Cross-medium virtual phased array communication system based on MOPA laser and scanning galvanometer

Abstract

The invention discloses a cross-medium virtual phased array communication system based on an MOPA laser and a scanning galvanometer, and relates to the technical field of communication. The system comprises an emission control subsystem (10), an optical path scanning subsystem (20), a photoacoustic conversion interface subsystem (30) and an underwater receiving subsystem (40) which are interacted in sequence, according to the method, an MOPA laser is controlled to emit low-repetition-frequency high-energy pulses, a galvanometer is used for deflecting laser beams to different positions on the surface of a dielectric layer, a time division multiplexing virtual sound source array is constructed, the dielectric layer efficiently converts light energy into point sound source signals, and a receiving end conducts time sequence alignment and superposition on the sound signals through the synthetic aperture focusing technology. The invention effectively overcomes the defects of low opto-acoustic conversion efficiency and uncontrollable beam in traditional cross-medium communication, realizes high signal-to-noise ratio directional communication without a physical array, and has the advantages of simple structure, low cost, flexible and reconfigurable beam pointing and the like.

Description

Technical Field

[0001] This invention relates to the field of communication technology, and in particular to a cross-medium virtual phased array communication system based on a MOPA laser and a scanning galvanometer. Background Technology

[0002] In the field of communications, different communication methods are typically used for different channel transmission media. For example, electromagnetic wave communication is typically used in air, while acoustic signal communication is typically used underwater.

[0003] With the rapid development of marine observation networks, air-to-water (AUV) vehicles, and submarine technology, achieving high-speed, covert communication between airborne platforms (such as drones and aircraft) and underwater nodes (i.e., "air-to-water cross-medium communication") has become a strategic high ground in the field of marine information. Due to the significant difference in acoustic impedance between air and water (approximately 3600 times), traditional radio electromagnetic waves attenuate extremely rapidly in water, making deep communication difficult. While underwater acoustic communication can travel long distances, it suffers severe energy loss when crossing interfaces. Therefore, laser-induced sound technology, with its ability to use laser beams to penetrate the air-water interface and generate sound waves in water, has become an important means of solving the downlink (air-to-water) communication problem.

[0004] However, the inventors discovered through research that existing cross-media communication technologies still suffer from the following significant technical bottlenecks in practical applications: One drawback is the deployment challenges and high costs of physical sonar arrays. Existing phased array communication solutions are mostly based on underwater physical sonar arrays. These solutions require the deployment of large transducer arrays with numerous elements underwater. For airborne or shipborne mobile communication scenarios, this means deploying buoys or towed sonars, which not only lacks deployment flexibility and concealment but also incurs high hardware costs. Furthermore, maintenance is extremely difficult once array elements are damaged. This makes them unsuitable for lightweight, highly maneuverable UAV cross-media communication scenarios.

[0005] The second drawback is the low signal-to-noise ratio and omnidirectional nature of traditional single-point laser-induced acoustics. Traditional laser-induced acoustic communication typically uses a single pulsed laser beam to directly illuminate the water surface. Firstly, the photoacoustic conversion efficiency is low: commonly used wavelengths (such as 1064nm) have a low light absorption coefficient in pure water, resulting in a large light penetration depth. This creates a long, thin "line sound source" rather than an ideal "point sound source," leading to extremely low energy radiation efficiency in the vertical direction. Secondly, it lacks beam control capability: sound waves generated by single-point excitation typically diffuse omnidirectionally or cylindrically, and the energy attenuates extremely rapidly with distance (1 / r or 1 / r). 2Furthermore, it cannot achieve directional beamforming. This not only results in a short effective communication distance and a low signal-to-noise ratio (SNR), but also makes it extremely easy for non-target nodes to eavesdrop on the signal because it radiates in all directions, thus compromising communication security.

[0006] The third drawback is the response lag in mechanical focusing schemes. To improve energy density, some existing technologies attempt to adjust the focal point by mechanically moving the lens or changing the laser's orientation. However, the movement of mechanical components has significant inertia, and its response speed (typically milliseconds or even slower) is far lower than the modulation rate required for acoustic communication. This method cannot rapidly switch between multiple positions in a very short time, thus making it impossible to construct an effective phased array through timing control and difficult to adapt to the demands of high-speed communication.

