Underwater wireless optical communication transmitter based on blue-green light phased array

Abstract

The invention discloses an underwater wireless optical communication transmitter based on a blue-green light phased array, and the transmitter comprises a narrow-linewidth seed laser source which is used for generating narrow-linewidth laser; the beam splitting device is used for splitting the narrow linewidth laser into a plurality of sub light beams; a blue-green laser diode array, each blue-green laser diode receives a path of sub-beam through an optical injection locking technology and outputs high-power narrow-linewidth blue-green laser, and the blue-green laser diode is based on a gallium nitride multi-quantum well structure; the phase control array corresponds to each blue-green laser diode and is used for adjusting the phase of each path of high-power narrow-linewidth blue-green laser; and the large-aperture transmitting antenna array is connected with the phase control array and is used for carrying out collimation processing on the laser beam after phase modulation and transmitting the laser beam to an underwater environment to form a large-aperture optical phased array. The device can significantly improve the power of emitted light beams, greatly improves the quality of the light beams, and improves the communication distance.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and in particular to an underwater wireless optical communication transmitter based on a blue-green phased array. Background Technology

[0002] In existing wireless communication methods, electromagnetic waves suffer severe attenuation in seawater; a 100MHz electromagnetic wave attenuates by 3.2 × 10⁵ dB / km in water, making it unsuitable for underwater communication. Compared to electromagnetic waves, sound attenuates much less in water; a 1kHz sound signal attenuates by approximately 0.1 dB / km. However, underwater acoustic communication suffers from very low bandwidth and high latency. For short-to-medium distance transmission scenarios below 100 meters, underwater wireless optical communication technology offers greater bandwidth and lower latency. Green light with a wavelength of 520nm attenuates by approximately 0.2 dB / m in seawater.

[0003] There are two main types of light sources currently used in underwater wireless optical communication: LEDs (light-emitting diodes) and laser diodes (LDs). LEDs have a larger divergence angle and shorter transmission distance, while LDs have a smaller divergence angle and longer transmission distance. Therefore, optical system design for communication systems using LDs as the light source has received increasing attention. The underwater environment contains abundant natural resources, and currently 95% of the underwater environment remains undeveloped. For example... Figure 1 As shown in the application scenarios, autonomous underwater vehicles (AUVs) and underwater sensor networks (UWSNs) are key equipment and infrastructure for underwater environment development. These underwater systems require a long-range, high-bandwidth wireless communication method for data transmission.

[0004] In recent years, the communication distance and communication rate of UWOC have made gratifying progress. However, based on the Monte Carlo simulation calculation prediction, the UWOC communication distance in clear seawater can theoretically reach 500 meters. In actual engineering applications, underwater acoustic communication usually provides more than one kilometer of communication, and laser communication is often used as a supplement to traditional underwater acoustic communication for short-distance high-speed communication. However, the longest laser communication can only provide underwater communication distance of hundreds of meters. It can be seen that 500 meters to kilometer-level communication is the blind area of underwater wireless communication, and it is an urgent need to expand the blue-green laser communication distance to more than 500 meters, which has extremely high research value for both theoretical exploration and engineering application. However, when the underwater transmission distance reaches 500 meters, the laser communication will inevitably be greatly affected by seawater absorption, scattering, and ocean turbulence. The high absorption and strong scattering of long-distance underwater transmission have posed a great challenge to traditional light sources, and there is currently no report of a light source that can achieve effective transmission of 500 meters underwater. Moreover, the refractive index fluctuation of seawater caused by turbulence causes random changes in the amplitude and phase of light, resulting in wavefront distortion and speckle flicker, which has a fatal impact on long-distance UWOC. SUMMARY

[0005] The purpose of the present application is to provide a blue-green light phased array based underwater wireless optical communication transmitter, which can significantly improve the power of the transmitted light beam, greatly improve the beam quality, and thus improve the communication distance.

