Design method of projection dot matrix system

Abstract

The invention discloses a projection dot matrix system design method, which is suitable for the design of a composite super lens with a single-layer super surface, and is used for designing a collimation phase by using a binary surface type based on a specific light source. Designing a DOE phase by using a phase recovery algorithm; combining the collimation phase with the DOE phase, and performing phase filling replacement on the micro-nano structures arranged in the array in the metasurface to obtain an actual metasurface phase; a light field diffraction propagation theory is used to carry out projection system full simulation, a light source is modeled, then a near-field diffraction algorithm is used to obtain light field distribution before light is transmitted to a metasurface, an obtained metasurface phase is superposed to a light field before the metasurface, and a projection system is obtained. A far field diffraction algorithm is utilized to transmit a light field behind the metasurface to a far detector for sampling, a result of a speckle spot matrix is checked to evaluate the uniformity and efficiency value of the dot matrix, a simulation theoretical model of the whole system can be provided, and therefore performance evaluation analysis can be conveniently carried out on the system.

Description

Technical Field

[0001] The present application relates to the technical field of optical devices, and particularly relates to a design method for a projection dot matrix system. Background Art

[0002] The dot matrix projection system is a key component of today's face recognition technology. Generally, the system includes an array of light-emitting units, lenses, and beam split gratings. The lens system and the grating work together to project and replicate the array source pattern multiple times. With the upgrade of technology, the dot matrix projection system has begun to use metalenses.

[0003] Metalenses, also known as metasurface lenses, are a two-dimensional planar lens structure made of optical elements that focus light by a metasurface (a planar two-dimensional metamaterial with a subwavelength thickness). Metalenses have the advantages of being thinner, lighter, lower in cost, better in imaging, and easier to integrate, providing a potential solution for a compact and integrated optical system. And the properties of light such as polarization, phase, and amplitude can be regulated by adjusting parameters such as the shape, rotation direction, and height of the structure.

[0004] However, the design process of the existing projection dot matrix system using metalenses has the following defects: in the specific design process, there is a lack of a simulation theoretical model for the entire system, making it difficult to evaluate and analyze the performance of the system. In addition, during the design process, a coupling effect will occur between the nanocolumns, and there will be a deviation in the conversion between the phase diagram and the actual micro-nano structure. Summary of the Invention

[0005] An object of the present application is to provide a design method for a projection dot matrix system that can facilitate the evaluation and analysis of the performance of the system.

[0006] Another object of the present application is to provide a design method for a projection dot matrix system that can reduce the coupling effect between nanocolumns and the conversion deviation between the phase diagram and the actual micro-nano structure.

[0007] To achieve the above object, the technical solution adopted by the present application is: a design method for a projection dot matrix system, applicable to the design of a composite metalens of a single-layer metasurface, including the steps of:

[0008] S100, based on a specific light source, design using the binary surface type to collimate the phase;

[0009] S200, design the DOE phase using a phase retrieval algorithm to make the uniformity and efficiency between the dot matrices at different incident angles meet the design specifications;

[0010] S300, combine the collimated phase and the DOE phase, and perform phase filling replacement on the micro-nano structures arranged in an array in the metasurface to obtain the actual metasurface phase;

[0011] For S400, a full simulation of the projection system is carried out using the theory of light field diffraction propagation. First, the light source is modeled, and then the near-field diffraction algorithm is used to obtain the light field distribution before the light reaches the metasurface. The metasurface phase obtained in step S300 is superimposed on the light field before the metasurface, and the far-field diffraction algorithm is used to transmit the light field after the metasurface to a distant detector for sampling. The result of the speckle pattern is viewed, and the uniformity and efficiency value of the pattern are used as optimization indicators for evaluation, and it is determined whether the design of the micro-nano structure needs to be optimized.

[0012] In some embodiments, the far-field diffraction algorithm is a spherical wave projection algorithm, and the calculation formula is as follows:

[0013]

[0014] where γ is the cosine of the angle between the propagation direction and the z-axis, j is the imaginary unit, k is the free-space wave vector, k = 2π / λ, λ is the free-space wavelength, and R’ is the corresponding radius of a spherical wave on the detector.

[0015] In some embodiments, a resampling step is used to interpolate the output plane U(α; β; R0) to U(x2; y2; Z) on a uniform sampling grid with a sampling interval of δ2.

