Optical element defect detection method based on transmission type phase deflectometry wavefront reconstruction

Abstract

This invention relates to the field of optical inspection technology, and particularly to a method for detecting defects in optical components based on transmission-type phase-deflection wavefront reconstruction. The method includes: S1: constructing the system's detection optical path; S2: calibrating the camera's intrinsic parameters; S3: calibrating the system's extrinsic parameters; S4: acquiring a fringe image using a five-step phase-shifting method; S5: obtaining a continuous phase distribution using the center-extended rhombus method and calculating the wavefront slope; S6: reconstructing the wavefront slope based on the Poisson equation, constructing a diffusion tensor to define the affine transformation matrix, solving the Poisson equation adapted to the affine transformation, and obtaining the reconstructed wavefront of the optical component under test; S7: using Zernike polynomial fitting to obtain the three-dimensional distribution of defects, determining the defect type, and obtaining defect parameters. This invention employs a wavefront reconstruction algorithm based on the Poisson equation, achieving three-dimensional reconstruction and quantitative characterization of internal defects in optical components, and effectively suppressing the interference of surface contaminants on the detection results.

Description

Technical Field

[0001] This invention belongs to the field of optical inspection technology, and in particular relates to a method for detecting defects in optical components based on transmission phase deflection wavefront reconstruction. Background Technology

[0002] With the widespread application of high-precision optical components in cutting-edge fields such as semiconductor lithography, space remote sensing, and laser fusion, as well as in everyday life, surface and internal defects have become key factors affecting the performance and reliability of the entire optical system. Therefore, high-precision defect detection is a crucial link in the production and application of optical components. Transmission-based phase deflection, as an emerging non-interferometric, full-field measurement technique, analyzes the distortion of sinusoidal fringes after passing through a transmitting element to invert the wavefront slope distribution of the outgoing light field. It boasts advantages such as high measurement accuracy, large dynamic range, vibration resistance, and system simplicity. However, in defect detection applications, existing research based on this technology largely focuses on using image features such as modulation density for two-dimensional defect identification and classification. While these methods have some effectiveness, their core limitations lie in the following three aspects: I. Limitations in Detection Dimensions and Lack of 3D Reconstruction Capability: Existing transmission phase deflection detection schemes essentially analyze the results as an integral projection of the optical path changes caused by defects onto a two-dimensional plane. This fails to accurately reconstruct the 3D spatial distribution, depth, and true geometric shape of defects within the component along the optical axis. Currently, there are no publicly available cases demonstrating true 3D reconstruction of internal defects in optical components based on this method.

[0003] Second, it is sensitive to non-defect factors and lacks specificity: Traditional methods, such as modulation analysis, are easily affected by surface contaminants (such as dust and water stains) on components, which can cause significant modulation changes and be easily misjudged as internal defects.

[0004] Third, the lack of precise quantitative standards for defect characterization: Existing methods for defect detection using transmission phase deflection mostly focus on the identification and rough location of defects, lacking the ability to accurately quantify the key physical parameters of defects.

[0005] Therefore, a novel detection method is urgently needed to overcome the aforementioned limitations. This method should be based on the principle of transmission phase deflection, enabling not only the three-dimensional localization and morphological reconstruction of internal defects in optical components, but also effectively suppressing interference from surface contaminants, and ultimately outputting accurate and objective quantitative parameters. This would provide a reliable and traceable standard for quantitative defect detection and evaluation in optical manufacturing. Summary of the Invention

[0006] In view of this, the present invention aims to provide a defect detection method for optical components based on transmission phase deflection wavefront reconstruction. By building a transmission phase deflection optical measurement system and using a wavefront reconstruction algorithm based on the Poisson equation, the three-dimensional morphology reconstruction and quantitative characterization of internal defects of optical components are realized, and the interference of surface contaminants on the detection results of optical components is effectively suppressed.