[0007] In summary, there is an urgent need for a low-cost cross-medium communication solution that does not require an underwater physical array, can overcome the bottleneck of photoacoustic conversion efficiency, and has flexible beam pointing capabilities. This invention addresses these technical deficiencies by proposing a cross-medium virtual phased array communication system based on a MOPA laser and scanning galvanometer to solve the aforementioned problems in the prior art. Summary of the Invention

[0008] The purpose of this invention is to address the technical problems existing in current cross-medium communication technologies, such as the large size and high cost of physical sonar arrays, the low efficiency and lack of beam directivity of traditional single-point laser-induced acoustic conversion, and the slow mechanical focusing response speed that cannot meet the requirements of high-speed communication. This invention provides a cross-medium virtual phased array communication system based on MOPA lasers and scanning galvanometers.

[0009] This invention utilizes high-speed spatiotemporal scanning of a single-source laser to construct a virtual sound source array, achieving high signal-to-noise ratio and reconfigurable directional cross-medium communication without the need for an underwater physical array.

[0010] The present invention also provides a cross-medium communication method, which is applied to cross-medium communication in a cross-medium communication system, the cross-medium communication system including an air platform and an underwater platform.

[0011] The objective of this invention is achieved as follows: 1. A cross-medium virtual phased array communication system based on a MOPA laser and scanning galvanometer, comprising: This system includes a sequentially interacting transmission control subsystem, optical path scanning subsystem, photoacoustic conversion interface subsystem, and underwater receiving subsystem; A photoacoustic conversion medium layer and sound waves are installed inside the water tank; Above the photoacoustic conversion medium layer, the host computer and control card are connected front and back. The signal then enters the laser through the MOPA pulse laser and the galvanometer driver respectively. The laser, collimator, dual-axis scanning galvanometer and flat-field scanning lens are connected in sequence. Below the photoacoustic conversion medium layer The sound waves, hydrophone, charge amplifier, and high-speed oscilloscope interact in sequence; The high-speed oscilloscope is then connected to the host computer.

[0012] 2. The present invention also provides a communication method based on the above system. This method involves controlling a MOPA laser to emit low-repetition-rate, high-energy pulses, using a galvanometer to deflect the laser beam to different positions on the surface of a dielectric layer, and constructing a time-division multiplexed virtual sound source array. The dielectric layer efficiently converts optical energy into point sound source signals. The receiver uses synthetic aperture focusing technology to perform time-series alignment and superposition of the sound signals.

[0013] Specifically, it includes the following steps: ① Parameter initialization: Set the number of array elements, the spacing between array elements, and the target beam pointing angle of the virtual array; ②Time-division excitation: The control unit drives the galvanometer to deflect to the coordinates of the Nth array element, and at the same time triggers the MOPA laser to emit a single pulse laser; after the laser hits the photoacoustic conversion interface, it generates the Nth omnidirectional acoustic pulse; ③ Array scanning: According to the preset timing sequence, the deflection angle of the galvanometer is changed sequentially to traverse the positions of all virtual array elements and complete one complete array excitation cycle; ④ Signal synthesis: The receiver collects the acoustic signals generated by each excitation, calculates the phase delay required for each array element based on the target beam pointing angle, and performs time-shifted superposition on the collected signals to form a directional beam signal with high gain.

[0014] Compared with the prior art, the present invention has the following advantages and positive effects: ① It innovatively utilizes a "single laser source + high-speed galvanometer" to construct a virtual array, replacing the traditional bulky and expensive underwater physical transducer array; this "software-defined array" architecture greatly reduces system hardware costs and deployment difficulty, and is particularly suitable for load-sensitive mobile platforms such as drones and unmanned vessels.

[0015] ② By introducing a photoacoustic conversion medium layer, the problem of large penetration depth and low energy density of 1064nm laser in pure water is effectively solved. This design compresses the originally loose line sound source into a sub-millimeter point sound source, which significantly improves the energy conversion efficiency of light-heat-sound, enabling high-intensity sound signals to be obtained even at low laser power.