[0006] To achieve the above-mentioned purpose, the present application provides the following scheme: A blue-green light phased array based underwater wireless optical communication transmitter, comprising: a narrow linewidth seed laser source for generating a narrow linewidth laser; a beam splitting device connected to the narrow linewidth seed laser source for splitting the narrow linewidth laser into multiple sub-beams; a blue-green laser diode array composed of multiple blue-green laser diodes connected in series and connected to the beam splitting device, each blue-green laser diode receiving a sub-beam through optical injection locking technology and outputting high-power narrow linewidth blue-green laser, wherein the blue-green laser diode is based on a gallium nitride multiple quantum well structure; a phase control array composed of multiple piezoelectric ring phase modulators corresponding to each blue-green laser diode for adjusting the phase of each high-power narrow linewidth blue-green laser; a large-aperture transmitting antenna array connected to the phase control array for collimating and transmitting the phase-modulated laser beam into the underwater environment to form a large-aperture optical phased array.

[0007] Preferably, the phase control array is also used to execute an active phase control algorithm to realize coherent synthesis of multiple laser beams to generate a high-power, high-brightness, and high-beam-quality light beam to counteract wavefront distortion and speckle flicker caused by underwater turbulence.

[0008] Preferably, the active phase control algorithm is based on scalar diffraction theory, and the light field complex amplitude distribution is controlled by mathematical modeling and simulation calculation, and the piston phase and tilt phase of the sub-beam are controlled to realize far-field coherent synthesis, and the formula is as follows:

[0009] wherein, (X, Y, Z n ) is the position coordinate of the nth light beam in the emission plane, (X, Y, Z t ) is the light field center coordinate of the nth light beam at the target, is the light intensity amplitude value, is the X coordinate of the nth sub-beam, is the Y coordinate of the nth sub-beam, is the spot waist radius, is the initial frequency, is a constant, is the phase of the nth sub-beam, is the phase plane curvature radius.

[0010] Preferably, the transmitter further comprises a driving modulation circuit for cascade driving and high-speed modulation of the blue-green laser diode array; the driving modulation circuit superimposes the direct current bias and the high-speed modulation signal through a bias circuit, and directly injects the series-connected blue-green laser diode array to reduce the influence of the RC response time constant on the bandwidth.

[0011] Preferably, the transmitter further comprises a circulator arranged in the optical path between the beam splitting device and the blue-green laser diode, the sub-beam enters the circulator from the first port, excites the blue-green laser diode through the second port, and the high-power narrow linewidth blue-green laser is output from the third port; for allowing unidirectional transmission of light, effectively preventing the light reflected from the blue-green laser diode from re-entering the high-power narrow linewidth blue-green laser.

[0012] Preferably, the blue-green laser diode is based on a gallium nitride multiple quantum well structure of a ridge waveguide, and the front and rear two end faces constitute a Fabry-Perot resonant cavity of the blue-green laser diode.

[0013] Preferably, the large-aperture transmitting antenna array is composed of a plurality of large-aperture collimators for collimating and transmitting the phase-modulated multi-channel high-power narrow linewidth blue-green laser beams to the underwater free space.

[0014] Preferably, the beam splitting device specifically adopts a fiber-coupled beam splitter or a planar waveguide beam splitter.

