Polarization multiplexing bifocal metasurface light machine, design method and ar display device

Abstract

The application belongs to the technical field of micro-nano super surface optics, and discloses a polarization multiplexing double-focal-plane super surface light machine, a design method and an AR display device. The light path of the polarization multiplexing double-focal-plane super surface light machine starts from an image generation component, sequentially passes through a polarization shaping component, a super surface / coupler two-in-one structure and an optical waveguide, and finally reaches a human eye receiving end. Two types of materials TiO2 and Al2O3 are tested and verified, and can support a high refractive index strong phase control scheme and a wide spectrum low loss optimization scheme respectively. Process tolerance design gives determination standards such as transmittance, phase error, focal plane offset and coupling angle margin, which provides a basis for subsequent tape-out and mass production evaluation.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano metasurface optical technology, and particularly relates to the optomechanics, design methods and AR display devices of polarization multiplexed dual-focal-plane metasurfaces. Background Technology

[0002] The basic components of an optical waveguide display: An optical waveguide AR display system generally consists of an image generation unit, collimation or relay components, an in-coupler, a waveguide transmission area, a pupil expansion area, and an out-coupler. Image light is first shaped by the front-end optical link, then enters the waveguide and propagates through total internal reflection, finally being coupled out from the exit area to the human eye. The overall performance is mainly affected by the system size, coupling efficiency, display depth, and assembly accuracy.

[0003] The working principle of polarization-multiplexed metasurfaces: Polarization-multiplexed metasurfaces are typically composed of anisotropic subwavelength units. Taking a rectangular nanofin as an example, its major and minor axes correspond to different equivalent refractive indices, thus enabling the modulation of the transmission phase and transmittance of two orthogonal polarization states. Utilizing this, a single device can carry two sets of phase functions, providing a foundation for dual-channel displays and dual-focal-plane designs.

[0004] However, existing optical waveguide structures or couplers have the following problems and defects: (1) Narrow operating bandwidth. Existing unit structures and material selections are mostly focused on a single design wavelength, lacking a unified screening of phase response and transmittance response across the entire visible light band, resulting in insufficient expansion capability for color displays.

[0005] (2) The metasurface and the in-coupler are separate. Existing phase gradient designs are mostly focused on the imaging target, without simultaneously considering waveguide coupling angle matching and total internal reflection propagation conditions. Therefore, the system still needs to set up a separate coupling structure.

[0006] (3) Physical polarization beam splitting elements are required. Since the metasurface itself does not directly undertake the function of polarization channel splitting, polarization management is usually left to the front-end additional optical components, resulting in a longer system link and more assembly and adjustment links.

[0007] (4) Narrow manufacturing tolerance window. The structural parameters, material refractive index and system propagation conditions are strongly coupled, and many schemes do not provide tolerance design for mass production. Summary of the Invention

[0008] In view of this, this specification provides a polarization-multiplexed dual-focal-surface metasurface optomechanism, a design method, and an AR display device. This invention also belongs to the fields of AR display and optical waveguide display, particularly relating to a polarization-multiplexed dual-focal-surface metasurface optomechanism for optical waveguide displays and an AR display device. It addresses the challenges of the typically narrow operating bandwidth of polarization-multiplexed metasurfaces, making it difficult to directly cover the visible light range required for color displays. Furthermore, metasurfaces and in-couplers are often discrete structures, resulting in large system sizes and long assembly / adjustment links. Dual-focal-surface displays often require additional mirror groups or phase devices, limiting the size of the AR display optomechanism. Additionally, existing solutions are sensitive to width, height, and material refractive index deviations, hindering mass production feasibility.

[0009] The technical solution is as follows: a polarization multiplexing dual-focal-plane metasurface optomechanic, the optical path starts from the image generation component, passes sequentially through the polarization shaping component, the metasurface / in-coupler two-in-one structure and the optical waveguide, and finally reaches the human eye receiving end; The image generation component outputs an image light that carries the displayed content; The polarization shaping component organizes the image light into a first polarization state channel and a second polarization state channel; The metasurface / coupler dual-structure is composed of periodically arranged anisotropic subwavelength units, specifically a rectangular nanofin array. This structure loads different phase distributions on different polarization states of the first polarization state channel and the second polarization state channel, and outputs polarized light with different phase distributions. At the same time, it imparts transverse momentum to the output polarized light to meet the waveguide coupling conditions. Furthermore, this structure, through the same set of anisotropic micro / nano units, respectively modulates the focal plane phase of the two orthogonal polarization channels and superimposes a linear phase gradient that meets the waveguide coupling requirements. The optical waveguide couples in two polarized lights that impart the transverse momentum and enables the two polarized lights to propagate under total internal reflection conditions. The output region then couples the two polarized beams propagating within the waveguide to the human eye.

[0010] Furthermore, the metasurface / coupler dual-structure is composed of periodically arranged anisotropic subwavelength units.

[0011] Another object of the present invention is to provide a design method for a polarization-multiplexed dual-focal-plane metasurface optical mechanism. This design method is used to design the aforementioned polarization-multiplexed dual-focal-plane metasurface optical mechanism and includes the following steps: S1. With the working bandwidth of 380nm-780nm visible light range as the target, we screened metasurface / coupler dual-structure and materials around the expansion of color display. S2. Based on the screening results of the metasurface / coupler dual-structure and materials, perform dual-focal-plane phase gradient design; S3. Based on the dual-focal-plane phase gradient design results, perform coupling angle matching design to constrain the waveguide coupling angle; S4. Perform process tolerance design on the parameters in the design and design a polarization multiplexing dual focal plane metasurface optical engine.

[0012] In step S1, the metasurface / coupler dual-structure is a rectangular nanofin.

[0013] Furthermore, the material of the metasurface / coupler combined structure is either TiO2 or Al2O3.

[0014] In step S1, the working bandwidth of 380nm-780nm visible light includes: firstly, using an equivalent refractive index model for initial screening of combinations, then using an RCWA two-dimensional periodic model to verify the transmittance, polarization phase splitting, and focal plane formation trends of the shortlisted combinations at three representative wavelengths of 450nm, 550nm, and 650nm, and checking the response changes in the 380nm-780nm band.

[0015] In step S2, the dual-focal-plane phase gradient design includes: First, determine the focal plane positions of the two targets and the corresponding target waves; Then, the converging phase required to form the focal plane is combined with the linear phase gradient required for waveguide coupling. Subsequently, based on the phase lookup table of rectangular nanofins in the two polarization directions, unit parameters that simultaneously satisfy the phase requirements of both channels are selected. Finally, propagation simulation was used to verify the focal peak positions and energy distribution of the two channels.