[0016] ③ Thanks to the microsecond-level response speed of the galvanometer and the adjustable parameters of the MOPA laser, this system can adjust the aperture size, element spacing and transmission frequency of the virtual array in real time; this means that the communication system can optimize beam characteristics in real time according to the channel environment (such as wave size and communication distance), and has extremely strong environmental adaptability and anti-interference ability.

[0017] ④ By utilizing synthetic aperture focusing (SAFT) technology, this invention can coherently superimpose dispersed acoustic energy in a specific direction to achieve significant array gain, thereby greatly improving the signal-to-noise ratio of communication. At the same time, the high directivity of the beam effectively suppresses sidelobe leakage, improving the stealth and security of underwater communication.

[0018] In summary, this invention effectively overcomes the shortcomings of low photoacoustic conversion efficiency and uncontrollable beam in traditional cross-medium communication, and realizes high signal-to-noise ratio directional communication without physical arrays. It has the advantages of simple structure, low cost, and flexible and reconfigurable beam pointing. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of this communication system; Figure 2 This is a flowchart of the communication method (SAFT algorithm).

[0020] In the picture: 10—Launch Control Subsystem 11—Host computer, 12—Control card, 13—MOPA pulsed laser, 14—Galvanometer driver; 20—Optical Path Scanning Subsystem 21—Laser, 22—Collimator, 23—Dual-axis scanning galvanometer, 24—Plan-field scanning lens; 30—Photoacoustic Conversion Interface Subsystem 31—Water tank; 32—Photoacoustic conversion medium layer; 40—Underwater receiving subsystem, 41—Hydrophone, 42—Charge amplifier, 43—High-speed oscilloscope.

[0021] English to Chinese: 1. MOPA (Master Oscillator Power Amplifier): A physical instrument based on a combination of master oscillator and power amplifier. It is mainly used to generate high-quality seed light and amplify its power. It is widely used in optical fiber communication, industrial processing (such as lithium battery cutting and photovoltaic etching), medical diagnosis and treatment (ophthalmic surgery and skin treatment) and scientific research (spectral analysis and mass spectrometry detection).

[0022] 2. SAFT (Synthetic Aperture Focusing): This is a digital signal processing method based on the "delay-and-sum" principle. This technique involves sequentially acquiring or exciting signals at different locations in space, and then, in the post-processing stage, precisely compensating for the phase (delay) and coherently superimposing the signals from each acquisition point according to geometric path differences. This mathematically synthesizes an equivalent large-aperture physical array or acoustic lens. In the fields of ultrasonic testing and communication, this technique is widely used to suppress incoherent noise, improve the signal-to-noise ratio (SNR), and achieve high-precision spatial directional focusing. Detailed Implementation

[0023] The following is a detailed description with reference to the accompanying drawings and embodiments: I. System 1) Structure like Figure 1 The system includes a sequentially interacting transmission control subsystem 10, an optical path scanning subsystem 20, an optical-acoustic conversion interface subsystem 30, and an underwater receiving subsystem 40. 1. Transmission Control Subsystem 10: A host computer 11 is used as the main control unit, connected to a multi-axis synchronous control card 12 (e.g., a Golden Orange board or a self-developed FPGA control card) via a USB / PCIe interface. The control card 12 has two outputs: one is a PWM / Gate signal, connected to a MOPA pulsed laser (model: YFPN-200-GME) 13, used to precisely control the laser's repetition frequency (1kHz-5kHz) and pulse width (200ns); the other is an XY2-100 protocol digital signal, connected to a galvanometer driver 14.

[0024] 2. Optical path scanning subsystem 20: The 1064nm fiber laser output from the laser 21 is collimated by the collimator 22 and then incident on the dual-axis scanning galvanometer (10mm aperture) 23; an F-theta flat field scanning lens (focal length f=254mm) 24 is arranged below the scanning galvanometer 23 to ensure that the laser focus is always focused on the same horizontal plane within the 175mm×175mm scanning area.

[0025] 3. Photoacoustic Conversion Interface Subsystem 30: A photoacoustic conversion medium layer 32 is provided at the water-air interface of the water tank 31. In this embodiment, the photoacoustic conversion medium layer 32 is modulated by adding carbon-based water-soluble ink to pure water until the light penetration depth of the water in the 1064nm band is less than 1mm; the function of the photoacoustic conversion medium layer 32 is to convert the line source energy deposition mode of the laser into the point source thermal expansion mode.

