Method and system for suppressing rayleigh scattering noise of a distributed acoustic sensing system

Abstract

This application relates to a Rayleigh scattering noise suppression method and system for a distributed acoustic wave detection system. The method includes: performing optical phase sinusoidal modulation on a high-coherence continuous laser output from a narrow-linewidth laser in an FBG-based distributed acoustic detection system according to a set modulation scheme using an optical phase modulator; the set modulation scheme is Csin(2πf m t), C is the phase modulation amplitude, f m The phase modulation frequency and satisfying f m τ = k, where τ is the time difference between two adjacent reflected light pulses being detected, t is time, and k is an integer. A highly coherent continuous laser beam with sinusoidal phase modulation is passed through an unbalanced interferometer to generate dual light pulses. These dual light pulses are then injected into an FBG array for distributed acoustic wave detection. This achieves low-noise distributed acoustic wave detection and effectively improves the detection performance of FBG-based distributed acoustic wave detection.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber distributed acoustic wave detection technology, and relates to a Rayleigh scattering noise suppression method and system for a distributed acoustic wave detection system. Background Technology

[0002] Fiber optic distributed acoustic wave detection technology has significant application value in fields such as perimeter security, seismic wave detection, oil and gas exploration, road traffic flow monitoring, and safety monitoring of large structures such as pipelines and railways due to its advantages such as simple sensor array structure, large-scale multiplexing of sensor channels, and wide detection range. Compared with traditional fiber optic Rayleigh scattering-based distributed acoustic wave detection technology, fiber grating (FBG)-based distributed acoustic wave detection technology has advantages such as stable detection and low noise, and is gradually becoming a research hotspot in the field of fiber optic distributed acoustic wave detection both domestically and internationally.

[0003] The basic principle of FBG-based distributed acoustic detection technology is as follows: A probe optical pulse propagates within an FBG array, generating a back-reflected optical pulse at each FBG. When an external acoustic wave acts on the optical fiber between two adjacent FBGs, it causes stretching and a change in the refractive index of the fiber, resulting in the phase of the optical pulse passing through this segment being modulated by the acoustic wave. By detecting the reflected optical pulse and combining it with phase demodulation technology, complete information on the frequency, amplitude, phase, and position of the external acoustic wave can be obtained simultaneously, achieving distributed acoustic detection. However, in the process of developing this invention, the inventors discovered that traditional FBG-based distributed acoustic detection technology suffers from insufficient detection performance. Summary of the Invention

[0004] To address the technical problems existing in the above-mentioned traditional methods, this invention proposes a Rayleigh scattering noise suppression method and a Rayleigh scattering noise suppression system for a distributed acoustic wave detection system, which can achieve distributed acoustic wave detection with low Rayleigh scattering noise.

[0005] To achieve the above objectives, the embodiments of the present invention adopt the following technical solutions:

[0006] On the one hand, a Rayleigh scattering noise suppression method for a distributed acoustic wave detection system is provided, including the following steps:

[0007] The high-coherence continuous laser output from a narrow-linewidth laser in an FBG-based distributed acoustic detection system is sinusoidally modulated using an optical phase modulator according to a set modulation scheme; the set modulation scheme is Csin(2πf m t), C is the phase modulation amplitude, f m The phase modulation frequency and satisfying f m τ = k, where τ is the time difference between two adjacent reflected light pulses being detected, t is time, and k is an integer;

[0008] A highly coherent continuous laser beam with sinusoidal phase modulation is passed through an unbalanced interferometer to generate two optical pulses.

[0009] Distributed acoustic wave detection is achieved by injecting dual light pulses into an FBG array.

[0010] In one embodiment, the step of injecting dual optical pulses into an FBG array for distributed acoustic wave detection includes:

[0011] Obtain the interference pulses at each access after the dual-light pulse is injected into the FBG array;

[0012] Each interference pulse is multiplied by a cosine time-varying parameter and a sine time-varying parameter respectively, and the carrier and higher-order carrier frequency components corresponding to the transformation frequency are filtered out to obtain each orthogonal zero-frequency signal;

[0013] Differentiate and cross-multiply each of the orthogonal zero-frequency signals to obtain the phase information of each orthogonal zero-frequency signal;

[0014] The phase information is arranged in the order of access to obtain the time-varying phase; the time-varying phase is used to indicate the results of distributed acoustic wave detection.

[0015] In one embodiment, the step of injecting dual optical pulses into an FBG array for distributed acoustic wave detection includes:

[0016] Obtain the interference pulses at each access after the dual-light pulse is injected into the FBG array;

[0017] Each interference pulse is multiplied by a cosine time-varying parameter and a sine time-varying parameter respectively, and the carrier and higher-order carrier frequency components corresponding to the transformation frequency are filtered out to obtain each orthogonal zero-frequency signal;

[0018] The phase information of each orthogonal zero-frequency signal is obtained by processing each orthogonal zero-frequency signal using the arctangent algorithm.

[0019] The phase information is arranged in the order of access to obtain the time-varying phase; the time-varying phase is used to indicate the results of distributed acoustic wave detection.

[0020] In one embodiment, the FBG-based distributed acoustic detection system is a distributed acoustic wave detection system based on FBG and a direct detection system based on heterodyne phase demodulation technology.