[0007] To achieve the above objectives, the technical solution created by this invention is implemented as follows: A method for detecting defects in optical components based on transmission-type phase-deflection wavefront reconstruction includes the following steps: S1: Construct a transmission phase deflection wavefront measurement system consisting of a screen, the optical element under test, and a camera; adjust the camera aperture and focal length to enable the camera to produce clear images within a preset axial range. S2: The camera's internal parameters are calibrated using Zhang's calibration method; S3: The external parameters of the transmission phase deflection wavefront measurement system are calibrated using the inverse direct linear transformation method; S4: Acquire fringe images of the screen at position L1 with and without the optical element under test (DUT) using a five-step phase-shifting method. Then, translate the screen along the optical axis to position L2 and acquire fringe images of the screen at position L2 with and without the DUT. All fringe images acquired at positions L1 and L2 are saved to the corresponding storage directories, and all fringe images are preprocessed. S5: The preprocessed stripe image is unwrapped using the center-expanded rhombus method to obtain a continuous phase distribution. Combined with the camera intrinsic parameters obtained in step S2, the extrinsic parameters of the transmission phase deflection wavefront measurement system obtained in step S3, and the geometric parameters, the wavefront slope of the optical element under test is calculated using the full-link mapping method. S6: Based on the Poisson equation, the wavefront slope of the optical element under test obtained in step S5 is reconstructed. By constructing the diffusion tensor to define the affine transformation matrix, the affine transformation matrix is ​​introduced to solve the Poisson equation and obtain the reconstructed wavefront of the optical element under test. S7: The reconstructed wavefront of the optical element under test is fitted using Zernike polynomials, and low-order terms are eliminated to obtain the three-dimensional distribution of defects in the optical element under test. Based on the three-dimensional distribution of defects, the defect type is determined and the defect parameters are obtained.

[0008] Furthermore, step S2 includes the following steps: controlling the screen to display a black and white checkerboard image, changing the screen pose, and using a camera to acquire a set of images; using the camera to acquire images of the screen at positions L1 and L2 respectively; after grayscale processing of the acquired images, extracting corner points, and calculating camera intrinsic parameters.

[0009] Furthermore, step S3 includes the following steps: adjusting the camera optical axis to coincide with the screen optical axis, controlling the screen to display a circular feature dot matrix image with a preset number of rows and columns, and after the camera acquires images of the screen at positions L1 and L2, identifying the feature point region through circular Hough transform; after binarizing the feature point region, extracting and sorting the centroid coordinates, and combining the distance from the screen to the camera optical center calculated by the black and white checkerboard image, constructing an overdetermined linear equation system using the inverse direct linear transformation method, and solving the extrinsic parameters of the transmission phase deflection wavefront measurement system through singular value decomposition.

[0010] Furthermore, the method for preprocessing the stripe image in step S4 is as follows: the stripe image is converted to grayscale to obtain a preprocessed initial stripe image, and then a circular mask is used to crop the preprocessed initial stripe image according to the center coordinates and radius of the optical element to be measured, retaining the effective measurement area in the preprocessed initial stripe image, and thus obtaining the preprocessed stripe image.

[0011] Furthermore, the full-link mapping method in step S5 is as follows: when the camera acquires the stripe image, after the light is deflected by the optical element under test, the stripe image on the camera image plane will generate pixel displacement. The pixel displacement is calculated according to the continuous phase distribution described in step S5, and then the pixel displacement is mapped to world coordinates fixed in space according to the principle of geometric optics.

[0012] Furthermore, the method for solving the Poisson equation by introducing an affine transformation matrix in step S6 includes the following steps: S61: The structural tensor of the wavefront slope of the optical element under test obtained in step S5 using an n×n neighborhood. S62: Introduce diffusion coefficient regularization to construct the diffusion tensor; S63: Decompose the diffusion tensor to obtain the affine transformation matrix, apply the affine transformation matrix to the wavefront slope of the optical element under test obtained in step S5, obtain the corrected wavefront slope, and solve the Poisson equation.

[0013] Furthermore, the defect types in step S7 include surface defects, subsurface defects, and volume defects.

[0014] Furthermore, the defect parameters in step S7 include the location and size of the defect on the optical element under test.

[0015] Furthermore, the optical element under test is a light-transmitting lens, including plane lenses, spherical lenses, aspherical lenses, and freeform lenses.

