Distributed acoustic sensing system and demodulation method thereof

Abstract

The application provides a distributed acoustic wave sensing system and a demodulation method thereof. The distributed acoustic wave sensing system comprises a laser, an optical modulation device, an optical fiber, an unbalanced interference device, a balanced photodetector and a signal processor. The optical modulation device is used for receiving laser light, modulating the laser light into chirp frequency pulse light and amplifying and outputting the chirp frequency pulse light. The optical fiber comprises a plurality of scattering enhancement points, which are used for receiving the amplified chirp frequency pulse light and outputting reflected light of the scattering enhancement points. The unbalanced interference device comprises two interference elements with an arm length difference, and interference spectra of the two scattering enhancement points are formed by using the time delay of the two interference elements. The balanced photodetector is used for converting the interference spectra of the two scattering enhancement points formed by the reflected light of the two scattering enhancement points into corresponding electrical signals. The signal processor is used for collecting the electrical signals and analyzing and demodulating the electrical signals to output acoustic wave information. The acoustic wave sensing with a large dynamic range is realized.

Description

Technical Field

[0001] This application relates to the field of fiber optic sensing technology, and in particular to a distributed acoustic wave sensing system and its demodulation method. Background Technology

[0002] Distributed fiber optic acoustic sensing systems have gained widespread attention in fields such as structural health monitoring, perimeter security, underwater acoustic detection, and resource exploration due to their advantages of numerous components, long sensing distance, and high sensitivity. By analyzing the backscattered light information of the probe pulse in the fiber under test, the sensing and localization of external sound waves can be achieved. In distributed sensing systems based on phase demodulation, there is a linear correspondence between the demodulated phase and the amplitude of the acoustic signal. Changes in the demodulated phase can effectively reflect changes in the sound wave, thus distributed acoustic sensing technology based on phase demodulation has been widely applied. However, the dynamic range of distributed acoustic sensing systems is limited in these technologies. Summary of the Invention

[0003] This application provides a distributed acoustic wave sensing system with an ultra-large dynamic range and a demodulation method thereof.

[0004] This application provides a distributed acoustic wave sensing system, including:

[0005] Laser, used to generate laser light;

[0006] An optical modulation device is connected to the laser, which receives the laser light, modulates the laser light into chirped frequency pulses, and amplifies and outputs them.

[0007] An optical fiber includes a plurality of scattering enhancement points, wherein there is a gap between every two scattering enhancement points; the optical fiber is used to receive amplified chirped frequency pulse light and output reflected light from the scattering enhancement points;

[0008] An unbalanced interferometer includes two interferometer elements with a difference in arm length, both of which are connected to the optical fiber. The two interferometer elements are respectively used to receive the reflected light at the scattering enhancement point, and the delay of the two interferometer elements is used to form the interference spectrum of the two scattering enhancement points.

[0009] A balanced photodetector is connected to the unbalanced interferometer; the balanced photodetector is used to convert the interference spectrum of the two scattering enhancement points formed by the reflected light at the two scattering enhancement points into corresponding electrical signals; and

[0010] A signal processor is connected to the balanced photodetector. The signal processor is used to acquire the electrical signal and analyze and demodulate the electrical signal to output acoustic wave information.

[0011] Optionally, the optical modulation device includes at least:

[0012] An acousto-optic modulator is connected to the laser; the acousto-optic modulator is used to receive the laser and modulate the laser into pulsed light.

[0013] An electro-optic modulator is connected to the acousto-optic modulator; the electro-optic modulator is used to receive the pulsed light and modulate the pulsed light into chirped frequency pulsed light;

[0014] An optical amplifier, connected to the electro-optic modulator, is used to receive the chirped frequency pulse light, amplify the chirped frequency pulse light, and output it.

[0015] Optionally, the pulse width of the pulsed light is less than the interval between two adjacent scattering enhancement points.

[0016] Optionally, the distributed acoustic wave sensing system further includes a first circulator, comprising a first transmission channel and a second transmission channel that are isolated from each other. The optical modulation device is connected to the optical fiber through the first transmission channel, and the optical fiber is connected to the unbalanced interferometer through the second transmission channel.

[0017] Optionally, the first circulator includes a first port, a second port, and a third port, wherein the first port and the second port are connected to form the first transmission channel, and the second port and the third port are connected to form the second transmission channel.

[0018] Optionally, the distributed acoustic wave sensing system further includes a second circulator, comprising a mutually isolated third transmission channel and a fourth transmission channel. The optical fiber is connected to the unbalanced interferometer in sequence through the second transmission channel and the third transmission channel. The unbalanced interferometer is connected to the balanced photodetector at least through the fourth transmission channel.

[0019] Optionally, the second circulator includes a fourth port, a fifth port, and a sixth port, wherein the fourth port and the fifth port are connected to form the third transmission channel, and the fifth port and the sixth port are connected to form the fourth transmission channel.

[0020] Optionally, the interferometric element includes a Faraday rotator; the unbalanced interferometer further includes a first coupler connected to the second circulator, the two Faraday rotators with a difference in arm length, and the balanced photodetector.

[0021] Optionally, the interferometric element includes a second coupler; the unbalanced interferometric device further includes a third coupler connected to the second coupler and the balanced photodetector.

[0022] Optionally, the linewidth of the laser satisfies the following condition: Δv ≤ c / 2n(ΔL1-ΔL2); where,

[0023] 2n(ΔL1-ΔL2) is used to represent the optical path difference of the unbalanced interferometer.

[0024] c represents the propagation speed of the laser in a vacuum;

[0025] n is used to represent the effective refractive index of the fiber core;

[0026] ΔL1 is used to indicate that there is a gap between every two of the scattering enhancement points;

[0027] ΔL2 is used to represent the difference in arm length between the two interference elements.

[0028] Optionally, the plurality of scattering enhancement points in the optical fiber are uniformly or non-uniformly distributed.

[0029] Optionally, the chirped frequency pulse light is a linear frequency modulated pulse light or a nonlinear frequency modulated pulse light.

[0030] Optionally, the signal processor is used for:

[0031] The electrical signal is then filtered, denoised, and normalized.

[0032] Frequency analysis was performed on the normalized electrical signal to obtain the optical path difference of the signal.

[0033] The demodulated reference signal is obtained using the optical path difference and compared with the normalized electrical signal to obtain the phase difference between the normalized electrical signal and the reference signal.

