Non-diffraction laser communication terminal based on Bessel beam

Abstract

The invention discloses a non-diffraction laser communication terminal based on Bessel beams. The terminal comprises a beacon transmitting module, an optical antenna module, a beacon receiving module, a signal transmitting module, a signal receiving module and a light splitting module. The beacon transmitting module and the signal transmitting module respectively convert the Gaussian beam into a Bessel beam through an axicon, and the Bessel beam is output through a collimating lens; a primary mirror and a secondary mirror of the optical antenna module are mounted in an off-axis manner, so that light beams are shrunk and expanded; the light splitting module completes light path switching and light splitting through a fast reflecting mirror, a 1 / 4 wave plate, a dichroscope and a polarizing beam splitter; the beacon receiving module obtains beacon light position information through a CMOS detector, and the signal receiving module receives signal light through an APD detector. The non-diffraction characteristic of the Bessel beam is utilized, and the off-axis optical antenna and the polarization beam splitting design are combined, so that high-precision and low-loss laser communication is realized.

Description

Technical Field

[0001] The present invention relates to the field of laser communication technology, and in particular to a diffraction-free laser communication terminal based on Bessel beams. Background Art

[0002] Laser communication uses laser beams as information carriers to transmit data across free space (e.g., in the atmosphere, in space, or underwater). Compared to traditional radio communications (e.g., microwave and millimeter-wave), laser communication offers advantages such as ultra-high bandwidth, low latency, strong anti-interference capabilities, and high security. It is widely used in satellite communications, military secure communications, drone links, deep space exploration, and other fields. However, in these fields, the diffraction effect of the beam has been one of the main factors limiting communication distance and stability.

[0003] In the field of laser communications, traditional Gaussian beams undergo diffraction and diffusion during free-space transmission, causing the light spot to expand with distance, reducing the optical power density at the receiving end and affecting communication distance and signal quality. Furthermore, the energy of a Gaussian beam is mostly concentrated in the center, requiring extremely high alignment precision at both the transmitter and receiver. Slight offsets can lead to significant signal attenuation, increasing the difficulty of system adjustment. Furthermore, disturbances in complex environments such as atmospheric turbulence and scattering can distort the wavefront of the Gaussian beam, causing light intensity flicker and phase distortion, reducing communication stability. Summary of the Invention

[0004] In view of this, an embodiment of the present invention provides a diffraction-free laser communication terminal based on Bessel beam to solve the above technical problems.

[0005] To achieve the above object, a diffraction-free laser communication terminal based on Bessel beam is provided, which includes a beacon transmitting module, an optical antenna module, a beacon receiving module, a signal transmitting module, a signal receiving module and a spectrometer module; The beacon transmitting module includes a beacon transmitting laser, a first collimating beam expander, a first axicon, and a first collimating lens. The beacon transmitting laser transmits a laser signal, which is then expanded by the first collimating beam expander and then enters the first axicon. The first axicon generates a Bessel beam, which is then emitted into free space through the first collimating lens. The optical antenna module includes a primary mirror and a secondary mirror, wherein the optical axes of the primary mirror and the secondary mirror are parallel and installed off-axis, and the magnification of the optical antenna module is used to shrink the received external light or collimate and expand the internal outgoing light; The beacon receiving module includes a first narrowband filter, a first beamforming mirror, and a CMOS detector. After the beacon light is received by the optical antenna module, it is reflected by the primary mirror to the secondary mirror, and then reflected to the fast reflector in the spectrometer module. After being transmitted through the quarter-wave plate in the spectrometer module and reflected by the dichroic mirror, it enters the beacon receiving module, is filtered by the first narrowband filter, and is focused by the first beamforming mirror to the CMOS detector. The CMOS detector images and analyzes the light spot to obtain position information. The signal transmission module includes a signal transmission laser, a second collimating beam expander, a second axicon, and a second collimating lens. The signal transmission laser transmits a laser signal, which is expanded by the second collimating beam expander and then enters the second axicon. The second axicon generates a Bessel beam, which is then collimated by the second collimating lens and then transmitted to the polarization beam splitter in the light splitting module. After being reflected by the polarization beam splitter, the dichroic mirror, and the quarter-wave plate, the laser signal is reflected by the fast reflector and enters the optical antenna module. After being collimated and expanded by the optical antenna module, the laser signal is emitted into free space. The signal receiving module includes a second narrowband filter, a second condenser mirror, and an APD detector. After the signal light is received by the optical antenna module, it is reflected by the primary mirror to the secondary mirror, and then reflected to the fast reflection mirror. After passing through the 1 / 4 wave plate, the dichroic mirror, and the polarization beam splitter, it enters the signal receiving module, is filtered by the second narrowband filter, and the second condenser mirror focuses the light spot to the APD detector, which receives the signal light. The light splitting module includes the fast reflection mirror, the quarter wave plate, the dichroic mirror and the polarization beam splitter.

