Metalens array and display device having the metalens array

Abstract

A metalens array and display device, wherein the metalens array includes at least one optically transparent substrate and a plurality of nanostructures disposed on the at least one optically transparent substrate, the plurality of nanostructures arranged in a predetermined shape to define a plurality of metalenses, the plurality of metalenses being arranged overlapping one another.

Description

[Technical Field]

[0001] [Cross-reference to related documents] This application claims priority to U.S. Provisional Application No. 63 / 454586, filed with the United States Patent and Trademark Office (USPTO) on March 24, 2023, U.S. Provisional Application No. 63 / 439685, filed on January 18, 2023, U.S. Provisional Application No. 63 / 470167, filed on May 31, 2023, U.S. Provisional Application No. 63 / 53510, filed on August 18, 2023, and U.S. Application No. 18 / 374320, filed on September 28, 2023, the contents of which are incorporated herein by reference.

[0002] The present invention relates to the field of optics, and more particularly to metalens arrays and displays having such metalens arrays. [Background technology]

[0003] Augmented reality (AR) is a display technology that combines virtual information with the real world. That is, it integrates virtual image information projected by an electronic device based on the real world as seen by the human eye. Conventional head-mounted AR display devices include a camera for capturing images within the viewer's field of view, and project virtual image information based on the captured images at a predetermined position within the viewer's field of view.

[0004] As shown in Figures 1A and 1B, a lens array configuration provides a possible solution to reduce the gap between the microdisplay and the optical system. However, conventional glass (or polymer) microlens arrays have drawbacks such as large volume, heavy weight, large chromatic aberration and spherical aberration, poor image quality, and lack of free adjustment.

[0005] Metalenses offer a simple way to manipulate the properties of light, and they offer a high degree of design flexibility, are ultra-thin and lightweight, and are often compatible with CMOS fabrication techniques.

[0006] However, using metalenses with higher numerical apertures (NA) instead of conventional metalenses seems less practical. Therefore, the focal length of a metalense is typically greater than half the diameter of the metalense (NA < 0.7). Therefore, to significantly reduce the difference between microdisplays and metalenses, it is necessary to design metalenses in an array format. However, even with metalens arrays, pixelation issues still exist due to imperfections in the space between adjacent lenses and the edges of the metalenses. These issues are detrimental to the need for focusing and using digital images to eliminate pixelation, hindering the real-time application of metalens arrays.

[0007] Based on the above deficiencies, the applicant has discovered that an overlapping metalens array can be used to uniformly illuminate the light projected by the microdisplay to the user's eyes, thereby overcoming the above deficiencies. Therefore, a head-mounted display system is needed to solve the pixelation problem, realize a thinner and lighter system, and improve the user experience. Summary of the Invention

[0008] In view of the above, there is a need to provide a metalens array and a display device having the metalens array in order to solve the above problems.

[0009] A metalens array according to a first aspect of the present invention includes at least one optically transparent substrate and a plurality of nanostructures, the plurality of nanostructures being disposed on the at least one optically transparent substrate, the plurality of nanostructures being arranged in a predetermined shape to define a plurality of metalenses, the plurality of metalenses being arranged overlapping one another.

[0010] One embodiment of the first aspect discloses a plurality of nanostructures disposed on at least one optically transparent substrate, the plurality of nanostructures arranged in a predetermined shape to define a plurality of metalenses, and the plurality of metalenses arranged in an overlapping manner to effectively eliminate the problem of pixelation in lens images.

[0011] An embodiment of the first aspect also includes a plurality of nanostructures formed in isotropic shapes, anisotropic shapes, or a combination of isotropic and anisotropic shapes.

[0012] The metalens array according to one embodiment of the first aspect further comprises a residual resin mixture deposited on the at least one optically transparent substrate.

[0013] In one embodiment of the first aspect, the metalens array further comprises a pair of optically transparent electrodes, and the at least one optically transparent substrate is two optically transparent substrates; the plurality of nanostructures are coated with a filler; the plurality of nanostructures and the filler are sandwiched between the two optically transparent substrates via the pair of optically transparent electrodes; the filler material is selected from an electrolyte or a gel electrolyte such that a voltage is applied to the pair of optically transparent electrodes to tune the metalens array between a conductive state and an insulating state.

[0014] In one embodiment of the first aspect, the plurality of nanostructures are made of at least one phase change material, and the plurality of nanostructures are provided on the surface of the at least one optically transparent substrate via a resistive heating film, and the resistive heating film is configured to have an electric current applied to it.

[0015] In one embodiment of the first aspect, the plurality of nanostructures comprises a patterned 2D material; the plurality of nanostructures are provided on a surface of the at least one optically transparent substrate via a dielectric thin film and a conductive layer; The conductive layer and the plurality of nanostructures are configured such that a voltage can be applied to tune the metalens array between a conductive state and an insulating state.

