Aluminum-based oblique-axis large-view-field off-axis three-reflector system and rapid assembling and adjusting method

Abstract

The invention provides an aluminum-based oblique-axis large-view-field off-axis three-mirror system and a rapid installation and adjustment method, and belongs to the technical field of optical system detection.The off-axis three-mirror optical system is composed of a first reflector, a second reflector, a third reflector, a substrate and a mirror frame, and the substrate is provided with installation faces of the first reflector and the third reflector; the space poses of the first reflector and the third reflector which are installed on the installation face of the substrate meet the optical design of an off-axis three-reflector system, the surface precision requirement is met through common ultra-precision machining of the first reflector and the third reflector, then the substrate is installed on the back face of the mirror frame, and the second reflector is installed on the front face of the mirror frame through a mirror bracket. And an off-axis three-mirror system is formed. According to the off-axis three-reflector system, the original assembling and adjusting problem of the first reflector and the third reflector is transferred to accurate machining of the first reflector and the third reflector, repeated assembling and adjusting of the first reflector and the third reflector are avoided, and then assembling and adjusting of the off-axis three-reflector system can be achieved only by adjusting the spatial pose of the second reflector.

Description

Technical Field

[0001] This invention belongs to the field of optical system testing technology, specifically relating to an aluminum-based oblique-axis large field-of-view off-axis three-mirror system, and a rapid assembly and adjustment method for the aluminum-based oblique-axis large field-of-view off-axis three-mirror system. Background Technology

[0002] With the increasing demand for miniaturization, lightweight design, and high image quality in optoelectronic systems, off-axis three-mirror optical systems have become an ideal choice. Currently, these systems mostly employ high-order aspherical or freeform surface mirror designs. Although these designs can meet optical performance requirements, the fabrication, testing, and system assembly of the mirrors are extremely difficult, severely hindering the advancement of optoelectronic payload technology.

[0003] Most existing large field-of-view off-axis three-mirror systems adopt a coaxial design for the primary three mirrors, relying on computer-aided assembly and adjustment to precisely calibrate the secondary and tertiary mirrors. However, this approach has significant drawbacks: the combination of the primary and secondary mirrors does not produce a perfect image point, requiring compensation and detection via a compensator, and the secondary mirrors need to be adjusted in multiple degrees of freedom, resulting in high assembly and adjustment difficulty, low efficiency, and difficulty in achieving rapid integration.

[0004] Existing related assembly and adjustment technologies also have limitations in applicability: For example, Chinese patent CN113126272A discloses an assembly and adjustment method for an off-axis three-mirror system, which requires placing a theodolite between the first, second, and third mirrors and using an interferometer for compensation measurement. However, this method is only suitable for large off-axis three-mirror systems and cannot be adapted to compact structures. Furthermore, it requires separate surface compensation testing for the second and third mirrors, resulting in low assembly and adjustment efficiency. Chinese patent CN111929879A discloses a small F-number oblique axis large field-of-view off-axis three-mirror system and its assembly and adjustment method, which achieves coaxial assembly and adjustment of the second and third mirrors by combining a theodolite and an interferometer. However, this method is only suitable for three-mirror systems that require coaxial design and is not applicable to the assembly and adjustment of three-mirror systems where each mirror is off-axis. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of high assembly and adjustment difficulty, low efficiency and difficulty in rapid integration of existing large field-of-view off-axis three-mirror systems, and to provide an aluminum-based oblique-axis large field-of-view off-axis three-mirror system and a rapid assembly and adjustment method for the aluminum-based oblique-axis large field-of-view off-axis three-mirror system.

[0006] To achieve the above objectives, the technical solution provided by this invention is:

[0007] An aluminum-based oblique-axis large-field-of-view off-axis three-mirror system is provided, comprising a first mirror, a second mirror, and a third mirror. The spatial orientation of the first, second, and third mirrors is such that the incident light beam is reflected sequentially by the first mirror, the second mirror, and the third mirror before exiting. A non-zero off-axis angle exists between the optical axes of the first and third mirrors, thus forming an off-axis three-mirror optical structure. The first, second, and third mirrors are all integral mirrors, with the optical reflecting surfaces and mirror mounting structures integrally formed using ultra-precision machining. The off-axis three-mirror system also includes a substrate and a frame. The first and third mirrors are mounted on the upper surface of the substrate, and the mounting of the first and third mirrors... The position is determined based on the spatial theoretical position in optical design; the optical reflecting surfaces of the first and third mirrors mounted on the substrate are conformally machined with the same reference; the frame is a hollow structure with openings at both ends for connecting the substrate and the second mirror; the substrate is mounted at the opening on the back of the frame, and the second mirror is mounted at the opening on the front of the frame via a frame, with the optical reflecting surface of the second mirror facing the optical reflecting surfaces of the first and third mirrors; the outer side of the second mirror has multiple mounting platforms that mate with the frame, and the mounting platforms have positioning reference surfaces for machining the optical reflecting surface of the second mirror and adjusting the second mirror, the positioning reference surfaces being perpendicular to the bottom surface of the second mirror.