[0026] 4. Underwater receiving subsystem 40: includes a broadband standard hydrophone 41 (model: B&K 8104), a charge amplifier 42 and a high-speed oscilloscope 43 connected in sequence; the bandpass filter range of the charge amplifier 42 is set to 10Hz-100kHz to match the main frequency of the sound wave excited by a 200ns pulse width and to filter out high-frequency noise.

[0027] Specifically: A photoacoustic conversion medium layer 32 and a sound wave 33 are provided inside the water tank 31; Above the photoacoustic conversion medium layer 32, the host computer 11 and the control card 12 are connected one after the other. The signal then passes through the MOPA pulse laser 13 and the galvanometer driver 14 respectively and enters the laser 21. The laser 21, collimator 22, dual-axis scanning galvanometer 23 and flat-field scanning lens 24 are connected in sequence. Below the photoacoustic conversion medium layer 32, the acoustic wave 33, hydrophone 41, charge amplifier 42 and high-speed oscilloscope 43 interact in sequence; The high-speed oscilloscope 43 is then connected to the host computer 11.

[0028] (ii) Functional components 1) Host computer 11 Definition: It is the core control and data processing terminal of the entire system, usually a high-performance computer with professional measurement and control software (such as LabVIEW or MATLAB) installed.

[0029] Functions: It is responsible for sending scanning commands (such as array pattern and scanning speed) to the control card 12; at the same time, it receives acoustic wave data collected by the high-speed oscilloscope 43 through the interface, and uses the synthetic aperture focusing technology (SAFT) algorithm to process the data offline or online to realize beamforming and image / signal reconstruction.

[0030] 2) Control Card 12 Definition: It is an intermediate interface unit that connects the host computer 11 to hardware devices, such as a multi-function data acquisition card (DAQ) or an FPGA board.

[0031] Function: Responsible for system time synchronization and signal distribution. It receives digital instructions from the host computer 11, converts them into analog voltage signals or TTL level signals, and synchronously triggers the pulse emission of the MOPA laser 13 and the deflection of the galvanometer driver 14, ensuring the precise timing correspondence between "laser emission" and "beam position".

[0032] 3) MOPA pulsed laser 13 Definition: A fiber laser employing a master oscillator power amplifier architecture (in this embodiment, the center wavelength is 1064nm).

[0033] Function: Serves as the system's energy source for generating high-repetition-rate (e.g., 5 kHz) and narrow-pulse-width (e.g., nanosecond level) high-energy pulsed lasers. Its MOPA architecture allows for flexible tuning of the pulse waveform and frequency to meet the peak power density required for inducing nonlinear photoacoustic effects on the water surface.

[0034] 4) Mirror driver 14 Definition: It is a power amplifier electronic module used to drive the scanning galvanometer motor.

[0035] Function: Receives control voltage signals from control card 12 and converts them into the current required to drive the dual-axis scanning galvanometer motor, thereby precisely controlling the deflection angle of the galvanometer lens and ensuring the speed and accuracy of laser spot positioning on the water surface.

[0036] 5) Laser 21 Note: This refers to the optical output head (optical isolator output end) of the MOPA laser.

[0037] Function: Outputs a high-power pulsed laser beam transmitted through optical fiber, serving as the starting point of the optical path system.

[0038] 6) Collimator 22 Definition: An optical device installed at the output end of an optical fiber.

[0039] Function: Converts the diverging Gaussian beam output from the optical fiber into a parallel beam (collimated beam) that propagates in free space to match the aperture requirements of the subsequent galvanometer system and ensure beam quality during long-distance transmission.

[0040] 7) Dual-axis scanning galvanometer 23 Definition: A beam deflection device consisting of two reflectors on the X and Y axes and their driving motors.

[0041] Function: By rapidly changing the angle of the reflector, the propagation direction of the laser beam is altered. In this system, it is responsible for executing the scanning strategy of the "virtual array," that is, sequentially projecting the laser spot onto different coordinate positions (x, y, y) on the water surface according to a preset timing sequence. i This allows for the temporal synthesis of spatial sound source arrays.