[0016] In one embodiment of the first aspect, the metalens array further comprises two ITO layers and two alignment layers; the at least one optically transparent substrate is two optically transparent substrates; the plurality of nanostructures are coated with a liquid crystal; the plurality of nanostructures and the liquid crystal are sandwiched between the two optically transparent substrates via the two alignment layers and the two ITO layers; The two ITO layers are arranged such that a voltage is applied to them.

[0017] In one embodiment of the first aspect, the metalens array further comprises a top electrode patterned on one of the two ITO layers, wherein the two ITO layers are configured to be supplied with a voltage.

[0018] In one embodiment of the first aspect, the plurality of nanostructures are passive structures and can be converted into active, focusable metalenses using a phase change material.

[0019] A second aspect of the present application provides a display device, the display device comprising: a microdisplay configured to emit light; and at least one metalens array spaced apart from the microdisplay and configured to transmit light from the microdisplay; The at least one metalens array comprises: at least one optically transparent substrate; a plurality of nanostructures disposed on the at least one optically transparent substrate; the plurality of nanostructures are arranged in a predetermined shape to define a plurality of metalenses; The plurality of metalenses are arranged in an overlapping relationship.

[0020] In one embodiment of the second aspect, the plurality of nanostructures are disposed on a surface of the at least one optically transparent substrate facing the microdisplay.

[0021] In one embodiment of the second aspect, the display device further comprises a transparent flexible substrate; the at least one metalens array is disposed to space the microdisplay and the transparent flexible substrate; The nanostructures are disposed on two opposing surfaces of the at least one optically transparent substrate and are directed toward the microdisplay and the transparent flexible substrate, respectively.

[0022] In one embodiment of the second aspect, the display device further comprises a first metalens array and a second metalens array, the first metalens array being disposed between the second metalens array and the microdisplay; in the first metalens array, the plurality of nanostructures are disposed on a surface of the at least one optically transparent substrate facing the second metalens array; In the second metalens array, the plurality of nanostructures are disposed on a surface of the at least one optically transparent substrate facing the first metalens array.

[0023] In one embodiment of the second aspect, the display device further comprises a polarizer spaced between the microdisplay and the at least one metalens array; The polarizer is positioned to polarize the light emitted from the microdisplay towards the at least one metalens array.

[0024] In one embodiment of the second aspect, the microdisplay and the at least one metalens array are positioned on-axis or off-axis; The at least one metalens array is configured to transmit light emitted by the microdisplay such that the light passing through the at least one metalens array is collimated, tilted, or focused.

[0025] In one embodiment of the second aspect, the plurality of nanostructures are formed with isotropic shapes, anisotropic shapes, or a combination of isotropic and anisotropic shapes.

[0026] In one embodiment of the second aspect, the metalens array further comprises a residual resin mixture deposited on the at least one optically transparent substrate.

[0027] In one embodiment of the second aspect, the metalens array further comprises a pair of optically transparent electrodes; the at least one optically transparent substrate is two optically transparent substrates; the plurality of nanostructures are coated with a filler; the plurality of nanostructures and the filler are provided between the two optically transparent substrates via the pair of optically transparent electrodes; The filler material is selected from an electrolyte or a gel electrolyte so that a voltage is supplied to the pair of optically transparent electrodes.

[0028] In one embodiment of the second aspect, the device further comprises a plurality of nanostructures made of at least one phase change material, the plurality of nanostructures being disposed on a surface of at least one optically transparent substrate via a resistive heating film, the resistive heating film being arranged to allow an electric current to be applied thereto.

[0029] Embodiments of the second aspect further include a plurality of nanostructures comprised of a patterned 2D material, the plurality of nanostructures being disposed on a surface of the at least one optically transparent substrate via a thin dielectric film and a conductive layer, the conductive layer and the plurality of nanostructures being configured such that a voltage is applied to the metalens array such that the metalens array is tuned between a conductive state and an insulating state. [Brief explanation of the drawings]

[0030] Many aspects of the present disclosure can be better understood with reference to the following drawings, in which components are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Also in the drawings, like reference characters refer to corresponding parts throughout the several views.