[0008] Furthermore, the first reflector, second reflector, third reflector, substrate, and frame are all made of microcrystalline aluminum.

[0009] Furthermore, the substrate is provided with a first mounting surface for mounting the first reflector and a second mounting surface for mounting the third reflector; the positions of the first mounting surface and the second mounting surface on the substrate are set based on the spatial theoretical positions of the first reflector and the third reflector in the optical design.

[0010] Furthermore, the edge of the upper surface of the substrate is provided with threaded holes for connecting to the back of the mirror frame; the outer side of the first mounting surface is provided with multiple threaded holes for mounting the first reflector; the outer side of the second mounting surface is provided with multiple threaded holes for mounting the third reflector; the upper surface of the mounting platform is provided with multiple threaded holes for connecting to the mirror frame; and stress isolation grooves are provided around the threaded holes.

[0011] Furthermore, the surface accuracy requirements for the first mounting surface, the second mounting surface, and the stress isolation groove are 0.004mm-0.006mm; the positional accuracy requirements for the positioning reference surface are 0.004mm-0.006mm.

[0012] A rapid assembly and adjustment method for an aluminum-based skew-axis large field-of-view off-axis three-mirror system is also provided. This method, used for assembling and adjusting the aforementioned aluminum-based skew-axis large field-of-view off-axis three-mirror system, includes the following steps:

[0013] S1. Preparation of reference components and parts:

[0014] Prepare a substrate; fix the substrates of the first and third reflectors onto the substrate respectively; using the side and back of the substrate as references, machine the optical reflective surfaces of the first and third reflectors sequentially by ultra-precision turning in a single clamping operation; use a shared compensator to simultaneously detect the surface accuracy of the optical reflective surfaces of the first and third reflectors, and machine a qualified reference assembly; machine the positioning reference surface on the mirror body of the second reflector by ultra-precision turning, and machine the optical reflective surface of the second reflector using the positioning reference surface as a reference.

[0015] S2, System Integration and Fine-tuning:

[0016] The reference component is fixed to the back of the mirror frame, and the back normal of the substrate is used as the optical axis reference for system assembly. Based on the optical axis reference, the spatial angle of the plane mirror in front of the first mirror is determined by collimating with the back of the substrate using a collimator. The second mirror is then installed on the front of the mirror frame using a mirror mount. An optical detection path is established based on the optical axis reference. An interferometer is used to detect the wavefront aberration of the optical system. The system wavefront aberration is made to meet the preset index by adjusting the spatial attitude of the second mirror.

[0017] Furthermore, in step 1, during substrate fabrication, a first mounting surface for mounting the first reflector and a second mounting surface for mounting the second reflector are fabricated using the back and side surfaces of the substrate as references. Based on the theoretical poses of the first and third reflectors in the optical design, the positional relationship between the first and second mounting surfaces is determined by the side surface of the substrate, and the tilt angle relationship between the first and second mounting surfaces is determined by the back surface of the substrate.

[0018] Furthermore, in step 2, the incident angle of the off-axis three-mirror system is determined based on the optical axis reference, and a plane mirror is installed based on the incident angle; the optical detection path detection specifically involves making the laser emitted by the interferometer pass through the third mirror, the second mirror, and the first mirror before being reflected to the plane mirror, and returning along the original path to form phase interference fringes and system wave aberration.

[0019] Furthermore, in step 2, the plane mirror detects the off-axis directional wave aberration formed by the first, second, and third mirrors. If the off-axis directional wave aberration is asymmetrical, the spatial attitude of the second mirror is adjusted until the off-axis directional wave aberration is symmetrical and meets the wave aberration index requirements of the off-axis three-mirror system, thus completing the assembly and adjustment of the off-axis three-mirror system.

[0020] The advantages of this invention are:

[0021] 1. This invention presents an aluminum-based oblique-axis large-field-of-view off-axis three-mirror system. The system employs an integral mirror where the optical reflecting surface and mirror body mounting structure are molded as a single unit, eliminating assembly stress from discrete components and establishing a high-precision, high-stability unit foundation. Based on optical theory, the machining angles of the first and second mounting surfaces on the substrate are set and optimized, permanently and precisely fixing the complex pose relationship between the first and third mirrors in traditional optical systems onto the substrate, forming a "reference assembly." This shifts the most difficult multi-degree-of-freedom optical alignment problem in traditional assembly to a controllable machining stage. Simultaneously, the positioning reference surface formed in the same machining process on the second mirror body, together with the back of the substrate serving as the system-level assembly reference, constitutes a high-precision mounting system. These structural features transform the entire system's assembly into a rapid installation process guided by mechanical references, requiring only fine-tuning of the second mirror, thereby improving assembly efficiency while ensuring optical performance.

