A distributed optical fiber acoustic sensor and sensing method for coherent fading suppression

Abstract

The present application relates to the technical field of signal processing, in particular to a kind of distributed optical fiber acoustic sensing method and sensor of coherent fading suppression.Method includes: coupler divides continuous light into probe light and local oscillator light;Probe light is modulated into difference frequency delay double pulse by double pulse generator;Difference frequency delay double pulse is power amplified by erbium-doped fiber amplifier;After power amplification, after spontaneous emission noise is filtered out by optical band-pass filter, by circulator, inject into the optical fiber to be measured;Two pulses in pulse train generate RBS signal in the optical fiber to be measured and pass through circulator, pass through coupler and divide into two beams with equal power;One is mixed with local oscillator light by coupler, and the mixed light beam is received by balanced photodetector and then collected by data acquisition system;Another is directly received by ordinary photodetector;The present application realizes coherent fading suppression of distributed optical fiber acoustic sensor by combination processing of the output signals of two photodetectors.

Description

Technical Field

[0001] This invention relates to the field of signal processing technology, and in particular to a distributed fiber optic acoustic wave sensing method and sensor for coherent fading suppression. Background Technology

[0002] Distributed optical fiber sensing (DOFS) technology is a novel sensing method that utilizes the intrinsic scattering phenomena in optical fibers, including Rayleigh scattering, Raman scattering, and Brillouin scattering, to achieve online distributed monitoring of various physical quantities (such as temperature, strain, and sound waves) [He Z, Liu Q. Optical Fiber Distributed Acoustic Sensors: A Review[J]. Journal of Lightwave Technology,2021,39(12):3671-3686.]. Among them, distributed acoustic sensors (DAS), which utilize Rayleigh scattering in optical fibers to sense sound waves and vibration signals, have made significant progress and been widely used in recent years. Thanks to the continuous development of technologies such as narrow-linewidth lasers, high-speed low-noise data acquisition cards, and large-scale digital signal processing, DAS technology has made significant progress in various indicators [He Z, Liu Q. Optical Fiber Distributed Acoustic Sensors: A Review[J]. Journal of Lightwave Technology, 2021,39(12):3671-3686.]. For example, its spatial resolution can currently reach the order of 1~10 m, while the sensing distance can be extended to more than 100 km, and the detection frequency can range from mHz to kHz, which can meet various needs in production, daily life, and scientific research. The unique advantages of DAS, such as distributed sensing capability, anti-electromagnetic interference, and resistance to harsh environments, make it suitable for extreme environments, such as underground, deep earth, and deep sea. In these scenarios, traditional electronic sensors cannot work or have a high probability of failure, which is also a major advantage of DAS technology. At present, DAS technology has been successfully applied in many fields such as seismic exploration, smart city construction, oil and gas industry, and defense industry, achieving good results and showing great application potential. It has become the forefront of the current optoelectronic field.

[0003] Currently, DAS systems mainly employ two types of techniques to suppress coherent fading. One approach involves obtaining RBS signals with different characteristics through variations in frequency, mode, and transmission fiber, then combining them and eliminating the minimum amplitude points in the RBS signals to suppress the effects of coherent fading. This method typically places high demands on system complexity. The other approach uses various signal processing techniques on the RBS to suppress demodulation noise caused by coherent fading. However, this method requires assumptions about certain characteristics of the RBS signal, has a limited scope of application, and lacks universal applicability. Summary of the Invention

[0004] To address the technical problem that existing solutions require assumptions about certain characteristics of the RBS signal, resulting in a limited scope and lack of universality, this invention provides a distributed fiber optic acoustic sensor and sensing method for coherent fading suppression. The technical solution is as follows:

[0005] On the one hand, a distributed fiber optic acoustic wave sensing method with coherent fading suppression is provided, the method comprising:

[0006] A distributed fiber optic acoustic wave sensing method for coherent fading suppression, characterized in that the method comprises:

[0007] S1. A continuous light wave is emitted by a narrow linewidth laser. The continuous light wave passes through coupler 1 and is split into two beams, namely the probe light and the local oscillator light.

