Underwater frontal light beam generation method and system based on blue-green light phased array regulation and control

Abstract

The invention discloses an underwater frontal light beam generation method and system based on blue-green light phased array regulation and control. The method comprises the following steps: S1, generating high-power narrow-linewidth blue-green laser; s2, constructing an optical fiber laser phased array based on the high-power narrow-linewidth blue-green laser; s3, determining the phase distribution of sub-beams required for generating the frontal light beam in the target underwater transmission distance according to the generation mechanism of the frontal light beam; s4, performing active phase regulation and control on each sub-beam in the optical fiber laser phased array according to the phase distribution; s5, coherent combination is carried out on the sub-beams after phase regulation and control through an emission aperture, a high-power beach beam is generated, and when the beach beam is transmitted underwater to the target transmission distance, a central light spot of the beach beam is kept unchanged or has a self-focusing characteristic; through active phase regulation and control and coherent combination based on the optical fiber laser phased array, a high-power frontal light beam with a central light spot kept unchanged or with a self-focusing characteristic is generated at an underwater target distance.

Description

A method and system for generating underwater sharp beams based on blue-green phased array control Technical Field

[0001] This invention relates to the field of underwater wireless optical communication technology, and more specifically to a method and system for generating underwater sharp beams based on blue-green phased array control. Background Technology

[0002] In existing wireless communication methods, electromagnetic waves attenuate severely in seawater; for example, a 100MHz electromagnetic wave attenuates by as much as 3.2 × 10⁻⁶ MHz in water. 5 The bandwidth of 520nm green light is only about 0.1dB / km, making it unsuitable for underwater communication. Although sound attenuates less in water (approximately 0.1dB / km for a 1kHz sound signal), underwater acoustic communication suffers from low bandwidth and high latency. In contrast, underwater wireless optical communication technology offers advantages in short-to-medium distance (below 100 meters) transmission scenarios due to its larger bandwidth and lower latency, especially since the attenuation of 520nm green light in seawater is only about 0.2dB / m.

[0003] Current underwater wireless optical communication primarily utilizes LEDs (light-emitting diodes) and LDs (laser diodes) as light sources. LEDs have a relatively large divergence angle, resulting in shorter transmission distances; while LDs have a smaller divergence angle, enabling longer transmission distances. Therefore, optical system design for communication systems using LDs as light sources has become a key research focus for improving underwater optical communication performance. However, light transmission underwater inevitably involves attenuation and scattering. Light attenuation directly shortens the effective transmission distance, while scattering causes the light spot to enlarge. An enlarged light spot means a decrease in laser energy density, which severely restricts communication performance. Therefore, optimizing the transmitting optical system to improve beam quality and collimation is crucial to ensuring sufficient power density during underwater transmission.

[0004] Traditional optical phased arrays are theoretically based on Fraunhofer or Fresnel diffraction of light beams, radiating Gaussian beams. The divergence angle of a Gaussian beam is inversely proportional to the aperture, thus limited by the underwater aperture. As transmission distance increases, the beam diverges significantly, making it impossible to maintain the same spot size over long distances. While non-diffractive beams can maintain a relatively constant central spot size during transmission and are more resistant to seawater scattering and ocean turbulence, the radiation power of beams generated by traditional methods is low due to material damage threshold limitations. This makes it difficult to effectively counteract seawater attenuation over long distances, failing to meet the demands of high-speed underwater communication. These factors collectively result in significant limitations in communication distance and anti-interference capabilities for traditional underwater wireless optical communication systems. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for generating underwater sharp beams based on blue-green phased array control. By actively controlling the phase and coherently combining the beams based on fiber laser phased arrays, a high-power sharp beam with a fixed center spot or self-focusing characteristics can be generated at the distance from the underwater target.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for generating an underwater sharp beam based on blue-green phased array control, comprising the following steps: S1, using a narrow-linewidth laser to optically inject and lock a blue-green semiconductor laser diode to generate a high-power narrow-linewidth blue-green laser; S2, splitting the high-power narrow-linewidth blue-green laser into multiple sub-beams, which are respectively coupled to the laser channels of a fiber laser phased array; wherein the fiber laser phased array includes multiple laser channels, each laser channel outputting a sub-beam; S3, determining the phase distribution of the sub-beams required to generate the sharp beam based on the sharp beam generation mechanism and the target underwater transmission distance; S4, performing active phase modulation on the sub-beams of the laser channels in the fiber laser phased array according to the phase distribution; S5, collimating the actively phase-modulated sub-beams and coherently combining them through the emission aperture to generate a high-power sharp beam; wherein the sharp beam, when transmitted underwater to the target transmission distance, has a central spot that remains unchanged or has self-focusing characteristics.