[0022] 2. This invention presents a rapid assembly and adjustment method for an aluminum-based oblique-axis large-field-of-view off-axis three-mirror system, transforming the challenges of traditional assembly and adjustment into a precisely controllable processing and benchmark assembly problem. In the ultra-precision machining stage, this method utilizes a unified benchmark on the substrate to form and verify the optical surfaces of the first and third mirrors in a single process, permanently solidifying the core optical path relationship and forming a "benchmark assembly." Subsequently, in the system integration and assembly stage, the principle of using the substrate's back surface normal as the system's optical axis benchmark is applied, and rapid initial mechanical positioning is achieved using a pre-fabricated precision positioning benchmark on the second mirror body. Ultimately, the assembly and adjustment of the entire complex system is simplified to only requiring wavefront aberration fine-tuning of the second mirror component, thereby simplifying the assembly and adjustment process and improving efficiency. Attached Figure Description

[0023] The features and advantages of the invention will become more readily apparent from the following description with reference to the accompanying drawings, which are not drawn to scale and some features are enlarged or reduced to show details of specific parts.

[0024] Figure 1 This is an optical path diagram of an aluminum-based oblique-axis large field-of-view off-axis three-mirror system according to the present invention;

[0025] Figure 2 This is a schematic diagram of the integrated structure design of the first and third reflecting mirrors of the present invention;

[0026] Figure 3 This is a schematic diagram of conformal detection of the first and third reflecting mirrors of the present invention;

[0027] Figure 4 This is a schematic diagram of the second reflecting mirror structure design of the present invention;

[0028] Figure 5This is a schematic diagram of the assembly of the first reflector and the mounting substrate of the present invention;

[0029] Figure 6 This is a schematic diagram of the assembly and adjustment of the off-axis three-reflector system of the present invention;

[0030] Figure 7 This is an assembly drawing of the off-axis three-reflector system of the present invention;

[0031] Figure 8 This is a schematic diagram of the mirror frame of the off-axis three-reflector system of the present invention.

[0032] In the figure: 1-First reflecting mirror; 2-Second reflecting mirror; 2.1-Optical reflecting surface; 2.2-Processing reference surface; 3-Third reflecting mirror; 4-Substrate; 4.1-Second mounting surface; 4.2-Stress isolation groove; 5-Interferometer; 6-Plane reflecting mirror; 7-Plane mirror; 8-Theodolite; 9-Mirror frame. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and exemplary embodiments thereof. It should be noted that the following detailed description of the present invention is for illustrative purposes only and is not intended to limit the scope of the invention.

[0034] This invention provides an aluminum-based oblique-axis large field-of-view off-axis three-mirror system, such as... Figure 1 As shown, it includes a first reflector 1, a second reflector 2, a third reflector 3, a substrate 4, and a mirror frame 9. The first reflector 1, the second reflector 2, and the third reflector 3 are all integral reflectors, and the optical reflecting surface 2.1 and the mirror mounting structure are integrally formed by ultra-precision machining; the off-axis three-reflector system also includes the substrate 4 and the mirror frame 9.

[0035] The first reflector 1 and the third reflector 3 are mounted on the upper surface of the substrate 4, and their mounting positions are determined based on the spatial theoretical positions in the optical design. The optical reflecting surfaces 2.1 of the first reflector 1 and the third reflector 3 mounted on the substrate 4 are conformally machined with the same reference. "With the same reference" means that the two optical reflecting surfaces 2.1 are machined with the side and back of the substrate 4 as spatial references. "Conformally machined" actually means that the optical reflecting surfaces 2.1 of the first reflector 1 and the third reflector 3 are machined sequentially in one operation with the same reference.

[0036] like Figure 8As shown, the frame 9 is a hollow structure with openings at both ends, used to connect the substrate 4 and the second reflector 2; the substrate 4 is installed at the opening on the back of the frame 9, and the second reflector 2 is installed at the opening on the front of the frame 9 through the frame, and the optical reflecting surface 2.1 of the second reflector 2 is opposite to the optical reflecting surface 2.1 of the first reflector 1 and the optical reflecting surface 2.1 of the third reflector 3.

