Large dynamic range distributed sound wave sensing device and method

Abstract

The invention discloses a large dynamic range distributed sound wave sensing device and method, and relates to the technical field of optical fiber sensing, and the device comprises a laser end which is used for generating two light beams with a Brillouin frequency difference, and injecting the two light beams into a sensing optical fiber, so that the two light beams excite a Brillouin dynamic grating in the sensing optical fiber; the detection end is used for generating a detection pulse and injecting the detection pulse into the sensing optical fiber, so that the detection pulse generates a Rayleigh scattering signal in the sensing optical fiber, and meanwhile, the detection pulse and the Brillouin dynamic grating interact in the sensing optical fiber to generate a Brillouin dynamic grating reflection signal; the sensing optical fiber is respectively connected with the laser end and the detection end and is used for transmitting a mixed optical signal comprising a Rayleigh scattering signal and a Brillouin dynamic grating reflection signal to the signal processing end; and the signal processing end is connected with the sensing optical fiber and is used for processing the mixed optical signal to obtain distributed sound wave information. According to the invention, high-sensitivity and large-dynamic-range sound wave measurement can be realized.

Description

Technical Field

[0001] This application relates to the field of fiber optic sensing technology, and in particular to a large dynamic range distributed acoustic wave sensing device and method. Background Technology

[0002] With the continuous development of distributed acoustic wave sensing technology, phase-sensitive optical time-domain reflectometry (OTDR) technology has emerged. This technology utilizes the Rayleigh scattering effect in optical fibers to detect phase changes in backscattered light caused by external disturbances, thereby achieving long-distance, continuous distributed acoustic wave measurement. Due to its advantages such as multiplexing communication optical cables, intrinsic safety, and accurate positioning, this technology has become a core solution in fields such as pipeline security, perimeter intrusion detection, and traffic monitoring.

[0003] Traditional techniques primarily employ phase demodulation or spectral correlation demodulation based on Rayleigh scattering. However, existing phase demodulation methods are limited by the ±π phase entanglement phenomenon, and the inherent interference fading of Rayleigh scattering leads to signal anomalies, severely restricting measurement stability and effective range. While spectral correlation demodulation can suppress interference fading, its measurable strain range is essentially linearly related to the sweep bandwidth of the probe pulse. To increase the range, the sweep bandwidth must be increased, which directly leads to a sharp increase in system acquisition bandwidth, sampling rate, and processing costs, with limited improvement.

[0004] Therefore, existing distributed acoustic wave sensing technologies based on a single Rayleigh scattering mechanism inherently present a contradiction between sensitivity and measurement range: high-sensitivity systems struggle to handle large-strain scenarios, while pursuing a large dynamic range sacrifices system sensitivity or significantly increases costs. How to simultaneously achieve high sensitivity and a large dynamic range has become a critical technical bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0005] The purpose of this application is to provide a large dynamic range distributed acoustic wave sensing device and method, which can realize high sensitivity and large dynamic range acoustic wave measurement.

[0006] To achieve the above objectives, this application provides the following solution: In a first aspect, this application provides a large dynamic range distributed acoustic wave sensing device, comprising: Laser end, detection end, sensing fiber optic cable and signal processing end; The laser end is used to generate two beams with a Brillouin frequency difference and inject the two beams into the sensing fiber so that the two beams excite the Brillouin dynamic grating in the sensing fiber. The detector end is used to generate a detection pulse and inject the detection pulse into the sensing fiber, so that the detection pulse generates a Rayleigh scattering signal in the sensing fiber, and at the same time, the detection pulse interacts with the Brillouin dynamic grating in the sensing fiber to generate a Brillouin dynamic grating reflection signal. The sensing fiber is connected to the laser end and the detection end respectively, and is used to transmit the mixed optical signal, including Rayleigh scattering signal and Brillouin dynamic grating reflection signal, to the signal processing end. The signal processing unit, connected to the sensing fiber, is used to process the mixed optical signal to obtain distributed acoustic wave information.

[0007] Optionally, the laser end includes: a laser generating module for generating a laser beam split into a first beam and a second beam; a first optical processing module connected to the laser generating module and the sensing fiber, for modulating the first beam into a pulse beam, amplifying and adjusting the polarization state of the pulse beam to obtain an adjusted pulse beam, and injecting the adjusted pulse beam into the sensing fiber; and a second optical processing module connected to the beam splitter and the sensing fiber, for frequency modulation of the second beam to create a Brillouin frequency difference between the modulated second beam and the first beam; amplifying and adjusting the polarization state of the modulated second beam to obtain an adjusted second beam, and injecting the adjusted second beam into the sensing fiber.

[0008] Optionally, the detection end includes: a detection light source for generating continuous light; a sweep frequency modulation module for connecting to the detection light source and for frequency modulation of the continuous light for detection to generate sweep frequency continuous light; and a third optical processing module for connecting to the sweep frequency modulation module and the sensing fiber respectively, for modulating the sweep frequency continuous light into an initial detection pulse, amplifying and adjusting the polarization state of the initial detection pulse to obtain a detection pulse, and injecting the detection pulse into the sensing fiber.

