detection capacity of the distributed optical fiber acoustic sensing system is greatly improved.

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 by measuring the backscattered Rayleigh scattering signal, 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 fiber, 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 seismometer and other sensors, and cannot extract the direction of signal propagation to 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: 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: The laser output by the narrow linewidth continuous laser is split into two paths by the first fiber coupler, one of which is input into 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 to enter the multi-core fiber, and the other is input into the local oscillator light input end of the polarization diversity receiver; The signal emitting device sends an electric 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 the signal into the signal light input end of the polarization diversity receiver through the third fiber coupler; The radio frequency signal output end of the polarization diversity receiver is connected to the signal collecting and processing device.

[0005] Further, the acousto-optic modulator group includes a plurality of acousto-optic modulators, the center frequencies of the plurality of acousto-optic modulators are different, 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 emitting device.

[0006] Further, the signal emitting device sends a synchronous electric pulse signal to the plurality of acousto-optic modulators.

[0007] Further, the optical circulator group includes 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 core of the multi-core fiber through 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.

[0008] Further, it further 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 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.

[0009] Further, it further includes a first optical filter group and a second optical filter group, wherein: 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.

[0010] The second aspect of the present application provides a distributed optical fiber two-dimensional vector sensing method, which is applied to the distributed optical fiber two-dimensional vector sensing system, and the sensing method includes: sampling and processing, by the signal acquisition and processing device, the output signal of the polarization diversity receiver to obtain the line phase distribution of different cores of the multi-core optical fiber; According to the line phase distribution of different cores of the multi-core optical fiber, the strain of the line of different cores of the multi-core optical fiber is obtained. According to the strain of the line of different cores of the multi-core optical fiber, the distribution of the cores of the multi-core optical fiber, and the two-dimensional vector direction angle of the sound source to be solved, an equation is constructed for each core, and a super-equation set is obtained by integrating the equations corresponding to all cores. Solving the super-equation set, the two-dimensional vector direction angle of the sound source is obtained.

[0011] Further, the sampling and processing, by the signal acquisition and processing device, the output signal of the polarization diversity receiver to obtain the line phase distribution of different cores of the multi-core optical fiber, comprises: Sampling the output signal of the polarization diversity receiver to obtain a sampled signal; Digital filtering the sampled signal to obtain core signals of different cores; For each core signal, the complex amplitude of the core signal is obtained by a phase generation carrier algorithm; After the complex amplitudes of the core signals are sequentially subjected to spatial difference operation, phase initialization, and spatial sliding average, the preprocessed complex amplitudes are obtained. Taking the phase of the preprocessed complex amplitudes, the line phase distribution of different cores of the multi-core optical fiber is obtained.

[0012] Further, the digital filtering of the sampled signal comprises: Respectively taking the frequency shift frequency of a plurality of acousto-optic modulators as a center frequency to perform digital band-pass filtering to obtain core signals of different cores.

[0013] Further, the distribution of the cores of the multi-core optical fiber comprises the included angle between each core and the line connecting the middle point of the cross section of the multi-core optical fiber.

[0014] Compared with the prior art, the technical scheme of the present application has the following advantages: The distributed optical fiber two-dimensional vector sensing system provided by the present application uses an acousto-optic modulator group and an optical circulator group in parallel to interrogate a plurality of cores of a multi-core optical fiber from the hardware aspect, and uses heterodyne coherent detection and polarization diversity reception to improve the signal-to-noise ratio, and accurately restores the two-dimensional vector signal through the relationship between the core position difference and the direction angle of the two-dimensional sound wave from the algorithm aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic structural diagram of a distributed optical fiber two-dimensional vector sensing system provided by an embodiment of the present invention; Figure 2 A schematic diagram of a process flow of a distributed optical fiber two-dimensional vector sensing method provided by an embodiment of the present invention; Figure 3 A schematic diagram of a signal processing flow of a distributed optical fiber two-dimensional vector sensing method provided by an embodiment of the present invention; Figure 4 This is an example diagram of two-dimensional vector direction angle calculation provided by an embodiment of the present invention.