[0016] In step S3, the coupling angle matching design includes: First, determine the total internal reflection propagation window based on the waveguide refractive index and the external medium. The critical angle is determined according to... Calculate; where, This is the critical angle at which total internal reflection occurs at the waveguide-air interface. The refractive index of air, The refractive index of the waveguide core material; Subsequently, the target propagation angle of the two polarization channels in the waveguide is selected, which is higher than the critical angle while retaining process and wavelength drift margins; The target propagation angle is then converted into the transverse wave vector component required at the metasurface output end, and this transverse momentum constraint is superimposed on the phase of the dual-focal-plane target. Finally, the output angle, total internal reflection propagation, and focal plane formation results were verified at 450nm, 550nm, and 650nm, respectively.

[0017] In step S4, the process tolerance design for the parameters in the design includes: First, determine the nominal period, height, major axis width, and minor axis width of the rectangular nanofin, and then establish the phase and transmittance references for the two polarization channels based on the nominal structure. Then, width deviation, height deviation, and material refractive index drift are introduced separately to form multiple sets of deviation samples; Subsequently, the transmittance, phase error, coupling angle shift, and focal plane position change of the two polarization channels were recalculated for each group of samples. Finally, determine whether it falls within an acceptable range based on the display effect and waveguide propagation requirements.

[0018] Another object of the present invention is to provide an AR display device fabricated using the aforementioned polarization multiplexing dual-focal-plane metasurface optical engine.

[0019] Combining all the above technical solutions, the beneficial effects of this invention are as follows: First, this invention proposes a monolithic integrated solution for optical waveguide AR displays: integrating metasurface imaging and in-coupler functions into the same anisotropic micro / nano structure, with polarization channel division directly completed by the metasurface body, and simultaneous completion of dual focal plane phase gradient design and waveguide coupling angle matching; at the same time, through broadband structure screening, material screening, and process tolerance window design, the color display expansion capability and mass production feasibility are improved.

[0020] Secondly, the metasurface / in-coupler dual-structure integrates imaging phase modulation and waveguide coupling lateral momentum within the same micro / nano structure, reducing the need for separate coupling devices and assembly interfaces, resulting in a more compact optomechanical system. The anisotropic response of the rectangular nanofins allows for independent phase distributions for the two orthogonal polarization states. A single device can form two distinguishable focal planes of approximately 3.73 mm and 5.22 mm, thereby improving the depth representation capability of near-eye displays. The coupling angle matching design ensures that the two polarization channels, within the same optical waveguide with a refractive index of approximately 1.9 and a thickness of approximately 2 mm, satisfy the total internal reflection condition with internal propagation angles of approximately 47.0° and 56.0°, allowing both image beams to be received and propagated through the same waveguide. Both TiO2 and Al2O3 materials were tested and validated, supporting high-refractive-index strong phase modulation schemes and broadband low-loss optimization schemes, respectively. The process tolerance design provides criteria for transmittance, phase error, focal plane offset, and coupling angle margin, providing a basis for subsequent fabrication and mass production evaluation.

[0021] Third, this invention integrates polarization channel splitting, dual-focal-plane phase modulation, and waveguide coupling onto a single anisotropic metasurface. This reduces the number of independent polarization splitters, couplers, and additional phase elements, shortens the optical path of the AR display optical engine, reduces system size and assembly complexity, and minimizes the cumulative errors caused by assembling multiple optical components separately. The two orthogonal polarization channels correspond to different focal planes, enabling a single optical engine to present two distinguishable display depths. This design helps enhance the depth-of-field representation capability of near-eye displays and provides a hardware foundation for mitigating convergence and focusing inconsistencies. Regarding product commercialization, this invention proposes a structure and material selection method applicable to the 380nm-780nm visible light band, a dual-polarization response lookup table, a coupling angle matching method, and a process tolerance judgment standard. This reduces the time required for repeated trial production and parameter adjustments, improving consistency between design, fabrication, and mass production. The related achievements can be applied to AR glasses, near-eye display modules, vehicle head-up displays and industrial auxiliary display equipment, and form products or services such as metasurface devices, AR optomechanical modules, design software and patent licensing, which can reduce the overall cost, improve product integration and establish differentiated technological barriers.

[0022] Fourth, within the scope of the existing prior art, existing technologies mainly focus on single functions in metasurface imaging, waveguide coupling, polarization beam splitting, or multifocal plane display, and have not yet formed a complete scheme that simultaneously considers polarization-multiplexed dual-focal plane imaging, lateral momentum loading, waveguide total internal reflection coupling, broadband material selection, and manufacturing tolerance design. This invention utilizes the same set of anisotropic micro / nano units to separately control the focal plane phase of two orthogonal polarization channels, and then superimposes a linear phase gradient that satisfies the waveguide coupling requirements. By calculating the actual coupling angle and verifying the total internal reflection propagation conditions, two polarized beams can be coupled into the same waveguide and carry image information from different focal planes. Therefore, the value of this invention lies not only in integrating a dual-focal plane metasurface and a waveguide coupler onto the same device, but also in establishing a complete design process from broadband selection, unit matching, coupling angle design to process tolerance verification, supplementing the technical solutions for the collaborative design of polarization-multiplexed dual-focal plane metasurfaces and optical waveguides.

[0023] Fifth, traditional optomechanical systems typically require separate polarization splitters, imaging elements, and waveguide couplers, resulting in longer optical paths, more assembly and adjustment steps, and a higher risk of accumulated errors. Furthermore, the two focal planes, two polarization channels, and two waveguide propagation angles need to be matched separately, further increasing the complexity of system design and assembly. This invention utilizes the anisotropic response of rectangular nanofins in two orthogonal polarization directions, enabling a single physical unit to simultaneously carry two sets of phase information. Based on this, the convergent phase of the dual focal planes is superimposed with the linear phase required for waveguide coupling, allowing the two polarized beams to form different focal planes and enter the same waveguide with internal propagation angles of approximately 47.0° and 56.0°. These angles are both higher than the critical angle for total internal reflection (approximately 31.8°), thus enabling propagation within the waveguide. Therefore, this invention provides a clear technical path for a single device to simultaneously perform polarization channel splitting, dual focal plane imaging, and waveguide coupling.