[0042] 8) Flat field scanning lens 24 Definition: A specially designed focusing lens whose image height is proportional to the scanning angle.

[0043] Function: Focuses a parallel beam deflected by a galvanometer onto the same focal plane (i.e., the water surface). Regardless of the incident angle, it ensures that the size of the focused spot is uniform throughout the entire scanning field, thus ensuring the consistency of acoustic characteristics (such as frequency and intensity) excited at different array element positions.

[0044] 9) Sink 31 Definition: A container for holding experimental water and underwater equipment, usually made of glass or acrylic.

[0045] Function: Simulates real underwater communication channels or detection environments, providing a medium space for the propagation of sound waves.

[0046] 10) Photoacoustic conversion medium layer 32 Definition: An enhanced absorption layer that floats or is coated at the water-air interface. In this embodiment, a carbon-based ink layer or a similar strong light-absorbing material is used.

[0047] Function: It is the core region for photoacoustic energy conversion. This layer strongly absorbs the focused laser energy, causing the local medium temperature to rise instantaneously and exceed the boiling point, inducing a vaporization mechanism, thereby generating a high-intensity photoacoustic shock wave, significantly improving the sound source level and signal-to-noise ratio.

[0048] 11) Hydrophone 41 Definition: It is an underwater acoustic-electric transducer. In this embodiment, a broadband piezoelectric hydrophone (such as BK8104) is selected.

[0049] Function: It acts as a receiver, responsible for sensing sound pressure fluctuations in water and converting the sound signal into a weak charge or voltage signal.

[0050] 12) Charge Amplifier 42 Definition: A preamplifier with high input impedance.

[0051] Function: To perform impedance matching and voltage amplification on the high-impedance weak signal output by hydrophone 41, thereby enhancing the signal strength for long-distance transmission and subsequent acquisition, while filtering out some low-frequency noise.

[0052] 13) High-speed oscilloscope 43 Definition: A data acquisition instrument with a high sampling rate (e.g., above 100 MS / s).

[0053] Function: Receives analog signals from a charge amplifier and converts them into digital signals (A / D conversion). It is typically triggered synchronously by an external trigger signal (from control card 12 or a photodetector) to ensure precise time alignment between the recorded acoustic signal and the laser emission time, which is crucial for achieving SAFT beamforming.

[0054] III) Work Process The detailed working process of the cross-medium virtual phased array communication system described in this invention is as follows: Step 1: Parameter Setting and System Initialization First, the user sets the scanning parameters of the virtual array (including the number of array elements $N$, the element spacing $d$, and the scanning path) and the modulation parameters of the communication signals (such as pulse repetition rate and encoding sequence) in the host computer 11. The host computer 11 then sends these instructions to the control card 12.

[0055] Step 2: Synchronous Triggering and Timing Control. Control card 12 generates two strictly synchronized control signals based on the received instructions: The first signal (after trigger delay) is sent to the MOPA laser 13 to trigger it to emit a single pulse laser; at the same time, the trigger signal is also sent to the high-speed oscilloscope 43 as a synchronization signal to serve as the "zero time" reference for signal acquisition.

[0056] The second signal is sent to the galvanometer driver 14 to control the dual-axis scanning galvanometer 23 to deflect the lens to the position coordinates of the first virtual array element; Step 3: Beam Deflection and Focusing. The high-energy pulsed laser emitted by the MOPA laser 13 is transmitted through an optical fiber and then converted into a parallel beam by the fiber collimator 22, which then enters the dual-axis scanning galvanometer 23. After two-dimensional rapid deflection by the dual-axis scanning galvanometer 23, the beam enters the flat-field scanning lens 24 and is focused and incident perpendicularly at a predetermined position at the water-air interface of the water tank 31.

[0057] Step 4: Photoacoustic Conversion and Shock Wave Generation. The focused pulsed laser energy is instantaneously absorbed by the photoacoustic conversion medium layer 32 (carbon-based ink layer) floating on the water surface. Due to the high peak power density of the MOPA laser 13, the photoacoustic conversion medium layer 32 locally experiences a rapid temperature rise and induces a vaporization mechanism, resulting in explosive evaporation and plasma expansion, thereby exciting high-intensity acoustic waves 33 in the water.