[0031] [Figure 1A] FIG. 1 is a block diagram of an exemplary head-mounted display device. [Figure 1B] FIG. 1 is a block diagram of an exemplary head-mounted display device. [Figure 2A] FIG. 1 is a diagram illustrating a configuration of a metalens array applied to a display device provided according to an embodiment of the present application. [Figure 2B] FIG. 10 is a structural diagram of a metalens array applied to a display device provided by another embodiment of the present application. [Figure 3] 2C and 2D are side and top views (four metalens case) of the metalens array shown in FIGS. 2A and 2B provided in accordance with one embodiment of the present application, showing single overlapping lenses. [Figure 4A] FIG. 4 is a schematic diagram of a unit cell of a passive metalens of a metalens array such as that shown in FIG. 3 provided in accordance with one embodiment of the present application. [Figure 4B] FIG. 4 is a schematic diagram of a unit cell of a passive metalens of a metalens array such as that shown in FIG. 3 provided in accordance with one embodiment of the present application. [Figure 5] FIG. 4 is a schematic diagram of a unit cell of a metallopolymer-based active metalens of a metalens array such as that shown in FIG. 3 provided in accordance with one embodiment of the present application. [Figure 6] FIG. 4 is a schematic diagram of a unit cell of an active metalens based on a phase-change material of a metalens array such as that shown in FIG. 3 provided in accordance with another embodiment of the present application. [Figure 7] FIG. 4 is a schematic diagram of a unit cell of an active metalens based on 2D materials in a metalens array such as that shown in FIG. 3 provided in accordance with one embodiment of the present application. [Figure 8A] FIG. 4 is a schematic diagram of a unit cell of a liquid crystal active metalens of the metalens array shown in FIG. 3 provided in accordance with one embodiment of the present application. [Figure 8B] FIG. 4 is a schematic diagram of a unit cell of a liquid crystal active metalens of the metalens array shown in FIG. 3 provided in accordance with one embodiment of the present application. [Figure 9A] ~ [Figure 9E] 1 is a top view of an isotropic or anisotropic nanostructure provided by an embodiment of the present application. [Figure 10] FIG. 1 is a schematic diagram illustrating a metalens array provided by an embodiment of the present application when applied to an AR-VR device. [Figure 11A] ~ [Figure 11I] FIG. 1 is a schematic diagram of a non-overlapping metalens array and an overlapping metalens array provided by some embodiments of the present application. [Figure 12] FIG. 10 is a schematic diagram of the effective area of ​​each metalens provided in accordance with an embodiment of the present application as a function of overlap factor (d) after being overlapped with an adjacent metalens. [Figure 13A] ~ [Figure 13D] FIG. 10 is a schematic illustration of the elimination of pixelation effects by a circular metalens array with 30% overlap provided in accordance with one embodiment of the present application. [Figure 14A] ~ [Figure 14C] 4A-4C are schematic diagrams of different optical configurations of the metalens array applied to the metalens array of FIG. 3 provided in accordance with three examples of the present application. [Figure 15A] ~ [Figure 15F] FIG. 1 is a schematic diagram of a metalens array having different collimating, deflecting, and focusing characteristics provided by some embodiments of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0032] Embodiments of the present disclosure will now be described, by way of example only, with reference to the drawings. The present disclosure is merely exemplary and details may be modified within the principles of the disclosure. It is therefore to be understood that modifications may be made to the embodiments within the scope of the claims.

[0033] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are intended to provide a thorough understanding of the embodiments described herein, but should not be construed as limiting the scope of the embodiments.

[0034] Here are some definitions that will be used throughout this disclosure.

[0035] The term "coupled" is not necessarily limited to a physical connection, but is defined as connecting directly or indirectly through intermediate components. The term "essentially" is defined to substantially conform to the particular dimensions, shape, or other words to which the term is modified, so that the components do not require precision. The term "comprises" when used means "including," but is not necessarily limited to, and specifically expresses open inclusion or membership in combinations, groups, series, etc.

[0036] Augmented reality (AR) is a display technology that integrates virtual information and the real world. That is, it integrates virtual image information projected by an electronic device based on the real world as seen by the human eye. Conventional head-mounted AR display devices typically include a camera for capturing images within the viewer's field of view, and project virtual image information based on the captured images at a predetermined location within the viewer's field of view.

[0037] 1A and 1B show two exemplary head-mounted display devices 9A (single lens) and 9B (lens array) that are common on the market, transmitting or displaying Augmented Reality (AR), Virtual Reality (VR), or Mixed Reality (MR).

[0038] To shorten the distance between the attached microdisplay and a single lens in display device 9A (as shown in FIG. 1A), FIG. 1B shows a lens array method applied to display device 9B. However, to highly diffract light at the lens edge, a sharp phase gradient is required, which is usually not possible due to manufacturing defects. Furthermore, edge effects result in serious distortion. Especially for rectangular and circular lenses, the dead zone between lenses is a supplement to the above-mentioned problem. In this case, to solve the above-mentioned problem, the present application proposes an overlapping metalens array. Furthermore, pixelation caused by the lens array can be significantly reduced.

[0039] FIG. 2A shows the configuration of a metalens array 30 applied to a display device 90A (without a polarizer 20) according to one embodiment of the present invention. As shown in FIG. 2A, a microdisplay 10 emits a light beam and displays a real image to a user's eye. However, depending on the design and the distance between the microdisplay 10 and the metalens array 30, real or virtual, polarization-based 3D, stereoscopic, panoramic, and floating images can be formed. The microdisplay 10 and the metalens array 30 are uniformly separated by a spacer 51. The light beam is confined by a light shield 8. In this embodiment, the display device 90A does not include a polarizer 20 and an optically transparent gel 53 as shown in FIG. 2B.