[0034] Based on the relationship between the phase difference and the optical path difference, the phase difference is fed back to compensate for the optical path difference;

[0035] The changes in the optical path difference at the same position after feedback compensation are compared in different frames, and the acoustic information is obtained through the demodulation result of the compensated optical path difference.

[0036] This application also provides a demodulation method for a distributed acoustic wave sensing system, employing the distributed acoustic wave sensing system described in any of the above embodiments, the demodulation method comprising:

[0037] Provide lasers for generating laser light;

[0038] An optical modulation device is provided for receiving the laser, modulating the laser into chirped frequency pulsed light, and amplifying and outputting it;

[0039] An optical fiber is provided for receiving the amplified chirped frequency pulse light and outputting the reflected light from the scattering enhancement point;

[0040] An unbalanced interferometer is provided to receive the reflected light at the scattering enhancement point, and to form the interference spectrum of the two scattering enhancement points by utilizing the delay of the two interferometer elements;

[0041] Provide a balanced photodetector for converting the interference spectrum of the two scattering enhancement points formed by the reflected light from the two scattering enhancement points into corresponding electrical signals; and

[0042] A signal processor is provided for acquiring the electrical signal and analyzing and demodulating the electrical signal to output acoustic wave information.

[0043] Optionally, the provision of an optical modulation device for receiving the laser, modulating the laser into chirped frequency pulses, and amplifying and outputting them includes:

[0044] An acousto-optic modulator is provided for receiving the laser and modulating the laser into pulsed light;

[0045] An electro-optic modulator is provided for receiving the pulsed light and modulating the pulsed light into chirped frequency pulsed light; and

[0046] An optical amplifier is provided for receiving the chirped frequency pulse light, amplifying the chirped frequency pulse light, and outputting it.

[0047] Optionally, the provided signal processor, used to acquire the electrical signal and analyze and demodulate the electrical signal to output sound wave amplitude information, includes:

[0048] The electrical signal is then filtered, denoised, and normalized.

[0049] Frequency analysis was performed on the normalized electrical signal to obtain the optical path difference of the signal.

[0050] The demodulated reference signal is obtained using the optical path difference and compared with the normalized electrical signal to obtain the phase difference between the normalized electrical signal and the reference signal.

[0051] Based on the relationship between the phase difference and the optical path difference, the phase difference is fed back to compensate for the optical path difference;

[0052] The changes in the optical path difference at the same position after feedback compensation are compared in different frames, and the acoustic information is obtained through the demodulation result of the compensated optical path difference.

[0053] Optionally, the acousto-optic modulator for receiving the laser and modulating the laser into pulsed light includes:

[0054] The pulse width of the pulsed light is less than the interval between two adjacent scattering enhancement points.

[0055] Optionally, the laser provided for generating laser light includes:

[0056] The linewidth of the laser satisfies the following condition: Δv≤c / 2n(ΔL1-ΔL2); where,

[0057] 2n(ΔL1-ΔL2) is used to represent the optical path difference of the unbalanced interferometer.

[0058] c represents the propagation speed of the laser in a vacuum;

[0059] n is used to represent the effective refractive index of the fiber core;

[0060] ΔL1 is used to indicate that there is a gap between every two of the scattering enhancement points;

[0061] ΔL2 is used to represent the difference in arm length between the two interference elements.

[0062] Optionally, the optical fiber, used to receive the amplified chirped frequency pulse light and output the reflected light from the scattering enhancement point, includes:

[0063] The optical fiber has multiple scattering enhancement points, with a gap between each pair of scattering enhancement points; the multiple scattering enhancement points are uniformly or non-uniformly distributed.

[0064] Optionally, the acousto-optic modulator for receiving the laser and modulating the laser into pulsed light includes:

[0065] The chirped frequency pulse light is either a linear frequency modulated pulse light or a nonlinear frequency modulated pulse light.

[0066] The distributed acoustic wave sensing system and demodulation method of this application embodiment use an optical fiber with multiple scattering enhancement points as the sensing fiber, and two interferometers with a difference in arm length of an unbalanced interferometer are used to form an interference spectrum with a small optical path difference by utilizing the delay of the two interferometers. The laser is modulated into chirped frequency pulse light as the probe light by an optical modulation device, and the light intensity distribution at different wavelengths is obtained by a balanced photodetector. The electrical signal corresponding to the interference spectrum is collected by a signal processor, and the optical path difference of the electrical signal is demodulated to realize acoustic wave sensing with a large dynamic range. Attached Figure Description

[0067] Figure 1 The diagram shown is a schematic block diagram of one embodiment of the distributed acoustic wave sensing system of this application.

[0068] Figure 2 The diagram shown is a flowchart of one embodiment of the demodulation method of the distributed acoustic wave sensing system of this application.

[0069] Figure 3 As shown Figure 2 The flowchart shows the demodulation method steps of the distributed acoustic wave sensing system. Detailed Implementation

[0070] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0071] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit the application. Unless otherwise defined, the technical or scientific terms used in this application should be understood in their ordinary sense by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in this application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, "a" or "one," and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. "A plurality" or "several" indicates at least two. Unless otherwise stated, terms such as "front," "rear," "lower," and / or "upper" are for ease of description only and are not limited to a location or spatial orientation. Terms such as "comprising" or "including" indicate that the elements or objects preceding "comprising" encompass the elements or objects listed following "comprising" or "including" and their equivalents, and do not exclude other elements or objects. Terms such as "connected" or "linked" are not limited to physical or electrical connections and can include electrical connections, whether direct or indirect.

[0072] The singular forms “a,” “said,” and “the” used in this application specification and appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0073] This application provides a distributed acoustic wave sensing system and its demodulation method. The distributed acoustic wave sensing system includes a laser, an optical modulator, an optical fiber, an unbalanced interferometer, a balanced photodetector, and a signal processor. The laser is used to generate laser light. The optical modulator is connected to the laser and is used to receive the laser light, modulate it into chirped frequency pulses, and amplify and output them. The optical fiber includes multiple scattering enhancement points, with a gap between each pair of scattering enhancement points; the optical fiber is used to receive the amplified chirped frequency pulses and output the reflected light from the scattering enhancement points. The unbalanced interferometer includes two interferometer elements with a difference in arm length, both connected to the optical fiber. The two interferometer elements are used to receive the reflected light from the scattering enhancement points, and the delay between the two interferometer elements forms the interference spectrum of the two scattering enhancement points. The balanced photodetector is connected to the unbalanced interferometer; the balanced photodetector is used to convert the interference spectrum of the two scattering enhancement points into corresponding electrical signals. The signal processor is connected to the balanced photodetector and is used to acquire the electrical signals and analyze and demodulate them to output acoustic wave information.

