A large-aperture, high-precision off-axis two-reflector laser beam expander

Abstract

This utility model discloses a large-aperture, high-precision off-axis two-mirror laser beam expander, solving the problems of chromatic aberration and thermal effects in existing transmission-type laser beam expanders, the problem of central obstruction in coaxial reflection-type laser beam expanders, and low environmental adaptability. The laser beam expander system includes a vacuum tank, a system base plate and an optical system disposed within the vacuum tank; the vacuum tank has a first light inlet and a first light outlet; the first light inlet is arranged along the axial direction of the vacuum tank, and the first light outlet is arranged along the radial direction of the vacuum tank; the optical system is an off-axis two-mirror optical system, including a primary reflector, a secondary reflector, and a folding mirror mounted on the system base plate and arranged sequentially along the optical path; a first aperture is provided on the incident light path of the primary reflector; the secondary reflector is located near the first light inlet, and a second aperture is provided on its incident light path; the folding mirror is used to change the optical path, and the first light outlet is located on the reflected light path of the folding mirror.

Description

Technical Field

[0001] This utility model relates to a beam expander for a space laser communication system, specifically to a large-aperture, high-precision off-axis two-reflector laser beam expander suitable for vacuum environments, equipped with full-duplex communication mode, and capable of providing a high-polarity-maintaining collimated light source. Background Technology

[0002] In space laser communication systems, laser beam expanders are one of the core components, mainly used to compress the divergence angle of the laser beam and improve energy concentration, thereby enabling long-distance, high signal-to-noise ratio optical signal transmission.

[0003] Existing laser beam expanders mostly adopt transmission or coaxial reflection structures, which have the following limitations: (1) Transmission structures have chromatic aberration and thermal effects, and large-aperture, high-precision lenses are difficult to manufacture and costly; (2) Coaxial reflection structures have central obstruction problems, which can easily cause energy loss and diffraction effects, thereby reducing the signal-to-noise ratio of the system; (3) Conventional transmission or coaxial reflection structures are mostly designed for ground atmospheric environments, and their thermal expansion coefficients and structural stability are difficult to meet the requirements of vacuum, high and low temperature alternating space application environments, and generally lack the ability to effectively maintain the polarization state of the laser, thus making it difficult to meet the stringent requirements of high-precision laser communication for polarization-maintaining characteristics.

[0004] Therefore, there is an urgent need for a laser beam expander that combines large aperture, high precision, high stability, high polarization-maintaining characteristics, and is suitable for vacuum environments. Utility Model Content

[0005] The purpose of this invention is to solve the problems of chromatic aberration and thermal effect in existing transmissive laser beam expanders, the problem of central obstruction in coaxial reflective laser beam expanders, and the low environmental adaptability of both, and to provide a large-aperture, high-precision off-axis two-reflective laser beam expander.

[0006] To achieve the above objectives, the technical solution adopted by this utility model is as follows: A large-aperture, high-precision off-axis two-reflector laser beam expander is characterized by including a vacuum chamber, a system base plate and an optical system disposed inside the vacuum chamber. The vacuum container is used to connect to an external vacuum pumping device. The vacuum container is provided with a first light inlet and a first light outlet. The first light inlet is arranged along the axial direction of the vacuum container, and the first light outlet is arranged along the radial direction of the vacuum container and close to the first light inlet. The optical system is an off-axis two-mirror optical system, including a primary mirror, a secondary mirror, and a folding mirror mounted on the system base plate and arranged sequentially along the optical path; the primary mirror is located away from the first light entrance and its reflecting surface faces the first light entrance, and a first aperture is provided on its incident optical path; the secondary mirror is located close to the first light entrance, and a second aperture is provided on its incident optical path; the folding mirror is located on the reflected optical path of the secondary mirror and is used to change the optical path; the first light exit is located on the reflected optical path of the folding mirror.

[0007] Furthermore, the aperture of the off-axis two-reflector optical system is ≥220mm, and the beam expansion ratio is 20x ± 0.5x.

[0008] Furthermore, the primary reflector has an aperture of 240±0.5mm and an off-axis distance of 255±0.05mm. The secondary reflector has an aperture of 20±0.5mm and an off-axis distance of 12.75±0.05mm.