[0024] Sixth, existing optomechanical designs typically treat imaging, polarization channel splitting, and waveguide coupling as relatively independent functions, configuring imaging elements, polarization elements, and coupling structures separately. Following this design approach, when the system needs to simultaneously achieve dual-focal-plane display and waveguide coupling, it often requires adding independent polarization beam splitters, couplers, or additional phase elements. This not only makes the system structure more complex but also easily increases optical loss and assembly / adjustment errors. This invention does not follow the aforementioned discrete design but utilizes the different equivalent refractive indices of rectangular nanofins along the long and short axes to separately control the phase of the two orthogonal polarization channels; simultaneously, a linear coupling phase is added to the convergent phase of the dual-focal-plane, allowing imaging and waveguide coupling to be jointly completed by the same set of micro / nano structures. With the coordination of structure and material selection and process tolerance design, this integrated solution also considers device performance and fabrication feasibility. Therefore, this invention breaks through the traditional design approach where multiple optical functions must rely on multiple independent devices, demonstrating that a single anisotropic metasurface can simultaneously perform independent dual-polarization phase adjustment, dual-focal-plane imaging, and waveguide coupling functions. Attached Figure Description

[0025] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the disclosure of this invention and, together with the description, serve to explain the principles of this disclosure; Figure 1 This is a schematic diagram of the hardware components and optical path structure of the polarization multiplexing dual-focal-plane metasurface optomechanism provided by the present invention; In the diagram: 1. Illumination source; 2. Microdisplay; 3. Linear polarizer; 4. Half-wave plate; 5. Relay / collimating lens group; 6. Metasurface / coupler combined structure; 7. Optical waveguide; 8. Coupling grating region; 9. Human eye; Figure 2This is a diagram showing the polarization axis, rotation angle, and geometric phase of a rectangular nanofin provided by this invention, wherein (a) represents the rotational orientation of the nanofin while maintaining its size, with a period of Long axis short axis ; Figure 2 The left, middle, and right images in (a) correspond to respectively ; Figure 2 Figure (b) shows the geometric phase relationship between the rotation angle and the cross-circular polarization transmission component, satisfying... ; Figure 3(a) is a diagram showing the effect of width variation on phase provided by the present invention; Figure 3(b) is a graph showing the effect of width variation on transmittance provided by the present invention; Figure 4 This is a flowchart of the design method for a polarization multiplexing dual-focal-plane metasurface optomechanic provided by the present invention; Figure 5 This is a schematic diagram of dual-polarization channel dual-focal-plane propagation calculation provided by the present invention; Figure 6 These are simulation diagrams of five material units—TiO2, GaN, Si3N4, Ta2O5, and Al2O3—provided by this invention; where (a) shows the focal plane formation trend of the five materials; (b) shows the polarization phase splitting diagram; and (c) shows the transmittance diagram. Figure 7(a) is a waveguide interface diagram provided by the present invention; Figure 7(b) is a total internal reflection coupling window diagram provided by the present invention; Figure 8 These are simulation results of process tolerance provided by the present invention, wherein (a) is a width deviation diagram, (b) is a height deviation diagram, and (c) is a material refractive index deviation diagram; Figure 9 These are Lumerical FDTD simulation images of the TiO2 rectangular nanofin unit provided by this invention; (a) shows the metasurface unit using TiO2 rectangular nanofins with a period of 320nm, a major axis width of 9nm, and a minor axis width of 120nm; within the current 550nm height scan range, the selected height is 950nm; (b) shows the Lumerical FDTD simulation with a 25nm grid and a 550nm height scan under the conditions of an upper cladding refractive index of 1.0, a substrate refractive index of 1.9, and normal incidence; (c) shows the recalculated image of the selected structure with a 20nm grid. Figure 10The following are Lumerical FDTD simulation images of the Al2O3 rectangular nanofin unit provided by this invention, wherein (a) is a selected unit with a period of 320nm, a major axis width of 210nm, a minor axis width of 90nm, and a height of 1250nm; (b) is a 550nm geometric scan image completed with Lumerical FDTD boundary conditions and a 25nm grid; and (c) is a recalculated image of the selected structure with a 20nm grid. Figure 11(a) is a broad-spectrum comprehensive score chart of the structure-material combination provided by the present invention; Figure 11(b) is an average polarization phase splitting diagram of the structure-material combination provided by the present invention; Figure 12(a) is a graph showing the polarization phase splitting of the shortlisted structure-material combination provided by the present invention as a function of wavelength; Figure 12(b) is a graph showing the minimum zero-order transmittance of the shortlisted structure-material combination provided by the present invention as a function of wavelength. Detailed Implementation

[0026] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0027] The innovation of this invention lies in the following: This invention proposes a polarization multiplexing dual-focal-plane metasurface optomechanism, which integrates dual-polarization independent phase modulation, dual-focal-plane imaging and optical waveguide coupling through a single anisotropic metasurface, thereby reducing the size of the AR display optomechanism and improving the system integration.

[0028] In the prior art, regarding devices such as polarization multiplexing metasurfaces, the first prior art is represented by the optical waveguide structure scheme described in Chinese Invention Patent No. CN1531268B, Publication Date 20210625, which describes an optical waveguide structure. This type of scheme mainly focuses on the waveguide functional region, diffraction coupling structure, and dispersion control path. Structurally, it relies on waveguide functional partitions or independent coupling regions, and does not integrate polarization channel separation, dual-focal-plane display, and monolithic metasurface into a single design object.

[0029] The second prior art is the metasurface waveguide coupler approach represented by the US invention patent for metasurface couplers (publication number US11867912B2, publication date 20240109). This approach demonstrates that metasurfaces can be used as waveguide couplers, but the focus remains on the coupling relationship between the metasurface coupler and the waveguide. The operating bandwidth is mostly focused on a single or limited band, and polarization channel separation, dual-focal plane imaging, and broadband display have not yet been considered as a holistic goal.

[0030] Existing publications already cover areas such as the combination of metasurfaces and waveguides, polarization multiplexing devices, and waveguide coupling structures. Further searches reveal that Chinese invention patents, including "A Near-Eye Display Optical Mechanism and Method and Near-Eye Display Device" (Publication No. CN2051671A, Publication Date 20201208) and "A Near-Eye Display Optical Mechanism and Method and Near-Eye Display Device" (Publication No. CN2051671B, Publication Date 20201208), both disclose a near-eye display optical mechanism comprising an image source unit, a polarization beam splitting unit, a perspective reflection unit, a polarization conversion unit, and a lens group unit, focusing on polarization beam splitting, reflection, and polarization conversion optical paths; and Chinese invention patent "A Biased Display Optical Mechanism and Method and Near-Eye Display Device" (Publication No. CN114690). Chinese Invention Patent No. 432A (Publication Date 20220701) and Chinese Invention Patent No. CN114690432B (Publication Date 20220701) disclose a biased display optical engine, which focuses on tilting the image beam to the waveguide coupling region through a biased imaging component to improve ghosting; Chinese Invention Patent No. CN116953928A (Publication Date 20231027) discloses a near-eye holographic display optical engine, which focuses on the holographic display optical path between the polarization illumination component, the beam splitter prism and the spatial light modulator.

