Distributed optical fiber sound sensing system, device and sound detection method

Abstract

Embodiments of the present invention disclose a distributed fiber optic sound sensing system, device, and sound detection method. The system includes: a laser source assembly for generating a continuous initial laser; a coupler, whose input is connected to an output of the laser source assembly and is used to split the initial laser into a first laser beam and a second laser beam; an acousto-optic modulator, whose input is connected to an output of the coupler and whose output is connected to a first input of an interferometer or an input of an erbium-doped amplifier and is used to modulate the first laser beam into a single-pulse laser; and an interferometer for modulating the single-pulse laser into a dual-pulse laser and performing sound detection, while also interfering with the second laser beam to generate a reverse laser beam and thereby adjusting the frequency of the laser source assembly. This improves the signal-to-noise ratio and detection accuracy of the sensing system.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensors, and in particular to a distributed optical fiber sound sensing system, device and sound detection method. Background Art

[0002] Distributed fiber-optic sound sensing systems use narrow-linewidth laser pulses to sense ambient vibrations within a fiber loop, generating and returning Rayleigh scattered light that carries the vibration information. Using the principle of optical coherence, these pulses create interference intensity variations, thereby demodulating the vibration conditions at various points within the fiber loop. This system exhibits extremely high detection sensitivity. This type of sensor is also known as a phase-type optical time-domain reflectometer.

[0003] Optical interference signals are typically generated using two methods: interference between local light and echoes (local light interferometry) and interference between dual-pulse echoes (dual-pulse interferometry). Commonly used methods for generating dual pulses include electrical modulation and unbalanced Mach-Zehnder interferometry (UB-MZI). The stability of the dual pulses generated by UB-MZI can affect the final sound detection results. To improve stability, existing technologies often employ thermal stabilization and anti-vibration methods, which can achieve a certain degree of dual-pulse time-domain stabilization. However, the performance improvement is limited, and such systems are complex and bulky, making them unsuitable for commercialization. Furthermore, the performance ceiling of both local light interferometry and dual-pulse interferometry is limited by the linewidth parameters of the narrow-linewidth light source, which cannot mitigate the impact of linewidth.

[0004] There is currently no effective solution to the above problems in the prior art. Summary of the Invention

[0005] To solve the above problems, the present invention provides a distributed fiber optic sound sensing system, device and sound detection method, in which the fiber optic ring used to generate dual pulses is also used as a laser interferometer to generate a feedback control signal for the laser source frequency, thereby solving the problem in the existing technology that it is unable to effectively alleviate interference such as environmental vibration and thermal fluctuations, and how to effectively eliminate the influence of light source noise.

[0006] To achieve the above-mentioned object, the present invention provides a distributed fiber optic acoustic sensing system, comprising: a laser source assembly, the laser source assembly being configured to generate a continuous initial laser; a coupler, the input end of the coupler being connected to the output end of the laser source assembly and being configured to split the initial laser into a first laser beam and a second laser beam; an acousto-optic modulator, the input end of the acousto-optic modulator being connected to one output end of the coupler and the output end being connected to a first input end of an interferometer or an input end of an erbium-doped fiber amplifier and being configured to modulate the first laser beam into a single-pulse laser; when the output end of the acousto-optic modulator is connected to the first input end of the interferometer, the first output end of the interferometer is connected to the input end of the erbium-doped fiber amplifier; the second input end of the interferometer is connected to the other output end of the coupler via an isolator, and the second output end is connected to the laser source assembly via a feedback assembly. The device is connected to a coupler, configured to convert the second laser beam into interference light and adjust the frequency of the laser source assembly according to a reference value and an intensity value of the interference light; the output end of the erbium-doped fiber amplifier is connected to the first port of the circulator; the second port of the circulator is connected to the sensing fiber, and the third port is connected to the receiving assembly; when the output end of the acousto-optic modulator is connected to the input end of the erbium-doped amplifier, the output end of the erbium-doped fiber amplifier is connected to the first port of the circulator; the second port of the circulator is connected to the sensing fiber, and the third port is connected to the second input end of the interferometer; the second output end of the interferometer is connected to the receiving assembly; the first input end of the interferometer is connected to the other output end of the coupler through an isolator, and the first output end is connected to the laser source assembly through a feedback assembly, configured to receive the second laser beam and convert it into interference light, and adjust the frequency of the laser source assembly according to the reference value and the intensity value of the interference light.

