A distributed acoustic sensing method, apparatus and system

Abstract

The application discloses a kind of distributed acoustic wave sensing method, device and system, method includes: utilizing tunable laser output linear sweep continuous light, is formed by stimulated Brillouin scattering and Rayleigh backscattering feedback in optical fiber Brillouin random laser;Two different center frequency sweep signals are obtained as double-chirp signal source by band selection, and two signals have different sweep rates;After pulse modulation, inject sensing optical fiber, obtain Rayleigh backscattering signal;The scattering signal is separated and demodulated by band, and the vibration or strain parameter distributed along optical fiber is obtained.The application improves the measurement ability of different vibration amplitude signals by double-chirp signal cooperative detection, so as to expand system dynamic range and improve detection precision.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, specifically relating to a distributed acoustic wave sensing method, device, and system. Background Technology

[0002] Fiber-optic distributed acoustic sensing (DAS) utilizes the sensitivity of Rayleigh scattering in optical fibers to external vibrations, temperature, and strain to achieve continuous distributed measurements along the fiber. This technology boasts advantages such as high measurement density, good synchronization, high sensitivity, wide frequency response range, long measurement distance, and strong resistance to electromagnetic interference, and has been widely applied in fields such as oil and gas exploration, geothermal monitoring, hydraulic fracturing, and seismic observation.

[0003] In DAS systems, phase-sensitive optical time-domain reflectometry (φ-OTDR) has attracted widespread attention due to its high sensitivity. Its key feature is that chirped pulse φ-OTDR achieves rapid measurement of temperature or strain by linearly modulating the probe pulse, utilizing the time-frequency mapping relationship, and combining a cross-correlation algorithm to demodulate changes in the Rayleigh scattering signal. However, this method relies on high correlation between adjacent Rayleigh scattering curves. When external disturbances are significant, the correlation decreases, leading to correlation peak shift and waveform distortion, thus affecting the extraction of time delay information and limiting the system's dynamic range.

[0004] To address these issues, existing technologies primarily employ two methods: one is to increase the sweep bandwidth of the chirped pulses to enhance signal correlation and improve the measurement upper limit; however, this method requires higher sampling rates and acquisition bandwidth, leading to a significant increase in system cost and data processing pressure. The second method uses a dual-chirped pulse structure, which multiplexes narrowband and wideband chirped pulses and combines them with adaptive filtering to improve dynamic range while maintaining sensitivity. However, this approach typically relies on high-speed RF signals and electro-optic modulation devices, resulting in system complexity, high cost, and high energy consumption.

[0005] Current mainstream solutions mostly employ external modulation, using arbitrary waveform generators and IQ modulators to modulate continuous laser light. However, their performance is limited by the electrical modulation bandwidth and rate bottlenecks, and they suffer from low electro-optical conversion efficiency. Therefore, a new modulation method is urgently needed to overcome electrical limitations and reduce system complexity. Summary of the Invention

[0006] To address the aforementioned issues, this application proposes a distributed acoustic wave sensing method, device, and system. By constructing dual-chirped signal sources with different sweep rates and performing demodulation and fusion processing on them respectively, signals within different vibration amplitude ranges can be measured in a targeted manner. This improves the sensitivity of weak vibration signal detection while suppressing distortion of strong vibration signals, thereby expanding the dynamic range of distributed vibration signal measurement.

[0007] The first aspect of this application provides a distributed acoustic wave sensing method, comprising: S1: using a tunable laser to output linearly swept continuous light as pump light, and injecting the pump light into a first standard single-mode fiber after optical coupling, generating first-order Stokes light in the first standard single-mode fiber through stimulated Brillouin scattering, and cascading to generate at least second-order and above Stokes light under Rayleigh backscattering feedback, so as to form a Brillouin random laser output containing pump light and multiple-order Stokes light.

[0008] S2: Select at least two swept-frequency optical signals with different center frequencies and non-overlapping frequency bands from the Brillouin random laser output as dual-chirped signal sources, including a first chirped-rate optical signal and a second chirped-rate optical signal, wherein the sweep rate of the first chirped-rate optical signal is greater than the sweep rate of the second chirped-rate optical signal, and the center frequency interval between the two is greater than their respective sweep bandwidth to achieve frequency domain separability.

[0009] S3: Select the frequency bands of the first chirped optical signal and the second chirped optical signal respectively, and input them into the optical modulator for pulse modulation after optical coupling to generate a dual-chirped pulse probe light containing two different sweep rates.

