A method and equipment for detecting the focal length of a microlens array based on image-shifting fitting.

Abstract

This invention discloses a method and device for detecting the focal length of a microlens array based on image-shifting fitting. The method includes: setting up a camera and adjusting it to focus on the microlens array; adjusting the optical axis distance between the camera and the array; acquiring star spot images and Pero plate line-to-plate images at multiple adjusted positions; determining the focal plane coordinates and performing corresponding PSF reconstruction based on the spot sub-images corresponding to the same sub-lens in the multiple spot images; selecting a pair of light plate images and line-to-plate images, and using the Wiener filtering algorithm to restore the sub-images corresponding to the sub-lens in the images; performing convolution operation between the restored image and the reconstructed PSF function to obtain the reconstructed line-to-plate image corresponding to the focal plane coordinates; calculating the focal length of the sub-lens based on the focal length of the collimator, the actual line spacing of the Pero plate, and the line spacing determined by the reconstructed line-to-plate image. The method involves acquiring array images near the focal point using image-shifting, and detecting the focal lengths of multiple sub-lenses in parallel.

Description

Technical Field

[0001] This invention relates to the field of detection technology, and in particular to a method and device for detecting the focal length of a microlens array based on image-shifting fitting. Background Technology

[0002] A microlens array (MLA) is an integrated optical device composed of a large number of microlens units with feature sizes ranging from micrometers to millimeters, arranged according to specific geometric configuration rules. Its structural characteristics are as follows: the microlens units can be designed as spherical, aspherical, or composite optical structures (such as diffraction-refractive hybrid lenses) based on optical functional requirements, and can achieve complex optical control functions such as wavefront splitting, beam shaping, and multifocal parallel imaging through periodic array arrangement or gradient parameter distribution.

[0003] The focal length of a microlens array is one of the core parameters of its optical characteristics, directly affecting the array's ability to focus, collimate, and shape beams. The focal length of a microlens array is closely related to its focusing effect on incident light and the beam propagation characteristics. It is worth noting that each lens in a microlens array has an independent focal length; therefore, focal length measurement of the microlens array is crucial.

[0004] The above background information is provided only to aid in understanding the concept and technical solution of this application. It does not necessarily belong to the prior art of this application, nor does it necessarily provide technical guidance. In the absence of clear evidence that the above information was disclosed before the filing date of this application, the above background information should not be used to evaluate the novelty and inventiveness of this application. Summary of the Invention

[0005] The purpose of this invention is to provide a high-precision MLA focal length detection method, which uses image-shifting fitting to detect multiple sub-lenses in parallel.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for detecting the focal length of a microlens array based on image-shifting fitting, wherein the microlens array comprises multiple sub-lenses, and the focal length detection method includes the following steps:

[0008] Set up an image acquisition device and adjust the image acquisition device to focus on the microlens array, and determine the position at this time as the reference position;

[0009] The optical axis distance between the image acquisition device and the microlens array is adjusted with the reference position as the origin, and array images are acquired at multiple adjusted positions. The array images include a first image formed by the star points in the collimator after passing through the microlens array and a second image formed by the Pero plate in the collimator after passing through the microlens array.

[0010] The target sub-image set is determined by identifying the light spot sub-images corresponding to the same sub-lens in multiple first images. PSF reconstruction is then performed on this set, including: determining the light spot size and optical axis position in the multiple light spot sub-images based on this set, and using a fitting algorithm to determine the optical axis position corresponding to the smallest light spot, defined as the focal plane coordinates. Z t ; Obtain the pixel grayscale value of the line passing through the center point of the light spot in each light spot sub-image of the set, and then fit a Gaussian curve corresponding to each light spot sub-image, wherein the Gaussian curve includes Gaussian curve parameters; determine the focal plane coordinates through a fitting algorithm. Z t The corresponding Gaussian curve parameters are used to reconstruct the PSF function of the sub-lens;

[0011] First and second images acquired at the same location are selected. The Wiener filtering algorithm is used to restore the sub-images corresponding to the sub-lens in the first and second images, resulting in the restored image, denoted as . I re ( x , y The restored image I re ( x , y The focal plane coordinates are reconvolved by performing a convolution operation with the PSF function. Z t The corresponding reconstructed line-to-plate image;

[0012] The focal length of the sub-lens is calculated using the following formula. f : f =( f c × y ') / y 0, where, f c This indicates the focal length of the collimator. y 'Indicates the line spacing determined based on the reconstructed line-pair image. y 0 indicates the actual line spacing of the Pero plate.