[0040] FIG. 2B shows the configuration of a metalens array 30 applied to a display device 90B (having a polarizer 20) according to another embodiment of the present disclosure. In this embodiment, the display device 90B may be an augmented reality (AR), virtual reality (VR), or mixed reality (MR) device. As shown in FIG. 2B , the configuration of the display device 90B includes a microdisplay 10, a polarizer 20 (a linear or circular polarizer), and a metalens array 30. An optically transparent gel 53 is positioned between the polarizer 20 and the microdisplay 10, and a spacer 51 is positioned between the polarizer 20 and the metalens array 30. A light shield 8 is positioned in front of the metalens array 30.

[0041] As shown in FIG. 2B, polarizer 20 is a circular polarizer for circularly polarizing the light irradiated onto microdisplay 10. In another embodiment, polarizer 20 is a linear polarizer or a circular polarizer formed by combining a linear polarizer with a quarter-wave plate. Polarizer 20 is bonded to microdisplay 10 using optically transparent gel 53. The light beam may be confined by light shield 8. When anisotropic nanostructures 41 are utilized, this polarizer-dependent scheme is used, as shown in FIGS. 9C, 9D, and 9E. Then, the light emitted from microdisplay 10 is completely manipulated based on the geometric phase principle or other principles that can realize 2π phase transitions.

[0042] In some embodiments, the nanostructured materials can be dielectrics (such as TiO, GaN, Si, NbO, SiO, photoresist, metal oxide nanoparticles, and sol-gel mixtures), metals (e.g., gold, silver, aluminum, etc.), or / and other active materials (2D materials, VO, GST, metallopolymers).

[0043] FIG. 3 shows a side view and a top view (four metalenses) of one embodiment of the metalens array 30 in FIGS. 2A and 2B, illustrating a single overlapping lens. In plan view, the metalens array 30 is an overlapping metalens array. An overlapping metalens array has a tightly packed geometry and minimal dead zone to fully utilize the resolution of the microdisplay. The columns of the metalens array 30 may be uniformly distributed, or each column or row may have an offset relative to the previous column or row. Each metalens may also have a different diameter. The overlap factor d varies depending on the pixel size and arrangement of the microdisplay, smoothing out pixelation caused by the metalens array mesh as shown in FIG. 13.

[0044] As shown in FIG. 3 , each metalens 35 in the metalens array 30 overlaps with its adjacent metalens. Each metalens 35 in the metalens array 30 includes a plurality of nanostructures 41 and a base layer 42. The base layer 42 can be any type of optically transparent base layer, such as glass made of fused silica (SiO 2 ) or sapphire, or reflective glass made of silicon and other materials. A plurality of nanostructures 41 are designed and fabricated on the surface of the base layer 42 to form a metasurface. The plurality of nanostructures 41 form a plurality of metalenses 40 and can be arranged in any desired configuration, such as a mesh or rows and columns of the plurality of metalenses 40. The plurality of metalenses 40 are arranged so that they overlap. The plurality of nanostructures 41 are passive structures made of dielectric materials such as TiO 2 , GaN, Si, Nb 2 O 5 , SiO 2 , photoresist, metal oxide nanoparticles, and sol-gel mixtures, or metals of varying thicknesses such as gold (Au), silver (Ag), or aluminum (Al). The dielectric superatom ranges from 150 nanometers to several thousand nanometers, and the metal shell ranges from 20 nanometers to 400 nanometers, although the present application is not limited to these ranges. In some embodiments, the metalens array 30 includes at least one base layer 42 (e.g., an optically transparent substrate) and a plurality of nanostructures 41 disposed on the at least one base layer 42. The plurality of nanostructures 41 are arranged in a predetermined shape to define a plurality of metalenses 40. The plurality of metalenses 40 are arranged one on top of the other (see FIG. 3 ). In other embodiments, the plurality of nanostructures 41 can be modified to form an active, focus-adjustable metalens using a phase-change material.

[0045] 5, 6, 7, 8A, and 8B, the plurality of nanostructures 41 can utilize any phase change material, such as GST (Ge2Sb2Te5), vanadium dioxide (VO2), and gallium (GA), as well as other active materials, such as transparent conductive oxides such as ITO and AZO, thin 2D materials (graphene, hBN, and WS2), liquid crystals, metal-polymers, etc. Thus, a programmable metalens can be realized to completely or locally alter the light modulation.