[0010] S4: Inject the dual-chirped pulse probe light into the second standard single-mode fiber as the sensing fiber, so that it propagates along the sensing fiber and excites the Rayleigh backscattering signal.

[0011] S5: The returned Rayleigh backscattered signal is separated by frequency band through at least two optical filters to obtain Rayleigh scattering signals corresponding to the first chirp rate optical signal and the second chirp rate optical signal, respectively.

[0012] S6: Based on the spectral or phase information of the Rayleigh scattering signal, extract the vibration or strain parameters distributed along the sensing fiber using spectral correlation demodulation or phase demodulation methods.

[0013] According to one embodiment of this application, the generation of the multi-order Stokes light satisfies the laser oscillation condition where the stimulated Brillouin gain is greater than the system loss.

[0014] According to one embodiment of this application, the first chirp rate optical signal is selected from high-order Stokes light, and the second chirp rate optical signal is selected from pump light or low-order Stokes light.

[0015] According to one embodiment of this application, the optical modulator is an acousto-optic modulator or a semiconductor optical amplifier, used to modulate continuous light into a pulse signal with a preset pulse width.

[0016] According to one embodiment of this application, the vibration or strain parameters are obtained by performing spectral correlation calculation on the Rayleigh scattering signal to obtain time delay information, and demodulated according to the preset correspondence between the time delay information and the sweep rate.

[0017] According to one embodiment of this application, an adaptive filtering fusion is performed on the first demodulation result corresponding to the first chirped pulse and the second demodulation result corresponding to the second chirped pulse to obtain a measurement result within a set vibration amplitude range.

[0018] According to one embodiment of this application, in the adaptive filtering fusion, a signal with lower noise is used as a reference signal, and the other signal is processed to minimize the error.

[0019] A second aspect of this application provides a distributed acoustic wave sensing device, comprising: The light source module is used to output linearly swept continuous light and provide swept light signals with different sweep rates.

[0020] The Brillouin random laser generation module includes a first standard single-mode fiber, a circulator, and an optical amplifier. It is used to generate a Brillouin random laser output containing pump light and multi-order Stokes light in the first standard single-mode fiber through stimulated Brillouin scattering and Rayleigh backscattering feedback.

[0021] The dual-chirped pulse generation module includes an optical filter bank, an optical coupler, and an optical modulator, which is used to select two swept-frequency optical signals with different center frequencies from the Brillouin random laser output through frequency band selection, and generate two pulse optical signals with different sweep rates.

[0022] The sensing module includes a second standard single-mode optical fiber for receiving the pulsed optical signal and generating a Rayleigh backscattered signal. The signal separation module includes multiple optical filters for band separation of the Rayleigh backscattered signal. The signal processing module includes a photodetector and a data processing unit for converting the optical signal into an electrical signal and performing spectral correlation demodulation or phase demodulation based on spectral or phase information to extract vibration or strain parameters.

[0023] According to one embodiment of this application, the optical filter is a fiber optic grating filter used to reflect optical signals within a set wavelength range.

[0024] According to one embodiment of this application, the signal processing module further includes a data acquisition card or oscilloscope for sampling and processing electrical signals.

[0025] According to one embodiment of this application, the drive signal for the optical modulator is provided by a signal generator.

[0026] According to one embodiment of this application, the first standard single-mode fiber is an optical fiber structure with randomly distributed refractive index perturbations, used to provide Rayleigh backscattering feedback.

[0027] A third aspect of this application provides a distributed acoustic wave sensing system, including the distributed acoustic wave sensing device described above, for acquiring distributed vibration or strain parameters along the length of an optical fiber.

[0028] According to one embodiment of this application, the system is applied to oil and gas exploration, downhole monitoring, or seismic wave detection.

[0029] According to one embodiment of this application, the system detects signals in different vibration amplitude ranges using pulsed light signals with two different sweep rates under a set sampling rate.

[0030] The technical effects achieved by this application are as follows: First, by introducing Brillouin random lasers, especially high-order random lasers, as modulation sources, large bandwidth and high speed chirped modulation can be directly realized in the optical domain, avoiding the bandwidth limitation of traditional electrical modulation devices and fundamentally improving the modulation capability.

[0031] Secondly, by adopting the "optical modulation of light" method, the losses caused by the electro-optical conversion process are reduced, making the overall energy utilization efficiency of the system higher and reducing energy consumption.