[0016] In some embodiments, the resampling step includes nearest-neighbor interpolation, and the calculation formula for the output plane U(x2; y2; Z) at the position (x2 = mδ2; Y2 = nδ2) is: U(mδ2,nδ2; z) ≈ U(pδ α , qδ β ; R′);

[0018] where m; n; p; q are integers, -N / 2 ≤ m; n; p; q ≤ N / 2 - 1, pδα ≈ x2 = R0, qδβ ≈ y2 = R0, and the sampling interval in the cosine direction is δα = δβ = λδf, where δf = 1 / (Nδ1) and δ1 is the plane sampling interval.

[0019] In some embodiments, when modeling the light source, a light source array is established, and the light intensity distribution of the light source array is optimized based on the Gaussian beam light intensity distribution formula, as follows:

[0020]

[0021] where I r represents the light intensity at a position r away from the center point, I0 represents the light intensity at the center point, r represents the distance from the center point, w0 represents the radius of the Gaussian beam, and exp is the exponential function.

[0022] In some embodiments, the calculation formula for the collimation phase is as follows:

[0023]

[0024] where N is the number of terms of the polynomial, M is the diffraction order, ρ represents the normalized polar coordinate aperture coordinate, and A i is the coefficient corresponding to the polar coordinate point on the aperture.

[0025] In some embodiments, the near-field diffraction algorithm includes at least one of the Rayleigh-Sommerfeld diffraction algorithm, the angular spectrum diffraction algorithm, and the Fresnel diffraction algorithm.

[0026] A method for designing a projection dot matrix system, applicable to the design of a composite metalens with two layers of metasurfaces, includes the steps of:

[0027] T100, based on a specific light source, design the collimation phase of the metasurface using a binary surface profile;

[0028] T200, given the collimated incident FOV, incident wavelength, and large periods in the x and y directions, select appropriate small-period micro-nano structure units in the x and y directions to fill the large periods;

[0029] T300, set the shape of the micro-nano structure unit, take the geometric parameters of each micro-nano structure unit as optimization variables, and at the same time select an appropriate height to satisfy the 2π phase interval;

[0030] T400, calculate the performance of the micro-nano structure unit under the current optimization variables using a performance algorithm, substitute it into the objective function, and then output new optimization variables by an optimization algorithm;

[0031] T500, repeat step T400 until the result of the objective function approaches 0, take the finally output optimization variables as the geometric parameters of each micro-nano structure unit, and complete the design of the DOE phase.

[0032] In some embodiments, the objective function FoM = RMSE + (1 - Eff), where the calculation formulas for RMSE and Eff are respectively:

[0033]

[0034]

[0035] In some embodiments, the performance algorithm includes the finite-difference time-domain method or the Fourier modal method.

[0036] In some embodiments, the optimization algorithm includes the intelligent swarm algorithm or the gradient descent algorithm.

[0037] Compared with the prior art, the beneficial effects of the present application are as follows:

[0038] 1. A design method of a projection dot matrix system in this application is a design method of a projection dot matrix system using a compound metalens. The compound metalens has the characteristics of low cost and excellent performance. The specific design steps of the compound metalens are proposed, and a simulation theoretical model of the whole system is provided. The performance of the whole system can be conveniently evaluated and analyzed using the simulation theoretical model, and the micro-nano structure can be adjusted in time according to the results of the evaluation and analysis.

[0039] 2. Another design method of a projection dot matrix system in this application optimizes the design steps of a reset metalens, which can be applied to the design of a compound metalens with two layers of metasurfaces. The geometric parameters of the micro-nano structure can be directly optimized to obtain the final micro-nano structure, which is more in line with the actual situation. By considering the coupling effect between micro-nano structures in the design process, the deviation problem existing when the phase diagram is converted into a micro-nano structure is improved. Description of the Drawings

[0040] Figure 1 is a schematic structural diagram of a compound metalens with a single-layer metasurface according to a preferred embodiment of this application.

[0041] Figure 2 is a schematic design diagram of a collimated phase according to a preferred embodiment of this application.

[0042] Figure 3 is a schematic result diagram of a DOE phase according to a preferred embodiment of this application.

[0043] Figure 4 is a schematic diagram of light rays of a light source avoiding overlap according to a preferred embodiment of this application.

[0044] Figure 5 is a schematic result diagram of a speckle dot matrix according to a preferred embodiment of this application.