[0007] Further optionally, the laser source assembly includes: a laser source; the output end of the laser source is connected to the input end of the coupler, and the input end is connected to the output end of the feedback assembly, for generating the initial laser; or, the laser source assembly includes: a laser source and an acousto-optic frequency shifter; the output end of the laser source is connected to the input end of the coupler, and the input end is connected to the output end of the acousto-optic frequency shifter, for generating the initial laser; an acousto-optic frequency shifter, the input end of the acousto-optic frequency shifter is connected to the output end of the feedback assembly, and the output end is connected to the laser source, for frequency shifting the laser source.

[0008] Further optionally, the feedback component includes: a photodetector, the input end of the photodetector is connected to the output end of the interferometer, and is used to detect the intensity value of the interference light; a feedback controller, the input end of the feedback controller is connected to the output end of the photodetector, and the output end is connected to the laser source or the acousto-optic modulator, and is used to calculate a frequency correction signal based on the intensity value and a reference value, and control and adjust the frequency of the laser source or the acousto-optic frequency shifter according to the correction signal.

[0009] Further optionally, the laser source is a narrow linewidth laser seed source; and the interferometer is an unbalanced Mach-Zehnder interferometer.

[0010] Further optionally, the receiving component includes: an avalanche photodetector, an AD collector and a data analyzer connected in sequence.

[0011] On the other hand, the present invention provides a sound detection method, which uses the above-mentioned distributed optical fiber sound sensing system to perform sound detection, including: dividing the initial laser into a first laser beam and a second laser beam; pulse-modulating the first laser beam to obtain a single-pulse laser; interfering and amplifying the single-pulse laser and then transmitting it to the sensing optical fiber, receiving the echo signal of the sensing optical fiber, and interfering and analyzing the echo signal to obtain pending sound information; or amplifying the single-pulse laser and then transmitting it to the sensing optical fiber, receiving the echo signal of the sensing optical fiber, and interfering and analyzing the echo signal to obtain pending sound information; interfering with the second laser beam to obtain interference light; adjusting the frequency of the laser source component according to the intensity value of the interference light and a reference value; repeating this step until the difference between the intensity value and the reference value is within a preset difference range, and taking the pending sound information in the corresponding time period at the current moment as reliable sound information; wherein the reference value is pre-set according to the laser source component.

[0012] Further optionally, adjusting the frequency of the laser source assembly according to the intensity value of the interference light and a reference value includes: calculating a frequency correction signal according to the intensity value of the interference light and the reference value; and adjusting the corresponding frequency of the laser source assembly according to the frequency correction signal.

[0013] Further optionally, the parsing of the echo signal includes: performing photoelectric conversion on the echo signal to obtain an electrical signal; and performing AD acquisition on the electrical signal and then performing signal analysis to obtain the pending sound information.

[0014] On the other hand, the present invention further provides a distributed optical fiber sound sensing device, comprising the above-mentioned distributed optical fiber sound sensing system.

[0015] On the other hand, the present invention further provides a computer-readable storage medium having a computer program stored thereon, wherein the program implements the above-mentioned sound detection method when executed by a processor.

[0016] The above technical solution has the following beneficial effects: by utilizing part of the laser output from the laser source to inject into an optical fiber ring that generates a dual-pulse laser, reverse optical interference is formed. The laser frequency in the reverse interference process is completely equivalent to the interference process between the interference arm and the dual-pulse echo of the main laser. Therefore, by detecting the intensity of the reverse interference light and then controlling the feedback signal of the laser frequency or laser modulation frequency, the intensity of the reverse interference light is stabilized, which can eliminate the system noise caused by various types of jitter in conventional dual-pulse distributed optical fiber sensors. It can also eliminate the influence of the light source phase noise on the system noise to a certain extent (equivalently compressing the laser linewidth of the light source), thereby improving the overall signal-to-noise ratio of the sensor, facilitating the detection of weaker vibration signals, and improving detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 1 is a schematic structural diagram of a distributed optical fiber sound sensing system provided by an embodiment of the present invention;

[0019] Figure 2 is a schematic structural diagram of a distributed optical fiber sound sensing system provided by another embodiment of the present invention;

[0020] Figure 3 is a schematic structural diagram of a distributed optical fiber sound sensing system provided by another embodiment of the present invention;

[0021] Figure 4 is a schematic structural diagram of a distributed optical fiber sound sensing system provided by another embodiment of the present invention;

[0022] Figure 5 is a flow chart of a sound detection method provided by an embodiment of the present invention;

[0023] Figure 6 is a flow chart of a frequency adjustment method provided by an embodiment of the present invention;

[0024] Figure 7 This is a flow chart of a sound echo signal processing method provided by an embodiment of the present invention.