[0015] According to the specific embodiments provided by the present application, the following technical effects are disclosed. The application aims at the industry "pain point" problem that the divergence of Gaussian beams in the case of underwater long-distance transmission, the spot flicker caused by turbulence leads to the limited communication distance of traditional underwater wireless optical communication system and the system is easy to be interfered. The semiconductor laser injection locking technology is adopted to provide high-power narrow linewidth blue-green laser. The array arrangement based on narrow linewidth blue-green laser is used to realize large aperture and high power blue-green light phased array. The beam coherence synthesis technology is used to improve the spot quality of the outgoing beam. Then, based on the mechanism of fiber laser phased array, the phased array active phase control method is adopted to provide high-power, high-brightness and high-beam quality "three high" underwater blue-green beam, realize long-distance underwater transmission, and resist the spot flicker caused by turbulence. Finally, the long-distance high-speed underwater wireless optical communication system based on large aperture and high power blue-green light phased array is verified by experiment. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0017] Figure 1 It is a schematic diagram of typical application scenario of the present application. Figure 2 It is a structure schematic diagram of underwater wireless optical communication transmitter based on blue-green light phased array of the present application. Figure 3 It is a schematic diagram of blue-green LD with gallium nitride multiple quantum well structure of the present application. Figure 4 It is a schematic diagram of high-power narrow linewidth blue-green laser system of the present application. Figure 5 It is a simulation result diagram of light intensity distribution of underwater coherent synthesis beam at different underwater transmission distances of the present application. Figure 6 It is a diagram of cascade driving and high-speed modulation mode of high-power blue-green LD array of the present application. Figure 7 It is an experimental system diagram of long-distance underwater wireless laser communication based on blue-green light phased array of the present application. Figure 8 It is a diagram of light attenuation in water. DETAILED DESCRIPTION

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] The underwater environment contains abundant natural resources, and currently 95% of the underwater environment remains undeveloped and unutilized. For example... Figure 1 The application scenarios shown depict autonomous underwater vehicles (AUVs) and underwater sensor networks (UWSNs) as key equipment and infrastructure for underwater environment development. These underwater systems require a long-range, high-bandwidth wireless communication method for data transmission. To meet these needs, this invention proposes a novel underwater wireless optical communication transmitter. It employs a large-aperture, high-power blue-green phased array and utilizes an active phase modulation algorithm based on a fiber laser phased array to achieve coherent beam combining over long distances, providing a high-power, high-brightness, and high-beam-quality underwater blue-green beam. This system boasts advantages such as compact structure, fewer required optical components, small system size, and low assembly precision, making it highly suitable for integration as a transmission system in underwater wireless optical communication networks.

[0021] like Figure 2 As shown, the present invention provides an underwater wireless optical communication transmitter based on a blue-green phased array, comprising: Narrow linewidth seed laser source, used to generate narrow linewidth laser; The beam splitting device is connected to a narrow linewidth seed laser source. Specifically, it uses an optical fiber coupled beam splitter or a planar waveguide beam splitter to split the narrow linewidth laser into multiple sub-beams. The blue-green laser diode array consists of multiple blue-green laser diodes connected in series and connected to a beam splitter. Each blue-green laser diode receives a sub-beam through optical injection locking technology and outputs high-power narrow-linewidth blue-green laser. The blue-green laser diodes are based on gallium nitride multi-quantum-well structures. The phase control array, consisting of multiple piezoelectric ring phase modulators, corresponds to each blue-green laser diode and is used to adjust the phase of each high-power narrow-linewidth blue-green laser. A large-aperture transmitting antenna array, connected to a phase control array, is used to collimate the phase-modulated laser beam and transmit it into the underwater environment, forming a large-aperture optical phased array.

[0022] Furthermore, the transmitter also includes a circulator, which is disposed in the optical path between the beam splitter and the blue-green laser diode. The sub-beam enters the circulator through the first port, excites the blue-green laser diode through the second port, and outputs high-power narrow-linewidth blue-green laser from the third port. This allows light to be transmitted in one direction and effectively prevents light reflected from the blue-green laser diode from re-entering the high-power narrow-linewidth blue-green laser.

[0023] Specifically, according to the Fresnel-Kirchhoff diffraction law, arrayed Gaussian beams exhibit coherent combining in the far field. Coherent combining techniques developed based on this theory have been theoretically verified and experimentally implemented in infrared wavelength phased arrays propagating through air, while also exhibiting resistance to air turbulence. Based on this method, similar phased arrays with arrayed blue-green beams can theoretically and practically be achieved in similar long-distance underwater transmission environments.