[0045] Figure 6 is a schematic light field diagram at a modeled light source according to a preferred embodiment of this application.

[0046] Figure 7 is a schematic light field diagram before a micro-nano structure according to a preferred embodiment of this application.

[0047] Figure 8 is a visualization image of a spherical wave projection algorithm according to a preferred embodiment of this application.

[0048] Figure 9 is a schematic result diagram of a speckle dot matrix after phase superposition of a metasurface according to a preferred embodiment of this application.

[0049] Figure 10The schematic structural diagram of a compound metalens according to a preferred embodiment of the present application is a structure of two metasurfaces.

[0050] Figure 11 The schematic design flow diagram according to a preferred embodiment of the present application.

[0051] Figure 12 The schematic diagram of the optimization situation according to a preferred embodiment of the present application.

[0052] In the figure: 1. Light source; 2. Metasurface; 21. Substrate; 22. Micro-nano structure; 3. Detector. Detailed implementation manners

[0053] Next, in combination with the detailed implementation manners, the present application will be further described. It should be noted that, on the premise of no conflict, the following-described embodiments or technical features can be arbitrarily combined with each other to form new embodiments.

[0054] In the description of the present application, it should be noted that for orientation terms, such as terms "center", "transverse", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., the indicated orientation and position relationships are based on the orientation or position relationships shown in the drawings, and are only for facilitating the description of the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and should not be construed as limiting the specific protection scope of the present application.

[0055] It should be noted that the terms "first", "second", etc. in the description and claims of the present application are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence.

[0056] The terms "including" and "having" in the description and claims of the present application, and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or devices.

[0057] Next, the present application will be further described with reference to the accompanying drawings:

[0058] Currently, in the existing technologies, there is little public content on the design method of the compound metalens used in the projection dot matrix system, and the specific design links are missing. At the same time, in the existing technologies, there is no establishment of a simulation theoretical model for the projection dot matrix system for simulation, and it is difficult to evaluate the performance such as the uniformity and efficiency value of the projection dot matrix system.

[0059] As Figures 1 to 9 shown, the present application provides a design method for a projection dot matrix system, which is applicable to the design of a compound metalens of a single-layer metasurface 2.

[0060] In some embodiments, the structure of the compound metalens of the single-layer metasurface 2 includes a substrate 21 and a micro-nano structure 22 located on one side of the substrate 21. By fusing the collimation phase and the DOE (diffractive optical element) phase onto the micro-nano structure 22 on this side, the combination of two functions is achieved, making the processing more convenient and the cost lower.

[0061] As Figure 1 shown in the embodiment, the substrate 21 is located on the side close to the light source 1, and the micro-nano structure 22 is located on the side close to the detector 3.

[0062] In some embodiments, the micro-nano structures 22 are arranged in an array on the substrate 21.

[0063] It includes the steps of:

[0064] S100, based on the specific light source 1, design the collimation phase using a binary surface profile.

[0065] The calculation formula for the collimation phase is as follows:

[0066]

[0067] where N is the number of terms of the polynomial, M is the diffraction order, ρ represents the normalized polar coordinate aperture coordinate, and A i is the coefficient corresponding to the polar coordinate point on the aperture.

[0068] As Figure 2 shown, the detailed design of the collimation phase can be carried out using software such as zemax and CodeV through a binary surface, etc. The design of the binary surface collimation system can be carried out according to the size, divergence angle of the VCSEL array, and the range of the object space NA (numerical aperture) and field of view in the control simulation system.

[0069] The design method is to propose a function for the binary surface, and select one of them as binary surface 2 (also known as Binary 2. The diffraction effect of the Binary 2 surface causes a continuous phase change to be introduced over the entire surface. Since the phase change is continuous over the entire surface, the Binary 2 surface represents an ideal binary diffractive optical element, where the size of the discrete step is infinitely small or small enough compared to the wavelength).

[0070] During the design stage, the structure is simulated to reduce the actual production steps required for testing, improve efficiency, and reduce costs.

[0071] In some embodiments, the light source 1 can use a VCSEL light source 1, preferably a VCSEL array light source 1. VCSEL stands for Vertical-Cavity Surface-Emitting Laser, which is a semiconductor whose laser emits perpendicular to the top surface.

