A Shack-Hartmann wavefront reconstruction method and system based on displacement identification

Abstract

This invention discloses a Shakhartmann wavefront reconstruction method and system based on displacement identifiers. It includes: under reference wavefront conditions, acquiring two spot images—one unloaded and one loaded with preset phase modulation—using a Shakhartmann detector unit, recording the displacement of the spot within each sub-aperture before and after modulation, and establishing a displacement identifier library; under the wavefront condition to be measured, acquiring two spot images before and after modulation with the same preset phase, calculating the displacement of each spot as the measured displacement; matching the measured displacement with the displacements in the displacement identifier library, and identifying the sub-aperture of each spot based on the matching results; calculating the local wavefront slope of each sub-aperture based on the identified spot position, and reconstructing the wavefront. This invention establishes a distinguishable displacement identifier for each sub-aperture through a preset phase, and uses displacement matching instead of absolute position identification, enabling accurate identification when the spot crosses boundaries or there is crosstalk between sub-apertures, significantly improving the dynamic range of the Shakhartmann sensor.

Description

Technical Field

[0001] This invention relates to the field of wavefront sensing and optical measurement technology, specifically to a Shaker-Hartmann wavefront reconstruction method and system based on displacement identification. Background Technology

[0002] The Shaker-Hartmann wavefront sensor divides the incident wavefront into multiple sub-apertures using a microlens array, forming a corresponding focal array on the detector. By measuring the displacement of each focal point relative to a reference position, the local wavefront slope at each sub-aperture can be obtained, thus enabling reconstruction of the wavefront under test. This method offers advantages such as high measurement speed, relatively simple structure, and strong resistance to environmental disturbances, and has been widely applied in fields such as astronomical observation, biological imaging, ophthalmic diagnosis, and adaptive optics.

[0003] Traditional Shaker-Hartmann wavefront measurements typically assume that the spot formed by each microlens always falls within the detection area of ​​its original corresponding sub-aperture. When the wavefront under test has large aberrations and a high local slope, some spots may extend beyond the original sub-aperture boundary, or even swap or overlap with adjacent spots, causing the spot assignment determination based on the fixed window to fail, thus affecting the wavefront reconstruction results.

[0004] To address the issues of large displacement or light spot aliasing, existing technologies have proposed various solutions, such as multi-plane imaging, global search matching, neural network recognition, and holographic or diffraction-coded wavefront sensing. However, multi-plane imaging typically requires additional probe planes; global search matching usually suffers from large search spaces and high computational costs; neural network recognition often depends on the quality of training samples and the model's generalization ability; and holographic or diffraction-coded wavefront sensing typically relies on customized coding devices such as digital microlens arrays, reconfigurable microlens arrays, or microholographic arrays, combined with pattern correlation or pattern recognition to complete measurements, thus making device design and system implementation quite complex.

[0005] Therefore, it is necessary to propose a new Shaker-Hartmann wavefront measurement technique that, without increasing the system complexity too much, can still achieve reliable correspondence between the light spot and the sub-aperture when the light spot undergoes large displacement, crosses boundaries, or is repositioned, and on this basis, complete wavefront reconstruction. Summary of the Invention

[0006] The purpose of this invention is to provide a Shaker-Hartmann wavefront reconstruction method and system based on displacement identification, so as to solve the problem in the prior art that it is difficult to accurately determine the sub-aperture correspondence and stably perform wavefront reconstruction under the conditions of large aberration, large displacement, and spot transposition.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A Shaker-Hartmann wavefront reconstruction method based on displacement identification, comprising the following steps:

[0008] Under reference wavefront conditions, the first reference spot image without a preset phase and the second reference spot image with a preset phase are acquired by the Shaker-Hartmann detector unit.

[0009] The first and second reference spot images are segmented and their positions are extracted to obtain the position parameters of each reference spot. The displacement identifiers corresponding to each sub-aperture are established based on the displacement of the corresponding reference spot before and after loading the preset phase.

[0010] Under the conditions of the wavefront to be measured, the first spot image of the light under test without the preset phase and the second spot image of the light under test with the preset phase are respectively acquired by the Shaker-Hartmann detector unit.

[0011] The first and second light spot images to be tested are segmented and their positions are extracted to obtain a set of position parameters of the light spot to be tested.

[0012] Based on the displacement to be measured formed between the first and second light spot images to be measured, the displacement identifier is compared and matched to determine the correspondence between the light spot to be measured and each sub-aperture.

[0013] Based on the correspondence, the positional offset of each test spot in the first test spot image relative to the corresponding reference spot in the first reference spot image is calculated to obtain the local wavefront slope at each sub-aperture.

[0014] Wavefront reconstruction is performed based on the local wavefront slope to obtain the wavefront distribution to be measured.

