Zero-order elimination large-point number projector based on polarization conversion metasurface and design method thereof

Abstract

The application discloses a zero-order elimination large-point-number projector based on a polarization conversion super surface and a design method thereof, and belongs to the field of optical devices, comprising a linear polarization VCSEL point array light source and a super surface diffraction device; the super surface diffraction device comprises a two-in-one super surface structure layer and a linear polarizer layer; the two-in-one super surface structure layer simultaneously collimates and splits the incident point array light beam generated by the linear polarization VCSEL point array light source by superimposing a collimation phase distribution and a Daman spectroscopy phase distribution, realizes large-point-number replication and splicing of the incident point array light beam in a far field, and the linear polarizer layer cross-polarization modulates the light beam, so that the modulated light is orthogonal to the polarization state of the incident light, the zero-order light which is not modulated is filtered out, and thus the problem that the two-in-one projector of the large-point-number is seriously affected by the zero-order light is overcome. The application has a compact structure, low assembly and adjustment cost, and can inhibit the interference of the zero-order light in principle, and is suitable for the needs of speckle points from several thousand to tens of thousands of points required by the market.

Description

Technical Field

[0001] This invention relates to the field of optical devices, and in particular to a zero-order large-dot projector based on a polarization conversion metasurface and its design method. Background Technology

[0002] Structured light-based depth reconstruction is an active vision-based method. In this method, a structured light projector generates a random speckle pattern covering the desired field of view, providing feature points for depth reconstruction. Combined with binocular or monocular detection systems, triangulation is used to obtain depth information. Compared to other depth detection methods such as laser time-of-flight ranging, interferometric wavefront reconstruction, and sonar detection, structured light depth detection offers advantages in accuracy, speed, and cost at close range. Therefore, it is widely used in depth detection systems for consumer electronics such as mobile phones, robotic vacuum cleaners, drones, and augmented reality devices.

[0003] Traditional structured light projectors typically consist of a light source, a collimating lens, and diffractive optical elements (DOEs), resulting in a large size and complex structure and assembly. With the iteration and development of electronic products and new technologies, optoelectronic devices are increasingly moving towards miniaturization, lightweighting, integration, multifunctionality, and lower cost, while ensuring device performance. Currently, new dual-function diffractive optical elements (DOEs) can effectively reduce device size and cost by integrating collimation and beam splitting functions. However, due to limitations in exposure, overlay, and etching processes, the low phase step number of DOEs makes it difficult to meet the requirements for device diffraction efficiency and beam splitting uniformity. On the other hand, compared to dual-function DOEs, emerging dual-function metasurface devices can improve device performance, but their high sensitivity to processing makes the ideal phase distribution easily disturbed. This causes a small portion of the divergent incident light to be projected into the far field without modulation and superimposed on the desired speckle pattern. Especially for large-spot projections with more than 20,000 spots, the power proportion of each small spot after beam splitting is even lower, and the contrast of the central region after interference from the unmodulated zero-order light will be significantly affected, making it difficult to apply to real-world depth exploration scenarios. Summary of the Invention

[0004] In view of this, the present invention provides a zero-order large-spot projector based on a polarization conversion metasurface, comprising a linearly polarized VCSEL lattice light source and a metasurface diffraction device. It not only realizes the functions of collimation and beam splitting, reduces the device size and reduces device and assembly costs, and provides high diffraction efficiency and point cloud uniformity, but also suppresses the interference of zero-order light in principle by using a polarization conversion metasurface in combination with a linearly polarized sheet, making it suitable for the market demand for speckle counts ranging from several thousand to tens of thousands of points.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A zero-order large-dot-count projector based on a polarization conversion metasurface includes a linearly polarized VCSEL lattice light source and a metasurface diffraction device.

[0007] The linearly polarized VCSEL lattice light source includes a control module and a driving circuit. After being excited, the linearly polarized VCSEL lattice light source will generate a linearly polarized lattice beam with a certain divergence angle as the incident light of the metasurface diffraction device.

