Metalens array and display device including same

Abstract

Provided are a metalens array and a display device, the metalens array comprising at least one optically transmissive base layer and a plurality of nanostructures disposed on the at least one optically transmissive base layer, the plurality of nanostructures defining one or more metalenses arranged in a predetermined array, and the at least one optically transmissive base layer and the plurality of nanostructures configured to transmit light.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims priority to and incorporates by reference U.S. Patent and Trademark Office (USPTO) Provisional Application No. 63 / 439,685, filed January 18, 2023, U.S. Provisional Application No. 63 / 454,586, filed March 24, 2023, U.S. Provisional Application No. 63 / 470,167, filed May 31, 2023, U.S. Provisional Application No. 63 / 533,510, filed August 18, 2023, and U.S. Provisional Application No. 18 / 374,314, filed September 28, 2023.

[0002] The present invention relates to the field of optics, and in particular to a metalens array and a display device including the same. [Background technology]

[0003] Augmented reality (AR) is a display technology that blends virtual information with the real world. That is, it integrates virtual image information projected by electronic devices based on the real world as seen by the human eye. Conventional head-mounted AR display devices typically include a camera that captures images within the viewer's field of view and projects virtual image information at a default location within the viewer's field of view according to the captured images. Metalens-based systems require filtering of unwanted light rays that significantly affect the brightness of the output light without using a polarizer. [Brief explanation of the drawings]

[0004] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals indicate corresponding parts throughout the several views.

[0005] [Figure 1A] ~ [Figure 1F]FIG. 1 is a schematic diagram showing a conventional optical solution for building an AR / VR device. [Figure 2A] ~ [Figure 2C] FIG. 1 is a schematic diagram showing one prior art optical solution using a dielectric PB-metalens and a metal PB-metalens with and without a second polarizer. [Figure 3A] ~ [Figure 3C] FIG. 1 is a schematic diagram showing an example of a typical manufacturing flow for a dielectric and metal metalens. [Figure 4A] ~ [Figure 4B] FIG. 1 is a schematic diagram of transmission (a) and reflection (b) aspects using a metal metalens. [Figure 5] FIG. 1 is a schematic diagram of the transmission and reflection spectra of a transmissive metallic metasurface according to one embodiment of the present application. [Figure 6A] ~ [Figure 6B] FIG. 1 is a schematic diagram of a metalens-based optical system for transmissive and reflective surfaces in accordance with one embodiment of the present application. [Figure 6C] FIG. 1 is a side view of a metal metalens array according to an embodiment of the present application. [Figure 6D] FIG. 1 is a side view of a metal metalens array according to another embodiment of the present application. [Figure 7A] FIG. 1 is a schematic diagram illustrating one of a plurality of cell structures of a transmission-reflection type metal metalens in accordance with an embodiment of the present application. [Figure 7B] FIG. 1 is a schematic diagram showing an example of a cell structure of a transmission-reflection type metal metalens in accordance with another embodiment of the present application. [Figure 8A] ~ [Figure 8C] FIG. 10 is a plan view illustrating the shape types of cellular nanostructures of metalenses provided by some embodiments of the present application. [Figure 9A] ~ [Figure 9B] FIG. 10 is a plan view illustrating the shape types of cellular nanostructures of metalenses provided by some embodiments of the present application. [Figure 10A] ~ [Figure 10B] , [Figure 11A] ~ [Figure 11B] and [Figure 12A] ~ [Figure 12D] 1A-1C are several schematic diagrams illustrating multi-cell structures of metal metalens arrays with one or more metalens configured in different configurations provided by some embodiments of the present application. Summary of the Invention

[0006] The present application relates to metalens arrays and display devices.

[0007] A first aspect of the present application discloses a metalens array comprising at least one optically transmissive base layer and a plurality of nanostructures disposed on the at least one optically transmissive base layer, the plurality of nanostructures defining one or more metalenses arranged in a predetermined array, and the at least one optically transmissive base layer and the plurality of nanostructures configured to transmit light.

[0008] In an embodiment of the first aspect, a plurality of nanostructures disposed on at least one optically transmissive substrate is disclosed, the plurality of nanostructures defining one or more metalens arranged in a predetermined array, and the at least one optically transmissive substrate and the plurality of nanostructures are configured to transmit light, thereby effectively filtering out unfocused light and increasing the contrast of an image of the metalens.