[0025] Figure 1: 1-laser source assembly; 101-laser source; 102-acousto-optic frequency shifter; 2-coupler; 3-acousto-optic modulator; 4-interferometer; 5-feedback assembly; 501-photodetector; 502-feedback controller; 6-erbium-doped fiber amplifier; 7-circulator; 8-sensing fiber; 9-receiving assembly; 901-avalanche photodetector; 902-AD collector; 903-data analyzer; 10-isolator. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] The principle of the existing local light interferometry method is as follows: a small portion of the continuous light output by a narrow-linewidth laser seed source is first separated by a first coupler as the local light. The remaining portion is pulse-modulated by an acousto-optic modulator, amplified by an erbium-doped fiber amplifier (EDFA), and then injected into the sensing fiber via a circulator. The echo signal scattered by the sensing fiber is output by the circulator to a second coupler, where it is cohered with the local light and received by a balanced detector. The output electrical signal of the balanced detector is collected by an analog-to-analog device (ADC) for vibration signal analysis. This method is subject to the influence of optical depolarization and overall optical path perturbations, making it unstable. The double-pulse interferometry method can effectively eliminate these two effects.

[0028] A commonly used dual-pulse interferometry method is electrical modulation. Its principle is to use a dual electrical pulse sequence input into an acousto-optic modulator to modulate a narrow-linewidth laser seed source, generating a dual-pulse laser. This dual-pulse laser is amplified by an EDFA and injected into a sensing fiber. The dual-pulse laser interferes with the scattered echoes in the sensing fiber, allowing for analysis of environmental vibration signals. The dual-pulse laser in the dual-pulse interferometry method serves as the basis for the interference of scattered echoes in the sensing fiber. Its stability significantly impacts system performance: the more stable the dual pulses generated by the system, the higher the vibration sensitivity. Because the modulation signal of electrical modulation is an electrical pulse signal, it is currently nearly impossible to increase it to a level equivalent to the optical wave period. Therefore, distributed fiber-optic acoustic sensing systems based on this type of dual-pulse interferometry have a low signal-to-noise ratio.

[0029] The principle of the unbalanced Mach-Zehnder interferometer (UB-MZI) dual-pulse phase-type distributed fiber optic acoustic sensing system is as follows: the laser output from a narrow-linewidth laser seed source is electrically modulated by a single pulse input from an acousto-optic modulator to produce a single laser pulse, which is then passed through the UB-MZI to obtain a dual-pulse laser. The subsequent working principle is the same as the electrical modulation method. To stabilize the dual-pulse laser, a common method is to protect the UB-MZI with a thermally stable and anti-vibration system. This can protect the dual pulses from environmental interference to a certain extent, maintain stability, and improve the signal-to-noise ratio of the sensing fiber echo interference signal. However, this method has limited performance improvement, and such systems are relatively complex and large in size, making them unsuitable for commercialization. In addition, the system performance upper limit of the above three acoustic sensing systems is limited by the linewidth parameters of the narrow-linewidth laser source, which cannot alleviate the impact of the linewidth.