[0046] FIG. 4A shows an example of a unit cell of a passive metalens in the metalens array 30 of FIG. 3. FIGS. 4A, 4B, 5, 6, 7, 8A, and 8B show at least one unit of a passive metalens in the metalens array 30 of FIG. 3. A plurality of unit cells may make up a metalens, and a plurality of metalens may make up a metalens array. Alternatively, a metalens array may be made up of a plurality of metalens arranged, with each metalens being made up of a plurality of unit cells arranged. A unit cell includes nanostructures 41 having dimensions of radius R and height H, and a base layer 42 having a pitch Px (along the x-direction) and a pitch Py (along the y-direction). In some embodiments, the unit cells of the metalens array 30 may have the same or different dimensions. For example, three or more different unit cells may be used, since each color requires a different pitch, width, and length, but all colors require the same height. However, in some particular embodiments, the same unit cell (same pitch) can be used for all colors (having different widths and lengths, but the same height). In some other embodiments, metalens array 30 includes at least one optically transparent substrate 42 and a plurality of nanostructures 41 disposed on at least one optically transparent substrate 42.

[0047] FIG. 4B shows an example of a unit cell of a passive metalens of the metalens array 30 of FIG. 3. The unit cell includes nanostructures 41 having dimensions of radius R and height H, and a base layer 42 having dimensions of pitch Px (along the x-direction) and pitch Py (along the y-direction). The nanostructures are directly nanoimprinted into the transparent base layer using a mixture of metal oxide nanoparticles and sol-gel (e.g., TiO and ITO) and sol-gel, eliminating the need to deposit / grow any high refractive index dielectric or metal material. FIG. 4B shows the residual resin mixture 41A after direct nanoimprinting. In some other examples, the metalens array 30 further includes a residual resin mixture 41A deposited on at least one optically transparent substrate 42.

[0048] Figure 5 shows another example of a unit cell of a metal-polymer-based active metalens of the metalens array 30 of Figure 3. The metal-polymer can be, for example, PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)) or any conductive polymer. The nanostructures 41 are disposed between two pieces of glass 42. Each piece of glass 42 has a transparent electrode 46 deposited on it. The transparent electrodes 46 are made of indium tin oxide (indium tin oxide). The nanostructures 41 and the filler material 47 may be made of a material selected from the group consisting of a metal-lens array, an oxide, an ITO, and an electrolyte. The unit cells are then filled with a filler material 47. That is, the nanostructures 41 and the filler material 47 are provided between two base layers 42 via a pair of transparent electrodes 46. In some embodiments, the filler material 47 is an electrolyte or a gel electrolyte. Thus, the unit cells of the metalens array 30 are adjusted between a conductive state and an insulating state by an applied voltage. In some other embodiments, the metalens array 30 further includes a pair of optically transparent electrodes 46, and the at least one optically transparent substrate 42 refers to two optically transparent substrates 42, and the plurality of nanostructures 41 are covered with the filler material 47. The plurality of nanostructures 41 and the filler material 47 are provided between the two optically transparent substrates 42 via the pair of optically transparent electrodes 46, and the filler material 47 is selected from an electrolyte or a gel electrolyte. Thus, the pair of optically transparent electrodes 46 are arranged to apply a voltage such that the metalens array 30 is adjusted between a conductive state and an insulating state.

[0049] FIG. 6 shows another embodiment of a unit cell of an active metalens based on a phase-change material in the metalens array 30 of FIG. 3. The nanostructures 41 may be a phase-change material such as GST (Ge2Sb2Te5), vanadium dioxide (VO2), or gallium (Ga), but are not limited to these three materials that primarily operate based on a resistive heating film 46R. The base layer 42 may be made of glass, sapphire, silicon, polycrystalline silicon, or the like. The resistive heating film 46R is configured to receive an electric current. In some other embodiments, the plurality of nanostructures 41 are made of at least one phase-change material, and the plurality of nanostructures 41 are disposed on the surface of at least one optically transparent base layer 42 via a resistive heating film 46R, and the resistive heating film 46R is configured to receive an electric current.

[0050] FIG. 7 shows another embodiment of a unit cell of an active metalens based on the 2D material of the metalens array 30 of FIG. 3. The nanostructures 41 are made of a patterned 2D material such as graphene, hexagonal boron nitride, and WS2, and are separated by a thin dielectric film 42A such as Al2O3, SiO2, or TOPAS. The conductive layer 46A is a transparent or opaque conductive layer, and can be made of gold, silver, aluminum, ITO, AZO, or polycrystalline silicon, for example. The base layer 42 may be made of a dielectric material such as SiO2 or sapphire, or may be made of a metal or semiconductor material. The conductive layer 46A and the nanostructures 41 are configured so that a voltage can be applied to tune the metalens array 30 between a conductive state and an insulating state. In some other embodiments, the nanostructures 41 are made of a patterned 2D material and are disposed on the surface of at least one optically transparent substrate 42 via the thin dielectric film 42A and the conductive layer 46A. Conductive layer 46A and plurality of nanostructures 41 are configured to be supplied with a voltage such that metalens array 30 is tuned between a conductive state and an insulating state.