[0006] In some possible implementations, the first collimating beam expander and the second collimating beam expander both adopt a double-piece lens structure and are respectively located behind the beacon emitting laser and the signal emitting laser, and are used to convert the lasers emitted by the corresponding lasers into parallel Gaussian beams.

[0007] In some possible implementations, both the first axicon and the second axicon are made of fused quartz, and the cone angle is used to convert an incident parallel Gaussian beam into a Bessel beam.

[0008] In some possible implementations, both the first collimating lens and the second collimating lens are aspherical lenses; For the first collimating lens, its optimal installation position is determined by the formula Determine, where L is the distance from the vertex of the first axicon to the front focus of the first collimating lens, f is the effective focal length of the first collimating lens, D is the diameter of the Gaussian beam incident on the first axicon, n is the refractive index of the material of the first axicon, and α is the cone angle of the first axicon; For the second collimating lens, its optimal installation position is determined by the formula Determine, where L is the distance from the vertex of the second axicon to the front focus of the second collimating lens, f is the effective focal length of the second collimating lens, D is the diameter of the Gaussian beam incident on the second axicon, n is the refractive index of the material of the second axicon, and α is the cone angle of the second axicon.

[0009] In some possible implementations, the primary mirror is a concave parabola, the secondary mirror is a convex parabola, and both the primary mirror and the secondary mirror are designed with polarization-maintaining coatings and have the ability to maintain circular polarization.

[0010] In some possible implementations, the beacon transmitting laser emits a laser signal with a wavelength of 808 nm, the signal transmitting laser emits a laser signal with a wavelength of 1540 nm, and the signal receiving module receives signal light with a wavelength of 1563 nm.

[0011] In some possible implementations, the magnification of the optical antenna module is 8 times, and the operating wavelengths of the primary mirror and the secondary mirror cover 808-1563 nm.

[0012] In some possible embodiments, the first narrowband filter of the beacon receiving module has a central wavelength of 808 nm and a bandwidth of ±2 nm, and is located between the dichroic mirror and the first beam-forming mirror; the second narrowband filter of the signal receiving module has a central wavelength of 1563 nm and a bandwidth of ±2 nm, and is located between the polarization beam splitter and the second beam-forming mirror.

[0013] In some possible embodiments, the cone angle of the first axicon and the second axicon is 2°, the first collimating lens and the second collimating lens are aspheric lenses with a focal length of 400 mm, the diameter of the Gaussian light beam incident on the first axicon and the second axicon is 10 mm, and the optimized distances from the vertices of the first axicon and the second axicon to the front focal points of the first collimating lens and the second collimating lens, respectively, are 89.5 mm.

[0014] In some possible embodiments, the fast reflector is installed at an angle of 45° behind the secondary mirror, and achieves sub-milliradian beam control through micro-angle deflection; the 1 / 4 wave plate is located between the fast reflector and the dichroic mirror, and is used to convert linearly polarized light into circularly polarized light or convert circularly polarized light into circularly polarized light; the dichroic mirror is installed at an angle of 45°, reflects 808nm wavelength, and transmits 1540nm and 1563nm wavelengths; the polarization beam splitter is installed at an angle of 45°, reflects S-polarized light, transmits P-polarized light, and is coaxial with the 1 / 4 wave plate and the dichroic mirror.

[0015] In some possible embodiments, the method of generating the Bessel beam can also be replaced by a structure of an annular slit combined with a Fourier lens in the physical optics method, where the annular slit is located between the beacon transmitting laser or the signal transmitting laser and the Fourier lens, and the incident light is amplitude modulated by the annular slit, and then the modulated light is phase transformed by the Fourier lens to generate a Bessel beam.