[0008] S2. The probe light passes through a dual-pulse generator, which modulates the probe light into a difference-frequency delayed dual pulse;

[0009] S3. The difference-frequency delay dual pulse is amplified to a suitable power by an erbium-doped fiber amplifier;

[0010] S4. The difference-frequency delay double pulse after power amplification is filtered out by an optical bandpass filter to remove spontaneous emission noise, and then propagated through port 1 of circulator 1 to port 2 and injected into the optical fiber under test; wherein, circulator 1 includes three ports: port 1, port 2 and port 3.

[0011] S5. The two pulses in the pulse train will generate RBS signals in the fiber under test. After the RBS signals are propagated from port 2 to port 3 of circulator 1, they are split into two beams of equal power by coupler 4. One beam is mixed with the local oscillator light split from coupler 1 through coupler 5. The mixed beam is received by the balanced photodetector, and the other beam is directly received by the photodetector.

[0012] S6, the balanced photodetector, and the electrical signal output by the photodetector are acquired by the data acquisition system.

[0013] Optionally, coupler 1 is a coupler with a splitting ratio of 1:99, wherein the two beams after splitting consist of 99% probe light and 1% local oscillator light, respectively.

[0014] Optionally, the dual pulse can be implemented in the form of integrated modulation or discrete modulation.

[0015] Optionally, the integrated modulation method includes:

[0016] The required pulse electrical signal is generated by an arbitrary signal generator and input into the driver. The driver modulates the electrical signal and outputs the electrical signal to the dual pulse generator to generate the corresponding optical pulse waveform.

[0017] Optionally, discrete modulation forms include:

[0018] The probe light is split into two beams of equal power by a coupler 2 with a splitting ratio of 50:50. The two beams enter the upper and lower arms of the Mach-Zehnder interferometer, respectively.

[0019] Insert optical modulator 1 into the upper arm to modulate a continuous beam of probe light into pulsed light;

[0020] Optical modulator 2 is inserted into the lower arm to modulate another continuous probe light into pulsed light; and a delay fiber is simultaneously inserted into the lower arm, and the time interval between the two pulses in the generated difference frequency delay double pulse is determined by the length of the delay fiber.

[0021] The pulses generated by the upper and lower arms are combined through a 50:50 coupler 3 to obtain a difference frequency delay double pulse.

[0022] Optionally, the dual-pulse generator also includes:

[0023] The change in optical frequency caused by optical modulation is controlled by the AWG and driver in the system and adjusted according to actual needs.

[0024] Optionally, the AWG and driver in the integrated modulation scheme are in single-channel form;

[0025] In the discrete modulation format, the AWG and driver are in dual-channel configuration.

[0026] On the other hand, a distributed fiber optic acoustic wave sensor for coherent fading suppression is provided, characterized in that the sensor is applied to the distributed fiber optic acoustic wave sensing method for coherent fading suppression described above, and the sensor includes:

[0027] Narrow linewidth laser, dual pulse generator, erbium-doped fiber amplifier, optical bandpass filter, circulator 1, coupler 1, balanced photodetector, photodetector and data acquisition system;

[0028] A continuous light wave is emitted by a narrow linewidth laser. The continuous light wave passes through coupler 1 and is split into two beams, namely the probe beam and the local oscillator beam.

[0029] The probe light passes through a dual-pulse generator, which modulates the probe light into a difference-frequency delayed dual pulse;

[0030] The difference-frequency delay dual pulses are amplified to a suitable power by an erbium-doped fiber amplifier;

[0031] The difference-frequency delay double pulse, after being amplified by power, is filtered out by an optical bandpass filter to remove spontaneous emission noise, and then propagated from port 1 of circulator 1 to port 2 and injected into the optical fiber under test. Circulator 1 includes three ports: port 1, port 2, and port 3.

[0032] The two pulses in the pulse train will generate RBS signals in the fiber under test. The RBS signals are propagated from port 2 to port 3 of circulator 1 and split into two beams of equal power by coupler 4. One beam is mixed with the local oscillator light split from coupler 1 through coupler 5. The mixed beam is received by the balanced photodetector, and the other beam is directly received by the photodetector.

[0033] The electrical signals output by the balanced photodetector and the photodetector are collected by the data acquisition system.

[0034] On the other hand, a distributed fiber optic acoustic wave sensing device with coherent fading suppression is provided, the distributed fiber optic acoustic wave sensing device with coherent fading suppression includes: a processor; a memory, the memory storing computer-readable instructions, which, when executed by the processor, implement any of the methods in the distributed fiber optic acoustic wave sensing method with coherent fading suppression described above.

