Adjustment method suitable for large-aperture long-focal-length total-reflection type optical system

Abstract

The invention belongs to the technical field of precise optical machine adjustment testing, and provides an adjustment method suitable for a large-caliber long-focus total reflection type optical system, which is used for solving the problem of low adjustment efficiency of the long-focus total reflection type optical system, and can be used for positioning a primary mirror and a secondary mirror in a high-precision manner by manufacturing primary and secondary mirror detection areas through a CGH compensator. The folding lens and the focusing lens are fixed according to optical axis reference transmission, and the three lenses are iteratively and finely adjusted in combination with computer assistance. According to the invention, the degree of freedom of adjustment of the total-reflection space camera optical system can be reduced from 30 to 5, the adjustment efficiency is improved, and high-precision adjustment of the large-aperture long-focal-length total-reflection space camera optical system is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of precision optical and mechanical assembly and testing. Background Art

[0002] With the development of science and technology, aerospace remote sensing technology has been widely used in fields such as agriculture, surveying and mapping, ocean exploration, and military reconnaissance, becoming one of the important means for people to obtain spatial information. Space cameras have also developed in the direction of high resolution, and the focal length has continued to increase. Totally reflective optical systems can achieve the requirements of long focal length and large field of view, improving image quality. However, the optical system of a long-focal-length, fully reflective space camera contains five reflectors: a primary mirror, a secondary mirror, a tertiary mirror, a folding mirror, and a focusing mirror. The large number of reflectors leads to an increase in the number of adjustable variables. During the assembly and adjustment of the optical system, the relative spatial positions of each reflector are difficult to accurately adjust, resulting in low adjustment efficiency and increased difficulty in assembly and detection, which has restricted the development of fully reflective space cameras.

[0003] The CGH (Computer-generated hologram) compensator is a binary diffraction optical element, and its theoretical basis is the wavefront recording and wavefront reconstruction principle in traditional optical holography. CGH creates a diffraction pattern on a substrate and uses the diffraction effect to modulate the incident wavefront, so that the test wavefront propagates to the measured surface and ideally matches it. The CGH compensator is used in the field of interferometric detection of aspheric surfaces due to its unique wavefront transformation capability and simple structure for easy installation and adjustment. The existing multi-mirror detection feature of the CGH compensator is used for off-axis reflective system installation and adjustment. The existing technology can only position the main mirror and two mirrors of the third mirror, and there are still many degrees of freedom of the mirrors that need to be adjusted. Summary of the Invention

[0004] In order to further improve the efficiency and accuracy of the alignment of large-aperture, long-focal-length total reflection optical systems, the present invention proposes an alignment method for large-aperture, long-focal-length total reflection optical systems, such as Figure 1 As shown, the following steps are included:

[0005] Step 1: Figure 2 As shown, the CGH compensator 1 substrate is divided as follows according to the reflector to be adjusted:

[0006] A circular detection area 101 coinciding with the center of the substrate is used to detect the secondary mirror shape and determine the secondary mirror spatial position;

[0007] The concentric circular detection area 2 102 located outside the detection area 101 is used to detect the main mirror shape and determine the main mirror spatial position;

[0008] A square reflecting area 103 is located above the second detection area 102, and the normal line of the reflecting area 103 is used as the reference optical axis during the adjustment process;

[0009] The remaining area after removing the detection area 101, the detection area 2 102 and the reflection area 103 is the alignment area 104, which is used for interference alignment with the interferometer 4;

[0010] Step 2: Adjust the position of the interferometer 4 to align with the alignment area 104;

[0011] Step 3: Determine the position of the primary mirror 2: Figure 3 As shown, the wavefront emitted by the interferometer passes through the detection area 2 102 and the primary mirror and then returns to the interferometer. The posture of the primary mirror is adjusted so that the light reflected back to the interferometer 4 forms zero-order fringes after interference on the interferometer and the wave aberration meets the requirements. The surface accuracy test of the primary mirror 2 is completed, the actual measuring optical axis is connected to the reference optical axis, and the position of the primary mirror is determined.

[0012] Step 4: Determine the position of the secondary mirror 3: Figure 3 As shown, the wavefront emitted by the interferometer passes through the detection area 101 and then returns to the secondary mirror and the interferometer. The posture of the secondary mirror is adjusted so that the light reflected back to the interferometer 4 forms zero-order fringes after interference on the interferometer and the wave aberration meets the requirements. The surface accuracy test of the secondary mirror 3 is completed, the actual measuring optical axis is connected to the reference optical axis, and the position of the secondary mirror is determined.