[0072] Different from edge-emitting lasers generally made of cut independent chips with laser emitted from the edge, edge-emitting lasers emit light along the direction parallel to the substrate surface and perpendicular to the cleavage plane, while surface-emitting lasers emit light perpendicular to the substrate surface. VCSELs have the advantages of being easy to realize two-dimensional planar and optoelectronic integration; circular beams are easy to realize effective coupling with optical fibers; high-speed modulation can be achieved, and they can be applied to long-distance and high-rate optical fiber communication systems; the active region size is extremely small, enabling high packaging density and low threshold current; no cleavage is required after chip growth, and on-chip experiments can be carried out after packaging; it operates in single longitudinal mode within a wide temperature and current range; and it has a low price.

[0073] S200, use the phase retrieval algorithm to design the DOE phase so that the uniformity and efficiency between dot arrays at different incident angles meet the design specifications.

[0074] In some embodiments, the phase retrieval algorithm can use the GS (Gerchberg-Saxton) algorithm or the iterative Fourier transform correlation algorithm, and the phase result Figure 3 is shown to cover the interval from -π to π, 2π.

[0075] The periods in the X and Y directions are specified by the angular requirements of the dot array and can be calculated according to the grating equation sin(θ t ) - sin(θ i ) = mλ / d. The left side of the equation is the part of the refraction angle and the incident angle, the right side m is the order, λ is the wavelength in vacuum, d is the period, and there should be no overlapping parts between dot arrays at different incident angles. As Figure 4 shown, the black line and the green line are the positive and negative marginal rays of the FOV respectively. After passing through the periodic phase of the DOE, the -1 order of the positive marginal ray should avoid overlapping with the 0 order of the negative marginal ray and needs to be staggered by about 1°.

[0076] Similarly, it can also be considered to avoid the 0 order of the positive marginal ray from overlapping with the +1 order of the negative marginal ray.

[0077] The reason for the above approach is that the dot arrays of the VCSEl light source 1 need to not overlap on the detector 3, that is, it is necessary to ensure that the emitted light does not overlap at the edge, reduce the influence on the light range, and increase the field of view range.

[0078] S300 combines the collimation phase and the DOE phase, performs phase filling replacement on the micro-nano structures 22 arranged in an array in the metasurface 2, and obtains the actual metasurface 2 phase.

[0079] In some embodiments, the process of phase filling replacement uses the nearest neighbor selection algorithm to replace the optimized discrete phase with 8n specific microstructures (equidistant discrete sampling from 0 to 2π, n being a positive integer, that is, the number of selected units is a multiple of 8, such as 0, 0.125π, 0.25π...). The selection formula is where is the actual phase of the optimized microstructure unit, is the discrete phase, i is an integer between 1 and N, and usually, N is a multiple of 8.

[0080] At this time, when an ideal grating is selected and the diffraction efficiency of each order is equally divided, the specific speckle pattern results obtained in Zemax at a distance of 21m from the metasurface 2 are as Figure 5 shown. However, in actual operation, the ideal effect is usually not achieved. Therefore, it is necessary to perform step S400 for full simulation of the projection dot matrix system, and adjust the micro-nano structures 22 according to the results of the full simulation to reverse-optimize the system.

[0081] S400 performs full simulation of the projection system using the light field diffraction propagation theory. First, model the light source 1, then use the near-field diffraction algorithm to obtain the light field distribution before the light rays reach the metasurface 2. Superimpose the metasurface 2 phase obtained in step S300 on the light field before the metasurface 2, and use the far-field diffraction algorithm to transmit the light field after the metasurface 2 to the detector 3 at a distance for sampling, view the results of the speckle pattern, evaluate with the uniformity and efficiency value of the dot matrix as the optimization index, and determine whether it is necessary to optimize the design of the micro-nano structures.

[0082] If the uniformity and efficiency value meet the design requirements, the design of the composite superlens and the projection dot matrix system is completed.

[0083] If the uniformity and efficiency value do not meet the design requirements, one or more steps in steps S100, S200, and S300 can be reselected to adjust the micro-nano structures 22. During this process, the influence caused by calculation errors in the design process can also be reduced or even eliminated.

