Irregular dot matrix projector based on metasurface and design method thereof
By selecting diffraction orders at high density outside the light field and low density in the center of the light field, and using an optimization algorithm to design the diffraction element period, the problem of low three-dimensional reconstruction accuracy caused by regular diffraction order arrangement in the existing technology is solved, and the uniform distribution of diffraction orders and the improvement of three-dimensional reconstruction accuracy in the lattice projector is achieved.
Patent Information
- Application Number
- CN202311444239.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-11-02
- Publication Date
- 2025-05-06
AI Technical Summary
In the prior art, regular diffraction order arrangement results in high density of the projection center area and low density of the edge part point, which reduces the three-dimensional reconstruction accuracy of the edge area.
The design method of non-regular lattice projector based on metasurface is adopted. By selecting diffraction orders at high density outside the target light field and selecting diffraction orders at low density in the center of the light field, the uniformity of diffraction orders is optimized, and an optimization algorithm is used to design a single period of the diffraction element to ensure that the order intensity between the levels is low enough to avoid redundant orders during replication.
The uniform distribution of diffraction orders in the lattice projector is achieved, the three-dimensional reconstruction accuracy of the edge area is improved, and the energy distribution of the lattice is ensured.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention belongs to the field of optical devices, and in particular relates to an irregular dot matrix projector based on a metasurface and a design method thereof. Background Art
[0002] Structured light is a 3D face measurement method that is widely used in facial unlocking, financial payment, smart driving, and smart door locks. The core of this technology is the dot matrix projector and the 3D reconstruction algorithm. Excellent dot matrix design and projection effect are crucial to the performance of the module. The diffractive optical element is one of the components of the dot matrix projector. Its main function is to produce a regular diffraction order distribution with a certain separation angle, and to replicate the arrangement of the vcsel lamp beads between the diffraction orders to produce the expected dot matrix arrangement.
[0003] However, after the regular arrangement of diffraction orders is replicated, the density in the center of the projection is high and the density in the edge is low, which reduces the accuracy of 3D reconstruction in the edge area. This can be achieved by reducing distortion or increasing the number of diffraction orders at the edge. This solution requires the design of the arrangement of diffraction orders rather than a regular arrangement. To achieve an arbitrary arrangement of diffraction orders, it is necessary to accurately set the diffraction angles of each order and ensure that the order intensity between each order is low enough to avoid redundant orders during replication. The above are the main means to solve the uneven distribution of dot matrix projectors, but the implementation method is difficult. Summary of the invention
[0004] The present application provides an irregular dot matrix projector based on a metasurface and a design method thereof to at least solve the above technical problems existing in the prior art.
[0005] On the one hand, an embodiment of the present application provides a design method for an irregular dot matrix projector based on a metasurface, wherein the dot matrix projector includes a light source and a metasurface device; the method includes: confirming the arrangement of the target diffraction orders, selecting the diffraction orders with high density outside the target light field and selecting the diffraction orders with low density in the central area of the light field; optimizing the uniformity of the diffraction orders, and using an optimization algorithm to design a single period of the diffraction element, specifically including: determining an evaluation function according to the optimization target zero-order energy, diffraction efficiency, global uniformity, etc.; performing initial iterative optimization, and performing accurate diffraction order design according to the phase of the optimal initial solution obtained; and obtaining a phase distribution that matches the initial diffraction order intensity distribution.
[0006] In one possible implementation mode, all possible values of θ are traversed and solved for pix, N, i within a specified range according to the formula pix×N×sinθ=i×λ, and the final period d=pix×N, i, θ is recorded in three columns of the matrix; wherein pix represents the sampling period of the diffraction element, N represents the number of sampling points, θ is the deflection angle of each diffraction order in the x and y directions, and λ is the design wavelength of the device.