[0016] In the figure, 1 represents a narrow-linewidth continuous laser, 2 represents a first fiber coupler, 3 represents a second fiber coupler, 4 represents an acousto-optic modulator group, 5 represents a signal transmitting device, 6 represents a first erbium-doped fiber amplifier group, 7 represents a first optical filter group, 8 represents an optical circulator group, 9 represents a multi-core fiber fan-in device, 10 represents a third fiber coupler, 11 represents a second erbium-doped fiber amplifier group, 12 represents a second optical filter group, 13 represents a polarization diversity receiver, 14 represents a signal acquisition and processing device, and 15 represents a multi-core optical fiber. DETAILED DESCRIPTION

[0017] The accompanying drawings are for illustrative purposes only and are not to be construed as limiting this patent; In order to better illustrate this embodiment, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product size; It is understandable to those skilled in the art that some well-known structures and descriptions thereof may be omitted in the drawings.

[0018] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0019] Example 1 This embodiment provides a distributed optical fiber two-dimensional vector sensing system, such as Figure 1 As shown, it includes a narrow linewidth continuous 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 light output by the narrow linewidth continuous laser is divided into two paths by the first fiber coupler, one of which is input into 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, and the other is input into the local oscillator light input end of the polarization diversity receiver; 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 optical fiber through the multi-core fiber fan-in device, and inputs the signal to the signal light input end of the polarization diversity receiver through the third fiber coupler; The radio frequency signal output end of the polarization diversity receiver is connected to the signal acquisition and processing device.

[0020] In this embodiment, when the multi-core optical fiber is strained due to external vector acoustic waves, different cores have different responses to the same vector acoustic wave. By interrogating the multi-core optical fiber in parallel, the phase changes corresponding to different cores are demodulated, the response differences of the cores to the vector acoustic wave are obtained, and the cross-sectional geometric positions of the cores in the optical fiber are calculated, thereby realizing high-precision vector direction angle measurement of acoustic waves and improving the detection signal dimension of the distributed optical fiber acoustic wave sensing technology.

[0021] In a further embodiment, the acousto-optic modulator group includes a plurality of acousto-optic modulators, and each acousto-optic modulator has an optical input end connected to one of the output ends of the second fiber coupler and an electrical input end connected to the signal transmitting device.

[0022] In this embodiment, the acousto-optic modulator group includes a plurality of acousto-optic modulators, each of which has a different center frequency to achieve frequency division multiplexing. The different frequency light 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 different cores of the multi-core optical fiber, thereby achieving spatial division multiplexing and parallel interrogation.

[0023] In a further embodiment, the signal transmitting device sends synchronous electrical pulse signals to the plurality of acousto-optic modulators.

[0024] In a further embodiment, the optical circulator group includes a plurality of optical circulators, wherein each first port of the optical circulators receives an output of one of the acousto-optic modulators, each second port of the optical circulators is connected to a different core of the multi-core optical fiber through the multi-core fiber fan-in device, and each third port of the optical circulators is connected to one input end of the third fiber coupler.

[0025] In a further embodiment, a first erbium-doped fiber amplifier group and a second erbium-doped fiber amplifier group are further included, wherein: 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.

[0026] In a further embodiment, a first optical filter group and a second optical filter group are further included, wherein: 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.

[0027] Specifically, the working process of the distributed optical fiber two-dimensional vector sensing system provided in the embodiment is as follows: The output light of the narrow-linewidth continuous laser is split into two paths through a first optical fiber coupler, one of which is input into the polarization diversity receiver as a local oscillator light, and the other of which is split into multiple paths through a second optical fiber coupler and input into an acousto-optic modulator group, the signal sending device sends strictly synchronized electrical pulse signals to the multiple acousto-optic modulators in the acousto-optic modulator group, and the multiple two virtual lights are modulated into multiple light pulse signals with strict synchronization and different frequencies due to the different center frequencies of the acousto-optic modulators, the probe signal is input into the first ports of multiple optical circulators in the optical circulator group after power amplification by the first erbium-doped fiber amplifier group and filtering by the first optical filter group, the probe signal is output from the second ports of the multiple optical circulators in the optical circulator group, enters the to-be-detected multi-core optical fiber through a multi-core fiber fan-in device, and generates Rayleigh scattering signals in the back transmission at different positions along the to-be-detected multi-core optical fiber, the probe signal is input into the polarization diversity receiver after optical power amplification by the second erbium-doped fiber amplifier and filtering by the second optical filter, the signal light and the local oscillator light interfere in the polarization diversity receiver and are converted into electrical signals, and the electrical signals are collected and processed by the signal collection and processing device.