[0009] Furthermore, the wavefront RMS value of the primary reflector is ≤0.017λ, the wavefront RMS value of the secondary reflector is ≤0.012λ, and the wavefront RMS value of the folding mirror is ≤0.012λ, where λ=632.8nm.

[0010] Furthermore, the aperture of the first aperture is 235mm, and its distance from the primary mirror is 105±0.1mm; The second aperture has two light-transmitting holes. One light-transmitting hole has a diameter of 235 mm and is coaxial with the light-transmitting hole of the first aperture. The other light-transmitting hole has a diameter of 50 mm and is coaxial with the incident light path of the secondary reflector. The distance between the second aperture and the secondary reflector is 223 ± 0.1 mm.

[0011] Furthermore, the system base plate is mounted inside the vacuum tank via a sliding pair, and a height adjustment mechanism is provided at the bottom; The sliding pair includes a guide rail installed inside the vacuum tank and parallel to the incident optical axis, and multiple rollers installed at the bottom of the system base plate and sliding along the guide rail; There are two sets of height adjustment mechanisms, located at both ends of the system base plate. One end of the height adjustment mechanism is movably connected to the bottom of the system base plate; the other end separates from the guide rail when the system base plate needs to slide, and after height adjustment, it abuts against the guide rail and lifts the system base plate, causing the roller to disengage from the guide rail.

[0012] Furthermore, the height adjustment range of the height adjustment mechanism is 0~5mm.

[0013] Furthermore, it also includes a housing disposed inside the vacuum chamber; the housing is mounted on the system base plate and forms a closed cavity with the system base plate, and the optical system is located inside the closed cavity; The cover has a second light inlet on the side near the first light inlet, directly opposite the first light inlet, and a second light outlet on the side near the first light outlet, opposite to the first light outlet. mouth The second light output port directly opposite.

[0014] Furthermore, the primary reflector, secondary reflector, and folding mirror are all made of microcrystalline material, and their reflective surfaces are coated with a silver film, with an oxide dielectric protective film coated on top of the silver film.

[0015] Furthermore, the supporting structures for the primary reflector, secondary reflector, and folding mirror, as well as the system base plate, are all made of Invar steel.

[0016] The advantages of this utility model compared to the prior art are as follows: 1. The optical system of this utility model is an off-axis dual-reflector structure. This structure has no central obstruction, high energy utilization, and excellent imaging quality. At the same time, by setting the optical system inside a vacuum chamber, its environmental adaptability is improved, thereby ensuring the system's polarization maintenance rate.

[0017] 2. The optical system of this utility model has a light transmission aperture of ≥220mm and a beam expansion ratio of 20x ± 0.5x, which combines the characteristics of large aperture and high precision. Moreover, the precise beam expansion ratio of 20x ± 0.5x meets the stringent requirements of long-distance laser communication for beam quality.

[0018] 3. This utility model has a first aperture on the incident light path of the main reflector and a second aperture on the incident light path of the secondary reflector. By precisely designing and positioning the two apertures, stray light rays can be effectively blocked, thus improving the accuracy of the system.

[0019] 4. The system base plate of this utility model is installed in the vacuum tank through a sliding pair, and the bottom is equipped with a height adjustment mechanism, which facilitates the final precise assembly and locking of the optical system in a vacuum environment, thereby improving the engineering applicability of the equipment.

[0020] 5. This utility model sets the optical system in a closed cavity formed by the housing and the system base plate, thereby enhancing the environmental tolerance and reliability of the optical system; at the same time, the modular design of each lens group facilitates later maintenance and adjustment.

[0021] 6. The wavefront RMS values ​​of the primary reflector, secondary reflector, and folding mirror of this invention are all optimized to ensure imaging quality. At the same time, the primary reflector, secondary reflector, and folding mirror are all made of microcrystalline materials, and their reflective surfaces are coated with silver films. Furthermore, an oxide dielectric protective film is coated on top of the silver films, which makes the polarization maintenance rate of the optical system better than 95%, perfectly supporting the full-duplex mode of coherent laser communication based on polarization modulation.

[0022] 7. In this utility model, the support structure of the primary reflector, secondary reflector and folding mirror, as well as the system base plate, are all made of Invar steel, which is a material with an ultra-low coefficient of thermal expansion. This ensures that each mirror group has extremely high dimensional stability and surface accuracy in the high and low temperature thermal vacuum environment simulated by the vacuum tank, and overcomes the problem of optical path misalignment caused by unavoidable thermal expansion and contraction of traditional materials. Attached Figure Description

[0023] Figure 1 This is a structural schematic diagram of an embodiment of the present utility model.

