All-fiber variable carrier laser acoustic field measurement device and variable carrier modulation method

Abstract

The application relates to an all-fiber variable carrier laser sound field measuring device and a variable carrier modulation method, and relates to the technical field of laser application. The device comprises a main laser, a third fiber coupler, a fiber attenuator, a second fiber coupler, a balanced photoelectric detector, a signal acquisition card and an industrial computer; the third fiber coupler is further connected with an optical phase-locked loop; the optical phase-locked loop comprises the following components connected in sequence: a first fiber coupler, a phase detector, a signal amplifier, a frequency mixer, a voltage-controlled oscillator and a slave laser; wherein the frequency mixer is further connected with a local oscillator. The all-fiber laser coherent vibration measuring light path is adopted as the light path structure of the spatial sound field measuring system, can be disassembled and simply installed, and all the light paths are transmitted through optical fibers, so that the influence of ambient light can be avoided. The fiber attenuator in the local light path can adjust the attenuation coefficient in real time according to factors such as a detection distance and a detection angle, and the matching efficiency of the local light and the signal light is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser application, in particular to a full-fiber variable carrier laser sound field measuring device and a variable carrier modulation method. BACKGROUND

[0002] Laser sound field measurement technology is developing rapidly and is another high-tech field in the laser information technology industry. Laser coherent spatial sound field measurement method is based on the principle of acousto-optic effect, and has the advantages of non-contact measurement, fast response speed, high reconstruction accuracy, etc. For some devices that need to measure sound field, such as micro-nano fiber sensors, acoustic sensors, precision microphones, etc., accurate measurement of the dynamic distribution of the spatial sound field of the device is crucial for the calibration and development of the device.

[0003] The rapidly developing laser coherent vibration measurement technology has become an important means of flow field measurement. As a special flow field, the transmission of sound field in space can modulate the intensity of the medium refractive index. The laser coherent vibration measurement method can obtain the sound field modulation information, and the target sound field parameters can be inverted through the arctangent demodulation algorithm. The use of full-fiber optical path can simplify the optical path construction process, and the full-fiber optical path occupies a small space, and can avoid the influence of ambient light on the optical path, with high signal-to-noise ratio.

[0004] Optical phase-locked loop technology can provide a variable carrier signal for the laser coherent vibration measurement system. The optical phase-locked loop realizes the phase locking between two independent lasers through the feedback control of the electrical signal, and keeps the frequency difference of the two lasers dynamically stable. The traditional carrier modulation method usually uses a fixed frequency acousto-optic modulator. When the signal vibration frequency is much smaller than the acousto-optic modulator frequency, the data acquisition system will still be collected at a high frequency, causing waste of system resources. When the signal vibration frequency is higher than the acousto-optic modulator frequency, the carrier modulation device needs to be replaced, otherwise signal distortion will occur. The use of optical phase-locked loop technology can avoid this situation. The optical phase-locked loop can generate a wideband ultra-high frequency dynamic carrier signal in the range of MHz to GHz through the phase locking of the master and slave lasers. The carrier frequency can be adjusted according to the frequency range of the target vibration signal, perfectly solving the matching problem of signal frequency and modulation frequency.

[0005] At present, the laser coherent vibration measurement technology is mature, and the calibrated laser sound field measuring device can be used for dynamic visualization of the sound field, which will form a new sound field calibration method for acoustic sensor devices, and has important theoretical significance and application value for the development of laser sound field measurement technology. SUMMARY

[0006] The present application solves the technical problem of spatial sound field measurement in the prior art, and provides a full-fiber variable carrier laser sound field measuring device and a variable carrier modulation method.

[0007] To solve the above technical problems, the technical scheme of the present application is as follows:

[0008] A kind of all-fiber variable carrier laser sound field measuring device, in signal transmission direction in turn include: main laser, third fiber coupler, fiber attenuator, second fiber coupler, balanced photodetector, signal acquisition card and industrial computer;Third fiber coupler is also connected with optical phase-locked loop;Optical phase-locked loop includes first fiber coupler, phase detector, signal amplifier, frequency mixer, voltage-controlled oscillator and slave laser connected in series;Wherein, frequency mixer is also connected with local oscillator;

[0009] The light path direction of the output of optical phase-locked loop is sequentially provided with three-port polarization-maintaining fiber circulator, fiber transceiver lens, acoustic signal generator and hard reflecting plate;Three-port polarization-maintaining fiber circulator is also connected with second fiber coupler;