[0028] Another embodiment of the application provides a distributed optical fiber two-dimensional vector sensing method, which is applied to the distributed optical fiber two-dimensional vector sensing system. Figure 2 As shown in the figure, the sensing method comprises the following steps: The output signals of the polarization diversity receiver are sampled and processed by the signal collection and processing device to obtain the phase distribution along the line of different cores of the multi-core optical fiber. According to the phase distribution along the line of different cores of the multi-core optical fiber, the strain of the different cores of the multi-core optical fiber along the line is obtained. According to the strain of the different cores of the multi-core optical fiber along the line, the distribution of the cores of the multi-core optical fiber, and the two-dimensional vector direction angle of the sound source to be solved, an equation is constructed for each core, and a super-determined equation group is obtained by integrating all the equations corresponding to the cores. The super-determined equation group is solved to obtain the two-dimensional vector direction angle of the sound source.

[0029] In this embodiment, the strain of different cores is approximately linearly related to the distance from the sound source, and the multi-core optical fiber is interrogated in parallel, and the strain difference between the cores changes with the distribution of the direction angle of the sound source on the plane of the optical fiber cross section, as shown in Figure 4 The distance difference of the sound source of the core is the difference of the bending radius of the different cores, and the bending length of the core caused by the modulation of the sound wave can be obtained by the arc length and the bending radius , the diffusion angle of the sound wave The relationship is obtained, and the strain measured by the above spatially multiplexed distributed optical fiber acoustic sensing system is linearly related to the arc length , assuming that the diffusion angle of the sound wave is fixed, the bending radius can be mapped by the strain , the connecting line between each core and the middle point, and the included angle between the connecting lines corresponding to each core , the included angle can express the bending radius relationship of different cores by geometry For example , wherein is the diameter of the optical fiber cross section, the strain amplitude measured by each core is , and the actual two-dimensional vector direction angle of the sound source to be solved is , then the corresponding included angle of the multi-core optical fiber core is , the strain amplitude is , and the solved direction angle is , which can form n equations , and the number of n is determined by the number of cores of the multi-core optical fiber interrogated by the above spatially multiplexed distributed optical fiber acoustic sensing system. This overdetermined equation set can be solved by the least squares method to obtain the two-dimensional vector direction angle .

[0030] In a further embodiment, the sampling and processing of the output signal of the polarization diversity receiver by the signal acquisition and processing device to obtain the along-line phase distribution of different cores of the multi-core optical fiber includes: Figure 3 As shown in , the sampling of the output signal of the polarization diversity receiver to obtain a sampled signal; Digital filtering of the sampled signal to obtain core signals of different cores; For each core signal, the complex amplitude of the core signal is obtained by a phase generation carrier algorithm; After spatial difference operation, phase initialization, and spatial sliding average are sequentially performed on the complex amplitude of the core signal, a preprocessed complex amplitude is obtained; The pre-processed complex amplitudes are de-phased to obtain the phase distribution along the line of different cores of the multi-core fiber.

[0031] In a further embodiment, after obtaining the phase distribution along the line of different cores of the multi-core fiber, based on the linear relationship between the phase and the strain of the fiber, the data of the strain along the line of the fiber changing with time can be obtained.

[0032] In a further embodiment, the digital filtering of the sampling signal comprises: The frequency shift frequency of each of the plurality of acousto-optic modulators is taken as the center frequency for digital band-pass filtering, and the core signals of different cores are obtained.

[0033] In a further embodiment, the distribution of the cores of the multi-core fiber comprises the included angle between each core and the line connecting the middle points of the cross section of the multi-core fiber.