[0009] In an embodiment of the first aspect, the plurality of nanostructures are made of a dielectric material.

[0010] In an embodiment of the first aspect, the plurality of nanostructures are made of a metallic material.

[0011] In one embodiment of the first aspect, the metalens array further comprises a covering layer, the covering layer covering the plurality of nanostructures and the at least one optically transparent base layer.

[0012] In an embodiment of the first aspect, the metalens array further includes a reflective layer disposed on the at least one optically transparent base layer, and a spacer layer disposed between the plurality of nanostructures and the reflective layer.

[0013] In one embodiment of the first aspect, the spacer layer is made of a non-conductive material and the reflective layer is made of a reflective metal.

[0014] In one embodiment of the first aspect, the metalens array includes a plurality of metalens unit cells, each of the plurality of metalens unit cells including anisotropically shaped nanostructures, and each of the plurality of metalens unit cells are spaced apart from one another by a first predetermined pitch.

[0015] In one embodiment of the first aspect, the unit cell of the plurality of metalenses is configured as a single rectangular metal metalens.

[0016] In an embodiment of the first aspect, the plurality of nanostructures are arranged into a plurality of rectangular metalenses.

[0017] In one embodiment of the first aspect, the plurality of rectangular metalenses are spaced apart from one another by a second predetermined pitch.

[0018] A second aspect of the present application discloses a display device, the display device comprising: a microdisplay that displays a real image and emits light; and at least one metalens array embedded within a housing of the display device; the at least one metalens array and the microdisplay are spaced apart, the at least one metalens array being configured to transmit light illuminated by the microdisplay; The at least one metalens array comprises at least one optically transmissive base layer and a plurality of nanostructures disposed on the at least one optically transmissive base layer, the plurality of nanostructures defining one or more metalens arranged in a predetermined array, and the at least one optically transmissive base layer and the plurality of nanostructures are configured to transmit light.

[0019] In an embodiment of the second aspect, the display device further comprises a polarizer disposed between the microdisplay and the at least one metalens array, the polarizer being configured to circularly polarize light emitted by the microdisplay.

[0020] In an embodiment of the second aspect, the plurality of nanostructures are made of a dielectric material or a metallic material.

[0021] In one embodiment of the second aspect, the metalens array further comprises a cover layer, the cover layer being disposed over the plurality of nanostructures and the at least one optically transmissive base layer.

[0022] In one embodiment of the second aspect, the metalens array further includes a reflective layer disposed on the at least one optically transparent base layer, and a spacer layer disposed between the plurality of nanostructures and the reflective layer.

[0023] In one embodiment of the second aspect, the spacer layer is made of a non-conductive material and the reflective layer is made of a reflective metal.

[0024] In one embodiment of the second aspect, the metalens array includes a plurality of metalens unit cells, each of the plurality of metalens unit cells including anisotropically shaped nanostructures, and each of the plurality of metalens unit cells are spaced apart from one another by a first predetermined pitch.

[0025] In one embodiment of the second aspect, the unit cell of the plurality of metalenses is configured as a single rectangular metalens.

[0026] In an embodiment of the second aspect, the plurality of nanostructures are arranged into a plurality of rectangular metalenses.

[0027] In one embodiment of the second aspect, the plurality of rectangular metalenses are spaced apart from one another by a second predetermined pitch. DETAILED DESCRIPTION OF THE INVENTION

[0028] The following disclosure provides many different embodiments or examples for realizing different configurations of the present application. The disclosure is merely exemplary, and modifications can be made to the details within the scope of the principles of the disclosure. All modifications within the meaning and scope of the equivalent elements of the claims are included in the present invention.

[0029] Unless otherwise defined, all technical terms used in this disclosure have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of fully understanding the embodiments described herein, but are not intended to limit the scope of the embodiments.

[0030] The following are some definitions that apply throughout this disclosure:

[0031] The term "coupled" is defined as connected, whether directly or indirectly through intervening elements, and is not necessarily limited to a physical connection. The term "substantially" is defined as essentially conforming to the particular dimensions, shape or other terms that the term modifies, such that elements are not necessarily precise. The term "comprises," when used, means "including, but not necessarily limited to," and specifically denotes open inclusion or membership in combinations, groups, series, etc.