[0074] The distributed acoustic wave sensing system and demodulation method of this application embodiment use an optical fiber with multiple scattering enhancement points as the sensing fiber, and two interferometers with a difference in arm length of an unbalanced interferometer device. The delay of the two interferometers is used to form an interference spectrum with a small optical path difference. The laser is modulated into chirped frequency pulse light as the probe light using an optical modulation device. The light intensity distribution at different wavelengths is detected by a balanced photodetector. The electrical signal corresponding to the interference spectrum is collected by a signal processor, and the optical path difference of the electrical signal is demodulated to realize acoustic wave sensing with a large dynamic range.

[0075] In the field of fiber optic sensing technology, distributed fiber optic acoustic wave sensing systems have gained widespread attention in structural health monitoring, perimeter security, underwater acoustic detection, and resource exploration due to their advantages such as a large number of components, long sensing distance, and high sensitivity. By analyzing the backscattered light information of the probe pulse in the fiber under test, the perception and location of external sound waves can be achieved. Based on phase demodulation, distributed sensing systems exhibit a linear correspondence between the demodulated phase and the amplitude of the acoustic wave signal. Changes in the demodulated phase can effectively reflect changes in the sound wave, thus distributed acoustic wave sensing technology based on phase demodulation has been widely applied.

[0076] Due to phase winding, the demodulation phase is limited to a small range. Although the demodulation range can be expanded using phase dewinding algorithms and improved dewinding algorithms, there are still requirements on the rate of phase change or higher-order rate of change, resulting in a limitation on the amplitude-bandwidth product. This means that high-frequency, strong acoustic waves acting on optical fibers may still cause transitions that cannot be corrected by dewinding, manifesting as severe signal distortion. Furthermore, distributed acoustic wave sensing systems based on Rayleigh scattering have low signal-to-noise ratios at coherent fading points, making them more prone to transitions that cannot be repaired by dewinding, thus failing to accurately measure acoustic signal information.

[0077] To address the limited dynamic range of acoustic waves in distributed acoustic sensing systems, several solutions have been developed, including dual-wavelength differential phase method, chirped pulse method, and differential expansion integration algorithm. However, the dual-wavelength differential phase method has limited improvement in strain amplitude, the demodulation range of the chirped pulse method depends on the sweep bandwidth, and the differential expansion integration algorithm also exhibits abrupt changes at coherent fading points, resulting in a deterioration in the signal-to-noise ratio of the demodulated signal and thus hindering accurate measurement.

[0078] Therefore, this application provides a distributed acoustic wave sensing system and its demodulation method that achieves an ultra-large dynamic range. The distributed acoustic wave sensing system and its demodulation method of this application will be described in detail below with reference to the accompanying drawings. Unless otherwise specified, the features of the following embodiments and implementations can be combined with each other.

[0079] Figure 1 The diagram shown is a schematic block diagram of an embodiment of the distributed acoustic wave sensing system 1 of this application. Figure 1As shown, the distributed acoustic wave sensing system 1 includes a laser 101, an optical modulator 102, an optical fiber 103, an unbalanced interferometer 104, a balanced photodetector 105, and a signal processor 106. The laser is used to generate laser light. In this embodiment, the laser light can be continuous light. The optical modulator 102 is connected to the laser 101 and is used to receive the laser light, modulate it into chirped frequency pulses, and amplify and output them. In this embodiment, the instantaneous frequency of the chirped frequency pulses varies with time. The optical fiber 103 includes a plurality of scattering enhancement points 107, with a gap between each pair of scattering enhancement points 107. In this embodiment, the plurality of scattering enhancement points 107 of the optical fiber 103 are uniformly or non-uniformly distributed. For example, the gap between each pair of scattering enhancement points 107 is ΔL1. The optical fiber 103 is used to receive the amplified chirped frequency pulses and output the reflected light from the scattering enhancement points. The unbalanced interferometer 104 includes two interferometer elements 108 with a difference in arm length, both connected to an optical fiber 103. The two interferometer elements 108 are used to receive reflected light from the scattering enhancement points, and the delay between the two interferometer elements 108 forms the interference spectrum of the two scattering enhancement points. In this embodiment, the scattering enhancement points can be either weak reflection gratings or weak reflection points. A balanced photodetector 105 is connected to the unbalanced interferometer 104. The balanced photodetector 105 is used to convert the interference spectrum of the two scattering enhancement points into corresponding electrical signals. A signal processor 106 is connected to the balanced photodetector 105. The signal processor 106 is used to acquire the electrical signals and analyze and demodulate them to output acoustic wave information. The electrical signals acquired by the signal processor 106 are electrical signals whose light intensity varies with the cosine frequency. The optical path difference of the interference spectrum can be deduced from the change in light intensity over time. By using optical path difference as the demodulation quantity of the distributed acoustic wave sensing system, a one-to-one correspondence between optical path difference and acoustic wave amplitude is established, enabling acoustic wave measurement with a large dynamic range.

[0080] In the above scheme, an optical fiber 103 with multiple scattering enhancement points is used as the sensing fiber, and two interferometer elements 108 with arm length difference of the unbalanced interferometer device 104 are used to form an interference spectrum with a small optical path difference by utilizing the delay of the two interferometer elements. The laser is modulated into chirped frequency pulse light by the optical modulation device 102 as the probe light. The light intensity distribution at different wavelengths is detected by the balanced photodetector 105. The electrical signal corresponding to the interference spectrum is collected by the signal processor 106, and the optical path difference of the electrical signal is demodulated to realize the acoustic wave sensing with a large dynamic range.