[0021] On the other hand, a Rayleigh scattering noise suppression system for a distributed acoustic wave detection system is also provided, comprising:

[0022] The modulation module controls the optical phase modulator to perform sinusoidal optical phase modulation on the high-coherence continuous laser output from the narrow-linewidth laser in the FBG-based distributed acoustic detection system, according to a set modulation scheme; the set modulation scheme is Csin(2πfm t), C is the phase modulation amplitude, f m The phase modulation frequency and satisfying f m τ = k, where τ is the time difference between two adjacent reflected light pulses being detected, t is time, and k is an integer;

[0023] The pulse generation module is used to generate dual light pulses by passing highly coherent continuous laser light with sinusoidal phase modulation through an unbalanced interferometer.

[0024] The injection detection module is used to inject dual optical pulses into the FBG array for distributed acoustic wave detection.

[0025] In one embodiment, the injection detection module includes:

[0026] The interference acquisition submodule is used to acquire each interference pulse during each access after the dual-light pulse is injected into the FBG array;

[0027] The zero-frequency submodule is used to multiply each interference pulse by the cosine time-varying parameter and the sine time-varying parameter respectively, filter out the carrier and higher-order carrier frequency components corresponding to the transformation frequency, and obtain each orthogonal zero-frequency signal;

[0028] The phase submodule is used to perform differential cross-multiplication on each orthogonal zero-frequency signal to obtain the phase information of each orthogonal zero-frequency signal;

[0029] The time-varying submodule is used to arrange the phase information in the order of access to obtain the time-varying phase; the time-varying phase is used to indicate the results of distributed acoustic wave detection.

[0030] In one embodiment, the injection detection module includes:

[0031] The interference acquisition submodule is used to acquire each interference pulse during each access after the dual-light pulse is injected into the FBG array;

[0032] The zero-frequency submodule is used to multiply each interference pulse by the cosine time-varying parameter and the sine time-varying parameter respectively, filter out the carrier and higher-order carrier frequency components corresponding to the transformation frequency, and obtain each orthogonal zero-frequency signal;

[0033] The phase submodule is used to process each orthogonal zero-frequency signal using the arctangent algorithm to obtain the phase information of each orthogonal zero-frequency signal;

[0034] The time-varying submodule is used to arrange the phase information in the order of access to obtain the time-varying phase; the time-varying phase is used to indicate the results of distributed acoustic wave detection.

[0035] In one embodiment, the FBG-based distributed acoustic detection system is a distributed acoustic wave detection system based on FBG and a direct detection system based on heterodyne phase demodulation technology.

[0036] One of the above technical solutions has the following advantages and beneficial effects:

[0037] The Rayleigh scattering noise suppression method and system described above for distributed acoustic detection systems utilize an optical phase modulator to perform sinusoidal optical phase modulation on the high coherence continuous laser output from a narrow-linewidth laser in an FBG-based distributed acoustic detection system according to a set modulation scheme. This suppresses the coherent accumulation of the Rayleigh scattering light signal, thereby reducing the intensity of the Rayleigh scattering light and preventing its intensity from approaching that of the reflected light pulse. This suppresses Rayleigh scattering noise and reduces detection noise and crosstalk introduced between adjacent acoustic detection channels. Furthermore, the sinusoidally modulated high coherence continuous laser is passed through an unbalanced interferometer to generate dual optical pulses, which are then injected into the FBG array for distributed acoustic detection. Ultimately, this achieves low-noise distributed acoustic detection and effectively improves the detection performance of FBG-based distributed acoustic detection. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology 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.

[0039] Figure 1 This is a flowchart illustrating a Rayleigh scattering noise suppression method for a distributed acoustic detection system in one embodiment.

[0040] Figure 2 This is a schematic diagram of a distributed acoustic wave detection system based on FBG and heterodyne phase demodulation technology for direct detection.

[0041] Figure 3 This is a schematic diagram of a pulse sequence in one embodiment;

[0042] Figure 4 This is a schematic diagram of the module structure of the Rayleigh scattering noise suppression system in a distributed acoustic wave detection system according to one embodiment. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0045] It should be noted that, in this document, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The presentation of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments.

[0046] Those skilled in the art will understand that the embodiments described herein can be combined with other embodiments. The term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items, and all possible combinations thereof.

[0047] A typical system architecture for a distributed acoustic detection system based on fiber optic cables (FBGs) consists of an FBG array and a photoelectric system. The FBG array comprises several FBGs etched at equal intervals on an optical fiber, with two adjacent FBGs forming an acoustic detection channel. Reflected light pulses can be collected using either direct detection or coherent detection methods. Based on the method of collecting the reflected light pulses, the photoelectric system can be categorized into direct detection systems and coherent detection systems. Based on the phase demodulation method, direct detection systems can be further classified into direct detection systems based on heterodyne phase demodulation, direct detection systems based on phase generation carrier phase demodulation (PGC) technology, and direct detection systems based on 3×3 phase demodulation technology.