[0032] Augmented reality (AR) is a display technology that blends 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 generally include a camera that captures images within the viewer's field of view and projects virtual image information at a default position within the viewer's field of view according to the captured images.

[0033] Figures 1A-1F show examples of common commercially available optical systems for transmitting or displaying augmented reality (AR) or virtual reality (VR). Because the focal length of the human eye is longer than the distance between the eye and conventional glasses, optical systems are required to project objects in a way that is easy for users to see. Optical systems are mainly divided into two types: diffractive optics (e.g., diffractive waveguides, tilted diffraction gratings, surface relief gratings, volume holographic diffraction gratings, metalenses) and geometric optics (e.g., partial reflectors, reflector arrays, freeform prisms, beam splitters, etc.).

[0034] Figures 1A-1F show solutions that enable AR / VR applications to project images directly below the user's eyes. Figures 1A and 1B show a partial mirror technique. The dashed lines in Figures 1A and 1B indicate a partial mirror structure. One side of the partial mirror structure reflects light emitted from the microdisplay, while the other side of the partial mirror structure transmits ambient light to the eye. A configuration like AR / VR goggles offers the simplest solution but is expensive. Figure 1C shows another solution using a freeform prism. However, the prism needs to be compensated to eliminate the refraction of ambient light from the main freeform prism. Figures 1D and 1E show surface relief grating (SRG) and volume holographic grating (VHG) types, respectively. Figures 1D and 1E show other configurations with better transmission in a smaller volume. This method allows for a limited range of beam angles due to the use of a waveguide, and therefore the achievable field of view (FOV) is inherently limited. The efficiency of the above method is generally below 10%.

[0035] Figures 1F and 2A-2C show a highly efficient, cutting-edge technology based on so-called metalens (metasurfaces), which outperforms the concept described in Figures 1A-1E. The content illuminated from the microdisplay passes through a circular polarizer and reaches the metalens, as shown in Figure 2A. The focal length of the metalens is adjusted to be exactly the same as the gap between the microdisplay and the metalens (or smaller to create a virtual image for AR applications). The metalens then cross-polarizes the collimated light forming the video content from the microdisplay, this time with respect to the first polarizer, so that the user can finally view the video content. A cross polarizer can be used to retain only the focused light, as shown in Figure 2A. This method filters all co-polarized light, but at the cost of brightness, since a typical polarizer allows less than 50% of the incident light to pass through. If the metalens were designed based on the Pancharatnam-Berry (PB) principle (also known as geometric phase), the second polarizer would likely be unnecessary.

[0036] However, due to the difficulty of fabricating high-aspect-ratio dielectric nanostructures, metalenses cannot efficiently convert the polarization of incident light, as shown in Figure 2B. Consequently, the final image contains both co-polarized light, which contains out-of-focus content (unwanted information) from the microdisplay, and cross-polarized light, which contains the in-focus image from the microdisplay. This is done to reduce the unwanted light, which significantly reduces brightness, without adding a second polarizer (a cross polarizer relative to the first polarizer), as shown in Figure 2C. The goal is to maximize the reduction of unwanted light using a special metal metalens. PB phase metalenses are theoretically promising because they can support full-color implementation in AR / VR devices and exhibit minimal degradation at different wavelengths. However, most PB phase metalenses are made from high-aspect-ratio dielectric materials, such as GaN and TiO2, which hinder their use in AR / VR systems, primarily due to the difficult and non-reproducible fabrication of these nanomaterials. That is, due to manufacturing imperfections, dielectric metalenses cannot fully convert polarization, resulting in the user's line of sight simultaneously seeing both co-polarized and cross-polarized light. Note that fabrication errors primarily occur as co-polarization in the dielectric metasurface, which is expected to significantly affect the device efficiency. Because the metalens is designed to focus only cross-polarized light, co-polarization can be considered background noise (DC) and significantly reduce the image contrast. Note that the dimensions in the schematic diagrams in Figures 2A-2C are not realistic and are drawn proportionally for ease of viewing.

[0037] Therefore, metalens systems need to filter out unwanted light rays that significantly affect the brightness of the output light without using polarizers.

[0038] 2A-2C show one conventional optical solution using a dielectric PB-metalens and a metal PB-metalens with and without a second polarizer. Figures 2A-2C show a microdisplay 10, polarizers (first polarizer 20, second polarizer 70), circularly polarized light 30, 50 with the same rotation direction, circularly polarized light 60 with a crossed rotation direction relative to the circularly polarized light 30, 50, and a metalens array 40 as proposed in the present application. However, the first polarizer 20 can also be a circular polarizer, and the second polarizer 70 has an opposite rotation direction to the first polarizer 20.