[0013] Furthermore, based on any one or a combination of the aforementioned technical solutions, the focal plane coordinates are determined in the following manner. Z t :

[0014] Using the reference position as the origin, the optical axis position between the image acquisition device and the microlens array is determined as […]. Z 1, Z 2, Z 3,…, Z n ], and respectively acquire the first image set at the n optical axis positions [ I 1, I 2, I 3,…, I n ];

[0015] For the same sub-lens, extract its sub-images from the first image set to form a sub-image set. I sub =[ I sub-1 , I sub-2 , I sub-3 ,…, I sub-n ];

[0016] The subgraph set was determined based on image processing techniques. I sub The diameter of the light spot in each sub-image is [ d 1, d 2, d 3,…, d n ];

[0017] Constructing higher-order polynomials ,in, d Indicates the diameter of the light spot. Z This indicates the optical axis position between the image acquisition device and the microlens array, with the reference position as the origin. λ i In a polynomial, the th i The coefficient of the term;

[0018] The optical axis position [ Z 1, Z 2, Z 3,…, Z n ],diameter[ d 1, d 2, d 3,…, d n Substitute the coefficients into the higher-order polynomial to calculate the coefficients. λ i ;

[0019] Calculated coefficients λi Find the minimum point of a higher-order polynomial, denoted as ( Z lim , d lim );

[0020] Determine the extreme points Z lim The focal plane coordinates Z t .

[0021] Furthermore, based on any one or a combination of the aforementioned technical solutions, the PSF function of the sub-lens is reconstructed in the following manner:

[0022] Regarding the optical axis position between the image acquisition device and the microlens array Z The first image acquired at location 1 I 1. Determine the sub-lens in the first image. I The corresponding subgraph in 1 I sub-1 ;

[0023] In subgraph I sub-1 Draw a virtual line along a preset direction passing through the center point of the light spot, and sequentially determine the coordinate position and grayscale value of the pixels located on the virtual line in the preset direction. x 1, G 1),( x 2, G 2),( x 3, G 3),…,( x m , G m )];

[0024] Substitute into Gaussian curve distribution Calculate the position of the optical axis Z 1 corresponds to the Gaussian curve parameters[ a 1, b 1, c 1];

[0025] Repeat the above steps to determine the positions of the remaining optical axes. Z 2, Z 3,…, Z n The corresponding Gaussian curve parameters {[ a 2, b 2, c 2], [ a 3, b 3, c 3],…,[a n , b n , c n ]};

[0026] The focal plane coordinates are obtained by fitting. Z t The corresponding Gaussian curve parameters [ a t , b t , c t ];

[0027] The PSF function of the sub-lens is determined as follows: .

[0028] Furthermore, based on any one or a combination of the aforementioned technical solutions, the processing object of the Wiener filtering algorithm is determined in the following manner:

[0029] The optical axis position corresponding to the adjustment of the optical axis distance between the image acquisition device and the microlens array, with the reference position as the origin, is defined as [ Z 1, Z 2, Z 3,…, Z n ];

[0030] Determine the coordinates relative to the focal plane. Z t The closest optical axis position is denoted as Z adj ;

[0031] Get the position on the optical axis Z adj The first and second images were captured at the location;

[0032] The first and second sub-images corresponding to the sub-lens are extracted from the first and second images and used as the processing objects of the Wiener filtering algorithm.

[0033] Furthermore, following any one or a combination of the aforementioned technical solutions, the optical axis distance between the image acquisition device and the microlens array is adjusted in the following manner:

[0034] Using a star point within a collimator, the image acquisition device is adjusted to the focus position when the light spot formed by the star point after being focused by the microlens array is less than the diffraction limit of the image acquisition device.

[0035] The image acquisition device is moved along the optical axis between the image acquisition device and the microlens array, so that it floats a preset distance on both sides with the focus position as the reference position, and the floating points on both sides are symmetrically distributed relative to the reference position.

[0036] Furthermore, based on any one or a combination of the aforementioned technical solutions, the two sides can float in the following manner:

[0037] Make the distance between adjacent floating points equal;

[0038] Alternatively, with the reference position as the origin, the distance that floats along the optical axis each time is the focal depth distance of the image acquisition device or multiple times the focal depth distance.

[0039] Furthermore, based on any or a combination of the aforementioned technical solutions, if the microlens array extends beyond the field of view of the image acquisition device, the microlens array is divided into several sub-regions.

[0040] After acquiring the first and second images of the previous sub-region, the image acquisition device or microlens array is shifted to acquire the first and second images of the next sub-region.