[0024] Figure 2 This is a top view of the internal structure of an embodiment of the present utility model.

[0025] The attached figures are labeled as follows: 1-Vacuum tank, 2-System base plate, 3-First light inlet, 4-First light outlet, 5-Primary reflector, 6-Secondary reflector, 7-Folding mirror, 8-First aperture, 9-Second aperture, 10-Height adjustment mechanism, 11-Guide rail, 12-Roller, 13-Cover, 14-Second light inlet, 15-Second light outlet. Detailed Implementation

[0026] To make the objectives, advantages and features of this utility model clearer, the following describes in further detail a large-aperture, high-precision off-axis two-reflector laser beam expander proposed by this utility model in conjunction with the accompanying drawings and specific embodiments.

[0027] like Figure 1 and Figure 2 As shown, this embodiment provides a large-aperture, high-precision off-axis two-reflector laser beam expander, including a vacuum tank 1, a system base plate 2 disposed inside the vacuum tank 1, and an optical system.

[0028] Vacuum container 1 is connected to an external vacuum pump to provide a vacuum environment for the optical system. Vacuum container 1 has a first light inlet 3 and a first light outlet 4. The first light inlet 3 is arranged along the axial direction of vacuum container 1, and the first light outlet 4 is arranged radially along vacuum container 1 and close to the first light inlet 3. To ensure the airtightness of vacuum container 1, a window glass is installed at the first light outlet 4, and a sealing door is provided at the first light inlet 3. The sealing door is opened when in use. In addition, other interfaces are reserved on the body of vacuum container 1.

[0029] The optical system is an off-axis two-mirror optical system with an aperture diameter ≥220mm and a beam magnification of 20x ± 0.5x. This optical system includes a primary reflector 5, a secondary reflector 6, and a folding mirror 7, all mounted on a system base plate 2 and arranged sequentially along the optical path. The primary reflector 5 is positioned away from the first light entrance 3, with its reflective surface facing the first light entrance 3. The secondary reflector 6 is positioned close to the first light entrance 3. The folding mirror 7 is located on the reflected optical path of the secondary reflector 6 and is used to change the optical path. The first light exit 4 is located on the reflected optical path of the folding mirror 7. In this embodiment, the primary reflector 5, secondary reflector 6, and folding mirror 7 are individually fixed yet cooperate to form an off-axis two-mirror optical structure. The incident light beam first reaches the primary reflector 5, is reflected by the primary reflector 5 to the secondary reflector 6, and then reflected again by the secondary reflector 6 to the folding mirror 7. The folding mirror 7 is positioned in the system's optical path to fold the optical path by 90°, facilitating system layout and alignment.

[0030] Meanwhile, the substrates of the primary reflector 5, secondary reflector 6, and folding mirror 7 are all made of microcrystalline material, and the optical working surface (reflective surface) is coated with a silver film, and an oxide dielectric protective film is coated on the silver film. Through film system optimization design and experimental verification, the optical system can effectively ensure that the reflectivity is ≥95% and the polarization retention is ≥95% in the wavelength range of 400nm~1700nm.

[0031] The primary reflector 5 has an aperture of 240mm and an off-axis distance of 255mm; the secondary reflector 6 has an aperture of 20mm and an off-axis distance of 12.75mm. In this embodiment, the optical lenses of the primary reflector 5, secondary reflector 6, and folding-axis mirror 7 are all processed using a single-lens grinding method to remove off-axis aspherical surfaces. Fine grinding is performed using a robotic small-head grinding and polishing integrated machine, followed by controlled polishing using a flexible polishing head. Finally, high-precision magnetorheological polishing (MRF) is used to refine the surface shape. After processing, the wavefront RMS value of the primary reflector 5 is ≤0.017λ, the wavefront RMS value of the secondary reflector 6 is ≤0.012λ, and the wavefront RMS value of the folding-axis mirror 7 is ≤0.012λ, where λ=632.8nm, thus ensuring the forming quality of the primary reflector 5, secondary reflector 6, and folding-axis mirror 7.