[0013] Step 5: Determine the position of the folding mirror 5: Figure 4 As shown, the interferometer is removed, theodolite 1 601 is aligned with the reflection area 103, the optical axis is folded 90° and then transferred to theodolite 2 602 to achieve self-alignment of the two theodolites, and the posture of the folding mirror 5 is adjusted so that the folding mirror folds the optical axis 45°, and the position of the folding mirror is determined;

[0014] Step 6: Determine the position of the focusing mirror 7: Figure 5 As shown, the optical axis is folded 90° and then transferred to theodolite 3 603 on the opposite side of theodolite 2 602 to achieve self-alignment of the two theodolites. Theodolite 3 is self-aligned with the back reference of the focusing mirror, and the posture of the focusing mirror is adjusted so that the pitch direction and yaw direction of the focusing mirror meet the requirements of the 90° folding of the optical axis. The position of the focusing mirror 7 is determined.

[0015] Step 7: Figure 6 As shown, the CGH compensator is removed, a plane mirror 9 is provided on the left side of the secondary mirror 3, and a dynamic interferometer 10 is provided at the focal plane position of the optical system. The wave aberration of the optical system is tested by the self-collimation interference method. Combined with the wave aberration values and the Zernike coefficient measured in each field of view, the postures of the three mirrors 8 are adjusted iteratively with the aid of a computer until the wave aberration of each field of view of the optical system meets the requirements, the positions of the three mirrors are determined, and the assembly and adjustment of the long-focal-length total reflection optical system is completed.

[0016] Technical effects:

[0017] The present invention provides a method for assembling and adjusting a large-aperture, long-focal-length, fully reflective optical system. The method detects the surface accuracy of the primary and secondary mirrors through a CGH compensator to determine the spatial positions of the primary and secondary mirrors. Simultaneously, the positions of the folding mirror and the focusing mirror are precisely positioned in combination with the coating area on the CGH compensator that represents the optical axis. Ultimately, the 30 degrees of freedom of the five reflective mirrors in the optical system are reduced to a total of 5 degrees of freedom of the three mirrors, namely, pitch, yaw, up and down, front and back, and left and right, thereby achieving high-precision and high-efficiency assembly and adjustment of the large-aperture, long-focal-length, fully reflective optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flowchart of the overall process of the present invention.

[0019] Figure 2 Schematic diagram of the CGH compensator substrate in the present invention.

[0020] Figure 3 Schematic diagram of the adjustment system when positioning the primary and secondary mirrors.

[0021] Figure 4 Schematic diagram of the adjustment system for positioning the folding mirror.

[0022] Figure 5 Schematic diagram of the adjustment system when positioning the focusing mirror.

[0023] Figure 6 Schematic diagram of the overall test optical path when adjusting three mirrors using the self-collimation interferometer method.

[0024] Among them, 1. CGH compensator, 101. Detection area 1, 102. Detection area 2, 103. Reflection area, 104. Alignment area, 2. Primary mirror, 3. Secondary mirror, 4. Interferometer, 5. Folding mirror, 601. Theodolite 1, 602. Theodolite 2, 603. Theodolite 3, 7. Focusing mirror, 8. Three mirrors, 9. Plane mirror, 10. Dynamic interferometer. DETAILED DESCRIPTION

[0025] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] After the CGH compensator 1 substrate is divided, it is mounted on an adjustment frame, and the interferometer 4 is mounted on the interferometer adjustment frame. When the wavefront emitted by the interferometer 4 is aligned with the alignment area 104 through the interferometer standard lens and returns to the interferometer 4 to generate interference fringes, the interferometer 4 is adjusted in posture by adjusting the interferometer adjustment frame. When the interference fringes become zero-order fringes, the interference alignment between the interferometer 4 and the alignment area 104 is completed.

[0027] After the positions of the primary and secondary mirrors are determined, remove the interferometer 4. Figure 4As shown, theodolite 1 601 is aligned with reflective area 103, and the reference optical axis is transferred to theodolite 1 601. A mechanical reference transfer method allows theodolite 1 601 and theodolite 2 602 to align with each other. After the optical axis is rotated 90°, the reference optical axis is transferred to theodolite 2 602, achieving self-alignment of the two theodolites. Light emitted by theodolite 2 602 passes through folding mirror 5 and is incident on CGH compensator 1. The light is then reflected back by folding mirror 5 and incident on theodolite 2 602. The spatial position of folding mirror 5 is adjusted so that the incident light coincides with the crosshairs in theodolite 2 602. Folding mirror 5 then rotates the optical axis 45°, completing the position adjustment of folding mirror 5.