[0084] In some embodiments, when modeling the light source 1, a VCSEL light source 1 is selected, a VCSEL light source 1 array is established, and the light intensity distribution of the light source 1 array is optimized based on the Gaussian beam light intensity distribution formula. The formula is as follows:

[0085]

[0086] where Ir The light intensity at a position with a distance r from the center point is represented by I(r), I0 represents the light intensity at the center point, r represents the distance from the center point, w0 represents the radius of the Gaussian beam, and exp is the exponential function.

[0087] The light field distribution image of the VCSEL light source 1 array after modeling is as Figure 6 shown.

[0088] In some embodiments, the near-field diffraction algorithm can use the Rayleigh-Sommerfeld diffraction algorithm, the angular spectrum diffraction algorithm, or the Fresnel diffraction algorithm. The light field distribution image of the VCSEL light before it is transmitted to the metasurface 2 through the above near-field diffraction algorithm is as Figure 7 shown.

[0089] In some embodiments, when the phase of the metasurface 2 is superposed on the light field before the metasurface 2, due to the large diffraction angle of the lattice, the sampling is suitable for the large-angle diffraction propagation algorithm, that is, the spherical wave projection algorithm. The calculation formula is as follows:

[0090]

[0091] where γ is the cosine of the angle between the propagation direction and the z-axis, j is the imaginary number, k is the free-space wave vector, k = 2π / λ, λ is the wavelength of free space, R’ is the corresponding radius of a spherical wave on the detector 3, and FT represents the Fourier transform function.

[0092] As Figure 8 shown, in the simulations in all cases, the direction cosines α and β are equally spaced, and γ = (1 - α 2 - β 2 ) 1 / 2 (spherical equation) is a non-linear function, and the output plane spatial coordinates x2 are obtained. Therefore, the x2 and y2 calculated by the spatial mapping are not equally spaced, and each point on the observation plane is considered to belong to different hemispheres R with different radii.

[0093] In some embodiments, a resampling step can be used to interpolate the output plane U(α; β; R0) to U(x2; y2; Z) on a uniform sampling grid with a sampling interval of δ2.

[0094] Resampling refers to a method for processing image data, that is, a gray-scale processing method during the reorganization of image data. Image sampling is to collect image gray-scale values at certain intervals. When the threshold value is not the value of the original function at the sampling points, interpolation using the sampled points is required, which is called resampling. Resampling includes methods such as nearest neighbor interpolation, bilinear interpolation, and bicubic interpolation.

[0095] In some embodiments, the resampling step includes nearest neighbor interpolation, which is relatively simple and easy to use. The calculation formula for the output plane U(x2; y2; Z) at the position (x2 = mδ2; Y2 = nδ2) is as follows:

[0096]

[0097] where m, n, p, q are integers, -N / 2 ≤ m, n, p, q ≤ N / 2 - 1, pδα ≈ x2 = R0, qδβ ≈ y2 = R0, the sampling interval in the cosine direction is δα = δβ = λδf, where δf = 1 / (Nδ1), and δ1 is the plane sampling interval.

[0098] Through the above calculations, a preferred microstructure arranged in a circular center diffusion can be formed. The specific speckle pattern result superimposed at a distance of 21m from the metasurface is as Figure 10 shown, and it is relatively easy to evaluate the uniformity and efficiency value of the speckle pattern, so as to draw a conclusion on whether it is necessary to adjust the micro-nano structure 22. As shown in Figures 10 to 12 shown, a projection dot matrix system design method is applicable to the design of a compound superlens of two-layer metasurface 2.

[0099] In some embodiments, the structure of the compound superlens of two-layer metasurface 2 includes a substrate 21 and micro-nano structures 22 located on both sides of the substrate 21 respectively. The micro-nano structures 22 on both sides are used to realize the functions of collimation phase and DOE phase respectively, which is more convenient for performance evaluation, has a higher design freedom, and more controllable performance.

[0100] As Figure 10 shown in the embodiment, one side of the micro-nano structure 22 is located close to the light source 1, and the other side of the micro-nano structure 22 is located close to the detector 3.

[0101] In some embodiments, the micro-nano structure 22 arrays on the same side are arranged on the substrate 21.

[0102] Including the steps:

[0103] T100, based on the specific light source 1, use the binary surface profile to design the collimation phase of the metasurface 2.

[0104] In some embodiments, the light source 1 can use a VCSEL light source 1, and preferably use a VCSEL array light source 1.

[0105] T200, given the collimated incident FOV, incident wavelength, and large periods in the x and y directions, select appropriate small-period micro-nano structure 22 units in the x and y directions to fill the large periods.