[0032] Furthermore, in this embodiment, a first aperture 8 is provided on the incident light path of the primary reflector 5. The aperture of the first aperture 8 is 235 mm, and its distance from the primary reflector 5 is 105 ± 0.1 mm. A second aperture 9 is provided on the incident light path of the secondary reflector 6. The second aperture 9 has two apertures, one with an aperture of 235 mm and coaxial with the aperture of the first aperture 8, and the other with an aperture of 50 mm and coaxial with the incident light path of the secondary reflector 6. The distance between the first aperture 8 and the secondary reflector 6 is 223 ± 0.1 mm. The first aperture 8 and the second aperture 9 are respectively located near the primary reflector 5 and the secondary reflector 6 to effectively suppress stray light and improve the signal-to-noise ratio of the optical system.

[0033] In this embodiment, the supporting structures for the primary reflector 5, secondary reflector 6, and folding-axis mirror 7, as well as the system base plate 2, are all made of Invar steel, a material with a linear expansion coefficient ≤1.0×10⁻⁶. -6 / ℃ ensures the stability of the optical system.

[0034] In summary, the optical system of this invention has a magnification of 20x, a tolerance of ±0.5x, a polarization retention rate of better than 95%, and a beam parallelism of ≤1″.

[0035] The optical system has a full-duplex mode: as a transmitter, it simulates the conditions for emitting a far-field laser beam; as a receiver, it provides a beam channel to receive the beam emitted by the product and allow it to enter the optical camera.

[0036] like Figure 1 As shown, the system base plate 2 is installed inside the vacuum tank 1 via a sliding pair, and a height adjustment mechanism 10 is provided at the bottom. The sliding pair and the height adjustment mechanism 10 cooperate with each other to achieve precise positioning and fixation of the optical system inside the vacuum tank 1.

[0037] Specifically, the sliding pair includes a guide rail 11 installed inside the vacuum tank 1 and parallel to the incident optical axis, and multiple rollers 12 installed on the bottom of the system base plate 2 and sliding along the guide rail 11. Each roller 12 has a built-in vacuum-lubricated bearing. There are two sets of height adjustment mechanisms 10, located at opposite ends of the system base plate 2. One end of the height adjustment mechanism 10 is movably connected to the bottom of the system base plate 2; the other end separates from the guide rail 11 when the system base plate 2 needs to slide, and after height adjustment, it abuts against the guide rail 11 and lifts the system base plate 2 to the corresponding height, at which point the rollers 12 disengage from the guide rail 11. In this embodiment, the height adjustment range of the height adjustment mechanism 10 is 0~5mm.

[0038] This embodiment also includes a housing 13 disposed inside the vacuum chamber 1. The housing 13 is mounted on the system base plate 2 and forms a closed cavity with the system base plate 2, and the optical system is located inside the closed cavity. The design of the housing 13 further ensures the vacuum environment of the optical system and can protect the internal optical components from dust and moisture contamination in non-vacuum environments.

[0039] Meanwhile, the cover 13 has a second light inlet 14 on the side near the first light inlet 3, which is directly opposite to the first light inlet 3 and has the same size, and a second light outlet 15 on the side near the first light outlet 4, which is directly opposite to the first light outlet 4 and has the same size. When the device assembled with the cover 13 and the system base plate 2 (including the optical system) is placed in the vacuum tank 1 for operation, the second cover plates at the second light inlet 14 and the second light outlet 15 are opened. After the vacuum tank 1 is evacuated, the internal and external pressures of the sealed cavity can be kept balanced, preventing the mirror and important structural components from deforming due to pressure difference.

[0040] The optical system of this invention adopts an off-axis dual-mirror structure to avoid central obstruction. It uses materials with ultra-low coefficient of thermal expansion to ensure the dimensional stability of each mirror and related structural components in vacuum high and low temperature environments. Through innovative structural design and material processing, it achieves large-aperture, high-precision, and high polarization-maintaining performance, making it particularly suitable for full-duplex operation in space laser communication.

[0041] The above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, and such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this utility model.