[0037] The outer side of the second reflector 2 has multiple mounting platforms that are fitted with the mirror frame. The mounting platforms have an optical reflecting surface 2.1 for machining the second reflector 2 and a positioning reference surface 2.2 for assembling and adjusting the second reflector 2. The positioning reference surface 2.2 is perpendicular to the bottom surface of the second reflector 2.

[0038] In this embodiment, the structural design adopts an integrated design of the reflector functions, involving the combined design of the first reflector 1 and the third reflector 3 in the off-axis three-mirror system, as well as the positioning design of the assembly of the second reflector 2 with the first reflector 1 and the third reflector 3. The design arranges the positions of the first reflector 1 and the third reflector 3 according to the dimensional requirements of the optical system, while also considering the smoothness requirements of the first reflector 1 and the second reflector 2 during surface machining, enabling the machining of two optical reflecting surfaces 2.1 in a single setup. The machine tool machining positional accuracy ensures the mirror surface and positional requirements of the two reflectors, avoiding the need for precise adjustments of the spatial positions of the first reflector 1 and the third reflector 3 by the assembly personnel. The integrated design of the structural forms of the first reflector 1 and the third reflector 3 is as follows: Figure 2 As shown, the first reflector 1 and the third reflector 3 are manufactured conformally to the same reference, ensuring the optical and structural design achieves the manufacturability of the co-fabricated manufacturing of the first reflector 1 and the third reflector 3. This achieves ultra-precision manufacturing of the first reflector 1 and the third reflector 3 while simultaneously solving the problem of precise assembly and positioning of the first reflector 1 and the third reflector 3. In this embodiment, to ensure that the first reflector 1 and the third reflector 3 can be independently inspected, a detection method using a shared compensator is designed to achieve simultaneous inspection of the first reflector 1 and the third reflector 3, as shown below. Figure 3 As shown, this solves the need for rapid detection and compensation of processing errors.

[0039] To meet the requirements of small size and light weight in optoelectronic systems, microcrystalline aluminum is selected as the material for the core components: the first reflector 1, the second reflector 2, and the third reflector 3. Furthermore, the reflectors, substrate 4, and frame 9 are designed as a single, homogeneous material. This improves the processing efficiency of the aspherical reflector. In other embodiments, ultra-precision aluminum alloys can be used as the material for the aforementioned components, or other aluminum-based materials that meet the requirements can be used.

[0040] The substrate 4 has a first mounting surface for mounting the first reflector 1 and a second mounting surface 4.1 for mounting the third reflector 3. The positions of the first mounting surface and the second mounting surface 4.1 on the substrate 4 are set based on the theoretical spatial positions of the first reflector 1 and the third reflector 3 in the optical design. The tilt angles of the first mounting surface and the second mounting surface 4.1 relative to the back surface of the substrate 4 are set based on the angle range that makes the first mounting surface and the second mounting surface 4.1 suitable for ultra-precision turning.

[0041] like Figure 2 , 4 As shown, the edge of the upper surface of the substrate 4 is provided with threaded holes for connecting to the back of the mirror frame 9; the outer side of the first mounting surface is provided with multiple threaded holes for mounting the first reflector 1; the outer side of the second mounting surface is provided with multiple threaded holes for mounting the third reflector 3; the upper surface of the mounting platform is provided with multiple threaded holes for connecting to the mirror frame; and stress isolation grooves 4.2 are provided around the threaded holes. By designing stress isolation grooves 4.2, the assembly stress caused by screw assembly is reduced and transferred to the reflector surface, thus preventing changes in the surface accuracy of the first reflector 1, the second reflector 2, and the third reflector 3 during assembly and improving assembly reliability.

[0042] like Figure 5 As shown, in the assembly design of the first reflector 1, the second reflector 2, the third reflector 3 with the substrate 4 and the frame 9, ultra-precision machining parameters and stress isolation design requirements are proposed for the assembly contact surfaces. The accuracy requirement for the mounting contact surface between the substrate 4 and the frame 9 is 0.004mm-0.006mm. In this embodiment, the surface shape accuracy requirement for the mounting contact surface 4.1 of the third reflector 3 and the stress isolation groove 4.2 is preferably 0.005mm. The stress isolation groove 4.2 avoids changes in surface shape accuracy during the assembly of the reflectors, thus improving assembly reliability.

[0043] like Figure 4 As shown, the structure of the second reflector 2 is designed. An optical reflecting surface 2.1 and a positioning reference surface 2.2 are designed on the mirror body of the second reflector 2. The positional accuracy requirement of the positioning reference surface 2.2 is 0.004mm-0.006mm. In this embodiment, the preferred positional accuracy requirement is 0.005mm, which ensures the positional accuracy requirements of the second reflector 2 and the second reflector frame during installation.