[0041] Furthermore, following any one or a combination of the aforementioned technical solutions, the image acquisition device, microlens array, and collimator are arranged in the following manner:

[0042] The microlens array is placed horizontally, and the image acquisition device is positioned above the microlens array;

[0043] The inlet of the collimator is positioned opposite to the light source, and the light beam emitted from the collimator is either directly incident on the lower surface of the microlens array or after reflection.

[0044] Furthermore, based on any one or a combination of the aforementioned technical solutions, the focal length detection result of the microlens array is determined in the following manner:

[0045] Determine the calculated focal length of each sub-lens of the microlens array;

[0046] Obtain the target focal length value from the sub-lens design parameters of the microlens array;

[0047] Calculate the mean square error between the calculated focal length of each sub-lens and its corresponding target focal length. If the mean square error is less than a preset mean square error threshold, then the focal length of the microlens array is determined to be qualified; otherwise, the focal length of the microlens array is unqualified.

[0048] Alternatively, the difference between the calculated focal length of each sub-lens and the corresponding target focal length can be calculated. If the difference is less than a preset deviation threshold, the sub-lens is determined to be a qualified sub-lens. The number or proportion of qualified sub-lenses in the microlens array can be calculated to determine whether the focal length of the microlens array is qualified.

[0049] According to another aspect of the present invention, a microlens array focal length detection device is provided, comprising the following apparatus:

[0050] The stage is configured to load the microlens array to be tested;

[0051] An optical component configured to provide an optical path incident on the lower surface of the microlens array, wherein optional star points and Perot plates are disposed along the optical path;

[0052] An image acquisition device is disposed above the stage and is configured to acquire images of the microlens array on the stage.

[0053] A lifting device, which is equipped with a lifting rail and a lifting drive mechanism configured to drive the image acquisition device or the platform to move along the lifting rail;

[0054] The microlens array focal length detection device uses the method described above to detect the focal length of the microlens array.

[0055] Furthermore, in accordance with any or a combination of the aforementioned technical solutions, the microlens array focal length detection device further includes a horizontal drive mechanism, which is configured to drive the image acquisition device to move in a horizontal plane;

[0056] The lifting drive mechanism is configured to drive the image acquisition device to move up and down.

[0057] Furthermore, based on any or a combination of the aforementioned technical solutions, the optical component includes a light source, a collimator, a reflector, and a microscope objective, wherein the light beam emitted from the light source is used to generate a parallel light beam through the collimator, and the reflector reflects the parallel light beam output from the collimator onto the lower surface of the microlens array on the stage.

[0058] The image acquisition device is a camera, and the microscope objective is located at the lens of the camera.

[0059] The beneficial effects of the technical solution provided by this invention are as follows:

[0060] a. A device for detecting the focal length of a microlens array is provided, which can detect the focal length of each sub-lens of the microlens array in parallel with high precision, large format, and fast speed;

[0061] b. Use focal length detection results to provide feedback on the production process, and adjust the process parameters of products in production in a timely manner to improve yield and reduce quality risks. Attached Figure Description

[0062] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0063] Figure 1 A schematic flowchart of a microlens array focal length detection method based on image-shifting fitting method provided as an exemplary embodiment of the present invention;

[0064] Figure 2 A three-dimensional schematic diagram of a microlens array focal length detection device provided as an exemplary embodiment of the present invention;

[0065] Figure 3 A side view of a microlens array focal length detection device provided as an exemplary embodiment of the present invention. Detailed Implementation

[0066] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0067] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, apparatus, product, or device that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0068] When measuring the focal length of a microlens array, each sub-lens unit needs to be measured and calibrated individually to ensure the consistency and accuracy of the focal length. Relying on a clear focal plane image for focal length measurement is clearly inefficient for thousands of sub-lenses; therefore, parallel testing of multiple sub-lenses is considered. This also presents challenges: for microlens arrays on flexible substrates, it is difficult to ensure that all sub-lenses are on the same standard datum plane, inevitably introducing clamping errors during the measurement process and causing a decrease in measurement accuracy; simultaneously, since most microlens arrays have small apertures, a large F-number will lead to an increased depth of focus, further interfering with focal length measurement and reducing its accuracy.

[0069] The focal length detection scheme proposed in this invention involves receiving images of a standard line pair and star points formed by the sub-lenses of a microlens array through an image acquisition device, then reconstructing the focal plane image using an image-shifting fitting method, and finally calculating the focal length using the reconstructed image. In a specific embodiment, a microlens array focal length detection method based on the image-shifting fitting method is provided, wherein the microlens array includes multiple sub-lenses, such as... Figure 1 As shown, the focal length detection method includes the following steps:

[0070] S100: Set up an image acquisition device and adjust the image acquisition device to focus on the microlens array, and determine the current position as the reference position;

[0071] In one embodiment of the present invention, the microlens array is placed horizontally, and an image acquisition device (such as a camera) is positioned above it. A microscope objective can be placed at the lens of the camera to achieve clearer imaging of the microlens array.