[0035] On the other hand, a computer-readable storage medium is provided, wherein at least one instruction is stored therein, the at least one instruction being loaded and executed by a processor to implement any of the above-described distributed fiber optic acoustic sensing methods for coherent fading suppression.

[0036] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following:

[0037] This invention proposes a novel distributed acoustic wave sensor scheme capable of suppressing coherent fading. This scheme, through difference-frequency delay dual-pulse and composite detection, introduces three RBS signals with different carrier frequencies into the RBS interference signal in a simple manner. Subsequent signal combination then suppresses the coherent fading problem caused by the single-carrier RBS signal. Compared to traditional schemes, the proposed scheme only adds a few optical couplers and one detector to the hardware structure, resulting in a limited increase in hardware cost. Furthermore, the required difference-frequency delay dual-pulse can be implemented in various flexible ways. In terms of backend signal processing, this scheme does not impose any pre-defined assumptions about the RBS signal, making it widely applicable. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. 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 of a distributed optical fiber acoustic wave sensing method for coherent fading suppression provided in an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the structure of the distributed optical fiber acoustic sensor for coherent fading suppression provided in an embodiment of the present invention;

[0041] Figure 3 This is a structural diagram of a dual-pulse generator provided in an embodiment of the present invention;

[0042] Figure 4 This is a schematic diagram of the structure of the electronic device provided in an embodiment of the present invention. Detailed Implementation

[0043] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0044] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0045] In the embodiments of this invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that, without emphasizing the distinction between them, they convey the same meaning. Similarly, the terms "of," "corresponding (relevant)," and "corresponding" may sometimes be used interchangeably. It should be noted that, without emphasizing the distinction between them, they convey the same meaning.

[0046] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0047] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0048] This invention provides a distributed fiber optic acoustic wave sensing method with coherent fading suppression. This method can be implemented using a distributed fiber optic acoustic wave sensing device with coherent fading suppression, which can be a terminal or a server. Figure 1 The flowchart shown is a distributed fiber optic acoustic wave sensing method for coherent fading suppression. The processing flow of this method may include the following steps:

[0049] S1. A continuous light wave is emitted by a narrow linewidth laser. The continuous light wave passes through coupler 1 and is split into two beams, namely the probe light and the local oscillator light.

[0050] In one feasible implementation, Figure 2 This is a schematic diagram of the innovative structure of the present invention. The light source is a narrow-linewidth laser, which provides a low-noise, high-stability continuous light wave for the subsequent DAS system, and its output light frequency is denoted as f0. Subsequently, the continuous light wave is split into two beams by a coupler 1 with a splitting ratio of 1:99. The 99% beam is called the "probe light", and the 1% beam is called the "local oscillator light".

[0051] S2. The probe light passes through a dual-pulse generator, which modulates the probe light into a difference-frequency delay dual pulse.

[0052] In one feasible implementation, the probe light then passes through a double-pulse generator and is modulated into two pulses, one preceding the other. The time delay between the two pulses is denoted as τ, the width of each pulse is w, and the corresponding light frequencies are f1 and f2, respectively. The above pulse train is called the "difference frequency delay double pulse," which repeats in the time domain at a repetition frequency of frep (the reciprocal of the pulse train repetition period Trep).

[0053] In one feasible implementation, depending on the working principle, the dual pulse has two different implementation forms, such as... Figure 3 As shown. Dual-pulse implementations include: integrated modulation methods (such as...) Figure 3 a) and discrete modulation formats (such as Figure 3 b).

[0054] In one feasible implementation, the integrated modulation method includes:

[0055] An arbitrary waveform generator (AWG) generates the desired modulated pulse electrical signal, which is then input into a driver. The driver amplifies and conditions the signal, performing impedance matching and other functions, before outputting the signal to an optical modulator. This enables the optical modulator to generate the corresponding optical pulse waveform. Figure 3 The difference-frequency delay double pulse (in the context of optical modulators) can be either an electro-optic modulator (EOM) or an acousto-optic modulator (AOM). The parameters in the resulting difference-frequency delay double pulse include the modulated frequency f1 (f2), the time interval τ between the double pulses, the pulse width w, and the double pulse repetition frequency f. rep All of these are controlled by an AWG. Therefore, this solution can flexibly generate dual pulse trains as needed, and only one optical modulator is required to complete the corresponding functions. However, it places high demands on the AWG and the driver.