[0044] This invention also provides a rapid assembly and adjustment method for an aluminum-based skew-axis large field-of-view off-axis three-mirror system, a method for assembling and adjusting the aforementioned aluminum-based skew-axis large field-of-view off-axis three-mirror system, comprising the following steps:

[0045] S1. Preparation of reference components and parts:

[0046] Prepare substrate 4; fix the substrates of the first reflector 1 and the third reflector 3 onto substrate 4 respectively; using the side and back of substrate 4 as references, process the optical reflective surfaces 2.1 of the first reflector 1 and the third reflector 3 in sequence by ultra-precision turning in one clamping; and use a common compensator to simultaneously detect the surface accuracy of the optical reflective surfaces 2.1 of the first reflector 1 and the third reflector 3 to process qualified reference components.

[0047] The positioning reference surface 2.2 on the mirror body of the second reflector 2 is machined by ultra-precision turning, and the optical reflecting surface 2.1 of the second reflector 2 is machined with the positioning reference surface 2.2 as the reference.

[0048] S2, System Integration and Fine-tuning:

[0049] The reference component is fixed to the back of the mirror frame 9, and the back normal of the substrate 4 is used as the optical axis reference for system assembly. Based on the optical axis reference, the spatial angle of the plane mirror 6 located in front of the first mirror 1 is determined by collimating the collimator with the back of the substrate 4. Then, the second mirror 2 is installed on the front of the mirror frame 9 through the mirror frame. Based on the optical axis reference, an optical detection path is established. The interferometer 5 is used to perform wavefront aberration detection on the optical system composed of the first mirror 1, the second mirror 2, and the third mirror 3. By adjusting the spatial attitude of the second mirror 2, the wavefront aberration of the system is made to meet the preset index.

[0050] This embodiment provides a rapid assembly and adjustment method for an aluminum-based oblique-axis large-field-of-view off-axis three-mirror system, transforming the difficulties of traditional assembly and adjustment into a precisely controllable machining and benchmark assembly problem. In the ultra-precision machining stage, this method utilizes the substrate 4 as a unified benchmark to form and verify the optical reflecting surfaces 2.1 of the first and third mirrors 1 and 3 in a single process, permanently solidifying the core optical path relationship and forming a "benchmark assembly." Subsequently, in the system integration and assembly stage, the principle of using the back normal of the substrate 4 as the system's optical axis benchmark is applied, and rapid initial mechanical positioning is achieved using the pre-fabricated positioning reference surface 2.2 on the second mirror 2. Ultimately, the assembly and adjustment of the entire complex system is simplified to only requiring wavefront aberration fine-tuning of the second mirror 2, thereby simplifying the assembly and adjustment process and improving efficiency.

[0051] The following is a detailed explanation of each step.

[0052] In step 1, based on the small size and light weight of the optoelectronic system and the requirements of the optical system, the optical design of the oblique axis large field of view off-axis three-mirror system is determined; among them, the first mirror 1, the second mirror 2, and the third mirror 3 all adopt an integrated design of mirror function configuration in terms of structure.

[0053] like Figure 1 , 5As shown, during the fabrication of substrate 4, the first mounting surface for mounting the first reflector 1 and the second mounting surface 4.1 for mounting the second reflector 2 are fabricated using the back and side surfaces of substrate 4 as references. Based on the theoretical poses of the first reflector 1 and the third reflector 3 in the optical design, the positional relationship between the first mounting surface and the second mounting surface 4.1 is determined by the side surface of substrate 4, and the tilt angle relationship between the first mounting surface and the second mounting surface 4.1 is determined by the back surface of substrate 4. Substrate 4, the first mounting surface, the second mounting surface, and the stress isolation groove 4.2 are fabricated.

[0054] In the optical design, the spatial orientation relationship between the first reflecting mirror 1 and the third reflecting mirror 3 includes: the height difference between the first reflecting mirror 1 and the third reflecting mirror 3 does not exceed 10mm, which is set based on not exceeding the processing capacity of the machine tool, and the center distance is designed based on the center distance requirements of the first reflecting mirror 1 and the third reflecting mirror 3.

[0055] like Figure 3 As shown, the substrates of the first reflector 1 and the third reflector 3 are mounted on the substrate 4. Ultra-precision turning is used to conformally machine the substrates of the first reflector 1 and the third reflector 3 with reference to the side and back sides of the substrate. Simultaneously, the surface machining of the first reflector 1 and the third reflector 3 is designed to meet the smoothness requirements of the turning process, enabling the machining of two mirror surfaces in a single setup. The machine tool's positional accuracy ensures the mirror surfaces and positions of the two reflectors, avoiding the need for precise spatial adjustments by the assembly personnel. Microcrystalline aluminum, suitable for ultra-precision turning, is selected as the substrate for the reflectors, achieving high surface accuracy and improving machining and assembly efficiency. After machining, an interferometer 5 and a designed shared compensator are used to simultaneously inspect the machined first reflector 1 and the third reflector 3.