[0007] Furthermore, in S1, the process of acquiring high-power narrow-linewidth blue-green laser is as follows: the narrow-linewidth laser is injected into the resonant cavity of the blue-green semiconductor laser diode, and the blue-green semiconductor laser diode is optically injected and locked to output high-power narrow-linewidth blue-green laser.

[0008] Furthermore, in S1, the device structure of the blue-green semiconductor laser diode is a gallium nitride multiple quantum well with a ridge waveguide structure; wherein the resonant cavity of the blue-green semiconductor laser diode is 1.1 mm long, the ridge waveguide is 0.8 μm high and 10 μm wide.

[0009] Furthermore, in S1, the operation mode of the blue-green semiconductor laser diodes adopts cascaded driving and direct modulation. Specifically, multiple blue-green semiconductor laser diodes are connected in series to form a cascaded LD array; a high-speed modulation signal RF is superimposed on the DC bias DC through a bias circuit, and the DC bias DC is applied to the cascaded LD array. The resulting RF+DC signal is directly injected into the cascaded LD array to ensure that the driving current flowing through each LD is the same, thereby ensuring the uniformity and stability of the laser array output.

[0010] Furthermore, in S3, the expression for the sharp beam of light is specifically as follows:

[0011] in, The radial coordinates are represented by kρ, the radial wave vector, and the longitudinal wave vector by kz. It is a zeroth-order Bessel function. This indicates the scalar modulation term. It is the oscillation factor.

[0012] Furthermore, in S3, the phase distribution is an Airy spatial phase distribution.

[0013] In S5, the high-power sharp beam generation process is as follows: each sub-beam is actively phase-modulated and then coupled to the corresponding fiber in the fiber array; the fiber array is coupled to the microlens array, and the microlens collimates the corresponding sub-beam in the fiber array and outputs it through the emission aperture.

[0014] This invention also provides a system for generating underwater sharp beams based on blue-green phased array control, comprising: a laser source module for optically injecting and locking a blue-green semiconductor laser diode using a narrow-linewidth laser to generate a high-power narrow-linewidth blue-green laser; a beam splitting and coupling module for splitting the high-power narrow-linewidth blue-green laser into multiple sub-beams, which are respectively coupled to the laser channels of a fiber laser phased array; wherein the fiber laser phased array includes multiple laser channels, each laser channel outputting a sub-beam; an active phase control module for determining the phase distribution of the sub-beams required to generate the sharp beam based on the sharp beam generation mechanism and the target underwater transmission distance; and actively phase controlling the sub-beams of the laser channels in the fiber laser phased array according to the phase distribution; and an optical emission module for collimating the actively phase-controlled sub-beams and coherently combining them through an emission aperture to generate a high-power sharp beam; wherein the sharp beam maintains its central spot or has self-focusing characteristics when it is transmitted underwater to the target transmission distance.