[0030] To solve the above problems, the present invention provides a distributed optical fiber sound sensing system. Figure 1 、 Figure 2 As shown, the distributed fiber optic sound sensing system includes: a laser source assembly 1, which is used to generate a continuous initial laser; a coupler 2, the input end of the coupler 2 is connected to the output end of the laser source assembly 1, and is used to split the initial laser into a first laser beam and a second laser beam; an acousto-optic modulator 3, the input end of the acousto-optic modulator 3 is connected to one output end of the coupler 2, and the output end is connected to the first input end of the interferometer 4 or the input end of the erbium-doped amplifier, and is used to modulate the first laser beam into a single-pulse laser; when the output end of the acousto-optic modulator 3 is connected to the first input end of the interferometer 4, the first output end of the interferometer 4 is connected to the input end of the erbium-doped fiber amplifier 6; the second input end of the interferometer 4 is connected to the other output end of the coupler 2 through the isolator 10, and the second output end is connected to the laser source assembly 1 through the feedback assembly 5, and is used to convert the second laser beam into a single-pulse laser. The output end of the erbium-doped fiber amplifier 6 is connected to the first port of the circulator 7; the second port of the circulator 7 is connected to the sensing fiber 8, and the third port is connected to the receiving component 9; when the output end of the acousto-optic modulator 3 is connected to the input end of the erbium-doped amplifier, the output end of the erbium-doped fiber amplifier 6 is connected to the first port of the circulator 7; the second port of the circulator 7 is connected to the sensing fiber 8, and the third port is connected to the second input end of the interferometer 4; the second output end of the interferometer 4 is connected to the receiving component 9; the first input end of the interferometer 4 is connected to the other output end of the coupler 2 through the isolator 10, and the first output end is connected to the laser source component 1 through the feedback component 5, for receiving the second laser beam and converting it into interference light, and adjusting the frequency of the laser source component 1 according to the reference value and the intensity value of the interference light.

[0031] like Figure 1As shown, the laser source assembly 1 is connected to a coupler 2, which divides the initial laser generated by the laser source assembly 1 into two parts, namely a first laser beam and a second laser beam. The first laser beam enters the acousto-optic modulator 3, and is electrically modulated by the input single pulse to obtain a single-pulse laser. The single-pulse laser is input into the first input end (port A in the figure) of the interferometer 4 to obtain a double-pulse laser. The double-pulse laser is output from the first output end (port C in the figure) of the interferometer 4, and then amplified by the erbium-doped fiber amplifier 6 and injected into the sensing fiber 8 through the circulator 7. The echo signal returned by the sensing fiber 8 is input into the receiving assembly 9 through the circulator 7. The receiving assembly 9 obtains the sound detection result after a series of processing.

[0032] The second laser beam is injected into the second input port (port D in the diagram) of interferometer 4 through isolator 10. After being processed by interferometer 4, interference light is generated and output from the second output port (port B in the diagram). Feedback component 5 receives this interference light and detects its intensity value I. Based on a preset reference value I0, it calculates a frequency correction signal U(I, I0). The frequency of laser source component 1 is adjusted based on this frequency correction signal. This then proceeds to the next round of light intensity detection and frequency correction until the output intensity value I approaches the reference value I0.

[0033] Figure 2 For Figure 1 The structure of a structurally equivalent distributed fiber optic sound sensing system, such as Figure 2 As shown, it is Figure 1 The difference in structure lies in the interferometer 4 being located between the circulator 7 and the receiving assembly 9. Specifically, the laser source assembly 1 is connected to a coupler 2, which splits the initial laser light generated by the laser source assembly 1 into two parts, namely a first laser beam and a second laser beam. The first laser beam enters the acousto-optic modulator 3, where it is electrically modulated by the input single pulse to produce a single-pulse laser. The single-pulse laser light is then input into the erbium-doped fiber amplifier 6, amplified, and then input into the sensing fiber 8 through the circulator 7. The echo signal returned by the sensing fiber 8 enters the second input end (port D in the figure) of the interferometer 4 for interference before being output from the second output end (port B in the figure). The receiving assembly 9 performs a series of processing on the echo signal to obtain the sound detection result.

[0034] The second laser beam is injected into the first input port (port A in the diagram) of interferometer 4 through isolator 10. After being processed by interferometer 4, interference light is generated and output from the first output port (port C in the diagram). Feedback component 5 receives this interference light and detects its intensity value I. Based on a preset reference value I0, it calculates a frequency correction signal U(I, I0). This frequency correction signal is then used to adjust the frequency of laser source assembly 1. This process then proceeds to the next round of light intensity detection and frequency correction until the output intensity value I approaches the reference value I0.

[0035] It should be noted that the first input port corresponds to the first output port, and the second input port corresponds to the second output port. The laser beams in the two paths (D→B and A→C) travel in opposite directions. The amounts of the first and second laser beams can be the same or different. Preferably, a small portion of the initial laser beam is used to generate interference light. Ports A, B, C, and D are labeled for ease of explanation only and do not represent actual port definitions.