[0056] The shared compensator is designed according to the following idea: Based on the surface equations of the first reflector 1 and the third reflector 3, and according to Fermat's equal optical path principle, the phase distribution at any point on the compensator can be obtained. Based on the relative theoretical positions of the first reflector 1 and the third reflector 3, the compensators used for the first reflector 1 and the second reflector 3 are designed on a substrate material to complete the design of the shared compensator.

[0057] When machining the second reflector 2 using ultra-precision turning technology, the positioning reference surface 2.1 and the reflecting optical surface on it are machined simultaneously. This ensures the positional accuracy requirements of the second reflector 2 and the mirror frame during installation, providing a reference for the assembly and adjustment of the second reflector 2 and improving the system's assembly and adjustment efficiency. It also provides a reference for the assembly and adjustment of the second reflector 2 in the off-axis three-mirror system, further improving the system's assembly and adjustment efficiency.

[0058] The mirror frame and mirror housing 9 are machined using ultra-precision turning technology. The surface accuracy of the contact surface on the mirror frame used to install the second reflecting mirror 2, as well as the contact surface between the mirror frame and the mirror housing 9, is 0.004mm-0.006mm. The surface accuracy of the contact surface between the mirror housing 9 and the substrate 4 is required to be 0.004mm-0.006mm.

[0059] In step 2, such as Figure 6 , 7 As shown in Figure 8, the qualified reference component is installed on the back of the mirror frame 9 via the substrate 4, and the second reflector 2 is installed on the front of the mirror frame 9. The back of the substrate 4 is used as the positioning and orientation reference to provide a reference for the installation and adjustment of the incident angle of the off-axis three-mirror system. Specifically, a plane mirror 7 is installed on the back of the first reflector 1, which is the back of the substrate 4, and the angle of the off-axis three-mirror system is determined by the theodolite 8 through autocollimation, which is the incident angle.

[0060] The back of the substrate 4 is on the same plane as the back of the mirror frame, and the optical reflecting surfaces 2.1 of the first reflecting mirror 1 and the third reflecting mirror 3 face the front of the mirror frame 9. The second reflecting mirror 2 is mounted on the front of the mirror frame 9 through the mirror frame, and the second reflecting mirror 2 is opposite to the optical reflecting surfaces 2.1 of the first reflecting mirror 1 and the second reflecting mirror 2.

[0061] The incident angle is determined based on the surface normal direction on the back of the substrate 4. The plane mirror 7 is installed based on the incident angle, and the attitude of the second reflector 2 is adjusted so that the laser emitted by the interferometer 5 is reflected to the plane mirror 7 after passing through the third reflector 3, the second reflector 2, and the first reflector 1, and returns along the original path to form phase interference fringes and system wave aberration.

[0062] like Figure 6 As shown, after the off-axis three-mirror system wave aberration is qualified, the off-axis field-of-view wave aberration is detected by rotating the plane mirror 6 by an angle. If the off-axis directional wave aberration is asymmetrical, the second mirror 2 can be reinstalled and adjusted. The spatial attitude of the second mirror 2 is adjusted based on the phase interference fringes and the systematized wave aberration.

[0063] Under the effective aperture conditions of an off-axis three-mirror system, the surface shape accuracy of the first mirror 1 and the third mirror 3 detected by a shared compensator is better than 0.025. ( In an off-axis three-mirror system, the required detection accuracy is a wavefront aberration Rms better than 0.066. ( ).

[0064] The specific processing and assembly should be carried out according to the following methods:

[0065] 1. Parts processing: mainly complete the processing of mechanical parts, including base plate 4, mirror frame 9, mirror frame, and mirror frame. At the same time, process the blanks of the first reflecting mirror 1, the second reflecting mirror 2, and the third reflecting mirror 3. The assembly contact surfaces of base plate 4, mirror frame 9, and mirror frame are required to reach a certain surface accuracy. The blank processing of the three mirrors shall produce each feature platform and stress relief groove 4.2.

[0066] 2. Machining the first reflecting mirror 1: Machining the first reflecting mirror 1 on an ultra-precision diamond lathe, using the feature platform and side surface of the first reflecting mirror 1 blank as references, until the surface shape meets the required specifications. Simultaneously, using this reference, precision-machine the second reflecting mirror 2, until the surface shape accuracy meets the required specifications.