[0056] In one feasible implementation, the discrete modulation scheme includes:

[0057] Its basic structure is a Mach-Zehnder interferometer. The probe light is split into two beams by a coupler 2 with a splitting ratio of 50:50, and enters the upper and lower arms of the Mach-Zehnder interferometer. In the upper arm, an optical modulator 1 is inserted, which modulates the continuous probe light into pulsed light and shifts the light frequency from f0 to f1; similarly, the optical modulator 2 in the lower arm modulates the passing continuous light into pulsed light and shifts the light frequency from f0 to f2. Additionally, a section of length [missing information] is inserted in the lower arm. The delay fiber, the length of which determines the time interval between the two pulses in the generated difference-frequency delay double pulse, i.e. Where n is the refractive index of the optical fiber and c is the speed of light in a vacuum. The pulses generated in the upper and lower arms are combined together by another 50:50 coupler 3, forming a difference-frequency delayed double pulse with a time interval of τ and preceding and following optical frequencies of f1 and f2, respectively. In this scheme, the pulse width w and the repetition frequency f of the pulse train are... rep The parameters are controlled by the AWG and driven by the driver to make the generated optical pulse train meet the design requirements.

[0058] In one feasible implementation, for the dual-pulse generator, it should be noted that: (1) the optical modulator here can be an acousto-optic modulator or an electro-optic modulator, and there are no specific requirements for its form; (2) the changes in the optical frequency produced by the optical modulation, i.e., the values ​​of f1-f0 and f2-f0, are controlled by the AWG and driver in the system, and can be adjusted according to actual needs; (3) for Figure 3 The integrated modulation method in a requires that the AWG and driver be in single-channel form; while Figure 3 The discrete modulation method in b requires the AWG and driver to be in dual-channel form to meet the needs when there are optical modulators in both the upper and lower arms.

[0059] S3. The difference frequency delay dual pulse is amplified to a suitable power by an erbium-doped fiber amplifier (EDFA).

[0060] S4. The amplified difference-frequency delay dual pulse is filtered by an optical bandpass filter to remove spontaneous emission noise, and then propagated from port 1 of circulator 1 to port 2, and injected into the fiber under test (FUT). Circulator 1 includes three ports: port 1, port 2, and port 3.

[0061] S5. The two pulses in the pulse train will generate RBS signals in the fiber under test. After the RBS signals are propagated from port 2 to port 3 of circulator 1, they are split into two beams of equal power by coupler 4. One beam is mixed with the local oscillator light split from coupler 1 through coupler 5. The mixed beam is received by a balanced photodetector (BPD), i.e., "coherent detection mode". The other beam is directly received by the photodetector.

[0062] S6, the balanced photodetector, and the electrical signal output by the photodetector are acquired by the data acquisition system.

[0063] In one feasible implementation, the photocurrent signal can be written as:

[0064] (1)

[0065] The summation symbol represents the superposition of signals from all Rayleigh scattering points in the optical fiber. Here, we assume there are N Rayleigh scattering points in the fiber. Where r... 1i (r 2i )and τ represents the scattering intensity and the introduced additional phase at each Rayleigh scattering point in the optical fiber under the action of optical frequencies f1 (f2), respectively. iThis represents the delay caused by each Rayleigh scattering point. W is the window size of the optical pulse, here a default rectangular window. The difference between f1 and f2 should be greater than the bandwidth of the optical pulse, i.e.:

[0066] (2)

[0067] Under the premise of satisfying formula (2), the Rayleigh scattering coefficients and the introduced additional phase of two optical signals of different frequencies are not the same, that is , The spatial distribution of the coherent fading produced by these factors is also different. Meanwhile, phase changes introduced by external disturbances... The same applies to two optical signals of different frequencies. In a computer, the phase information contained in the RBS in formula (1) can be obtained using the following method: Using two bandpass filters with center frequencies of f1 and f2 and bandwidths greater than 1 / w, the RBS signals at two different carriers contained in formula (1) can be separated, and their complex expression can be obtained using Hilbert transform. Simultaneously, by aligning the delay in the pulse signal, the following two signals can be obtained:

[0068] (3)

[0069] By extracting the phase of the signals in the two expressions of formula (3) and performing a difference operation with a time interval of τ, the phase change can be obtained as follows:

[0070] (4)

[0071] Additional phase introduced by Rayleigh scattering or It can be done in or Remove by subtracting direct current.