[0016] In some possible embodiments, the Bessel beam generation method can also be replaced by metasurface technology, where the metasurface is a nanostructure array located on the outgoing light path of the beacon emitting laser or the signal emitting laser. The wavefront phase of the incident light is directly modulated by the nanostructure array to generate a Bessel beam, and the working bandwidth of the metasurface satisfies the wavelength range of 808-1563nm.

[0017] In some possible implementations, the Bessel beam generation method can also be replaced by computational holography, dynamically generated using a spatial light modulator (SLM). The SLM is located in the outgoing optical path of the beacon transmitting laser or the signal transmitting laser. A hologram of the Bessel beam is first calculated and loaded into the SLM, which then modulates the incident light to generate the Bessel beam, supporting the real-time generation of Bessel beams of any order. The phase hologram of the Bessel beam can be generated by superimposing the tilt phase and the axicon phase. The specific operation can be implemented using Python code, and any order Bessel beam can be generated.

[0018] In some possible implementations, the Bessel beam can also be generated by using a digital micromirror device (DMD). The DMD is located on the outgoing light path of the beacon transmitting laser or the signal transmitting laser, and the incident light is amplitude modulated by the micromirror array of the DMD to generate a Bessel beam.

[0019] In some possible embodiments, the collimation method of the Bessel beam can also be replaced by a dual-axis pyramid system, which includes two axis pyramids with the same cone angle, which are placed relatively between the beacon emitting laser or the signal emitting laser and the first collimating lens or the second collimating lens, and the collimation of the output Bessel beam is dynamically controlled by adjusting the spacing between the two axis pyramids.

[0020] The above technical solution has the following beneficial technical effects: This invention proposes a non-diffraction laser communication terminal based on Bessel beams. This terminal utilizes the non-diffraction properties of Bessel beams to significantly improve transmission distance, signal stability, and anti-interference capabilities. On the one hand, anti-interference capabilities are significantly enhanced. The non-diffraction property of Bessel beams means that they can maintain their shape and intensity over long distances and do not diffuse rapidly like Gaussian beams, thereby improving communication transmission distance and signal stability. Furthermore, Bessel beams exhibit excellent self-healing capabilities. Even if obstructed or scattered during transmission, the beams can repair themselves through their own structure, ensuring signal continuity. This is particularly important in complex environments or under atmospheric interference. On the other hand, transmission performance is significantly improved. Bessel beams possess the ability to perform multimode superposition, allowing multiple Bessel beam modes to be generated simultaneously within a single transmission channel, each carrying a different data stream, thereby achieving spatial multimode multiplexing. This multimode superposition technology significantly increases the capacity of laser communication systems because each mode can function as an independent channel for information transmission. Compared to traditional single-mode Gaussian beams, multimode Bessel beams can significantly increase data rates and bandwidth utilization without adding additional hardware complexity, meeting the needs of future high-speed, high-capacity communications. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings are provided for a better understanding of the present invention and are not intended to limit the present invention. Figure 1 The present invention is a structural diagram of a non-diffraction laser communication terminal based on Bessel beams according to an embodiment of the present invention.

[0022] Description of Figure Numbers: 001, beacon transmitting laser; 002, first collimating beam expander; 003, first axicon; 004, first collimating lens; 005, primary mirror; 006, secondary mirror; 007, first narrow-band filter; 008, first focusing mirror; 009, CMOS detector; 010, dichroic mirror; 011, 1 / 4 wave plate; 012, fast reflector; 013, signal transmitting laser; 014, second collimating beam expander; 015, second axicon; 016, second collimating lens; 017, polarization beam splitter; 018, second narrow-band filter; 019, second focusing mirror; 020, APD detector. DETAILED DESCRIPTION

[0023] The following description of exemplary embodiments of the present invention is made in conjunction with the accompanying drawings, in which various details of the embodiments of the present invention are included to facilitate understanding. These details should be considered as merely exemplary. Therefore, it should be appreciated by those skilled in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for the sake of clarity and conciseness, descriptions of well-known functions and structures are omitted in the following description.

