An optical system calibration method based on the aperture division of a corner cube prism

Abstract

This invention discloses an optical system calibration method based on aperture segmentation using cornerstone prisms, comprising a cornerstone prism array, an interferometer, and an optical system under test. The main steps are: (1) uniformly fixing cornerstone prisms onto a substrate according to the shape of the aperture of the optical system under test to form a cornerstone prism array; (2) adjusting the cornerstone prism array to cover the aperture of the optical system under test; (3) placing the interferometer at the focal point of the optical system under test, and the light waves emitted by the interferometer are reflected back by the cornerstone prism array after passing through the optical system under test, forming a multi-aperture interferogram; (4) acquiring multiple interferograms at once, calculating the wavefront slope of each region from the multiple interferograms, obtaining the wavefront through integration, and finally fitting to obtain the system wavefront aberration. This invention allows for flexible changes in the cornerstone prism splicing method for different apertures, quickly adapting to different optical systems, and is convenient to assemble and adjust, possessing good applicability.

Description

Technical Field

[0001] This invention belongs to the field of optical detection technology, specifically relating to an optical system calibration method based on the aperture division of a cornerstone prism. Background Technology

[0002] With advancements in optical design and manufacturing technologies, an increasing number of large-aperture optical components are being applied to advanced optical systems, enabling higher light-gathering capabilities and resolutions. However, this also increases the complexity of system assembly and adjustment. In the assembly and adjustment of large optical systems, measuring the system's assembly and adjustment errors allows for better evaluation and feedback of the system's accuracy. This measurement results guide the assembly and adjustment process, ensuring the system achieves the designed optical performance. Therefore, measuring assembly and adjustment errors is a crucial step in the optical system assembly and adjustment process.

[0003] A common method for testing optical systems is interferometric testing, which utilizes the interferometry of light. This involves detecting the wavefront under test by observing the interference between the wavefront and a reference wavefront. Autocollimating interferometry using a plane mirror matched to the aperture of the optical system under test is the most direct and effective method, allowing direct measurement of the system's wavefront aberration. However, this method is highly dependent on the fabrication of the plane mirror. For large-aperture optical systems, fabricating a matching large-aperture plane mirror is difficult, time-consuming, and costly, making it impractical for actual assembly and adjustment. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of existing technologies. It proposes an optical system calibration method based on the segmentation of apertures using a cornerstone prism. This method allows for flexible changes in the cornerstone prism splicing method for different apertures, quickly adapting to different optical systems. Furthermore, due to the retro-radiating characteristics of the cornerstone prism, it does not require precise adjustment of attitude and position as with plane mirrors, making this method more convenient and widely applicable.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] An optical system calibration method based on a cornerstone prism aperture division comprises the following steps:

[0007] Step 1: Divide the substrate into multiple sub-apertures according to the aperture of the optical system under test, and fix a small-aperture corner prism to each sub-aperture to form a corner prism array;

[0008] Step 2: Align the cornerstone prism array with the optical system under test, ensuring that the cornerstone prism array completely covers the aperture of the optical system under test;

[0009] Step 3: Place the interferometer at the focal point of the optical system under test. The light wave emitted by the interferometer is reflected by the pyramidal mirror array after passing through the optical system under test and returns. Establish a rectangular coordinate system XOY with the center of the outgoing wavefront of the optical system under test as the origin, and denote the outgoing wavefront as W(x,y). With the center of the pyramidal mirror array as the origin, its end face is taken as the X'O'Y' plane.

[0010] Step 4: Use a pyramidal prism array to measure and acquire multiple interferograms at once. The relative positions of the wavefronts corresponding to each interferogram are (x0, y0), (x1, y0), ..., (x i ,y0)

[0011] (x0,y0),(x0,y1),…,(x0,y i The slope of the tangent line at the center point of each sub-aperture of the wavefront being measured is K. xi (x,y),K yi (x,y); Wavefront reconstruction is performed using modal integration, with the wavefront W(x,y) constructed using an orthogonal polynomial F. k (x,y) represents: Where C k These are the coefficients of an orthogonal polynomial, where n is the number of terms; the average slope within the i-th sub-aperture is:

[0012] S i It is the area of ​​the sub-aperture, and the polynomial coefficients C k The wavefront W(x,y) and the system assembly error can be obtained by using the least squares method.