[0009] Optionally, the signal processing unit includes: a signal separation module connected to the sensing fiber, used to separate the Brillouin dynamic grating reflection signal and the Rayleigh scattering signal from the mixed signal; a first demodulation module connected to the signal separation module, used to demodulate the Brillouin dynamic grating reflection signal to obtain a first acoustic signal; a second demodulation module, used to demodulate the Rayleigh scattering signal to obtain a second acoustic signal; and a fusion processing module, used to fuse the first acoustic signal and the second acoustic signal based on an adaptive filtering algorithm to obtain distributed acoustic information.

[0010] Optionally, the sensing fiber has a first polarization axis and a second polarization axis that are orthogonal to each other; the first polarization axis is used to conduct two beams to excite the Brillouin dynamic grating, and the second polarization axis is used to conduct the probe pulse.

[0011] Optionally, the device further includes: a circulator; a first port of the first circulator connected to the output of the probe end for receiving probe pulses; a second port of the first circulator connected to the sensing fiber for injecting probe pulses into the sensing fiber and receiving the mixed optical signal returned from the sensing fiber; and a third port of the first circulator connected to the signal processing end for exporting the mixed optical signal to the signal processing end.

[0012] Secondly, this application provides a large dynamic range distributed acoustic wave sensing method, which is applied to the apparatus of any one of the first aspects, and the method includes: Two beams with a Brillouin frequency difference are generated using a laser end; the two beams are used to excite a Brillouin dynamic grating in a sensing fiber. A probe pulse is generated using the probe end; the probe pulse is used to generate a Rayleigh scattering signal in the sensing fiber, and at the same time interacts with the Brillouin dynamic grating in the sensing fiber to generate a Brillouin dynamic grating reflection signal. The mixed optical signal is processed by the signal processing terminal to obtain distributed acoustic wave information; the mixed optical signal includes a mixed optical signal of Rayleigh scattering signal and Brillouin dynamic grating reflection signal.

[0013] Optionally, the mixed optical signal is processed to obtain distributed acoustic information, including: separating the Brillouin dynamic grating reflection signal and the Rayleigh scattering signal from the mixed signal; demodulating the Brillouin dynamic grating reflection signal to obtain a first acoustic signal; demodulating the Rayleigh scattering signal to obtain a second acoustic signal; and fusing the first acoustic signal and the second acoustic signal based on an adaptive filtering algorithm to obtain distributed acoustic information.

[0014] Optionally, the first and second acoustic signals are fused based on an adaptive filtering algorithm to obtain distributed acoustic information, including: using the second acoustic signal as the reference signal of the adaptive filter and the first acoustic signal as the signal to be filtered by the adaptive filter; iteratively updating the weight coefficients of the adaptive filter according to the minimum mean square error criterion based on the reference signal and the signal to be filtered, so that the mean square value of the error between the output signal of the adaptive filter and the reference signal is minimized; and using the output signal of the adaptive filter after iterative convergence as the distributed acoustic information.

[0015] Optionally, the sweep frequency range of the probe pulse covers the frequency band variation range of the Brillouin dynamic grating reflection signal.

[0016] According to the specific embodiments provided in this application, this application has the following technical effects: This application provides a large dynamic range distributed acoustic wave sensing device and method. A Brillouin dynamic grating is excited in the sensing fiber using a laser, and its optical response characteristics determine the device's potential to measure a wide range of disturbances. A probe pulse is injected into the same fiber at the detection end, which simultaneously produces two effects: first, it interacts with the Brillouin dynamic grating to generate a Brillouin dynamic grating reflection signal; second, it excites a Rayleigh scattering signal in the fiber. The Rayleigh scattering mechanism endows the device with high sensitivity for detecting minute disturbances. Therefore, the mixed optical signal output from the sensing fiber essentially contains two parts of information about the same disturbance event, but with drastically different sensing characteristics: one part (the Brillouin reflection signal) carries the ability to measure a large dynamic range, and the other part (the Rayleigh scattering signal) carries the ability to detect with high sensitivity. The signal processing unit receives this mixed signal and can simultaneously acquire these two complementary sensing information. This allows for the subsequent combination of their advantages through signal processing technology, ultimately generating distributed acoustic wave information that is both sensitive and contains large disturbances. Therefore, by using the same pulse to measure Brillouin dynamic gratings and Rayleigh scattering, this device can not only accommodate a large measurement range but also has the advantage of high sensitivity, enabling high-sensitivity and large dynamic range acoustic wave measurements. Attached Figure Description

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

[0018] Figure 1 This is a schematic diagram of the structure of a large dynamic range distributed acoustic wave sensing device provided in Embodiment 1 of this application; Figure 2 This is a schematic diagram of the Brillouin dynamic grating and Rayleigh scattering sensing principle based on a single chirped pulse in Embodiment 1 of this application; Figure 3 This is a schematic diagram of the adaptive filtering demodulation correction result in Embodiment 1 of this application; Figure 4 This is a schematic diagram of the dynamic range improvement result of Embodiment 1 of this application; Figure 5 This is a flowchart illustrating a large dynamic range distributed acoustic wave sensing method provided in Embodiment 2 of this application. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1 This embodiment provides a large dynamic range distributed acoustic wave sensing device, including: Laser end, detection end, sensing fiber and signal processing end.