[0007] In one possible implementation, classification is performed according to d values, all θ values corresponding to each d are generated, and all diffraction orders of the target are matched with the obtained d, i, θ matrix. During the matching process, the angular deviation within Δθ is considered to be a successful match; the d, i, θ matrix is sorted and extracted from high to low according to the matching degree, and the number of angles corresponding to the d with the highest matching degree, and the target diffraction orders that meet the requirements are eliminated and counted; until all target diffraction orders have corresponding d to match them.
[0008] In one possible implementation, the matching results may be as follows:
[0009] a. A single d covers all target diffraction orders;
[0010] b. Two or more d cover the target diffraction orders;
[0011] When the matching result is case b, the phase plane photosensitive area corresponding to different d is proportional to the number of target diffraction orders covered by different d, so as to ensure uniform energy distribution of the dot array.
[0012] In one possible implementation, the optimization algorithm includes initial value screening, feedback suppression, and vector-assisted correction.
[0013] In one possible implementation, the formula of the evaluation function is as follows:
[0014]
[0015] Where η represents the evaluation function, β i represents the i-th evaluation target, α i Represents the weight coefficient.
[0016] In one embodiment, the initial iterative optimization includes the following process:
[0017] a. Start the iteration with a random phase, and add a random phase every 50 iterations (this value can be adjusted according to the actual situation) to jump out of the local optimal solution.
[0018] b. During the iterative process, if the value of η is improved, the phase of the optimal initial solution is updated.
[0019] c. The amplitude replacement process performs reverse correction according to the difference ΔI between the current diffraction order distribution and the target diffraction order distribution.
[0020] In one embodiment, the diffraction order design includes the following process:
[0021] Perform vector simulation on the initial optimal solution and obtain the result of the evaluation function; according to the result of the evaluation function, adjust the weight of the evaluation index in the iteration process (if the index is low, the weight is adjusted up, otherwise it is adjusted down) and the intensity distribution of the target diffraction order; repeat the above process until all evaluation functions meet the standards.
[0022] In one possible implementation manner, vector simulation is performed every five iterations to update the evaluation function weight distribution and the diffraction order intensity values.
[0023] On the other hand, an embodiment of the present application provides an irregular dot matrix projector, including a collimating mirror, a metasurface device and a receiving plane, wherein the metasurface device is obtained by phase processing obtained by any of the above methods. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 is a schematic diagram of the target diffraction order arrangement in the embodiment of the present application;
[0025] Figure 2 is a schematic diagram of the period corresponding to the diffraction order situation 1 in the embodiment of the present application;
[0026] Figure 3 is a schematic diagram of the period corresponding to the diffraction order situation 2 in the embodiment of the present application;
[0027] Figure 4 This is a schematic diagram of the structural area ratios of different periods in the embodiment of the present application;
[0028] Figure 5 is an algorithm flow chart of an embodiment of the present application;
[0029] Figure 6 is a schematic diagram of a dot matrix projector according to an embodiment of the present application;
[0030] Figure 7 This is a schematic diagram of a vcsel light board in an embodiment of the present application;
[0031] Figure 8 is a schematic diagram of the diffraction order distribution of uniform distribution without treatment;
[0032] Fig. 9 It is a schematic diagram of the diffraction order distribution after the edge density is improved in the embodiment of the present application. DETAILED DESCRIPTION
[0033] The present invention will be further described in detail below in conjunction with the accompanying drawings.
[0034] In the description of the present application, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.
[0035] This application discloses a design method of an irregular dot matrix projector based on a metasurface, which mainly involves the following two modules:
[0036] 1. Grating period selection algorithm to achieve arbitrary diffraction order arrangement
[0037] It involves a grating period selection algorithm for any diffraction order arrangement. At the beginning of its design, it is necessary to first confirm the arrangement of the target diffraction order. In order to achieve the uniformity of the target diffraction order arrangement, the diffraction order can be selected with high density outside the target light field and with low density in the center of the light field.