[0036] As an optional implementation, the reference value I0 corresponds to the combined state of the fiber ring and the laser frequency, that is, the reference state of the stable interference of the laser double pulses. In principle, I0 can be any value of the measured interference value, but considering the control efficiency and effect, the selected value of I0 should maximize |dI / df| (f is the frequency of the light source).

[0037] When calculating the frequency correction signal U(I, I0), an error signal is generated by comparing the reference value of the interference intensity with the real-time intensity value. This error signal can be used to set the light source frequency, acting as negative feedback, allowing the measured interference intensity value to gradually approach the reference value. Furthermore, since setting the light source frequency is based on the frequency correction signal U(I, I0), this function requires the laser source assembly 1 to have a fast frequency adjustment function.

[0038] Because interferometer 4 is constantly affected by environmental interference and the frequency of laser source assembly 1 is constantly fluctuating (phase noise), the intensity value I of the interference light is constantly fluctuating. The above-mentioned stabilization process can greatly reduce the interference intensity changes caused by environmental interference and light source frequency jitter, and stabilize it near I0. The intensity of the output interference light reflects the combined effect of the interferometer and light source frequencies. Therefore, by detecting the intensity value of the interference light and generating a light source frequency adjustment signal, the light source frequency is controlled to maintain the stability of the dual-pulse laser interferometry, thereby ensuring the signal-to-noise ratio of the sensor.

[0039] As an optional implementation, Figure 1 、 Figure 2 As shown, the laser source assembly 1 includes: a laser source 101; the output end of the laser source 101 is connected to the input end of the coupler 2, and the input end is connected to the output end of the feedback assembly 5 for generating an initial laser; or Figure 3 、 Figure 4 As shown, the laser source assembly 1 includes: a laser source 101 and an acousto-optic frequency shifter 102; the output end of the laser source 101 is connected to the input end of the coupler 2, and the input end is connected to the output end of the acousto-optic frequency shifter 102, for generating an initial laser; the acousto-optic frequency shifter 102, the input end of the acousto-optic frequency shifter 102 is connected to the output end of the feedback assembly 5, and the output end is connected to the laser source 101, for shifting the frequency of the laser source 101.

[0040] There are two ways to set up the laser source assembly 1. One is that the laser source assembly 1 only includes the laser source 101. In this case, Figure 1 、 Figure 2 As shown, the feedback component 5 directly controls the laser source 101 , that is, directly adjusts the frequency of the laser source 101 through the frequency correction signal U (I, I0).

[0041] Another way is that the laser source assembly 1 includes a laser source 101 and an acousto-optic frequency shifter 102. In this case, Figure 3 、 Figure 4 As shown, the feedback component 5 controls the acousto-optic frequency shifter 102, that is, adjusts the modulation frequency of the acousto-optic frequency shifter 102 through the frequency correction signal U (I, I0). The adjusted acousto-optic frequency shifter 102 then shifts the frequency of the laser source 101, which can improve the fineness of the adjustment.

[0042] As an optional implementation, Figure 1-4 As shown, the feedback component 5 includes: a photodetector 501, the input end of the photodetector 501 is connected to the output end of the interferometer 4, and is used to detect the intensity value of the interference light; a feedback controller 502, the input end of the feedback controller 502 is connected to the output end of the photodetector 501, and the output end is connected to the laser source 101 or the acousto-optic modulator 3, and is used to calculate a frequency correction signal based on the intensity value and a reference value, and control and adjust the frequency of the laser source 101 or the acousto-optic frequency shifter 102 based on the correction signal.

[0043] like Figure 1-4 As shown, feedback component 5 includes a photodetector 501 and a feedback controller 502. Photodetector 501 converts the interference light into an electrical signal. Feedback component 5 receives this electrical signal and compares it with a reference value to generate an error signal. Based on this error signal, it calculates a frequency correction signal U(I, I0). This frequency correction signal U(I, I0) is then used to adjust the frequency of the corresponding device (the modulation frequency of the acousto-optic frequency shifter 102 or the frequency of the laser source 101).

[0044] As an optional embodiment, the feedback component 5 can be implemented by a combination of software and hardware. For example, a predetermined program is set on the single-chip microcomputer to extract the intensity of the electrical signal, calculate the difference between the intensity value and the reference value, determine the frequency correction signal based on the difference, and adjust the frequency of the acousto-optic frequency shifter 102 or the laser source 101.