[0048] During transmission of the probe light pulse through the FBG array, Rayleigh scattering occurs wherever it travels. This scattered light propagates backward along the fiber and is collected simultaneously with the reflected light pulse. The probe light pulse has a certain pulse width (typically tens to hundreds of ns), spatially covering a section of fiber. For example, a 100 ns probe light pulse covers a 20m fiber length. The intensity of the Rayleigh scattering is determined by the coherent accumulation of the Rayleigh scattering signals generated within the covered fiber area. The FBG array uses conventional communication fiber, with a Rayleigh scattering reflectivity of approximately 10-1 per meter of fiber. -7 The Rayleigh scattering reflectivity of a 20m fiber (corresponding to a probe pulse with a pulse width of 100ns) can reach 2×10⁻⁶. -6The reflectivity is similar to that of a weak reflectivity FBG (reflectivity <0.01%). The intensity of Rayleigh scattered light exhibits spatiotemporal randomness, becoming Rayleigh scattering noise in FBG-based distributed acoustic detection systems. In practical research, the inventors discovered that when the intensity of the reflected light pulse is similar to that of the Rayleigh scattered light, Rayleigh scattering noise not only worsens the acoustic detection noise but also introduces crosstalk between adjacent acoustic detection channels, severely impacting the detection performance of FBG-based distributed acoustic detection systems.

[0049] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0050] Please see Figure 1 In one embodiment, this application provides a Rayleigh scattering noise suppression method for a distributed acoustic wave detection system, including the following processing steps S12 to S16:

[0051] S12, the high coherence continuous laser output from the narrow-linewidth laser in the FBG distributed acoustic detection system is sinusoidally modulated by an optical phase modulator according to a set modulation scheme; the set modulation scheme is Csin(2πf m t), C is the phase modulation amplitude, f m The phase modulation frequency and satisfying f m τ = k, where τ is the time difference between two adjacent reflected light pulses being detected, t is time, and k is an integer.

[0052] It is understood that optical phase modulators and FBG-based distributed acoustic detection sensing systems are existing systems and components in this field. The aforementioned modulation scheme is set as Csin(2πf m t) can be determined through pre-experimental testing, comparative analysis and induction, etc. It can be used to set the optical phase modulation mode of the optical phase modulator. The specific values ​​of each parameter in the modulation mode can be selected and set according to the actual needs of different application scenarios. As long as the optical phase sinusoidal modulation of the high coherence continuous laser output by the narrow linewidth laser can be performed according to the above-mentioned modulation mode to achieve the purpose of suppressing the coherent accumulation of Rayleigh scattering light signal, it is acceptable.

[0053] S14, the highly coherent continuous laser with sinusoidal phase modulation is passed through an unbalanced interferometer to generate two optical pulses;

[0054] S16 injects dual optical pulses into the FBG array for distributed acoustic wave detection.

[0055] It is understood that the aforementioned dual-light pulse generation, injection into the FBG array, and subsequent detection and processing processes can all be understood by referring to the dual-light pulse generation, injection into the FBG array, and subsequent detection and processing processes of existing FBG-based distributed acoustic wave detection systems in this field, and will not be elaborated further in this specification.

[0056] The Rayleigh scattering noise suppression method of the aforementioned distributed acoustic detection system uses an optical phase modulator to perform sinusoidal optical phase modulation on the high coherence continuous laser output from a narrow-linewidth laser in the FBG-based distributed acoustic detection system according to a set modulation scheme. This suppresses the coherent accumulation of the Rayleigh scattering light signal, thereby reducing the intensity of the Rayleigh scattering light and preventing its intensity from approaching that of the reflected light pulse. This suppresses Rayleigh scattering noise and reduces detection noise and crosstalk introduced between adjacent acoustic detection channels. Furthermore, the sinusoidally modulated high coherence continuous laser is passed through an unbalanced interferometer to generate dual optical pulses, which are then injected into the FBG array for distributed acoustic detection. Ultimately, this achieves low-noise distributed acoustic detection and effectively improves the detection performance of FBG-based distributed acoustic detection.

[0057] In one embodiment, the FBG-based distributed acoustic detection system is a distributed acoustic wave detection system based on FBG and a direct detection system based on heterodyne phase demodulation technology.

[0058] It is understood that the above methods can be applied to distributed acoustic wave detection systems based on FBG and heterodyne phase demodulation techniques in this field, such as... Figure 2 As shown, it can specifically include a signal generator, a dual-light pulse generation component, a circulator, an FBG array, a photodetector, a data acquisition card, and a signal processor. The signal generator provides control pulse modulation signals, sinusoidal modulation signal 1, and sinusoidal modulation signal 2 to the dual-light pulse generation component, and provides clock and trigger signals to the data acquisition card.

[0059] The dual-pulse generation assembly comprises a narrow-linewidth laser, an optical phase modulator, an optical intensity modulator, and an unbalanced interferometer connected in sequence. The narrow-linewidth laser is used to generate highly coherent continuous laser light. The optical phase modulator generates a modulation frequency f based on the sinusoidal modulation signal 1 from the signal generator. m The optical phase modulation amplitude is C, which is a sinusoidal modulation. The optical intensity modulator modulates the signal according to the pulse modulation signal from the signal generator at a repetition frequency f. pAn optical pulse is generated. The unbalanced interferometer includes a first fiber coupler, an acousto-optic modulator, a delay fiber, and a second fiber coupler. The input of the first fiber coupler is connected to the output of the optical phase modulator, and its two outputs are connected to the inputs of the acousto-optic modulator and the delay fiber, respectively. The outputs of the acousto-optic modulator and the delay fiber are connected to the two inputs of the second fiber coupler, respectively. The output of the second fiber coupler is connected to the first port of the circulator. The fiber length difference between the two fiber arms of the unbalanced interferometer is L. p It is used to generate a dual optical pulse with a time delay and an optical frequency difference of Δv based on the sinusoidal modulation signal 2 of the signal generator.