[0038] 2. Diffraction order uniformity optimization algorithm
[0039] After the period is determined, the uniformity of the diffraction order needs to be optimized. This embodiment uses an optimization algorithm to design a single period of the diffraction element.
[0040] The specific steps of the above two modules are as follows:
[0041] S1. Confirm the arrangement of the target diffraction order
[0042] S11. Determine Figure 1 The dot array arrangement shown in the figure can obtain the deflection angle of the point as the matching target according to the distribution of the point in the angle space;
[0043] The angle of the diffraction order in the arrangement is θ ix and θ iy Represents, where i represents the i-th diffraction order, and θ represents the separation angle of the i-th diffraction order in the x and y directions.
[0044] S12. According to the formula pix×N×sinθ=i×λ, all possible θ values are traversed for pix, N, i within the specified range, and the final period d=pix×N, i, θ is recorded in the three columns of the matrix.
[0045] Where pix represents the sampling period of the diffraction element, N represents the number of sampling points, θ is the deflection angle of each diffraction order in the x and y directions, and λ is the design wavelength of the device.
[0046] S13, classify according to the d value, generate all the θ values corresponding to each d, match all the diffraction orders of the target with the obtained d, i, θ matrix, and the matching is considered successful if the angle deviation is within Δθ during the matching process.
[0047] The d, i, and θ matrices are sorted and extracted according to the matching degree from high to low. The number of angles corresponding to the d with the highest matching degree and the target diffraction orders that meet the requirements are eliminated and counted until all the target diffraction orders have corresponding ds that match them.
[0048] The matching results are as follows:
[0049] a. A single d covers all target diffraction orders;
[0050] b. Two or more d cover the target diffraction orders;
[0051] When the matching result is case b, the phase plane photosensitive area corresponding to different d is proportional to the number of target diffraction orders covered by different d, so as to ensure uniform energy distribution of the dot array.
[0052] S2. Optimizing the uniformity of diffraction orders
[0053] An optimization algorithm of initial value screening, feedback suppression and vector-assisted correction is used to design a single period of the diffraction element.
[0054] S21. Determine the evaluation function according to the optimization target zero-order energy, diffraction efficiency, global uniformity, etc. The formula is as follows:
[0055]
[0056] Where η represents the evaluation function, β i represents the i-th evaluation target, α i Represents the weight coefficient. The higher the attention paid to the evaluation target, the larger the weight coefficient should be.
[0057] S22. Perform initial iterative optimization
[0058] Its purpose is to select a set of optimal initial solutions as the initial values for accurate iteration.
[0059] The initial iteration process is as follows:
[0060] a. Start the iteration with a random phase, and add a random phase every 50 iterations (this value can be adjusted according to the actual situation) to jump out of the local optimal solution.
[0061] b. During the iteration process, if the value of η is improved, the phase of the optimal initial solution is updated.
[0062] c. The amplitude replacement process performs reverse correction based on the difference ΔI between the current diffraction order distribution and the target diffraction order distribution. The correction coefficient is given based on the historical change trend of ΔI.
[0063] S23. Perform vector diffraction order design
[0064] d. Perform vector simulation on the initial optimal solution and obtain the result of the evaluation function.
[0065] e. According to the result of the evaluation function, adjust the weight of the evaluation index in the iteration process (if the index is low, the weight is adjusted up, otherwise it is adjusted down) and the intensity distribution of the target diffraction order. Perform a vector simulation every 5 iterations to update the evaluation function weight distribution and the diffraction order intensity value.
[0066] f. Repeat the above process until all evaluation functions meet the standards.
[0067] S3, obtain the phase distribution that matches the initial diffraction order intensity distribution
[0068] After processing this phase into the corresponding metasurface device, the following Figure 6 A dot matrix projector can be formed in the optical path shown.