[0015] According to specific embodiments provided by the present invention, the present invention has the following technical effects compared with the prior art: By constructing a fiber laser phased array and combining it with active phase modulation technology, the present invention effectively utilizes the low-loss window advantage of blue-green lasers in underwater transmission. While generating narrow-linewidth high-power lasers, it employs active phase modulation of a large-scale blue-green phased array to generate a high-power sharp beam, achieving underwater wireless communication with a communication distance exceeding 500 meters, a communication rate of 1Gbps, and a central spot energy more than 10 times higher than that of a Gaussian beam. This is the first application of a large-scale, high-power blue-green phased array in the field of underwater wireless optical communication. The generated high-power sharp beam retains its central spot unchanged after long-distance transmission, which can counteract the effects of high absorption, strong scattering, and ocean turbulence on the channel. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] The following description, in conjunction with the accompanying drawings, further illustrates the underwater sharp beam generation method and system based on blue-green phased array control of the present invention. Figure 1 is a flowchart illustrating the underwater sharp beam generation method based on blue-green phased array control in Embodiment 1 of the present invention. Figure 2 is a schematic diagram illustrating the generation of a diffraction-free beam using large-scale active phase modulation in Embodiment 1 of the present invention. Figure 3 is a schematic diagram illustrating the cascaded driving and high-speed modulation method of the high-power blue-green LD array in Embodiment 1 of the present invention. Figure 4 is a schematic diagram illustrating the gallium nitride multi-quantum-well structure blue-green LD in Embodiment 1 of the present invention. Figure 5 is a schematic diagram illustrating the high-power narrow-linewidth blue-green laser system in Embodiment 1 of the present invention. Figure 6 is a simulation using Matlab software in Embodiment 1 of the present invention. Figure 7 is a schematic diagram of the near-field sharp beam synthesized by a large-scale laser phased array and the blue light coherently synthesized Gaussian beam at 550 meters; (a) and (b) show the near-field lateral and longitudinal distributions of the sharp beam generated by a 256×256 sub-beam phased array, respectively; (c) and (d) show the lateral light field intensity distribution of the sharp beam at 550 meters and the longitudinal light field distribution propagating from 549 to 550 meters, respectively; Figure 8 is a schematic diagram of the underwater sharp beam generation system based on blue-green light phased array control in Embodiment 3 of the present invention; Figure 9 is a graph of the long-distance underwater wireless laser communication experimental system based on a high-power sharp beam in Embodiment 3 of the present invention; Figure 9 is a graph of light attenuation in water. Detailed Implementation

[0018] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0019] To better understand the purpose, structure, and function of this invention, the invention will be described in further detail below with reference to the accompanying drawings.

[0020] As shown in Figure 1, the present invention provides a method for generating underwater sharp beams based on blue-green phased array control, comprising the following steps: S1, using a narrow-linewidth laser to optically inject and lock a blue-green semiconductor laser diode to generate a high-power narrow-linewidth blue-green laser; in S1, the process of obtaining the high-power narrow-linewidth blue-green laser is as follows: injecting the narrow-linewidth laser into the resonant cavity of the blue-green semiconductor laser diode, and optically injecting and locking the blue-green semiconductor laser diode to output a high-power narrow-linewidth blue-green laser.

[0021] This embodiment specifically describes how to obtain high-power, narrow-linewidth blue-green laser output based on optical injection-locking technology. A narrow-linewidth laser (100kHz) is injected into the blue-green LD resonant cavity to achieve injection-locking of the high-power blue-green semiconductor laser, ensuring stable output of the high-power, narrow-linewidth laser. A schematic diagram of its working principle is shown in Figure 2.

[0022] In S1, the device structure of the blue-green semiconductor laser diode is a gallium nitride multiple quantum well with a ridge waveguide structure, as shown in Figure 4.

[0023] This embodiment specifically describes the design of a blue-green semiconductor laser diode (LD) device structure based on a gallium nitride multiple quantum well (GaN MQW) ridge waveguide structure, as shown in Figure 5. The laser resonant cavity is 1.1 mm long, and the ridge waveguide is 0.8 μm high and 10 μm wide. The front and rear end faces constitute the Fabry-Perot (FP) resonant cavity of the laser.