[0022] The laser end is used to generate two beams with a Brillouin frequency difference and inject the two beams into the sensing fiber so that the two beams excite the Brillouin dynamic grating in the sensing fiber.

[0023] Optionally, the laser end includes: a laser generating module for generating a laser beam split into a first beam and a second beam; a first optical processing module connected to the laser generating module and the sensing fiber, for modulating the first beam into a pulse beam, amplifying and adjusting the polarization state of the pulse beam to obtain an adjusted pulse beam, and injecting the adjusted pulse beam into the sensing fiber; and a second optical processing module connected to the beam splitter and the sensing fiber, for frequency modulation of the second beam to create a Brillouin frequency difference between the modulated second beam and the first beam; amplifying and adjusting the polarization state of the modulated second beam to obtain an adjusted second beam, and injecting the adjusted second beam into the sensing fiber.

[0024] The detector end is used to generate a probe pulse and inject the probe pulse into the sensing fiber, so that the probe pulse generates a Rayleigh scattering signal in the sensing fiber, and at the same time, the probe pulse interacts with the Brillouin dynamic grating in the sensing fiber to generate a Brillouin dynamic grating reflection signal.

[0025] Optionally, the detection end includes: a detection light source for generating continuous light; a sweep frequency modulation module for connecting to the detection light source and for frequency modulation of the continuous light for detection to generate sweep frequency continuous light; and a third optical processing module for connecting to the sweep frequency modulation module and the sensing fiber respectively, for modulating the sweep frequency continuous light into an initial detection pulse, amplifying and adjusting the polarization state of the initial detection pulse to obtain a detection pulse, and injecting the detection pulse into the sensing fiber.

[0026] The sensing fiber is connected to the laser end and the detection end respectively, and is used to transmit the mixed optical signal, including Rayleigh scattering signal and Brillouin dynamic grating reflection signal, to the signal processing end.

[0027] Optionally, the sensing fiber has a first polarization axis and a second polarization axis that are orthogonal to each other; the first polarization axis is used to conduct two beams to excite the Brillouin dynamic grating, and the second polarization axis is used to conduct the probe pulse.

[0028] The signal processing unit, connected to the sensing fiber, is used to process the mixed optical signal to obtain distributed acoustic wave information.

[0029] Optionally, the signal processing unit includes: a signal separation module connected to the sensing fiber, used to separate the Brillouin dynamic grating reflection signal and the Rayleigh scattering signal from the mixed signal; a first demodulation module connected to the signal separation module, used to demodulate the Brillouin dynamic grating reflection signal to obtain a first acoustic signal; a second demodulation module, used to demodulate the Rayleigh scattering signal to obtain a second acoustic signal; and a fusion processing module, used to fuse the first acoustic signal and the second acoustic signal based on an adaptive filtering algorithm to obtain distributed acoustic information.

[0030] Optionally, the fusion processing module is specifically used to: separate the Brillouin dynamic grating reflection signal and the Rayleigh scattering signal from the mixed signal; demodulate the Brillouin dynamic grating reflection signal to obtain the first acoustic signal; demodulate the Rayleigh scattering signal to obtain the second acoustic signal; and fuse the first acoustic signal and the second acoustic signal based on an adaptive filtering algorithm to obtain distributed acoustic information.

[0031] As an optional implementation, the device further includes: a circulator; a first port of the first circulator connected to the output of the probe end for receiving probe pulses; a second port of the first circulator connected to the sensing optical fiber for injecting probe pulses into the sensing optical fiber and receiving the mixed optical signal returned from the sensing optical fiber; and a third port of the first circulator connected to the signal processing end for exporting the mixed optical signal to the signal processing end.

[0032] This embodiment employs the same chirped sweep pulse to detect both the Brillouin dynamic grating and Rayleigh scattering in the optical fiber, demodulating the two sensing signals separately, and then using adaptive filtering to fuse their measurement advantages, thereby achieving a large dynamic range. The Brillouin dynamic grating handles the large measurement range, while Rayleigh scattering handles high-precision detection, achieving complementary advantages within the same sensing framework and expanding the device's acoustic wave detection range.

[0033] The following is combined with Figure 1 This paper introduces a specific structure of a large dynamic range distributed acoustic wave sensing device.