[0072] For the RBS signal output from the right branch of coupler 4, a photodetector (PD) is used to directly convert the optical signal into an electrical signal (i.e., "direct detection mode"), which is then acquired by the data acquisition system. Its expression is:

[0073] (5)

[0074] The carrier frequency of the RBS signal detected by the PD is the difference between f1 and f2, that is... , and For the Rayleigh scattering coefficient and its introduced additional phase at this frequency to differ from the Rayleigh scattering coefficient of the fiber at frequencies f1 or f2, the following relationship should hold:

[0075] (6)

[0076] For example, f1 can be set to 180 MHz, f2 to 220 MHz, and pulse width w = 100 ns. In this case, the conditions of formula (2) and formula (6) can be satisfied.

[0077] Based on the above conditions, a similar algorithm can be used in a computer to obtain the phase information: first, through the center frequency... A bandpass filter with a bandwidth of 1 / w is used to bandpass filter the signal in expression (5); furthermore, by applying the Hilbert transform, its complex form signal is obtained as follows:

[0078] (7)

[0079] Using the angle of solution, the phase change at this point can be obtained as follows:

[0080] (8)

[0081] The introduced additional phase You can filter them out by subtracting the average value.

[0082] As can be seen from formulas (3) and (7), the different RBS signals obtained in this scheme correspond to different Rayleigh scattering coefficients and additional phases. Therefore, the locations and distributions of coherent fading are also different. Consequently, coherent fading can be suppressed using a weighted average (WA) method. The specific method is as follows:

[0083] (9)

[0084] This refers to the RBS phase signal obtained by coherent fading suppression after adopting this scheme, which is proportional to the external acoustic wave or vibration signal received by the optical fiber under test. The key to this scheme is to generate three sets of RBS signals with different scattering coefficient distributions. Therefore, the selection of the optical frequency in the pulse is crucial. Formulas (2) and (6) are prerequisites for the success of this scheme. For most optical modulators and their matching AWG and drivers, these conditions are very easy to achieve.

[0085] Note that the AWG and the data acquisition system in this solution need to be synchronized (including clock synchronization and trigger synchronization) to ensure that the acquired data is not corrupted in the time domain.

[0086] This invention aims to propose a novel distributed acoustic wave sensor scheme capable of suppressing coherent fading. This scheme, through difference-frequency delay dual-pulse and composite detection, introduces three RBS signals with different carrier frequencies into the RBS interference signal in a simple manner. Subsequent signal combination then suppresses the coherent fading problem caused by the single-carrier RBS signal. Compared to traditional schemes, the proposed scheme only adds a few optical couplers and one detector to the hardware structure, resulting in a limited increase in hardware cost. Furthermore, the required difference-frequency delay dual-pulse can be implemented in various flexible ways. In terms of back-end signal processing, this scheme does not impose any pre-defined assumptions about the RBS signal, making it widely applicable.

[0087] Figure 2 This is a block diagram illustrating a distributed fiber optic acoustic wave sensing sensor with coherent fading suppression according to an exemplary embodiment. The sensor is used in a distributed fiber optic acoustic wave sensing method with coherent fading suppression. (Refer to...) Figure 2 The sensor includes a narrow linewidth laser, a dual pulse generator, an erbium-doped fiber amplifier, an optical bandpass filter, a circulator 1, a coupler 1, a balanced photodetector, a photodetector, and a data acquisition system.

[0088] A continuous light wave is emitted by a narrow linewidth laser. The continuous light wave passes through coupler 1 and is split into two beams, namely the probe beam and the local oscillator beam.

[0089] The probe light passes through a dual-pulse generator, which modulates the probe light into a difference-frequency delayed dual pulse;

[0090] The difference-frequency delay dual pulses are amplified to a suitable power by an erbium-doped fiber amplifier;

[0091] The difference-frequency delay double pulse, after being amplified by power, is filtered out by an optical bandpass filter to remove spontaneous emission noise, and then propagated from port 1 of circulator 1 to port 2 and injected into the optical fiber under test. Circulator 1 includes three ports: port 1, port 2, and port 3.