[0032] Furthermore, by combining a dual-chirped pulse structure with adaptive filtering, the advantages of both large-range large chirps and highly sensitive small chirps are combined, enabling the system to measure large disturbances while maintaining high sensitivity, thus achieving a balance between dynamic range and accuracy.

[0033] Finally, compared with solutions that rely on high-speed electrical equipment (AWG, IQ modulator, etc.), this application reduces the reliance on high-performance electrical devices, making the system structure simpler and more integrated, while significantly reducing the implementation cost.

[0034] In summary, this application achieves broadband modulation in the optical domain using Brillouin random lasers, which not only overcomes electrical bottlenecks but also enables distributed acoustic sensing with high energy efficiency, large dynamic range, and high sensitivity under low cost conditions. Attached Figure Description

[0035] Figure 1 This is a flowchart of a distributed acoustic wave sensing method disclosed in an embodiment of this application; Figure 2 This is a schematic diagram of dual-chirped signal selection based on Brillouin random laser disclosed in the embodiments of this application; Figure 3 This is a schematic diagram of the working principle of a dual-chirped signal based on a Brillouin random laser, as disclosed in the embodiments of this application. Figure 4 This is a structural diagram of a distributed acoustic wave sensing device disclosed in the embodiments of this application; Figure 5 This is a structural diagram of another distributed acoustic wave sensing device disclosed in the embodiments of this application. Detailed Implementation

[0036] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0037] This application provides a distributed acoustic wave sensing method, such as Figure 1 As shown, it includes: S1: Using the linearly swept continuous light output from a tunable laser as the pump light, and injecting the pump light into a first standard single-mode fiber after optical coupling, generating first-order Stokes light in the first standard single-mode fiber through stimulated Brillouin scattering, and cascading to generate at least second-order and above Stokes light under Rayleigh backscattering feedback, so as to form a Brillouin random laser output containing pump light and multi-order Stokes light.

[0038] S2: Select at least two swept-frequency optical signals with different center frequencies and non-overlapping frequency bands from the Brillouin random laser output as a dual-chirped signal source, including a first chirped-rate optical signal and a second chirped-rate optical signal, wherein the sweep rate of the first chirped-rate optical signal is greater than the sweep rate of the second chirped-rate optical signal, such as... Figure 2 As shown, the center frequency interval between the two is greater than their respective sweep bandwidth to achieve frequency domain separability.

[0039] S3: Select the frequency bands of the first chirped optical signal and the second chirped optical signal respectively, and input them into the optical modulator for pulse modulation after optical coupling to generate a dual-chirped pulse probe light containing two different sweep rates.

[0040] S4: Inject the dual-chirped pulse probe light into the second standard single-mode fiber as the sensing fiber, so that it propagates along the sensing fiber and excites the Rayleigh backscattering signal.

[0041] S5: The returned Rayleigh backscattered signal is separated by frequency band through at least two optical filters to obtain Rayleigh scattering signals corresponding to the first chirp rate optical signal and the second chirp rate optical signal, respectively.

[0042] S6: Based on the spectral or phase information of the Rayleigh scattering signal, extract the vibration or strain parameters distributed along the sensing fiber using spectral correlation demodulation or phase demodulation methods.

[0043] The generation of the multi-order Stokes light satisfies the laser oscillation condition that the stimulated Brillouin gain is greater than the system loss.

[0044] The first chirp rate optical signal is selected from high-order Stokes light, and the second chirp rate optical signal is selected from pump light or low-order Stokes light.

[0045] The optical modulator is an acousto-optic modulator or a semiconductor optical amplifier, used to modulate continuous light into a pulse signal with a preset pulse width.

[0046] The vibration or strain parameters are obtained by performing spectral correlation calculation on the Rayleigh scattering signal to obtain time delay information, and then demodulated according to the preset correspondence between the time delay information and the sweep rate.

[0047] like Figure 3 As shown, the first demodulation result corresponding to the first chirped pulse and the second demodulation result corresponding to the second chirped pulse are adaptively filtered and fused to obtain the measurement result within the set vibration amplitude range.

[0048] In the adaptive filtering fusion, the signal with lower noise is used as the reference signal, and the other signal is processed to minimize the error.

[0049] This application utilizes the characteristic that different sweep rates correspond to different frequency-time mapping relationships, making high sweep rate signals suitable for measuring large amplitude vibration signals and low sweep rate signals suitable for detecting small amplitude vibration signals. Furthermore, it achieves coordinated characterization of signals in different amplitude ranges through fusion processing, thereby breaking through the limitations of traditional single sweep rate methods in terms of dynamic range.