[0024] An embodiment of the present invention proposes a non-diffraction laser communication terminal based on Bessel beams. By using a collimating beam expansion system to convert the laser into a parallel Gaussian beam, and then injecting the Gaussian beam into the axicon, after precise optical transformation, the generation and transmission of the Bessel beam are realized. Replacing the Gaussian beam with a Bessel beam has obvious advantages in laser communication. The non-diffraction characteristics of the Bessel beam can only expand the light spot by 3%-5% in kilometer-level transmission, while the Gaussian beam will spread by more than 300%, greatly improving the quality of long-distance communication. In addition, the Bessel beam has a stronger ability to resist atmospheric turbulence than the Gaussian beam, which provides a practical solution to the communication stability problems faced in complex environments such as satellite-to-ground links.

[0025] Based on the diffraction problem of the light beam during laser communication, the embodiment of the present invention proposes a non-diffraction laser communication terminal based on Bessel beam, see Figure 1 The communication terminal includes a beacon transmitting module, an optical antenna module, a beacon receiving module, a signal transmitting module, a signal receiving module and a light splitting module.

[0026] The beacon transmitter module includes a beacon transmitter laser 001, a first collimating beam expander 002, a first axicon 003, and a first collimating lens 004. The beacon transmitter laser 001 emits a laser signal with a wavelength of 808nm. After being expanded by the first collimating beam expander 002, the laser signal enters the first axicon 003. Due to the unique conical shape of the first axicon 003, a Bessel beam can be generated. The beam is then emitted into free space through the first collimating lens 004. The optical antenna module consists of a primary mirror 005 and a secondary mirror 006. It has an 8x magnification and can both narrow incoming external light and collimate and expand internally emitted light. To account for manufacturing errors, the magnification tolerance of the optical antenna module is ±2%, meaning the actual magnification ranges from 7.84x to 8.16x.

[0027] The beacon receiving module includes an 808nm first narrowband filter 007, a first focusing lens 008, and a CMOS (Complementary Metal-Oxide-Semiconductor) detector 009. Beacon light is received by the optical antenna module and first reflected by the primary mirror 005 to the secondary mirror 006. From there, it is reflected to the fast mirror 012. After being reflected by the fast mirror 012, it passes through the quarter-wave plate 011 and is reflected by the dichroic mirror 010 before entering the beacon receiving module. Stray light is first filtered out by the 808nm first narrowband filter 007. The first focusing lens 008 then focuses the light spot onto the CMOS detector 009, which analyzes the light spot and calculates its centroid to obtain its position information, which is the two-dimensional spatial coordinate of the light spot on the detector image plane. The quarter-wave plate can convert linearly polarized light to circularly polarized light, and vice versa. At the transmitter, circularly polarized light is emitted, reducing polarization degradation caused by atmospheric scattering. At the receiver, linearly polarized light is restored for demodulation by a polarization-sensitive detector. The "fast" in fast reflector 012 refers to its high-frequency dynamic response capability and ability to quickly and precisely adjust the optical path. The essence of "fast" is millisecond-level response and kHz-level bandwidth, far faster than traditional mechanical adjustment (in seconds).

[0028] The signal transmission module includes a signal transmission laser 013, a second collimating beam expander 014, a second axicon 015, and a second collimating lens 016. The signal transmission laser 013 emits a laser signal with a wavelength of 1540nm. After being expanded by the second collimating beam expander 014, it enters the second axicon 015. The second axicon 015 can generate a Bessel beam. The second collimating lens 016 then collimates the light and transmits it to the polarization beam splitter 017. The light beam is reflected by the polarization beam splitter 017, passes through the dichroic mirror 010 and the quarter-wave plate 011, and is reflected by the fast reflector 012 into the optical antenna module. After further collimation and beam expansion by the optical antenna module, it is emitted into free space.

[0029] The signal receiving module includes a 1563nm second narrowband filter 018, a second focusing lens 019, and an APD (Avalanche Photodiode) detector 020. Signal light with a wavelength of 1563nm is received by the optical antenna module. It is first reflected by the primary mirror 005 to the secondary mirror 006, from which it is then reflected to the fast mirror 012. After reflecting from the fast mirror 012, it passes through the quarter-wave plate 011, the dichroic mirror 010, and the polarization beam splitter 017 before entering the signal receiving module. Stray light is first filtered out by the 1563nm second narrowband filter 018, and then the second focusing lens 019 focuses the light spot onto the APD detector 020, which receives the signal light.

[0030] The beam splitting module includes a fast reflection mirror 012 , a quarter wave plate 011 , a dichroic mirror 010 and a polarization beam splitter 017 .