[0067] 3. Machining the third reflecting mirror 3: Before machining, assemble the first reflecting mirror 1 onto the substrate 4, and accurately position the first reflecting mirror 1 using a coordinate measuring machine (CMM). Then, use the CMM to control the assembly of the third reflecting mirror 3 blank onto the substrate 4, ensuring the assembly position meets the design requirements. Machining the third reflecting mirror 3 is performed on a diamond lathe on the substrate 4. After the first machining pass, the surface accuracy of the first reflecting mirror 1 and the third reflecting mirror 3 can be checked using a CGH compensator combined with an interferometer. During the check, the surface accuracy of the third reflecting mirror 3 is checked using the good surface accuracy of the first reflecting mirror 1 as a reference, and the error between the surface accuracy and the theoretical surface accuracy is detected. This error is compensated for and then further processed on the diamond lathe for finishing. After machining, the surface accuracy is checked again, and the compensation is repeated until the surface accuracy of the first reflecting mirror 1 and the third reflecting mirror 3 meets the required specifications, as determined by the interferometer and CGH compensator.

[0068] 4. The assembly substrate 4, including (first reflector 1 and third reflector 3), is assembled on the mirror frame 9. The interferometer 5 and CGH compensator are used to check that the surface shape of the first reflector 1 and the third reflector 3 meets the index requirements, so as to avoid the deformation of the substrate caused by assembly contact surface error, which would affect the accuracy of the first reflector 1 and the third reflector 3.

[0069] 5. Assemble the mirror frame and the second reflecting mirror 2.

[0070] 6. System installation and adjustment

[0071] The back normal of substrate 4 is used as the optical axis reference for system assembly and adjustment; the back of substrate 4 is used as the positioning and orientation reference, and the second reflector 2 is mounted on the frame 9 through the mirror bracket; an optical detection path is established based on the optical axis reference, and a large-diameter plane reflector 6 is set up with a theodolite 8, which has an off-axis angle with the back of substrate 4. The interferometer 5 is used to perform wavefront aberration detection on the optical system composed of the first reflector 1, the second reflector 2, and the third reflector 3, and the system wavefront aberration is made to meet the preset index by adjusting the spatial attitude of the second reflector 2.

[0072] Finally, it should be noted that the features mentioned and / or shown in the above description of exemplary embodiments of the present invention can be combined in the same or similar manner with one or more other embodiments, combined with features in other embodiments, or substituted for corresponding features in other embodiments. These combined or substituted technical solutions should also be considered to be included within the scope of protection of the present invention.

Claims

1. An aluminum-based oblique-axis large field-of-view off-axis three-mirror system, comprising a first mirror (1), a second mirror (2), and a third mirror (3), wherein the spatial orientation of the first mirror (1), the second mirror (2), and the third mirror (3) is such that the incident beam is reflected sequentially by the first mirror (1), the second mirror (2), and the third mirror (3) before exiting, and the optical axis of the first mirror (1) and the optical axis of the third mirror (3) have a non-zero off-axis angle, thereby forming an off-axis three-mirror optical structure; characterized in that, The first reflector (1), the second reflector (2), and the third reflector (3) are all integral reflectors. The optical reflecting surface (2.1) and the mirror mounting structure are integrally formed by ultra-precision machining. The off-axis three-reflector system also includes a substrate (4) and a mirror frame (9). The first reflector (1) and the third reflector (3) are mounted on the upper surface of the substrate (4), and the mounting positions of the first reflector (1) and the third reflector (3) are determined based on the spatial theoretical positions in the optical design; the optical reflecting surfaces (2.1) of the first reflector (1) and the third reflector (3) mounted on the substrate (4) are conformally processed with the same reference. The frame (9) is hollow inside and has openings at both ends, and is used to connect the substrate (4) and the second reflector (2). The substrate (4) is installed at the opening on the back of the mirror frame (9), and the second reflector (2) is installed at the opening on the front of the mirror frame (9) through the mirror frame. The optical reflective surface (2.1) of the second reflector (2) is opposite to the optical reflective surface (2.1) of the first reflector (1) and the optical reflective surface (2.1) of the third reflector (3). The outer side of the mirror body of the second reflector (2) has a plurality of mounting platforms that are fitted with the mirror frame. The mounting platforms have a positioning reference surface (2.2) for processing the optical reflecting surface (2.1) of the second reflector (2) and for assembling and adjusting the second reflector (2). The positioning reference surface (2.2) is perpendicular to the bottom surface of the mirror body of the second reflector (2).