[0015] Furthermore, the displacement identifier is a displacement vector, displacement direction, or displacement amplitude, which is obtained by generating additional displacements that can be distinguished from each other by preset phase to make the light spots corresponding to different sub-apertures.

[0016] Furthermore, the preset phase is set at a preset phase loading position that is conjugate to the wavefront plane to be measured and the entrance pupil plane of the microlens array.

[0017] Furthermore, the spot segmentation and location extraction includes: binarizing the spot image to obtain candidate spot regions; then performing small connected component removal and morphological closing operations on the binary image to suppress noise and connect broken regions; next, performing connected component detection on the processed image and calculating the coarse centroid position of each candidate spot; then constructing a coarse search window centered on each coarse centroid position, and performing local threshold centroid calculation within each coarse search window to obtain the fine centroid position of each spot.

[0018] Furthermore, determining the correspondence between the light spot to be measured and each sub-aperture includes:

[0019] Based on the candidate spot positions obtained by spot segmentation in the first and second test spot images, candidate spot pairings are established. For each candidate spot pairing, the test displacement is calculated, and a cost function corresponding to the test displacement and the sub-aperture displacement identifier is constructed. Under the condition of satisfying the one-to-one matching constraint, the matching result with the minimum cost function corresponding to each sub-aperture displacement identifier is solved. When the minimum cost value is greater than the preset threshold, the matching is regarded as an abnormal result and is removed.

[0020] Furthermore, the method for obtaining the preset phase includes: calculating the minimum distance between adjacent light spots that can be distinguished according to the Rayleigh criterion, determining the displacement design step size according to the minimum distance; selecting several discrete displacement quantities as candidate displacement identifiers, and assigning different displacement identifiers to different sub-apertures; and finally obtaining the preset phase distribution inside each sub-aperture according to the corresponding displacement identifier.

[0021] According to another aspect of the specification, a Shakhartmann wavefront reconstruction system based on displacement identification for implementing the method is also provided, comprising: a pre-stage relay optical unit, a preset phase loading unit, a post-stage relay optical unit, a Shakhartmann detection unit, and a processing unit arranged sequentially along the propagation direction of the wavefront to be measured.

[0022] The front-stage relay optical unit is used to adjust the beam size and conjugate the wavefront to be measured to a preset phase loading position.

[0023] The preset phase loading unit is set at the preset phase loading position and can switch between the loaded state and the unloaded state, so as to generate a displacement mark that can be distinguished from each other between the light spots corresponding to different sub-apertures and the loaded state.

[0024] The subsequent relay optical unit is used to adjust the beam size and transmit the beam modulated by the preset phase loading unit to the Shackleham-Hartmann detection unit.

[0025] The Shaker-Hartmann detection unit includes a microlens array and a camera, and the preset phase loading position is conjugate to the entrance pupil plane of the microlens array;

[0026] The processing unit is electrically connected to the camera and is used for:

[0027] Under reference wavefront conditions, displacement markers corresponding to each sub-aperture are established based on the first reference spot image acquired when no preset phase is applied and the second reference spot image acquired when the preset phase is applied.

[0028] Under the conditions of the wavefront to be measured, the displacement to be measured is formed based on the first spot image to be measured acquired when the preset phase is not applied and the second spot image to be measured acquired when the preset phase is applied.

[0029] Based on the comparison and matching between the displacement to be measured and the displacement identifier, the correspondence between the light spot to be measured and each sub-aperture is determined;

[0030] Based on the positional offset of the corresponding test spot in the first test spot image relative to the corresponding reference spot in the first reference spot image, the local wavefront slope at each sub-aperture is calculated and wavefront reconstruction is performed.

[0031] Furthermore, the preset phase loading unit is one of a fixed phase plate, a multi-stage switchable phase plate, or a deformable mirror.

[0032] Furthermore, the multi-stage switchable preset phase plate assembly adopts a turntable structure, which allows different workstations to sequentially enter the preset phase loading position by rotation. It includes multiple switchable workstations, each workstation corresponding to an optical state, including at least one blank light-transmitting workstation and one preset phase loading workstation.

[0033] Furthermore, the deformable mirror is a reflective deformable mirror with multiple driving units. The deformable mirror can switch between a reference state and a preset surface shape state. The reference state is a state in which the mirror surface maintains a planar shape as a whole. The preset surface shape state is a state in which the mirror surface forms a preset surface shape under the control of the driving signal, thereby introducing a preset phase modulation to the reflected beam. When using the reflective deformable mirror, the optical path adopts a folded structure so that the beam output from the front-stage relay optical unit is incident on the surface of the deformable mirror.