[0010] The main laser emits a laser beam, which is divided into local oscillator light and signal light after passing through the third fiber coupler;

[0011] The local oscillator light enters the second fiber coupler through the fiber attenuator;

[0012] The signal light enters the first fiber coupler of the optical phase-locked loop;The optical phase-locked loop keeps the frequency difference between the main laser and the slave laser consistent with the frequency parameter setting of the local oscillator;The carrier-modulated signal light processed by the optical phase-locked loop output by the first fiber coupler enters the three-port polarization-maintaining fiber circulator, then passes through the fiber transceiver lens, penetrates the acoustic field generated by the acoustic signal generator, and the echo light reflected by the hard reflecting plate enters the fiber transceiver lens;The echo light enters the second fiber coupler together with the local oscillator light through the three-port polarization-maintaining fiber circulator;

[0013] The local oscillator light and the echo light are mixed in the balanced photodetector, and the signal acquisition card is processed in the industrial computer.

[0014] In the above technical scheme, the signal light entering the optical phase-locked loop and the slave laser pass through the first fiber coupler and mix on the photosensitive surface of the phase detector, the mixed signal passes through the signal amplifier and is compared with the signal of the local oscillator in the frequency mixer in real time, the voltage signal corresponding to the phase difference output by the frequency mixer enters the voltage-controlled oscillator, and the voltage-controlled oscillator modulates the output frequency of the slave laser in real time according to the voltage signal;

[0015] When the optical phase-locked loop works stably, the frequency difference signal generated by the main laser and the slave laser always tracks the reference signal generated by the local oscillator;If the reference signal frequency changes, the mixed signal automatically tracks the reference signal frequency under the action of the optical phase-locked loop, forming a dynamic stable loop structure.

[0016] In the technical scheme, the balanced photoelectric detector has a wavelength range of 800-1700nm and a bandwidth of 100Hz-500MHz.

[0017] In the technical scheme, the sampling frequency of the signal acquisition card is at least 2 times of the carrier signal frequency.

[0018] In the technical scheme, the hard reflection plate is made of metal material.

[0019] In the technical scheme, the maximum frequency of the signal generated by the local oscillator is at least 2 times of the highest frequency of the signal light.

[0020] In the technical scheme, the third fiber coupler is a 1x2 fiber coupler, and the first and second fiber couplers are 2x2 fiber couplers.

[0021] A variable carrier modulation method suitable for the all-fiber variable carrier laser sound field measurement device described above, comprising the following steps:

[0022] Step 1: the main laser emits a laser beam, which is divided into local oscillator light and signal light after passing through the third fiber coupler;

[0023] Step 2: the local oscillator light enters the second fiber coupler through the fiber attenuator;

[0024] Step 3: the signal light enters the first fiber coupler of the optical phase-locked loop;

[0025] Step 4: the optical phase-locked loop keeps the frequency difference between the main laser and the slave laser consistent with the frequency parameter setting of the local oscillator;

[0026] Step 5: the carrier modulation signal light output by the first fiber coupler and processed by the optical phase-locked loop enters the three-port polarization-maintaining fiber circulator, then passes through the fiber transceiver lens, penetrates the sound field generated by the sound signal generator, and the echo light reflected by the hard reflection plate enters the fiber transceiver lens;

[0027] Step 6: the echo light enters the second fiber coupler together with the local oscillator light through the three-port polarization-maintaining fiber circulator;

[0028] Step 7: the local oscillator light and the echo light are mixed in the balanced photoelectric detector, and the signal acquisition card is used to process the sound field inversion in the industrial computer.

[0029] The present application has the following beneficial effects:

[0030] The all-fiber variable carrier laser sound field measuring device of the application adopts an all-fiber laser coherent vibration measuring light path as the light path structure of a spatial sound field measuring system, has the advantages of being detachable and simple to install, and all the light paths in the whole structure are transmitted through optical fibers, so that the influence of ambient light on the light path transmission can be avoided.

[0031] The variable carrier modulation method of the application generates a dynamically stable carrier signal by using an optical phase-locked loop and a feedback type fiber laser, and the dynamic range of the carrier signal frequency can be from MHz to GHz. The optical phase-locked loop technology can modulate the carrier frequency according to the signal frequency, so that the carrier frequency is always within a reasonable range of signal acquisition, and while realizing efficient real-time acquisition, the system resources are smaller and the efficiency is higher. BRIEF DESCRIPTION OF DRAWINGS

[0032] The application will be further described in detail below in combination with the drawings and specific embodiments.

