CGH design method for detecting axisymmetric complex curved surface

Abstract

The invention belongs to the technical field of optical processing and detection, and particularly relates to a CGH design method for detecting an axisymmetric complex curved surface, which is characterized in that a half-side phase diagram is binarized according to the characteristics of axisymmetric parts, and the calculation power is saved through symmetric complementation subsequently; accurately determining a stripe curve contour through a Newton iteration method; based on a chord height error control method, adaptive fast coding of CGH stripe positions is realized, and stripe coding accuracy and processing error evaluation consistency are improved. And a Python writing program is applied to complete the generation of a processing file GDSII, and the processing file GDSII is saved in a segmented manner, so that the requirement on the computer performance is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of optical processing detection, and in particular relates to a CGH design method for detecting axisymmetric complex curved surfaces. Background Art

[0002] The computer-generated hologram compensator (CGH) can flexibly generate wavefronts of arbitrary shapes, making it increasingly used as a compensation device in the detection of high-order aspheric surfaces, free-form surfaces, etc. At present, the design and production process of CGH compensators is generally to use optical design software such as Zemax to build an optical path to optimize the phase function that needs to be compensated, and then encode the phase function into a binary step graph, convert it into a dxf file that can be recognized by the processing equipment, import it into the laser direct writing equipment to expose the pre-processed quartz substrate, and then obtain the required phase compensation element by means of wet etching or plasma etching.

[0003] CGH stripe coding and the generation of processing files are important links in CGH design and processing, which determine the final accuracy of the CGH compensator. However, there are few studies on this aspect. The CGH coding method proposed by Harbin University of Science and Technology is only applicable to rotationally symmetric aspheric surfaces (CN103791855A); the CGH coding method proposed by Peng Jiantao et al. of Changchun Institute of Optics, Fine Mechanics and Physics can be applied to non-rotationally symmetric surface detection, but it has the disadvantages of inaccurate description of stripe line width and large error of "variable step length" coding when the curvature of the stripe curve changes greatly; in addition, the current CGH processing files usually have a large amount of data, and the commonly used dxf format has high memory usage and high requirements on computer performance. Summary of the invention

[0004] In view of this, and in combination with the current situation that most non-rotationally symmetrical parts are axisymmetric off-axis aspheric surfaces or xy polynomial surfaces, the present invention provides a CGH design method for detecting axisymmetric complex surfaces.

[0005] The technical solution of the present invention is:

[0006] A CGH design method for detecting axisymmetric complex curved surfaces, the method comprising:

[0007] S101: Design the optical path of the CGH of the axisymmetric complex surface to be measured based on the optical design software, add tilted carrier frequency to the CGH to separate different diffraction poles, and output the CGH phase diagram expressed by Zernike polynomials;

[0008] S102: Using the basic equation

[0009]

[0010] Among them, 0≤q≤1 is the duty cycle used for encoding, n is a positive integer, φ(x, y) is the phase function expressed by x and y, and the phase map is binarized to generate CGH fringes on complex surfaces.

[0011] Furthermore, the S102 specifically includes the following steps:

[0012] S102.1: Divide the CGH phase image into two halves along the symmetry axis, and perform binary processing on one half of the phase image;

[0013] S102.2: Calculate the number of fringes n contained in half of the CGH phase image:

[0014] n is a positive integer;

[0015] S102.3: Arrange a sparse data matrix on half of the CGH phase image to generate point cloud data, divide the point cloud data into unit grids, set n0=1 to select an initial unit grid, and determine the φ min ≤2π≤φ max Is it true? If so, perform linear interpolation on the unit grid and find the coordinate point corresponding to the value of φ(x, y) closest to 2π in the unit grid as the initial value of the first stripe; traverse all unit grids in turn and preliminarily determine the curve shape of the first stripe;

[0016] S102.4: Select the stripe duty cycle as q, and translate the stripe curve generated in step S102.3 by q / 2 to both sides along its normal direction; the two curve points obtained by the translation are used as the initial values ​​of the contour boundary of the first stripe; use the Newton iteration method to substitute the initial boundary value into the phase equation, and solve the exact solutions corresponding to φ(x, y) = 0.5π and φ(x, y) = 1.5π to solve the exact contour curve points of the stripes.

[0017] Furthermore, the step S102.4 further includes:

[0018] S102.5: interpolating the precise contour curve points obtained in S102.4 according to the chord height error control method to achieve encoding of the first stripe;

[0019] S102.6: Repeat steps S102.3-S102.5 to sequentially complete the discretization description of the curves of the remaining n-1 stripes, thereby achieving accurate encoding of the half-side CGH phase stripes.