[0034] The beneficial effects of this invention are as follows:

[0035] (1) By loading a preset phase at a position conjugate to the entrance pupil plane of the microlens array, a designable and distinguishable additional displacement is introduced for the light spots corresponding to different sub-apertures, thereby transforming the traditional sub-aperture assignment problem that relies on a fixed spatial position into a corresponding determination problem based on displacement identification.

[0036] (2) When the light spot to be measured crosses the boundary or changes position, the displacement marker can still be used to improve the correspondence accuracy between the light spot and the sub-aperture, which is conducive to improving the effectiveness of Shaker-Hartmann wavefront measurement in a large dynamic range scenario.

[0037] (3) The method can be implemented by either a fixed phase plate or a programmable phase modulator, making the system implementation flexible;

[0038] (4) After completing the sub-aperture correspondence determination, it can be compatible with existing wavefront reconstruction processes such as mode method and region method, which is convenient for engineering applications. Attached Figure Description

[0039] Figure 1 This is a flowchart of the method of the present invention;

[0040] Figure 2 This is a schematic diagram illustrating the principle of sub-aperture identification using displacement markers in this invention;

[0041] Figure 3 This is a schematic diagram of the system structure in Embodiment 1 of the present invention;

[0042] Figure 4 This is a schematic diagram of the morphological processing of the local area of ​​the light spot and the construction of the search window in Embodiment 1 of the present invention;

[0043] Figure 5 This is a schematic diagram showing the comparison of results in Embodiment 1 of the present invention. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0045] Example 1: Based on a fixed preset phase plate

[0046] This embodiment provides a method and system for Shakhartmann wavefront reconstruction based on displacement identification. For example... Figure 1 As shown, the process includes the following steps: First, under reference wavefront conditions, two reference spot images are acquired using a Shakhartmann detector unit, one with a preset phase applied and the other with a preset phase applied. The positions of the reference spots are obtained through spot segmentation and position extraction, and the displacement markers corresponding to each sub-aperture are calculated. Then, under the wavefront conditions to be measured, two spot images to be measured are acquired using a Shakhartmann detector unit, one with a preset phase applied and the other with a preset phase applied. Spot segmentation and position extraction are performed to obtain the positions of the spots to be measured. Next, the displacements to be measured are matched with the displacement markers corresponding to each sub-aperture, and the sub-aperture identification is completed by comparing the displacement differences. Finally, the local wavefront slope at each sub-aperture is calculated based on the identified spot positions, and the results are input into the wavefront reconstruction program to recover the wavefront phase to be measured.

[0047] like Figure 2 As shown, Figure 2 (a) shows a schematic diagram of the reference spot distribution when the preset phase is not loaded; Figure 2 (b) shows a schematic diagram of the additional spot displacement caused only by the preset phase, where the red arrows indicate the displacement caused by the preset phase; Figure 2 (c) shows a schematic diagram of the spot displacement caused only by the wavefront to be measured, where the green arrow indicates the displacement caused by the wavefront to be measured; Figure 2 Figure (d) shows a schematic diagram illustrating the change in the beam spot position when the preset phase displacement and the wavefront displacement to be measured act together. Figure 2As can be seen, the core idea of ​​this embodiment is: for each sub-aperture, a distinguishable additional displacement vector is introduced in advance using a preset phase, so that different sub-apertures correspond to different displacement identifiers; when the light spot is to be measured, even if the light spot goes out of bounds, shifts, or no longer falls within the original geometric sub-aperture range due to aberrations, it can still be matched with the pre-established displacement identifier by its displacement change before and after the preset phase is applied, thereby determining the sub-aperture to which the light spot belongs.

[0048] Specifically, under the condition that the reference wavefront is a plane wave, the preset phase plate is moved out of the optical path and the first reference light spot image I0 is acquired; then the preset phase plate is inserted into the optical path and the second reference light spot image I1 is acquired.

[0049] Subsequently, spot segmentation and centroid extraction were performed on the two reference spot images, as follows: Figure 4 As shown. Figure 4 This paper illustrates the processing steps from the original spot array and candidate spot region extraction to fine-tuning. Since the spots in this embodiment may extend beyond the corresponding sub-aperture range, the criterion of "spot located within a fixed sub-aperture" is no longer used. Instead, the candidate spots in the entire image are directly located. Specifically, the spot image is first binarized to obtain candidate spot regions. Then, small connected component removal and morphological closing operations are performed on the binary image to suppress noise and connect broken regions. Next, connected component detection is performed on the processed image, and the coarse centroid position of each candidate spot is calculated. Finally, a coarse search window is constructed centered on each coarse centroid position, and local threshold centroid calculation is performed within each coarse search window to obtain the fine centroid position of each spot.

[0050] Therefore, the reference spot positions corresponding to the j-th sub-aperture are calculated as follows:

[0051] ,

[0052] ,

[0053] The displacement identifier of the j-th sub-aperture is defined as:

[0054] ,

[0055] All sub-apertures To construct a displacement identifier library.