[0008] The metasurface diffraction device includes a dual metasurface structure layer and a linear polarizer layer, both arranged parallel to the incident light and perpendicular to it. The phase distribution of the dual metasurface structure layer is formed by superimposing a collimated phase distribution and a Damman beam splitting phase distribution. The collimated phase distribution is used to compensate the diverging lattice beam into collimated light, and the Damman beam splitting phase distribution is used to excite the corresponding diffraction order of the collimated light. This enables the lattice beam generated by the linearly polarized VCSEL lattice light source to be replicated and stitched together in the far field with a large number of dots, generating a structured light speckle pattern. At the same time, the linear polarizer layer performs cross-polarization modulation on the split lattice beam, making the polarization state of the modulated light orthogonal to that of the incident light, filtering out the interference of the unmodulated zero-order light on the structured light speckle pattern.

[0009] Preferably, the two-in-one metasurface structure layer includes a substrate, a cladding layer, and half-wave plate dielectric pillars of different sizes; the half-wave plate dielectric pillars are processed on the substrate material and then covered by the cladding layer to form a two-in-one metasurface structure layer unit structure; the optical response of the half-wave plate dielectric pillars is characterized by equal TE and TM transmittance and a transmission phase difference of π, while the TE or TM transmission phases corresponding to the half-wave plate dielectric pillars of different sizes exhibit a multi-step arrangement covering 0~2π.

[0010] Preferably, the collimated phase distribution is generated by hyperbolic phase or other wavefront-corrected phase; the Damman beam splitting phase distribution is a periodic phase distribution, wherein the phase distribution of a single period is generated by simulated annealing algorithm or... Algorithm iterative generation.

[0011] The present invention also provides a design method for the aforementioned zero-order large-dot-count projector based on a polarization conversion metasurface, comprising the following steps:

[0012] S1, Connects the linearly polarized VCSEL dot matrix light source, control module, and driving circuit;

[0013] S2. Determine the diffraction order order to be excited, the period of the Damman phase distribution, the effective focal length (EFL) corresponding to the collimated phase distribution, and the required area of ​​the metasurface diffraction device.

[0014] S3. Construct a two-in-one metasurface structure layer unit structure model, use the model to calculate the transmittance and phase of half-wave plate dielectric pillars of different sizes under TE and TM incident light, and establish a phase library of half-wave plate dielectric pillars.

[0015] S4. Construct periodic Damman beam splitting phase distribution and collimation phase distribution, superimpose them to obtain the final phase distribution of the two-in-one metasurface structure layer, and perform phase matching with the phase library of the half-wave plate dielectric pillar to determine the size of the half-wave plate dielectric pillar selected for each unit structure in the two-in-one metasurface structure layer.

[0016] S5. A two-in-one metasurface structure layer is formed according to the determined size of the half-wave plate dielectric column. A linear polarization layer is arranged on the light-emitting side of the two-in-one metasurface structure layer to make a metasurface diffraction device.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] This invention achieves miniaturized, high-performance structured light lattice projection and significantly overcomes the interference of zero-order light in large-dot-count projectors, while maintaining high efficiency and significantly improving the contrast and uniformity of the output point cloud. By employing a linearly polarized VCSEL lattice light source and a polarization-conversion metasurface structure layer, the emitted light can be phase-modulated and transformed into the orthogonal polarization state of the incident light. Combined with a linear polarizer layer, zero-order light is eliminated, significantly improving the signal-to-noise ratio. Furthermore, the phase design of the metasurface structure, which combines collimation and beam splitting, also significantly reduces device size and cost. The zero-order elimination large-dot-count projector based on the polarization-conversion metasurface and the receiving mirror group with a linear polarizer can be used together in special scenarios such as eliminating reflected specular highlights. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a zero-order large-dot projector based on a polarization conversion metasurface provided by the present invention;

[0020] Figure 2 This is a schematic diagram of a metasurface half-wave plate unit structure provided in one embodiment of the present invention;

[0021] Figure 3 This is a collimation and beam splitting phase profile design provided in one embodiment of the present invention;

[0022] Figure 4 This is a target for the misaligned diffraction order distribution with optimized beam splitting phase in one embodiment of the present invention;

[0023] Figure 5 This is the transmittance response function of a metal polarization grating in one embodiment of the present invention;

[0024] Figure 6These are three configurations of the metasurface diffraction device provided in the embodiments of the present invention.

[0025] Among them, 10-linearly polarized VCSEL lattice light source, 20-metasurface diffraction device, 210-two-in-one metasurface structure layer, 211-half-wave plate dielectric pillar, 212-cladding layer, 213-substrate, 220-linearly polarized sheet layer, and 30-structured light speckle pattern. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings.