[0034] like Figure 1The distributed acoustic wave sensing device shown includes three modules: a chirped detection pulse generation module 1, a Brillouin dynamic grating generation module 2, and a Brillouin dynamic grating reflection signal and Rayleigh scattering signal acquisition and processing module 3. The main components include: an internally modulated laser 101, a narrow-linewidth laser 201, an RF signal source 204, a 3dB coupler 202, a circulator 212, a circulator 310, an electro-optic modulator 205, an acousto-optic modulator 203, a signal generator 102, an oscilloscope 301, optical filters 308 (i.e., optical filter 1, also known as the first optical filter), 309 (i.e., optical filter 2, also known as the second optical filter), optical amplifiers 206 (i.e., optical amplifier 1, also known as the first optical amplifier), 207 (i.e., optical amplifier 2, also known as the second optical amplifier), 104 (i.e., optical amplifier 3, also known as the third optical amplifier), 306 (i.e., optical amplifier 4, also known as the fourth optical amplifier), 307 (i.e., optical amplifier 5, also known as the fifth optical amplifier), and semiconductor optical... Amplifier 103, sensing fiber 213, polarization controller 208 (i.e., polarization controller 1, also known as the first polarization controller), polarization controller 209 (i.e., polarization controller 2, also known as the second polarization controller), polarization controller 105 (i.e., polarization controller 3, also known as the third polarization controller), polarization diversity unit 210 (i.e., polarization diversity unit 1, also known as the first polarization diversity unit), polarization diversity unit 211 (i.e., polarization diversity unit 2, also known as the second polarization diversity unit), photodetector 302 (i.e., photodetector 1, also known as the first photodetector), photodetector 303 (i.e., photodetector 2, also known as the second photodetector), dense wavelength division multiplexer 304 (i.e., dense wavelength division multiplexer 1, also known as the first dense wavelength division multiplexer), dense wavelength division multiplexer 305 (i.e., dense wavelength division multiplexer 2, also known as the second dense wavelength division multiplexer).

[0035] The receiving end 101a of the internal modulation laser 101 (including the aforementioned detection light source and sweep frequency modulation module) is connected to the output end 102a of the signal generator 102. The signal generator 102 outputs a modulation voltage to the internal modulation laser 101, and its output end 101b is connected to the input end 103a of the semiconductor optical amplifier 103 for pulse modulation, outputting an optical pulse (i.e., the aforementioned initial detection pulse). The input end 103b of the semiconductor optical amplifier 103 is connected to the output end 102c of the signal generator 102. The signal generator 102 outputs a pulse electrical signal to the semiconductor optical amplifier 103, and its output end 103c is connected to the input end 104a of the optical amplifier 104 to amplify the optical pulse. The output end 104b of the optical amplifier 104 is connected to the input end 105a of the polarization controller 105, which adjusts the polarization state of the optical pulse. The output terminal 105b of the polarization controller 105 is connected to the port 212a of the circulator 212. The aforementioned third optical processing module may include a semiconductor optical amplifier 103, an optical amplifier 104, and a polarization controller 105.

[0036] The output terminal 201a of the narrow linewidth laser 201 is connected to a 3dB coupler 202 (i.e., the laser generation module mentioned above, which may include the narrow linewidth laser 201 and the 3dB coupler 202, used to generate a laser beam split into a first beam and a second beam) for beam splitting. Its output is connected to the input terminals 203a and 205a of the acousto-optic modulator 203 and electro-optic modulator 205, respectively, generating Stokes pulse light (i.e., the pulse beam mentioned above) and pump light (i.e., the modulated second beam mentioned above). The input terminal 203c of the acousto-optic modulator 203 is connected to one end 102b of the signal generator 102. The signal generator 102 outputs an electrical pulse signal to the acousto-optic modulator 203. The output terminal 203b is connected to the input terminal 206a of the optical amplifier 206, which amplifies the Stokes pulse light. The output terminal 206b of the optical amplifier 206 is connected to the input terminal 208a of the polarization controller 208, which adjusts the polarization state of the Stokes pulse light. The output terminal 208b of the polarization controller 208 is connected to the input terminal 210a of the polarization diversity converter 210. The Stokes pulse light enters the slow axis (i.e., the first polarization axis or the second polarization axis) of the polarization-maintaining fiber (i.e., the sensing fiber) 213 through the polarization diversity converter 210. One end 210c of the polarization diversity converter 210 is connected to one end 211b of the polarization diversity converter 211 through the polarization-maintaining fiber (i.e., the aforementioned sensing fiber) 213. One end 210b of the polarization diversity converter 210 is connected to the circulator 212b. The aforementioned first optical processing module may include: an acousto-optic modulator 203, an optical amplifier 206, a polarization controller 208, and a polarization diversity converter 210.

[0037] The receiving end 205b of the electro-optic modulator 205 is connected to the output end 204a of the radio frequency signal source 204. The radio frequency signal source 204 outputs a radio frequency signal to the electro-optic modulator 205 to shift the pump light frequency. The output end 205c of the electro-optic modulator 205 is connected to the input end 207a of the optical amplifier 207. The optical amplifier 207 amplifies the frequency-shifted pump light (i.e., the modulated second beam mentioned above). The output end 207b of the optical amplifier 207 is connected to the input end 209a of the polarization controller 209. The polarization controller 209 adjusts the polarization state of the amplified pump light. The output end 209b of the polarization controller 209 is connected to the end 211a of the polarization diversity converter 211. The aforementioned second optical processing module may include the electro-optic modulator 205, the optical amplifier 207, the polarization controller 209, and the polarization diversity converter 211, and may also include the radio frequency signal source 204.