[0020] Furthermore, after S102.6, the following further includes: S102.7: mirror-copying the discretized description of the half-side CGH phase fringes obtained in S102.6 along the symmetry axis to achieve encoding of the phase fringes of the entire CGH.

[0021] Furthermore, after S102, the following steps are also included:

[0022] S103:

[0023] A program based on Python is written to generate GDSⅡ files for processing CGH, and the GDSⅡ files are saved in segments.

[0024] Compared with the existing CGH stripe encoding and processing file generation method, the main advantages of the present invention are:

[0025] First, based on the commonly used surface shapes currently designed in the field of optics, a CGH design and processing method for axisymmetric complex surface shape detection is proposed, which can be applied to the detection of axisymmetric and rotationally symmetric surfaces at the same time. Figure 2 Meta method saves computing power;

[0026] Second, compared with the existing method of generating stripe profiles with fixed line width, the Newton iteration method is more accurate in describing the stripe profile and reduces design errors;

[0027] Third, the proposed chord height error control method can adaptively interpolate on the curve stripes and reasonably arrange the sampling point density to ensure the curve accuracy while improving efficiency;

[0028] Fourth, Python is used to write programs to generate GDSⅡ files, which reduces the demand for computer performance compared to the dxf format. The idea of ​​segmented storage further reduces the requirement for computer memory due to the large amount of CGH file data. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 A schematic diagram of the design process of the method of the present invention;

[0031] Figure 2 Principle diagram of chord height error control method;

[0032] Figure 3 Off-axis aspheric surface to be tested;

[0033] Figure 4 Example CGH detection phase contour distribution map;

[0034] Figure 5Schematic diagram of the steps for accurate encoding of CGH stripe profile based on Newton iteration method. DETAILED DESCRIPTION

[0035] The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings.

[0036] The following describes the embodiments of the present disclosure through specific examples, and those skilled in the art can easily understand other advantages and effects of the present disclosure from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all of the embodiments. The present disclosure can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present disclosure. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present disclosure.

[0037] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present disclosure, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this device and / or practice this method.

[0038] It should also be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present disclosure. The illustrations only show components related to the present disclosure rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0039] Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, it will be understood by those skilled in the art that the aspects described may be practiced without these specific details.

[0040] In one embodiment of the present invention, a CGH design method for detecting axisymmetric complex surfaces is proposed. Figure 1-Figure 4 , the method is:

[0041] S101: Design the optical path of the CGH of the axisymmetric complex surface to be measured based on the optical design software, add tilted carrier frequency to the CGH to separate different diffraction poles, and output the CGH phase diagram expressed by Zernike polynomials;

[0042] S102: Using the basic equation

[0043]

[0044] Among them, 0≤q≤1 is the duty cycle used for encoding, n is a positive integer, φ(x, y) is the phase function expressed by x and y, and the phase map is binarized to generate CGH fringes on complex surfaces.

[0045] In this embodiment, S102 specifically includes the following steps:

[0046] S102.1: Divide the CGH phase image into two halves along the symmetry axis, and perform binary processing on one half of the phase image;

[0047] S102.2: Calculate the number of fringes n contained in half of the CGH phase image:

[0048] n is a positive integer;

[0049] S102.3: Arrange a sparse data matrix on half of the CGH phase image to generate point cloud data, divide the point cloud data into unit grids, set n0=1 to select an initial unit grid, and determine the φ min ≤2π≤φ max Is it true? If so, perform linear interpolation on the unit grid and find the coordinate point corresponding to the value of φ(x, y) closest to 2π in the unit grid as the initial value of the first stripe; traverse all unit grids in turn and preliminarily determine the curve shape of the first stripe;

[0050] S102.4: Select the stripe duty cycle as q, and translate the stripe curve generated in step S102.3 by q / 2 to both sides along its normal direction; the two curve points obtained by the translation are used as the initial values ​​of the contour boundary of the first stripe; use the Newton iteration method to substitute the initial boundary value into the phase equation, and solve the exact solutions corresponding to φ(x, y) = 0.5π and φ(x, y) = 1.5π to solve the exact contour curve points of the stripes.

[0051] In this embodiment, after S102.4, the following steps are further included:

[0052] S102.5: interpolating the precise contour curve points obtained in S102.4 according to the chord height error control method to achieve encoding of the first stripe;

[0053] S102.6: Repeat steps S102.3-S102.5 to sequentially complete the discretization description of the curves of the remaining n-1 stripes, thereby achieving accurate encoding of the half-side CGH phase stripes.

[0054] In this embodiment, after S102.6, the following further includes: S102.7: mirror-copying the discretized description of the half-side CGH phase fringes obtained in S102.6 along the symmetry axis to achieve encoding of the phase fringes of the entire CGH.