[0027] Figure 1 A zero-level large-dot-count projector based on a polarization-conversion metasurface is disclosed, comprising a linearly polarized VCSEL lattice light source 10 and a metasurface diffraction device 20. The linearly polarized VCSEL lattice light source 10 is either a VCSEL lattice light source that directly outputs linearly polarized light or a VCSEL lattice light source with added linear polarizers, along with its control module and driving circuit. The linearly polarized VCSEL lattice light source 10 is arranged in a regular or random pattern, with the number of dots typically ranging from tens to hundreds. After being excited, the linearly polarized VCSEL lattice light source 10 generates a linearly polarized lattice beam with a certain divergence angle, which serves as the incident light for the metasurface diffraction device 20. The divergence angle typically ranges from 15 to 25 degrees, mainly determined by the oxide aperture size during its design. The metasurface diffraction device 20 comprises a two-in-one metasurface structure layer 210 and a linear polarizer layer 220, such as... Figure 3 As shown, the phase distribution of the two-in-one metasurface structure layer 210 Collimated phase distribution Daman spectral phase distribution It is formed by superposition, in which the collimated phase distribution Damman beam phase distribution is used to compensate divergent incident light into collimated light. This is used to excite the corresponding diffraction order of the collimated light; the metasurface diffraction device 20 and the linearly polarized VCSEL lattice light source 10 are both placed parallel to the incident light perpendicularly, and the effective distance between them is equal to the effective focal length (EFL) corresponding to the collimated phase distribution of the two-in-one metasurface structure layer 210. The effective focal length (EFL) corresponding to the collimated phase distribution of the two-in-one metasurface structure layer 210 is jointly determined by the target projection field of view (FoV), the diffraction order used, and the effective emitting area of ​​the linearly polarized VCSEL lattice light source 10. The maximum effective focal length (EFL) of the two-in-one metasurface structure layer 210 is determined by the target projection field of view (FoV), the diffraction order used, and the effective emitting area of ​​the linearly polarized VCSEL lattice light source 10. The small area is determined by the EFL, the divergence angle of the linearly polarized VCSEL lattice light source 10, and the effective luminous area. The incident light generated by the linearly polarized VCSEL lattice light source 10 is collimated and split by the two-in-one metasurface structure layer 210, realizing the large-number replication and splicing of the lattice beam generated by the linearly polarized VCSEL lattice light source 10 in the far field, ultimately forming a structured light speckle pattern 30. The linearly polarizing layer 220 performs cross-polarization modulation on the beam, making the polarization state of the modulated light orthogonal to that of the incident light, filtering out the zero-order light, and eliminating interference with the structured light speckle pattern 30. The linearly polarizing layer 220 adopts a periodic one-dimensional or two-dimensional dielectric or metal grating structure or thin film material, and the polarization state of its transmitted light is orthogonal to that of the incident light. As a preferred embodiment, Figure 5 The paper presents a schematic diagram of a metal grating structure and its transmission performance. For a subwavelength periodic metal grating, it will have different transmission responses to light with electric field vibration directions parallel to (TM) and perpendicular to (TE) the grating ridge: for TM light, the oscillation effect caused by the metal grating is weak, and most of the light will pass through directly; for TE light, its electric field vector is parallel to the grating ridge, so the electric field will oscillate back and forth along the metal grating ridge, causing the incident light to be absorbed or reflected, resulting in extremely low transmittance, thus achieving the effect of linearly polarized light emission. For example, this metal grating is composed of a glass substrate and an aluminum film grating structure. The period of the aluminum film grating structure is 400 nm, the grating ridge linewidth is 180 nm, and the thickness is 200 nm. It achieves the effect of a transmission linear polarizer with TM light transmittance exceeding 75% and TE light transmittance less than 0.5% at and near a working wavelength of 850 nm.