[0038] One end 212c of circulator 212 is connected to one end 310a of circulator 310. One end 310b of circulator 310 is connected to the input 308b of optical filter 308. One end 310c of circulator 310 is connected to the input 309b of optical filter 309. Optical filters 308 and 309 filter and separate the Rayleigh scattering signal and the Brillouin dynamic grating reflection signal, respectively. The output 308a of optical filter 308 is connected to the input 306b of optical amplifier 306, which amplifies the Rayleigh scattering signal. The output 306a of optical amplifier 306 is connected to the input 304b of dense wavelength division multiplexer 304, filtering out ASE noise introduced by optical amplifier 306. The output 304a of dense wavelength division multiplexer 304 is connected to the input 302b of photodetector 302, which performs photoelectric conversion on the Rayleigh scattering signal, converting it into a Rayleigh scattering electrical signal. The output terminal 302a of the photodetector 302 is connected to the input terminal 301b of the oscilloscope 301, and the oscilloscope 301 acquires the Rayleigh scattering electrical signal.

[0039] The output terminal 309a of the optical filter 309 is connected to the input terminal 307b of the optical amplifier 307, which amplifies the Brillouin dynamic grating reflection signal. The output terminal 307a of the optical amplifier 307 is connected to the input terminal 305b of the dense wavelength division multiplexer 305, which filters out ASE noise introduced by the optical amplifier 307. The output terminal 305a of the dense wavelength division multiplexer 305 is connected to the input terminal 303b of the photodetector 303. The photodetector 303 performs photoelectric conversion on the Brillouin dynamic grating reflection signal, converting it into a Brillouin dynamic grating reflection electrical signal. The output terminal 303a of the photodetector 303 is connected to the input terminal 301c of the oscilloscope 301 to acquire the Brillouin dynamic grating reflection electrical signal.

[0040] One end 301a of the oscilloscope 301 is connected to one end 102d of the signal generator 102, and the oscilloscope 301 and the signal generator 102 are clock synchronized.

[0041] The aforementioned signal processing unit may include optical filter 308, optical filter 309, optical amplifier 306, optical amplifier 307, dense wavelength division multiplexer 304, dense wavelength division multiplexer 305, photodetector 302, photodetector 303, oscilloscope 301, and signal processing module (such as computer equipment). The signal processing module is located in... Figure 1 It is not shown in the text.

[0042] The principle of the Brillouin dynamic grating generation section is as follows: By injecting two laser beams with a frequency difference equal to the Brillouin frequency shift into the slow axis of the polarization-maintaining fiber, the two beams satisfy the phase matching condition, thus generating a Brillouin dynamic grating in the slow axis. This dynamic grating exists uniformly in the polarization-maintaining fiber and is a weakly reflective grating, capable of reflecting light injected from the other axis of the polarization-maintaining fiber, while simultaneously exhibiting a Brillouin frequency shift. The principle of the Brillouin dynamic grating and Rayleigh scattering detection section is as follows: A linearly frequency-modulated chirped pulse is injected into the fast axis of the polarization-maintaining fiber. Due to the presence of the dynamic grating, the backscattered light simultaneously contains the reflected light from the dynamic grating and the Rayleigh scattered light, which differ in frequency by a Brillouin frequency. Therefore, they can be extracted separately using a filter and demodulated using acoustic waves, such as... Figure 2 As shown. The principle of the signal demodulation section is as follows: the Brillouin dynamic grating has low sensitivity, resulting in relatively high noise in the demodulated acoustic wave; while Rayleigh scattered light has high sensitivity, resulting in relatively low noise in the demodulated acoustic wave. For example... Figure 3 As shown, the acoustic wave obtained by Rayleigh scattering light demodulation is used as the reference input of an adaptive filter to enhance the noisy acoustic signal obtained by Brillouin dynamic grating optical demodulation, thereby improving its sensitivity. Since the Brillouin dynamic grating has a large measurement range, a distributed acoustic wave sensing system that balances high sensitivity and large dynamic range can be realized.

[0043] The signal processing module also needs to fuse the Brillouin dynamic grating reflection electrical signal and the Rayleigh scattering electrical signal to obtain distributed acoustic wave information. The specific process is as follows: The expressions for the excited Rayleigh backscattering and Brillouin dynamic grating reflection electric fields are respectively , With two returning light sources excited by the same chirped pulse, it is possible to simultaneously receive the reflected light from the Brillouin Dynamic Grating (BDG) and the backscattered light from the Rayleigh scattering system (CPDAS). The electric field formula for the acquired signal can be expressed as: (1) The expressions for the reflected electric field and Rayleigh backscattering of the excited Brillouin dynamic grating are as follows: , As can be seen from formula (1), since the optical frequencies of the two returning beams have a certain frequency interval and the frequency bandwidths they occupy do not overlap, the two signals can be separated by an optical filter.

[0044] Both sensors employ similar sensing mechanisms, performing time-domain cross-correlation on the acquired raw curves. The frequency shift can be derived from the chirp rate of the modulated chirped pulse, thus obtaining the specific numerical change in strain or temperature. Therefore, their unified expression can be represented as: (2) in This represents the frequency shift caused by temperature or strain. and These represent the sweep frequency range and pulse width of the chirped pulse, respectively. This represents the corresponding delay obtained.

[0045] For a Brillouin dynamic grating system, the magnitude of the frequency shift can be expressed as: , This indicates the change in birefringence caused by temperature or strain. Represents the center frequency of the pump light. The group refractive index represents the optical fiber.