[0039] 2A, the lens and the microdisplay 10 are spaced apart, a first polarizer 20 is spaced apart between the microdisplay 10 and the lens, and a lens is also spaced apart between the first polarizer 20 and a second polarizer 70. The microdisplay 10 displays a real image and emits light. The first polarizer 20 circularly polarizes light to form circularly polarized light 30, which passes through the lens to form circularly polarized light 60 whose rotation direction crosses that of the circularly polarized light 50. The circularly polarized light 60 is then further circularly polarized by the second polarizer 70 to generate an image.

[0040] As shown in FIG. 2B, the second polarizer 70 is not provided as compared to FIG. 2A, and the circularly polarized light 50 and the crossed circularly polarized light 60 are directly imaged.

[0041] As shown in FIG. 2C , compared to FIG. 2B , the lens is a metalens array 40, and circularly polarized light 30 is circularly polarized by metalens array 40 to become circularly polarized light 60 with a crossed rotation direction, and circularly polarized light 60 generates an image.

[0042] Metasurfaces have received little attention, especially in the visible spectrum where metallic loss (or joule loss) is quite significant. Furthermore, for transmission applications, thin metal metalenses are physically limited in their polarization conversion efficiency, reaching a maximum of 25%. However, thick metal metalenses, multilayer metalenses, and reflection applications do not have such limitations. The proposed metalenses are not physically limited and can perform similarly to dielectrics, depending on whether the multipolar equilibrium and Kerker conditions are met.

[0043] As shown in Figure 3A, the fabrication of the proposed metal metalens requires four main steps, and patterned metal nanostructures can be easily obtained immediately after photoresist stripping. Figure 3B shows a two-layer metal nanostructure. The advantage of this design is that it does not require a "stripping" process and only requires coating a single thin metal layer on the resist / resin. The typical thickness of the metal in this method is 15 nm to 50 nm, but is not limited to this range. However, fabricating a dielectric metalens requires a more complex process, and the quality of the fabricated nanostructures essentially depends on the quality of the dry etching, which generally leads to tapering issues as shown in Figure 3C. In other words, reproducibility of the proposed metalens is no longer an issue, and unlike dielectric metalens, it can be mass-produced easily and with nearly consistent quality.

[0044] As shown in Figures 4A and 4B, to overcome the physical limitations of the transport mode, a single-layer thick metal metasurface (metal thickness greater than 80 nm) or a two-layer thin metal metasurface (metal thickness less than 50 nm) may be used. One advantage of the proposed example is that a device in an optical system using metalenses can effectively employ both reflection and transmission modes. In one embodiment, the metalens does not necessarily need to be located at the center of the glasses, but can be off-center. In another example, at least one metalens array 40 is embedded within the display device housing, with at least one metalens array 40 spaced apart from the microdisplay 10 and configured to transmit light emitted from the microdisplay 10.

[0045] Figure 5 shows an example of a schematic diagram comparing the maximum contrast of an optical system using the metalens of the present application with that of conventional technology. The results confirmed the co-polarized transmission (Tco), cross-polarized transmission (Tcross), co-polarized reflection (Rco), cross-polarized reflection (Rcross), and absorption components of the proposed metasurface. The Tco value is much smaller than Tcross and can be ignored. Fabrication defects appear as an additional factor in absorption, not Tco. Therefore, the ratio of focused light (cross-polarized) is always kept high compared to Tco, resulting in the highest contrast of the device.

[0046] The present application therefore proposes a metalens array. The metalens array comprises at least one base layer (e.g., an optically transparent base layer) and a plurality of nanostructures disposed on the at least one base layer, the plurality of nanostructures defining one or more metalenses arranged in a predetermined array, wherein the at least one base layer and the plurality of nanostructures are configured to transmit light. In some embodiments, the plurality of nanostructures are formed from a dielectric material or a metallic material, and if a covering layer is required, the nanostructures are made from a metallic material.