[0056] Wavefront to be measured Under incident conditions, the preset phase plate is moved out of the optical path and the first test spot image I0´ is acquired; then the preset phase plate is inserted into the optical path and the second test spot image I1´ is acquired.

[0057] Spot segmentation and position extraction were performed on I0´ and I1´ respectively, resulting in:

[0058] ,

[0059] ,

[0060] Among them, c 0,m Let c be the position of the m-th candidate spot in the first test spot image. 1,n This represents the position of the nth candidate spot in the second test spot image.

[0061] For any candidate pair (m,n), its displacement to be measured is defined as:

[0062] ,

[0063] And construct the cost function corresponding to the j-th sub-aperture displacement identifier:

[0064] ,

[0065] Under the condition of satisfying the one-to-one matching constraint, the matching result with the minimum cost function is solved to determine the correspondence between the light spot to be tested and the sub-aperture. Preferably, when the minimum cost value is greater than a preset threshold, the matching is regarded as an abnormal result and discarded.

[0066] After completing the sub-aperture identification, let c be the position of the corresponding spot in the first light spot image to be measured. 0,π(j) Then the actual displacement caused by the aberration to be measured is:

[0067] ,

[0068] Let the focal length of the microlens be f, then the local wavefront slope at the j-th sub-aperture can be expressed as:

[0069] ,

[0070] ,

[0071] Finally, the local wavefront slopes of all effective sub-apertures are input into the wavefront reconstruction program, and the wavefront to be measured is recovered using the mode method.

[0072] Systems for implementing the above methods include Figure 3As shown, the system includes a pre-stage relay optical unit, a preset phase loading unit, a post-stage relay optical unit, a Shakhartmann detector unit, and a processing unit (not shown in the figure), arranged sequentially along the propagation direction of the wavefront to be measured. The pre-stage relay optical unit adjusts the beam size and conjugates the wavefront to be measured to the preset phase loading position. The preset phase loading unit is located at the preset phase loading position and can switch between a loaded state and an unloaded state, enabling the light spots corresponding to different sub-apertures to generate mutually distinguishable displacement indicators between the loaded and unloaded states. The post-stage relay optical unit adjusts the beam size and transmits the beam modulated by the preset phase loading unit to the Shakhartmann detector unit. The Shakhartmann detector unit includes a microlens array and a camera for acquiring images of the focal array. The preset phase loading position is conjugate to the entrance pupil plane of the microlens array.

[0073] The processing unit is electrically connected to the camera and is used for:

[0074] Under reference wavefront conditions, displacement markers corresponding to each sub-aperture are established based on the first reference spot image acquired without a preset phase and the second reference spot image acquired with a preset phase. Under the wavefront condition to be measured, the displacement to be measured is formed based on the first spot image to be measured acquired without a preset phase and the second spot image to be measured acquired with a preset phase. The correspondence between the spot to be measured and each sub-aperture is determined by comparing and matching the displacement to be measured with the displacement markers. Based on the positional offset of the corresponding spot to be measured in the first spot image to be measured relative to the corresponding reference spot in the first reference spot image, the local wavefront slope at each sub-aperture is calculated and wavefront reconstruction is performed.

[0075] In this embodiment, the wavelength λ of the light to be measured is 532 nm, and the wavefront aberration to be measured is set as a linear combination of the first 15 Zernike polynomials (excluding the first term), with each Zernike coefficient randomly generated. The pre-stage relay optical unit includes a first lens 1 and a second lens 2, and the post-stage relay optical unit includes a third lens 3 and a fourth lens 4. The preset phase loading unit is located at a preset phase loading position between the second lens 2 and the third lens 3. The microlens array is the Edmund 64-483, with 20×20 sub-lenses; the camera is the Thorlabs CC126MU. The preset phase loading unit is an insertable / removable fixed phase plate, which is used to create distinguishable additional displacements on the detection surface for light spots corresponding to different sub-apertures.

[0076] To ensure that the additional displacements of different sub-apertures are distinguishable from each other, this embodiment calculates the minimum distance between adjacent light spots that can be distinguished based on the Rayleigh criterion:

[0077] ,

[0078] Where NA is the numerical aperture of the microlens array. The displacement design step size is determined based on the minimum spacing; in this embodiment, a step size of 65 μm is selected. Subsequently, 20 discrete displacements are selected symmetrically around 0 as candidate displacements in the lateral and longitudinal directions, respectively. Then, different displacement vectors are assigned to different sub-apertures by combining the lateral and longitudinal displacements. Finally, the preset phase distribution inside each sub-aperture is obtained based on the corresponding displacement vector, thereby forming a fixed preset phase plate.