[0031] However, the problem with the existing technology is that the metasurface and the in-coupler are separate. Existing phase gradient designs are mostly centered around the imaging target and do not simultaneously consider waveguide coupling angle matching and total internal reflection propagation conditions. Therefore, the system still needs to set up a separate coupling structure.

[0032] To address the aforementioned issues, this invention proposes a polarization-multiplexed dual-focal-plane metasurface optomechanic. This invention integrates polarization channel separation, dual-focal-plane phase modulation, a metasurface / in-coupler two-in-one structure, broadband material screening, and waveguide coupling angle synchronization constraint onto the same metasurface device, providing a monolithic integrated solution for optical waveguide display scenarios.

[0033] Example 1.

[0034] like Figure 1 As shown, the polarization-multiplexed dual-focal-plane metasurface optomechanism of this embodiment includes an illumination source 1, a microdisplay 2, a linear polarizer 3, a half-wave plate 4, a relay / collimating lens group 5, a metasurface / coupler combined structure 6, an optical waveguide 7, a coupling grating region 8 disposed on the exit side of the optical waveguide 7, and a human eye 9 located within the exit pupil. These components are arranged sequentially along the propagation direction of the image light. The metasurface / coupler combined structure 6 is disposed at the coupling end of the optical waveguide 7, and its anisotropic subwavelength unit both modulates the wavefront and provides the transverse wave vector required for coupling into the optical waveguide 7.

[0035] The illumination light emitted by the illumination source 1 is homogenized or collimated before illuminating the microdisplay 2. The microdisplay 2 modulates the intensity or phase of the incident light according to the image to be displayed, and outputs image light carrying image information. The image generation component can select the appropriate illumination method according to the type of the microdisplay 2, and its specific modulation form does not affect the subsequent polarization multiplexing and dual-focal-plane control.

[0036] The image light then passes through linear polarizer 3 and half-wave plate 4. Linear polarizer 3 selects the polarization direction of the incident light, and half-wave plate 4 rotates this direction to a direction that does not coincide with either the major or minor axis of the rectangular nanofin. Adjusting the angle between the optical axis of half-wave plate 4 and the transmission axis of linear polarizer 3 can change the energy ratio of the two orthogonal components; when two channels with equal amplitude input are required, the output polarization direction can be adjusted to a position of approximately 45° between the two principal axes of the rectangular nanofin. This polarized light can be decomposed into X-polarized and Y-polarized components along the two principal axes of the rectangular nanofin, forming the first polarization state channel and the second polarization state channel, respectively. The two components propagate coaxially, without the need to split the light into two beams in space. The relay / collimating lens group 5 relays the polarization-shaped image light to the metasurface / coupler combined structure 6, and matches the principal ray direction and beam aperture with its effective area.

[0037] The metasurface / coupler hybrid structure 6 is composed of periodically arranged anisotropic subwavelength units, specifically a rectangular nanofin array. This structure loads different phase distributions onto the first and second polarization channels, outputting polarized light with different phase distributions. Simultaneously, it imparts transverse momentum to the output polarized light, satisfying the waveguide coupling condition. Furthermore, this structure, through the same set of anisotropic micro / nano units, controls the focal plane phase of the two orthogonal polarization channels and superimposes a linear phase gradient satisfying the waveguide coupling requirement. The rectangular nanofins have different equivalent refractive indices along their major and minor axes, and the X-polarization and Y-polarization components accumulate different propagation phases when passing through the same unit. During the design phase, the period, height, major axis width, and minor axis width of the units are changed to calculate the transmittance and transmission phase of the two polarization components, establishing a unit parameter lookup table accordingly. For each position on the metasurface, the target phases required for the first and second virtual focal planes are calculated, and unit parameters that can simultaneously approximate both target phases and satisfy the transmittance requirements are selected from the lookup table. The first polarization state channel obtains the first phase distribution accordingly, and the second polarization state channel obtains the second phase distribution.

[0038] The target phase for each channel includes a convergent phase and a linear phase. The convergent phase determines the position of the corresponding focal plane, while the linear phase forms a phase gradient within the metasurface plane. After the incident light passes through this phase gradient, its transverse wave vector satisfies... During the design process, the target transverse wave vector is obtained based on the refractive index of the optical waveguide 7, the refractive index of the external medium, and the predetermined propagation angle. The corresponding linear phase is then superimposed onto the converging phase. Thus, the same set of anisotropic subwavelength units forms two sets of focal plane phases and introduces two polarization channels into the optical waveguide 7 respectively.

[0039] After the two polarized beams enter the optical waveguide 7, they are reflected between the upper and lower interfaces of the waveguide at their respective propagation angles. When the incident angle at the interface is greater than the critical angle for total internal reflection, the beams are confined within the waveguide to continue propagating. Taking a waveguide refractive index of approximately 1.9 and an external medium of air as an example, the critical angle is approximately 31.8°; in this embodiment, the propagation angles of the two channels, approximately 47.0° and 56.0°, are both within the range of total internal reflection. Light with an incident angle below the critical angle will be transmitted or leaked from the waveguide interface and cannot form effective waveguide transmission. The metasurface / coupler combined structure 6, by limiting the transverse wave vector, allows the target channel to enter the range of total internal reflection angles and reduces non-target angle components.

[0040] When the two polarized lights propagate to the coupling grating region 8, the periodic coupling structure provides an additional grating vector to the light inside the waveguide, causing a portion of the light to no longer satisfy the total internal reflection condition and exit into the exit pupil range where the human eye 9 is located. The first polarization state channel and the second polarization state channel retain their respective phase distributions, and after coupling, they form wavefronts corresponding to the first virtual focal plane and the second virtual focal plane, respectively. The human eye 9 thus receives image light from two display depths.

[0041] (1) Metasurface / coupler combined structure; The core device is a monolithic metasurface / coupler dual-structure 6, which consists of periodically arranged anisotropic subwavelength units, preferably a rectangular nanofin array.