Claims

1. A large-aperture, high-precision off-axis two-reflector laser beam expander, characterized in that: Includes a vacuum tank (1), a system base plate (2) disposed inside the vacuum tank (1), and an optical system; The vacuum tank (1) is used to connect to an external vacuum pumping device. The vacuum tank (1) is provided with a first light inlet (3) and a first light outlet (4). The first light inlet (3) is arranged along the axial direction of the vacuum tank (1), and the first light outlet (4) is arranged along the radial direction of the vacuum tank (1) and close to the first light inlet (3). The optical system is an off-axis two-mirror optical system, including a primary mirror (5), a secondary mirror (6) and a folding mirror (7) mounted on the system base plate (2) and arranged sequentially along the optical path; the primary mirror (5) is located away from the first light inlet (3) and its reflecting surface faces the first light inlet (3), and a first aperture (8) is provided on its incident light path; the secondary mirror (6) is located close to the first light inlet (3), and a second aperture (9) is provided on its incident light path; the folding mirror (7) is located on the reflected light path of the secondary mirror (6) and is used to change the optical path; the first light outlet (4) is located on the reflected light path of the folding mirror (7).

2. The large-aperture, high-precision off-axis two-reflector laser beam expander according to claim 1, characterized in that: The aperture of the off-axis two-reflector optical system is ≥220mm, and the beam expansion ratio is 20x ± 0.5x.

3. The large-aperture, high-precision off-axis two-reflector laser beam expander according to claim 2, characterized in that: The aperture of the primary reflector (5) is 240±0.5mm, and the off-axis distance is 255±0.05mm; The secondary reflector (6) has an aperture of 20±0.5mm and an off-axis distance of 12.75±0.05mm.

4. The large-aperture, high-precision off-axis two-reflector laser beam expander according to claim 3, characterized in that: The wavefront RMS value of the primary reflector (5) is ≤0.017λ, the wavefront RMS value of the secondary reflector (6) is ≤0.012λ, and the wavefront RMS value of the folding mirror (7) is ≤0.012λ, where λ=632.8nm.

5. The large-aperture, high-precision off-axis two-reflector laser beam expander according to claim 1, characterized in that: The aperture of the first aperture (8) is 235 mm, and its distance from the main reflector (5) is 105 ± 0.1 mm. The second aperture (9) is provided with two light-transmitting holes. One of the light-transmitting holes has a diameter of 235 mm and is coaxial with the light-transmitting hole of the first aperture (8). The other light-transmitting hole has a diameter of 50 mm and is coaxial with the incident light path of the secondary reflector (6). The distance between the second aperture (9) and the secondary reflector (6) is 223 ± 0.1 mm.

6. The large-aperture, high-precision off-axis two-reflector laser beam expander according to claim 1, characterized in that: The system base plate (2) is installed inside the vacuum tank (1) via a sliding pair, and a height adjustment mechanism (10) is provided at the bottom. The sliding pair includes a guide rail (11) installed inside the vacuum tank (1) and parallel to the incident optical axis, and a plurality of rollers (12) installed at the bottom of the system base plate (2) and sliding along the guide rail (11). The height adjustment mechanism (10) has two sets, located at both ends of the system base plate (2); one end of the height adjustment mechanism (10) is movably connected to the bottom of the system base plate (2); the other end is separated from the guide rail (11) when the system base plate (2) needs to slide, and after the height adjustment is performed, it abuts against the guide rail (11) and lifts the system base plate (2), so that the roller (12) disengages from the guide rail (11).

7. The large-aperture, high-precision off-axis two-reflector laser beam expander according to claim 6, characterized in that: The height adjustment range of the height adjustment mechanism (10) is 0~5mm.

8. The large-aperture, high-precision off-axis two-reflector laser beam expander according to claim 1, characterized in that: It also includes a cover (13) installed inside the vacuum tank (1); The housing (13) is mounted on the system base plate (2) and forms a closed cavity with the system base plate (2), and the optical system is located in the closed cavity; The cover (13) has a second light inlet (14) on the side near the first light inlet (3) that is directly opposite to the first light inlet (3), and a second light outlet (15) on the side near the first light outlet (4) that is directly opposite to the first light outlet (4).

9. The large-aperture, high-precision off-axis two-reflector laser beam expander according to any one of claims 1 to 8, characterized in that: The primary reflector (5), secondary reflector (6) and folding mirror (7) are all made of microcrystalline material, and their reflective surfaces are coated with a silver film, and an oxide dielectric protective film is coated on the silver film.

10. The large-aperture, high-precision off-axis two-reflector laser beam expander according to claim 9, characterized in that: The supporting structure of the main reflector (5), secondary reflector (6) and folding mirror (7) as well as the system base plate (2) are all made of Invar steel.

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