[0047] FIGS. 6A and 6B show two examples of a metalens-based optical system. As shown in FIG. 6A, the optical system includes a microdisplay 10, a first polarizer 20, and a metalens array 40 (the metalens array may be a metalens module or a metalens array module). Light is emitted from the microdisplay 10, which displays a real image to be displayed to a viewer. According to one example, the first polarizer 20 may be a circular polarizer that circularly polarizes the light emitted from the microdisplay 10. In some examples, the first polarizer 20 may be a linear polarizer or a combination of a linear polarizer and a quarter-wave plate. According to an example, the metalens array 40 may be held by a user in a frame (not shown) and embedded in an eyepiece (not shown) worn by the user. The same applies to the reflective method if we change the microdisplay to a microprojector 91, as shown in FIG. 6B, which has a collimating lens 92 to collimate the display light on the metalens 80, and then the light is reflected by a black mirror to focus it on the user's eyes.

[0048] FIG. 6C shows a transmissive metalens array 40 according to one embodiment. As shown, the metalens array 40 includes a cover layer 41, a plurality of nanostructures 42, and a base layer 43. The cover layer 41 can be formed from any suitable impedance-matching material, such as photoresist, that has a refractive index comparable to that of the usable base layer. The base layer 43 can be any type of transparent base layer, such as glass made from fused silica (SiO2) or sapphire. The refractive index of the cover layer 41 can be close to that of the base layer 43. The cover layer 41 is spin-coated (or evaporated) onto the patterned nanostructures 42 as the final step in the method for fabricating the metalens array 40. The plurality of nanostructures 42 are nano-sized pillars deposited on the base layer 43, defining one or more metalenses. The cover layer 41 overlies the plurality of nanostructures 42 and the base layer 43. Although FIGS. 6A , 6B , 6C , and 6D illustrate only one metalens for ease of illustration, metalens array 40 may include any number of metalenses and may be arranged in any arrangement, such as a grid, row, or column of metalenses. The plurality of nanostructures 42 may be formed from a metallic material, such as a noble metal such as gold (Au), silver (Ag), or aluminum (Al). These nanostructures may have different anisotropic shapes. In other embodiments, the plurality of nanostructures 42 may be composed of a dielectric material. That is, the plurality of nanostructures may be composed of a dielectric material or a metallic material. In some embodiments, metallic nanostructures 42 are used when a cover layer 41 is required (as shown at least in FIGS. 6C and 6D ), while dielectric nanostructures 42 are typically used when a cover layer 41 is not required. In other embodiments, metallens array 40 includes at least one optically transparent base layer 43 and a plurality of nanostructures 42 disposed on at least one optically transparent base layer 43. Metalens array 40 further includes a coating layer 41 that coats the plurality of nanostructures 42 and at least one optically transparent base layer 43. In some embodiments, the thickness of reflective layer 85 is greater than the thickness of spacer layer 84.

[0049] FIG. 6D illustrates a reflective metalens array 80 according to one embodiment. As shown in FIG. 6D, the metalens array 80 includes a cover layer 81, a plurality of nanostructures 82, a base layer 83, a spacer layer 84, and a thick reflective layer 85. The cover layer 81 covers the plurality of nanostructures 82 and the base layer 83. The base layer 83 may be any type of transparent base layer, such as glass made of fused silica (SiO) or sapphire. The spacer layer 84 is a spacer between the plurality of nanostructures 82 and the thick reflective layer 85. The spacer layer 84 can be made of a thin layer (5 nm to 110 nm) of a non-conductive material (e.g., a dielectric material) such as a polymer, SiO, AlO, HfO, an optical dielectric, or any oxide and dielectric material. The thickness of the spacer layer 84 is denoted as TO. Light passing through the covering layer 81, the plurality of nanostructures 82, and the spacer layer 84 is reflected from the surface of the thick reflective layer 85. The thick reflective layer 85 used as a backlight (mirror) is typically made of a thick layer of pure silver, gold, or other reflective metal, and typically has a thickness of 60 nm to 200 nm, although thinner or thicker layers may also be used. The plurality of nanostructures 82 may be formed of a metallic material, such as noble metals such as gold (Au), silver (Ag), or aluminum (Al). In other embodiments, the plurality of nanostructures 82 may be made of a dielectric material. Specifically, if the covering layer 81 is required, the plurality of nanostructures 82 may be made of a metallic material. In other embodiments, the metalens array 40 includes a reflective layer 85 disposed on at least one optically transparent base layer 83 and a spacer layer 84 disposed between the plurality of nanostructures 82 and the reflective layer 85. The spacer layer 84 is made of a non-conductive material, and the reflective layer 85 is made of a reflective metal.