[0046] For CPDAS systems This is expressed as the frequency shift caused by changes in relative refractive index due to temperature or strain in the CPDAS system.

[0047] Since the two signals have different emphases in the overlapping region of their detection ranges, an adaptive filtering method can be used to combine the advantages of both signals. This allows the system to maintain both large strain measurement and high detection sensitivity. The expression for the strain perturbation result of the two signal beams is as follows: (3) In expression (3), The demodulation result of the Brillouin dynamic grating reflection signal is shown, where The system noise floor is mainly characterized by broadband white noise. This is the demodulation result of the Rayleigh signal, where It is 1 / f noise. This represents a demodulated signal with low system noise during adaptive filtering correction, representing a true acoustic signal. As a reference signal in the adaptive filtering algorithm ,and The signal to be filtered The schematic diagram is as follows Figure 4In the graph, the horizontal axis represents the frequency sweep range of the probe light, and the vertical axis represents the dynamic range improvement effect. The error expression is: (4) Its cost function is defined as: (5) The cost function in formula (5) is the expectation of the square of the error signal, and the filter weight matrix is... The update criterion is to minimize the cost function. The fastest gradient descent algorithm is used. This yields the update expression for adjusting the filter weight vector: (6) Filter final output result The expression is as follows: (7) Since both sets of signals measure the same vibration, The system is correlated, while the noise is independent. As shown in equation (7), the final output at system iteration convergence is... Remove white noise from the Brillouin dynamic grating system and 1 / f noise in the CPDAS system This achieves noise removal and sensitivity correction, resulting in a near-realistic sound wave signal. The signal can be used to determine distributed acoustic wave information.

[0048] In this embodiment, Rayleigh-Brillouin fusion sensing is used, which can improve the dynamic range of the device without significantly increasing the complexity of the device.

[0049] As an optional implementation method, Figure 1 The structure provided in this embodiment is only one implementation of the distributed acoustic wave sensing device provided in this example. Further implementations can be made according to requirements. Figure 1 The structure is adaptively replaced, for example: The electro-optic modulator 205 can be replaced with an acousto-optic frequency shifter.

[0050] The signal generator 102 can be replaced with a combination of a voltage-controlled oscillator and a controllable voltage source.

[0051] The acousto-optic modulator 203 can be a semiconductor optical amplifier.

[0052] Photodetector 302 and photodetector 303 can be replaced with low-bandwidth, low-noise detectors.

[0053] The oscilloscope 301 can be replaced with a data acquisition card.

[0054] The narrow-linewidth laser 201 outputs laser light, which is split into two paths by coupler 202 and modulated to obtain pump light. These pump light paths pass through polarization diversity dividers 210 and 211, respectively, and are input towards the x-axis of polarization-maintaining fiber 213. Meanwhile, the chirped pulse light is input towards the y-axis of polarization-maintaining fiber 213 through a circulator. Alternatively, the output laser light of the narrow-linewidth laser 201 can be split into two paths by coupler 202 and modulated to obtain pump light, which is then input towards the y-axis of polarization-maintaining fiber 213 through polarization diversity dividers 210 and 211, respectively, while the chirped pulse light is input towards the x-axis of polarization-maintaining fiber 213 through a circulator. In other words, the chirped pulse input axis and the Brillouin dynamic grating generation axis can be interchanged.

[0055] The circulator 310 can be replaced by a coupler to split the return light into two paths that enter different filters, filtering out the Brillouin dynamic grating reflected light and the Rayleigh backscattered light respectively.

[0056] The semiconductor optical amplifier 103 can be replaced by an acousto-optic modulator and an optical amplifier 206, which can also modulate pulse signals and amplify optical signals.

[0057] The narrow linewidth laser 201 can be increased from one to two, so that it can be split into two paths without the need for a coupler. The laser outputs of the two lasers enter the acousto-optic modulator and the electro-optic modulator respectively for modulation.

[0058] The radio frequency signal source 204 can be replaced by a voltage-controlled oscillator. By connecting the signal generator 102, the sawtooth wave signal is input into the voltage-controlled oscillator to generate a radio frequency signal that is input into the electro-optic modulator 205.

[0059] The acousto-optic modulator 203 can be replaced by the electro-optic modulator 205 and the acousto-optic modulator 203. That is, the signal is first frequency-shifted by a factor equal to the Brillouin frequency shift of the optical fiber, and then pulse cutting is performed.

[0060] Dense wavelength division multiplexer 304 and dense wavelength division multiplexer 305 can be replaced by an 8GHz bandwidth optical filter to filter the received signal and further filter other noise, thereby improving the signal-to-noise ratio.

[0061] In addition to using the internal modulation laser 101, the chirped pulse can also be modulated by external modulation. By using a narrow linewidth laser and an electro-optic modulator to modulate the swept light, and then inputting it into the semiconductor optical amplifier 103 to modulate the swept light, the chirped pulse light is generated.

[0062] The measurement can be replaced by multiple high-frequency single-frequency pulses by injecting chirped pulse light. The step-frequency scheme is used for sensing. The principle is the same: the time delay is calculated by cross-correlation, and then the corresponding temperature and strain changes are calculated.