[0092] The two pulses in the pulse train will generate RBS signals in the fiber under test. The RBS signals are propagated from port 2 to port 3 of circulator 1 and split into two beams of equal power by coupler 4. One beam is mixed with the local oscillator light split from coupler 1 through coupler 5. The mixed beam is received by the balanced photodetector, and the other beam is directly received by the photodetector.

[0093] The balanced photodetector and the electrical signal output by the photodetector are acquired by the data acquisition system.

[0094] This invention aims to propose a novel distributed acoustic wave sensor scheme capable of suppressing coherent fading. This scheme, through difference-frequency delay dual-pulse and composite detection, introduces three RBS signals with different carrier frequencies into the RBS interference signal in a simple manner. Subsequent signal combination then suppresses the coherent fading problem caused by the single-carrier RBS signal. Compared to traditional schemes, the proposed scheme only adds a few optical couplers and one detector to the hardware structure, resulting in a limited increase in hardware cost. Furthermore, the required difference-frequency delay dual-pulse can be implemented in various flexible ways. In terms of back-end signal processing, this scheme does not impose any pre-defined assumptions about the RBS signal, making it widely applicable.

[0095] Figure 4 This is a schematic diagram of the structure of a distributed fiber optic acoustic wave sensing device for coherent fading suppression provided in an embodiment of the present invention, as shown below. Figure 4 As shown, the distributed fiber optic acoustic sensing device with coherent fading suppression can include the above-mentioned Figure 2 The distributed fiber optic acoustic wave sensor with coherent fading suppression is shown. Optionally, the distributed fiber optic acoustic wave sensor 410 with coherent fading suppression may include a first processor 2001.

[0096] Optionally, the distributed fiber optic acoustic sensing device 410 with coherent fading suppression may also include a memory 2002 and a transceiver 2003.

[0097] The first processor 2001, memory 2002, and transceiver 2003 can be connected via a communication bus.

[0098] The following is combined with Figure 4 The various components of the distributed fiber optic acoustic sensing device 410 for coherent fading suppression are described in detail below:

[0099] The first processor 2001 is the control center of the distributed fiber optic acoustic wave sensing device 410 for coherent fading suppression. It can be a single processor or a collective term for multiple processing elements. For example, the first processor 2001 can be one or more central processing units (CPUs), application-specific integrated circuits (ASICs), or one or more integrated circuits configured to implement embodiments of the present invention, such as one or more digital signal processors (DSPs), or one or more field-programmable gate arrays (FPGAs).

[0100] Optionally, the first processor 2001 can perform various functions of the distributed fiber optic acoustic wave sensing device 410 for coherent fading suppression by running or executing software programs stored in the memory 2002 and calling data stored in the memory 2002.

[0101] In a specific implementation, as one example, the first processor 2001 may include one or more CPUs, for example... Figure 4 CPU0 and CPU1 are shown in the diagram.

[0102] In a specific implementation, as one example, the distributed fiber optic acoustic sensing device 410 for coherent fading suppression may also include multiple processors, for example... Figure 4 The first processor 2001 and the second processor 2004 are shown in the diagram. Each of these processors can be a single-core processor or a multi-core processor. Here, a processor can refer to one or more devices, circuits, and / or processing cores used to process data (such as computer program instructions).

[0103] The memory 2002 is used to store the software program that executes the present invention, and is controlled by the first processor 2001 to execute it. The specific implementation method can be referred to the above method embodiment, and will not be repeated here.

[0104] Optionally, the memory 2002 may be a read-only memory (ROM) or other type of static storage device capable of storing static information and instructions, random access memory (RAM) or other type of dynamic storage device capable of storing information and instructions, or electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM) or other optical disc storage, optical disc storage (including compressed optical discs, laser discs, optical discs, digital universal optical discs, Blu-ray discs, etc.), magnetic disk storage media or other magnetic storage devices, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and accessible by a computer, but not limited thereto. The memory 2002 may be integrated with the first processor 2001 or may exist independently, and may be connected via the interface circuit of the coherent fading suppressed distributed fiber optic acoustic wave sensing device 410. Figure 4 (Not shown in the image) is coupled to the first processor 2001, and this embodiment of the invention does not specifically limit this.

[0105] The transceiver 2003 is used to communicate with network devices or with terminal devices.