[0106] T300, set the shape of the micro-nano structure 22 units, take the geometric parameters of each micro-nano structure 22 unit as the optimization variables, and at the same time select an appropriate height to satisfy the 2π phase interval.

[0107] T400, use the performance algorithm to calculate the performance of the micro-nano structure 22 units under the current optimization variables, substitute it into the objective function, and then output the new optimization variables by the optimization algorithm.

[0108] In some embodiments, the first current optimization variable can be randomly selected, and the new optimization variables are output through continuous cycling for iteration, so that the optimization variables can continuously approach and even tend to the optimal selection.

[0109] In some embodiments, when the micro-nano structure 22 adopts a cylindrical unit structure, the radius of each unit structure can be used as the optimization variable.

[0110] It can be understood that the micro-nano structure 22 includes but is not limited to the cylindrical unit structure, and can be selected and designed according to the actual situation.

[0111] T500, repeat step T400 until the result of the objective function approaches 0, take the finally output optimization variables as the geometric parameters of each micro-nano structure 22 unit, and complete the design of the DOE phase.

[0112] As Figure 11 shown, the top view and side view of the metasurface 2 are shown in the figure. The columnar structures in the top view and side view are the micro-nano structure 22. Taking the geometric parameters of the micro-nano structure 22 as the optimization variables, the geometric parameters can be randomly given first, and then calculated by FDTD. Substitute the calculation results into the FoM calculation, and then calculate the calculation results through the optimization algorithm to obtain the optimized geometric parameters. In this cycle, the size of the FoM is the evaluation index of the optimization algorithm. According to the size of the FoM, the optimization algorithm will adjust the value of the geometric parameters to ensure that the numerical change of the FoM meets the expectations. When the result of the FoM approaches 0, it means that the obtained result is the best. At this time, the output optimization variables can be directly used as the geometric parameters of the micro-nano structure 22 for actual use.

[0113] In some embodiments, the objective function FoM = RMSE + (1 - Eff), where the calculation formulas of RMSE (uniformity) and Eff (efficiency value) are respectively:

[0114]

[0115]

[0116] It can be understood that to make the result of the objective function FoM approach 0 means that RMSE should approach 0 and Eff should approach 1.

[0117] In some embodiments, the performance algorithm includes the Finite Difference Time Domain (FDTD) method, or the Fourier Modal Method (FMM, also known as the Rigorous Coupled Wave Analysis (RCWA)). The performance algorithm can calculate the performance results of all micro-nano structures 22, such as the transmittance at each point and the efficiency at different points, and then convert them into RMSE and Eff for substitution into the objective function.

[0118] In some embodiments, the optimization algorithm includes intelligent swarm algorithms (such as the particle swarm algorithm) or gradient descent algorithms.

[0119] As Figure 12 shown, by comparing the phase diagrams before and after 60 iterations of the optimization variables, it can be seen that the uniformity between orders has been significantly improved, indicating that the design optimization method is effective.

[0120] Due to the fact that under the surface of microstructures with extremely high density, adjacent micro-nano structures 22 will almost inevitably produce a coupling phenomenon due to the tiny deflection after light diffraction. This design method directly optimizes the geometric parameters of the micro-nano structures 22, and the coupling effect between nano-columns can be considered during the optimization process to improve or even eliminate the possible deviation when converting the phase diagram to the actual micro-nano structures 22. Using an algorithm of strict computational electromagnetics such as FDTD in this application, when calculating the diffraction light field with high precision, the physical characteristics of the mutual influence of the micro-nano structures 22 can be taken into account, so that the accuracy can be increased by 10 times or even 100 times. The compound superlens designed by this design method is more in line with the actual situation.

[0121] The basic principles, main features and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of this application. Without departing from the spirit and scope of this application, there will be various changes and improvements to this application, and these changes and improvements all fall within the scope of this application claimed. The scope of protection required by this application is defined by the appended claims and their equivalents.