[0013] Furthermore, the number and aperture size of the cornerstone prisms depend on the optical system under test; the modal function F k (x,y) is selected based on the shape of the aperture of the optical system under test.

[0014] Furthermore, the cornerstone prism has the characteristics of a retro-radiator, which eliminates the need for precise adjustment of its orientation and position in the method.

[0015] Furthermore, the optical system under test includes a primary mirror and a secondary mirror, and the cornerstone prisms are uniformly fixed in two rows on the substrate in an alternating manner according to the shape of the annular region of the primary mirror.

[0016] Furthermore, in step 2, the projector is adjusted to be on the reference plane of the desired line; with the inner ring of the primary mirror as the reference, crosshairs are stretched on the back of the primary mirror, and similarly, crosshairs are stretched on the back of the secondary mirror; the projector is turned on and rotated horizontally so that the vertical laser line is simultaneously aligned with the crosshairs of the primary and secondary mirrors, thus achieving the projector on the optical axis of the ring telescope system.

[0017] Furthermore, in step 2, a crosshair is stretched at the center of the substrate so that the crosshairs of the pyramidal prism array are aligned with the projector and the ring telescope system.

[0018] Furthermore, the substrate is made of aluminum.

[0019] Compared with the prior art, the advantages of the present invention are:

[0020] This invention presents an optical system calibration method based on a cornerstone prism aperture division. It can measure the assembly and adjustment errors of large-aperture optical systems. By using a cornerstone prism to divide the optical system aperture for interferometry, the cornerstone prism can ensure that the reflected light returns along the incident light direction without changing the direction of the outgoing light, eliminating the need for precise adjustment of the cornerstone prism's attitude and position. This greatly simplifies assembly and adjustment. This method can quickly and accurately measure the assembly and adjustment errors of optical systems, providing reliable and accurate feedback and evaluation for assembly and adjustment testing, ensuring that the performance of the optical system meets design requirements. This invention is highly versatile and applicable to various optical systems. The testing process is simple, and it only introduces wavefront aberrations with low spatial frequencies, facilitating identification and subsequent assembly and adjustment. Attached Figure Description

[0021] Figure 1 This is a flowchart of the optical system calibration method of the present invention;

[0022] Figure 2 This is a schematic diagram of the sub-aperture of a 2m annular primary mirror;

[0023] Figure 3 This is a schematic diagram of the detection optical path;

[0024] Figure 4 This is a diagram of a crosshair.

[0025] The markings in the diagram are: 1-Laser line projector, 2-Pyramidal prism, 3-Substrate, 4-Interferometer, 5-Crosswire, 6-Primary mirror, 7-Secondary mirror. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings.

[0027] This invention presents an optical system calibration method based on the use of cornerstone prisms to divide the aperture. This method can conveniently measure the assembly and adjustment errors of different large-aperture optical systems, thereby guiding the calibration of the optical system. This invention uses a cornerstone prism array instead of large-aperture plane mirrors for precise assembly and adjustment. The cornerstone prism array consists of N small-aperture cornerstone prisms arranged according to the aperture shape of the optical system under test.

[0028] like Figure 1 As shown, the optical system calibration method based on the aperture division of a cornerstone prism of the present invention includes the following steps:

[0029] Step 1: Divide the substrate (the substrate is customized according to the optical aperture) into multiple sub-regions according to the aperture of the optical system under test, and fix a small-aperture corner prism in each sub-region to form a corner prism array. The total number and aperture size of the corner prisms depend on the optical system under test.

[0030] Step 2: Align the cornerstone prism array with the optical system under test, ensuring that the cornerstone prism array completely covers the aperture of the optical system under test.