[0033] Figure 1 The drawing is a light path structure schematic diagram of the all-fiber variable carrier laser sound field measuring device of the application.

[0034] The reference signs in the drawing are as follows:

[0035] 1-main laser; 2-third optical fiber coupler; 3-optical fiber attenuator; 4-local oscillator; 5-mixer; 6-signal amplifier; 7-phase detector; 8-first optical fiber coupler; 9-voltage controlled oscillator; 10-slave laser; 11-second optical fiber coupler; 12-balance photoelectric detector; 13-signal acquisition card; 14-industrial computer; 15-three-port polarization maintaining fiber ring; 16-fiber transceiver lens; 17-acoustic signal generator; 18-hard reflecting plate. DETAILED DESCRIPTION

[0036] The inventive idea of the application is:

[0037] The application adopts the technical route of combining laser coherent vibration measurement and spatial sound field visualization measurement, and realizes the visualization measurement of spatial ultrasonic field in an optical non-contact manner on the basis of laser coherent vibration measurement technology. The change of spatial sound field sound pressure will cause the change of refractive index of the transmission medium, the signal light is reflected on the hard reflecting plate after passing through the transmission medium, the reflected echo light phase carries the sound field modulation information, the target sound field parameters can be inverted through phase demodulation, and the dynamic visualization characterization of spatial sound field is realized.

[0038] The all-fiber variable carrier laser acoustic field measurement device of this invention adopts an all-fiber optical path structure and a dynamic variable carrier modulation method, which reduces the difficulty of building the optical path for laser acoustic field measurement and solves the matching problem between signal frequency and modulation frequency. A laser spatial acoustic field measurement system is built using all-fiber devices, with both signal light and echo light transmitted through fiber optic structures, reducing the influence of ambient light on the transmission optical path. Simultaneously, an optical phase-locked loop system is composed of a phase detector, a loop filter, and an optical voltage-controlled oscillator. The mixing signal automatically tracks the reference signal frequency under the action of the optical phase-locked loop, and dynamic synchronization between the slave laser and the master laser is achieved through feedback control of electrical signals, maintaining a dynamically stable frequency difference between them.

[0039] The present invention will now be described in detail with reference to the accompanying drawings.

[0040] like Figure 1 As shown, the optical path structure of the all-fiber variable carrier laser acoustic field measurement device of the present invention includes, in the signal transmission direction, a main laser 1, a third fiber coupler 2, a fiber attenuator 3, a second fiber coupler 11, a balanced photodetector 12, a signal acquisition card 13, and an industrial control computer 14. The third fiber coupler 2 is also connected to an optical phase-locked loop. The optical phase-locked loop includes, end-to-end, a first fiber coupler 8, a phase detector 7, a signal amplifier 6, a mixer 5, a voltage-controlled oscillator 9, and a slave laser 10. The mixer 5 is also connected to a local oscillator 4. In the optical path direction output from the optical phase-locked loop, a three-port polarization-maintaining fiber circulator 15, a fiber optic transceiver lens 16, an acoustic signal generator 17, and a rigid reflector 18 are arranged in sequence. The three-port polarization-maintaining fiber circulator 15 is also connected to the second fiber coupler 11. The third fiber coupler 2 is a 1×2 fiber coupler, and the first fiber coupler 8 and the second fiber coupler 11 are 2×2 fiber couplers, respectively.

[0041] The main laser 1 emits a laser beam, which is then split into two optical signals after passing through the third fiber coupler 2: the local oscillator beam and the signal beam.

[0042] The local oscillator optical signal enters the second optical fiber coupler 11 after passing through the optical fiber attenuator 3.

[0043] The signal light enters a first fiber coupler 8 of an optical phase-locked loop; the optical phase-locked loop comprises the first fiber coupler 8, a phase detector 7, a signal amplifier 6, a frequency mixer 5, a voltage-controlled oscillator 9 and a slave laser 10 connected in sequence; wherein the frequency mixer 5 is further connected with a local oscillator 4. The optical phase-locked loop is used to keep the frequency difference between the master laser 1 and the slave laser 10 and the frequency parameter setting of the local oscillator 4 dynamically consistent. The signal light and the slave laser 10 are mixed on the photosensitive surface of the phase detector 7 through the first fiber coupler 8, and the mixed signal is compared with the signal of the local oscillator 4 in the frequency mixer 5 after passing through the signal amplifier 6, and the voltage signal corresponding to the phase difference of the two is output by the frequency mixer 5 into the voltage-controlled oscillator 9, which modulates the output frequency of the slave laser 10 according to the voltage signal in real time; when the optical phase-locked loop works stably, the frequency difference signal generated by the master laser 1 and the slave laser 10 always tracks the reference signal generated by the local oscillator 4, and if the frequency of the reference signal changes, the mixed signal will automatically track the frequency of the reference signal under the action of the optical phase-locked loop, forming a dynamic stable loop structure.