[0024] Large-aperture blue-green phased arrays are constructed based on fiber laser array technology, such as... Figure 2 As shown, a narrow-linewidth seed laser (100kHz) is split into multiple beams and injected into the blue-green LD resonant cavity, achieving injection locking of the semiconductor laser and outputting multiple high-power, narrow-linewidth lasers with equal phase. Each laser then passes through its own piezoelectric ring phase modulator (PZT-PC), and a phase control array achieves coherent beam combining or deflection. All lasers are then emitted into underwater free space via a large-aperture collimator, and the transmitting array forms a phased array large-aperture antenna array, enabling long-distance underwater transmission.

[0025] PZT-PC boasts advantages such as a high damage threshold and low cost, making it a potential candidate for application in large-scale phased array systems. Currently, the resonant frequency of PZT-PC has reached tens of kHz, meeting the requirements for combating underwater turbulence. The single-tube output power of high-power blue LEDs has exceeded 30W, and through coherent beam combining of multiple high-power blue LEDs, it is expected to output a high-brightness, high-beam-quality far-field spot exceeding 100W.

[0026] Among them, the device structure of blue-green semiconductor laser diodes (LDs) is designed based on gallium nitride multiple quantum wells (GaN MQW) with ridge waveguide structures, such as... Figure 3 As shown. The laser resonant cavity is 1.1 mm long, and the ridge waveguide is 0.8 mm high. Width 10 The front and rear end faces constitute the Fabry-Perot (FP) resonant cavity of the laser.

[0027] Next, this invention achieves narrow-linewidth, high-power blue-green laser output based on optical injection-locking technology. The narrow-linewidth laser (100kHz) is injected into the blue-green LD resonant cavity, achieving injection-locking of the high-power blue-green semiconductor laser and ensuring stable output of the high-power, narrow-linewidth laser. A schematic diagram of its working principle is shown below. Figure 4 As shown.

[0028] Furthermore, the phase control array is also used to execute active phase modulation algorithms to achieve coherent combining of multiple laser beams, thereby generating high-power, high-brightness, and high-beam-quality beams to counteract wavefront distortion and spot flicker caused by underwater turbulence.

[0029] The implementation plan is as follows: (a) Technical Approach: A combination of theoretical simulation analysis and experimental verification was adopted. Based on scalar diffraction theory and mathematical modeling in the underwater environment, the relationship between the complex amplitude distribution of the optical field and the propagation distance of a 450nm blue light array beam under coherent combining technology was simulated and analyzed using Matlab software. Simultaneously, experimental research was conducted, and a corresponding experimental platform was built to verify and optimize the theoretical analysis results.

[0030] (b) Technical Approach and Experimental Methods: Based on scalar diffraction theory, the optical field propagation model of the array beam under coherent combining technology is derived, and the influence of sub-beam phase manipulation on the far-field intensity distribution is analyzed. Based on the theoretical analysis results, suitable phase modulation devices, such as piezoelectric ceramic ring phase modulators and adaptive fiber collimators, are selected to build an experimental system for fiber laser phased arrays based on fiber combining technology. The system is designed to precisely control the piston phase and tilt phase of the sub-beams, achieving coherent combining in the far field.

[0031] (c) Key Technology: Taking the co-emission of seven beams as an example, the complex amplitude of the optical field at the target of the nth (n≤7) sub-beam can be expressed as: (1) Where (X, Y, Z) n Let (X, Y, Z) be the position coordinates of the nth beam on the emission plane. t Let be the coordinates of the center of the optical field of the nth beam at the target. This represents the amplitude of light intensity. Let X be the x-coordinate of the nth sub-beam. Let Y be the Y coordinate of the nth sub-beam. The radius of the beam waist is denoted as . The initial frequency, It is a constant. Let n be the phase of the nth sub-beam. Let be the radius of curvature of the phase surface.