[0045] As an optional implementation, regarding the relationship U(I, I0) between the frequency correction signal and the error signal, the relationship between the two can be obtained in advance through simulation experiments, for example, a relationship curve or a relationship function can be obtained.

[0046] As an optional implementation, the laser source 101 is a narrow-linewidth laser seed source; and the interferometer 4 is an unbalanced Mach-Zehnder interferometer 4 .

[0047] A narrow-linewidth laser seed source is a laser whose output laser has an extremely narrow spectral linewidth. Its main characteristics are extremely high coherence and stability.

[0048] The unbalanced Mach-Zehnder interferometer 4 is an instrument that uses an amplitude division method to generate a dual-beam to achieve interference, and can generate a dual-path echo based on a single-path echo to achieve interference.

[0049] As an optional implementation, the receiving component 9 includes: an avalanche photodetector 901 , an AD collector 902 and a data analyzer 903 connected in sequence.

[0050] like Figure 1-4 As shown, the echo signal directly output from the circulator 7 or output from the interferometer 4 enters the avalanche photodetector 901 for photoelectric conversion to output an electrical signal. The electrical signal is converted into digital form and sampled by the AD collector 902 and then input into the data analyzer for data analysis to obtain the sound detection result.

[0051] The present invention also provides a sound detection method, which uses the above-mentioned distributed optical fiber sound sensing system to perform sound detection. Figure 5 is a flow chart of a sound detection method provided by an embodiment of the present invention, such as Figure 5 Shown, including:

[0052] S1, dividing the initial laser into a first laser beam and a second laser beam;

[0053] The laser source component emits an initial laser, which is then divided into a first laser beam and a second laser beam after passing through a coupler.

[0054] S2, pulse-modulating the first laser beam to obtain a single-pulse laser;

[0055] The first laser beam is electrically modulated by a single pulse through an acousto-optic modulator to obtain a single pulse laser.

[0056] S3. A single laser pulse is amplified and then transmitted to a sensing optical fiber, an echo signal from the sensing optical fiber is received, and the echo signal is analyzed to obtain the pending sound information; or a single laser pulse is amplified and then transmitted to a sensing optical fiber, an echo signal from the sensing optical fiber is received, and the echo signal is amplified and then transmitted to a sensing optical fiber, and the echo signal is amplified and then analyzed to obtain the pending sound information;

[0057] like Figure 1As shown, if the interferometer is set between the acousto-optic modulator and the interferometer, a single-pulse laser is first input through the first input port (port A) of the interferometer, and then a dual-pulse laser is output through the first output port (port C). The dual-pulse laser is amplified by the erbium-doped fiber amplifier and then input into the sensing fiber through the circulator. The echo signal output by the sensing fiber enters the receiving component through the circulator for analysis to obtain the pending sound information.

[0058] like Figure 2 As shown, if the interferometer is installed between the circulator and the receiving component, the single-pulse laser is directly amplified by the erbium-doped fiber amplifier and then input into the sensing fiber through the circulator. The echo signal output by the sensing fiber enters the second input port (D port) of the interferometer through the circulator, and after interference, it is output to the receiving component through the second output port (B port) for analysis to obtain the pending sound information.

[0059] S4. Interfere the second laser beam to obtain interference light; adjust the frequency of the laser source assembly according to the intensity value of the interference light and a reference value; repeat this step until the difference between the intensity value and the reference value is within a preset difference range, and take the pending sound information in the time period corresponding to the current moment as reliable sound information; wherein the reference value is pre-set according to the laser source assembly.

[0060] After the second laser beam interferes through the interferometer, interference light is obtained. After the interference light enters the feedback component, it is calculated with the reference value to obtain the adjustment frequency of the laser source component and adjust the laser source component accordingly. The interference light intensity detection and frequency correction are repeated until the intensity value is close to the reference value (the difference between the intensity value and the reference value is within the preset difference range). The pending sound information in the time period corresponding to the current moment can be regarded as reliable sound information. The determination of the time period can be achieved by presetting the time range. For example, if the current moment is the middle value, the pending sound information in the time range before and after it is all reliable sound information; or, the pending sound information in the time range before the current moment is all reliable sound information; or, the pending sound information in the time range after the current moment is all reliable sound information. This time range can be pre-set.