[0079] Figure 5 A set of results from this embodiment is shown. Among them, Figure 5 (a) in this embodiment is the preset phase distribution designed in this embodiment; Figure 5 (b) is the reference spot pattern obtained when the reference wavefront is a plane wave and no preset phase is applied; Figure 5 (c) in the image is a reference spot pattern obtained after the reference wavefront is a plane wave and a preset phase is applied. Figure 5 (d) in the figure represents the light spot image obtained when the wavefront aberration exists and no preset phase is applied; Figure 5 (e) in the figure is the light spot image obtained after the wavefront aberration exists and a preset phase is applied; Figure 5 Figure (f) shows a comparison of wavefront reconstruction results, where the left image represents the true wavefront, the middle image represents the reconstruction result of the method in this embodiment, and the right image represents the reconstruction result of the traditional method. Figure 5 As can be seen from (f) in the figure, even when the light spot goes out of bounds, this embodiment can still accurately complete the sub-aperture identification and recover the wavefront to be measured, while the traditional method has a large error in the reconstruction result because it is difficult to correctly establish the correspondence between the light spot and the sub-aperture.

[0080] The processing unit can be implemented by a personal computer, workstation, industrial control computer or other data processing equipment; in this embodiment, the processing unit is a personal computer.

[0081] Example 2: Based on a reflective deformable mirror

[0082] This embodiment provides a Shaker-Hartmann wavefront reconstruction method and system based on displacement identification. The basic principle of this embodiment is the same as that of Embodiment 1, the difference being that the preset phase loading unit in this embodiment is not a transmission-type fixed preset phase plate, but a reflection-type deformable mirror.

[0083] The method of this embodiment includes the following steps: First, under the reference wavefront condition, two reference spot images are acquired using a Shakhartmann detector unit, one with a preset phase and the other with a preset phase. The positions of the reference spots are obtained through spot segmentation and position extraction, and then the displacement markers corresponding to each sub-aperture are calculated. Subsequently, under the wavefront condition to be measured, two spot images to be measured are acquired using a Shakhartmann detector unit, one with a preset phase and the other with a preset phase. Spot segmentation and position extraction are performed similarly to obtain the positions of the spots to be measured. Then, the displacements to be measured are matched with the displacement markers corresponding to each sub-aperture, and the sub-aperture identification is completed by comparing the displacement differences. Finally, the local wavefront slope at each sub-aperture is calculated based on the identified spot positions, and the results are input into the wavefront reconstruction program to recover the wavefront phase to be measured.

[0084] For each sub-aperture, a distinguishable additional displacement vector is introduced in advance using a preset phase, so that different sub-apertures correspond to different displacement identifiers. When the light spot is to be measured, even if it goes out of bounds, shifts, or no longer falls within the original geometric sub-aperture range due to aberrations, it can still be matched with the pre-established displacement identifier by its displacement change before and after the preset phase is applied, thereby determining the sub-aperture to which the light spot belongs.

[0085] The system for implementing the above method includes a pre-stage relay optics unit, a reflective deformable mirror, a post-stage relay optics unit, a Shakhartmann detector unit, and a processing unit. Since the deformable mirror is a reflective phase modulator, the optical path in this embodiment adopts a folded structure, allowing the beam output from the pre-stage relay optics unit to be incident on the surface of the deformable mirror. After being reflected by the deformable mirror and loaded with a preset phase, the beam enters the post-stage relay optics unit and is finally transmitted to the microlens array and camera. The pre-stage relay optics unit is used to adjust the beam size and conjugate the wavefront to be measured to the preset phase loading position. The post-stage relay optics unit is used to adjust the beam size and transmit the beam modulated by the preset phase loading unit to the Shakhartmann detector unit. The Shakhartmann detector unit includes a microlens array and a camera for acquiring images of the focal array. The deformable mirror is conjugate to the entrance pupil plane of the microlens array, and the reflective surface of the deformable mirror constitutes the preset phase loading position.

[0086] The processing unit is electrically connected to the camera and is used for: under reference wavefront conditions, establishing displacement markers corresponding to each sub-aperture based on a first reference spot image acquired without a preset phase and a second reference spot image acquired with a preset phase; under the wavefront condition to be measured, forming a displacement to be measured based on a first spot image to be measured acquired without a preset phase and a second spot image to be measured acquired with a preset phase; determining the correspondence between the spot to be measured and each sub-aperture based on a comparison and matching of the displacement to be measured and the displacement markers; and calculating the local wavefront slope at each sub-aperture and performing wavefront reconstruction based on the positional offset of the corresponding spot to be measured in the first spot image to be measured relative to the corresponding reference spot in the first reference image.