[0058] Step 5: Virtual Array Scanning (Spatiotemporal Conversion) The system repeats steps 2 to 4. Control card 12 sequentially controls the galvanometer to deflect to the next array element position and triggers laser emission. Through this "time-division scanning" method, sound sources are generated sequentially at different spatial locations on the water surface, thereby synthesizing an equivalent spatial virtual sound source array in the time series.

[0059] Step 6: Underwater Signal Reception and Acquisition. The generated sound wave 33 propagates in the water and reaches the hydrophone 41. The hydrophone converts the sound pressure signal into a weak electrical signal, which is then amplified and filtered by the charge amplifier 42 before being input to the high-speed oscilloscope 43. Under the control of the synchronous trigger signal, the oscilloscope 43 records the sound wave waveform data corresponding to the position of each virtual array element.

[0060] Step 7: SAFT Beamforming and Signal Reconstruction (Core Step) The high-speed oscilloscope 43 transmits the acquired multiple sets of time-domain waveform data back to the host computer 11. The host computer uses the Synthetic Aperture Focusing (SAFT) algorithm for post-processing: 1. Calculate the acoustic path difference from each virtual array element to the focal point based on the set underwater target focal position; 2. Apply appropriate delay compensation to the signals acquired from each channel; 3. Coherently superimpose the delayed signals.

[0061] Final result: After superposition processing, acoustic signals from different locations are enhanced in phase in the target direction, achieving directional focusing and gain amplification of the beam. At the same time, incoherent bubble noise is suppressed, thereby demodulating a communication signal with a high signal-to-noise ratio.

[0062] 2. Communication method This communication method employs a "time-division excitation-post-synthesis" approach to achieve virtual phased array communication. 1. Virtual array construction: Set the number of virtual array elements N=5, the element spacing d=6mm, and the host computer calculates the 5 deflection voltage coordinates corresponding to the galvanometer. 2. Time-division scanning acquisition: 1) Control the galvanometer to jump to the coordinates of the first array element and wait for the galvanometer to stabilize (approximately 0.5ms); 2) Control the MOPA laser to emit a single pulse (energy set to 100%, approximately 1 mJ). At this time, transient thermal expansion occurs on the surface of the ink layer, generating the first acoustic signal. 3) The acquisition card synchronously acquires the sound signal in external trigger mode (using the laser Sync signal) and records it as... ; 4) Repeat the above steps to traverse all 5 array element positions in turn to obtain the original signal group. ; 3. SAFT Beamforming: Assuming the target communication direction is... Speed ​​of sound in water Digital beamforming using MATLAB: 1) Calculate the relative delay of the nth array element. ; 2) Perform time-domain shifting and coherent superposition on the original signal: .

[0063] like Figure 2 The communication method is as follows: ①Start -201; ② Parameter initialization -202; ③ Determine whether it is less than or equal to 5-203; Then proceed to the following steps in sequence: ④ Control the deflection of the galvanometer, i.e., jump to the nth point -204; ⑤ Laser emission (1kHz, 200ns) -205; ⑥ Data acquisition (recording waveform S) n -206; Otherwise, proceed to the following steps in sequence: ⑦SAFT Beamforming-207; ⑧ Output directional signal -208; ⑨ End - 209.

[0064] III. Example 3: Parameter Optimization and Comparative Experiment To verify the effectiveness of the present invention, the inventors conducted a comparative experiment.

[0065] Control group: Laser directly irradiated pure water. Due to the low absorption coefficient of 1064nm laser in pure water (approximately 0.14 / cm), the photothermal interaction region is elongated cylindrical, and the energy density does not reach the photobreakdown threshold, so the hydrophone did not detect an effective acoustic signal; Experimental group (preferred embodiment of the invention): An ink medium layer was introduced, and the laser repetition rate was set to 1 kHz and the pulse width was set to 200 ns. At this time, the laser energy was compressed in the sub-millimeter region of the medium surface, generating a high signal-to-noise ratio N-shaped acoustic wave signal. The experiment shows that the low repetition rate setting effectively avoids the multipath reverberation interference generated by the continuous wave and ensures the accuracy of the zero point of time required by the SAFT algorithm.