[0031] In the above optical path, the beacon transmitting module is independent, so as to reduce the signal-to-noise ratio pressure of the receiving optical path. The first collimating beam expander 002 adopts a double-piece lens structure and is located after the beacon transmitting laser 001, which can effectively reduce problems such as chromatic aberration. The laser is converted into a parallel Gaussian beam through the first collimating beam expander 002. The first axicon 003 is made of fused quartz and has a cone angle of 2°. After passing through the first axicon 003, the parallel Gaussian beam can be converted into a Bessel beam. The first collimating lens 004 is an aspheric lens, which can optimize the generated Bessel beam and collimate it for output. The optimal installation position of the first collimating lens 004 is determined by the following formula: (1) Where L is the distance from the axicon vertex to the front focal point of the lens, i.e., the optimized positioning point; f is the effective focal length of the collimating lens; D is the diameter of the incident Gaussian beam; n is the refractive index of the axicon material; and α is the cone angle of the axicon, generally expressed in radians. In the beacon transmitter module, the diameter of the incident Gaussian beam of the axicon is 10 mm. An aspheric lens with a focal length of 400 mm is selected. According to formula (1), the final optimized distance is 89.5 mm, which only requires fine-tuning to meet communication requirements. The axicons here refer to the first axicon 003 and the second axicon 015 mentioned above.

[0032] Considering the reliability of the experiment and the difficulty of processing, the above-mentioned axicon is preferably made of fused quartz. It has a very low absorption rate for light in the ultraviolet (UV) to near infrared (NIR) band (193 nm ~ 2.1 μm). Its refractive index inhomogeneity can be controlled to less than , avoiding the introduction of wavefront distortion and ensuring the quality of the Bessel beam. The thermal expansion coefficient is only , with thermal shock resistance far exceeding that of ordinary glass. Its transmission band covers 170 nm to 2.1 μm (UV to near-infrared), making it compatible with multi-wavelength system designs. Its mature processing technology allows fused quartz to be precisely polished to a surface roughness of less than 1 nm RMS, meeting the processing requirements of axicons with steep cone angles (e.g., 0.5° to 30°).

[0033] The above-mentioned cone angle refers to the angle between the inclined surface of the axicon and the central axis. 2° is a small-angle axicon, which is suitable for generating long-distance non-diffracting Bessel beams. Taking into account the processing error, the cone angle tolerance can be achieved. ±0.05°, that is, 1.95-2.05°.

[0034] The acceptable error range for the aforementioned aspheric lens with a focal length of 400mm is ±1% (±4 mm), or 396-404mm. This value is derived from a simulated optical path, which takes into account the clear aperture, center thickness, and aberration correction.

[0035] In the optical antenna module, the optical axes of the primary mirror 005 and the secondary mirror 006 are parallel, but they are mounted off-axis. This avoids optical obstruction issues associated with coaxial mirrors and reduces energy loss. The primary mirror 005 of the optical antenna module is a concave parabola, while the secondary mirror 006 is a convex parabola. The optical magnification is 8x, and the operating wavelength covers 808-1563nm. Both mirrors are designed with polarization-maintaining coatings, enabling circular polarization preservation. Specifically, the polarization-maintaining coatings applied to the primary and secondary mirrors in this embodiment of the present invention precisely control the amplitude and phase relationship of the S / P light, enabling the system to maintain circular polarization. This capability is demonstrated by maintaining a 90° phase difference between the S / P light to ensure constant handedness; balancing the S / P light reflectivity to prevent polarization degradation; and offsetting accumulated errors through system-level compensation through the coordinated design of the primary and secondary mirrors. Maintaining a 90° phase difference requires precise control of the film material, thickness, and structure, and utilizing interference effects to compensate for the s / p light phase difference.

[0036] In the beacon receiving module, the central wavelength of the 808nm first narrowband filter 007 is 808nm and the bandwidth is ±2nm. It is located between the dichroic mirror 010 and the first beamforming mirror 008. The first beamforming mirror 008 adopts a double-piece lens structure, which can effectively reduce spherical aberration, chromatic aberration and other problems. The CMOS detector 009 can effectively respond to the 808nm wavelength, has a pixel size of 5.5um, and is installed at the focal plane of the first beamforming mirror 008.