[0055] In this embodiment, the following steps are further included after S102:

[0056] S103:

[0057] A program based on Python is written to generate GDSⅡ files for processing CGH, and the GDSⅡ files are saved in segments.

[0058] This embodiment, in view of the characteristics of axisymmetric parts, binarizes the half-side phase image, and then completes it symmetrically to save computing power; accurately determines the fringe curve profile through the Newton iteration method; based on the chord height error control method, realizes the adaptive fast encoding of the CGH fringe position, improves the fringe encoding accuracy and the consistency of processing error evaluation; uses Python to write a program to complete the generation of the processing file GDSⅡ, and saves it in segments to reduce the requirements for computer performance. Finally, an efficient, accurate, and universal CGH fringe encoding and processing file generation method is formed.

[0059] The process steps are as follows:

[0060] (1) Based on Zemax optical software, the optical path design of the CGH of the axisymmetric complex surface to be measured is carried out, and the tilted carrier frequency is added to separate different diffraction poles to avoid stray light interference. After optimizing the design, the CGH phase diagram expressed by Zernike polynomials is output;

[0061] (2) Using the basic equation:

[0062]

[0063] Among them, 0≤q≤1 is the duty cycle used for encoding, n is a positive integer, and the phase image is binarized to generate CGH fringes. The specific steps are as follows:

[0064] Step 1: First, because it is used to detect axisymmetric complex surfaces, the CGH phase image is divided into two halves along the symmetry axis, and only one half of the phase image needs to be binary processed;

[0065] Step 2: Calculate the number of fringes n contained in the phase image:

[0066] n is a positive integer;

[0067] Step 3: Arrange a sparse data matrix on the phase map to generate point cloud data, divide the point cloud data into unit grids, set n0 = 1, that is, φ0 = 2π, select an initial unit grid, and determine the φ within the unit grid and on the boundary. min ≤2π≤φ max Is it true? If so, perform linear interpolation on the unit grid to find the coordinate point corresponding to the value closest to 2π as the initial value of the first stripe, and traverse all unit grids in turn to roughly determine the curve shape of the first stripe;

[0068] Step 4: According to experience, the fringe duty cycle is selected as q, and the fringe curve generated in step 3 is translated to both sides by q / 2. The two curve points obtained are used as the initial values ​​of the contour boundary of the first fringe. The initial values ​​are substituted into the phase equation using the Newton iteration method to solve the exact solutions corresponding to φ(x, y) = 0.5π and φ(x, y) = 1.5π, and the exact contour curve points of the fringe are solved; the principle is as follows: Figure 5 shown.

[0069] Step 5: Interpolate the precise contour curve points obtained in step 4 according to the chord height error control concept. Figure 2 , realize the encoding of the first stripe;

[0070] Step 6: According to steps 3-5, the discretization description of the curves of the remaining n-1 stripes is completed in sequence to achieve accurate encoding of the half-side CGH phase stripes;

[0071] Step 7: The discretized description of the half-side CGH phase fringes obtained in step 6 is mirror-copied along the symmetry axis to achieve the encoding of the phase fringes of the entire CGH;

[0072] (3) After completing the CGH encoding, a program is written based on Python to generate the GDSⅡ file for processing CGH, and the GDSⅡ file is saved in segments to reduce the demand for computer memory performance.

[0073] The invention method is described in detail below together with an example of CGH design and processing implementation for off-axis aspheric surface measurement.

[0074] The off-axis convex aspheric parameters are as follows:

[0075] The diameter of the component to be tested is 50mm, and the off-axis distance is 74mm. Figure 3 As shown;

[0076] Aspheric equations

[0077]

[0078] Where Z is the aspheric surface height, c = -1 / 200.065, k = -0.5, h is the radial radius, A = 7.7114e-9, B = 5.8894e-14,

[0079] Surface accuracy RMS≤0.02λ;

[0080] The process steps are as follows:

[0081] (1) According to the equation of the surface to be measured, the CGH phase compensation optical path is designed in Zemax optics, the CGH phase distribution is optimized, and the tilted carrier frequency is added to separate the multi-level diffraction stray light and avoid stray light interference. The CGH is tilted 1.3° relative to the plane lens. The corresponding CGH phase contour line distribution is shown as follows: Figure 4 As shown;

[0082] (2) Using the basic equation:

[0083]

[0084] Among them, 0≤q≤1 is the duty cycle used for encoding, n is a positive integer, and the phase image is binarized to generate CGH fringes. The specific steps are as follows:

[0085] Step 1: First, because it is used to detect off-axis aspheric surfaces along the y-axis, the CGH phase image is divided into two halves along the symmetry axis x, and only one half of the phase image needs to be binary processed;