[0050] 7A and 7B show two examples of multiple cell structures for metalens arrays 40, 80 of the present application. Each of the metalens arrays 40, 80 has a plurality of cell nanostructures. The plurality of cell nanostructures defines one or more metalenses. In one example, a metalens 45 is composed of a plurality of cells (i.e., cell nanostructures 42, 82), and the metalens array 40, 80 is formed of a plurality of metalenses 45, or alternatively, the metalens array 40, 80 is formed by an array of a plurality of metalenses 45, each of which is formed by an array of a plurality of cells (i.e., cell nanostructures 42, 82). In one example, each cell structure of the metalens array 40 shown in FIG. 7A includes a cladding layer 41, a cell nanostructure 42, and a base layer 43. In another example, each cell structure of the metalens array 80 shown in FIG. 7B includes a cladding layer 81, a plurality of nanostructures 82, a base layer 83, a spacer layer 84, and a thick reflective layer 85. The cell nanostructures 42, 82 may have different anisotropic shapes depending on the desired spectrum of light to be filtered. Each cell nanostructure 42, 82 is designed to fully accommodate a single wavelength while minimizing interaction with other wavelengths (e.g., the smallest cell nanostructures 42, 82 are designed for blue light and will only focus blue light—ideally, not green or red light). As the wavelength increases, the size of the nanostructures also increases. The cell nanostructures 42, 82 may have a generally circular, triangular, square, rectangular, or anisotropic shape. In one embodiment, the shape of the cell nanostructures 42, 82 is rectangular, as shown in FIGS. 7A and 7B. The multiple cell structures 42, 82 of the metalens array 40, 80 are spaced apart from one another with a pitch Px in the X direction of 150 nm to 700 nm and a pitch Py in the Y direction of 150 nm to 700 nm. The cell nanostructures 42, 82 have a width W of 30 to 650 nm. The cell nanostructures 42, 82 have a length L of 30 nm to 650 nm. The cell nanostructures 42, 82 have a height H of 20 nm to 300 nm.

[0051] FIGS. 8A-8C illustrate shape types of the cell nanostructures 42, 82 of a metalens from a top view. FIG. 8A illustrates a first type of shape for the cell nanostructures 42, 82, in which the plurality of cell nanostructures 42, 82 have a fully isotropic shape and may be separate from the polarizer. For example, the isotropic shape may be circular or rectangular, with the same dimensions when viewed from either side. FIG. 8B illustrates a second type of shape for the cell nanostructures 42, 82, in which the plurality of cell nanostructures 42, 82 have a fully anisotropic shape and may participate in the polarizer. For example, the anisotropic shape may be rectangular, "L," "H," or any shape with different dimensions when viewed from different sides. 8C illustrates a third type of shape for the cellular nanostructures 42, 82, where the plurality of cellular nanostructures 42, 82 are a combination of the first and second types of shapes (i.e., a combination of isotropic and anisotropic shapes) and may be associated with a polarizer. Preferably, the nanostructures 42, 82 of the polarizer block unwanted cross-polarized light, i.e., the plurality of nanostructures 42, 82 have at least one anisotropic shape or a combination of isotropic and anisotropic shapes to block unwanted cross-polarized light. A metalens or metalens array 40, 80 associated with a polarizer (where the nanostructures 42, 82 associated with the polarizer have at least one anisotropic shape or a combination of isotropic and anisotropic shapes) may have higher contrast than a metalens or metalens array 40, 80 including isotropic nanostructures 42, 82. That is, the present application requires a solution that relies on polarizers (as shown in Figures 8B and 8C) to increase the contrast ratio using either transmission or reflection techniques.

[0052] It is understood that the plurality of nanostructures 42, 82 may have any anisotropic shape (or a combination of isotropic and anisotropic shapes) in order to block unwanted cross-polarized light. However, all of the nanostructures 42, 82 may be formed as an arrangement of regular-shaped metalenses 45 (e.g., circular lenses such as those currently commercially available) or irregular-shaped metalenses 45 (e.g., “L” shaped). Similarly, the metalens array 40, 80 does not necessarily have to have any particular shape; conversely, the metalens array 40, 80 may have any irregular or anisotropic shape.