[0037] In the signal transmission module, the second collimating beam expander 014 also uses a two-piece lens structure and is located after the signal transmission laser 013. It converts the laser light emitted by the signal transmission laser 013 into a parallel Gaussian beam. After passing through the second axicon 015, the parallel Gaussian beam is converted into a Bessel beam. The second collimating lens 016 is an aspheric lens and is installed in the optimal position according to formula (1). In the signal transmission module, the diameter of the Gaussian beam incident on the axicon is 10 mm. An aspheric lens with a focal length of 400 mm is selected. The final optimized distance is 89.5 mm. In other words, fine-tuning at 89.5 mm behind the axicon vertex can meet the transmission requirements.

[0038] In the signal receiving module, the central wavelength of the 1563nm second narrowband filter 018 is 1563nm and the bandwidth is ±2nm. It is located between the polarization beam splitter 017 and the second beam focusing mirror 019. The second beam focusing mirror 019 also adopts a double-piece lens structure. The APD detector 020 is installed at the focal plane of the second beam focusing mirror 019, which can convert optical signals into electrical signals and has a high gain.

[0039] In the spectrometer module, the fast reflector 012 is located behind the secondary mirror 006 and is installed at a 45° tilt. The fast reflector 012 can achieve sub-milliradian beam control through micro-angle deflection, accurately track dynamic targets, and maintain the collimation of the optical path; the 1 / 4 wave plate 011 is located between the fast reflector 012 and the dichroic mirror 010 and can be installed horizontally. The 1 / 4 wave plate 011 is a polarization phase adjustment element, which can not only convert linearly polarized light into circularly polarized light, but also reduce the impact of complex environments on signal transmission. The circularly polarized light can also be converted into linearly polarized light with a polarization direction perpendicular to the original polarization direction after passing through the 1 / 4 wave plate 011 again. When used with the polarization beam splitter 017, the transmitted light beam and the received light beam can be split; the dichroic mirror 010 reflects 808nm wavelength and transmits 1563nm and 1540nm wavelengths, and is installed at an angle of 45°; the polarization beam splitter 017 reflects S-polarized light and transmits P-polarized light, and is installed at an angle of 45°, coaxial with the 1 / 4 wave plate 011 and the dichroic mirror 010.

[0040] The Fast Mirror 012 (FSM) achieves sub-milliradian (<1 mrad) beam steering through a combination of precision actuator drive, optical leverage, high-bandwidth closed-loop control, and disturbance suppression. Its specific parameters include an angular range of ±1 to 10 mrad (to compensate for satellite platform jitter and pointing errors), a resolution of less than 0.1 mrad (sub-milliradian, e.g., 10 to 100 μrad), and a bandwidth greater than 500 Hz (to rapidly track dynamic deviations). The Fast Mirror operates through a high-precision micromotor that rotates the mirror at small angles to achieve large-angle beam deflection. A fast-response control system enables real-time fine-tuning of the mirror and automatically offsets external influences to maintain beam stability.

[0041] In the above technical solution, all the optical elements should be matched with corresponding adjustment frames to perform fine adjustment of azimuth and pitch angles.

[0042] In this embodiment, a parallel Gaussian beam is converted into a Bessel beam through an axicon, and the Bessel beam is collimated and output using an aspheric lens; the emission of the beacon light does not pass through the splitting optical path, which can improve system reliability and optimize communication performance.

[0043] In the above technical solution, the generation and collimation of the Bessel beam can be replaced by the following solution: Methods for generating Bessel beams can be broadly categorized into physical optics and computational holography. In physical optics, in addition to the axicon used in this solution to generate Bessel beams, the method of combining annular slits with Fourier lenses offers good tunability, but suffers from energy loss exceeding 90%. Emerging metasurface technology utilizes nanostructure arrays to directly modulate the wavefront phase, enabling ultra-integrated designs but with a narrow operating bandwidth. Computational holography primarily utilizes a spatial light modulator (SLM) for dynamic generation. A Bessel beam hologram is first calculated and then loaded onto the SLM to modulate the incident light. This method supports real-time generation of Bessel beams of arbitrary order, but is limited by refresh rate and low energy efficiency. Digital micromirror devices (DMDs) offer lower costs but only approximately 30% efficiency. Each of these methods has its own unique characteristics, and selection should be based on factors such as energy efficiency, tunability, and cost for the specific application scenario.