[0086] Step 2: Calculate the number of fringes n contained in the phase image:

[0087] n is a positive integer;

[0088] Step 3: Arrange a sparse data matrix on the phase map to generate point cloud data, divide the point cloud data into unit grids, set n0 = 1, that is, φ0 = 2π, select an initial unit grid, and determine the φ within the unit grid and on the boundary. min ≤2π≤φ max Is it true? If so, perform linear interpolation on the unit grid to find the coordinate point corresponding to the value closest to 2π as the initial value of the first stripe, and traverse all unit grids in turn to roughly determine the curve shape of the first stripe;

[0089] Step 4: According to experience, the duty cycle of the stripe is selected as 0.5, and the stripe curve generated in step 3 is translated to both sides by 0.25. The two curve points obtained are used as the initial values ​​of the contour boundary of the first stripe. The initial values ​​are substituted into the phase equation using the Newton iteration method to solve the exact solutions corresponding to φ(x, y) = 0.5π and φ(x, y) = 1.5π, and the exact contour curve points of the stripes are solved.

[0090] Step 5: Interpolate the precise contour curve points obtained in step 4 according to the chord height error control concept. Figure 2 , realize the encoding of the first stripe;

[0091] Step 6: According to steps 3-5, the discretization description of the curves of the remaining n-1 stripes is completed in sequence to achieve accurate encoding of the half-side CGH phase stripes;

[0092] Step 7: The discretized description of the half-side CGH phase fringes obtained in step 6 is mirror-copied along the symmetry axis to achieve the encoding of the phase fringes of the entire CGH;

[0093] (3) After completing the CGH encoding, a program is written based on Python to generate the GDSⅡ file for processing CGH, and the GDSⅡ file is saved in segments to reduce the demand for computer memory performance.

[0094] The above is only a specific implementation of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present disclosure should be included in the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be based on the protection scope of the claims.

Claims

1. A CGH design method for detecting axisymmetric complex surfaces, characterized in that: The method is: S101: Design the optical path of the CGH of the axisymmetric complex surface to be measured based on the optical design software, add tilted carrier frequency to the CGH to separate different diffraction poles, and output the CGH phase diagram expressed by Zernike polynomials; S102: Using the basic equation Among them, 0≤q≤1 is the duty cycle used for encoding, n is a positive integer, φ(x, y) is the phase function expressed by x and y, and the phase map is binarized to generate CGH fringes on complex surfaces.

2. The CGH design method for detecting axisymmetric complex surfaces according to claim 1, characterized in that: The S102 specifically includes the following steps: S102.1: Divide the CGH phase image into two halves along the symmetry axis, and perform binary processing on one half of the phase image; S102.2: Calculate the number of fringes n contained in half of the CGH phase image: n is a positive integer; S102.3: Arrange a sparse data matrix on half of the CGH phase image to generate point cloud data, divide the point cloud data into unit grids, set n0=1 to select an initial unit grid, and determine the φ min ≤2π≤φ max Is it true? If so, perform linear interpolation on the unit grid and find the coordinate point corresponding to the value of φ(x, y) closest to 2π in the unit grid as the initial value of the first stripe; traverse all unit grids in turn and preliminarily determine the curve shape of the first stripe; S102.4: Select the stripe duty cycle as q, and translate the stripe curve generated in step S102.3 by q / 2 to both sides along its normal direction; the two curve points obtained by the translation are used as the initial values ​​of the contour boundary of the first stripe; use the Newton iteration method to substitute the initial boundary value into the phase equation, and solve the exact solutions corresponding to φ(x, y) = 0.5π and φ(x, y) = 1.5π to solve the exact contour curve points of the stripes.

3. The CGH design method for detecting axisymmetric complex surfaces according to claim 2, characterized in that: The S102.4 and later also include: S102.5: interpolating the precise contour curve points obtained in S102.4 according to the chord height error control method to achieve encoding of the first stripe; S102.6: Repeat steps S102.3-S102.5 to sequentially complete the discretization description of the curves of the remaining n-1 stripes, thereby achieving accurate encoding of the half-side CGH phase stripes.

4. The CGH design method for detecting axisymmetric complex surfaces according to claim 3, characterized in that: The step S102.6 also includes: S102.7: performing mirror copying along the symmetry axis on the discretized description of the half-side CGH phase fringes obtained in S102.6 to achieve encoding of the phase fringes of the entire CGH.

5. The CGH design method for detecting axisymmetric complex surfaces according to claim 4, characterized in that: The step S102 further includes the following steps: S103： A program based on Python is written to generate GDSⅡ files for processing CGH, and the GDSⅡ files are saved in segments.

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