[0072] In one embodiment, an optical component provides an optical path incident on the lower surface of the microlens array. The optical component includes a light source and a collimator. The inlet of the collimator is positioned opposite to the light source. The light beam emitted from the light source passes through the collimator to generate a parallel light beam. The light beam emitted from the collimator is incident on the lower surface of the microlens array on the stage, either directly or after reflection. Star points can be used inside the collimator to generate a spot image, or a Perlo plate can be used to generate a line-to-plate image.

[0073] When using a star point in a collimator, if the light spot formed by the star point after being focused by the microlens array is less than the diffraction limit of the image acquisition device, it can be considered that the image acquisition device is adjusted to the focus position at this time.

[0074] In this architecture, the optical axis between the image acquisition device and the microlens array is vertical, and the reference position is the origin on the optical axis.

[0075] S200: Adjust the optical axis distance between the image acquisition device and the microlens array, and acquire array images at multiple adjusted positions respectively. The array images include a first image formed by the star points in the collimator after passing through the microlens array (which is a spot image type) and a second image formed by the Pero plate in the collimator after passing through the microlens array (which is a line-to-plate image type).

[0076] There are many ways to adjust the optical axis distance. Move the image acquisition device along the optical axis (vertical direction) between the image acquisition device and the microlens array so that it floats a preset distance on both sides with the focus position as the reference position, and the floating points on both sides are symmetrically distributed relative to the reference position.

[0077] The floating methods on both sides are as follows: Method 1: Make the distance between adjacent floating points equal; Method 2: Take the reference position as the origin and float along the optical axis for a distance equal to or multiple times the focal depth of the image acquisition device.

[0078] In a specific embodiment, with the reference position as the origin on the optical axis, the first image is acquired and recorded as follows: I 11 Second image I 11b Then, shortening the optical axis distance between the camera and the microlens array, for example, by 10 micrometers, allows the microlens array to rise. Taking a lowering camera as an example, the camera descends by 10 micrometers, at which point the first image is acquired. I 12 Second image I 12b Then, for every 10 micrometers of descent, a first image and a second image are acquired. Therefore, when the descent reaches 100 micrometers, the first image is acquired. I 21 Second image I 21b ;

[0079] Returning to the starting point, we collect the first and second images every 10 micrometers as we move upwards. Therefore, when we ascend 100 micrometers, we collect the first image. I 1 and second images I 1b Thus, the corresponding optical axis positions from top to bottom [ Z 1, Z 2, Z 3,…, Z n ] = [100, 90, ..., 0, -10, -20, ..., -100], the first image set was acquired. I 1, I 2, I 3,…, I21 ] and second image set [ I 1b , I 2b , I 3b ,…, I 21b ].

[0080] S300: Determine the target sub-image set as the light spot sub-images corresponding to the same sub-lens in multiple first images, and reconstruct their PSF, including: based on the size and optical axis position of the light spots in the multiple light spot sub-images of this set, determine the optical axis position corresponding to the smallest light spot through a fitting algorithm, and define it as the focal plane coordinates. Z t ;

[0081] For the same sub-lens, extract its sub-images from the first image set to form a sub-image set. I sub =[ I sub-1 , I sub-2 , I sub-3 ,…, I sub-21 ];

[0082] The subgraph set was determined based on image processing techniques. I sub The diameter of the light spot in each sub-image is [ d 1, d 2, d 3,…, d 21 ];

[0083] Constructing higher-order polynomials ,in, d Indicates the diameter of the light spot. Z This indicates the optical axis position between the image acquisition device and the microlens array, with the reference position as the origin. λ i In a polynomial, the th i The coefficient of the term;

[0084] The optical axis position [ Z 1, Z 2, Z 3,…, Z 21 ],diameter[ d 1, d 2, d 3,…, d 21Substitute the coefficients into the higher-order polynomial to calculate the coefficients. λ i ;

[0085] Calculated coefficients λ i Find the minimum point of a higher-order polynomial, denoted as ( Z lim , d lim );

[0086] Determine the extreme points Z lim The focal plane coordinates Z t .