[0044] In addition to the axicon combined with a collimating lens system design used in this embodiment, the collimated Bessel beam can also adopt a dual-axic pyramid system, that is, using two axicons with the same cone angle and placed opposite each other, and dynamically controlling the collimation of the output beam by adjusting the spacing.

[0045] Compared with the existing technology, the present invention proposes a non-diffraction laser communication terminal based on Bessel beams. It uses the non-diffraction characteristics of Bessel beams to significantly improve the transmission distance, signal stability and anti-interference ability. The specific gain effects are as follows: On the one hand, anti-interference capabilities are significantly enhanced. The non-diffraction property of Bessel beams means they can maintain their shape and intensity over long distances, unlike Gaussian beams that rapidly diffuse, thereby improving communication distance and signal stability. Furthermore, Bessel beams possess excellent self-healing capabilities. Even if they encounter obstruction or scattering during transmission, the beams can repair themselves through their own structure, ensuring signal continuity. This is particularly important in complex environments or under atmospheric interference conditions.

[0046] On the other hand, transmission performance is significantly improved. Bessel beams possess the ability to superimpose multiple modes, allowing the simultaneous generation of multiple Bessel beam modes within a single transmission channel. Each mode carries a different data stream, thus achieving spatial multimode multiplexing. This multimode superposition technology significantly increases the capacity of laser communication systems, as each mode can function as an independent channel for information transmission. Compared to traditional single-mode Gaussian beams, multimode Bessel beams can significantly increase data rates and bandwidth utilization without adding additional hardware complexity, meeting the needs of future high-speed, high-capacity communications.

[0047] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0048] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may occur depending on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A non-diffraction laser communication terminal based on Bessel beam, characterized in that: It includes a beacon transmitting module, an optical antenna module, a beacon receiving module, a signal transmitting module, a signal receiving module and a spectrometer module; The beacon transmitting module comprises a beacon transmitting laser (001), a first collimating beam expander (002), a first axicon (003) and a first collimating lens (004); the beacon transmitting laser (001) transmits a laser signal, which enters the first axicon (003) after being expanded by the first collimating beam expander (002); a Bessel beam is generated by the first axicon (003), and then emitted to free space through the first collimating lens (004); The optical antenna module comprises a primary mirror (005) and a secondary mirror (006), wherein the optical axes of the primary mirror (005) and the secondary mirror (006) are parallel and are installed off-axis; The beacon receiving module comprises a first narrowband filter (007), a first focusing mirror (008) and a CMOS detector (009). After the beacon light is received by the optical antenna module, it is reflected by the primary mirror (005) to the secondary mirror (006), and then reflected to the fast reflection mirror (012) in the spectroscopic module. After being transmitted by the 1 / 4 wave plate (011) in the spectroscopic module and reflected by the dichroic mirror (010), it enters the beacon receiving module, is filtered by the first narrowband filter (007) in sequence, and is focused by the first focusing mirror (008) to the CMOS detector (009). The CMOS detector (009) images and analyzes the light spot to obtain position information. The signal transmitting module comprises a signal transmitting laser (013), a second collimating beam expander (014), a second axis pyramid (015) and a second collimating lens (016); the signal transmitting laser (013) transmits a laser signal, which enters the second axis pyramid (015) after being expanded by the second collimating beam expander (014); the second axis pyramid (015) generates a Bessel beam, which is then collimated by the second collimating lens (016) and transmitted to the polarization beam splitter (017) in the light splitting module; after being reflected by the polarization beam splitter (017), the dichroic mirror (010) and the 1 / 4 wave plate (011), the laser signal is reflected by the fast reflecting mirror (012) and enters the optical antenna module; and after being collimated and expanded by the optical antenna module, the laser signal is emitted into free space; The signal receiving module comprises a second narrowband filter (018), a second focusing mirror (019) and an APD detector (020); after the signal light is received by the optical antenna module, it is reflected by the primary mirror (005) to the secondary mirror (006), and then reflected to the fast reflection mirror (012); after being transmitted through the 1 / 4 wave plate (011), the dichroic mirror (010) and the polarization beam splitter (017), it enters the signal receiving module, is filtered by the second narrowband filter (018), and converged by the second focusing mirror (019) to the APD detector (020); and the signal light is received by the APD detector (020); The light splitting module comprises the fast reflection mirror (012), the quarter wave plate (011), the dichroic mirror (010) and the polarization beam splitter (017).