[0016] Compared with the prior art, the present invention can achieve the following beneficial effects: This invention constructs a transmission-type phase-deflection optical measurement system. After light passes through the entire three-dimensional space of the optical element, it accurately collects the wavefront slope carrying complete defect information of the optical element. Then, it uses a wavefront reconstruction algorithm based on the Poisson equation to reconstruct the collected wavefront slope with high precision and globally. This achieves three-dimensional reconstruction and quantitative characterization of surface and internal defects of the optical element, and effectively suppresses the interference of surface contaminants on the test results. Attached Figure Description

[0017] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram of the transmission-type phase deflection wavefront measurement system described in an embodiment of the present invention; Figure 2 A schematic diagram of the principle of the transmission phase deflection wavefront measurement system described in the embodiment of the present invention; Figure 3 A schematic flowchart of the optical element defect detection method based on transmission phase deflection wavefront reconstruction as described in the embodiments of the present invention; Figure 4 A simulation diagram illustrating the lens distribution as described in the embodiments of the present invention; Figure 5 A schematic diagram of the optical simulation path of the transmission phase deflection wavefront measurement system described in the embodiment of the present invention; Figure 6 A simulation diagram of the reconstructed wavefront of the lens described in the embodiment of the present invention; Figure 7 A simulation diagram illustrating the theoretical defect distribution of the lens described in the embodiment of the present invention; Figure 8 A simulation diagram of the reconstruction defect distribution of the lens described in the embodiment of the present invention; Figure 9 A simulation diagram of the theoretical defect cross-section of the lens described in the embodiment of the present invention; Figure 10 A simulation diagram of the reconstructed defect section of the lens described in the embodiment of the present invention; Figure 11 A schematic diagram of the resin lens described in the embodiment of the present invention; Figure 12 A magnified schematic diagram of the defects of the resin lens described in the embodiment of the present invention; Figure 13 A schematic diagram of the reconstructed wavefront distribution of the resin lens described in the embodiment of the present invention; Figure 14A schematic diagram of the three-dimensional distribution of defects in the resin lens described in the embodiment of the present invention; Figure 15 This is a cross-sectional schematic diagram of the defect distribution of the resin lens described in an embodiment of the present invention.

[0018] Explanation of reference numerals in the attached figures: 1. Screen; 2. Optical component under test; 3. Camera. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] This invention provides a method for detecting defects in optical components based on transmission phase deflection wavefront reconstruction, which is implemented using a transmission phase deflection wavefront measurement system.

[0025] like Figure 1 and Figure 2 As shown, the transmission-type phase deflection wavefront measurement system includes a screen 1, an optical element under test 2, and a camera 3. The screen 1 displays a black and white checkerboard image, a circular feature dot matrix image with a preset number of rows and columns, and a stripe image. The camera 3 acquires the image on the screen 1 after passing the optical element under test 2. The screen 1 is moved from position L1 along its optical axis to position L2. The black and white checkerboard image displayed on the screen 1 is used to calibrate the intrinsic parameters of the camera 3. The circular feature dot matrix image with a preset number of rows and columns displayed on the screen 1 is used to calibrate the extrinsic parameters of the transmission-type phase deflection wavefront measurement system. The stripe image displayed on the screen 1 is used to obtain the wavefront slope of the optical element under test 2.

[0026] like Figure 3 As shown, the optical element defect detection method based on transmission phase deflection wavefront reconstruction provided by the present invention includes the following steps: S1: Construct a transmission phase deflection wavefront measurement system consisting of a screen, the optical element under test, and a camera to detect the optical path, and adjust the camera aperture and focal length to enable the camera to form a clear image within a preset axial range.

[0027] S2: The camera's intrinsic parameters are calibrated using Zhang's calibration method, including the following steps: control the screen to display a black and white checkerboard image, change the screen pose, and use the camera to acquire a set of images; use the camera to acquire images of the screen at positions L1 and L2 respectively; after grayscale processing of the acquired images, extract corner points and calculate the camera's intrinsic parameters.

[0028] The control screen displays a black and white checkerboard image. The screen pose is changed, and n images are captured using a camera. Images are then captured at positions L1 and L2, resulting in two images. These n+2 images are calibrated, and images with significant reprojection errors are discarded, ensuring that the two images captured at positions L1 and L2 are included. All retained images are converted to grayscale, and corner points are extracted. Further calculations yield the camera's intrinsic parameters, including the camera focal length. f x and f y Center point coordinates ( u 0, v 0) and distortion coefficient k .