[0050] This application constructs a dual-chirped signal source and uses optical signals with different sweep rates to detect the same sensing area, achieving coordinated measurement of signals with different vibration amplitudes, thereby effectively expanding the dynamic measurement range of the system. By selecting signals from different frequency bands of Brillouin random lasers as dual-chirped signal sources, the multi-laser structure is avoided, improving the simplification and stability of the system structure. By fusing the demodulation results of signals with different chirped rates, the nonlinear distortion caused by strong signals can be suppressed while ensuring the sensitivity of weak signal detection, thus improving measurement accuracy. It is compatible with the existing distributed fiber optic sensing system structure and is easy to implement in engineering.

[0051] The second aspect of this application provides a distributed acoustic wave sensing device, such as... Figure 4As shown, it includes a light source module, a Brillouin random laser generation module, a double-chirped pulse generation module, a sensing module, a signal separation module, and a signal processing module.

[0052] The device mainly includes the following components, such as... Figure 5 As shown, it includes a tunable laser 101, a first polarization controller 104, a second polarization controller 108, a standard single-mode fiber 106, a standard single-mode fiber 109, a standard single-mode fiber 202, a first optical amplifier 103, a second optical amplifier 116, a third optical amplifier 203, a signal generator 117, a first optical filter 110, a second optical filter 111, a third optical filter 115, a fourth optical filter 204, a fifth optical filter 206, an acousto-optic modulator 114, a first photodetector 205, a second photodetector 207, a data acquisition card 208, a data processing unit 209, a first 3dB coupler 102, a second 3dB coupler 107, a third 3dB coupler 112, a first circulator 105, a second circulator 113, and a third circulator 201.

[0053] The distributed acoustic wave sensing device includes: a light source module for outputting linearly swept continuous light and providing swept light signals at different sweep rates. The light source module includes a tunable laser 101, a first polarization controller 104, and a first optical amplifier 103.

[0054] A Brillouin random laser generation module includes a first standard single-mode fiber, a circulator, and an optical amplifier. It is used to generate a Brillouin random laser output containing pump light and multiple-order Stokes light through stimulated Brillouin scattering and Rayleigh backscattering feedback in the first standard single-mode fiber. The Brillouin random laser generation module includes a standard single-mode fiber 106, a first circulator 105, a second polarization controller 108, a second 3dB coupler 107, a standard single-mode fiber 109, and a second optical amplifier 116.

[0055] The dual-chirped pulse generation module includes an optical filter bank, an optical coupler, and an optical modulator. It is used to select two swept-frequency optical signals with different center frequencies from the Brillouin random laser output through frequency band selection, and generate two pulse optical signals with different sweep rates. The dual-chirped pulse generation module includes a first optical filter 110, a second optical filter 111, a third optical filter 115, an acousto-optic modulator 114, a signal generator 117, and a third 3dB coupler 112.

[0056] The sensing module is used to receive the pulsed optical signal and generate a Rayleigh backscattered signal. The sensing module includes a standard single-mode optical fiber 202, a third circulator 201, and a third optical amplifier 203.

[0057] The signal separation module includes multiple optical filters, including a fourth optical filter 204 and a fifth optical filter 206. It is used for frequency band separation of the Rayleigh backscattered signal.

[0058] The signal processing module includes a photodetector and a data processing unit, specifically including a first photodetector 205, a second photodetector 207, a data acquisition card 208, and a data processing unit 209. The signal processing module converts optical signals into electrical signals and performs spectral correlation demodulation or phase demodulation based on spectral or phase information to extract vibration or strain parameters.

[0059] Each of the above modules can be implemented by a combination of one or more devices, and the way the devices are divided does not constitute a limitation on the scope of protection of this application.

[0060] The output terminal 101a of the tunable laser 101 is connected to the input terminal 102a of the 3 dB coupler 102. The output terminal 102b of the 3 dB coupler 102 is divided into two paths: one path is connected in sequence to the optical amplifier 103, the polarization controller 104 and the circulator 105, and is injected into the standard single-mode fiber 106 through the circulator 105. In the standard single-mode fiber 106, multi-order Stokes light is generated through stimulated Brillouin scattering, thereby forming a random laser.