[0066] It should be noted that the above description is not intended to limit the present invention, and the present invention is not limited to the examples described above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A cross-medium virtual phased array communication system based on a MOPA laser and scanning galvanometer, characterized in that: It includes a sequentially interacting transmission control subsystem (10), optical path scanning subsystem (20), photoacoustic conversion interface subsystem (30), and underwater receiving subsystem (40). A photoacoustic conversion medium layer (32) and a sound wave (33) are provided inside the water tank (31); Above the photoacoustic conversion medium layer (32), the host computer (11) and the control card (12) are connected one after the other. The signal then enters the laser (21) through the MOPA pulse laser (13) and the galvanometer driver (14). The laser (21), collimator (22), dual-axis scanning galvanometer (23) and flat-field scanning lens (24) are connected in sequence. Below the photoacoustic conversion medium layer (32), the sound wave (33), the hydrophone (41), the charge amplifier (42), and the high-speed oscilloscope (43) interact in sequence; The high-speed oscilloscope (43) is then connected to the host computer (11).

2. The cross-medium virtual phased array communication system according to claim 1, characterized in that: 1) Host computer (11): It is the core control and data processing terminal of the entire system. It is a high-performance computer with professional measurement and control software installed. 2) Control card (12): It is the intermediate interface unit connecting the host computer (11) and the hardware device, namely the multi-functional data acquisition card or FPGA board. 3) MOPA pulsed laser (13): a fiber laser employing a master oscillation power amplification architecture; 4) Galvanometer driver (14): This is a power amplifier electronic module used to drive the scanning galvanometer motor; 5) Laser (21): The optical output head of the MOPA laser; 6) Collimator (22): An optical device installed at the output end of the optical fiber; 7) Dual-axis scanning galvanometer (23): A beam deflection device consisting of two mirrors on the X and Y axes and their driving motors; 8) Flat field scanning lens (24): A type of focusing lens whose image height is proportional to the scanning angle; 9) Water tank (31): A container for loading experimental water and underwater equipment; 10) Photoacoustic conversion medium layer (32): an enhanced absorption layer that floats or is coated at the water-air interface, using a carbon-based ink layer or similar strong light-absorbing material; 11) Hydrophone (41): It is an underwater acoustic-electric transducer; 12) Charge amplifier (42): A preamplifier with high input impedance; 13) High-speed oscilloscope (43): A data acquisition instrument with a high sampling rate.

3. The cross-medium virtual phased array communication method of the system according to claim 1 or 2, characterized in that: The MOPA laser is controlled to emit low-repetition-rate, high-energy pulses. A galvanometer is used to deflect the laser beam to different positions on the surface of the dielectric layer, thus constructing a time-division multiplexed virtual sound source array. The dielectric layer efficiently converts optical energy into point sound source signals. The receiver uses synthetic aperture focusing (SAFT) technology to perform time-series alignment and superposition of the sound signals. ① Parameter initialization: Set the number of array elements, the spacing between array elements, and the target beam pointing angle of the virtual array; ②Time-division excitation: The control unit drives the galvanometer to deflect to the coordinates of the Nth array element, and at the same time triggers the MOPA laser to emit a single pulse laser; after the laser hits the photoacoustic conversion interface, it generates the Nth omnidirectional acoustic pulse; ③ Array scanning: According to the preset timing sequence, the deflection angle of the galvanometer is changed sequentially to traverse the positions of all virtual array elements and complete one complete array excitation cycle; ④ Signal synthesis: The receiver collects the acoustic signals generated by each excitation, calculates the phase delay required for each array element based on the target beam pointing angle, and performs time-shifted superposition on the collected signals to form a directional beam signal with high gain.

4. The cross-medium virtual phased array communication method according to claim 3, characterized in that: ① Start (201); ② Parameter initialization -202; ③ Determine whether it is less than or equal to 5 (203) Then proceed to the following steps in sequence: ④ Control the deflection of the galvanometer, i.e. jump to the nth point (204); ⑤ Laser emission (1KHz, 200ns) (205); ⑥ Data acquisition (recording waveform S) n (206); Otherwise, proceed to the following steps in sequence: ⑦SAFT beamforming (207); ⑧ Output directional signal (208); ⑨ End (209).

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