[0031] Step 3: Place the interferometer at the focal point of the optical system under test. The light wave emitted by the interferometer is reflected back by the prism array after passing through the optical system under test. Establish a rectangular coordinate system XOY with the center of the outgoing wavefront of the optical system under test as the origin, and denote the outgoing wavefront as W(x,y); with the center of the prism array as the origin, its end face is taken as the X'O'Y' plane.

[0032] Step 4: Using a pyramidal prism array, multiple interferograms can be acquired simultaneously. The relative positions of the wavefronts corresponding to each interferogram are (x0, y0), (x1, y0), ..., (x...). i ,y0);(x0,y0),(x0,y1),…,(x0,y i The slope of the tangent at the center point of each sub-aperture of the wavefront being measured is K. xi (x,y),K yi (x,y). Wavefront reconstruction is performed using modal analysis for integration. The wavefront W(x,y) can be represented by an orthogonal polynomial F. k (x,y) represents: Where C k The coefficients are orthogonal polynomials, n is the number of terms, and F is the modal function. k (x, y) can be selected based on the shape of the aperture of the optical system under test. The average slope within the i-th sub-aperture can be written as: S i It is the area of ​​the sub-aperture, and the polynomial coefficients C k The wavefront W(x,y) and the system assembly error can be obtained by using the least squares method.

[0033] The following explanation uses a 2m ring telescope system as an example.

[0034] Step 1 (e.g.) Figure 2 As shown): Based on the aperture of the 2m annular primary mirror 6, it is divided into several sub-apertures. The corner cube prisms 2 are evenly fixed in two rows on the substrate 3 in an alternating manner according to the shape of the annular area of ​​the primary mirror 6. The substrate 3 can be made of aluminum plate.

[0035] Step 2: Adjust the projection device 1 onto the reference plane where the line is to be projected. Using the inner ring of the primary mirror as a reference, stretch crosshairs 5 on the back of the primary mirror 6, and similarly stretch crosshairs 5 on the back of the secondary mirror 7. Crosshairs 5 are as follows... Figure 4 As shown. Turn on the projector 1 and rotate the instrument horizontally so that the vertical laser line is simultaneously aligned with the primary mirror 6 and the crosshair 4 of the secondary mirror 7, thus aligning the projector 1 with the optical axis of the ring telescope system.

[0036] Step 3 (e.g.) Figure 3 As shown): A crosshair 5 is fixed at the center position of the fixed pyramidal prism array 2. The crosshair 5 of the pyramidal prism array 2 is aligned with the projector 1 and the ring telescope system.

[0037] Step 4 (e.g.) Figure 3 (As shown): Place the interferometer 4 at the focal point of the ring telescope system. Adjust the orientation and lateral translation of the cornerstone prism 2 array so that the light waves emitted by the interferometer 4 pass sequentially through the secondary mirror 7 and the primary mirror 6, are reflected by the cornerstone prism 2, and return, forming an interference pattern. Establish a rectangular coordinate system XOY with the center of the emitted wavefront of the primary mirror 6 as the origin, and denote the emitted wavefront as W(x,y). With the center of the substrate 3 as the origin, use the end face of the cornerstone prism 2 as the X'O'Y' plane.

[0038] Step 5: Use a pyramidal prism array 2 to simultaneously measure and acquire multiple interferograms. The relative positions of the wavefronts corresponding to each interferogram are (x0, y0), (x1, y0), ..., (x i ,y0);(x0,y0),(x0,y1),…,(x0,y i Using modal wavefront reconstruction, the slope of the tangent at the center point of each sub-aperture of the measured wavefront is: K x (x,y),K y (x,y), the wavefront function is described by a toroidal Zernike polynomial: but Where C k Here, is the coefficient of the orthogonal polynomial, and n is the number of terms. The Zernike polynomial coefficients C are solved using the least squares method. k The wavefront W(x,y) is obtained by fitting the data, which represents the system assembly error. Repeated measurements and iterative adjustments of the optical path are performed until the output wavefront PV and RMS meet the requirements.

[0039] The contents not described in detail in this specification are common knowledge to those skilled in the art.