2. The non-diffraction laser communication terminal based on Bessel beam according to claim 1, characterized in that: The first collimating beam expander (002) and the second collimating beam expander (014) both adopt a double-piece lens structure and are respectively located behind the beacon emitting laser (001) and the signal emitting laser (013), and are used to convert the laser light emitted by the corresponding laser into a parallel Gaussian beam.

3. The non-diffraction laser communication terminal based on Bessel beam according to claim 1, characterized in that: The first axicon (003) and the second axicon (015) are both made of fused quartz, and the cone angle is used to convert an incident parallel Gaussian beam into a Bessel beam.

4. The non-diffraction laser communication terminal based on Bessel beam according to claim 1, characterized in that: The first collimating lens (004) and the second collimating lens (016) are both aspherical lenses; For the first collimating lens (004), its optimal installation position is determined by the formula Determine, wherein L is the distance from the vertex of the first axicon (003) to the front focus of the first collimating lens (004), f is the effective focal length of the first collimating lens (004), D is the diameter of the Gaussian beam incident on the first axicon (003), n is the refractive index of the material of the first axicon (003), and α is the cone angle of the first axicon (003); For the second collimating lens (016), its optimal installation position is determined by the formula Determine, where L is the distance from the vertex of the second axicon (015) to the front focus of the second collimating lens (016), f is the effective focal length of the second collimating lens (016), D is the diameter of the Gaussian beam incident on the second axicon (015), n is the refractive index of the material of the second axicon (015), and α is the cone angle of the second axicon (015).

5. The non-diffraction laser communication terminal based on Bessel beam according to claim 1, characterized in that: The primary mirror (005) is a concave parabola, and the secondary mirror (006) is a convex parabola. Both the primary mirror (005) and the secondary mirror (006) are designed with polarization-maintaining coatings and have the ability to maintain circular polarization.

6. The non-diffraction laser communication terminal based on Bessel beam according to claim 1, characterized in that: The beacon emitting laser (001) emits a laser signal with a wavelength of 808 nm, the signal emitting laser (013) emits a laser signal with a wavelength of 1540 nm, and the signal receiving module receives signal light with a wavelength of 1563 nm.

7. The non-diffraction laser communication terminal based on Bessel beam according to claim 1, characterized in that: The magnification of the optical antenna module is used to shrink the received external light or collimate and expand the internal outgoing light. The magnification of the optical antenna module is 8 times, and the operating wavelengths of the primary mirror (005) and the secondary mirror (006) cover 808-1563nm.

8. The non-diffraction laser communication terminal based on Bessel beam according to claim 1, characterized in that: The first narrowband filter (007) of the beacon receiving module has a central wavelength of 808 nm and a bandwidth of ±2 nm, and is located between the dichroic mirror (010) and the first beam-forming mirror (008); the second narrowband filter (018) of the signal receiving module has a central wavelength of 1563 nm and a bandwidth of ±2 nm, and is located between the polarization beam splitter (017) and the second beam-forming mirror (019).

9. The non-diffraction laser communication terminal based on Bessel beam according to claim 1, characterized in that: The cone angles of the first axicon (003) and the second axicon (015) are 2°, the first collimating lens (004) and the second collimating lens (016) are aspheric lenses with a focal length of 400 mm, the diameter of the Gaussian beam incident on the first axicon (003) and the second axicon (015) is 10 mm, and the optimized distances from the vertices of the first axicon (003) and the second axicon (015) to the front focal points of the first collimating lens (004) and the second collimating lens (016) are 89.5 mm, respectively.

10. The non-diffraction laser communication terminal based on Bessel beam according to claim 1, characterized in that: The quick reflection mirror (012) is installed at an angle of 45 degrees behind the secondary mirror (006); the quarter wave plate (011) is located between the quick reflection mirror (012) and the dichroic mirror (010), and is used to convert linearly polarized light into circularly polarized light or convert circularly polarized light into circularly polarized light; the dichroic mirror (010) is installed at an angle of 45 degrees, reflects 808 nm wavelength, and transmits 1540 nm and 1563 nm wavelengths; the polarization beam splitter (017) is installed at an angle of 45 degrees, reflects S polarized light, and transmits P polarized light, and is coaxial with the quarter wave plate (011) and the dichroic mirror (010).

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