[0061] The random laser is output through circulator 105 and split into two paths through 3 dB coupler 107. One path is injected into standard single-mode fiber 109 after passing through polarization controller 108 and circulator 113 to introduce Rayleigh scattering feedback to maintain random laser oscillation; the other path is fed back to 3 dB coupler 102 to form a closed-loop structure.

[0062] Another optical route outputs from 3 dB coupler 102 and enters optical filter 110 and optical filter 111 to select Stokes optical components of different orders. The selected optical signals are combined by 3 dB coupler 112 and then enter optical amplifier 116 for amplification.

[0063] The amplified optical signal is filtered by optical filter 115 and then input to acousto-optic modulator 114, where it is modulated into a double-chirped pulse signal under the drive of the signal generator.

[0064] The dual-chirped pulses are injected into the standard single-mode fiber 202 via the circulator 201, generating Rayleigh backscattered signals during transmission.

[0065] The scattered signal is output by circulator 201 and then passes through optical amplifier 203, optical filter 204, and optical filter 206 for frequency band separation. It is then converted into electrical signals by photodetector 205 and photodetector 207, respectively, and input into acquisition card 208. Finally, it is demodulated and analyzed by data processing unit 209.

[0066] During operation, the tunable laser 101 outputs a sweeping continuous beam with a frequency range of B1 Hz as pump light. This beam is input to the first 3dB coupler 102 and split into two paths. One path is input to the first optical amplifier 103 and then to the first polarization controller 104 to maintain its polarization state. The next path passes through the first circulator 105 and is input to the standard single-mode fiber 106 to excite stimulated Brillouin scattering. The resulting first-order Stokes light enters the first circulator 105 and is then input from 105c to the second 3dB coupler 107, where it is split into two paths. One path is input to the first 3dB coupler 102, and the other path enters the second polarization controller 108 to maintain its polarization state. Then, the light is injected into a standard single-mode fiber 109 through a second circulator 113. Rayleigh scattering light generated by a first-order Stokes beam is produced in the standard single-mode fiber 109. The first-order Stokes beam is output to free space through port 109b, and the resulting scattered light is input into the standard single-mode fiber 106. This scattered light serves as the gain of the first-order Stokes beam. When the power of the first-order Stokes beam reaches a threshold, a second-order Stokes beam is excited in the standard single-mode fiber 106. As described above, an nth-order Stokes beam can be generated. The initial pump light has a sweep frequency range of B0 Hz, and the generated nth-order Stokes beam has a sweep frequency range of nB0 Hz. Another path of the standard single-mode fiber 106 serves as the probe light output port. The output light includes the initial pump light, first-order Stokes light to nth-order Stokes light. The light with a frequency sweep range of B1 and B2 Hz is filtered out by the first optical filter 110 and the second optical filter 111. It is then input into the third 3dB coupler 112 for frequency division multiplexing and then used as the probe light to be amplified by the second optical amplifier 116. The third optical filter 115 filters out spontaneous emission noise. The pulse with a pulse width of τ is generated by the acousto-optic modulator 114 driven by the signal generator 117. After being input into port 201a of the third circulator 201, it is output from port 201b and injected into the standard single-mode fiber 202. The backscattered Rayleigh light excited by the pulse returns and passes through the third circulator 201. It is then injected into the third optical amplifier 203 through port 201c for gain amplification. After amplification, the Rayleigh scattered light enters the fourth optical filter 204 to extract a swept-frequency Rayleigh scattered light signal with a center frequency of f1 and a bandwidth of B1. The signal output from the reflected light output port 204b of the fourth optical filter 204 is the extracted frequency band component, which is then connected to the first photodetector 205. The output 205b of the first photodetector 205 is connected to channel 208a of the acquisition card 208. The transmitted light output port 204c of the fourth optical filter 204 is connected to the input port 206a of the fifth optical filter 206 to extract a swept-frequency Rayleigh scattered light signal with a frequency of f2 and a bandwidth of B2. The output signal from the reflected light output port 206b of the fifth optical filter 206 is connected to the second photodetector 207. The RF signal output port 207b of the second photodetector 207 is connected to the ADC acquisition channel 208b of the acquisition card 208.The acquisition card 208 transmits digital signals to the data processing unit 209 through a link formed by the connection between port 208c and port 209a.

[0067] The continuously sweeping light output by the tunable laser 101 in the application is , The initial frequency of the chirped pulse. Let be the amplitude of the pump electric field at time 0. The initial sweep rate is [value], and the sweep range is [value]. .