[0029] Since Zhang Zhengyou's calibration method is existing technology, the specific calibration method for camera intrinsic parameters will not be described in this invention.

[0030] S3: The extrinsic parameters of the transmission phase deflection wavefront measurement system are calibrated using the inverse direct linear transformation method, including the following steps: The camera optical axis is aligned with the screen optical axis; the screen displays a circular feature point array image with a preset number of rows and columns; after the camera acquires images of the screen at positions L1 and L2, the feature point regions are identified through circular Hough transform; after binarization of the feature point regions, extraction and sorting of centroid coordinates, and calculation of the distance from the screen to the camera optical center using the black and white checkerboard image, an overdetermined linear equation system is constructed using the inverse direct linear transformation method; and the extrinsic parameters of the transmission phase deflection wavefront measurement system are solved through singular value decomposition.

[0031] The camera's optical axis is aligned with the screen's optical axis, and the screen displays a circular feature point array image with a preset number of rows and columns. The camera is then controlled to acquire images of the screen at positions L1 and L2. A circular Hough transform with a set radius range and sensitivity factor is used to identify dark circular feature points against a bright background. After binarization, the centroid coordinates of the feature points are accurately obtained using a centroid extraction algorithm. The centroid coordinates are sorted according to a preset rule and matched one-to-one with the feature point coordinates on the screen. Combining the calibrated camera intrinsic parameters and the distance from the screen to the camera's optical center calculated from the black and white checkerboard image, an overdetermined linear equation system is constructed using DLT. The rotation matrix R and translation vector T are obtained through singular value decomposition, completing the calibration of the system's extrinsic parameters at the two measurement positions L1 and L2.

[0032] Since the use of the inverse direct linear transformation method for calibrating the external parameters of the measurement system is an existing technology, it will not be described in detail in this invention.

[0033] S4: Acquire fringe images of the screen at position L1 with and without the optical element under test (DUT) by using a five-step phase-shifting method. Then, translate the screen along the optical axis to position L2 and acquire fringe images of the screen at position L2 with and without the DUT. All fringe images acquired at positions L1 and L2 are saved to the corresponding storage directories, and all fringe images are preprocessed.

[0034] The screen displays a stripe image. Without the optical element under test (DUT) placed, 10 background stripe images (5 each in the x and y directions) are acquired at position L1 using a five-step phase shift. After placing the DUT, 10 stripe images containing defect information are acquired at the same position and with the same phase shift parameters. After all 20 images are acquired, they are saved to the corresponding storage directory. The screen is then moved to position L2, and again, 10 background stripe images (5 each in the x and y directions) are acquired using a five-step phase shift without the DUT placed. After placing the DUT, 10 stripe images containing defect information are acquired at the same position and with the same phase shift parameters and saved to the corresponding storage directory. This yields a total of 40 stripe images at positions L1 and L2, which are then preprocessed. The preprocessing method is as follows: grayscale and double-precision conversion are performed on 40 fringe images to obtain the initial preprocessed fringe image. Then, based on the center coordinates and radius of the optical element to be measured, a circular mask is used to crop the initial preprocessed fringe image, retaining the effective measurement area in the initial preprocessed fringe image, and the preprocessed fringe image is obtained.

[0035] S5: The preprocessed fringe image is unwrapped using the center-expanded rhombus method to obtain a continuous phase distribution. Combined with the camera intrinsic parameters obtained in step S2, the extrinsic parameters of the transmission phase deflection wavefront measurement system obtained in step S3, and the geometric parameters, the wavefront slope of the optical element under test is calculated using the full-link mapping method.

[0036] The full-link mapping method is as follows: when the camera acquires a striped image, the light rays are deflected by the optical element under test, which causes pixel displacement in the striped image on the camera image plane. The pixel displacement is calculated according to the continuous phase distribution described in step S5, and then the pixel displacement is mapped to world coordinates fixed in space according to the principle of geometric optics.

[0037] The five-step phase-shifting method is used to extract the phase to be measured from the preprocessed fringe image. Its physical basis is that after the sinusoidal phase-shifted fringes displayed on the screen are deflected by the optical element under test, the fringe light intensity acquired by the camera satisfies the following model: (1); In equation (1), For the first i Amplitude phase shift fringe pattern in pixels Light intensity at ( =1,2…,5), The maximum number of phase shift steps, , For background light intensity component, For the fringe modulation amplitude component, The phase to be measured.