[0032] At this time, Un (X, Y, Z t The expressions for each parameter in the formula are as follows: (2) (3) (4) in, f These are confocal parameters, ω(z) is the beam waist radius of the Gaussian beam at z, R(z) is the radius of curvature of the equiphase surface at z, and φ(z) is the additional phase difference. Therefore, the m-channel array beam at z t The complex amplitude of the light field at that point can be expressed as: (5) In the above formula, (X,Y,Z) (including Z) n and Z t Coordinates and Cartesian coordinate system (x, y, z) t The relationship between the coordinate systems is as follows:

[0033] (6)

[0034] in, and All are beam deflection angles. This mathematical coordinate system transformation is physically manifested as controlling the initial emission tilt phase of each sub-beam. Based on the above theoretical formulas (1)-(6), the composite beam image at different distances can be simulated and calculated using Matlab software. Assuming that seven blue beams with an output aperture of 10mm and a wavelength of 450nm are initially arranged in a hexagon (Z=0m), the coherent composite beam transformation generated when propagating underwater is as follows: Figure 5 As shown.

[0035] Furthermore, the transmitter also includes a drive modulation circuit for cascaded driving and high-speed modulation of the blue-green laser diode array; the drive modulation circuit superimposes the DC bias and the high-speed modulation signal through the bias circuit and directly injects them into the series-connected blue-green laser diode array to mitigate the impact of the RC response time constant on the bandwidth.

[0036] Considering the low material damage threshold and high cost of high-speed external modulators in the blue-green light band, high-power blue-green LDs employ direct modulation to achieve high-speed optical communication at a low cost. The applicant uses a method of cascading multiple LDs to drive the LD array, such as... Figure 6As shown, a direct current (DC) bias is applied to the cascaded LD array to ensure that each LD has the same drive 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 a high-power LD is much greater than the threshold current, and its internal resistance is very small and can be ignored. Simultaneously, in the case of LDs in series, the cascaded capacitance is consistent with that of a single LD. Therefore, by using a cascaded drive method, the RC response time constant of the high-power LD array is essentially 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.

[0037] Furthermore, the RF and DC values ​​are optimized to obtain the lowest bit error rate (BER), thereby enabling the high-power LD array to operate at its optimal state.

[0038] 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.

[0039] Experimental verification of long-distance high-speed underwater wireless optical communication system Experimental system apparatus such as Figure 7 As shown, this system is used to verify the performance of a long-distance, high-speed UWOC based on a blue-green phased array. The system includes a high-power light source, detectors, a large water tank, and other equipment and devices.

[0040] The specific implementation plan is as follows: i) Using a water tank and simulating turbulence in the tank, coherent synthesis of underwater beams was achieved through a large-aperture, high-power blue-green phased array, preliminarily verifying the underwater long-distance transmission performance (>500 meters) of high-power blue-green lasers based on coherent beam synthesis. ii) Quantitatively study the effects of turbulence intensity and turbulence frequency on long-distance underwater transmission, verify the ability of coherent synthesized beams to suppress these effects, and conduct comparative analysis; iii) By changing the size and output power of the phased array, the transmission performance under different underwater attenuation lengths was verified.

[0041] Light waves experience significant attenuation when propagating in water. Figure 8The curves represent the attenuation of light waves ranging from 400nm to 550nm in clear water (where light waves experience minimal attenuation). Underwater wireless optical communication uses semiconductor laser diodes with wavelengths between 450nm and 530nm as the system's light source.

[0042] This invention provides a novel underwater wireless blue-green optical communication transmitter with a fiber laser phased array design. Employing a novel blue-green optical phased array architecture, it achieves underwater wireless communication with a communication distance exceeding 500 meters and a communication rate of 1Gbps. This is the first application of a large-aperture, high-power blue-green optical phased array in the field of underwater wireless optical communication, which can significantly improve the transmitted beam power and greatly improve the beam quality, thereby increasing the communication distance.