[0060] The circulator is used to inject the dual-light pulses generated by the dual-light pulse generator into the FBG array from the second port, and to receive (D+1) pulse light signals returned from the FBG array, where the 2nd to Dth returned pulse light signals are interference pulse light signals. The returned pulse light signals are then output from the third port. The FBG array consists of optical fibers with D FBGs etched at equal intervals. Two adjacent FBGs form a sensing channel for sensing external acoustic wave signals, thus the FBG array contains (D-1) sensing channels; the spacing between two adjacent FBGs is L. FBG The photodetector acquires (D+1) pulsed optical signals returned by the FBG array and converts them into pulsed electrical signals. The data acquisition card acquires the pulsed electrical signals output by the photodetector based on the trigger and clock signals from the signal generator and provides them to the signal processor. The signal processor mixes and low-pass filters the pulsed electrical signals, then uses orthogonal phase demodulation technology to calculate and extract the phase information of the interference pulsed optical signal from the filtered signal, thereby obtaining the information of the acoustic signal, from which the detection result can be determined.

[0061] In one embodiment, such as Figure 3 As shown, the steps for distributed acoustic wave detection by injecting dual optical pulses into an FBG array may include the following processing steps:

[0062] Obtain the interference pulses at each access after the dual-light pulse is injected into the FBG array;

[0063] Each interference pulse is multiplied by a cosine time-varying parameter and a sine time-varying parameter respectively, and the carrier and higher-order carrier frequency components corresponding to the transformation frequency are filtered out to obtain each orthogonal zero-frequency signal;

[0064] Differentiate and cross-multiply each of the orthogonal zero-frequency signals to obtain the phase information of each orthogonal zero-frequency signal;

[0065] The phase information is arranged in the order of access to obtain the time-varying phase; the time-varying phase is used to indicate the results of distributed acoustic wave detection.

[0066] It is understandable that the continuous light output from a narrow-linewidth laser, when passed through an optical phase modulator, generates a modulation frequency of f. m The phase modulation amplitude is C, and the optical phase sinusoidal modulation is Csin(2πf) m t), the phase-modulated continuous light passes through an arm difference of L. p An unbalanced interferometer generates two optical pulses with a frequency difference of Δv and a repetition frequency of f. p The fiber length between two adjacent FBGs in an FBG array is L. FBG .

[0067] The phase modulation frequency satisfies f m τ = k, to ensure that f m Let k be the phase modulation frequency, k be an integer, and τ = |L|. p -2L FBG |n / c is the time difference between two adjacent reflected light pulses being detected, c is the speed of light in vacuum, and n is the effective refractive index of the optical fiber.

[0068] Two optical pulses are injected into an array containing D FBGs. Two adjacent FBGs form an acoustic sensing channel, and the FBG array consists of a total of D-1 sensing channels. For example... Figure 3 As shown, O represents the reflected pulse sequence of the first optical pulse in the double pulse, P represents the reflected pulse sequence of the second optical pulse in the double pulse, and Q represents the interference pulse sequence. Figure 3 In this process, for each pair of dual optical pulses, the FBG array reflects back (D+1) optical pulses. The second to Dth returned pulses are interference pulse signals, corresponding sequentially to the interference signals output from the (D-1) acoustic wave sensing channels. Injecting dual optical pulses into the FBG array completes one access to each of the D-1 sensing channels, for a total of H accesses, at a frequency of f. p For the h-th visit, h = 1, 2, 3, ..., H, after dual-pulse injection into the FBG array, the d-th interference pulse in the returned pulsed light signal is I. d (h), d = 1, 2, 3, ..., D-1.

[0069] Interference pulse I d (h) can be expressed as shown in equation (1):

[0070]

[0071] In equation (1), I d+1 I is the intensity of the reflected light produced by the pulsed light at the (d+1)th FBG. d Let φ be the intensity of the reflected light produced at the d-th FBG of the pulsed light. sd (h) represents the phase value of the time-varying optical phase of the d-th FPI caused by the acoustic signal during the h-th access, kd The coefficients are polarization-dependent and satisfy 0 ≤ k d ≤1,2πΔνt represents the time-varying phase caused by the optical frequency difference between the two optical pulses. J0 is the 0th-order Bessel function, when f m When τ=k (k is an integer) is satisfied, |J0(2Csin(πf) m τ))|=1, at this point the sinusoidal phase modulation does not affect the amplitude of the AC term of the interference pulse. Since Δv is greater than f p Interference pulse I d The intensity of (h) is no longer constant within the pulse width, but changes periodically with time, with a transformation frequency of Δv.