[0081] exist Figure 1In the illustrated embodiment, the optical modulation device 102 includes at least an acousto-optic modulator 109, an electro-optic modulator 110, and an optical amplifier 111. The acousto-optic modulator 109 is connected to the laser 101 and is used to receive the laser light and modulate it into pulsed light. In this embodiment, the pulse width Δτ of the pulsed light should satisfy Δτ≤2nΔL1 / c, where c represents the speed of light in a vacuum, n represents the effective refractive index of the fiber core, and the pulse width is less than the interval between two adjacent scattering enhancement points, meaning one pulse covers at most one scattering enhancement point. The electro-optic modulator 110 is connected to the acousto-optic modulator 109 and is used to receive the pulsed light and modulate it into chirped frequency pulsed light. In this embodiment, the chirped frequency pulsed light is either linearly frequency-modulated (LFM) or nonlinearly frequency-modulated (NFM). Nonlinearly frequency-modulated light requires resampling or interpolation during data processing. In other embodiments, the chirped frequency pulsed light can also be other schemes that allow the light frequency to vary within a certain range. Optical amplifier 111 is connected to electro-optic modulator 110. Optical amplifier 111 is used to receive chirped frequency pulsed light, amplify the chirped frequency pulsed light, and output it. In this embodiment, optical amplifier 111 can be an erbium-doped fiber amplifier. In this embodiment, the light emitted by laser 101 is injected into acousto-optic modulator 109, and the acousto-optic modulator 109 modulates the continuous laser light into a pulse with a pulse width of Δτ, a frequency shift of Δf, and a repetition rate of f. r The pulsed light. The repetition rate f of the pulsed light. r The corresponding period should be greater than the time required for the pulse to travel back and forth in the optical fiber under test. Then, the pulsed light is modulated into chirped frequency pulsed light by electro-optic modulator 110. Next, the chirped frequency pulsed light is connected to optical amplifier 111 for amplification and output.

[0082] exist Figure 1 In the illustrated embodiment, laser 101 can be a distributed feedback laser. The linewidth of laser 101 satisfies the following condition: Δv ≤ c²n(ΔL1 - ΔL2); where 2n(ΔL1 - ΔL2) represents the optical path difference of the unbalanced interferometer. c represents the propagation speed of the laser in vacuum. n represents the effective refractive index of the fiber core. ΔL1 represents the interval between every two scattering enhancement points. ΔL2 represents the difference in arm length between the two interferometer elements. With this configuration, the optical path difference is significantly reduced relative to the associated detection scheme, thus greatly reducing the linewidth requirement for the laser.

[0083] exist Figure 1In the illustrated embodiment, the interference element 108 includes a Faraday rotator mirror. The unbalanced interferometer 104 includes two Faraday rotator mirrors with an arm length difference of ΔL2. A Faraday rotator mirror is a light-free device that utilizes the Faraday effect to rotate the polarization state of the input light before outputting it; it reflects the polarization state of the incident light in orthogonal polarization directions of 90°. The unbalanced interferometer 104 includes two interference elements with different optical path lengths, the tail ends of which are connected to the Faraday rotator mirror for reflecting the light from the interference elements.

[0084] exist Figure 1 In the illustrated embodiment, the distributed acoustic wave sensing system 1 further includes a first circulator 112, comprising a first transmission channel 113 and a second transmission channel 114 isolated from each other. An optical modulation device 102 is connected to an optical fiber 103 via the first transmission channel 113, and the optical fiber 103 is connected to an unbalanced interferometer 104 via the second transmission channel 114. The first circulator 112 propagates unidirectionally. An optical amplifier 111 is connected to the first transmission channel 113 of the first circulator 112 and the optical fiber 103. Amplified chirped frequency pulse light is injected into the optical fiber 103 via the first transmission channel 113. Reflected light from scattering enhancement points in the optical fiber 103 is injected into the unbalanced interferometer 104 via the second transmission channel 114 of the first circulator 112.

[0085] exist Figure 1 In the illustrated embodiment, the first circulator 112 includes a first port 115, a second port 116, and a third port 117. The first port 115 and the second port 116 are connected to the first transmission channel 113, and the second port 116 and the third port 117 are connected to form a second transmission channel 114. In this embodiment, the first port 115 can be an input port, and the second port 116 can be an output port. The optical modulation device 102 inputs amplified chirped frequency pulse light into the first transmission channel 113 through the first port 115 and outputs it to the optical fiber 103 through the second port 116. In this embodiment, the second port 116 can be an input port, and the third port 117 can be an output port. After the amplified chirped frequency pulse light enters the optical fiber 103, the optical fiber 103 inputs the reflected light from the scattering enhancement point into the second transmission channel 114 through the second port 116 and outputs it to the unbalanced interferometer 104 through the third port 117. Figure 1 In the illustrated embodiment, the first transmission channel 113 and the second transmission channel 114, as indicated by the arrows, are isolated from each other and are both unidirectional channels. Thus, the optical modulation device 102, the optical fiber 103, and the unbalanced interference device 104 are connected via the first circulator 112, ensuring that the transmitted signal is unaffected by interference.

[0086] exist Figure 1In the illustrated embodiment, the distributed acoustic wave sensing system 1 further includes a second circulator 118, comprising a mutually isolated third transmission channel 119 and a fourth transmission channel 120. An optical fiber 103 is sequentially connected to an unbalanced interferometer 104 via the second transmission channel 114 and the third transmission channel 119. The unbalanced interferometer 104 is connected to a balanced photodetector 105 via at least the fourth transmission channel 120. Figure 1 In the illustrated embodiment, the second circulator 118 includes a fourth port 121, a fifth port 122, and a sixth port 123. The fourth port 121 and the fifth port 122 are connected to form a third transmission channel 119, and the fifth port 122 and the sixth port 123 are connected to form a fourth transmission channel 120. In this embodiment, the fourth port 121 can be an input port, and the fifth port 122 can be an output port. The optical fiber 103 inputs the reflected light from the scattering enhancement point to the third transmission channel 119 through the second port 116, outputs it to the fourth port 121 of the second circulator 118 through the third port 117, and transmits it to the fourth port 121 through the fifth port 122. In this embodiment, the fifth port 122 can be an input port, and the sixth port 123 can be an output port. The unbalanced interferometer 104 inputs a portion of the interference spectrum from the two scattering enhancement points into the fourth transmission channel 120 through the fifth port 122, outputs it to the balanced photodetector 105 through the sixth port 123, and outputs the other portion directly to the balanced photodetector 105. Figure 1 In the illustrated embodiment, the third transmission channel 119 and the fourth transmission channel 120, as indicated by the arrows, are isolated from each other and are both unidirectional channels. Thus, the second circulator 118 connects the optical fiber 103, the unbalanced interferometer 104, and the balanced photodetector 105, ensuring uninterrupted signal transmission.

[0087] In some embodiments, the unbalanced interferometer 104 further includes a first coupler 124 connected to a second circulator 118, two interferometer elements with a difference in arm length, and a balanced photodetector 105. Figure 1 In the illustrated embodiment, a Faraday rotator with two arm length differences and a first coupler 124 form a non-equilibrium interferometer 104. This non-equilibrium interferometer 104 can be a Michelson interferometer. Due to the arm length difference between the two Faraday rotators, when reflected light from the two scattering enhancement points is input to the two Faraday rotators, they meet after a delay due to the arm length difference, forming an interference spectrum with a small optical path difference.