2. The aluminum-based oblique-axis large field-of-view off-axis three-mirror system according to claim 1, characterized in that, The materials of the first reflector (1), the second reflector (2), the third reflector (3), the substrate (4), and the frame (9) are all microcrystalline aluminum.

3. The aluminum-based oblique-axis large field-of-view off-axis three-mirror system according to claim 1 or 2, characterized in that, The substrate (4) is provided with a first mounting surface for mounting the first reflector (1) and a second mounting surface (4.1) for mounting the third reflector (3); the positions of the first mounting surface and the second mounting surface (4.1) on the substrate (4) are set based on the spatial theoretical positions of the first reflector (1) and the third reflector (3) in the optical design.

4. The aluminum-based oblique-axis large field-of-view off-axis three-mirror system according to claim 3, characterized in that, The edge of the upper surface of the substrate (4) is provided with threaded holes for connecting to the back of the mirror frame (9); The outer side of the first mounting surface is provided with a plurality of threaded holes for mounting the first reflector (1); The outer side of the second mounting surface (4.1) is provided with a plurality of threaded holes for mounting the third reflector (3); The upper surface of the mounting platform is provided with multiple threaded holes for connecting to the eyeglass frame; The threaded hole is provided with a stress isolation groove (4.2) on its outer periphery.

5. The aluminum-based oblique-axis large field-of-view off-axis three-mirror system according to claim 4, characterized in that, The surface accuracy requirements for the first mounting surface, the second mounting surface (4.1), and the stress isolation groove (4.2) are 0.004mm-0.006mm; The required positional accuracy of the positioning reference surface (2.2) is 0.004mm-0.006mm.

6. A rapid assembly and adjustment method for an aluminum-based skew-axis large field-of-view off-axis three-mirror system, used for assembling and adjusting the aluminum-based skew-axis large field-of-view off-axis three-mirror system according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Preparation of reference components and parts: Prepare substrate (4); fix the substrates of the first reflector (1) and the third reflector (3) onto the substrate (4) respectively. Using the side and back of the substrate (4) as reference, the optical reflective surfaces (2.1) of the first reflector (1) and the third reflector (3) are processed sequentially by ultra-precision turning in one clamping. The surface accuracy of the optical reflective surfaces (2.1) of the first reflector (1) and the third reflector (3) is detected synchronously using a common compensator to process qualified reference components. The positioning reference surface (2.2) on the mirror body of the second reflector 2 is machined by ultra-precision turning, and the optical reflecting surface (2.1) of the second reflector (2) is machined with the positioning reference surface (2.2) as the reference. S2, System Integration and Fine-tuning: The reference component is fixed to the back of the frame (9), and the back normal of the substrate (4) is used as the optical axis reference for system assembly. Based on the optical axis reference, the spatial angle of the plane mirror (6) located in front of the first mirror (1) is determined by collimator and self-collimation of the back of the substrate (4). Then, the second mirror (2) is installed on the front of the mirror frame (9) through the mirror frame. Based on the optical axis reference, an optical detection path is established. The interferometer (5) is used to detect the wavefront aberration of the optical system. By adjusting the spatial orientation of the second mirror (2), the wavefront aberration of the system meets the preset index.

7. The rapid assembly and adjustment method according to claim 6, characterized in that, In step 1, when the substrate (4) is prepared, the first mounting surface for mounting the first reflector (1) and the second mounting surface for mounting the second reflector (2) are processed based on the back and side surfaces of the substrate (4); based on the theoretical pose of the first reflector (1) and the third reflector (3) in the optical design, the positional relationship between the first mounting surface and the second mounting surface (4.1) is determined by the side surface of the substrate (4), and the tilt angle relationship between the first mounting surface and the second mounting surface (4.1) is determined by the back surface of the substrate (4).

8. The rapid assembly and adjustment method according to claim 6, characterized in that, In step 2, the incident angle of the off-axis three-mirror system is determined based on the optical axis reference, and the plane mirror (6) is installed based on the incident angle; the optical detection path detection is specifically as follows: the laser emitted by the interferometer (5) is reflected to the plane mirror (6) after passing through the third mirror (3), the second mirror (2), and the first mirror (1), and returns along the original path to form phase interference fringes and system wavelet aberration.

9. The rapid assembly and adjustment method according to claim 6, characterized in that, In step 2, the plane mirror (6) detects the off-axis directional wave aberration formed by the first mirror (1), the second mirror (2) and the third mirror (3). If the off-axis directional wave aberration is asymmetrical, the spatial attitude of the second mirror (2) is adjusted until the off-axis directional wave aberration is symmetrical and meets the wave aberration index requirements of the off-axis three-mirror system, thus completing the assembly and adjustment of the off-axis three-mirror system.

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