[0028] In this embodiment of the invention, the linearly polarized VCSEL lattice light source 10 is a random lattice with over 360 light-emitting apertures, operating at a wavelength of 850 nm and a divergence angle of 18 degrees. The effective focal length (EFL) corresponding to the collimated phase distribution of the two-in-one metasurface structure layer 210 is 4.3 mm. The pattern replication array after passing through the metasurface diffraction device 20 is 9 × 11. The total number of points in the structured light speckle pattern 30 formed in the far field is approximately 3.6w points, and the target projection field of view (FoV) of the structured light speckle pattern 30 is (104°, 74°). The x and y directions are defined as the directions of two mutually perpendicular axes on a plane perpendicular to the direction of incident light propagation. The beam generated by the linearly polarized VCSEL lattice light source 10 is linearly polarized light in the x-direction, while the linearly polarized sheet layer 220 on the metasurface diffraction device 20 transmits y-direction polarized light.

[0029] As a preferred implementation method, such as Figure 2 As shown, the dual-layer metasurface structure layer 210 is composed of a series of half-wave plate dielectric pillars 211 of different sizes, a cladding layer 212, and a substrate 213. The half-wave plate dielectric pillars 211 are structures fabricated on a single-layer glass substrate 213, and then clad by the cladding layer 212 to form a metasurface structure layer unit. The half-wave plate dielectric pillars 211 are made of materials suitable for visible light or infrared, such as silicon, silicon nitride, titanium dioxide, and germanium, and their optical response is consistent with that of a half-wave plate. A half-wave plate dielectric pillar refers to a unit composed of subwavelength-scale dielectric pillars arranged periodically. When TE-polarized light and TM-polarized light are incident, the half-wave plate dielectric pillars simultaneously satisfy the condition that the transmittance of TE-polarized light and TM-polarized light are equal and their phases are different. The requirement is to take half-wave plate dielectric pillars of different sizes, and let the initial phase of the corresponding TE or TM cover 0~2. This results in a multi-step phase distribution, forming a half-wave plate dielectric pillar 211. The cladding layer 212 can be a dielectric filling layer such as air, silicon oxide, or aluminum oxide, or a low-refractive-index filler. Preferably, the cladding layer 212 meets the following conditions: a refractive index as low as possible to avoid high aspect ratios and other difficult-to-process parameters in the half-wave plate dielectric pillar 211; good filling performance to avoid voids; good surface flatness to allow for the arrangement of the linear polarizer layer 220 on the cladding layer 212; and high temperature resistance to facilitate subsequent encapsulation processes. The period of the metasurface structure layer unit, i.e., the period of the half-wave plate dielectric pillar 211 (p... x p y This is equivalent to the sampling interval in diffraction calculations. Preferably, to satisfy the Nyquist law, its period should be less than half a wavelength, and specifically determined by the length of a single period of the Dammann spectral phase distribution and the number of samples.

[0030] In this embodiment of the invention, the period (p) of the half-wave plate dielectric pillar 211 x p yThe value is taken as (394nm, 424nm), p x p y The x and y directions represent the periods of the half-wave plate dielectric pillar 211, respectively. The half-wave plate dielectric pillar 211 is a rectangular silicon pillar, and the cladding layer 212 is a low-refractive-index, high-temperature resistant filler. After filling, the surface flatness of the cladding layer 212 is within 20nm. The half-wave plate dielectric pillar 211 finally presents an 8-step phase structure.

[0031] As a preferred embodiment, the metasurface diffraction device 20 can adopt different configurations, such as Figure 6 As shown, the linear polarizer layer 220 and the dual-layer metasurface structure layer 210 can be a double-layer structure built on the same side of the substrate 213, which is constructed by encapsulating the dual-layer metasurface structure layer 210 with a dielectric or adhesive before constructing the linear polarizer layer 220; or they can be single-layer structures built on both sides of the substrate 213, which is constructed by first exposing and processing one side of the substrate 213 and then encapsulating it with a dielectric or adhesive as a protective layer, and then exposing and processing the reverse side of the substrate 213; or they can be constructed by processing the dual-layer metasurface structure layer 210 and the linear polarizer layer 220 on two substrates 213 respectively and then bonding them together; or they can be two single-layer structures built on two substrates 213 respectively.

[0032] As a preferred embodiment, the dual-layer metasurface structure layer 210 and the linear polarizer layer 220 can be realized by methods such as electron beam direct writing, ultraviolet lithography, and nanoimprinting, and the alignment of the dual-layer structure can be achieved by overlay etching.