[0088] In some other embodiments, the interferometer 108 includes a second coupler (not shown). The unbalanced interferometer 104 also includes a third coupler (not shown) connected to the second coupler and the balanced photodetector 105. Figure 1The embodiments shown are similar, the main difference being that the second coupler and the third coupler are connected by a coupling optical fiber, and the second coupler and the third coupler form an unbalanced interferometer device 104.

[0089] The actual modulation process includes: first, injecting the light emitted by the laser 101 into the acousto-optic modulator 109, and then using the acousto-optic modulator 109 to modulate the continuous laser light into a pulse with a pulse width of Δτ, a frequency shift of Δf, and a repetition rate of f. r The pulsed light is then modulated into a chirped frequency pulsed light by an electro-optic modulator 110. The chirped frequency pulsed light is then amplified and output by an optical amplifier 111. The amplified chirped frequency pulsed light is injected into the first port 115 of the first circulator 112, passes through the first transmission channel 113, and is injected into an optical fiber 103 with multiple scattering enhancement points through the second port 116 of the first circulator 112. The optical fiber is composed of multiple scattering enhancement points with a spacing of ΔL1. The third port 117 of the first circulator 112 is connected to the fourth port 121 of the second circulator 118. The reflected light with enhanced scattering is input into the unbalanced interferometer 104 with an arm length difference of ΔL2 through the fifth port 122 of the second circulator 118. The reflected light from the two enhanced scattering points meets after a delay due to the arm length difference of the unbalanced interferometer 104, forming an interference spectrum between the two enhanced scattering points with a small optical path difference. This interference spectrum is input into the balanced photodetector 105 through the sixth port 123 of the second circulator 118, and directly injected into the balanced photodetector 105 through another port of the unbalanced interferometer 104. The balanced photodetector 105 converts the interference spectrum of the two enhanced scattering points into corresponding electrical signals. The signal processor 106 collects the converted electrical signals from the balanced photodetector 105 and analyzes and demodulates them to obtain high-resolution, large dynamic range acoustic wave information.

[0090] exist Figure 1 In the illustrated embodiment, the signal processor 106 is used to filter, denoise, and normalize the electrical signal. In this embodiment, it is necessary to extract the electrical signal corresponding to each received interference spectrum, and then demodulate each of these converted electrical signals separately. For example, one frame of the electrical signal corresponding to the interference spectrum output by the unbalanced interferometer 104 is acquired, and through analysis and extraction of the electrical signal of the interference spectrum, it is divided into M-1 electrical signals of the interference spectrum, and then denoising and normalizing these signals is performed. Denoising is mainly achieved through filtering or smoothing methods. Normalization mainly includes eliminating the influence of light intensity fluctuations in the probe pulse and de-envelope operation of the sensing signal to restore the standard interference spectrum shape. Figure 1In the illustrated embodiment, the signal processor 106 is further configured to perform frequency analysis on the normalized electrical signal to obtain the optical path difference of the electrical signal. In this embodiment, frequency analysis is performed on the normalized electrical signal to obtain the optical path difference of the electrical signal. In this embodiment, characteristic frequency analysis is performed on the electrical signal of each interference spectrum to obtain the optical path difference L0 of each interferometer, and the error of the optical path difference L0 is no greater than λ / 2n. Figure 1 In the illustrated embodiment, the signal processor 106 is further configured to acquire the demodulated reference signal using the optical path difference, and compare it with the normalized electrical signal to obtain the phase difference between the normalized electrical signal and the reference signal. In this embodiment, the demodulated reference signal is derived by combining the calculation formula of the unbalanced interferometer 104 with the optical path difference, and compared with the normalized electrical signal to obtain the phase difference between the normalized electrical signal and the reference signal. In this embodiment, the calculation formula of the unbalanced interferometer 104 can be expressed as: Where A represents the DC component of the interferometric spectrum, B represents the contrast of the interferometric spectrum, n represents the effective refractive index of the fiber core, l represents the effective physical length of the interferometer, λ represents the wavelength of the probe light, and the optical path difference can be expressed as 2nl. Figure 1 In the illustrated embodiment, the signal processor 106 is further configured to feed back the phase difference to compensate for the optical path difference based on the relationship between the phase difference and the optical path difference. In this embodiment, the relationship between the phase difference and the optical path difference is constructed using the calculation formula of the unbalanced interferometer 104, and the phase difference is compensated for to the optical path difference using a feedback compensation method. In this step, the relationship between the phase difference and the optical path difference is obtained through the interferometer spectral calculation formula, which can be expressed as φ = 2π·L / λ, where L represents the optical path difference of the interferometer, which is twice the product of the fiber refractive index and the physical length. Figure 1 In the illustrated embodiment, the signal processor 106 is further used to compare the changes in the optical path difference at the same position after feedback compensation in different frames, and obtain the acoustic wave information through the demodulation result of the compensated optical path difference. In this embodiment, the signal processor 106 is also used to compare the changes in the optical path difference of the interferometer at the same position in different frames, and obtain the acoustic wave information through the demodulation result of the optical path difference. In this step, the specific calculation methods for the optical path difference and the phase difference used in demodulation can also be freely selected according to the application.

[0091] In the above scheme, injecting a chirped frequency pulse into the optical fiber under test yields one frame of reflected light. Each frame of reflected light contains multiple interference spectra, each with a finite signal length and intervals between them. After extracting the k-th interference spectrum signal from the m-th frame, the extracted interference spectrum is first denoised and normalized to obtain the actual signal k. Then, it is determined whether this is the first calculation of the interferometer signal. If it is, the characteristic frequency of the interference spectrum is calculated using characteristic frequency analysis. The reference signal is then calculated using the characteristic frequency and the calculation formula of the interferometer device. Next, the phase difference between the reference signal and the actual signal is compared, and phase feedback compensation is achieved using the linear correspondence between the phase difference and the optical path difference. Through k demodulation operations, a large dynamic range and high-resolution demodulation of all interferometer optical path difference signals in one frame of signal can be achieved. The signal processor 106 is used to demodulate the optical path difference of the unbalanced interferometer 104 (Michelson interferometer) formed in the distributed acoustic wave sensing system frame by frame. The change in the optical path difference of each unbalanced interferometer 104 with the number of frames is calculated, and then the acoustic wave information is obtained by inversely analyzing the strain on the optical fiber caused by the acoustic wave. By establishing the relationship between the phase of the electrical signal corresponding to the interference spectrum and the optical path difference, phase feedback compensation technology is used to compensate the phase difference for the optical path difference, ensuring that the system achieves ultra-large dynamic range demodulation while maintaining high resolution.