[0042] During the design process, this structure serves two purposes: first, by adjusting the transmission phase of the two polarization channels through the geometry, major-minor axis ratio, and height of the nanofins, ensuring that the output wavefront meets the imaging requirements of the near-focal and far-focal planes respectively; second, by superimposing a linear phase gradient corresponding to the waveguide coupling direction into the target phase, enabling the output light to obtain the desired transverse wave vector component. This eliminates the need for a separate in-coupler, shortens the optical path, reduces assembly interfaces, and improves optomechanical integration.

[0043] (2) Polarization channel splitting principle of metasurface / in-coupler two-in-one structure; Rectangular nanofins exhibit different equivalent refractive indices and transmission phase responses in two orthogonal polarization directions. The polarization component vibrating along the long axis primarily experiences the equivalent refractive index corresponding to the long axis, while the polarization component vibrating along the short axis primarily experiences the equivalent refractive index corresponding to the short axis. Since the effective optical path lengths differ in the two directions, the same geometric unit can provide different phase delays to the first and second polarization states respectively. During the design process, a lookup table of unit size and the two polarization phase responses is first established. Then, unit sizes that are simultaneously close to the first and second target phases are selected at each position, allowing the two polarization states to obtain independent phase distributions after passing through the structure. Based on this, if the nanofins are rotated around the structural normal by an angle theta, and circular polarization is used as incident radiation to extract the cross-polarized transmission components with opposite rotation directions, the rotation can add geometric phase. ,in, or This indicates the chirality of the incident circular polarization.

[0044] Figure 2 This is a diagram showing the polarization axis, rotation angle, and geometric phase of the rectangular nanofin. Among them, Figure 2 (a) Maintenance period Long axis and short axis The left, middle, and right images remain unchanged, respectively representing... Rotational orientation; Figure 2 In (b), the geometric phase of the cross-circularly polarized transmission component is represented. With rotation angle Linear variation, in circularly polarized chiral Timely satisfaction . Figure 2 Figure (b) shows the rotation angle and the geometric phase of the cross-circularly polarized transmission components; circularly polarized incident and cross-polarized transmission: ; Figure 2 The relationship between rotation angles from 0 to 180 degrees and geometric phases from 0 to 2π is given, with the dimensions remaining constant. This rotational phase is a superimposed, adjustable degree of freedom and does not replace the two-channel propagation phases provided by the major and minor axis dimensions for X / Y linear polarization.

[0045] Figure 3(a) shows the effect of width variation on phase, and Figure 3(b) shows the effect of bit width variation on transmittance. For example, such as Figure 4 The design methods for polarization-multiplexed dual-focal-plane metasurface optomechanics include: S1. With the working bandwidth of 380nm-780nm visible light range as the target, the metasurface / coupler dual structure and material selection are carried out around the expansion of color display. S2. Based on the screening results of the metasurface / coupler dual-structure 6 and the materials, perform dual focal plane phase gradient design; S3. Based on the dual-focal-plane phase gradient design results, perform coupling angle matching design to constrain the waveguide coupling angle; S4. Perform process tolerance design on the parameters in the design and design a polarization multiplexing dual focal plane metasurface optical engine.

[0046] In step S1, broadband structure-material screening is completed first, and a dual-polarization element response database is established. Step S2 then uses this database to match the target phase of the dual focal plane with the element parameters. The two steps are executed in the order of "initial structure-material screening, representative wavelength verification, full-band verification, lookup table establishment, and dual-focal-plane phase matching." The output of step S1 serves as the input for step S2. Step S1 specifically includes: The target operating bandwidth is the 380nm-780nm visible light range, and the cell structure and materials are selected around the expansion of color display.

[0047] In terms of structure, rectangular nanofins, elliptical nanopillars, cylinders, and cross / composite multi-pillars are incorporated; In terms of materials, TiO2, GaN, Si3N4, Ta2O5, and Al2O3 were included. Among them, TiO2 and Al2O3 were the key materials for testing: TiO2 was mainly used to verify the strong phase modulation capability and compact unit size of high refractive index materials, while Al2O3 was mainly used to verify low loss, wide spectral transmittance, and process compatibility.

[0048] In the initial screening of the equivalent refractive index model, the dispersion data of each material in the 380-780 nm range were first read, and periodic units were established for rectangular nanofins, elliptical nanopillars, cylinders, and cross / composite multi-pillars. The geometric parameters of each structure-material combination were scanned to obtain the equivalent refractive index in the x and y intrinsic polarization directions. and Press again Estimating polarization direction The propagation phase, where, for or , The unit height is used. The combinations are sorted based on the phase difference between the two polarization directions, the transmission level, and their variation with wavelength, eliminating combinations with insufficient phase splitting, large transmission loss, or significant spectral fluctuations. Figures 11(a) and 11(b) show the broadband comprehensive score and average polarization phase splitting results of this initial screening process, respectively.

[0049] A two-dimensional periodic model of RCWA was established for the shortlisted combinations in the initial screening. Periodic boundaries were set in two directions along the unit plane, and applied respectively. Linear polarization and Linearly polarized normal incidence. For three representative wavelengths (450 nm, 550 nm, and 650 nm), scanning geometric parameters are used to extract the power-normalized zero-order transmission parameters. And extract from complex transmission coefficient Then calculate the package to Polarization phase splitting within the range This leads to the formation of "materials, structural parameters, wavelength - , , , The dual polarization response lookup table was used, and the phase distribution was substituted into the propagation calculation to check the focal plane formation trend of the two polarization channels.

[0050] After the representative wavelength verification is passed, keeping the shortlisted combinations and their parameter range unchanged, the minimum zero-order transmittance, polarization phase split, and spectral fluctuations at each wavelength are calculated point by point within the range of 380nm-780nm according to the set wavelength step size. The minimum transmittance level across the entire band, the average polarization phase split, and the response smoothness are used as the verification values; if narrowband resonance, a sudden drop in transmittance, or a sudden change in phase split occurs, the RCWA parameter scan is returned to readjust the structure dimensions. Figures 12(a) and 12(b) show the changes in polarization phase split and minimum zero-order transmittance of the shortlisted structure-material combinations with wavelength.

[0051] Figures 11(a) and 11(b), and Figures 12(a) and 12(b) show the normalized comparisons corresponding to the screening stage, used to determine the structure-material range for subsequent fine simulations, without limiting the final geometric dimensions of the embodiments. The shortlisted combinations also need to be re-optimized in conjunction with the target phase, waveguide coupling conditions, and processing constraints. Therefore, the specific dimensions in the subsequent TiO2 and Al2O3 embodiments are subject to the descriptions in each embodiment.