[0044] The carrier-modulated signal light output by the first fiber coupler 8 enters a three-port polarization-maintaining fiber ring 15, then passes through a fiber transceiver lens 16, penetrates the acoustic field generated by an acoustic signal generator 17, and the echo light reflected by a hard reflecting plate 18 enters the fiber transceiver lens 16; finally, the echo light enters a second fiber coupler 11 together with the local oscillator light through the three-port polarization-maintaining fiber ring 15.

[0045] The local oscillator light and the echo light are mixed in a balanced photodetector 12, pass through a signal acquisition card 13, and finally are processed in an industrial computer 14.

[0046] According to the working process of the all-fiber variable carrier laser acoustic field measurement device of the present application, the variable carrier modulation method of the present application comprises the following steps:

[0047] Step 1: the master laser 1 emits a beam of laser light, which is divided into local oscillator light and signal light after passing through the third fiber coupler 2;

[0048] Step 2: the local oscillator light enters the second fiber coupler 11 through the fiber attenuator 3;

[0049] Step 3: the signal light enters the first fiber coupler 8 of the optical phase-locked loop;

[0050] Step 4: the optical phase-locked loop keeps the frequency difference between the master laser 1 and the slave laser 10 and the frequency parameter setting of the local oscillator 4 dynamically consistent;

[0051] Step 5: The carrier wave modulation signal light output by the first optical fiber coupler 8 enters the three-port polarization-maintaining fiber circulator 15, and then passes through the optical fiber transceiver lens 16, penetrates the acoustic field generated by the acoustic signal generator 17, and enters the optical fiber transceiver lens 16 through the echo light reflected by the hard reflecting plate 18;

[0052] Step 6: The echo light enters the second optical fiber coupler 11 together with the local oscillator light through the three-port polarization-maintaining fiber circulator 15.

[0053] Step 7: The local oscillator light and the echo light are mixed in the balanced photodetector 12, and then pass through the signal acquisition card 13 and are processed by the industrial computer 14 to obtain the sound field inversion.

[0054] In the specific embodiment of the present application, the master laser 1 and the slave laser 10 are both linearly polarized lasers, and the optical fibers used in the entire optical path structure are all polarization-maintaining fibers, and all the optical fiber interfaces are FC / APC.

[0055] The master laser 1 has a wavelength of 1550nm, a power of 20mW (10%-100% adjustable), and a linewidth of ≤2KHz. The master laser 1 generates a laser beam, which is divided into two parts (the beam splitting ratio is 1:9) by the third optical fiber coupler 2. The low-power part is used as the local oscillator light, and the high-power part is used as the signal light. The local oscillator light enters the second optical fiber coupler 11 through the optical fiber attenuator 3 (attenuation range: 0-60dB).

[0056] The slave laser 10 has a tunable function, and the tunable distributed feedback laser is selected as the slave laser 10. The optical phase-locked loop can adjust the frequency difference between the master laser 1 and the slave laser 10 in real time according to the frequency setting parameters of the local oscillator 4, so that the frequency difference is dynamically consistent with the frequency of the local oscillator 4. The frequency parameters of the local oscillator 4 are adjusted according to the signal frequency. Finally, the function of the optical phase-locked loop is to build a dynamic stable carrier signal generation system that can adjust the frequency in real time, and the signal acquisition data rate is controlled within a reasonable range.

[0057] The acoustic signal generator 17 is used as a target sound source, and the change of the sound field intensity will cause the change of the refractive index of the transmission medium. The signal light is diffusely reflected on the hard reflecting plate 18, and the echo light carries the sound field information. The echo light is sent into the second optical fiber coupler 11 through the optical fiber transceiver lens 16 and the three-port polarization-maintaining fiber circulator 15 (isolation ≥40dB). The echo light and the local oscillator light are mixed on the photosensitive surface of the balanced photodetector 12.