[0087] In this embodiment, the deformable mirror is a reflective deformable mirror with multiple driving units. The deformable mirror can switch between a reference state and a preset surface shape state. The reference state is when the mirror surface maintains its overall planar shape, while the preset surface shape state is when the mirror surface forms a preset surface shape under the control of a driving signal, thereby introducing a preset phase modulation to the reflected light beam. The preset surface shape is used to create distinguishable additional displacements on the detection surface for light spots corresponding to different sub-apertures.

[0088] Under reference wavefront conditions, the deformable mirror is first set to a baseline state, and a first reference spot image is acquired. Then, a predetermined driving signal is applied to the deformable mirror to switch it to a preset surface shape state, and a second reference spot image is acquired. Subsequently, spot segmentation and centroid extraction are performed on the two reference spot images. Since the spot may also exceed the corresponding sub-aperture range in this embodiment, the criterion of "the spot being located within a fixed sub-aperture" is no longer used; instead, candidate spots in the entire image are directly located. Specifically, the spot image is first binarized to obtain candidate spot regions; then, small connected component removal and morphological closing operations are performed on the binary image to suppress noise and connect broken regions; next, connected component detection is performed on the processed image, and the coarse centroid position of each candidate spot is calculated; then, a coarse search window is constructed centered on each coarse centroid position, and local threshold centroid calculation is performed within each coarse search window to obtain the fine centroid position of each spot. Based on the changing relationship of the spot positions in the two reference spot images, displacement markers corresponding to each sub-aperture are established.

[0089] Under the conditions of the wavefront to be measured, the deformable mirror is first restored to the reference state, and a first test spot image is acquired. Then, the deformable mirror is switched to a preset surface shape state, and a second test spot image is acquired. After spot segmentation and centroid extraction of the two test spot images, the same displacement identifier matching and sub-aperture correspondence determination method as in Example 1 is used to determine the correspondence between the test spot and each sub-aperture. Based on the positional offset of the test spot relative to the reference spot under the reference state, the local wavefront slope at each sub-aperture is calculated. After obtaining the local wavefront slope, wavefront recovery is performed using the pattern method.

[0090] In this embodiment, since the deformable mirror switches between a reference state and a preset surface shape state electronically, the transition between the two states does not require mechanical insertion or removal. Compared to the method of inserting / removing a fixed preset phase plate in Embodiment 1, this embodiment improves the convenience and controllability of preset phase switching and facilitates flexible adjustment of the preset phase distribution according to different needs.

[0091] Example 3: Based on a multi-level switching preset phase plate assembly

[0092] This embodiment provides a Shaker-Hartmann wavefront reconstruction method and system based on displacement identification. The basic principle of this embodiment is the same as that of Embodiment 1, except that the preset phase loading unit in this embodiment is not a single fixed preset phase plate, but a multi-stage switchable preset phase plate assembly.

[0093] The method of this embodiment includes the following steps: First, under the reference wavefront condition, two reference spot images are acquired using a Shakhartmann detector unit, one with a preset phase and the other with a preset phase. The positions of the reference spots are obtained through spot segmentation and position extraction, and the displacement markers corresponding to each sub-aperture are calculated. Then, under the wavefront condition to be measured, two spot images to be measured are acquired using a Shakhartmann detector unit, one with a preset phase and the other with a preset phase. Spot segmentation and centroid extraction are performed to obtain the position of the spot to be measured. The displacement to be measured is then matched with the displacement markers corresponding to each sub-aperture, and the sub-aperture identification is completed by comparing the displacement differences. Finally, the local wavefront slope at each sub-aperture is calculated based on the spot position after identification, and the result is input into the wavefront reconstruction program to recover the wavefront phase to be measured.

[0094] For each sub-aperture, a distinguishable additional displacement vector is introduced in advance using a preset phase, so that different sub-apertures correspond to different displacement identifiers. When the light spot is to be measured, even if it goes out of bounds, shifts, or no longer falls within the original geometric sub-aperture range due to aberrations, it can still be matched with the pre-established displacement identifier by its displacement change before and after the preset phase is applied, thereby determining the sub-aperture to which the light spot belongs.

[0095] The system for implementing the above method includes a pre-stage relay optics unit, a multi-stage switchable preset phase plate assembly, a post-stage relay optics unit, a Shakhartmann detector unit, and a processing unit. The pre-stage relay optics unit adjusts the beam size and conjugates the wavefront to be measured to a preset phase loading position. The post-stage relay optics unit adjusts the beam size and transmits the beam modulated by the preset phase loading unit to the Shakhartmann detector unit. The Shakhartmann detector unit includes a microlens array and a camera for acquiring images of the focal array. The multi-stage switchable preset phase plate assembly is positioned at the preset phase loading position and conjugates with the entrance pupil plane of the microlens array.