[0063] The apparatus provided in this embodiment generates a Brillouin dynamic grating in one axis of a polarization-maintaining fiber, and simultaneously detects the reflected light and Rayleigh scattered light from the Brillouin dynamic grating using chirped pulses in the other axis, performing acoustic demodulation separately. Based on an adaptive filtering algorithm, it fuses the wide-range measurement advantages of the Brillouin dynamic grating and the high sensitivity of Rayleigh scattered light, achieving a large dynamic range fiber-optic distributed acoustic measurement that balances high sensitivity. The frequency sweep range of the chirped pulses can be adjusted as needed to increase the upper limit of the device's measurement and further expand the system's dynamic range.

[0064] Example 2 like Figure 5 As shown, this embodiment provides a large dynamic range distributed acoustic wave sensing method, which is applied to the device provided in Embodiment 1. The method includes: S1 uses a laser end to generate two beams with a Brillouin frequency difference.

[0065] Two beams are used to excite a Brillouin dynamic grating in the sensing fiber.

[0066] S2 generates a detection pulse using the detection end.

[0067] The probe pulse is used to generate a Rayleigh scattering signal in the sensing fiber, and at the same time interacts with the Brillouin dynamic grating in the sensing fiber to generate a Brillouin dynamic grating reflection signal.

[0068] S3 uses the signal processing terminal to process the mixed optical signal to obtain distributed acoustic wave information.

[0069] The mixed optical signal includes a mixture of Rayleigh scattering signal and Brillouin dynamic grating reflection signal.

[0070] Optionally, the mixed optical signal is processed to obtain distributed acoustic information, including: separating the Brillouin dynamic grating reflection signal and the Rayleigh scattering signal from the mixed signal; demodulating the Brillouin dynamic grating reflection signal to obtain a first acoustic signal; demodulating the Rayleigh scattering signal to obtain a second acoustic signal; and fusing the first acoustic signal and the second acoustic signal based on an adaptive filtering algorithm to obtain distributed acoustic information.

[0071] As an optional implementation, the first acoustic signal and the second acoustic signal are fused based on an adaptive filtering algorithm to obtain distributed acoustic information. This includes: using the second acoustic signal as the reference signal of the adaptive filter and the first acoustic signal as the signal to be filtered by the adaptive filter; iteratively updating the weight coefficients of the adaptive filter according to the minimum mean square error criterion based on the reference signal and the signal to be filtered, so that the mean square value of the error between the output signal of the adaptive filter and the reference signal is minimized; and using the output signal of the adaptive filter after iterative convergence as the distributed acoustic information.

[0072] It should be noted that the specific process of fusing the first and second acoustic signals based on the adaptive filtering algorithm can be referred to in Example 1, and will not be repeated here.

[0073] The method provided in this embodiment combines the wide-range measurement capability of the Brillouin dynamic grating with the high sensitivity advantage of Rayleigh scattering light through an adaptive filtering algorithm. The formula for calculating the dynamic range is as follows: ,in For the maximum measurable strain, The minimum measurable strain is the dynamic range, meaning the dynamic range depends on the ratio of the maximum to the minimum measurable strain. When Rayleigh scattering is used alone, its maximum measurable strain is low, thus limiting the dynamic range. However, this limitation is significantly overcome by enhancing the system with a Brillouin dynamic grating. Through the fusion of adaptive filtering algorithms, the large measurement range of the Brillouin dynamic grating is effectively combined with maintaining the high sensitivity of Rayleigh scattering, thereby greatly improving the overall dynamic range of the system. The results are as follows: Figure 4 As shown.

[0074] The distributed acoustic wave sensing method provided in this embodiment simultaneously excites Brillouin dynamic grating reflection and Rayleigh scattering using the same chirped sweep pulse. While Brillouin dynamic grating offers a large measurement range but low accuracy, and Rayleigh scattering offers high accuracy but a small measurement range, the acoustic wave signals measured by the two sensing principles are demodulated separately. An adaptive filtering algorithm is then used to fuse the demodulated signals, achieving a complementary balance between large measurement range and high accuracy. Compared to traditional dual-chirped schemes, this embodiment does not require further increasing the sweep bandwidth. By leveraging the large measurement range of the Brillouin dynamic grating and the high-precision acoustic wave detection achieved by Rayleigh scattering, the effective measurement range can be significantly expanded. Simultaneously, the simultaneous acquisition of both signals does not sacrifice measurement bandwidth, enabling wide-bandwidth, high-sensitivity, and ultra-large dynamic range distributed acoustic wave measurement.

[0075] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0076] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. In summary, the content of this specification should not be construed as a limitation of this application.