[0051] FIGS. 8A and 8B show several examples of unit cells for the liquid crystal-based active metalens of the metalens array 30 of FIG. 3. As shown in FIG. 8A, nanostructures 41 are sandwiched between two pieces of glass 42, which have two ITO (indium tin oxide) layers 46 deposited on them. An alignment layer 48 is either mechanically rubbed or a photo-alignment layer typically made from other organic compounds such as polyimide or azo dye molecules. The nanostructures 41 may be dielectric or metallic (or any of these materials). The unit cell is filled with two pieces of glass 42 with liquid crystal 49 and deposited ITO layers 46. As shown in FIG. 8A, spacers 48 are used to separate the two pieces of glass 42 and the ITO layers 46, maintaining a uniform thickness TLC throughout the unit cell. The nanostructures 41 are covered by liquid crystal 49. The two ITO layers 46 are configured to apply a voltage that can change the refractive index of the liquid crystal 49 relative to ambient light. In some other embodiments, the metalens array 30 further includes two ITO layers 46 and two alignment layers 48, the at least one optically transparent substrate 42 refers to two optically transparent substrates 42, the plurality of nanostructures 41 are covered by liquid crystal 49, the plurality of nanostructures 41 and the liquid crystal 49 are disposed between the two optically transparent substrates 42 via the two alignment layers 48 and the two ITO layers 46, and the two ITO layers 46 are configured to be supplied with a voltage.

[0052] The liquid crystal cell can function in two ways. In the first embodiment, as shown in FIG. 8A, liquid crystal is injected between two planar transparent electrodes (ITO layers) 46, which serve to change the refractive index of ambient light. Because the resonance of the nanostructure is highly sensitive to the refractive index of ambient light, the output light can be freely adjusted by manipulating the nanostructure 41. In the second embodiment, as shown in FIG. 8B, the liquid crystal can compensate and calibrate the metalens by patterning the top electrode 460P through a photolithography process, thereby achieving the goal of eliminating aberrations that cannot be eliminated by the overlapping metalens array. The patterned electrode 460P in FIG. 8B can be circular, rectangular, or any other shape, even in raster and array forms. Each electrode can be individually controlled. In some other embodiments, the metalens array 30 further includes a top electrode 460P patterned on one of the two ITO layers 46. The two ITO layers 46 are configured to be supplied with a voltage.

[0053] The nanostructures 41 may be formed in different isotropic shapes, anisotropic shapes, or a combination of isotropic and anisotropic shapes. This depends on the desired spectrum and the degree of phase and amplitude modulation. Each of the nanostructures 41 may have a substantially circular shape as shown in FIG. 9A, a triangular or square shape as shown in FIG. 9B, a rectangular shape as shown in FIG. 9C, or an anisotropic shape as shown in FIGS. 9D and 9E. For example, an isotropic shape may be a circle or a square, and its dimensions are the same when viewed from either side. For example, an anisotropic shape may be a rectangle, an "L," an "H," or any shape having different dimensions when viewed from different sides. In one embodiment, the nanostructures 41 have a circular shape as shown in FIG. 5. The nanostructures 41 are spaced apart from one another at a pitch size Px (150 nm to 700 nm) in the X direction and a pitch size Py (150 nm to 700 nm) in the Y direction. The pitch is defined in two ways: center-to-center of two adjacent nanostructures or edge-to-edge of two adjacent nanostructures. Each of the nanostructures 41 in the plurality of unit cells can have a diameter D of 40 nm to 400 nm. Each of the nanostructures 41 in the plurality of unit cells can have a height H of 20 nm to 3000 nm. However, for anisotropic nanostructures, these values ​​may be different. In other embodiments, the plurality of nanostructures 41 may be formed in an isotropic, anisotropic, or a combination of isotropic and anisotropic shapes.

[0054] FIG. 10 is a schematic diagram showing an example of an application of a metalens array 30 to an AR-VR device 9.

[0055] FIGS. 11A-11I show several examples of non-overlapping and overlapping metalens arrays. FIGS. 11A, 11B, and 11C show non-overlapping metalens arrays applied to the metalens array 30 of FIG. 3. According to some embodiments, multiple metalenses 40 are arranged in different configurations. Multiple metalenses 40 can be arranged into metalens arrays of different shapes, such as square, triangular, pentagonal, hexagonal, circular, etc. As shown in FIGS. 11D, 11E, 11F, 11G, 11H, and 11I, each metalens overlaps its adjacent metalens and includes nanostructures as described above. The overlapping arrays are fabricated using different methods, such as electron-beam lithography (EBL), deep ultraviolet (DUV) lithography, extreme ultraviolet lithography (EUV), nanoimprint lithography, and directional nanoimprint using a mixture of metal oxide nanoparticles and sol-gel. The size of the overlapping metalens arrays may vary from millimeters to centimeters, depending on the size of the microdisplay and its pixel size.