[0096] The processing unit is electrically connected to the camera and is used for: under reference wavefront conditions, establishing displacement markers corresponding to each sub-aperture based on a first reference spot image acquired without a preset phase and a second reference spot image acquired with a preset phase; under the wavefront condition to be measured, forming a displacement to be measured based on a first spot image to be measured acquired without a preset phase and a second spot image to be measured acquired with a preset phase; determining the correspondence between the spot to be measured and each sub-aperture based on a comparison and matching of the displacement to be measured and the displacement markers; and calculating the local wavefront slope at each sub-aperture and performing wavefront reconstruction based on the positional offset of the corresponding spot to be measured in the first spot image to be measured relative to the corresponding reference spot in the first reference image.

[0097] In this embodiment, the multi-position switchable preset phase plate assembly includes multiple switchable stations, each corresponding to an optical state. It includes at least one blank light-transmitting station and one preset phase loading station; furthermore, it may include multiple loading stations with different preset phase patterns. The multi-position switchable preset phase plate assembly adopts a turntable structure, and rotation causes different stations to sequentially enter the preset phase loading position. When entering the blank light-transmitting station, the light beam propagates in a state without preset phase loading; when entering the preset phase loading station, the light beam passes through the preset phase plate on the corresponding station, thereby introducing preset phase modulation. The preset phase loading station is used to create distinguishable additional displacements on the detection surface for light spots corresponding to different sub-apertures.

[0098] Under reference wavefront conditions, the multi-stage switchable preset phase plate assembly is first switched to the blank light transmission station to acquire the first reference spot image; then, it is switched to the selected preset phase loading station to acquire the second reference spot image. Subsequently, spot segmentation and position extraction are performed on the two reference spot images. Since the spot may also exceed the corresponding sub-aperture range in this embodiment, the criterion of "the spot being located within a fixed sub-aperture" is no longer used; instead, candidate spots in the entire image are directly located. Specifically, the spot image is first binarized to obtain candidate spot regions; then, small connected component removal and morphological closing operations are performed on the binary image to suppress noise and connect broken regions; next, connected component detection is performed on the processed image, and the coarse centroid position of each candidate spot is calculated; then, a coarse search window is constructed centered on each coarse centroid position, and local threshold centroid calculation is performed within each coarse search window to obtain the fine centroid position of each spot. Based on the changing relationship of the spot positions in the two reference spot images, displacement markers corresponding to each sub-aperture are established.

[0099] Under the conditions of the wavefront to be measured, the preset phase plate assembly is first switched to the blank light transmission station to acquire the first test spot image; then it is switched to the selected preset phase loading station to acquire the second test spot image. After performing spot segmentation and centroid extraction on the two test spot images respectively, the same displacement identifier matching and sub-aperture correspondence determination method as in Example 1 is used to determine the correspondence between the test spot and each sub-aperture, and the local wavefront slope at each sub-aperture is obtained based on the positional offset of the test spot relative to the reference spot under the blank light transmission station state. After obtaining the local wavefront slope, wavefront recovery is performed using the mode method.

[0100] In this embodiment, the multi-position switchable preset phase plate assembly can be pre-configured with multiple preset phase plates of different patterns, thereby selecting the appropriate preset phase loading station according to system parameters, displacement indicators, and specific measurement tasks. Compared to the scheme using a single fixed preset phase plate in Embodiment 1, this embodiment improves the flexibility of preset phase selection while maintaining a relatively simple system structure; compared to the scheme with only a single loading station, this embodiment can also switch different preset phase patterns according to different application scenarios to obtain a more suitable displacement indicator distribution.

[0101] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this application are indicated by the claims.

[0102] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this application. This application is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A method for reconstructing the Shakhartmann wavefront based on displacement identifiers, characterized in that, Includes the following steps: Under reference wavefront conditions, the first reference spot image without a preset phase and the second reference spot image with a preset phase are acquired by the Shaker-Hartmann detector unit. The first and second reference spot images are segmented and their positions are extracted to obtain the position parameters of each reference spot. The displacement identifiers corresponding to each sub-aperture are established based on the displacement of the corresponding reference spot before and after loading the preset phase. Under the conditions of the wavefront to be measured, the first spot image of the light under test without the preset phase and the second spot image of the light under test with the preset phase are respectively acquired by the Shaker-Hartmann detector unit. The first and second light spot images to be tested are segmented and their positions are extracted to obtain a set of position parameters of the light spot to be tested. Based on the displacement to be measured formed between the first and second light spot images to be measured, the displacement identifier is compared and matched to determine the correspondence between the light spot to be measured and each sub-aperture. Based on the correspondence, the positional offset of each test spot in the first test spot image relative to the corresponding reference spot in the first reference spot image is calculated to obtain the local wavefront slope at each sub-aperture. Wavefront reconstruction is performed based on the local wavefront slope to obtain the wavefront distribution to be measured.