[0068] (1) The stimulated Brillouin first-order Stokes light excited by the pump light in a standard single-mode fiber can be expressed as: (2) in For Brillouin shift, Let be the amplitude of the first-order Stokes beam at time 0. After being amplified by Rayleigh backscattering in a standard single-mode fiber, the first-order Stokes beam reaches the stimulated Brillouin threshold, which in turn excites a second-order Stokes beam. This process repeats until an nth-order Stokes beam is generated, at which point the frequency sweep range is... At this point, the random laser reaches a stable laser oscillation state, continuously outputting Stokes light of orders 1 to n. The required double-chirped pulses are filtered out using an optical filter and coupled through a 3 dB coupler, then input to the acousto-optic modulator 114 to generate the desired double-chirped pulse light. , , and For scan rate, Represents a rectangular window function. The pulse width. The initial frequency of the large-chirp pulse. The initial frequency of the chirping pulse is . The amplitude of the double-chirped pulsed photoelectric field at time 0 is expressed as .

[0069] (3) The expressions for the Rayleigh scattering electric field excited by the double-chirped pulse described in the application are as follows: , , The time delay required to receive the scattered light from the i-th scattering point Let be the Rayleigh scattering coefficient at the i-th scattering point. Let L be the amplitude of the scattered electric field at time 0, and L be the total number of scattering points on the entire sensing fiber.

[0070] (4) Since the starting frequencies of the two chirped pulses have a certain frequency interval and their occupied frequency bandwidths do not overlap, the backscattered Rayleigh signals excited by the large and small chirped pulses can be separated by an optical filter. Optical filter 204 is used to extract the large-chirped bandwidth Rayleigh scattering signal. The optical filter is essentially composed of a fiber optic grating, reflecting light of a specific wavelength to extract the target frequency band signal. The returned mixed Rayleigh scattering light, after having its large-chirped bandwidth component extracted by optical filter 115, is then fed into optical filter 206 to extract the small-chirped bandwidth Rayleigh scattering signal. Besides extracting the signal light of a specific frequency band, another function of optical filters 204 and 206 is to filter out ASE noise introduced during amplification by optical amplifier 203, improving signal quality. The signal acquired by acquisition card 208 is transmitted to data processing unit 209 for signal segmentation and time delay information extraction. The time delay information is extracted using spectral correlation demodulation to obtain the time delay information between Rayleigh scattering signals within the same group. The mapping relationship between temperature and strain disturbance is as follows: (5) in In response, Information on temperature changes The sweep rate term is the same as the term in formula (4). and The physical meaning is the same.

[0071] In this application, after being received by a photodetector, the AC term spectrum expression of the Rayleigh scattering signal is as follows: (6) Its features are, The value of the detector output current at time 0. The Rayleigh scattering coefficients are normalized in the frequency domain. This represents the sweep frequency range of the chirped pulses.

[0072] Harnessing a portion of the bandwidth energy of a large-chirped bandwidth signal can lead to sensitivity loss. However, using a small-chirped signal with the same bandwidth as a low-pass filter, which is bandwidth-multiplexed, is equivalent to adding a full-bandwidth Rayleigh scattering signal to the system. This signal does not suffer sensitivity loss and can compensate for the insufficient sensitivity of the large-chirped bandwidth signal acquired at low bandwidth and low sampling rate, thus enhancing the system's ability to detect small disturbances. Since the two signals have different strengths, an adaptive filtering method can be used in the overlapping region of their detection ranges to combine the advantages of both signals, allowing the system to maintain both large strain measurement and high detection sensitivity. The expression for the strain disturbance result of the two Rayleigh scattering signals is as follows: (7) The demodulation results are for a large-chirp, wide-bandwidth Rayleigh signal, where... The system noise floor is mainly characterized by broadband white noise. This is the demodulation result of a small-chirped bandwidth Rayleigh signal, where The system noise floor, which manifests as broadband white noise, is determined by formula (4). As can be seen, after partial bandwidth sampling, the sensitivity deteriorates, resulting in a decrease in signal noise floor. > The relationship. Signal Due to its limited range, demodulating large strains introduces a 1 / f noise term when using a different reference curve. (in the noise item) The number of times the reference curve was changed was mainly concentrated in the low-frequency range. For the actual measured dependent variable, two sets of signals ( and In ) The same parameter is used. During adaptive filtering correction, the demodulated signal with lower system noise floor... As a reference signal in the adaptive filtering algorithm ,and The signal to be filtered The error expression is: (8) Its cost function is defined as: (9) Traditional solutions generate a wide-range swept-frequency chirped signal using an arbitrary waveform generator in electrical equipment, then amplify the power through an RF driver, and finally input it into a quadrature modulator to modulate continuous light. This approach has high hardware requirements, high energy consumption, low electro-optical conversion efficiency, is difficult to integrate, and is expensive. Unlike traditional solutions that generate chirped pulses based on electrical modulation, this application uses a Brillouin random laser as the modulation source for dual-chirped pulses and leverages a high-order random laser to achieve broadband modulation output. This optical modulation method bypasses the bandwidth bottleneck of high-speed electrical devices, improving energy conversion efficiency. Furthermore, the dual-chirped pulse design, compared to a single-chirped pulse, expands the system's measurable dynamic range, providing a new implementation path for low-cost, high-dynamic-range distributed acoustic wave sensing.