[0024] In step S1, the blue-green semiconductor laser diodes operate using cascaded driving and direct modulation. Specifically, multiple blue-green semiconductor laser diodes are connected in series to form a cascaded LD array. A high-speed modulation signal RF is superimposed on the DC bias through a bias circuit. The DC bias is applied to the cascaded LD array, and the resulting RF+DC signal is directly injected into the cascaded LD array to ensure that the driving current flowing through each LD is the same, thereby ensuring the uniformity and stability of the laser array output.

[0025] In this embodiment, considering the low material damage threshold and high cost of high-speed external modulators in the blue-green light band, the high-power blue-green LD adopts direct modulation to achieve high-speed optical communication at a low cost. Multiple LDs are connected in series to drive the LD array, as shown in Figure 3. A direct current (DC) bias is applied to the cascaded LD array to ensure that each LD has the same driving current. The high-speed modulation signal RF is superimposed on the DC bias through the bias circuit bias-T, and the generated RF+DC signal is directly injected into the cascaded LD array. Under normal lasing conditions, the operating current of the high-power LD is much greater than the threshold current, and the internal resistance is very small and can be ignored. Simultaneously, in the case of cascaded LDs, the cascaded capacitance is consistent with that of a single LD. Therefore, by using a cascaded driving method, the RC response time constant of the high-power LD array is basically the same as that of a single LD, which can minimize the adverse impact on bandwidth and is beneficial for achieving high-speed optical communication.

[0026] Optimize RF and DC values ​​to obtain the lowest bit error rate (BER), thereby enabling the high-power LD array to operate at its best.

[0027] Long-distance UWOCs require high-power light sources and highly sensitive detectors with limited bandwidth. The limited bandwidth of these devices restricts the overall bandwidth of the UWOC link, leading to inter-symbol interference (ISI) and severely impacting communication performance. Simultaneously, both high-power light sources and highly sensitive detectors face significant nonlinearity issues. To eliminate these problems from affecting the performance of long-distance UWOCs, linear and nonlinear equalization techniques are needed to improve communication performance, including linear equalization, nonlinear equalization, and artificial neural network (ANN) equalizers.

[0028] S2. The high-power narrow-linewidth blue-green laser is split into multiple sub-beams, which are then coupled to the laser channels of a fiber laser phased array. The fiber laser phased array includes multiple laser channels, each outputting a sub-beam. In S2, the step of constructing a fiber laser phased array based on the high-power narrow-linewidth blue-green laser includes: splitting the high-power narrow-linewidth blue-green laser into N sub-beams using a 1×N beam splitter; each sub-beam is actively phase-tuned and then coupled to the corresponding fiber of the transmitting antenna array; the transmitting antenna array is coupled to a microlens array, and the microlens collimates the corresponding sub-beam in the transmitting antenna array and outputs it through the transmitting aperture.

[0029] As shown in Figure 2, each narrow linewidth blue light beam is split into N sub-beams by a 1×N beam splitter. After large-scale active phase modulation, the beams are coupled out through an optical fiber array and a microlens array at the emission aperture.

[0030] S3. Based on the sharp beam generation mechanism and the underwater transmission distance of the target, determine the phase distribution of the sub-beams required to generate the sharp beam; the phase distribution is the spatial phase distribution of the Airy distribution.

[0031] The implementation scheme of this embodiment includes the following steps: (a) Technical method: A combination of numerical simulation and experimental verification is adopted. Based on the theoretical model of the sharp beam, a high-efficiency sharp beam is generated by active phase modulation based on large-scale fiber laser phased array technology. According to formula (1), the light field distribution of the sharp beam at different underwater distances is simulated using software such as Matlab, and the optimal parameter value β at the required transmission distance is calculated. At the same time, experimental research is carried out to generate a beam that meets the phase requirements at the required transmission distance using a large-scale fiber phased array, simulate the generation of the sharp beam and verify its underwater long-distance transmission performance.