2. The method for Shakhartmann wavefront reconstruction based on displacement identification according to claim 1, characterized in that, The displacement identifier is a displacement vector, displacement direction, or displacement amplitude, which is obtained by generating additional displacements that can be distinguished from each other by preset phase to make the light spots corresponding to different sub-apertures.

3. The Shakhartmann wavefront reconstruction method based on displacement identification according to claim 1, characterized in that, The preset phase is set at a preset phase loading position that is conjugate to the wavefront plane to be measured and the entrance pupil plane of the microlens array.

4. The Shakhartmann wavefront reconstruction method based on displacement identification according to claim 1, characterized in that, The spot segmentation and location extraction includes: binarizing the spot image to obtain candidate spot regions; then performing small connected component removal and morphological closing operations on the binary image to suppress noise and connect broken regions; next, performing connected component detection on the processed image and calculating the coarse centroid position of each candidate spot; then constructing a coarse search window centered on each coarse centroid position, and performing local threshold centroid calculation within each coarse search window to obtain the fine centroid position of each spot.

5. The Shakhartmann wavefront reconstruction method based on displacement identifiers according to claim 1, characterized in that, Determining the correspondence between the light spot to be measured and each sub-aperture includes: Based on the candidate spot positions obtained by spot segmentation in the first and second test spot images, candidate spot pairings are established. For each candidate spot pairing, the test displacement is calculated, and a cost function corresponding to the test displacement and the sub-aperture displacement identifier is constructed. Under the condition of satisfying the one-to-one matching constraint, the matching result with the minimum cost function corresponding to each sub-aperture displacement identifier is solved. When the minimum cost value is greater than the preset threshold, the matching is regarded as an abnormal result and is removed.

6. The Shakhartmann wavefront reconstruction method based on displacement identification according to claim 1, characterized in that, The method for obtaining the preset phase includes: calculating the minimum distance between adjacent light spots that can be distinguished according to the Rayleigh criterion, determining the displacement design step size according to the minimum distance; selecting several discrete displacement quantities as candidate displacement identifiers, and assigning different displacement identifiers to different sub-apertures; and finally obtaining the preset phase distribution inside each sub-aperture according to the corresponding displacement identifier.

7. A Shakhartmann wavefront reconstruction system based on displacement identifiers, characterized in that, It includes a pre-stage relay optical unit, a preset phase loading unit, a post-stage relay optical unit, a Shaker-Hartmann detection unit, and a processing unit arranged sequentially along the propagation direction of the wavefront to be measured; The front-end relay optical unit conjugates the wavefront to be measured to the preset phase loading position; A preset phase loading unit is set at the preset phase loading position, and by switching between the loaded state and the unloaded state, a distinguishable displacement mark is generated between different loading states; The subsequent relay optical unit transmits the beam modulated by the preset phase loading unit to the Shackleham-Hartmann detector unit; The Shaker-Hartmann detector unit includes a microlens array and a camera, with the entrance pupil plane of the microlens array being conjugate to a preset phase loading position; The processing unit is electrically connected to the camera. Under the reference wavefront condition, it establishes the displacement markers corresponding to each sub-aperture and forms the displacement to be measured under the wavefront condition to be measured. Based on the comparison and matching between the displacement to be measured and the displacement markers, it determines the correspondence between the light spot to be measured and each sub-aperture. Based on the positional offset of the light spot to be measured relative to the corresponding reference light spot, it calculates the local wavefront slope at each sub-aperture and performs wavefront reconstruction.

8. The Shakhartmann wavefront reconstruction system based on displacement identifiers according to claim 7, characterized in that, The preset phase loading unit is one of a fixed phase plate, a multi-stage switchable phase plate, or a deformable mirror.

9. The Shakhartmann wavefront reconstruction system based on displacement identification according to claim 8, characterized in that, The multi-stage switchable preset phase plate assembly adopts a turntable structure. By rotating, different workstations are sequentially entered into the preset phase loading position. It includes multiple switchable workstations, each workstation corresponding to an optical state, including at least one blank light-transmitting workstation and one preset phase loading workstation.

10. The Shakhartmann wavefront reconstruction system based on displacement identifiers according to claim 8, characterized in that, The deformable mirror is a reflective deformable mirror with multiple driving units. The deformable mirror can switch between a reference state and a preset surface shape state. The reference state is when the mirror surface maintains a planar shape as a whole. The preset surface shape state is when the mirror surface forms a preset surface shape under the control of the driving signal, thereby introducing a preset phase modulation to the reflected beam. When using the reflective deformable mirror, the optical path adopts a folded structure so that the beam output from the front-stage relay optical unit is incident on the surface of the deformable mirror.

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