[0069] The irregular dot matrix projector includes a light source 61, a collimator 62, a metasurface device 63 and a receiving plane 64. The metasurface device 63 is obtained by phase processing obtained by any of the above methods. When the light source 61 is parallel light (such as collimated LD), the dot matrix it projects is the same as the target diffraction order. Figure 7 The vcsel light panel shown can project a large number of dots centered on the diffraction order. The unprocessed uniform distribution of the diffraction order is as follows Figure 8 As shown in Figure 2, the diffraction order distribution after improving the edge density is as follows: Fig. 9 shown.
[0070] The above are only specific embodiments of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present disclosure, which should be included in the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be based on the protection scope of the claims.
Claims
1. A design method for an irregular dot matrix projector based on a metasurface, characterized in that: The dot matrix projector includes a light source and a metasurface device; The method comprises: Confirm the arrangement of the target diffraction orders, select the diffraction orders with high density outside the target light field and the diffraction orders with low density in the center of the light field; Optimize the uniformity of the diffraction order and use the optimization algorithm to design a single period of the diffraction element, including: Determine the evaluation function according to the optimization target zero-order energy, diffraction efficiency, global uniformity, etc.; Perform initial iterative optimization and accurately design the diffraction order based on the phase of the optimal initial solution; A phase distribution matching the initial diffraction order intensity distribution is obtained.
2. A design method according to claim 1, characterized in that: According to the formula pix×N×sinθ=i×λ, all possible θ values are traversed for pix, N, i in the specified range, and the final period d=pix×N, i, θ is recorded in the three columns of the matrix; Where pix represents the sampling period of the diffraction element, N represents the number of sampling points, θ is the deflection angle of each diffraction order in the x and y directions, and λ is the design wavelength of the device.
3. A design method according to claim 2, characterized in that: Classify according to the d value, generate all the θ values corresponding to each d, match all the diffraction orders of the target with the obtained d, i, θ matrix, and the matching is considered successful if the angle deviation is within Δθ during the matching process; The d, i, and θ matrices are sorted and extracted according to the matching degree from high to low. The d with the highest matching degree can correspond to a large number of angles, and the target diffraction orders that meet the requirements are eliminated and counted; Until all target diffraction orders have corresponding d to match them.
4. A design method according to claim 3, characterized in that: The matching results are as follows: a. A single d covers all target diffraction orders; b. Two or more d cover the target diffraction orders; When the matching result is case b, the phase plane photosensitive area corresponding to different d is proportional to the number of target diffraction orders covered by different d, so as to ensure uniform energy distribution of the dot array.
5. A design method according to claim 1, characterized in that: The optimization algorithm includes initial value screening, feedback suppression, and vector-assisted correction.
6. A design method according to claim 1, characterized in that: The formula of the evaluation function is as follows: Where η represents the evaluation function, β i represents the i-th evaluation target, α i Represents the weight coefficient.
7. A design method according to claim 1, characterized in that: The initial iterative optimization process includes the following steps: a. Start the iteration with a random phase and add a random phase every n iterations (n≥50) to escape from the local optimal solution. b. During the iterative process, if the value of η is improved, the phase of the optimal initial solution is updated. c. The amplitude replacement process performs reverse correction according to the difference ΔI between the current diffraction order distribution and the target diffraction order distribution.
8. A design method according to claim 1, characterized in that: Diffraction order design includes the following processes: Perform vector simulation on the initial optimal solution and obtain the result of the evaluation function; According to the result of the evaluation function, the weight of the evaluation index in the iteration process is adjusted (if the index is low, the weight is adjusted up, otherwise it is adjusted down) and the intensity distribution of the target diffraction order; Repeat the above process until all evaluation functions meet the standards.
9. A design method according to claim 8, characterized in that: A vector simulation is performed every five iterations to update the evaluation function weight distribution and the diffraction order intensity value.
10. An irregular dot matrix projector, characterized in that: The invention comprises a collimating mirror, a metasurface device and a receiving plane, wherein the metasurface device is obtained by phase processing obtained by any one of the methods of claims 1-9.