[0056] Figure 12 shows the AA single_lens where A is the calculated effective area of ​​a cutoff circular metalens in an overlapping array given by . The overlap factor is d. Ac is the area of ​​a perfect circle with radius R. Aov represents the ablation area of ​​a single circular metalens. arccos represents the arc cosine. For d=2R, the circles do not overlap. Therefore, pixelation is lost as the overlap increases, and finding an appropriate value for d is important.

[0057] JPEG2026502299000002.jpg33125

[0058] 13A-13D show how overlapping metalens arrays effectively eliminate pixelation when the circles overlap by 30% (d=0.7*2R).

[0059] FIG. 13A shows the original image (ground truth) on the microdisplay. FIGS. 13B and 13C show the images after passing through overlapping and non-overlapping metalens arrays, respectively. FIG. 13D shows the grayscale values ​​calculated from the white dotted lines in FIGS. 13B and 13C.

[0060] Figure 13A shows the original image displayed on the microdisplay. Figures 13B and 13C show the overlapping and non-overlapping projected images, respectively, after passing through the metalens array. It is clearly observed that pixelation has been significantly eliminated. To quantitatively compare these two results, Figure 13D calculates the grayscale values ​​of the white dashed lines from Figures 13B and 13C. The results reveal that pixelation has been effectively eliminated using the proposed overlapping metalens array, which is a major advantage of the overlapping metalens array.

[0061] FIGS. 14A-14C show three examples of different optical configurations of a metalens array applied to the metalens array 30 of FIG. 3. The microdisplay 10 may or may not have a polarizer. This depends on the type of metalens (isotropic or anisotropic) in the display device 90A or display device 90B of FIGS. 2A and 2B described above. FIG. 14A shows a device with only a single overlapping metalens array that only resolves chromatic aberrations. The spacer 51, overlapping metalens array 35, and glass (sapphire) substrate 42 are arranged as shown in FIG. 14A. The overlapping metalens array 35 includes a plurality of nanostructures disposed on the surface facing the substrate of the microdisplay 10. To resolve coma aberrations, a doublet metalens array or two separate metalens arrays can be used. As shown in FIG. 14B, the overlapping metalens arrays 351 and 352 can be metalens arrays or large single metalens arrays. The order of the overlapping metalens arrays can also be interchanged. The spacer 52 and transparent flexible base layer 422 (e.g., glass, sapphire, PMMA, etc.) are positioned as shown in Figures 14B and 14C. The overlapping metalens arrays 351 and 352 are spaced apart between the microdisplay 10 and the flexible base layer 422. The nanostructures of the overlapping metalens arrays 351 and 352 are disposed on two opposing surfaces of the base layer and face the microdisplay and the transparent flexible base layer. Figure 14C shows two individual metalens arrays facing each other. One of the metalens arrays 353 or metalens array 354 is an overlapping metalens array, and the other is a metalens array or a single metalens. The metalens arrays 353 and 354 have a base layer made of glass (or sapphire, PMMA, etc.). The nanostructures of the metalens array 353 face toward the metalens array 354. The nanostructures of metalens array 354 face towards metalens array 353.

[0062] FIGS. 15A-15F show several examples of metalens arrays with different collimating, deflecting, and focusing characteristics. Multiple overlapping metalens arrays or metalens arrays 71, 72, 73, 74, 75, and 76 can be any of those shown in FIGS. 14A-14C. The presence or absence of polarizers in the microdisplay 10 depends on the type of metalens array (isotropic or anisotropic). FIGS. 15A and 15E are on-axis designs, while the rest are off-axis designs. The output light from the microdisplay 10 and passing through the metalens arrays 71-76 can be collimated, tilted, or focused. When using larger overlapping metalens arrays 72 proportional to larger microdisplays, the scheme shown in FIG. 15B is preferred. Therefore, the light beam must be focused toward the user's eye; otherwise, part of the displayed content will not be visible to the user. Also, when the microdisplay 10 is vertically displaced, the schemes shown in Figures 15C, 15D, and 15F can be used to enhance the visibility of ambient light.

[0063] Although the present disclosure has been described with reference to particular embodiments, these embodiments should not be construed as limiting the present disclosure. Accordingly, those skilled in the art may make various modifications to the present embodiments without departing from the scope of the present disclosure, which is defined by the appended claims.

Claims

1. 1. A metalens array, comprising: at least one optically transparent substrate; a plurality of nanostructures disposed on the at least one optically transparent substrate; the plurality of nanostructures are arranged in a predetermined shape to define a plurality of metalenses; The metalens array, wherein the plurality of metalenses are arranged to overlap each other.

2. 10. The metalens array of claim 1, wherein the plurality of nanostructures are formed with isotropic shapes, anisotropic shapes, or a combination of isotropic and anisotropic shapes.

3. 10. The metalens array of claim 1, further comprising a residual resin mixture deposited on the at least one optically transparent substrate.