[0072] Multiplying the interference pulse in equation (1) by the cosine time-varying parameter cos(2πΔνt) and the sinusoidal time-varying parameter sin(2πΔνt) respectively, we obtain equations (2) and (3):

[0073]

[0074]

[0075] Equations (2) and (3) filter out the carrier frequency of frequency Δv and its higher-order carrier frequency components, respectively, to obtain orthogonal zero-frequency signals, as shown in equations (4) and (5):

[0076]

[0077]

[0078] Using equations (4) and (5), the phase information φ can be obtained through differential cross-multiplication. sd (h).

[0079] H phases φ sd (h) Arrange in the order of access to obtain the time-varying phase [φ] sd (1),φ sd (2),…φ sd [H] represents the time-domain signal of the d-th FPI detector. Through the above steps, Rayleigh scattering noise is effectively suppressed, the detection noise and crosstalk introduced between adjacent acoustic detection channels are reduced, and low-noise distributed acoustic detection is achieved.

[0080] In another embodiment, the step of injecting dual optical pulses into the FBG array for distributed acoustic detection may also include the following processing steps:

[0081] Obtain the interference pulses at each access after the dual-light pulse is injected into the FBG array;

[0082] Each interference pulse is multiplied by a cosine time-varying parameter and a sine time-varying parameter respectively, and the carrier and higher-order carrier frequency components corresponding to the transformation frequency are filtered out to obtain each orthogonal zero-frequency signal;

[0083] The phase information of each orthogonal zero-frequency signal is obtained by processing each orthogonal zero-frequency signal using the arctangent algorithm.

[0084] The phase information is arranged in the order of access to obtain the time-varying phase; the time-varying phase is used to indicate the results of distributed acoustic wave detection.

[0085] It is understandable that the continuous light output from a narrow-linewidth laser, when passed through an optical phase modulator, generates a modulation frequency of f. m The phase modulation amplitude is C, and the optical phase sinusoidal modulation is Csin(2πf) m t), the phase-modulated continuous light passes through an arm difference of L. p An unbalanced interferometer generates two optical pulses with a frequency difference of Δv and a repetition frequency of f. p The fiber length between two adjacent FBGs in an FBG array is L. FBG .

[0086] The phase modulation frequency satisfies f m τ = k, to ensure that f m Let k be the phase modulation frequency, k be an integer, and τ = |L|. p -2L FBG |n / c is the time difference between two adjacent reflected light pulses being detected, c is the speed of light in vacuum, and n is the effective refractive index of the optical fiber.

[0087] Two optical pulses are injected into an array containing D FBGs. Two adjacent FBGs form an acoustic sensing channel, and the FBG array consists of a total of D-1 sensing channels. For example... Figure 3 As shown, for each pair of dual optical pulses, the FBG array reflects back (D+1) optical pulses. The second to Dth returned pulses are interference pulse signals, corresponding sequentially to the interference signals output by the (D-1) acoustic wave sensing channels. Injecting dual optical pulses into the FBG array completes one access to each of the D-1 sensing channels, for a total of H accesses, with an access frequency of f. p For the h-th visit, h = 1, 2, 3, ..., H, after dual-pulse injection into the FBG array, the d-th interference pulse in the returned pulsed light signal is I. d (h), d = 1, 2, 3, ..., D-1.

[0088] Interference pulse I d (h) can be expressed as shown in equation (1):

[0089]

[0090] In equation (1), I d+1 I is the intensity of the reflected light produced by the pulsed light at the (d+1)th FBG. d Let φ be the intensity of the reflected light produced at the d-th FBG of the pulsed light. sd (h) represents the phase value of the time-varying optical phase of the d-th FPI caused by the acoustic signal during the h-th access, k d The coefficients are polarization-dependent and satisfy 0 ≤ k d ≤1,2πΔνt represents the time-varying phase caused by the optical frequency difference between the two optical pulses. J0 is the 0th-order Bessel function, when f m When τ=k (k is an integer) is satisfied, |J0(2Csin(πf) m τ))|=1, at this point the sinusoidal phase modulation does not affect the amplitude of the AC term of the interference pulse. Since Δv is greater than f p Interference pulse I d The intensity of (h) is no longer constant within the pulse width, but changes periodically with time, with a transformation frequency of Δv.

[0091] Multiplying the interference pulse in equation (1) by the cosine time-varying parameter cos(2πΔνt) and the sinusoidal time-varying parameter sin(2πΔνt) respectively, we obtain equations (2) and (3):

[0092]

[0093]

[0094] Equations (2) and (3) filter out the carrier frequency of frequency Δv and its higher-order carrier frequency components, respectively, to obtain orthogonal zero-frequency signals, as shown in equations (4) and (5):

[0095]

[0096]

[0097] Using equations (4) and (5), the phase information φ can be obtained by performing the arctangent algorithm. sd (h).

[0098] H phases φ sd (h) Arrange in the order of access to obtain the time-varying phase [φ] sd (1),φ sd (2),…φ sd [H] represents the time-domain signal of the d-th FPI detector. Through the above steps, Rayleigh scattering noise is effectively suppressed, the detection noise and crosstalk introduced between adjacent acoustic detection channels are reduced, and low-noise distributed acoustic detection is achieved.