[0033] As a preferred embodiment, the zero-order large-dot projector based on polarization conversion metasurface and the receiving mirror group with linear polarizer are used together for scenarios such as eliminating reflected highlights.

[0034] The present invention also provides a design method for the aforementioned zero-order large-dot-count projector based on a polarization conversion metasurface, comprising the following steps:

[0035] S1. A VCSEL dot matrix light source that directly outputs linearly polarized light or a VCSEL dot matrix light source with a linear polarizer is used as the linearly polarized VCSEL dot matrix light source 10. The linearly polarized VCSEL dot matrix light source 10 is connected to the control module and the drive circuit.

[0036] S2. Determine the structural parameters of the two-in-one metasurface structure layer 210: For a linearly polarized VCSEL lattice light source 10 of a specific type, its effective light-emitting area is... The divergence angle is The target projection field of view (FoV) is By combining the number of target points of the metasurface diffraction device 20, the diffraction order order to be excited and the period (d) of the Damman spectral phase distribution of the two-in-one metasurface structure layer 210 can be determined sequentially. x d y The effective focal length (EFL) corresponding to the collimated phase distribution of the two-in-one metasurface structure layer 210 and the required area of ​​the metasurface diffraction device 20 (D) x D y );in, , These represent the lengths of the emitting region in the x and y directions of the linearly polarized VCSEL lattice light source 10, respectively. , d represents the maximum angle of the projected structured light speckle pattern 30 in the x and y directions, respectively. x d y D represents the period of the Dammann beam phase distribution in the x and y directions, respectively. x D y These represent the lengths of the metasurface diffraction device 20 in the x and y directions, respectively.

[0037] S3. Based on the predetermined material parameters of the half-wave plate dielectric pillar 211, the cladding layer 212, and the substrate 213, as well as the thickness h and dimensions (l) of the half-wave plate dielectric pillar 211... x , l y ), period (p) x p y Structural parameters such as substrate, half-wave plate dielectric pillar on the substrate, and cladding layer are used to construct a unit structure of a two-in-one metasurface structure. The optical response parameters of the dielectric pillars of different sizes are calculated using RCWA or full-wave simulation software. A unit structure model conforming to the optical response of a half-wave plate is searched, and a corresponding phase library of the half-wave plate dielectric pillar 211 is established, where l x l y These represent the lengths of the half-wave plate dielectric column 211 in the x and y directions, respectively.

[0038] S4. Construct a periodic Damman spectral phase distribution. Phase distribution within a single period Through gradient descent or The algorithm iteratively generates the data, which is then replicated to cover a metasurface diffraction device of size 20 (D). x D y The periodic phase distribution of the target diffraction order is constructed by setting an appropriate target diffraction order distribution. The method can optimize the diffraction order distribution of regular, staggered, or randomly illuminated arrays. As a preferred implementation, such as... Figure 4As shown, a horizontally staggered pattern arrangement can further enhance the randomness and distinctiveness of sub-regions; for example, the stagger period is set to d. x / 3, therefore, a design phase is required for one The period of the three-times Damman spectral phase distribution is optimized to obtain a far-field distribution with three times the sampling density. By presetting the target diffraction order distribution as a misaligned result, a misaligned pattern splicing effect is obtained. The spectral effect can be improved by adjusting the diffraction efficiency. and uniformity Evaluation, of which I i Let I be the intensity of the i-th diffraction order, M be the total number of diffraction orders designed, and I be the intensity of the i-th diffraction order. max and I min These are the maximum and minimum diffraction order intensities, respectively.

[0039] S5. Constructing the collimation phase distribution The collimated phase distribution satisfies a hyperbolic phase distribution or other wavefront-corrected phase distribution. As a preferred embodiment of a large-dot-count projector, in this example, the zero-order pattern covers an angle range of approximately 4 degrees, and the collimated phase distribution satisfies the hyperbolic phase distribution expression:

[0040] ;

[0041] In the formula, r is the radial distance. The operating wavelength;

[0042] S6. The Damman beam phase distribution and collimated phase distribution The phase distribution of the final two-in-one metasurface device 20 is obtained by superposition. , where mod(, For the modulus operation, the phase distribution of the two-in-one metasurface structure layer 210 is then... Phase matching is performed with the phase library of the half-wave plate dielectric pillar 211 to determine the size of the selected half-wave plate dielectric pillar 211. As a preferred embodiment, in this example, the optimized continuous phase distribution of the two-in-one metasurface structure layer 210 is used. Discretized into 8 steps, as exemplified, Table 1 details the process. The changes in the spectral performance of the two-in-one metasurface structure layer 210 under discrete steps of 4, 8, and 16 steps show that the number of discrete steps mainly affects the total diffraction efficiency, but it can still be stable at over 85% at 8 steps, which is far better than the traditional DOE's total diffraction efficiency of only 60%.