[0052] Current results show that rectangular nanofins and elliptical nanopillars are more suitable for further development in terms of broad-spectrum stability; TiO2 can be used as the high-refractive-index master embodiment material, while Al2O3 can be used as the broad-spectrum low-loss optimized embodiment material. Figure 6 Simulation diagrams of five material units: TiO2, GaN, Si3N4, Ta2O5, and Al2O3; among them, Figure 6 Figure (a) shows the focal plane formation trends of the five materials; Figure 6 Figure (b) shows the polarization phase splitting diagram; Figure 6 Figure (c) is a transmittance graph; Step S2, based on the aforementioned dual-polarization unit response database, completes the dual-focal-plane phase gradient design according to the following process: The two polarization states correspond to two sets of target phase gradients. The first polarization channel corresponds to the first wavefront and the first focal plane, while the second polarization channel corresponds to the second wavefront and the second focal plane.

[0053] First, set them separately polarization channels and The target focal plane position and target wavefront of the polarization channel. (Using device plane coordinates) and polarization channel target focus Based on this, calculate the convergence phase. ,in, for or , , To design the center wavelength. Consists of two different sets... Two independent dual-focal-plane target phases are obtained.

[0054] Secondly, based on the transverse wave vector corresponding to the waveguide coupling direction Calculate the linearly coupled phase And add it to the convergence phase to obtain . First, the nominal coupling direction is given; after step S3 completes the total reflection condition and waveguide mode matching, the corrected... Return to this step to update the synthesized phase.

[0055] Subsequently, at each discrete unit location, the parameters corresponding to each group of rectangular nanofins are read from the lookup table established in step S1. , , and Calculate separately and , and The phase error between the two channels is sorted according to the weighted sum of the phase errors after removing the cells that do not meet the transmission requirements. The same physical cell is selected to achieve the target phase of both channels simultaneously. When there is no cell that meets the requirements at a certain position, the geometric parameter scan is returned to expand the lookup table instead of placing two different cells for the two polarization channels.

[0056] Finally, using the transmitted amplitude and actual phase of the selected unit to form the complex amplitude aperture of the two polarization channels, the light intensity is calculated surface-by-surface along the propagation direction using the angular spectrum method. Scan the axial position at the design center wavelength of 550nm to determine the focal peak position, peak energy, and focal plane intensity distribution of the two channels, and check the residual energy at non-target focal planes; if the focal peak position or energy separation does not meet the design requirements, return to cell matching or linear phase gradient calculation for re-iteration. Figure 5 The results of the dual polarization channel dual focal plane obtained from the propagation verification are presented.

[0057] In this embodiment, the focal peaks of the two channels are located at approximately 3.73 mm and 5.22 mm, respectively, enabling the monolithic device to output two stable and distinguishable display depths within the same optomechanical system; for example... Figure 5 Schematic diagram of dual-polarization channel dual-focal-plane propagation calculation; For example, in step S3, the coupling angle matching design is performed; The phase gradient design constrains the waveguide coupling angle through lateral momentum matching. For polarization channel p, the propagation angle inside the target is first determined. Calculate the target transverse wave vector within the waveguide Press again The linearly coupled phase is written and added to the converging phase of the channel. After the synthesized phase is discretized using a cell lookup table, the propagation angle is calculated back based on the actual phase gradient, and it is checked whether it is still higher than the critical angle for total internal reflection. The specific implementation process is as follows.

[0058] In this embodiment, the optical waveguide 7 can be a high refractive index glass waveguide with a refractive index of about 1.9 and a thickness of about 2 mm. The external medium is air. The designed wavelength range is 380nm-780nm, and the coupling and propagation are verified using three representative wavelengths of 450nm, 550nm and 650nm.

[0059] The design process is as follows: First, determine the total internal reflection propagation window based on the waveguide refractive index and the external medium, and then determine the critical angle according to... Calculate; when Approximately 1 When the value is approximately 1.9, the critical angle is approximately 31.8°.

[0060] The first step is to determine the target propagation angle. Based on... After obtaining a critical angle of approximately 31.8° for total internal reflection, the nominal internal propagation angles for the x-polarization channel and the y-polarization channel were taken as 47.0° and 56.0°, respectively. The angular margins of the two relative to the critical angle were approximately 15.2° and 24.2°, respectively. The sign of the target angle is determined by the propagation direction of the beam within the waveguide. Only the absolute values ​​of the angles are shown in Figures 7(a) and 7(b).

[0061] The second step is to convert the target propagation angle into a transverse wave vector and a period-by-period phase increment. This is done at the designed center wavelength. Down, ;according to calculate, The absolute values ​​of the target transverse wave vectors of the polarization channels are approximately and For the period The linear phase increment of adjacent elements along the coupling direction. The two channels are approximately 5.08 rad and 5.76 rad, respectively.

[0062] The third step is to superimpose the linearly coupled phase onto the dual-focal-plane phase. For each discrete coordinate r∥ within the device plane, calculate... and the convergence phase obtained in step S2 After adding them and wrapping them to the range of 0-2π, we get... Then, select the same physical unit from the dual-polarization response lookup table in step S1, and make it... The actual polarization phase is simultaneously close to two sets And retain the corresponding transmittance amplitude.

[0063] The fourth step is to use the actual phase of the discrete element to verify the coupling angle. Expand the actual phase along the coupling direction and obtain the linear slope. .

[0064] Depend on Calculate the internal propagation angle. Verify the unit phase and transmission amplitude at 450nm, 550nm and 650nm respectively.

[0065] when If the total internal reflection angle is higher than the critical angle for that wavelength, and the propagation calculation still forms the corresponding target focal plane, then the matching round is completed; otherwise, return to adjust the linear phase increment or reselect the unit.

[0066] Finally, the output angle, total internal reflection propagation, and focal plane formation results were verified at 450nm, 550nm, and 650nm, respectively. In the main embodiment, the propagation angles of the two channels inside the waveguide are approximately 47.0° and 56.0°, respectively, both located within the total internal reflection propagation window, and can be received and propagated by the same waveguide.