Claims

1. A large dynamic range distributed acoustic wave sensing device, characterized in that, The device includes: Laser end, detection end, sensing fiber optic cable and signal processing end; The laser end is used to generate two beams with a Brillouin frequency difference and inject the two beams into the sensing fiber so that the two beams excite a Brillouin dynamic grating in the sensing fiber. The detection end is used to generate a detection pulse and inject the detection pulse into the sensing fiber, so that the detection pulse generates a Rayleigh scattering signal in the sensing fiber, and at the same time, the detection pulse interacts with the Brillouin dynamic grating in the sensing fiber to generate a Brillouin dynamic grating reflection signal. The sensing fiber is connected to the laser end and the detection end respectively, and is used to transmit the mixed optical signal including the Rayleigh scattering signal and the Brillouin dynamic grating reflection signal to the signal processing end; The signal processing terminal is connected to the sensing optical fiber and is used to process the mixed optical signal to obtain distributed acoustic wave information.

2. The apparatus according to claim 1, characterized in that, The laser end includes: The laser generation module is used to generate laser beams, which are divided into a first beam and a second beam. The first optical processing module is connected to the laser generating module and the sensing fiber, respectively, and is used to modulate the first beam into a pulse beam, amplify and adjust the polarization state of the pulse beam to obtain an adjusted pulse beam, and inject the adjusted pulse beam into the sensing fiber. The second optical processing module is connected to the beam splitter and the sensing fiber, respectively, and is used to frequency modulate the second beam so that there is a Brillouin frequency difference between the modulated second beam and the first beam; to amplify and adjust the polarization state of the modulated second beam to obtain an adjusted second beam, and to inject the adjusted second beam into the sensing fiber.

3. The apparatus according to claim 1, characterized in that, The detection end includes: A detection light source used to generate continuous light; A frequency sweep modulation module is used to connect to the detection light source and to modulate the frequency of the detection continuous light to generate frequency sweep continuous light; The third optical processing module is connected to the sweep frequency modulation module and the sensing optical fiber, respectively. It is used to modulate the sweep frequency continuous light into an initial detection pulse, amplify and adjust the polarization state of the initial detection pulse to obtain a detection pulse, and inject the detection pulse into the sensing optical fiber.

4. The apparatus according to claim 1, characterized in that, The signal processing terminal includes: A signal separation module, connected to the sensing optical fiber, is used to separate the Brillouin dynamic grating reflection signal and the Rayleigh scattering signal from the mixed signal; The first demodulation module is connected to the signal separation module and is used to demodulate the Brillouin dynamic grating reflection signal to obtain the first acoustic signal. The second demodulation module is used to demodulate the Rayleigh scattering signal to obtain the second acoustic signal; The fusion processing module is used to fuse the first acoustic signal and the second acoustic signal based on an adaptive filtering algorithm to obtain distributed acoustic information.

5. The apparatus according to claim 1, characterized in that, The sensing fiber has a first polarization axis and a second polarization axis that are orthogonal to each other; the first polarization axis is used to conduct the two beams to excite the Brillouin dynamic grating, and the second polarization axis is used to conduct the detection pulse.

6. The apparatus according to claim 1, characterized in that, The device further includes: a circulator; The first port of the first circulator is connected to the output of the probe end for receiving the probe pulse; The second port of the first circulator is connected to the sensing optical fiber, and is used to inject the probe pulse into the sensing optical fiber and receive the mixed optical signal returned from the sensing optical fiber. The third port of the first circulator is connected to the signal processing terminal and is used to export the mixed optical signal to the signal processing terminal.

7. A large dynamic range distributed acoustic wave sensing method, characterized in that, The method is applied to the apparatus according to any one of claims 1-6, and the method comprises: Two beams with a Brillouin frequency difference are generated using a laser end; wherein the two beams are used to excite a Brillouin dynamic grating in a sensing fiber. A detection pulse is generated using a detection end; wherein the detection pulse is used to generate a Rayleigh scattering signal in the sensing optical fiber, and at the same time interacts with the Brillouin dynamic grating in the sensing optical fiber to generate a Brillouin dynamic grating reflection signal. The mixed optical signal is processed by a signal processing terminal to obtain distributed acoustic wave information; wherein the mixed optical signal includes a mixed optical signal of the Rayleigh scattering signal and the Brillouin dynamic grating reflection signal.

8. The method according to claim 7, characterized in that, The process of processing the mixed optical signal to obtain distributed acoustic wave information includes: The Brillouin dynamic grating reflection signal and the Rayleigh scattering signal are separated from the mixed signal; The Brillouin dynamic grating reflection signal is demodulated to obtain the first acoustic signal; The Rayleigh scattering signal is demodulated to obtain the second acoustic signal; The first and second acoustic signals are fused using an adaptive filtering algorithm to obtain distributed acoustic information.

9. The method according to claim 8, characterized in that, The adaptive filtering algorithm is used to fuse the first acoustic signal and the second acoustic signal to obtain distributed acoustic information, including: The second acoustic signal is used as the reference signal of the adaptive filter, and the first acoustic signal is used as the signal to be filtered by the adaptive filter. Based on the reference signal and the signal to be filtered, the weight coefficients of the adaptive filter are iteratively updated according to the minimum mean square error criterion, so as to minimize the mean square value of the error between the output signal of the adaptive filter and the reference signal. The output signal of the adaptive filter after iterative convergence is used as distributed acoustic information.

10. The method according to claim 7, characterized in that, The frequency sweep range of the probe pulse covers the frequency band variation range of the Brillouin dynamic grating reflection signal.

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