[0092] In this embodiment, an optical fiber with multiple scattering enhancement points is used as the sensing fiber. After the reflected light from these points is injected into the unbalanced interferometer 104, the delay of the two interferometer elements 108 of the unbalanced interferometer 104 forms an interference spectrum with a small optical path difference between the scattering enhancement points. This significantly reduces the optical path difference of the unbalanced interferometer 104 compared to the coherent optical time-domain reflectometer system, thus greatly reducing the linewidth requirement of the light source and lowering system costs. Due to the delay of the unbalanced interferometer 104, the reflected light from the two scattering enhancement points meets within the unbalanced interferometer 104, forming an interference spectrum with a small optical path difference. The acoustic demodulation dynamic range of a phase-demodulated coherent time-domain reflectometer is limited to (-π, π]. Demodulation of the optical path difference in the interference spectrum of a scanning array interferometer can greatly increase the system's acoustic dynamic measurement range. Combining high-resolution phase demodulation technology with a large dynamic range characteristic frequency demodulation algorithm enables high-resolution, ultra-large dynamic range distributed acoustic sensing.

[0093] Figure 2 The diagram shows a flowchart of one embodiment of the demodulation method of the distributed acoustic wave sensing system 1 of this application. (In conjunction with...) Figure 1 and Figure 2 As shown, the demodulation method employs the distributed acoustic wave sensing system 1 described in the above embodiment. The demodulation method includes steps S1 to S6. Wherein,

[0094] Step S1: Provide a laser 101 for generating laser light. The laser light can be continuous light.

[0095] Step S2: Provide an optical modulation device 102 for receiving laser light, modulating the laser light into chirped frequency pulse light, and amplifying and outputting it. The instantaneous frequency of the chirped frequency pulse light changes with time.

[0096] Step S3: Provide an optical fiber 103 for receiving amplified chirped frequency pulse light. Scattering enhancement points in the optical fiber 103 will reflect the incident chirped frequency pulse light. The optical fiber 103 includes multiple scattering enhancement points 107, with a gap between each pair of scattering enhancement points 107. The multiple scattering enhancement points 107 of the optical fiber 103 are uniformly or non-uniformly distributed. For example, the spacing between each pair of scattering enhancement points 107 is ΔL1.

[0097] Step S4: Provide an unbalanced interferometer 104 to receive the reflected light from the scattering enhancement points, and use the delay of the two interferometer elements 108 to form the interference spectra of the two scattering enhancement points. The unbalanced interferometer 104 includes two interferometer elements 108 with a difference in arm length, both of which are connected to the optical fiber 103. The scattering enhancement point can be in the form of a weak reflection grating or a weak reflection point.

[0098] Step S5: A balanced photodetector 105 is provided to convert the interference spectrum of the two scattering enhancement points formed by the reflected light from the two scattering enhancement points into corresponding electrical signals. The unbalanced interferometer 104 transmits the interference spectrum of the scattering enhancement points to the balanced photodetector 105 in two paths.

[0099] Step S6: Provide a signal processor to acquire electrical signals and analyze and demodulate them to output acoustic wave information. The electrical signal acquired by the signal processor 106 is an electrical signal whose light intensity varies with the cosine frequency. The optical path difference of the interference spectrum can be deduced from the change of light intensity over time. Thus, by using the optical path difference as the demodulation quantity of the distributed acoustic wave sensing system, a one-to-one correspondence between the optical path difference and the acoustic wave amplitude is established, enabling acoustic wave measurement with a large dynamic range.

[0100] In the above scheme, an optical fiber 103 with multiple scattering enhancement points is used as the sensing fiber. Two interferometers 108 with arm length difference are used in conjunction with the unbalanced interferometer 104. The delay of the two interferometers forms an interference spectrum with a small optical path difference. The laser is modulated into chirped frequency pulse light by the optical modulation device 102 as the probe light. The light intensity distribution at different wavelengths is detected by the balanced photodetector 105. The electrical signal corresponding to the interference spectrum is collected by the signal processor 106, and the optical path difference of the electrical signal is demodulated to realize the acoustic wave sensing with a large dynamic range.

[0101] Figure 3 As shown Figure 2 The flowchart illustrates the demodulation method of the distributed acoustic wave sensing system 1. (Combined with...) Figures 1 to 3 As shown, step S2, providing an optical modulation device 102 for receiving laser light, modulating the laser light into chirped frequency pulsed light and amplifying the output, includes steps S21 to S23. Wherein,

[0102] Step S21: Provide an acousto-optic modulator 109 for receiving laser light and modulating it into pulsed light. The pulse width Δτ of the pulsed light should satisfy Δτ≤2nΔL1 / c, where c represents the speed of light in a vacuum, n represents the effective refractive index of the fiber core, and the pulse width of the pulsed light is less than the interval between two adjacent scattering enhancement points, that is, one pulse can cover at most one scattering enhancement point.

[0103] Step S22: Provide an electro-optic modulator 110 for receiving pulsed light and modulating it into chirped frequency pulsed light. The chirped frequency pulsed light can be linearly frequency-modulated (LFM) or nonlinearly frequency-modulated (NFM). Nonlinearly frequency-modulated light requires resampling or interpolation during data processing. In other embodiments, the chirped frequency pulsed light can also be other schemes that allow the light frequency to vary within a certain range.

[0104] Step S23: Provide an optical amplifier 111 for receiving chirped frequency pulse light, amplifying the chirped frequency pulse light, and outputting it. The optical amplifier 111 may be an erbium-doped fiber amplifier.

[0105] In the above steps, the light emitted by the laser 101 is injected into the acousto-optic modulator 109, and the acousto-optic modulator 109 modulates the continuous laser light into a pulse with a pulse width of Δτ, a frequency shift of Δf, and a repetition frequency of f. r The pulsed light. The repetition rate f of the pulsed light. r The corresponding period should be greater than the time required for the pulse to travel back and forth in the optical fiber under test. Then, the pulsed light is modulated into chirped frequency pulsed light by electro-optic modulator 110. Next, the chirped frequency pulsed light is connected to optical amplifier 111 for amplification and output.

[0106] exist Figure 3 In the illustrated embodiment, step S6 involves providing a signal processor 106 to acquire electrical signals and analyze and demodulate them to output sound wave amplitude information. The specific demodulation process includes steps S61 to S65.