[0043] Table 1. Spectroscopic performance of the device under discrete steps

[0044]

[0045] S7. The determined half-wave plate dielectric pillar 211 is fabricated on a single-layer glass substrate 213 and coated with a cladding layer 212 to form a metasurface structure layer unit. Multiple metasurface structure layer units are spliced ​​together to form a two-in-one metasurface structure layer 210. A linear polarization layer 220 is arranged on the side of the two-in-one metasurface structure layer 210 away from the linearly polarized VCSEL lattice light source 10 to form a metasurface diffraction device 20. The metasurface diffraction device 20 is arranged parallel to the optical path of the linearly polarized VCSEL lattice light source 10, and the effective distance between them is equal to the collimation phase distribution of the two-in-one metasurface structure layer 210. The corresponding effective focal length (EFL);

[0046] S8, Phase distribution of the beam generated by the linearly polarized VCSEL lattice light source 10 with the two-in-one metasurface structure layer 210 The superimposed structured light speckle pattern 30 is obtained by Fourier transform. The pattern replication and splicing are checked to avoid slits or point cloud overlap.

[0047] The method for determining the structural parameters of the two-in-one metasurface structure layer 210 in step S2 is as follows:

[0048] (1) Calculate the period (d) of the phase distribution of the Damman spectrometer. x d y Specifically, for example, for diffraction orders that need to be arranged symmetrically step by step, the number of rows and columns of the pattern to be replicated can be determined based on the total number M of the target structured light speckle pattern 30 and the number m of the emission points of the linearly polarized VCSEL lattice source. This allows the determination of the x and y-axis diffraction order distribution of the Damman phase-induced excitation, and the relationship satisfies... , where N x N y These are the maximum diffraction orders in the x and y directions, respectively. According to the grating equation... Calculate and This is to ensure that the outermost pattern after copying can cover the target's projection field of view (FoV);

[0049] (2) Calculate the period (p) of a single metasurface structural layer unit. x p y ): will (d x d y The sample is divided into multiple periods that are integer multiples of the wavelength and less than half a wavelength. Each period after the division represents the sampling interval, which is also the period of a single metasurface unit structure.

[0050] (3) Calculate the effective focal length EFL corresponding to the collimated phase distribution: The effective focal length EFL corresponding to the collimated phase distribution of the two-in-one metasurface structure layer 210 and the effective luminous area of ​​the linearly polarized VCSEL lattice light source 10 The angle range occupied by the zero-order pattern after projection is determined together. In order to avoid overlapping or gaps between adjacent patterns, the angle range occupied by the zero-order pattern after projection needs to be slightly smaller than the angle range between ±0.5 orders of the Damman spectral diffraction period. The effective focal length EFL corresponding to the collimated phase distribution of the two-in-one metasurface structure layer 210 is obtained from this angle range requirement.

[0051] (4) Calculate the required area (D) of the metasurface diffraction device. x D y The area size of the metasurface diffraction device should meet the following requirements: To cover the area of ​​incident light.

[0052] In step S3, the phase library of the half-wave plate dielectric pillar 211 can be established in the following two ways:

[0053] Method 1: Scan the dimensions of the half-wave plate dielectric pillar 211 in a certain step size (e.g., 5nm). x , l y Simulations were performed on the dielectric pillar 211 of each size of the half-wave plate to obtain the transmittance and phase at TE and TM incident points, thus obtaining a size-optical response sampling library. The data in the size-optical response sampling library were then filtered according to the required transmittance-phase relationship of the half-wave plate, such as retaining the difference in transmittance between TE and TM incident points. Phase difference Furthermore, the TE and TM transmittance are both greater than 0.9 for sampling; then the phase data of the size-optical response sampling library is matched with the pre-divided step phase, such as retaining the sampling data whose phase difference with a certain step phase is less than 0.05 rad, and finally the phase library of the half-wave plate dielectric column 211 is obtained.