[0087] S400: Obtain the pixel grayscale value of the line passing through the center point of the light spot in each light spot sub-image of the set, and then fit a Gaussian curve corresponding to each light spot sub-image, wherein the Gaussian curve includes Gaussian curve parameters; determine the focal plane coordinates through a fitting algorithm. Z t The corresponding Gaussian curve parameters are used to reconstruct the PSF function of the sub-lens;

[0088] Specifically, regarding the optical axis position Z Subgraph corresponding to 1 I sub-1 In the subgraph I sub-1 Along the preset direction (e.g.) x Draw a virtual line passing through the center point of the light spot (axis), and sequentially determine the coordinate position and gray value of the pixels located on the virtual line in the preset direction [( x 1, G 1),( x 2, G 2),( x 3, G 3),…,( x m , G m )];

[0089] Substitute into Gaussian curve distribution Calculate the position of the optical axis Z 1 corresponds to the Gaussian curve parameters[ a 1, b 1, c 1];

[0090] Repeat the above steps to determine the positions of the remaining optical axes. Z 2, Z 3,…, Z 21The corresponding Gaussian curve parameters {[ a 2, b 2, c 2], [ a 3, b 3, c 3],…,[ a 21 , b 21 , c 21 ]};

[0091] The focal plane coordinates are obtained by fitting. Z t The corresponding Gaussian curve parameters [ a t , b t , c t For example, first determine the optical axis position and parameters. a To perform fitting, the simplest way is to select with Z t Two adjacent optical axis positions, for example Z t If the value is -3 micrometers (negative if below the origin), then the optical axis position is selected. Z 11 and Z 12 The corresponding Gaussian curve parameters are determined as follows: a 11 and a 12 The equation of the straight line is obtained by fitting. a =α Z +β, can be calculated Z t Corresponding Gaussian curve parameters a t Similarly, the parameters of the Gaussian curve can be calculated. b t and c t .

[0092] The parameters of the Gaussian curve [ a t , b t , c t Substituting the Gaussian curve distribution, the PSF function of the sub-lens is obtained as follows: .

[0093] S500: Select the first and second images acquired at the same location, and use the Wiener filtering algorithm to restore the sub-images corresponding to the sub-lens in the first and second images to obtain the restored image, denoted as S500. I re ( x , y The restored image I re ( x , y The focal plane coordinates are reconvolved by performing a convolution operation with the PSF function. Z t The corresponding reconstructed line-to-plate image;

[0094] The Wiener filtering algorithm processes the sub-images corresponding to the sub-lens in the first and second images acquired at the same optical axis position. In a preferred embodiment, the distance coordinates from the focal plane can be selected. Z t Nearest optical axis position:

[0095] Taking the example above, the corresponding optical axis positions from top to bottom are [ Z 1, Z 2, Z 3,…, Z n [100, 90, ..., 0, -10, -20, ..., -100], the focal plane coordinates are determined through step 300 above. Z t If the value is -7, then the coordinates relative to the focal plane are determined. Z t The closest optical axis position is Z 12 The corresponding first image is I 12 Second image I 12b ;

[0096] The first sub-image corresponding to the sub-lens is cropped from the first image and the second image. I sub-12 Second subgraph I sub-12b , which is the object processed by the Wiener filtering algorithm.

[0097] Specifically, the Wiener filtering algorithm processes the image to obtain the restored image. I re ( x , y The method is as follows:

[0098] S510: Determine the first image (denoted as) corresponding to the optical axis position closest to the focal plane coordinates as described above. h ( x , y )) and the second image g ( x , y );

[0099] S520: During the imaging process, the propagation of light waves is considered to be a linear process. In this imaging process, the final image is formed by convolving the initial target with the PSF of the optical system and adding noise. Therefore, the initial target is determined by the following formula. f ( x , y ): ,in, n ( x , y () indicates image noise.

[0100] S530: The Wiener filtering algorithm is used to restore images by extracting the actual signal from noisy observations, that is, restoring a clear image of the initial target from the noisy and blurred output image. Wiener filtering is a linear minimum mean square error estimation method, aiming to find the actual output image of the initial target while minimizing the mean square error between the two. in, e 2 A measure representing the mean squared error. E {·} represents the expected value of the parameter. f This represents the initial target image. This represents the optimal estimate of the initial target image obtained through the Wiener filtering algorithm, i.e., the image restored using the Wiener filtering algorithm.

[0101] S540: Calculate the restored image The Fourier transform is: in, Represents the restored image Fourier transform image, Represents the first image h ( x , y The Fourier transform image of ) Represents the second image g ( x , y The Fourier transform image of ) Represents the noise power spectrum. This represents the power spectrum of the initial target image.

[0102] S550: For the restored image Fourier transform image Performing the inverse transform yields the restored image, i.e., the recovered image. I re ( x , y ).