[0061] The processing process of the first laser beam and the processing process of the second laser beam are parallel and continuous.

[0062] The reference value I0 corresponds to the combined state of the fiber ring and the laser frequency, that is, the reference state of the stable interference of the laser double pulses. In principle, I0 can be selected as any value of the measured interference value. However, considering the control efficiency and effect, the selected value of I0 should maximize |dI / df| (f is the frequency of the laser source).

[0063] As an optional implementation, Figure 6 is a flow chart of a frequency adjustment method provided by an embodiment of the present invention, such as Figure 6 As shown, the frequency of the laser source component is adjusted according to the intensity value of the interference light and the reference value, including:

[0064] S401, calculating a frequency correction signal according to the intensity value of the interference light and a reference value;

[0065] S402: Adjust the frequency corresponding to the laser source component according to the frequency correction signal.

[0066] Obtain the intensity value I of the collected interference light, calculate the difference e between the current intensity value I and the preset reference value I0, and calculate the frequency correction signal U (I, I0) based on the difference e. The calculation relationship between the two can be obtained through a simulation test in advance or calculated through a function (such as PID control).

[0067] The frequency of the laser source assembly is adjusted based on the correction signal U(I, I0). For example, the correction value obtained by the PID control algorithm is Δf. If it is greater than 0, the frequency |Δf| is increased; if it is less than 0, the frequency |Δf| is decreased.

[0068] As an optional implementation, Figure 7 Flowchart of a sound echo signal processing method provided by an embodiment of the present invention, which analyzes the echo signal, including:

[0069] S301, performing photoelectric conversion on the echo signal to obtain an electrical signal;

[0070] S302: After AD acquisition of the electrical signal, perform signal analysis to obtain pending sound information.

[0071] The echo signal directly output from the circulator or output from the interferometer enters the avalanche photodetector for photoelectric conversion to output an electrical signal. The electrical signal is converted into digital form and sampled by the AD collector, and then input into the data analyzer for data analysis to obtain the pending sound information.

[0072] An embodiment of the present invention further provides a distributed optical fiber sound sensing device, including the above-mentioned distributed optical fiber sound sensing system.

[0073] An embodiment of the present invention further provides a computer-readable storage medium having a computer program stored thereon, which implements the above-mentioned sound detection method when the program is executed by a processor.

[0074] The above storage media include but are not limited to: CDs, floppy disks, hard disks, erasable memory, etc.

[0075] The above technical solution has the following beneficial effects: by utilizing part of the laser output from the laser source to inject into an optical fiber ring that generates a dual-pulse laser, reverse optical interference is formed. The laser frequency in the reverse interference process is completely equivalent to the interference process between the interference arm and the dual-pulse echo of the main laser. Therefore, by detecting the intensity of the reverse interference light and then controlling the feedback signal of the laser frequency or laser modulation frequency, the intensity of the reverse interference light is stabilized, which can eliminate the system noise caused by various types of jitter in conventional dual-pulse distributed optical fiber sensors. It can also eliminate the influence of the light source phase noise on the system noise to a certain extent (equivalently compressing the laser linewidth of the light source), thereby improving the overall signal-to-noise ratio of the sensor, facilitating the detection of weaker vibration signals, and improving detection accuracy.