[0038] The phase was solved using the five-step phase shift method. for: (2); The original phase obtained by equation (2) Because the arctan value exhibits a 2π jump, the phase unwrapping method, which involves a centrally extended rhombus, is required to obtain a continuous phase distribution. .

[0039] by Taking direction as an example, after light is deflected by the optical element under test, it will cause the stripes to produce pixel displacement on the camera image plane. Its relationship with continuous phase distribution The relationship satisfies the periodic correspondence between phase and displacement: (3); In equation (3), T is the fringe period. After simplification, we obtain... Pixel displacement in direction for: (4).

[0040] According to the principles of geometric optics, light rays... The tangent of the deflection angle in direction, i.e. directional wavefront slope for: (5); In equation (5), The physical size of a single pixel in the camera. L Let L1 be the distance difference between the screen at positions L1 and L2 along the axial direction (Z-axis). Substituting equation (4) into equation (5), we finally obtain... directional wavefront slope The formula for calculation is: (6); Similarly, for The continuous phase distribution in the direction can be obtained using the same method. directional wavefront slope for: (7).

[0041] S6: Based on the Poisson equation, the wavefront slope of the optical element under test obtained in step S5 is reconstructed. By constructing a diffusion tensor to define an affine transformation matrix, the affine transformation matrix is ​​introduced to solve the Poisson equation, and the reconstructed wavefront of the optical element under test is obtained.

[0042] According to step S5 x and y Wavefront slope in direction and Based on the Poisson equation and Wavefront slope reconstruction: Let the wavefront to be reconstructed be: Its theoretical slope field is ( , Introducing a correction slope field ,satisfy , 。 Transforming a non-integrable slope field into an integrable slope field corresponds to the error function. for: (8); In equation (8), This represents the effective measurement area of ​​the wavefront.

[0043] To minimize the error function, the variational extremum condition must be satisfied: the Euler-Lagrange equations, combined with the Neumann boundary conditions ( )have to: (9); The Poisson equation is obtained by rearranging: (10).

[0044] The method for solving the Poisson equation by introducing an affine transformation matrix includes the following steps: S61: Calculate the structural tensor of the wavefront slope of the optical element under test obtained in step S5 using an n×n neighborhood.

[0045] For a two-dimensional slope field Affine transformation achieves direction correction of the slope field through linear transformation and translation. Its mathematical form is: = (11); In equation (11), This is the corrected slope field after affine transformation. It is a 2×2 affine transformation matrix (the core solution object, representing linear transformations such as rotation, scaling, and shearing). = This is a translation vector, whose physical meaning is to compensate for the system offset of the slope field. In this system, it is the default... .

[0046] Affine transformation matrix From diffusion tensor By definition, the diffusion tensor is the core tensor describing the local directional characteristics of a slope field, and its form is: ,in , They are respectively The diffusion coefficient in the direction (characterizing the smoothing weight of the slope in that direction). Cross-diffusion coefficient (characterized by...) (Directional coupling characteristics).

[0047] Affine transformation matrix With diffusion tensor satisfy: .

[0048] To calculate the diffusion tensor First, the structure tensor needs to be calculated. ,right local neighborhood Structure tensor for: (12); In equation (12), For local areas.

[0049] S62: Introduce diffusion coefficient regularization to construct the diffusion tensor.

[0050] Based on structure tensor Introducing the diffusion coefficient Diffusion tensor for: (13); In equation (13), For a 2×2 identity matrix, It is the Frobenius norm (normalized diffusion tensor).

[0051] S63: Decompose the diffusion tensor to obtain the affine transformation matrix, apply the affine transformation matrix to the wavefront slope of the optical element under test obtained in step S5, obtain the corrected wavefront slope, and solve the Poisson equation.

[0052] For diffusion tensor Perform eigenvalue decomposition: ,in The eigenvector matrix, It is a diagonal matrix of eigenvalues.