[0103] S600: Based on the reconstructed line-pair image obtained in step S500, the line spacing on it can be determined, defined as... y The focal length of the sub-lens is calculated using the following formula. f : f =( f c × y ') / y 0, where, f c This indicates the focal length of the collimator. y 0 indicates the actual line spacing of the Pero plate.

[0104] For some large microlens arrays whose area exceeds the field of view of the image acquisition device, the microlens array is divided into several sub-regions.

[0105] After acquiring the first and second images of the previous sub-region, the image acquisition device or microlens array is shifted to acquire the first and second images of the next sub-region.

[0106] The focal length of each sub-lens in each region can be determined locally and then integrated into the focal length distribution of the complete lens array. Alternatively, the first / second images corresponding to the same optical axis position in each sub-region can be stitched together to form a complete array spot image / complete array line-to-plate image, and then the focal length distribution of the complete lens array can be determined in the manner described above.

[0107] After determining the focal length of each sub-lens in the microlens array, different detection rules can be used to comprehensively judge whether the focal length performance of the current microlens array is qualified. For example, in one embodiment, the focal length detection result of the microlens array is determined in the following way:

[0108] Determine the calculated focal length of each sub-lens of the microlens array;

[0109] Obtain the target focal length value from the sub-lens design parameters of the microlens array;

[0110] The mean square error between the calculated focal length of each sub-lens and its corresponding target focal length is calculated. If the mean square error is less than a preset mean square error threshold, the focal length of the microlens array is determined to be qualified; otherwise, the focal length of the microlens array is unqualified.

[0111] In another embodiment, the calculated focal length of each sub-lens of the microlens array is also determined, and the target focal length value in the sub-lens design parameters of the microlens array is obtained; the difference between the calculated focal length of each sub-lens and the corresponding target focal length value is calculated. If the difference is less than a preset deviation threshold, the sub-lens is determined to be a qualified sub-lens; the number or proportion of qualified sub-lenses in the microlens array is calculated to determine whether the focal length of the microlens array is qualified. For example, if more than four unqualified sub-lenses appear in a microlens array (the difference between the calculated focal length value and the corresponding target focal length value reaches a preset deviation threshold), the microlens array is determined to be unqualified; or, if the proportion of qualified sub-lenses in a microlens array is less than 98% of all sub-lenses, the microlens array is determined to be unqualified.

[0112] In one embodiment, the production process can also be fed back based on the focal length detection results, which is beneficial for timely adjustment of the process parameters of products in production. For example, if the focal length detection results are detected in the array ( i , j If the focal length of the sub-lens at position () is not up to standard, then the master template for fabricating the microlens array should be adjusted accordingly. i , j The curvature of the surface at the specified location. In one embodiment of the present invention, a microlens array template is fabricated using grayscale lithography, and then a microlens array is prepared using embossing transfer. When the detection result shows that the focal length of the sub-lens is too small, a profilometer or similar device is used to check whether the surface morphology of the template is incorrect and whether the curvature is normal. If the curvature is abnormal, the template needs to be remade or the grayscale image data used in the grayscale lithography needs to be changed, and then the parameters of the newly fabricated template need to be adjusted to ensure the curvature is correct. If the actual curvature of the template is correct with the design, it is necessary to consider whether the error in the embossing transfer process is too large and adjust the embossing transfer process parameters, or consider whether the design tolerance is too low and improve the design scheme.

[0113] like Figure 2 and Figure 3 As shown, this embodiment of the invention provides a microlens array focal length detection device, including the following apparatus:

[0114] Stage 100, configured to load the microlens array 200 to be inspected (e.g., Figure 2 (as shown)

[0115] An optical component is configured to provide an optical path incident on the lower surface of the microlens array 200, and the optical path is provided with selectable star points and Perot plates;

[0116] An image acquisition device 400 is disposed above the stage 100 and is configured to acquire images of the microlens array 200 on the stage 100.

[0117] A lifting device, which is equipped with a lifting rail and a lifting drive mechanism 510 configured to drive the image acquisition device or the platform to move along the lifting rail;

[0118] The microlens array focal length detection device uses the method described above to detect the focal length of the microlens array.

[0119] Specifically, such as Figure 2 As shown, the microlens array focal length detection device also includes a horizontal drive mechanism 520, which is configured to drive the image acquisition device 400 to move in the horizontal plane;

[0120] The lifting drive mechanism 510 is configured to drive the image acquisition device 400 to move up and down.

[0121] Specifically, such as Figure 3 As shown, the optical components include a light source 310, a collimator 320, a reflector 330, and a microscope objective 340. The light beam emitted from the light source 310 is converted into a parallel beam by the collimator 320, and the reflector 330 reflects the parallel beam output from the collimator 320 onto the lower surface of the microlens array 200 on the stage 100.