Claims

1. A design method for a projection dot matrix system, characterized in that, Compound metalens design applicable to a single-layer metasurface, including the steps of: S100, based on a specific light source, design using a binary surface profile for collimated phase; S200, design the DOE phase using a phase retrieval algorithm to satisfy the design specifications for the uniformity and efficiency between dot arrays at different incident angles; S300, combine the collimated phase and the DOE phase, and perform phase filling replacement on the micro-nano structures arranged in an array in the metasurface to obtain the actual metasurface phase; S400, perform full simulation of the projection system using the optical field diffraction propagation theory. First, model the light source, then use the near-field diffraction algorithm to obtain the optical field distribution before the light rays reach the metasurface. Superimpose the metasurface phase obtained in step S300 on the optical field before the metasurface, and use the far-field diffraction algorithm to transmit the optical field after the metasurface to a detector at a distance for sampling. Check the results of the speckle pattern, and evaluate using the uniformity and efficiency values of the dot array as the optimization indicators, and determine whether it is necessary to optimize the design of the micro-nano structures.

2. The design method of a projection dot matrix system according to claim 1, characterized in that: The far-field diffraction algorithm is the spherical wave projection algorithm, and the calculation formula is as follows: where γ is the cosine of the propagation direction with respect to the z-axis direction, j is the imaginary number, k is the free space wave vector, k = 2π / λ, λ is the free space wavelength, and R’ is the corresponding radius of a spherical wave on the detector.

3. The design method of a projection dot matrix system according to claim 2, characterized in that: Use the resampling step to interpolate the output plane U(α; β; R0) to U(x2; y2; Z) on a uniform sampling grid with a sampling interval of δ2.

4. The design method of a projection dot matrix system according to claim 3, characterized in that: The resampling step includes nearest neighbor interpolation, and the calculation formula for the output plane U(x2; y2; Z) at the position (x2 = mδ2; Y2 = nδ2) is: U(mδ2, nδ2; z) ≈ U(pδ α , qδ β ; R′); where m; n; p; q are integers, -N / 2 ≤ m; n; p; q ≤ N / 2 - 1, pδα ≈ x2 = R0, qδβ ≈ y2 = R0, and the sampling intervals in the cosine directions are δα = δβ = λδf, where δf = 1 / (Nδ1), and δ1 is the plane sampling interval.

5. A method for designing a projection dot matrix system according to claim 1, characterized in that: When modeling the light source, establish a light source array and optimize the light intensity distribution of the light source array based on the Gaussian beam light intensity distribution formula, as follows: Among them, I r represents the light intensity at a position with a distance r from the center point, I0 represents the light intensity at the center point, r represents the distance from the center point, w0 represents the radius of the Gaussian beam, and exp is the exponential function.

6. The design method of a projection dot matrix system according to claim 1, characterized in that: The calculation formula for the collimated phase is as follows: where N is the number of terms of the polynomial, M is the diffraction order, ρ represents the normalized polar coordinate aperture coordinate, and A i is the coefficient corresponding to the polar coordinate point on the aperture.

7. A design method of a projection dot matrix system according to claim 1, characterized in that: The near-field diffraction algorithm includes the Rayleigh-Sommerfeld diffraction algorithm or the angular spectrum diffraction algorithm or the Fresnel diffraction algorithm.

8. A design method for a projection dot matrix system, characterized in that, Compound metalens design applicable to a two-layer metasurface, including the steps of: T100, based on a specific light source, design the collimated phase of the metasurface using a binary surface profile; T200, given the collimated incident FOV, incident wavelength, and large periods in the x and y directions, select appropriate small-period micro-nano structure units in the x and y directions to fill the large periods; T300, set the shape of the micro-nano structure units, use the geometric parameters of each micro-nano structure unit as optimization variables, and at the same time select an appropriate height to satisfy the 2π phase interval; T400, use the performance algorithm to calculate the performance of the micro-nano structure units under the current optimization variables, substitute them into the objective function, and then output new optimization variables by the optimization algorithm; T500, repeat step T400 until the result of the objective function approaches 0, and use the finally output optimization variables as the geometric parameters of each micro-nano structure unit to complete the design of the DOE phase.

9. The design method of a projection dot matrix system according to claim 8, characterized in that: The objective function FoM = RMSE + (1 - Eff), where the calculation formulas for RMSE and Eff are respectively:

10. A method for designing a projection dot matrix system according to claim 8, characterized in that: The performance algorithms include the finite-difference time-domain method or the Fourier modal method.

11. A method for designing a projection dot matrix system according to claim 8, characterized in that: The optimization algorithms include the intelligent swarm algorithm or the gradient descent algorithm.

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