[0067] For example, Figure 7(a) is a waveguide interface diagram, and Figure 7(b) is a total internal reflection coupling window diagram; For example, in step S4, process tolerance design is performed; the process tolerance is designed concurrently as part of the technical solution. The specific process is as follows: The first step is to establish a structural baseline. Record the nominal period used in the corresponding embodiment. Unit height Major axis width minor axis width and material refractive index Using the same upper cladding, substrate, incident polarization, boundary conditions, and mesh as the nominal design, calculations were performed respectively. Zero-order complex transmission coefficient of polarization , .Depend on and The transmittance, propagation phase, and polarization phase splitting reference of the two channels are obtained, and the reference coupling angle and reference focal plane position are calculated based on the nominal phase distribution.

[0068] The second step involves establishing a deviation sample and recalculating each group. While keeping the other parameters at their nominal values, a deviation of -20 nm to +20 nm is applied to the width parameter being evaluated, and a deviation of -50 nm to +50 nm is applied to the height parameter, while varying the refractive index within the allowable range of the material dispersion data. The recalculation is then performed for each group of samples. Calculate the zero-order transmittance of the two channels. Phase And the phase error relative to the nominal structure; then substitute the actual phase and transmission amplitude into the device aperture, calculate the coupling angle inversely according to the phase slope, and use the angular spectrum method to redetermine the focal peak position. Figure 8 Plot the polarization phase splitting and minimum transmittance response as the width, height and refractive index change.

[0069] The third step is to determine the tolerance results. For each set of deviation samples, record the minimum transmittance of the two channels, the maximum wrapping phase error, the coupling angle offset, and the focal plane position offset, and compare each item with the following judgment criteria. If any indicator exceeds the allowable range, return to the geometric parameters or phase gradient design for re-optimization; when all indicators meet the requirements, use the upper and lower bounds of the deviation set to form a manufacturable tolerance window.

[0070] The criteria include: the minimum zero-order transmittance of the two channels is not less than 0.80, preferably not less than 0.85; the maximum phase error relative to the target phase distribution is controlled within approximately ±0.30 rad; the focal peak position shift is controlled within approximately ±10% of the corresponding target focal length, and the two focal planes remain distinguishable; the angle of incidence is still higher than the critical angle of total internal reflection after the shift and propagation margin is retained.

[0071] The results show that, with a width error of approximately ±20 nm and a height error of approximately ±50 nm, the phase difference and minimum transmittance of the two channels remain within the aforementioned acceptable range. This tolerance window can provide a basis for subsequent fabrication and mass production evaluation.

[0072] like Figure 8 The simulation results of process tolerance are shown in the figure. Figure 8 Figure (a) shows the width deviation. Figure 8 Figure (b) shows the height deviation. Figure 8 Figure (c) shows the material refractive index deviation.

[0073] Example 2.

[0074] like Figure 9 The image shown is a Lumerical FDTD simulation of a TiO2 rectangular nanofin unit; a metasurface / in-coupler scheme using TiO2 rectangular nanofins is employed. After the image light output from the microdisplay 2 is polarized, it is shaped into X and Y linearly polarized channels. The metasurface unit uses TiO2 rectangular nanofins with a period of 320 nm, a major axis width of 9 nm, and a minor axis width of 120 nm; within the current 550 nm height scanning range, a height of 950 nm is selected, as shown... Figure 9 Figure (a) in the middle; The first polarization channel corresponds to the near-focal plane, and the second polarization channel corresponds to the far-focal plane. Both channels then enter the same high-refractive-index waveguide 7 with a refractive index of approximately 1.9 and a thickness of approximately 2 mm, and complete transmission with internal propagation angles of approximately 47.0° and 56.0°. The designed wavelength range covers 380-780 nm, and verification is performed using 450 nm, 550 nm, and 650 nm as representative wavelengths. Using a Lumerical FDTD, under conditions of an upper cladding refractive index of 1.0, a substrate refractive index of 1.9, and normal incidence, a 550 nm height scan is performed with a 25 nm grid. Figure 9 Figure (b) is shown in the middle; and the selected structure is recalculated using a 20nm grid, as shown in the figure. Figure 9 Figure (c) in the middle; At 450nm, 550nm, and 650nm, the average zero-order transmittance of the two channels is approximately 0.80, 0.86, and 0.96, respectively, and the phase splitting is approximately 1.96rad, 1.46rad, and 0.73rad, respectively. Figure 9The Lumerical FDTD simulation image of the TiO2 rectangular nanofin unit shows that after loading the selected unit with two target phase channels, the two focal peaks calculated by propagation are located at approximately 3.73 mm and 5.22 mm, respectively. This embodiment illustrates that imaging, coupling, and dual-focal-plane display can be implemented on the same device.

[0075] Example 3.

[0076] like Figure 10 The image shows a Lumerical FDTD simulation of an Al2O3 rectangular nanofin unit. A broad-spectrum optimization scheme using Al2O3 rectangular nanofins was adopted. This embodiment follows the system architecture of Example 2, replacing the material with Al2O3, and compensating for the phase modulation loss caused by the lower refractive index by increasing the structural height, adjusting the ratio of the major and minor axes, and recalibrating the phase gradient. The selected unit cell has a period of 320 nm, a major axis width of 210 nm, a minor axis width of 90 nm, and a height of 1250 nm. Figure 10 Figure (a) in the middle; The Al2O3 scheme was also tested and verified using the 380-780nm operating wavelength band, as well as three representative wavelengths: 450nm, 550nm, and 650nm. Using the same Lumerical FDTD boundary conditions as in Example 2, a 550nm geometric scan was performed at a 25nm grid. Figure 10 Figure (b) is shown in the middle; and the selected structure is recalculated using a 20nm grid, as shown in the figure. Figure 10 Figure (c) in the middle; At 450nm, 550nm, and 650nm, the average zero-order transmittance of the two channels is approximately 0.93, 0.92, and 0.94, respectively, and the phase splitting is approximately 1.29 rad, 0.79, and 0.60 rad, respectively. Figure 10 As shown. This scheme focuses more on the requirement of wide-spectrum, low-loss operation in the visible light spectrum, while retaining the overall technical approach of combining metasurface / in-coupler, polarization channel separation, dual focal plane design, and coupling angle matching.