[0032] (b) Technical Approach and Experimental Methods: An underwater wireless optical communication experimental platform was constructed, including a transmitter, an underwater transmission medium, and a receiver. At the transmitter, a large-scale fiber laser array, after passing through a beam expander and collimator system, underwent large-scale active phase modulation to form a spatial distribution of the Airy phase, generating a sharp beam. In the underwater transmission section, different transmission distances were set to study the transmission characteristics of the sharp beam at different propagation distances. At the receiver, the received light was focused onto a photodetector, and communication signal processing was performed at the back end to evaluate the performance of the sharp beam in underwater wireless optical communication, including key indicators such as bit error rate and signal-to-noise ratio.

[0033] (c) Key Technology: The sharp beam is obtained by adding a spatial phase modulation transformation of the Gaussian beam with an Airy distribution. The interference of the radially Airy beams, which are symmetrical in each direction, eliminates the transverse wave vector, thereby enabling stable beam transmission and self-focusing at a certain distance. The typical mathematical expression of the sharp beam is:

[0034] Where ρ represents the radial coordinate, k ρ It is the radial wave vector, k z It is the longitudinal wave vector; It is a zeroth-order Bessel function. This represents the sharpness modulation term; in this term, the key parameter is the β oscillation factor, which determines the focal point position for the sharpness beam to self-focus. Figure 6 shows the optical field distribution of the near-field sharpness beam synthesized by a large-scale laser phased array using Matlab software simulation, the blue light coherently synthesized Gaussian beam at 550 meters (Figure 6), and the horizontal and vertical propagation of the sharpness beam at 550 meters.

[0035] This embodiment specifically addresses the following: In underwater wireless optical communication, the divergence of Gaussian beams is a key bottleneck problem for long-distance transmission, as ideal beam patterns cannot be obtained at propagation distances ranging from 500 meters to one kilometer. Generating diffraction-free narrow beams for long-distance propagation using sharp beams provides a new approach to solving this problem. This embodiment proposes a large-scale fiber laser phased array to generate diffraction-free beams, such as Bessel beams, sharp beams, Airy beams, and vortex beams, through large-scale active phase modulation. A comparative analysis of the transmission characteristics of Gaussian, Bessel, Airy, and sharp beams is conducted, with a focus on analyzing the change in the central beam pattern of sharp beams after passing through ocean turbulence. The embodiment elucidates a method for generating high-power sharp beams based on an active phase modulation algorithm using a large-scale fiber laser phased array, improving transmission efficiency and achieving stable long-distance underwater transmission.

[0036] S4. Actively phase-modulate the sub-beams of the laser channel in the fiber laser phased array according to the phase distribution; S5. After collimating the actively phase-modulated sub-beams, coherently combine them through the emission aperture to generate a high-power sharp beam; wherein the sharp beam, when transmitted underwater to the target transmission distance, has its central spot unchanged or has self-focusing characteristics.

[0037] In S5, the high-power sharp beam generation process is as follows: each sub-beam is actively phase-modulated and then coupled to the corresponding fiber in the fiber array; the fiber array is coupled to the microlens array, and the microlens collimates the corresponding sub-beam in the fiber array and outputs it through the emission aperture.

[0038] The core points of this embodiment are: 1) High-power narrow-linewidth blue-green laser generation technology based on optical injection locking technology; 2) Large-scale, high-power blue-green optical phased array architecture based on narrow-linewidth blue-green laser; 3) High-power underwater sharp beam generation technology based on large-scale blue-green optical phased array; 4) Method to generate sharp beam by active phase modulation of large-scale phased array, suppressing wavefront distortion and spot flicker caused by underwater turbulence; 5) Long-distance high-speed underwater wireless optical communication method based on large-scale, high-power sharp beam.

[0039] In summary, this embodiment addresses the industry pain point of "Gaussian beam divergence and turbulence-induced beam flickering in long-distance underwater transmission, which limits the communication distance and makes traditional underwater wireless optical communication systems susceptible to interference." It employs semiconductor laser injection-locking technology to obtain high-power, narrow-linewidth blue-green lasers. Based on the array arrangement of these narrow-linewidth blue-green lasers, a large-aperture, high-power blue-green phased array is realized. According to the sharp beam generation mechanism, a large-scale phased array active phase modulation method is used to generate a high-efficiency sharp beam, enabling long-distance underwater transmission and counteracting beam flickering caused by turbulence. Finally, experiments verify the long-distance, high-speed underwater wireless optical communication system based on a large-scale, high-power blue-green phased array.