[0073] This application constructs a dual-chirped pulse generation scheme with a high-order Brillouin random laser as the core modulation source, achieving a breakthrough in key technologies. Through high-order Brillouin random laser modulation, high-bandwidth, high-speed linearly swept light is directly generated in the optical domain, fundamentally overcoming the bottleneck problem of traditional electrical modulation limited by device bandwidth, and eliminating the need for an electro-optical conversion stage. Simultaneously, the optical modulation design significantly improves energy conversion efficiency, reduces energy consumption, and ensures high-power pulse output. Furthermore, compared to single-chirped pulses, dual-chirped pulses expand the dynamic measurement range, achieving a synergistic improvement in measurement range and resolution; and the scheme's cost is controllable, enabling the system to possess stronger distributed acoustic sensing capabilities at a low cost.

[0074] This application proposes a distributed acoustic wave sensing method based on Brillouin random lasers with dual chirped pulses. The core of this method lies in utilizing Brillouin random lasers, especially high-order random lasers, as the modulation source for dual chirped pulses, achieving high-speed, wide-bandwidth optical modulation. Compared to traditional methods relying on high-speed electrical modulation devices, this method overcomes the limitations of electrical modulation rate and bandwidth, effectively reducing efficiency losses during electro-optical conversion, overcoming the limitation of electrical modulation rate, improving the dynamic measurement capability of the distributed acoustic wave sensing system, and reducing system implementation costs.

[0075] The technical effects achieved by this application are as follows: First, by introducing Brillouin random lasers, especially high-order random lasers, as modulation sources, large bandwidth and high speed chirped modulation can be directly realized in the optical domain, avoiding the bandwidth limitation of traditional electrical modulation devices and fundamentally improving the modulation capability.

[0076] Secondly, by adopting the "optical modulation of light" method, the losses caused by the electro-optical conversion process are reduced, making the overall energy utilization efficiency of the system higher and reducing energy consumption.

[0077] Furthermore, by combining a dual-chirped pulse structure with adaptive filtering, the advantages of both large-range large chirps and highly sensitive small chirps are combined, enabling the system to measure large disturbances while maintaining high sensitivity, thus achieving a balance between dynamic range and accuracy.

[0078] Finally, compared with solutions that rely on high-speed electrical equipment (AWG, IQ modulator, etc.), this application reduces the reliance on high-performance electrical devices, making the system structure simpler and more integrated, while significantly reducing the implementation cost.

[0079] In summary, this application achieves broadband modulation in the optical domain using Brillouin random lasers, which not only overcomes electrical bottlenecks but also enables distributed acoustic sensing with high energy efficiency, large dynamic range, and high sensitivity under low cost conditions.

[0080] The technical solutions of this application are illustrated below through specific embodiments. It should be understood that the one or more steps mentioned in this application do not preclude the existence of other methods and steps before or after the combined steps, or that other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are for illustrative purposes only and are not intended to limit the scope of this application. Unless otherwise stated, the numbering of each method step is only for the purpose of identifying each method step, and not for limiting the order of each method or defining the scope of this application. Changes or adjustments to their relative relationships, without substantial changes to the technical content, can also be considered as within the scope of implementation of this application.

[0081] The raw materials and instruments used in the examples are not subject to any specific restrictions on their source; they can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0082] The foregoing description of specific exemplary embodiments of this application is for illustrative and explanatory purposes. These descriptions are not intended to limit this application to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of this application and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of this application, as well as various different choices and variations. The scope of this application is intended to be defined by the claims and their equivalents.