[0053] Affine transformation matrix pass The solution obtained by finding the inverse square root of the matrix is: (14); affine transformation matrix Applying the wavefront slope of the optical element under test obtained in step S5, the corrected wavefront slope is obtained: = (15); Based on the corrected wavefront slope, construct the affine transformation Laplace operator: (16); Finally, solve the Poisson equation: (17); Solving This is the reconstructed wavefront of the optical element under test.

[0054] S7: The reconstructed wavefront of the optical element under test is fitted using Zernike polynomials, and low-order terms are eliminated to obtain the three-dimensional distribution of defects in the optical element under test. Based on the three-dimensional distribution of defects, the defect type is determined and the defect parameters are obtained.

[0055] Based on the wavefront reconstruction algorithm of the Poisson equation, the optical element under test is simulated and verified. The simulation parameters are as follows: Optical element selection for test: a lens with a refractive index of 1.56, a center thickness of 1.5 mm, a front surface refractive power of 4D and a rear surface refractive power of -2D; Defect types: Scratches, dents, etc. on the lens; Defect design: Simulating real physical defects; Scratch characteristics: surface grooves, buildup, length 9.4646 mm, width 0.97162 mm, depth -4.5542 μm; Features of the pit: central collapse, raised edges, asymmetrical material distribution, area 3.7725 mm². 2 Depth -8.0537μm.

[0056] Simulation results of lens wavefront reconstruction are as follows Figure 4 - Figure 10 As shown. Figure 4 This is a simulation diagram of the lens distribution; Figure 5 This is a schematic diagram of the optical path of the transmission phase deflection wavefront measurement system. In this diagram, the camera 3 is located at -300mm on the Z-axis, the optical element under test 2 (i.e., the lens) is located at 0mm on the Z-axis, the screen 1 is located at 100mm on the Z-axis, and the rest of the diagram represents light rays. Figure 6 This is a schematic diagram of the reconstructed wavefront simulation of the lens. The reconstructed wavefront of the lens is fitted using a Zernike polynomial, and low-order terms are removed to obtain the three-dimensional distribution of defects in the lens, i.e.: Figure 7 Simulation diagram of theoretical defect distribution of lens Figure 8 A simulation diagram of the defect distribution in the lens reconstruction. Figure 9 A simulation diagram of the theoretical defect cross-section of the lens and Figure 10 This is a simulation diagram of the defect cross-section of the lens.

[0057] Based on the three-dimensional distribution of defects in the lens, the following results were obtained: the reconstructed scratch length was 9.375 mm, with an error of 0.94708%; the scratch width was 0.98862 mm, with an error of 1.7503%; the scratch depth was -4.1814 μm, with an error of 8.1862%; and the reconstructed pit area was 3.8325 mm². 2 The error was 1.5905%; the pit depth was -7.9358μm, with an error of 1.4645%. This method effectively reconstructs the three-dimensional contour of the defect, providing a feasible approach for defect detection in transparent optical components.

[0058] According to the above embodiment of the optical element defect detection method based on transmission phase deflection wavefront reconstruction, the actual detection of the optical element under test was carried out. The optical element under test is a resin lens with a refractive index of 1.56, a size of 65mm, a spherical power (SPH) of +1.00D, and a cylindrical power (CYL) of 0. Figure 11 This is a schematic diagram of a resin lens. Figure 12 This is a magnified schematic diagram of the defects in the resin lens, obtained after performing steps S1 to S7: Figure 13 This is a schematic diagram of the reconstructed wavefront distribution of the resin lens. Figure 14 This is a schematic diagram of the three-dimensional distribution of defects in a resin lens. Figure 15 This is a schematic diagram of the cross-sectional distribution of defects in a resin lens. It can be determined that the defect type of the tested resin lens is a scratch, with a depth of 6.7593 μm and a length of 1.0634 mm.