[0058] The frequency range of the local oscillator 4 is dynamically adjusted according to the signal frequency, and the frequency of the local oscillator 4 is generally at least 2 times the highest frequency of the signal according to engineering experience. The mixer 5 is used to mix the signal amplified by the signal amplifier 6 and the local oscillator 4, and then transmitted to the first optical fiber coupler 8 via the voltage-controlled oscillator 9 and the laser 10. The voltage-controlled oscillator 9 generates a control signal through the mixer 5, which is used to control the output signal frequency of the laser 10.

[0059] The balanced photodetector 12 has a wavelength range of 800-1700 nm, an AC coupling mode, and a bandwidth of 100 Hz-500 MHz (adjustable).

[0060] The signal acquisition card 13 is used to perform analog-to-digital conversion on the signal output by the balanced photodetector 12 and input into the industrial computer 14. The phase demodulation algorithm is loaded in the data processing software of the industrial computer 14, and the target sound field information is inverted to visualize the spatial sound field. The frequency of the signal acquisition card 13 is at least 2 times the frequency of the carrier signal according to the Shannon sampling theorem. The data processing software of the industrial computer 14 writes the arctangent phase demodulation algorithm to invert the sound pressure intensity of the target sound field.

[0061] The material of the hard reflective plate 18 is selected to be a metal material that is not easy to vibrate, which can effectively reduce the echo light phase modulation noise caused by environmental vibration.

[0062] The optical fiber attenuator 3 is arranged in the local oscillator optical path structure, which dynamically adjusts the attenuation coefficient of the local oscillator light to prevent the beam splitting ratio of the main laser 1 passing through the third optical fiber coupler 2 from not matching the detection environment. Changes in detection distance and detection angle will change the echo light power, and dynamically adjusting the local oscillator light power can improve the matching efficiency of the local oscillator light and the signal light.

[0063] The local oscillator light and the echo light enter the balanced photodetector 12, and the balanced photodetector 12 outputs the differential signal of the local oscillator light and the signal light, which can effectively suppress the direct current component generated by the interference field of the signal light and the local oscillator light.

[0064] The three-port polarization-maintaining optical fiber circulator 15 is used to send the local oscillator light into the optical fiber transceiver lens 16 and output the echo light to the second optical fiber coupler 11.

[0065] The acoustic signal generator 17 generates a spatial sound field with varying intensity along the sound propagation path. The sound field with varying intensity will cause changes in the refractive index of the transmission medium. The signal light penetrates the sound field and is diffusely reflected by the hard reflective plate 18. The echo light enters the optical fiber transceiver lens 16 after passing through the target sound field, and the phase of the echo light carries the intensity modulation information of the target sound field.

[0066] The all-fiber variable carrier laser sound field measuring device of the application adopts an all-fiber laser coherent vibration measuring light path as the light path structure of a spatial sound field measuring system, has the advantages of being detachable and simple to install, the light paths in the whole structure are transmitted through optical fibers, and the influence of ambient light on the light path transmission can be avoided.

[0067] The variable carrier modulation method of the application generates a dynamically stable carrier signal by using an optical phase-locked loop and a feedback type fiber laser, and the frequency dynamic range of the carrier signal can be from MHz to GHz. The optical phase-locked loop technology can modulate the carrier frequency according to the signal frequency, so that the carrier frequency is always within a reasonable range of signal acquisition, while realizing efficient real-time acquisition, occupying smaller system resources and being more efficient.

[0068] Obviously, the above embodiments are only examples for clearly illustrating the application, and are not intended to limit the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. All the embodiments do not need to be exhausted here, and the obvious changes or variations derived therefrom are still within the protection scope of the application.