[0028] like Figure 5 As shown, theodolite 2 602 is removed and theodolite 3 603 is provided. A mechanical reference transfer method is used to align theodolite 1 601 and theodolite 3 603. After the optical axis is rotated 90°, the reference optical axis is transferred to theodolite 3 603, achieving self-alignment of the two theodolites. Light emitted by theodolite 3 603 is aligned with the back of focusing lens 7. The spatial orientation of focusing lens 7 is adjusted so that the self-aligning light coincides with the crosshairs on theodolite 3 603. The pitch and yaw directions of focusing lens 7 satisfy the 90° rotation of the optical axis, completing the position adjustment of focusing lens 7.

[0029] like Figure 6 As shown, a plane mirror 9 and a dynamic interferometer 10 are used to construct an optical path for self-alignment testing of the optical system. The plane mirror 9 is provided to the left of the secondary mirror 3, and the dynamic interferometer 10 is provided at the focal plane of the optical system. The light emitted by the dynamic interferometer 10 passes through the focusing mirror 7, the third mirror 8, the folding mirror 5, the secondary mirror 3, and the primary mirror 2 before being incident on the plane mirror 9. The light then returns along the original path and enters the dynamic interferometer 10 to produce interference fringes. The self-alignment interferometry method is used to measure the optical system wavefront aberration and various Zernike coefficients corresponding to the fields of view of ±1, ±0.5, and 0. A computer-assisted alignment method is used to calculate wavefront aberration and other data to guide the precise adjustment of the three mirrors 8 in the five dimensions of yaw, pitch, up and down, left and right, and front and back. The angle of the plane mirror 9 and the position of the dynamic interferometer 10 are simultaneously adjusted so that the wavefront aberration of each field of view meets the system requirements. The adjustment of the three mirrors 8 is completed, and the long-focal-length total reflection optical system is assembled and aligned.

[0030] The contents not described in detail in this specification belong to the existing technology known to those skilled in the art. At the same time, for those skilled in the art, according to the concept of the present invention, there may be changes in the specific implementation methods and application scope. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A method for assembling and adjusting a large-aperture, long-focal-length, fully reflective optical system, characterized in that: The steps include: Step 1: Divide the CGH compensator (1) substrate into the following sections according to the reflectors to be adjusted: A circular detection area (101) coinciding with the center of the substrate is used to detect the secondary mirror shape and determine the secondary mirror spatial position; A concentric circular detection area 2 (102) located on the outer circle of the detection area 1 (101) is used to detect the main mirror surface shape and determine the main mirror spatial position; A square reflecting area (103) is located above the second detection area (102), and a normal line of the reflecting area (103) is used as a reference optical axis during the adjustment process; The remaining area after removing the detection area 1 (101), the detection area 2 (102) and the reflection area (103) is the alignment area (104), which is used for interference alignment with the interferometer (4); Step 2, adjusting the position of the interferometer (4) to align the interferometer with the alignment area (104); Step 3, determining the position of the primary mirror (2): the wavefront emitted by the interferometer (4) passes through the detection area 2 (102) and the primary mirror (2) and then returns to the interferometer (4). The posture of the primary mirror is adjusted so that the light reflected back to the interferometer (4) forms zero-order fringes after interference on the interferometer and the wave aberration meets the requirements. The surface accuracy detection of the primary mirror (2) is completed, the actual measuring optical axis is connected to the reference optical axis, and the position of the primary mirror (2) is determined; Step 4, determining the position of the secondary mirror (3): the wavefront emitted by the interferometer (4) passes through the detection area 1 (101) and then returns to the secondary mirror (3) and the interferometer (4). The posture of the secondary mirror is adjusted so that the light reflected back to the interferometer (4) forms zero-order fringes after interference on the interferometer and the wave aberration meets the requirements. The surface accuracy detection of the secondary mirror (3) is completed, the actual measuring optical axis is connected to the reference optical axis, and the position of the secondary mirror (3) is determined; Step 5, determining the position of the folding mirror (5): remove the interferometer, align the theodolite 1 (601) with the reflection area (103), fold the optical axis 90° and transfer it to the theodolite 2 (602) to achieve self-alignment of the two theodolites, adjust the posture of the folding mirror (5) so that the folding mirror folds the optical axis 45°, and the position of the folding mirror (5) is determined; Step 6, determining the position of the focusing mirror (7): after the optical axis is folded 90°, it is transferred to theodolite 3 (603) on the opposite side of theodolite 2 (602) to realize the self-alignment of the two theodolites. Theodolite 3 (603) and the back reference of the focusing mirror (7) are self-aligned, and the posture of the focusing mirror (7) is adjusted so that the pitch direction and the yaw direction of the focusing mirror (7) meet the requirement of the optical axis folding 90°. The position of the focusing mirror (7) is determined; Step 7: Remove the CGH compensator, provide a plane reflector (9) on the left side of the secondary mirror (3), provide a dynamic interferometer (10) at the focal plane position of the optical system, use the self-collimation interference method to test the wave aberration of the optical system, combine the wave aberration values measured in each field of view and the Zernike coefficient, and iteratively adjust the posture of the three mirrors (8) with the aid of a computer until the wave aberration of each field of view of the optical system meets the requirements. The position of the three mirrors (8) is determined, and the long focal length total reflection optical system is assembled and adjusted.