[0122] The image acquisition device 400 is a camera, and the microscope objective 340 is disposed at the lens of the camera.

[0123] It should be noted that the microlens array focal length detection device provided in this embodiment is the main body for implementing the above-described microlens array focal length detection method. This microlens array focal length detection device is equipped with a processor to execute the image processing and calculation steps in the above-described microlens array focal length detection method embodiment, which will not be described again here.

[0124] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0125] The above description is only a specific embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for detecting the focal length of a microlens array based on image-shifting fitting, wherein the microlens array comprises multiple sub-lenses, characterized in that, The focal length detection method includes the following steps: Set up an image acquisition device and adjust the image acquisition device to focus on the microlens array, and determine the position at this time as the reference position; The optical axis distance between the image acquisition device and the microlens array is adjusted with the reference position as the origin, and array images are acquired at multiple adjusted positions. The array images include a first image formed by the star points in the collimator after passing through the microlens array and a second image formed by the Pero plate in the collimator after passing through the microlens array. The target sub-image set is determined by identifying the light spot sub-images corresponding to the same sub-lens in multiple first images. PSF reconstruction is then performed on this set, including: determining the light spot size and optical axis position in the multiple light spot sub-images based on this set, and using a fitting algorithm to determine the optical axis position corresponding to the smallest light spot, defined as the focal plane coordinate Z. t ; Obtain the pixel grayscale value of the line passing through the center point of the light spot in each light spot sub-image of the set, and then fit a Gaussian curve corresponding to each light spot sub-image, wherein the Gaussian curve includes Gaussian curve parameters; determine the focal plane coordinate Z by the fitting algorithm. t The corresponding Gaussian curve parameters are used to reconstruct the PSF function of the sub-lens; First and second images acquired at the same location are selected. The Wiener filtering algorithm is used to restore the sub-images corresponding to the sub-lens in the first and second images, resulting in the restored image, denoted as I. re (x,y); the restored image I re (x,y) is convolved with the PSF function to reconstruct the focal plane coordinates Z. t The corresponding reconstructed line-to-plate image; The focal length f of the sub-lens is calculated using the following formula: f = (f c ×y') / y0, where, f c y' represents the focal length of the collimator, y' represents the line spacing determined based on the reconstructed line-to-plate image, and y0 represents the actual line spacing of the Pero plate.

2. The microlens array focal length detection method based on image-shifting fitting according to claim 1, characterized in that, The focal plane coordinates Z are determined in the following manner. t : Using the reference position as the origin, the optical axis position between the image acquisition device and the microlens array is determined as [Z1, Z2, Z3, ..., Z]. n The first image set [I1, I2, I3, ..., I] was acquired at n optical axis positions. n ]; For the same sub-lens, extract its sub-images from the first image set to form sub-image set I. sub =[I sub-1 ,I sub-2 , I sub-3 ,…, I sub-n ]; The subgraph set I was determined based on image processing techniques. sub The diameters of the light spots in each sub-figure are [d1, d2, d3, ..., d n ]; Constructing higher-order polynomials Where d represents the diameter of the light spot, Z represents the optical axis position between the image acquisition device and the microlens array with the reference position as the origin, and λ i This represents the coefficient of the i-th term in the polynomial; The optical axis position [Z1, Z2, Z3, ..., Z] is... n ], diameter [d1,d2,d3,…,d n Substitute the coefficients into the higher-order polynomial to calculate the coefficients λ. i ; The coefficient λ was calculated. i The local minimum point of a higher-order polynomial is denoted as (Z). lim ,d lim ); Determine the extreme point Z lim The focal plane coordinates Z t .

3. The microlens array focal length detection method based on image-shifting fitting according to claim 1, characterized in that, The PSF function of the sub-lens is reconstructed using the following method: For the first image I1 acquired at optical axis position Z1 between the image acquisition device and the microlens array, determine the sub-image I corresponding to the sublens in the first image I1. sub-1 ; In subgraph I sub-1 Draw a virtual line along a preset direction passing through the center point of the light spot, and sequentially determine the coordinate position and grayscale value of the pixels located on the virtual line along the preset direction [(x1,G1),(x2,G2),(x3,G3),…,(x m G m )]; Substitute into Gaussian curve distribution Calculate the Gaussian curve parameters [a1,b1,c1] corresponding to the optical axis position Z1; Repeat the above steps to determine the positions of the remaining optical axes [Z2, Z3, ..., Z]. n The corresponding Gaussian curve parameters are {[a2,b2,c2],[a3,b3,c3],…,[a...}. n ,b n ,c n ]}; The focal plane coordinates Z were obtained by fitting. t The corresponding Gaussian curve parameters [a] t ,b t ,c t ]; The PSF function of this sub-lens is determined as follows: .