[0040] Example 2: This invention also provides a simulation process for the underwater sharp beam generation method based on blue-green phased array control in Example 1: Figures 6(a) and 6(b) show the simulation results of generating a sharp beam in the near field using 256×256 Gaussian beams with a sub-aperture of 0.3 mm. The simulation shows the lateral distribution of the sharp beam at the minimum beam position z=60 mm in the near field and the light field propagation distribution at 0-0.2 m. It can be seen that a sharp beam can be synthesized in the near field by directly controlling the phase of the initial sub-beams. When the phase is set reasonably, the sharp beam can be formed at a position of 550 m, as shown in Figures 6(c) and 6(d). It can be seen that the sharp beam has a better focusing effect than the Gaussian beam in the case of long-distance propagation. When the oscillation factor in the initial sharp beam phase modulation is reasonable, the diameter of the main beam is only 1% of that of the Gaussian beam at a propagation distance of 550 meters. For a detector with a receiving aperture of 1 mm, the incident light power is increased by more than 20 times. This means that it has unparalleled advantages in improving the signal-to-noise ratio and reducing the bit error rate of underwater wireless communication.

[0041] Light waves experience significant attenuation when propagating in water. As shown in Figure 9, the marked curves represent the attenuation of light waves with wavelengths from 400nm to 550nm in clear water (where attenuation is minimal). Underwater wireless optical communication uses semiconductor laser diodes with wavelengths between 450nm and 530nm as the system's light source.

[0042] As shown in Figure 7, Example 3 of the present invention also provides a system for generating underwater sharp beams based on blue-green phased array control, comprising: a laser source module for optically injecting and locking a blue-green semiconductor laser diode using a narrow-linewidth laser to generate a high-power narrow-linewidth blue-green laser; a beam splitting and coupling module for splitting the high-power narrow-linewidth blue-green laser into multiple sub-beams, which are respectively coupled to the laser channels of a fiber laser phased array; wherein the fiber laser phased array includes multiple laser channels, each laser channel outputting a sub-beam; an active phase control module for determining the phase distribution of the sub-beams required to generate the sharp beam based on the sharp beam generation mechanism and the target underwater transmission distance; and actively phase controlling the sub-beams of the laser channels in the fiber laser phased array according to the phase distribution; and an optical emission module for collimating the actively phase-controlled sub-beams and coherently combining them through an emission aperture to generate a high-power sharp beam; wherein the sharp beam maintains its central spot or has self-focusing characteristics when it is transmitted underwater to the target transmission distance.

[0043] As shown in Figure 8, this embodiment also provides an experimental system for verifying a long-distance high-speed UWOC based on a blue-green phased array. The system includes a high-power light source, a detector, a large water tank, and other equipment and devices.

[0044] The specific implementation plan is as follows: 1) Use a water tank and simulate turbulence in the water tank. Generate a sharp beam using the active phase modulation algorithm of a large-scale phased array and verify the underwater long-distance transmission performance of the sharp beam (>500m); 2) Quantitatively study the influence of turbulence intensity and turbulence frequency on underwater long-distance transmission, verify the ability of the sharp beam to suppress these influences, and conduct comparative analysis; 3) Change the size and output power of the phased array and verify the transmission performance under different underwater attenuation lengths.