Claims

1. A fully fiber-optic variable carrier laser acoustic field measurement device, characterized in that, The signal transmission direction includes, in sequence: a main laser (1), a third fiber coupler (2), a fiber attenuator (3), a second fiber coupler (11), a balanced photodetector (12), a signal acquisition card (13), and an industrial control computer (14); the third fiber coupler (2) is also connected to an optical phase-locked loop; the optical phase-locked loop includes, end to end: a first fiber coupler (8), a phase detector (7), a signal amplifier (6), a mixer (5), a voltage-controlled oscillator (9), and a slave laser (10); among which, the mixer (5) is also connected to a local oscillator (4); A three-port polarization-maintaining fiber circulator (15), a fiber optic transceiver lens (16), an acoustic signal generator (17), and a rigid reflector (18) are sequentially arranged along the optical path output from the optical phase-locked loop; the three-port polarization-maintaining fiber circulator (15) is also connected to a second fiber optic coupler (11). The main laser (1) emits a laser beam, which is then separated into a local oscillator beam and a signal beam after passing through the third fiber coupler (2). The local oscillator light passes through the fiber optic attenuator (3) and enters the second fiber optic coupler (11); The signal light enters the first fiber coupler (8) of the optical phase-locked loop; the optical phase-locked loop keeps the frequency difference between the master laser (1) and the slave laser (10) dynamically consistent with the frequency parameter settings of the local oscillator (4); the carrier-modulated signal light output from the first fiber coupler (8) and processed by the optical phase-locked loop enters the three-port polarization-maintaining fiber circulator (15), then passes through the fiber transceiver lens (16), penetrates the sound field generated by the acoustic signal generator (17), and the echo light reflected by the rigid reflector (18) enters the fiber transceiver lens (16); the echo light passes through the three-port polarization-maintaining fiber circulator (15) and enters the second fiber coupler (11) together with the local oscillator light; The local oscillator light and the echo light are mixed in the balanced photodetector (12), and after passing through the signal acquisition card (13), the sound field is inverted in the industrial control computer (14).

2. The all-fiber variable carrier laser acoustic field measurement device according to claim 1, characterized in that, The signal light entering the optical phase-locked loop and the signal from the laser (10) are mixed on the photosensitive surface of the phase detector (7) through the first fiber coupler (8). The mixed signal is then compared in real time with the signal from the local oscillator (4) after passing through the signal amplifier (6). The mixer (5) outputs a voltage signal corresponding to the phase difference between the two signals, which enters the voltage-controlled oscillator (9). The voltage-controlled oscillator (9) modulates the output frequency of the laser (10) in real time according to the voltage signal. When the optical phase-locked loop is working stably, the frequency difference signal generated by the main laser (1) and the laser (10) always tracks the reference signal generated by the local oscillator (4); if the frequency of the reference signal changes, the mixing signal automatically tracks the frequency of the reference signal under the action of the optical phase-locked loop, forming a dynamic stable loop structure.

3. The all-fiber variable carrier laser acoustic field measurement device according to claim 1 or 2, characterized in that, The balanced photodetector (12) has a wavelength range of 800–1700 nm and a bandwidth of 100 Hz–500 MHz.

4. The all-fiber variable carrier laser acoustic field measurement device according to claim 1, characterized in that, The sampling frequency of the signal acquisition card (13) is at least twice the carrier signal frequency.

5. The all-fiber variable carrier laser acoustic field measurement device according to claim 1, characterized in that, The rigid reflector (18) is made of metal.

6. The all-fiber variable carrier laser acoustic field measurement device according to claim 1, characterized in that, The local oscillator (4) generates a signal with a maximum frequency that is at least twice the highest frequency of the signal light.

7. The all-fiber variable carrier laser acoustic field measurement device according to claim 1, characterized in that, The third fiber coupler (2) is a 1×2 fiber coupler, while the first fiber coupler (8) and the second fiber coupler (11) are 2×2 fiber couplers respectively.

8. A variable carrier modulation method applicable to the all-fiber variable carrier laser acoustic field measurement device according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1: The main laser (1) emits a laser beam, which is then separated into a local oscillator beam and a signal beam after passing through the third fiber coupler (2); Step 2: The local oscillator light passes through the fiber optic attenuator (3) and enters the second fiber optic coupler (11); Step 3: The signal light enters the first fiber coupler (8) of the optical phase-locked loop; Step 4: The optical phase-locked loop keeps the frequency difference between the master laser (1) and the slave laser (10) dynamically consistent with the frequency parameter settings of the local oscillator (4); Step 5: The carrier modulation signal light output from the first fiber coupler (8) after being processed by the optical phase-locked loop enters the three-port polarization-maintaining fiber circulator (15), then passes through the fiber transceiver lens (16), penetrates the sound field generated by the acoustic signal generator (17), and the echo light reflected by the rigid reflector (18) enters the fiber transceiver lens (16). Step 6: The echo light passes through the three-port polarization-maintaining fiber circulator (15) and enters the second fiber coupler (11) together with the local oscillator light; Step 7: The local oscillator light and the echo light are mixed in the balanced photodetector (12), and after passing through the signal acquisition card (13), the sound field is inverted in the industrial control computer (14).

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