[0076] The specific implementation methods of the above inventions further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above content is only the specific implementation methods of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A distributed optical fiber sound sensing system, characterized in that: include: a laser source assembly, the laser source assembly being used to generate continuous initial laser light; a coupler, wherein an input end of the coupler is connected to an output end of the laser source assembly and is used to split the initial laser into a first laser beam and a second laser beam; an acousto-optic modulator, wherein the input end of the acousto-optic modulator is connected to an output end of the coupler, and the output end is connected to the first input end of the interferometer or the input end of the erbium-doped amplifier, and is used to modulate the first laser beam into a single-pulse laser; When the output end of the acousto-optic modulator is connected to the first input end of the interferometer, the first output end of the interferometer is connected to the input end of the erbium-doped fiber amplifier; the second input end of the interferometer is connected to the other output end of the coupler through an isolator, and the second output end is connected to the laser source assembly through a feedback component, so as to convert the second laser beam into interference light and adjust the frequency of the laser source assembly according to a reference value and the intensity value of the interference light; the output end of the erbium-doped fiber amplifier is connected to the first port of the circulator; the second port of the circulator is connected to the sensing fiber, and the third port is connected to the receiving assembly; When the output end of the acousto-optic modulator is connected to the input end of the erbium-doped amplifier, the output end of the erbium-doped fiber amplifier is connected to the first port of the circulator; the second port of the circulator is connected to the sensing fiber, and the third port is connected to the second input end of the interferometer; the second output end of the interferometer is connected to the receiving assembly; the first input end of the interferometer is connected to the other output end of the coupler through the isolator, and the first output end is connected to the laser source assembly through the feedback assembly, so as to receive the second laser beam and convert it into interference light, and adjust the frequency of the laser source assembly according to the reference value and the intensity value of the interference light; The interference light is used to reflect the combined effect of the interferometer and the light source frequency, and the interferometer is also used to perform frequency feedback adjustment of the laser source component and signal detection.

2. The distributed optical fiber sound sensing system according to claim 1, wherein: The laser source assembly includes: a laser source; The output end of the laser source is connected to the input end of the coupler, and the input end is connected to the output end of the feedback component, for generating the initial laser; Or, the laser source assembly includes: a laser source and an acousto-optic frequency shifter; The output end of the laser source is connected to the input end of the coupler, and the input end is connected to the output end of the acousto-optic frequency shifter, for generating the initial laser; An acousto-optic frequency shifter, wherein the input end of the acousto-optic frequency shifter is connected to the output end of the feedback component, and the output end is connected to the laser source, and is used to shift the frequency of the laser source.

3. The distributed optical fiber sound sensing system according to claim 2, characterized in that: The feedback component includes: A photodetector, the input end of which is connected to the output end of the interferometer, and is used to detect the intensity value of the interference light; A feedback controller, wherein the input end of the feedback controller is connected to the output end of the photodetector, and the output end is connected to the laser source or the acousto-optic modulator, and is used to calculate a frequency correction signal based on the intensity value and a reference value, and control and adjust the frequency of the laser source or the acousto-optic frequency shifter according to the correction signal.

4. The distributed optical fiber sound sensing system according to claim 2, wherein: The laser source is a narrow linewidth laser seed source; The interferometer is an unbalanced Mach-Zehnder interferometer.

5. The distributed optical fiber sound sensing system according to claim 1, characterized in that: The receiving component includes: Avalanche photodetector, AD collector and data analyzer.

6. A sound detection method, characterized in that: The distributed optical fiber sound sensing system according to any one of claims 1 to 5 is used for sound detection, comprising: Splitting the initial laser into a first laser beam and a second laser beam; Pulse-modulating the first laser beam to obtain a single-pulse laser; The single laser pulse is amplified and then transmitted to the sensing optical fiber, an echo signal from the sensing optical fiber is received, and the echo signal is analyzed to obtain the pending sound information; or the single laser pulse is amplified and then transmitted to the sensing optical fiber, an echo signal from the sensing optical fiber is received, and the echo signal is amplified and then transmitted to the sensing optical fiber, and the echo signal is amplified and then analyzed to obtain the pending sound information; Interfere the second laser beam to obtain interference light; adjust the frequency of the laser source assembly according to the intensity value of the interference light and a reference value; repeat this step until the difference between the intensity value and the reference value is within a preset difference range, and use the pending sound information in the time period corresponding to the current moment as reliable sound information; wherein the reference value is pre-set according to the laser source assembly.

7. The sound detection method according to claim 6, characterized in that: The adjusting the frequency of the laser source assembly according to the intensity value of the interference light and the reference value includes: Calculating a frequency correction signal based on the intensity value of the interference light and a reference value; The frequency corresponding to the laser source component is adjusted according to the frequency correction signal.

8. The sound detection method according to claim 6, characterized in that: The analyzing the echo signal includes: Performing photoelectric conversion on the echo signal to obtain an electrical signal; After AD acquisition of the electrical signal, signal analysis is performed to obtain the pending sound information.

9. A distributed optical fiber sound sensing device, characterized in that: The invention comprises a distributed optical fiber sound sensing system as described in any one of claims 1 to 5.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the sound detection method according to any one of claims 6 to 8 is implemented.

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