[0034] In a further embodiment, the phase generation carrier algorithm is that two mutually orthogonal cosine signals with equal frequency and center frequency are multiplied as the real part and the imaginary part respectively to obtain the complex amplitude of the signal component.

[0035] The same or similar reference signs correspond to the same or similar components; The terms describing the positional relationship in the drawings are only used for illustrative description, and should not be understood as a limitation on the patent; Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the implementation modes of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the implementation modes are not required or can not be exhausted. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the claims of the present application.

Claims

1. A distributed optical fiber two-dimensional vector sensing system, characterized in that: The device comprises a narrow linewidth continuous 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 light output by the narrow linewidth continuous laser is divided into two paths by the first fiber coupler, one of which is input into 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, and the other is input into the local oscillator light input end of the polarization diversity receiver; The signal transmitting device sends an electrical pulse signal to the acousto-optic modulator group; The optical circulator group receives the Rayleigh scattered signal transmitted by the multi-core optical fiber through the multi-core optical fiber fan-in device, and inputs the signal to the signal light input end of the polarization diversity receiver through the third optical fiber coupler; The radio frequency signal output end of the polarization diversity receiver is connected to the signal acquisition and processing device.

2. The distributed optical fiber two-dimensional vector sensing system according to claim 1, characterized in that: The AOM group includes a plurality of AOMs, each having a different center frequency. The optical input end of each AOM is connected to one of the output ends of the second fiber coupler, and the electrical input end of each AOM is connected to the signal transmitting device.

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

4. The distributed optical fiber two-dimensional vector sensing system according to claim 2, characterized in that: The optical circulator group includes multiple 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 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 an input end of the third optical fiber coupler.

5. The distributed optical fiber two-dimensional vector sensing system according to any one of claims 1 to 4, 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 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.

6. The distributed optical fiber two-dimensional vector sensing system according to claim 5, characterized in that: Also included are a first optical filter group and a second optical filter group, wherein: 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.

7. A distributed optical fiber two-dimensional vector sensing method, characterized in that: The sensing method is applied to the distributed optical fiber two-dimensional vector sensing system according to any one of claims 1 to 6, and the sensing method comprises: The signal acquisition and processing device samples the output signal of the polarization diversity receiver to obtain the phase distribution along the different cores of the multi-core optical fiber; Obtaining strain along different cores of the multi-core optical fiber according to the phase distribution along different cores of the multi-core optical fiber; According to the strain along different cores of the multi-core optical fiber, the distribution of the cores of the multi-core optical fiber, and the two-dimensional vector direction angle of the sound source to be determined, an equation is constructed for each core, and the equations corresponding to all cores are integrated to obtain an overdetermined system of equations; The overdetermined set of equations is solved to obtain the two-dimensional vector direction angle of the sound source.

8. The distributed optical fiber two-dimensional vector sensing method according to claim 7, characterized in that: The sampling and processing of the output signal of the polarization diversity receiver by the signal acquisition and processing device to obtain the phase distribution along different cores of the multi-core optical fiber includes: Sampling the output signal of the polarization diversity receiver to obtain a sampled signal; Digitally filtering the sampled signal to obtain core signals of different fiber cores; For each fiber core signal, the complex amplitude of the fiber core signal is obtained by using the phase generation carrier algorithm; performing spatial difference operation, phase initialization, and spatial sliding average on the complex amplitude of the core signal in sequence to obtain a preprocessed complex amplitude; The preprocessed complex amplitude is dephased to obtain phase distribution along different cores of the multi-core optical fiber.

9. The distributed optical fiber two-dimensional vector sensing method according to claim 8, characterized in that: Performing digital filtering on the sampled signal, comprising: Digital bandpass filtering is performed using the frequency shift frequencies of the multiple acousto-optic modulators as center frequencies to obtain core signals of different fiber cores.

10. The distributed optical fiber two-dimensional vector sensing method according to claim 7, characterized in that: The distribution of the cores of the multi-core optical fiber includes the angle between each core and the line connecting the middle point of the cross section of the multi-core optical fiber.

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