[0054] Method 2: Using RCWA or full-wave simulation software in conjunction with optimization algorithms such as particle swarm optimization, for each preset step phase, set optimization objectives that include conditions satisfying the optical response of the half-wave plate and the preset step phase conditions. Iterate through the dimensions of the half-wave plate dielectric pillar 211 to obtain the structural parameters required for each preset step phase, ultimately obtaining the phase library of the half-wave plate dielectric pillar 211. The optimization conditions can refer to the structural selection conditions in Method 1. In this embodiment of the invention, the optimization objective is further simplified by rotating the half-wave plate dielectric pillar 211 counterclockwise by 45 degrees: First, set the dimensions (l) of the optimized half-wave plate dielectric pillar 211. x , l yThe range is 90~300nm to meet processing requirements. Then, the transmittance T and phase of the TE polarized light obtained after the TM polarized light is incident on the dielectric pillar 211 of the half-wave plate are calculated. Taking an 8-step phase as an example, the phase of each step... The target loss is set as follows:

[0055]

[0056] In the formula, and These are weighting coefficients, which can be adjusted according to the target optimization effect. For example, Table 2 details the structural parameters and optical response parameters of the half-wave plate dielectric pillar 211 corresponding to the optimized 8-step phase library.

[0057] Table 2. Parameters of the 8-Step Phase Structure Library

[0058]

[0059] In particular, when the number of phase steps is large, such as 16 steps, a single-shape dielectric column structure may not be able to meet the required phase step requirements. In this case, various structures that can realize half-wave plates, such as rectangular, elliptical, rhomboid, and cross-shaped dielectric column structures, can be introduced to participate in the optimization to meet the corresponding multi-step phase requirements.

[0060] The half-wave plate dielectric column 211 is rotated by a certain angle relative to the vibration direction of the incident light. At that time, its phase will not change, but after the incident light exits through the linearly polarized sheet layer 220, which is orthogonal to the polarization state of the original incident light, its transmitted light intensity will satisfy Malus's law:

[0061]

[0062] Therefore, when change In this case, the two-in-one metasurface structure layer 210 can be designed as a complex amplitude metasurface. Since this example is a phase-type metasurface, i.e., the goal is to achieve the highest polarization conversion rate and the highest transmittance, all structures are arranged in a direction that is 45 degrees counterclockwise from the incident light polarization direction, such as... Figure 2As shown. At this time, most of the light will be modulated by the dual-layer metasurface structure layer 210, transformed into its orthogonal polarization state, and superimposed with a corresponding phase distribution. It should be noted that in the description of this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprising" or any other variation thereof is intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements, but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0063] Those skilled in the art will recognize that the embodiments described herein are intended to help readers understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the essence of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A zero-order large-dot projector based on a polarization conversion metasurface, characterized in that, Including linearly polarized VCSEL lattice light sources and metasurface diffraction devices; The linearly polarized VCSEL lattice light source includes a control module and a driving circuit. After being excited, the linearly polarized VCSEL lattice light source will generate a diverging linearly polarized lattice beam as the incident light for the metasurface diffraction device. The metasurface diffraction device includes a dual metasurface structure layer and a linear polarizer layer, both arranged parallel to the incident light and perpendicular to it. The phase distribution of the dual metasurface structure layer is formed by superimposing a collimated phase distribution and a Damman beam splitting phase distribution. The collimated phase distribution is used to compensate the diverging lattice beam into collimated light, and the Damman beam splitting phase distribution is used to excite the corresponding diffraction order of the collimated light. This enables the lattice beam generated by the linearly polarized VCSEL lattice light source to be replicated and stitched together in the far field with a large number of dots, generating a structured light speckle pattern. At the same time, the linear polarizer layer performs cross-polarization modulation on the split lattice beam, making the polarization state of the modulated light orthogonal to that of the incident light, filtering out the interference of the unmodulated zero-order light on the structured light speckle pattern.