4. the metalens array further comprises a pair of optically transparent electrodes; the at least one optically transparent substrate is two optically transparent substrates; the plurality of nanostructures are coated with a filler; the plurality of nanostructures and the filler are sandwiched between the two optically transparent substrates via the pair of optically transparent electrodes; 10. The metalens array of claim 1, wherein the filler material is selected from an electrolyte or a gel electrolyte such that the pair of optically transparent electrodes is configured to allow a voltage to be applied to tune the metalens array between a conductive state and an insulating state.

5. the plurality of nanostructures are made of at least one phase change material; the plurality of nanostructures are provided on a surface of the at least one optically transparent substrate via a resistive heating film; 10. The metalens array of claim 1, wherein the resistive heating film is configured to have an electric current applied to it.

6. the plurality of nanostructures are comprised of a patterned 2D material; the plurality of nanostructures are provided on a surface of the at least one optically transparent substrate via a dielectric thin film and a conductive layer; 10. The metalens array of claim 1, wherein the conductive layer and the plurality of nanostructures are configured such that a voltage can be supplied to tune the metalens array between a conductive state and an insulating state.

7. the metalens array further comprises two ITO layers and two alignment layers; the at least one optically transparent substrate is two optically transparent substrates; the plurality of nanostructures are coated with a liquid crystal; the plurality of nanostructures and the liquid crystal are sandwiched between the two optically transparent substrates via the two alignment layers and the two ITO layers; 10. The metalens array of claim 1, wherein the two ITO layers are arranged such that a voltage is applied to them.

8. the metalens array further includes a top electrode patterned on one of the two ITO layers; 8. The metalens array of claim 7, wherein the two ITO layers are configured to be supplied with a voltage.

9. 10. The metalens array of claim 1, wherein the plurality of nanostructures are passive structures that can be converted into active, focus-adjustable metalens using a phase change material.

10. A display device, a microdisplay configured to emit light; and at least one metalens array spaced apart from the microdisplay and configured to transmit light from the microdisplay; the at least one metalens array at least one optically transparent substrate; a plurality of nanostructures disposed on the at least one optically transparent substrate; the plurality of nanostructures are arranged in a predetermined shape to define a plurality of metalenses; The display device, wherein the plurality of metalenses are arranged to overlap each other.

11. The display device of claim 10 , wherein the plurality of nanostructures are disposed on a surface of the at least one optically transparent substrate facing the microdisplay.

12. The display device further includes a transparent flexible substrate; the at least one metalens array is disposed to space the microdisplay and the transparent flexible substrate; 11. The display device of claim 10, wherein the plurality of nanostructures are disposed on two opposing surfaces of the at least one optically transparent substrate, facing the microdisplay and the transparent flexible substrate, respectively.

13. further comprising a first metalens array and a second metalens array; the first metalens array is spaced apart between the second metalens array and the microdisplay; in the first metalens array, the plurality of nanostructures are disposed on a surface of the at least one optically transparent substrate facing the second metalens array; 11. The display device of claim 10, wherein in the second metalens array, the plurality of nanostructures are disposed on a surface of the at least one optically transparent substrate facing the first metalens array.

14. further comprising a polarizer spaced apart between the microdisplay and the at least one metalens array; 11. The display device of claim 10, wherein the polarizer is positioned to polarize the light emitted from the microdisplay towards the at least one metalens array.

15. the microdisplay and the at least one metalens array are positioned on-axis or off-axis; 11. The display device of claim 10, wherein the at least one metalens array is configured to transmit light emitted from the microdisplay, thereby collimating, tilting, or focusing light transmitted through the at least one metalens array.

16. The display device according to claim 10 , wherein the plurality of nanostructures are formed in an isotropic shape, an anisotropic shape, or a shape that is a combination of isotropy and anisotropy.

17. 11. The display of claim 10, wherein the metalens array further comprises a residual resin mixture deposited on the at least one optically transparent substrate.

18. the metalens array further comprises a pair of optically transparent electrodes; the at least one optically transparent substrate is two optically transparent substrates; the plurality of nanostructures are coated with a filler; the plurality of nanostructures and the filler are provided between the two optically transparent substrates via the pair of optically transparent electrodes; 11. The display device of claim 10, wherein the filler material is selected from an electrolyte or a gel electrolyte such that a voltage is supplied to the pair of optically transparent electrodes, thereby adjusting the metalens array between a conductive state and an insulating state.

19. 11. The display device of claim 10, wherein the plurality of nanostructures are made of at least one type of phase change material, the plurality of nanostructures are provided on the surface of the at least one optically transparent substrate via a resistive heating film, and the resistive heating film is configured to be applied with an electric current.

20. the plurality of nanostructures are comprised of a patterned 2D material; the plurality of nanostructures are provided on a surface of the at least one optically transparent substrate via a dielectric thin film and a conductive layer; 11. The display of claim 10, wherein the conductive layer and the plurality of nanostructures are configured to be supplied with a voltage such that the metalens array is tuned between a conductive state and an insulating state.

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