[0107] Step S61: Filter, denoise, and normalize the electrical signal. In this embodiment, it is necessary to extract the electrical signal corresponding to each received interference spectrum, and then demodulate each corresponding converted electrical signal separately. For example, obtain the electrical signal of one frame corresponding to the interference spectrum output by the unbalanced interferometer 104, and divide it into M-1 interference spectrum electrical signals through analysis and extraction. Then, denoise and normalize the electrical signals of the interference spectra. Denoising is mainly achieved through filtering or smoothing methods. Normalization mainly includes eliminating the influence of light intensity fluctuations in the probe pulse and removing the envelope of the sensing signal to restore the standard interference spectrum shape.

[0108] Step S62: Perform frequency analysis on the normalized electrical signal to obtain the optical path difference. In this embodiment, frequency analysis is performed on the normalized electrical signal to obtain the optical path difference. In this embodiment, characteristic frequency analysis is performed on the electrical signal of each interference spectrum to obtain the optical path difference L0 of each interferometer, and the error of the optical path difference L0 is not greater than λ / 2n.

[0109] Step S63: Obtain the demodulated reference signal using the optical path difference, and compare it with the normalized electrical signal to obtain the phase difference between the normalized electrical signal and the reference signal. In this embodiment, the demodulated reference signal is derived by combining the calculation formula of the unbalanced interferometer 104 with the optical path difference, and compared with the normalized electrical signal to obtain the phase difference between the normalized electrical signal and the reference signal. In this embodiment, the calculation formula of the unbalanced interferometer 104 can be expressed as: Where A represents the DC component of the dry spectrum, B represents the contrast of the interference spectrum, n represents the effective refractive index of the fiber core, l represents the effective physical length of the interferometer, λ represents the wavelength of the probe light, and the optical path difference can be expressed as 2nl.

[0110] Step S64: Based on the relationship between phase difference and optical path difference, the phase difference is fed back to compensate for the optical path difference. In this embodiment, the relationship between phase difference and optical path difference is constructed using the calculation formula of the unbalanced interferometer 104, and the phase difference is compensated to the optical path difference using a feedback compensation method. In this step, the relationship between phase difference and optical path difference is obtained through the interferometer spectrum calculation formula, which can be expressed as φ=2π·L / λ, where L represents the optical path difference of the interferometer, which is twice the product of the fiber refractive index and physical length.

[0111] Step S65: Compare the changes in optical path difference at the same position after feedback compensation in different frames, and obtain the acoustic wave information through the demodulation result of the compensated optical path difference. In this embodiment, the signal processor 106 is also used to compare the changes in optical path difference of the interferometer at the same position in different frames, and obtain the acoustic wave information through the demodulation result of the optical path difference. In this step, the specific calculation methods for optical path difference and phase difference used in demodulation can also be freely selected according to the application.

[0112] In the above scheme, injecting a chirped frequency pulse into the fiber under test yields one frame of reflected light. Each frame of reflected light contains multiple interference spectra, each with a finite length and intervals. After extracting the k-th interference spectrum from the m-th frame, the extracted spectrum is first denoised and normalized to obtain the actual signal k. Then, it is determined whether this is the first calculation of the interferometer signal. If it is, the characteristic frequency of the interference spectrum is calculated using characteristic frequency analysis. The reference signal is then calculated using the characteristic frequency and the calculation formula of the interferometer device. Next, the phase difference between the reference signal and the actual signal is compared, and phase feedback compensation is achieved using the linear correspondence between the phase difference and the optical path difference. Through k demodulation operations, a large dynamic range and high-resolution demodulation of all interferometer optical path difference signals in one frame can be achieved. The signal processor 106 is used to demodulate the optical path difference of the unbalanced interferometer 104 (Michelson interferometer) formed in the distributed acoustic wave sensing system frame by frame. The change in the optical path difference of each unbalanced interferometer 104 with the number of frames is calculated, and then the acoustic wave information is obtained by inversely analyzing the strain on the optical fiber caused by the acoustic wave. By establishing the relationship between the phase of the electrical signal corresponding to the interference spectrum and the optical path difference, phase feedback compensation technology is used to compensate the phase difference for the optical path difference, ensuring that the system achieves ultra-large dynamic range demodulation while maintaining high resolution.

[0113] In this embodiment, the unbalanced interferometer 104 can be a scanning array interferometer. When reflected light with multiple scattering enhancement points is injected into the unbalanced interferometer 104, an interference spectrum with small optical path differences is formed at these scattering enhancement points. This significantly reduces the optical path difference of the unbalanced interferometer 104 compared to a coherent optical time-domain reflectometer system, thus greatly reducing the linewidth requirement of the light source and lowering system costs. The acoustic demodulation dynamic range of a phase-demodulated coherent time-domain reflectometer is limited to (-π, π], while the demodulation of the optical path difference in the interference spectrum of a scanning array interferometer can greatly increase the system's acoustic dynamic measurement range. Combining high-resolution phase demodulation technology with a large dynamic range characteristic frequency demodulation algorithm enables high-resolution, ultra-large dynamic range distributed acoustic sensing.

[0114] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A distributed acoustic wave sensing system, characterized in that, include: Laser, used to generate laser light; An optical modulation device is connected to the laser, which receives the laser light, modulates the laser light into chirped frequency pulses, and amplifies and outputs them. An optical fiber includes a plurality of scattering enhancement points, wherein there is a gap between every two scattering enhancement points; the optical fiber is used to receive amplified chirped frequency pulse light and output reflected light from the scattering enhancement points; An unbalanced interferometer includes two interferometer elements with a difference in arm length, both of which are connected to the optical fiber. The two interferometer elements are respectively used to receive the reflected light at the scattering enhancement point, and the delay of the two interferometer elements is used to form the interference spectrum of the two scattering enhancement points. A balanced photodetector is connected to the unbalanced interferometer; the balanced photodetector is used to convert the interference spectrum of the two scattering enhancement points formed by the reflected light at the two scattering enhancement points into corresponding electrical signals; and A signal processor, connected to the balanced photodetector, is used to acquire the electrical signal and analyze and demodulate the electrical signal to output acoustic wave information; The linewidth of the laser satisfies the following condition: ;in, Used to represent the optical path difference of the unbalanced interferometer; Used to indicate the propagation speed of the laser in a vacuum; Used to represent the effective refractive index of the fiber core; This is used to indicate that there is a gap between every two scattering enhancement points; Used to represent the difference in arm length between the two interference elements.