2. The zero-suppression large-dot-count projector based on a polarization conversion metasurface according to claim 1, characterized in that, The dual-mode metasurface structure layer includes a substrate, a cladding layer, and half-wave plate dielectric pillars of different sizes. The half-wave plate dielectric pillars are units composed of subwavelength-scale dielectric pillars arranged periodically, which are processed on the substrate material and then covered by the cladding layer to form a dual-mode metasurface structure layer unit structure. The optical response of the half-wave plate dielectric pillars is characterized by equal TE and TM transmittance and a transmission phase difference of π. At the same time, the TE or TM transmission phases corresponding to the half-wave plate dielectric pillars of different sizes exhibit a multi-step arrangement covering 0~2π.

3. The zero-suppression large-dot-count projector based on a polarization conversion metasurface according to claim 2, characterized in that, The material of the half-wave plate dielectric pillar is silicon, silicon nitride, titanium dioxide, or germanium.

4. The zero-order large-dot-count projector based on a polarization conversion metasurface according to claim 2, characterized in that, The half-wave plate dielectric pillar is one or more of a rectangular pillar, an elliptical pillar, or a rhomboid pillar, and is at a 45-degree angle to the polarization direction of the incident light.

5. The zero-order large-dot-count projector based on a polarization conversion metasurface according to claim 1, characterized in that, The structure of the linearly polarized sheet is one of a periodic one-dimensional or two-dimensional dielectric structure, a metallic grating structure, or a thin film structure.

6. The zero-order large-dot-count projector based on a polarization conversion metasurface according to claim 1, characterized in that, The collimated phase distribution is generated by hyperbolic phase or other wavefront-corrected phase; the Damman beam splitting phase distribution is a periodic phase distribution, wherein the phase distribution of a single period is generated iteratively by a simulated annealing algorithm or a Gerchberg-Saxton algorithm.

7. The zero-order large-dot-count projector based on a polarization conversion metasurface according to claim 2, characterized in that, The structure of the two-in-one metasurface structure layer and the linear polarizer layer can be one of the following: a double-layer structure built on the same side of the substrate, a single-layer structure built on both sides of the substrate, or a single-layer structure built on two substrates.

8. A design method for a zero-order large-dot-count projector based on a polarization conversion metasurface as described in claim 2, characterized in that, Includes the following steps: S1, Connects the linearly polarized VCSEL dot matrix light source, control module, and driving circuit; S2. Determine the diffraction order order to be excited, the period of the Damman phase distribution, the effective focal length (EFL) corresponding to the collimated phase distribution, and the required area of ​​the metasurface diffraction device. S3. Construct a two-in-one metasurface structure layer unit structure model, use the model to calculate the transmittance and phase of half-wave plate dielectric pillars of different sizes under TE and TM incident light, and establish a phase library of half-wave plate dielectric pillars. S4. Construct periodic Damman beam splitting phase distribution and collimation phase distribution, superimpose them to obtain the final phase distribution of the two-in-one metasurface structure layer, and perform phase matching with the phase library of the half-wave plate dielectric pillar to determine the size of the half-wave plate dielectric pillar selected for each unit structure in the two-in-one metasurface structure layer. S5. A two-in-one metasurface structure layer is formed according to the determined size of the half-wave plate dielectric column. A linear polarization layer is arranged on the light-emitting side of the two-in-one metasurface structure layer to make a metasurface diffraction device.

9. The design method according to claim 8, characterized in that, The phase library of the half-wave plate dielectric pillar is constructed as follows: The size of the half-wave plate dielectric pillar is scanned, and simulation is performed on the half-wave plate dielectric pillar of each size to obtain the transmittance and phase of TE and TM corresponding to the half-wave plate dielectric pillar of different sizes, thus obtaining the size-optical response sampling library. The data in the size-optical response sampling library is filtered according to the transmittance-phase relationship required by the half-wave plate, and then the filtered phase data is matched with the pre-divided step phase to finally obtain the phase library of the half-wave plate dielectric pillar.

10. The design method according to claim 8, characterized in that, The phase library of the half-wave plate dielectric pillar is constructed as follows: Using RCWA or full-wave simulation software in conjunction with particle swarm optimization algorithm, for each preset step phase, an optimization objective is set that includes conditions that meet the optical response of the half-wave plate and conditions that meet the step phase. By optimizing the size of the half-wave plate dielectric pillar, the size parameters required for each preset step phase are iteratively obtained, and finally the phase library of the half-wave plate dielectric pillar is obtained.

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