[0083] The above detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0084] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0085] In the description of the embodiments of the present invention, it should be noted that the terms "inner", "outer", "upper", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

Claims

1. A distributed acoustic wave sensing method, characterized in that, The method includes: S1: A tunable laser outputs linearly swept continuous light as pump light, and the pump light is optically coupled and injected into a first standard single-mode fiber. In the first standard single-mode fiber, first-order Stokes light is generated through stimulated Brillouin scattering, and at least second-order and above Stokes light are cascaded under Rayleigh backscattering feedback to form a Brillouin random laser output containing pump light and multiple-order Stokes light. S2: Select at least two swept-frequency optical signals with different center frequencies and non-overlapping frequency bands from the Brillouin random laser output as dual-chirped signal sources, including a first chirped-rate optical signal and a second chirped-rate optical signal, wherein the sweep rate of the first chirped-rate optical signal is greater than the sweep rate of the second chirped-rate optical signal, and the center frequency interval between the two is greater than their respective sweep bandwidth to achieve frequency domain separability; S3: Select the frequency bands of the first chirp rate optical signal and the second chirp rate optical signal respectively, and input them into the optical modulator for pulse modulation after optical coupling to generate a dual-chirp pulse probe light containing two different sweep rates; S4: Inject the dual-chirped pulse probe light into the second standard single-mode fiber as a sensing fiber, so that it propagates along the sensing fiber and excites the Rayleigh backscattering signal. S5: The returned Rayleigh backscattered signal is separated by frequency band through at least two optical filters to obtain Rayleigh scattering signals corresponding to the first chirp rate optical signal and the second chirp rate optical signal, respectively; S6: Based on the spectral or phase information of the Rayleigh scattering signal, extract the vibration or strain parameters distributed along the sensing fiber using spectral correlation demodulation or phase demodulation methods.

2. The method according to claim 1, characterized in that, The generation of the multi-order Stokes light satisfies the laser oscillation condition that the stimulated Brillouin gain is greater than the system loss.

3. The method of claim 1, wherein, The first chirp rate optical signal is selected from high-order Stokes light, and the second chirp rate optical signal is selected from pump light or low-order Stokes light.

4. The method of claim 1, wherein, The optical modulator is an acousto-optic modulator or a semiconductor optical amplifier, used to modulate continuous light into a pulse signal with a preset pulse width.

5. The method of claim 1, wherein, The vibration or strain parameters are obtained by performing spectral correlation calculation on the Rayleigh scattering signal to obtain time delay information, and then demodulated according to the preset correspondence between the time delay information and the sweep rate.

6. The method of claim 1, wherein, Also includes: Adaptive filtering is performed to fuse the first demodulation result corresponding to the first chirped pulse and the second demodulation result corresponding to the second chirped pulse to obtain the measurement result within the set vibration amplitude range.

7. The method of claim 6, wherein, In the adaptive filtering fusion, the signal with lower noise is used as the reference signal, and the other signal is processed to minimize the error.

8. A distributed acoustic sensing apparatus, characterised in that, include: The light source module is used to output linearly swept continuous light and provide swept light signals with different sweep rates; The Brillouin random laser generation module includes a first standard single-mode fiber, a circulator and an optical amplifier, used to generate a Brillouin random laser output containing pump light and multi-order Stokes light in the first standard single-mode fiber through stimulated Brillouin scattering and Rayleigh backscattering feedback. The dual-chirped pulse generation module includes an optical filter bank, an optical coupler, and an optical modulator, which is used to select two swept-frequency optical signals with different center frequencies from the Brillouin random laser output through frequency band selection, and generate two pulse optical signals with different sweep rates. The sensing module includes a second standard single-mode optical fiber for receiving the pulsed optical signal and generating a Rayleigh backscattered signal; The signal separation module includes multiple optical filters for band separation of the Rayleigh backscattered signal; The signal processing module, including a photodetector and a data processing unit, is used to convert optical signals into electrical signals and perform spectral correlation demodulation or phase demodulation based on spectral information or phase information to extract vibration or strain parameters.

9. The apparatus of claim 8, wherein, The optical filter is a fiber optic grating filter, used to reflect optical signals within a set wavelength range.

10. The apparatus of claim 8, wherein, The signal processing module also includes a data acquisition card or oscilloscope for sampling and processing electrical signals.

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