[0045] The above description of the disclosed embodiments enables those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for generating underwater sharp beams based on blue-green phased array control, characterized in that, Includes the following steps: S1. Optically inject and lock a blue-green semiconductor laser diode using a narrow-linewidth laser to generate a high-power narrow-linewidth blue-green laser; S2. Split the high-power narrow-linewidth blue-green laser into multiple sub-beams, which are then coupled to the laser channels of a fiber laser phased array respectively. The fiber laser phased array includes multiple laser channels, each outputting a sub-beam; S3, based on the sharp beam generation mechanism and the target underwater transmission distance, the phase distribution of the sub-beams required to generate the sharp beam is determined; S4, the sub-beams of the laser channels in the fiber laser phased array are actively phase-controlled according to the phase distribution; S5, after the actively phase-controlled sub-beams are collimated, they are coherently combined through the emission aperture to generate a high-power sharp beam; wherein the sharp beam, when transmitted underwater to the target transmission distance, has its central spot remaining unchanged or possessing self-focusing characteristics.

2. The underwater sharp beam generation method based on blue-green phased array control according to claim 1, characterized in that, In S1, the process of acquiring high-power narrow-linewidth blue-green laser is as follows: the narrow-linewidth laser is injected into the resonant cavity of the blue-green semiconductor laser diode, and the blue-green semiconductor laser diode is optically injected and locked to output high-power narrow-linewidth blue-green laser.

3. The underwater sharp beam generation method based on blue-green phased array control according to claim 1, characterized in that, In S1, the device structure of the blue-green semiconductor laser diode is a gallium nitride multiple quantum well with a ridge waveguide structure; wherein the resonant cavity of the blue-green semiconductor laser diode is 1.1 mm long, the ridge waveguide is 0.8 μm high and 10 μm wide.

4. The underwater sharp beam generation method based on blue-green phased array control according to claim 1, characterized in that, In step S1, the blue-green semiconductor laser diodes operate using cascaded driving and direct modulation. Specifically, multiple blue-green semiconductor laser diodes are connected in series to form a cascaded LD array. A high-speed modulation signal RF is superimposed on the DC bias through a bias circuit. The DC bias is applied to the cascaded LD array, and the resulting RF+DC signal is directly injected into the cascaded LD array to ensure that the driving current flowing through each LD is the same, thereby ensuring the uniformity and stability of the laser array output.

5. The underwater sharp beam generation method based on blue-green phased array control according to claim 1, characterized in that, In S3, the expression for the sharp beam of light is specifically as follows: Where ρ represents the radial coordinate, kρ is the radial wave vector, and kz is the longitudinal wave vector; It is a zeroth-order Bessel function. This indicates the scalar modulation term. It is the oscillation factor.

6. The underwater sharp beam generation method based on blue-green phased array control according to claim 1, characterized in that, In S3, the phase distribution is a spatial phase distribution of Airy distribution.

7. The underwater sharp beam generation method based on blue-green phased array control according to claim 1, characterized in that, In S5, the high-power sharp beam generation process is as follows: each sub-beam is actively phase-modulated and then coupled to the corresponding fiber in the fiber array; the fiber array is coupled to the microlens array, and the microlens collimates the corresponding sub-beam in the fiber array and outputs it through the emission aperture.

8. An underwater sharp beam generation system based on blue-green light phased array control, used to implement the underwater sharp beam generation method based on blue-green light phased array control as described in any one of claims 1-7, characterized in that, include: The laser source module is used to optically inject and lock a blue-green semiconductor laser diode using a narrow-linewidth laser to generate a high-power narrow-linewidth blue-green laser; the beam splitting and coupling module is used to split the high-power narrow-linewidth blue-green laser into multiple sub-beams, which are then coupled to the laser channels of the fiber laser phased array respectively. The fiber laser phased array mentioned above includes multiple laser channels, each of which outputs a sub-beam; An active phase modulation module is used to determine the phase distribution of the sub-beams required to generate the sharp beam based on the sharp beam generation mechanism and the target underwater transmission distance; and to actively phase-modulate the sub-beams of the laser channel in the fiber laser phased array according to the phase distribution; an optical emission module collimates the actively phase-modulated sub-beams and coherently combines them through an emission aperture to generate a high-power sharp beam; wherein the sharp beam maintains its central spot or has self-focusing characteristics when it is transmitted underwater to the target transmission distance.

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