[0106] Alternatively, transceiver 2003 may include a receiver and a transmitter. Figure 4 (Not shown separately). The receiver is used to implement the receiving function, and the transmitter is used to implement the transmitting function.

[0107] Optionally, the transceiver 2003 can be integrated with the first processor 2001 or exist independently, and can be connected to the interface circuit of the distributed fiber optic acoustic sensing device 410 with coherent fading suppression. Figure 4 (Not shown in the image) is coupled to the first processor 2001, and this embodiment of the invention does not specifically limit this.

[0108] It should be noted that, Figure 4 The structure of the distributed fiber optic acoustic sensing device 410 with coherent fading suppression shown in the figure does not constitute a limitation on the router. Actual knowledge structure identification devices may include more or fewer components than shown, or combine certain components, or have different component arrangements.

[0109] Furthermore, the technical effect of the distributed fiber optic acoustic wave sensing device 410 with coherent fading suppression can be referred to the technical effect of the distributed fiber optic acoustic wave sensing method with coherent fading suppression described in the above method embodiments, and will not be repeated here.

[0110] It should be understood that the first processor 2001 in the embodiments of the present invention may be a central processing unit (CPU), or it may be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor, etc.

[0111] It should also be understood that the memory in the embodiments of the present invention can be volatile memory or non-volatile memory, or may include both volatile and non-volatile memory. The non-volatile memory can be read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory. The volatile memory can be random access memory (RAM), which is used as an external cache. By way of example, but not limitation, many forms of random access memory (RAM) are available, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate synchronous DRAM (DDR SDRAM), enhanced synchronous DRAM (ESDRAM), synchronous linked DRAM (SLDRAM), and direct rambus RAM (DR RAM).

[0112] The above embodiments can be implemented, in whole or in part, by software, hardware (such as circuits), firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable sensors. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more sets of available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium. A semiconductor medium can be a solid-state drive.

[0113] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0114] It should be understood that, in various embodiments of the present invention, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0115] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0116] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0117] In addition, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0118] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention.

[0119] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A distributed optical fiber acoustic wave sensing method for coherent fading suppression, characterized in that, The method includes: S1. A continuous light wave is emitted by a narrow linewidth laser. The continuous light wave passes through a coupler 1 and is split into two beams, which are a probe beam and a local oscillator beam, respectively. S2. The probe light passes through a dual-pulse generator, which modulates the probe light into a difference-frequency delay dual pulse; S3. The difference frequency delay dual pulse is amplified to a suitable power by an erbium-doped fiber amplifier; S4. The difference-frequency delay double pulse after power amplification is filtered out by an optical bandpass filter to remove spontaneous emission noise, and then propagated through port 1 of circulator 1 to port 2 and injected into the optical fiber under test; wherein, circulator 1 includes three ports: port 1, port 2 and port 3. S5. The two pulses in the pulse train will generate RBS signals in the fiber under test. After the RBS signals are propagated from port 2 to port 3 of circulator 1, they are split into two beams of equal power by coupler 4. One beam is mixed with the local oscillator light split from coupler 1 through coupler 5. The mixed beam is received by the balanced photodetector, and the other beam is directly received by the photodetector. S6. The balanced photodetector and the electrical signal output by the photodetector are acquired by the data acquisition system. For a balanced photodetector, the phase information contained in the RBS is obtained in a computer using the following method: Two bandpass filters with center frequencies of f1 and f2 and bandwidths greater than or equal to 1 / w are used to separate the RBS signals at two different carriers. The complex expression is then obtained using Hilbert transform. Simultaneously, the delay in the pulse signal is aligned to obtain the two signals. and w represents the width of each pulse; For the RBS signal output from the right branch of coupler 4, a photodetector is used to directly convert the optical signal into an electrical signal, which is then acquired by the data acquisition system. A similar algorithm to that used with balanced photodetectors is employed to obtain the phase information of the difference between carrier frequencies f1 and f2: firstly, through a center frequency of... A bandpass filter with a bandwidth of 1 / w is used to bandpass filter the signal; the complex form of the signal is obtained by applying the Hilbert transform. Where, Δf = |f1 - f2|; The absolute value of the difference between f1 and f2 should be greater than or equal to the bandwidth of the optical pulse, that is, greater than or equal to the reciprocal of the optical pulse width, i.e.: (2)； Different RBS signals correspond to different Rayleigh scattering coefficients and additional phases, therefore the locations and distributions of coherent fading are also different. A weighted averaging method is then used to suppress coherent fading. Specifically: ； That is, the RBS phase signal obtained by coherent fading suppression, which is proportional to the external sound wave or vibration signal received by the optical fiber under test; This represents the phase change carried by the center frequency f1; This represents the phase change carried by the center frequency f2; The center frequency is The phase change it carries.