[0099] In one embodiment, the FBG-based distributed acoustic detection system can also be a distributed acoustic wave detection system based on FBG and PGC phase demodulation technology for direct detection.

[0100] It is understood that the above method can also be applied to distributed acoustic wave detection systems based on FBG and PGC phase demodulation technologies in this field. The specific structure of the system can be understood by referring to existing systems, and will not be detailed further in this specification. This system adds an optical phase modulator and a sine wave generator after the narrow linewidth laser. The optical phase modulator generates a modulation frequency f based on the sinusoidal modulation signal from the sine wave generator. m The phase modulation amplitude is C, and the optical phase sinusoidal modulation is Csin(2πf) m t).

[0101] The main steps for suppressing Rayleigh scattering noise in this system are:

[0102] Sinusoidal optical phase modulation Csin(2πf) is applied to the high coherence continuous laser output from the narrow linewidth laser in the system. m t), modulation frequency is f m The resulting phase modulation amplitude is C;

[0103] The optical phase sinusoidal modulation frequency satisfies f m τ = k, to ensure that: f m Let k be the modulation frequency, k be an integer, and τ = |L|. MZI -2L FBG |n / c is the time difference between two adjacent reflected light pulses being detected, L FBG L is the fiber length between two adjacent FBGs in the FBG array. MZI denoted as , where is the difference in fiber length between the two arms of the Mach-Zehnder fiber interferometer in front of the photodetector, c is the speed of light in vacuum, and n is the effective refractive index of the fiber. Low-noise distributed acoustic wave detection was achieved.

[0104] In one embodiment, the FBG-based distributed acoustic detection system can also be a distributed acoustic wave detection system based on FBG and a direct detection system based on 3×3 phase demodulation technology.

[0105] It is understood that the above method can also be applied to distributed acoustic wave detection systems based on FBG and 3×3 phase demodulation technology in this field. The specific structure of such systems can be understood by referring to existing systems, and will not be detailed further in this specification. This system adds an optical phase modulator and a sine wave generator after the narrow linewidth laser. The optical phase modulator generates a modulation frequency of f based on the sinusoidal modulation signal from the sine wave generator. mThe phase modulation amplitude is C, and the optical phase sinusoidal modulation is Csin(2πf) m t).

[0106] The main steps for suppressing Rayleigh scattering noise in this system are:

[0107] Sinusoidal optical phase modulation Csin(2πf) is applied to the high coherence continuous laser output from the narrow linewidth laser in the system. m t), modulation frequency is f m The resulting phase modulation amplitude is C;

[0108] The optical phase sinusoidal modulation frequency satisfies f m τ = k, to ensure that: f m The modulation frequency is k, where k is an integer, and τ = |2L|. MI -2L FBG |n / c is the time difference between two adjacent reflected light pulses being detected, L FBG L is the fiber length between two adjacent FBGs in the FBG array. MI denoted as , where is the fiber length difference between the two arms of the Michelson fiber interferometer at the front end of the photodetector, c is the speed of light in vacuum, and n is the effective refractive index of the fiber. Low-noise distributed acoustic wave detection was achieved.

[0109] It should be understood that, although Figure 1 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise explicitly stated in this document, there is no strict order in which these steps are executed; they can be performed in other orders. Figure 1 At least some of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.

[0110] Please see Figure 4 In one embodiment, a Rayleigh scattering noise suppression system 100 for a distributed acoustic wave detection system is provided, including a modulation module 11, a pulse generation module 13, and an injection detection module 15. The modulation module 11 controls an optical phase modulator to perform sinusoidal optical phase modulation on a high-coherence continuous laser output from a narrow-linewidth laser in an FBG-based distributed acoustic detection system, according to a set modulation scheme; the set modulation scheme is Csin(2πf m t), C is the phase modulation amplitude, f m The phase modulation frequency and satisfying f mτ = k, where τ is the time difference between two adjacent reflected light pulses being detected, t is time, and k is an integer. Pulse generation module 13 is used to generate dual light pulses by passing the sinusoidally modulated, highly coherent continuous laser light through an unbalanced interferometer. Injection detection module 15 is used to inject the dual light pulses into the FBG array for distributed acoustic wave detection.

[0111] The Rayleigh scattering noise suppression system 100 of the aforementioned distributed acoustic detection system, through the cooperation of various modules, uses an optical phase modulator to perform optical phase sinusoidal modulation on the high coherence continuous laser output from the narrow-linewidth laser in the FBG-based distributed acoustic detection system according to a set modulation method. This suppresses the coherent accumulation of the Rayleigh scattering light signal, thereby reducing the intensity of the Rayleigh scattering light and preventing the intensity of the Rayleigh scattering light from approaching the intensity of the reflected light pulse. This suppresses Rayleigh scattering noise, reduces detection noise, and reduces crosstalk introduced between adjacent acoustic detection channels. Then, the high coherence continuous laser with optical phase sinusoidal modulation is passed through an unbalanced interferometer to generate dual light pulses, which are then injected into the FBG array for distributed acoustic detection. Ultimately, this achieves the goal of low-noise distributed acoustic detection and effectively improves the detection performance of FBG-based distributed acoustic detection.