[0040] In summary, the optical system calibration method based on the aperture division of a cornerstone prism in this invention includes a cornerstone prism array, an interferometer, and an optical system under test. The main steps are: (1) uniformly fixing the cornerstone prisms on a substrate according to the shape of the aperture of the optical system under test to form a cornerstone prism array; (2) adjusting the cornerstone prism array to cover the aperture of the optical system under test; (3) placing the interferometer at the focal point of the optical system under test, and the light wave emitted by the interferometer is reflected back by the cornerstone prism array after passing through the optical system under test, forming a multi-aperture interferogram; (4) acquiring multiple interferograms at once, calculating the wavefront slope of each region from the multiple interferograms, obtaining the wavefront through integration, and finally fitting to obtain the system wavefront aberration. The optical system calibration method based on the aperture division of a cornerstone prism in this invention can conveniently and accurately inspect and measure the assembly quality of large-aperture optical systems such as telescopes, providing a precise and reliable evaluation standard for subsequent assembly work.

[0041] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A calibration method for an optical system based on a cornerstone prism with segmented aperture, characterized in that, Follow these steps: Step 1: Divide the substrate into multiple sub-apertures according to the aperture of the optical system under test, and fix a small-aperture corner prism to each sub-aperture to form a corner prism array; Step 2: Align the cornerstone prism array with the optical system under test, ensuring that the cornerstone prism array completely covers the aperture of the optical system under test; Step 3: Place the interferometer at the focal point of the optical system under test. The light waves emitted by the interferometer are reflected back by the angular pyramidal mirror array of the optical system under test. A rectangular coordinate system XOY is established with the center of the outgoing wavefront of the optical system under test as the origin, and the outgoing wavefront is denoted as W(x,y); the center of the corner cube prism array is taken as the origin, and its end face is taken as the X'O'Y' plane. Step 4: Use a pyramidal prism array to measure and acquire multiple interferograms at once. The relative positions of the wavefronts corresponding to each interferogram are as follows: , The slope of the tangent at the center point of each sub-aperture of the wavefront under test is _____. ; Wavefront reconstruction is performed using modal integration, with the wavefront W(x,y) represented by an orthogonal polynomial. express: ,in These are the coefficients of an orthogonal polynomial, where n is the number of terms; the average slope within the i-th sub-aperture is: ， ， in, The area of ​​the sub-aperture is calculated using the least squares method to solve for the polynomial coefficients. The wavefront W(x,y) and system assembly error are obtained by fitting. The measurement and optical path are repeated and iteratively adjusted until the peak-to-valley value PV and root mean square value RMS of the emitted wavefront meet the requirements.

2. The optical system calibration method based on a cornerstone prism aperture division according to claim 1, characterized in that, The number and aperture size of the cornerstone prisms depend on the optical system under test; the modal function The selection is based on the shape of the aperture of the optical system under test.

3. The optical system calibration method based on a cornerstone prism aperture division according to claim 1, characterized in that, The cornerstone prism has the characteristics of a retroradiator, which means that the method does not require precise adjustment of its attitude and position.

4. The optical system calibration method based on a cornerstone prism aperture division according to claim 1, characterized in that, The optical system under test includes a primary mirror and a secondary mirror. The corner cube prisms are arranged in two rows on the substrate in an alternating manner, according to the shape of the annular region of the primary mirror.

5. The optical system calibration method based on a cornerstone prism aperture division according to claim 4, characterized in that, In step 2, adjust the projector to the reference plane where the line is to be projected; using the inner ring of the primary mirror as a reference, stretch the crosshairs on the back of the primary mirror, and similarly stretch the crosshairs on the back of the secondary mirror. Turn on the projector and rotate the instrument horizontally so that the vertical laser line is simultaneously aligned with the crosshairs of the primary and secondary mirrors, thus aligning the projector with the optical axis of the ring telescope system.

6. The optical system calibration method based on a cornerstone prism aperture division according to claim 5, characterized in that, In step 2, a crosshair is stretched at the center of the substrate so that the crosshairs of the pyramidal prism array are aligned with the projector and the ring telescope system.

7. The optical system calibration method based on a cornerstone prism aperture division according to claim 1, characterized in that, The substrate is made of aluminum plate.

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