[0043] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0044] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An underwater wireless optical communication transmitter based on a blue-green phased array, characterized in that, include: Narrow linewidth seed laser source, used to generate narrow linewidth laser; A beam splitter, connected to the narrow linewidth seed laser source, is used to split the narrow linewidth laser into multiple sub-beams. The blue-green laser diode array is composed of multiple blue-green laser diodes connected in series and connected to the beam splitter. Each blue-green laser diode receives a sub-beam through optical injection locking technology and outputs high-power narrow-linewidth blue-green laser. The phase control array, consisting of multiple piezoelectric ring phase modulators, corresponds to each of the blue-green laser diodes and is used to adjust the phase of each high-power narrow-linewidth blue-green laser. A large-aperture transmitting antenna array, connected to the phase control array, is used to collimate the phase-modulated laser beam and transmit it into the underwater environment, forming a large-aperture optical phased array.

2. The underwater wireless optical communication transmitter based on a blue-green phased array according to claim 1, characterized in that, The phase control array is also used to execute active phase modulation algorithms to achieve coherent combining of multiple laser beams, so as to generate high-power, high-brightness, and high-beam-quality beams to counteract wavefront distortion and spot flicker caused by underwater turbulence.

3. The underwater wireless optical communication transmitter based on a blue-green phased array according to claim 2, characterized in that, The active phase modulation algorithm is based on scalar diffraction theory. It controls the piston phase and tilt phase of the sub-beams through mathematical modeling and simulation calculation of the complex amplitude distribution of the optical field to achieve far-field coherent synthesis. The formula is as follows: in, (X, Y, Z n ) Let be the position coordinates of the nth beam on the emission plane. (X, Y, Z t ) Let be the coordinates of the center of the optical field of the nth beam at the target. This represents the amplitude of light intensity. Let X be the x-coordinate of the nth sub-beam. Let Y be the Y coordinate of the nth sub-beam. The radius of the beam waist is denoted as . The initial frequency, It is a constant. Let n be the phase of the nth sub-beam. Let be the radius of curvature of the phase surface.

4. The underwater wireless optical communication transmitter based on a blue-green phased array according to claim 1, characterized in that, The transmitter also includes a drive modulation circuit for cascading drive and high-speed modulation of the blue-green laser diode array; the drive modulation circuit superimposes the DC bias and the high-speed modulation signal through a bias circuit and directly injects them into the series-connected blue-green laser diode array to mitigate the influence of the RC response time constant on the bandwidth.

5. An underwater wireless optical communication transmitter based on a blue-green phased array according to claim 1, characterized in that, The transmitter further includes a circulator, which is disposed in the optical path between the beam splitter and the blue-green laser diode. The sub-beam enters the circulator through the first port, excites the blue-green laser diode through the second port, and outputs high-power narrow-linewidth blue-green laser from the third port. This allows light to be transmitted in one direction and prevents light reflected from the blue-green laser diode from re-entering the high-power narrow-linewidth blue-green laser.

6. The underwater wireless optical communication transmitter based on a blue-green phased array according to claim 1, characterized in that, The blue-green laser diode is based on a gallium nitride multi-quantum well structure with a ridge waveguide, and the front and rear end faces constitute the Fabry-Perot resonant cavity of the blue-green laser diode.

7. An underwater wireless optical communication transmitter based on a blue-green phased array according to claim 1, characterized in that, The large-aperture transmitting antenna array consists of multiple large-aperture collimators, which are used to collimate and transmit multiple high-power narrow-linewidth blue-green laser beams that have undergone phase modulation into underwater free space.

8. An underwater wireless optical communication transmitter based on a blue-green phased array according to claim 1, characterized in that, The beam splitting device specifically adopts an optical fiber coupled beam splitter or a planar waveguide beam splitter.

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