4. The method for detecting the focal length of a microlens array based on image-shifting fitting as described in claim 1, characterized in that, The processing target of the Wiener filtering algorithm is determined in the following way: With the reference position as the origin, the optical axis position corresponding to the adjustment of the optical axis distance between the image acquisition device and the microlens array is defined as [Z1, Z2, Z3, ..., Z]. n ]; Determine the focal plane coordinates Z from this. t The closest optical axis position is denoted as Z. adj ; Obtain the Z position on the optical axis adj The first and second images were captured at the location; The first and second sub-images corresponding to the sub-lens are extracted from the first and second images and used as the processing objects of the Wiener filtering algorithm.

5. The microlens array focal length detection method based on image-shifting fitting according to claim 1, characterized in that, The optical axis distance between the image acquisition device and the microlens array is adjusted in the following manner: Using a star point within a collimator, the image acquisition device is adjusted to the focus position when the light spot formed by the star point after being focused by the microlens array is less than the diffraction limit of the image acquisition device. The image acquisition device is moved along the optical axis between the image acquisition device and the microlens array, so that it floats a preset distance on both sides with the focus position as the reference position, and the floating points on both sides are symmetrically distributed relative to the reference position.

6. The microlens array focal length detection method based on image-shifting fitting according to claim 5, characterized in that, Float on both sides in the following way: Make the distance between adjacent floating points equal; Alternatively, with the reference position as the origin, the distance that floats along the optical axis each time is the focal depth distance of the image acquisition device or multiple times the focal depth distance.

7. The method for detecting the focal length of a microlens array based on image-shifting fitting as described in claim 1, characterized in that, If the microlens array extends beyond the field of view of the image acquisition device, the microlens array is divided into several sub-regions; After acquiring the first and second images of the previous sub-region, the image acquisition device or microlens array is shifted to acquire the first and second images of the next sub-region.

8. The microlens array focal length detection method based on image-shifting fitting according to claim 1, characterized in that, The image acquisition device, microlens array, and collimator are deployed in the following manner: The microlens array is placed horizontally, and the image acquisition device is positioned above the microlens array; The inlet of the collimator is positioned opposite to the light source, and the light beam emitted from the collimator is either directly incident on the lower surface of the microlens array or after reflection.

9. The method for detecting the focal length of a microlens array based on image-shifting fitting according to any one of claims 1 to 8, characterized in that, The focal length detection result of the microlens array is determined by the following method: Determine the calculated focal length of each sub-lens of the microlens array; Obtain the target focal length value from the sub-lens design parameters of the microlens array; Calculate the mean square error between the calculated focal length of each sub-lens and its corresponding target focal length. If the mean square error is less than a preset mean square error threshold, then the focal length of the microlens array is determined to be qualified; otherwise, the focal length of the microlens array is unqualified. Alternatively, calculate the difference between the calculated focal length of each sub-lens and the corresponding target focal length. If the difference is less than a preset deviation threshold, then the sub-lens is determined to be a qualified sub-lens. The number or proportion of qualified sub-lenses in the microlens array is calculated to determine whether the focal length of the microlens array is qualified.

10. A microlens array focal length detection device, characterized in that, Includes the following devices: The stage is configured to load the microlens array to be tested; An optical component configured to provide an optical path incident on the lower surface of the microlens array, wherein optional star points and Perot plates are disposed along the optical path; An image acquisition device is disposed above the stage and is configured to acquire images of the microlens array on the stage. A lifting device, which is equipped with a lifting rail and a lifting drive mechanism configured to drive the image acquisition device or the platform to move along the lifting rail; A processor for performing the method as described in any one of claims 1 to 9 to detect the focal length of a microlens array.

11. The microlens array focal length detection device according to claim 10, characterized in that, It also includes a horizontal drive mechanism configured to drive the image acquisition device to move in a horizontal plane; The lifting drive mechanism is configured to drive the image acquisition device to move up and down.

12. The microlens array focal length detection device according to claim 10 or 11, characterized in that, The optical components include a light source, a collimator, a mirror, and a microscope objective. The light beam emitted from the light source is converted into a parallel beam by the collimator, and the mirror reflects the parallel beam output from the collimator onto the lower surface of the microlens array on the stage. The image acquisition device is a camera, and the microscope objective is located at the lens of the camera.

Images