[0112] In one embodiment, the injection detection module includes an interferometric acquisition submodule, a zero-frequency submodule, a phase submodule, and a time-varying submodule. The interferometric acquisition submodule acquires each interferometric pulse from each access after the dual-light pulse is injected into the FBG array. The zero-frequency submodule multiplies each interferometric pulse by a cosine time-varying parameter and a sine time-varying parameter, respectively, filtering out the carrier frequency components corresponding to the transformed frequency and higher-order carrier frequency components to obtain each orthogonal zero-frequency signal. The phase submodule performs differential cross-multiplication on each orthogonal zero-frequency signal to obtain the phase information of each orthogonal zero-frequency signal. The time-varying submodule arranges the phase information in the order of access to obtain the time-varying phase; the time-varying phase is used to indicate the result of distributed acoustic wave detection.

[0113] In another embodiment, the injection detection module includes an interferometric acquisition submodule, a zero-frequency submodule, a phase submodule, and a time-varying submodule. The interferometric acquisition submodule acquires each interferometric pulse from each access after the dual-light pulse is injected into the FBG array. The zero-frequency submodule multiplies each interferometric pulse by a cosine time-varying parameter and a sine time-varying parameter, respectively, filtering out the carrier frequency components corresponding to the transformed frequency and higher-order carrier frequency components to obtain each orthogonal zero-frequency signal. The phase submodule processes each orthogonal zero-frequency signal using an arctangent algorithm to obtain the phase information of each orthogonal zero-frequency signal. The time-varying submodule arranges the phase information according to the access sequence to obtain the time-varying phase; the time-varying phase is used to indicate the result of distributed acoustic wave detection.

[0114] In one embodiment, the FBG-based distributed acoustic detection system is a distributed acoustic wave detection system based on FBG and a direct detection system based on heterodyne phase demodulation technology.

[0115] For specific limitations regarding the Rayleigh scattering noise suppression system 100 of the distributed acoustic wave detection system, please refer to the corresponding limitations of the Rayleigh scattering noise suppression method of the distributed acoustic wave detection system above, which will not be repeated here. Each module in the Rayleigh scattering noise suppression system 100 of the distributed acoustic wave detection system can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in hardware or independently of a device with specific signal detection and processing functions, or stored in software in the memory of the aforementioned device, so that the processor can call and execute the operations corresponding to each module. The aforementioned device can be, but is not limited to, various types of signal detection and processing devices already existing in the art.

[0116] In one embodiment, a signal detection and control device is also provided, including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to perform the following processing steps: optical phase sinusoidal modulation of the high coherence continuous laser output from a narrow-linewidth laser in an FBG-based distributed acoustic detection sensing system according to a set modulation method using an optical phase modulator; the set modulation method is Csin(2πf m t), C is the phase modulation amplitude, f m The phase modulation frequency and satisfying f m τ = k, where τ is the time difference between two adjacent reflected light pulses being detected, t is time, and k is an integer; the highly coherent continuous laser with sinusoidal phase modulation is passed through an unbalanced interferometer to generate dual light pulses; the dual light pulses are injected into the FBG array for distributed acoustic wave detection.

[0117] It is understood that, in addition to the memory and processor mentioned above, the signal detection and control equipment also includes other hardware and software components not listed in this specification. The specific components can be determined according to the model of the specific signal detection and processing equipment in different application scenarios, and will not be listed and described in detail in this specification.

[0118] In one embodiment, when the processor executes the computer program, it can also implement the additional steps or sub-steps in the various embodiments of the Rayleigh scattering noise suppression method for the distributed acoustic wave detection system described above.

[0119] In one embodiment, a computer-readable storage medium is also provided, on which a computer program is stored. When executed by a processor, the computer program performs the following processing steps: optical phase sinusoidal modulation of a highly coherent continuous laser output from a narrow-linewidth laser in an FBG-based distributed acoustic detection system is performed using an optical phase modulator according to a set modulation scheme; the set modulation scheme is Csin(2πf mt), C is the phase modulation amplitude, f m The phase modulation frequency and satisfying f m τ = k, where τ is the time difference between two adjacent reflected light pulses being detected, t is time, and k is an integer; the highly coherent continuous laser with sinusoidal phase modulation is passed through an unbalanced interferometer to generate dual light pulses; the dual light pulses are injected into the FBG array for distributed acoustic wave detection.

[0120] In one embodiment, when the computer program is executed by the processor, it can also implement the additional steps or sub-steps in the various embodiments of the Rayleigh scattering noise suppression method for the distributed acoustic wave detection system described above.

[0121] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), memory bus DRAM (RDRAM), and interface DRAM (DRDRAM), etc.

[0122] 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.

[0123] The above embodiments merely illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, all of which fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for suppressing Rayleigh scattering noise in a distributed acoustic wave detection system, characterized in that, Including the following steps: A sinusoidal optical phase modulation is applied to the high-coherence continuous laser output from a narrow-linewidth laser in an FBG-based distributed acoustic wave detection system according to a set modulation scheme, in order to suppress the coherent accumulation of Rayleigh scattering light signals; the set modulation scheme is as follows: , C For phase modulation amplitude, The phase modulation frequency and satisfying , The time difference between the detection of two adjacent reflected light pulses is denoted as . t For time, k It is an integer; in satisfying the above... Under these conditions, the optical phase sinusoidal modulation does not affect the amplitude of the AC term of the interference pulse formed after the dual optical pulses generated by the subsequent unbalanced interferometer return through the FBG array; A highly coherent continuous laser beam with sinusoidal phase modulation is passed through an unbalanced interferometer to generate two optical pulses. The dual optical pulses are injected into the FBG array for distributed acoustic wave detection.