2. The distributed fiber optic acoustic wave sensing method for coherent fading suppression according to claim 1, characterized in that, The coupler 1 is a coupler with a splitting ratio of 1:99, and the two beams after splitting consist of 99% probe light and 1% local oscillator light, respectively.

3. The distributed fiber optic acoustic wave sensing method for coherent fading suppression according to claim 1, characterized in that, The dual-pulse implementation includes both integrated modulation and discrete modulation.

4. The distributed fiber optic acoustic wave sensing method for coherent fading suppression according to claim 3, characterized in that, The integrated modulation method includes: The required pulse electrical signal is generated by an arbitrary signal generator and input into the driver. The driver modulates the electrical signal and outputs the electrical signal to the dual pulse generator to generate the corresponding optical pulse waveform.

5. The distributed fiber optic acoustic wave sensing method for coherent fading suppression according to claim 3, characterized in that, The discrete modulation formats include: The probe light is split into two beams of equal power by a coupler 2 with a splitting ratio of 50:

50. The two beams enter the upper and lower arms of the Mach-Zehnder interferometer, respectively. Insert optical modulator 1 into the upper arm to modulate a continuous beam of probe light into pulsed light; An optical modulator 2 is inserted into the lower arm to modulate another continuous probe light into pulsed light; and a delay fiber is simultaneously inserted into the lower arm, the time interval between the two pulses in the generated difference frequency delay double pulse is determined by the length of the delay fiber; The pulses generated by the upper and lower arms are combined through a 50:50 coupler 3 to obtain a difference frequency delay double pulse.

6. The distributed fiber optic acoustic wave sensing method for coherent fading suppression according to claim 4 or 5, characterized in that, The dual-pulse generator also includes: The change in optical frequency caused by optical modulation is controlled by the AWG and driver in the system and adjusted according to actual needs.

7. The distributed fiber optic acoustic wave sensing method for coherent fading suppression according to claim 3, characterized in that, The integrated modulation method uses a single-channel AWG and driver. The discrete modulation scheme uses a dual-channel configuration for both the AWG and the driver.

8. A distributed fiber optic acoustic sensor with coherent fading suppression, characterized in that, The sensor is applied to the distributed fiber optic acoustic wave sensing method for coherent fading suppression according to any one of claims 1-7, and the sensor comprises: Narrow linewidth laser, dual pulse generator, erbium-doped fiber amplifier, optical bandpass filter, circulator 1, coupler 1, balanced photodetector, photodetector and data acquisition system; The narrow linewidth laser emits a continuous light wave, which passes through the coupler 1 and is split into two beams, namely a probe beam and a local oscillator beam. The probe light passes through a dual-pulse generator, which modulates the probe light into a difference-frequency delay dual pulse; The difference-frequency delay dual pulses are amplified to a suitable power by an erbium-doped fiber amplifier; The power-amplified difference-frequency delay double pulse is filtered out for spontaneous emission noise by an optical bandpass filter, and then propagated from port 1 of circulator 1 to port 2 and injected into the optical fiber under test; wherein, circulator 1 includes three ports: port 1, port 2 and port 3. Two pulses in the pulse train will generate RBS signals in the fiber under test. The RBS signals are propagated from port 2 to port 3 of circulator 1 and split into two beams of equal power by coupler 4. One beam is mixed with the local oscillator light split from coupler 1 through coupler 5. The mixed beam is received by the balanced photodetector, and the other beam is directly received by the photodetector. The balanced photodetector and the electrical signal output by the photodetector are acquired by the data acquisition system.

9. A distributed fiber optic acoustic wave sensing device for coherent fading suppression, characterized in that, The distributed fiber optic acoustic sensing device for coherent fading suppression includes: processor; A memory storing computer-readable instructions that, when executed by the processor, implement the method as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium contains program code that can be invoked by a processor to execute the coherent fading suppression method as described in any one of claims 1 to 7.

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