2. The method for assembling and adjusting a large-aperture, long-focal-length, total-reflection optical system according to claim 1, characterized in that: When the wavefront emitted by the interferometer (4) is aligned with the alignment area (104) through the interferometer standard lens and returns to the interferometer (4), interference fringes are generated. When the interference fringes become zero-order fringes by adjusting the interferometer (4), the interference alignment between the interferometer (4) and the alignment area (104) is completed.

3. The method for assembling and adjusting a large-aperture, long-focal-length, total-reflection optical system according to claim 1, characterized in that: The first theodolite (601) is self-aligned with the reflection area (103), and the reference optical axis is transferred to the first theodolite (601). The mechanical reference transfer method makes the first theodolite (601) and the second theodolite (602) aim at each other. After the optical axis is folded 90 degrees, the reference optical axis is transferred to the second theodolite (602) to realize the self-alignment of the two theodolites. The light emitted by the second theodolite (602) is incident on the CGH compensator (1) through the folding mirror (5). The light is reflected back to the folding mirror (5) through the CGH compensator (1) and is incident on the second theodolite (602). The spatial posture of the folding mirror (5) is adjusted so that the incident light coincides with the crosshairs in the second theodolite (602). The folding mirror (5) folds the optical axis 45 degrees, and the position adjustment of the folding mirror (5) is completed.

4. The method for assembling and adjusting a large-aperture, long-focal-length, total-reflection optical system according to claim 1, wherein: Theodolite 2 (602) is removed and theodolite 3 (603) is provided. The mechanical reference transfer method is used to make theodolite 1 (601) and theodolite 3 (603) aim at each other. After the optical axis is folded 90°, the reference optical axis is transferred to theodolite 3 (603) to realize the self-alignment of the two theodolites. The light emitted by theodolite 3 (603) is self-aligned with the back of the focusing mirror (7). The spatial posture of the focusing mirror (7) is adjusted so that the self-alignment light coincides with the crosshairs in theodolite 3 (603). The pitch direction and yaw direction of the focusing mirror (7) meet the 90° rotation of the optical axis. The position adjustment of the focusing mirror (7) is completed.

5. The method for assembling and adjusting a large-aperture, long-focal-length, total-reflection optical system according to claim 1, wherein: A plane reflector (9) and a dynamic interferometer (10) are used to construct an optical system self-collimation test light path. A plane reflector (9) is provided on the left side of a secondary mirror (3), and a dynamic interferometer (10) is provided at the focal plane position of the optical system. Light emitted by the dynamic interferometer (10) passes through a focusing mirror (7), a third mirror (8), a folding mirror (5), a secondary mirror (3), and a primary mirror (2) and then irradiates the plane reflector (9). The light then returns along the original path and is incident on the dynamic interferometer (10) to generate interference fringes. The method is used to measure the wave aberration and the zernike coefficients of the optical system corresponding to the viewing fields of ±1, ±0.5 and 0. The computer-aided adjustment method is used to calculate the wave aberration and other data, and guide the precise adjustment of the posture of the three mirrors (8). The adjustment dimensions are the five dimensions of deflection, pitch, up and down, left and right, and front and back. At the same time, the angle of the plane reflector (9) and the position of the dynamic interferometer (10) are adjusted so that the wave aberration of each viewing field meets the system requirements. The adjustment of the three mirrors (8) is completed, and the adjustment of the long focal length total reflection optical system is completed.

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