[0077] As demonstrated by the above embodiments, this invention proposes a metasurface / in-coupler dual-structure, enabling simultaneous imaging and waveguide coupling on a single micro / nano structure. It proposes a wide-spectrum operating bandwidth design for the 380-780nm visible light range, along with screening methods focusing on unit structure and materials. The polarization channel division function is directly implemented by the anisotropic unit of the metasurface, eliminating the need for a separate physical polarization device to handle the core channel allocation task. A dual-focal-plane phase gradient design is proposed, with two polarization states corresponding to different wavefronts and focal planes. A coupling angle matching design is proposed, ensuring total internal reflection propagation conditions for both channels within the same optical waveguide 7. A process tolerance window design is proposed, encompassing a mass-producible range of approximately ±20nm in width and ±50nm in height. This achieves the following effects: by integrating the metasurface and in-coupler into a monolithic structure, the system reduces one independent coupling component, resulting in a shorter optomechanical link, fewer assembly interfaces, and a more compact structure. Monolithic anisotropic micro / nano structures can directly achieve polarization channel division and dual-focal-plane phase control, enabling dual-focal-plane display capabilities to be realized with a single device.

[0078] In the current simulation, the two focal peaks are located at approximately 3.73 mm and 5.22 mm, respectively. After the coupling angle matching and imaging phase design are synchronized, the propagation angles of the two channels are approximately 47.0° and 56.0°, both within the waveguide total reflection window, resulting in a more complete system coupling relationship. A wide-spectrum operating bandwidth is incorporated into the main scheme, with a target operating range of 380-780 nm, and three-color verification is performed using three representative wavelengths: 450 nm, 550 nm, and 650 nm. Both TiO2 and Al2O3 materials are included in the testing and verification, supporting the high-refractive-index strong phase modulation scheme and the wide-spectrum low-loss optimization scheme, respectively. The scheme provides process tolerance windows and judgment criteria. Under conditions of approximately ±20 nm in width and approximately ±50 nm in height, transmittance, phase error, focal plane offset, and coupling angle margin can be used to determine whether the scheme is qualified, providing a clearer basis for engineering implementation.

[0079] Example 4.

[0080] This invention utilizes a polarization-multiplexed dual-focal-plane metasurface optical engine that can be used in vegetation AR display devices.

[0081] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention and within the spirit and principles of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A polarization-multiplexed dual-focal-plane metasurface optical engine, characterized in that, The optical path starts from the image generation component, passes through the polarization shaping component, the metasurface / coupler combined structure (6) and the optical waveguide (7) in sequence, and finally reaches the human eye receiving end; The image generation component outputs an image light that carries the displayed content; The polarization shaping component organizes the image light into a first polarization state channel and a second polarization state channel; The metasurface / coupler dual-structure (6) is composed of periodically arranged anisotropic subwavelength units, specifically a rectangular nanofin array. This structure loads different phase distributions on different polarization states of the first polarization state channel and the second polarization state channel, and outputs polarized light with different phase distributions. At the same time, it imparts transverse momentum to the output polarized light to meet the waveguide coupling conditions. Furthermore, this structure, through the same set of anisotropic micro-nano units, respectively controls the focal plane phase of the two orthogonal polarization channels and superimposes a linear phase gradient that meets the waveguide coupling requirements. The optical waveguide (7) couples in two polarized lights that impart the transverse momentum and allows the two polarized lights to propagate under total internal reflection conditions. The output region then couples the two polarized beams propagating within the waveguide to the human eye.

2. A design method for a polarization-multiplexed dual-focal-plane metasurface optomechanism, characterized in that, This design method is used to design the polarization multiplexing dual-focal-plane metasurface optical mechanism according to claim 1. The design method includes the following steps: S1. With the working bandwidth of 380nm-780nm visible light range as the target, we carried out metasurface / coupler dual structure (6) and material screening around the color display extension; S2. Based on the screening results of the metasurface / coupler two-in-one structure (6) and materials, the dual focal plane phase gradient is designed. S3. Based on the dual-focal-plane phase gradient design results, perform coupling angle matching design to constrain the waveguide coupling angle; S4. Perform process tolerance design on the parameters in the design and design a polarization multiplexing dual focal plane metasurface optical engine.

3. The design method of the polarization multiplexing dual-focal-plane metasurface optomechanism according to claim 2, characterized in that, The material of the metasurface / coupler combined structure (6) is either TiO2 or Al2O3.

4. The design method of the polarization multiplexing dual-focal-plane metasurface optomechanism according to claim 2, characterized in that, In step S1, the working bandwidth of 380nm-780nm visible light includes: firstly, using an equivalent refractive index model for initial screening of combinations, then using an RCWA two-dimensional periodic model to verify the transmittance, polarization phase splitting, and focal plane formation trends of the shortlisted combinations at three representative wavelengths of 450nm, 550nm, and 650nm, and checking the response changes in the 380nm-780nm band.

5. The design method of the polarization multiplexing dual-focal-plane metasurface optomechanism according to claim 2, characterized in that, In step S2, the dual-focal-plane phase gradient design includes: First, determine the focal plane positions of the two targets and the corresponding target waves; Then, the converging phase required to form the focal plane is combined with the linear phase gradient required for waveguide coupling. Subsequently, based on the phase lookup table of rectangular nanofins in the two polarization directions, unit parameters that simultaneously satisfy the phase requirements of both channels are selected. Finally, propagation simulation was used to verify the focal peak positions and energy distribution of the two channels.

6. The design method of the polarization multiplexing dual-focal-plane metasurface optomechanism according to claim 2, characterized in that, In step S3, the coupling angle matching design includes: First, determine the total internal reflection propagation window based on the waveguide refractive index and the external medium. The critical angle is determined according to... Calculate; where, This is the critical angle at which total internal reflection occurs at the waveguide-air interface. The refractive index of air, The refractive index of the waveguide core material; Subsequently, the target propagation angle of the two polarization channels in the waveguide is selected, which is higher than the critical angle while retaining process and wavelength drift margins; The target propagation angle is then converted into the transverse wave vector component required at the metasurface output end, and this transverse momentum constraint is superimposed on the phase of the dual-focal-plane target. Finally, the output angle, total internal reflection propagation, and focal plane formation results were verified at 450nm, 550nm, and 650nm, respectively.

7. The design method of the polarization multiplexing dual-focal-plane metasurface optomechanism according to claim 2, characterized in that, In step S4, the process tolerance design for the parameters in the design includes: First, determine the nominal period, height, major axis width, and minor axis width of the rectangular nanofin, and then establish the phase and transmittance references for the two polarization channels based on the nominal structure. Then, width deviation, height deviation, and material refractive index drift are introduced separately to form multiple sets of deviation samples; Subsequently, the transmittance, phase error, coupling angle shift, and focal plane position change of the two polarization channels were recalculated for each group of samples. Finally, determine whether it falls within an acceptable range based on the display effect and waveguide propagation requirements.

8. An AR display device fabricated using the polarization multiplexing dual-focal-plane metasurface optical engine as described in claim 1.

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