2. The distributed acoustic wave sensing system according to claim 1, characterized in that, The optical modulation device includes at least: An acousto-optic modulator is connected to the laser; the acousto-optic modulator is used to receive the laser and modulate the laser into pulsed light. An electro-optic modulator is connected to the acousto-optic modulator; the electro-optic modulator is used to receive the pulsed light and modulate the pulsed light into chirped frequency pulsed light; An optical amplifier, connected to the electro-optic modulator, is used to receive the chirped frequency pulse light, amplify the chirped frequency pulse light, and output it.

3. The distributed acoustic wave sensing system according to claim 2, characterized in that, The pulse width of the pulsed light is less than the interval between two adjacent scattering enhancement points.

4. The distributed acoustic wave sensing system according to claim 1, characterized in that, The distributed acoustic wave sensing system further includes a first circulator, comprising a first transmission channel and a second transmission channel that are isolated from each other. The optical modulation device is connected to the optical fiber through the first transmission channel, and the optical fiber is connected to the unbalanced interferometer through the second transmission channel.

5. The distributed acoustic wave sensing system according to claim 4, characterized in that, The first circulator includes a first port, a second port, and a third port. The first port and the second port are connected to form the first transmission channel, and the second port and the third port are connected to form the second transmission channel.

6. The distributed acoustic wave sensing system according to claim 4, characterized in that, The distributed acoustic wave sensing system further includes a second circulator, comprising a mutually isolated third transmission channel and a fourth transmission channel. The optical fiber is connected to the unbalanced interferometer in sequence through the second transmission channel and the third transmission channel. The unbalanced interferometer is connected to the balanced photodetector at least through the fourth transmission channel.

7. The distributed acoustic wave sensing system according to claim 6, characterized in that, The second circulator includes a fourth port, a fifth port, and a sixth port. The fourth port and the fifth port are connected to form the third transmission channel, and the fifth port and the sixth port are connected to form the fourth transmission channel.

8. The distributed acoustic wave sensing system according to claim 6, characterized in that, The interference element includes a Faraday rotator; the unbalanced interference device further includes a first coupler connected to the second circulator, the two Faraday rotators with a difference in arm length, and the balanced photodetector.

9. The distributed acoustic wave sensing system according to claim 4, characterized in that, The interference element includes a second coupler; the unbalanced interference device also includes a third coupler, which is connected to the second coupler and the balanced photodetector.

10. The distributed acoustic wave sensing system according to claim 1, characterized in that, The plurality of scattering enhancement points in the optical fiber are uniformly or non-uniformly distributed; and / or The chirped frequency pulse light is either a linear frequency modulated pulse light or a nonlinear frequency modulated pulse light.

11. The distributed acoustic wave sensing system according to claim 1, characterized in that, The signal processor is used for: The electrical signal is then filtered, denoised, and normalized. Frequency analysis was performed on the normalized electrical signal to obtain the optical path difference of the signal. The demodulated reference signal is obtained using the optical path difference and compared with the normalized electrical signal to obtain the phase difference between the normalized electrical signal and the reference signal. Based on the relationship between the phase difference and the optical path difference, the phase difference is fed back to compensate for the optical path difference; The changes in the optical path difference at the same position after feedback compensation are compared in different frames, and the acoustic information is obtained through the demodulation result of the compensated optical path difference.

12. A demodulation method for a distributed acoustic wave sensing system, characterized in that, The demodulation method using the distributed acoustic wave sensing system according to any one of claims 1 to 11 includes: Provide a laser for generating laser light; An optical modulation device is provided for receiving the laser, modulating the laser into chirped frequency pulsed light, and amplifying and outputting it; An optical fiber is provided for receiving the amplified chirped frequency pulse light and outputting the reflected light from the scattering enhancement point; An unbalanced interferometer is provided to receive the reflected light at the scattering enhancement point, and to form the interference spectrum of the two scattering enhancement points by utilizing the delay of the two interferometer elements; Provide a balanced photodetector for converting the interference spectrum of the two scattering enhancement points formed by the reflected light from the two scattering enhancement points into corresponding electrical signals; and A signal processor is provided for acquiring the electrical signal and analyzing and demodulating the electrical signal to output acoustic wave information; The linewidth of the laser satisfies the following condition: ;in, Used to represent the optical path difference of the unbalanced interferometer; Used to indicate the propagation speed of the laser in a vacuum; Used to represent the effective refractive index of the fiber core; This is used to indicate that there is a gap between every two scattering enhancement points; Used to represent the difference in arm length between the two interference elements.

13. The demodulation method according to claim 12, characterized in that, The optical modulation device is provided for receiving the laser, modulating the laser into chirped frequency pulsed light, and amplifying and outputting it, including: An acousto-optic modulator is provided for receiving the laser and modulating the laser into pulsed light; An electro-optic modulator is provided for receiving the pulsed light and modulating the pulsed light into chirped frequency pulsed light; and An optical amplifier is provided for receiving the chirped frequency pulse light, amplifying the chirped frequency pulse light, and outputting it.

14. The demodulation method according to claim 12, characterized in that, The provided signal processor is used to acquire the electrical signal and analyze and demodulate the electrical signal to output sound wave amplitude information, including: The electrical signal is then filtered, denoised, and normalized. Frequency analysis was performed on the normalized electrical signal to obtain the optical path difference of the signal. The demodulated reference signal is obtained using the optical path difference and compared with the normalized electrical signal to obtain the phase difference between the normalized electrical signal and the reference signal. Based on the relationship between the phase difference and the optical path difference, the phase difference is fed back to compensate for the optical path difference; The changes in the optical path difference at the same position after feedback compensation are compared in different frames, and the acoustic information is obtained through the demodulation result of the compensated optical path difference.

15. The demodulation method according to claim 13, characterized in that, The acousto-optic modulator, used to receive the laser and modulate the laser into pulsed light, includes: The pulse width of the pulsed light is less than the interval between two adjacent scattering enhancement points.

16. The demodulation method according to claim 12, characterized in that, The optical fiber, used to receive the amplified chirped frequency pulse light and output the reflected light from the scattering enhancement point, includes: The optical fiber has multiple scattering enhancement points, with a gap between each pair of scattering enhancement points; the multiple scattering enhancement points are uniformly or non-uniformly distributed.

17. The demodulation method according to claim 13, characterized in that, The acousto-optic modulator, used to receive the laser and modulate the laser into pulsed light, includes: The chirped frequency pulse light is either a linear frequency modulated pulse light or a nonlinear frequency modulated pulse light.

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