2. The Rayleigh scattering noise suppression method for a distributed acoustic wave detection system according to claim 1, characterized in that, The step of injecting the dual optical pulses into the FBG array for distributed acoustic wave detection includes: Obtain the interference pulses for each access after the dual-light pulse is injected into the FBG array; Each interference pulse is multiplied by a cosine time-varying parameter and a sine time-varying parameter respectively, and the carrier and higher-order carrier frequency components corresponding to the transformation frequency are filtered out to obtain each orthogonal zero-frequency signal; Differentiate and cross-multiply each of the orthogonal zero-frequency signals to obtain the phase information of each of the orthogonal zero-frequency signals; The phase information is arranged in the order of access to obtain the time-varying phase; the time-varying phase is used to indicate the result of distributed acoustic wave detection.

3. The Rayleigh scattering noise suppression method for a distributed acoustic wave detection system according to claim 1, characterized in that, The step of injecting the dual optical pulses into the FBG array for distributed acoustic wave detection includes: Obtain the interference pulses for each access after the dual-light pulse is injected into the FBG array; Each interference pulse is multiplied by a cosine time-varying parameter and a sine time-varying parameter respectively, and the carrier and higher-order carrier frequency components corresponding to the transformation frequency are filtered out to obtain each orthogonal zero-frequency signal; The phase information of each of the orthogonal zero-frequency signals is obtained by processing each of the orthogonal zero-frequency signals using the arctangent algorithm; The phase information is arranged in the order of access to obtain the time-varying phase; the time-varying phase is used to indicate the result of distributed acoustic wave detection.

4. The Rayleigh scattering noise suppression method for a distributed acoustic wave detection system according to any one of claims 1 to 3, characterized in that, The FBG-based distributed acoustic wave detection system is a distributed acoustic wave detection system based on FBG and heterodyne phase demodulation technology for direct detection.

5. A Rayleigh scattering noise suppression system for a distributed acoustic wave detection system, characterized in that, include: The modulation module controls the optical phase modulator to perform sinusoidal optical phase modulation on the high-coherence continuous laser output from the narrow-linewidth laser in the FBG-based distributed acoustic wave detection system according to a set modulation scheme, in order to suppress the coherent accumulation of the Rayleigh scattering light signal; the set modulation scheme is as follows: , C For phase modulation amplitude, The phase modulation frequency and satisfying , The time difference between the detection of two adjacent reflected light pulses is denoted as . t For time, k It is an integer; in satisfying the above... Under these conditions, the optical phase sinusoidal modulation does not affect the amplitude of the AC term of the interference pulse formed after the dual optical pulses generated by the subsequent unbalanced interferometer return through the FBG array; The pulse generation module is used to generate dual light pulses by passing highly coherent continuous laser light with sinusoidal phase modulation through an unbalanced interferometer. An injection detection module is used to inject the dual optical pulses into the FBG array for distributed acoustic wave detection.

6. The Rayleigh scattering noise suppression system of the distributed acoustic wave detection system according to claim 5, characterized in that, The injection detection module includes: The interference acquisition submodule is used to acquire each interference pulse of each access after the dual-light pulse is injected into the FBG array; The zero-frequency submodule is used to multiply each of the interference pulses by the cosine time-varying parameter and the sine time-varying parameter respectively, filter out the carrier and higher-order carrier frequency components corresponding to the transformation frequency, and obtain each orthogonal zero-frequency signal; The phase submodule is used to perform differential cross-multiplication on each of the orthogonal zero-frequency signals to obtain the phase information of each of the orthogonal zero-frequency signals; The time-varying submodule is used to arrange the phase information in the order of access to obtain the time-varying phase; the time-varying phase is used to indicate the result of distributed acoustic wave detection.

7. The Rayleigh scattering noise suppression system of the distributed acoustic wave detection system according to claim 5, characterized in that, The injection detection module includes: The interference acquisition submodule is used to acquire each interference pulse of each access after the dual-light pulse is injected into the FBG array; The zero-frequency submodule is used to multiply each of the interference pulses by the cosine time-varying parameter and the sine time-varying parameter respectively, filter out the carrier and higher-order carrier frequency components corresponding to the transformation frequency, and obtain each orthogonal zero-frequency signal; The phase submodule is used to process each of the orthogonal zero-frequency signals using the arctangent algorithm to obtain the phase information of each of the orthogonal zero-frequency signals; The time-varying submodule is used to arrange the phase information in the order of access to obtain the time-varying phase; the time-varying phase is used to indicate the result of distributed acoustic wave detection.

8. The Rayleigh scattering noise suppression system for a distributed acoustic detection system according to any one of claims 5 to 7, characterized in that, The FBG-based distributed acoustic wave detection system is a distributed acoustic wave detection system based on FBG and heterodyne phase demodulation technology for direct detection.

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