[0059] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0060] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for detecting defects of an optical element based on transmission phase deflectometry wavefront reconstruction, characterized in that, Includes the following steps: S1: Construct a transmission phase deflection wavefront measurement system consisting of a screen, the optical element under test, and a camera; adjust the camera aperture and focal length to enable the camera to produce clear images within a preset axial range. S2: The camera's internal parameters are calibrated using Zhang's calibration method; S3: The external parameters of the transmission phase deflection wavefront measurement system are calibrated using the inverse direct linear transformation method; S4: Acquire fringe images of the screen at position L1 with and without the optical element under test (DUT) using a five-step phase-shifting method. Then, translate the screen along the optical axis to position L2 and acquire fringe images of the screen at position L2 with and without the DUT. All fringe images acquired at positions L1 and L2 are saved to the corresponding storage directories, and all fringe images are preprocessed. S5: The preprocessed stripe image is unwrapped using the center-expanded rhombus method to obtain a continuous phase distribution. Combined with the camera intrinsic parameters obtained in step S2, the extrinsic parameters of the transmission phase deflection wavefront measurement system obtained in step S3, and the geometric parameters, the wavefront slope of the optical element under test is calculated using the full-link mapping method. S6: Based on the Poisson equation, the wavefront slope of the optical element under test obtained in step S5 is reconstructed. By constructing the diffusion tensor to define the affine transformation matrix, the affine transformation matrix is ​​introduced to solve the Poisson equation and obtain the reconstructed wavefront of the optical element under test. The method for solving the Poisson equation by introducing an affine transformation matrix includes the following steps: S61: The structural tensor of the wavefront slope of the optical element under test obtained in step S5 using an n×n neighborhood. S62: Introduce diffusion coefficient regularization to construct the diffusion tensor; S63: Decompose the diffusion tensor to obtain the affine transformation matrix, apply the affine transformation matrix to the wavefront slope of the optical element under test obtained in step S5, obtain the corrected wavefront slope, and solve the Poisson equation. S7: The reconstructed wavefront of the optical element under test is fitted using Zernike polynomials, and low-order terms are eliminated to obtain the three-dimensional distribution of defects in the optical element under test. Based on the three-dimensional distribution of defects, the defect type is determined and the defect parameters are obtained.

2. The method according to claim 1, wherein, Step S2 includes the following steps: controlling the screen to display a black and white checkerboard image, changing the screen pose, and using a camera to acquire a set of images; using the camera to acquire images of the screen at positions L1 and L2 respectively; after grayscale processing of the acquired images, extracting corner points, and calculating camera intrinsic parameters.

3. The method of claim 1, wherein the method is a transmission-based phase deflectrometry wavefront reconstruction method. Step S3 includes the following steps: adjusting the camera optical axis to coincide with the screen optical axis, controlling the screen to display a circular feature dot matrix image with a preset number of rows and columns, and after the camera acquires images of the screen at positions L1 and L2, identifying the feature point region through circular Hough transform; after binarizing the feature point region, extracting and sorting the centroid coordinates, and combining the distance from the screen to the camera optical center calculated by the black and white checkerboard image, constructing an overdetermined linear equation system using the inverse direct linear transformation method, and solving the extrinsic parameters of the transmission phase deflection wavefront measurement system through singular value decomposition.

4. The method of claim 1, wherein the method is a transmission-based phase deflectrometry wavefront reconstruction method. The method for preprocessing the stripe image in step S4 is as follows: the stripe image is converted to grayscale to obtain a preprocessed initial stripe image. Then, based on the center coordinates and radius of the optical element to be measured, a circular mask is used to crop the preprocessed initial stripe image, retaining the effective measurement area in the preprocessed initial stripe image, and thus obtaining the preprocessed stripe image.

5. The method of claim 1, wherein the method is a transmission-based phase deflectrometry wavefront reconstruction method. The full-link mapping method in step S5 is as follows: When the camera acquires the stripe image, after the light is deflected by the optical element under test, the stripe image on the camera image plane will generate pixel displacement. The pixel displacement is calculated according to the continuous phase distribution described in step S5, and then the pixel displacement is mapped to world coordinates fixed in space according to the principle of geometric optics.

6. The method of claim 1, wherein the method is a transmission-based phase deflectrometry wavefront reconstruction method. The defect types in step S7 include surface defects, subsurface defects, and volume defects.

7. The method of claim 1, wherein the method is a transmission-based phase deflectrometry wavefront reconstruction method for detecting defects in an optical element, characterized in that, The defect parameters in step S7 include the location and size of the defect on the optical element under test.

8. The optical element defect detection method based on transmission phase deflection wavefront reconstruction according to claim 1, characterized in that, The optical element under test is a light-transmitting lens, including a plane lens, a spherical lens, an aspherical lens, and a freeform lens.

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