[0053] The single rule for creating a metalens 45 with isotropic or anisotropic nanostructures is that the finite number of nanostructures 42, 82 (e.g., 12-cell nanostructures 42, 82) should satisfy the "2*pi" phase transition (to fully control the incoming waves and achieve ultimate manipulation). In one example of an isotropic solution, shown in FIG. 8A, this condition is met only when different sizes are used. Also, in one example of an anisotropic solution, shown in FIG. 8B, this condition is met when the same nanostructures 42, 82 are rotated. A third solution combines isotropic and anisotropic nanostructures, as shown in FIG. 8C.

[0054] One difference between these metalenses is that the metalens 45, whose nanostructures are formed by isotropic nanostructures 42, 82, is "polarizer independent" and therefore operates without the need for a polarizer. However, the anisotropic solution requires ensuring that the displayed light is circularly polarized (i.e., a circular polarizer must be added in front of the display). However, it is not limited to one shape (e.g., rectangular shapes with different sizes for each wavelength), but requires the use of different anisotropic shapes for different colors. A third solution is a combination of these two solutions and also depends on the polarizer (i.e., a linear or circular polarizer must be added in front of the display, depending on the design).

[0055] 9A-9B show two different pitches based on which metalenses can be designed.CC defines the center-to-center pitch, while P EE defines the edge-to-edge pitch. Metalenses may be designed with any pitch. Any of these pitches can be selected to design a metalens array depending on the smallest characteristic dimension of the nanofabrication equipment. In other embodiments, a metalens array 40, 80 includes a plurality of metalens unit cells, each of which includes nanostructures 42, 82 with an anisotropic shape (including fully anisotropic shapes, and combinations of anisotropic and isotropic shapes). The plurality of metalens unit cells are each arranged with a first predetermined pitch (e.g., the center-to-center pitch P shown in FIG. 9A ). CC and the edge-to-edge pitch P shown in FIG. EE ) apart.

[0056] FIGS. 10A-10B and 11A-11B show multiple cell structures of metalens arrays 40, 80, respectively, with one or more metalens arranged in different configurations. In one embodiment, the multiple cell structures may be configured as multiple rectangular metalens as shown in FIGS. 10A and 10B. In one embodiment, the multiple cell structures may be configured as a single rectangular metalens as shown in FIGS. 11A and 11B. In another embodiment, metalens array 40 includes at least one optically transparent base layer 43 and a plurality of nanostructures 42 disposed on at least one optically transparent base layer 43. The plurality of nanostructures 42 define one or more metalens (e.g., multiple metalenses 45 as shown in FIG. 10B and a single metalens 45 as shown in FIGS. 11A and 11B) arranged in a predetermined array, and the at least one optically transparent base layer 43 and the plurality of nanostructures 42 are used to transmit light. The plurality of nanostructures 42 has at least one anisotropic shape or a combination of isotropic and anisotropic shapes.

[0057] In one embodiment, the plurality of cellular nanostructures 42 may be configured as a plurality of rectangular metalenses, as shown in FIGS. 10A and 10B . Each rectangular metalenses 45 has a width Wu and a length Lu, and the metalens array 40, 80 has a width M*Wu and a length N*Lu, and the rectangular metalenses 45 and the metalens array 40, 80 may be spaced apart from one another at a pitch Px in the X direction and a pitch Py in the Y direction. That is, in another embodiment, the plurality of metalenses 45 includes a plurality of nanostructures 42, 82. The plurality of metalenses 45 are spaced apart from one another by a second predetermined pitch Pa (e.g., a combination of the X-direction pitch Px and the Y-direction pitch Py). The number of rectangular metalenses 45 in the x direction (N) may be the same as or different from the number of rectangular metalenses 45 in the Y direction (M), and the size of Px may be the same as or different from the size of Py. In some embodiments, a metalens may include three or more cells of different colors, e.g., requiring a different pitch, width, and length for each color, but the same height for all colors. In other embodiments, a metalens may include the same cells (e.g., having the same pitch) for all colors (e.g., different widths and lengths, but the same height).

[0058] In one embodiment, the plurality of cell nanostructures 42 may be configured as a single rectangular metalens, as shown in Figures 11A and 11B. The single rectangular metalens 45 may have a width Wu and a length Lu, and the metalens array 40, 80 may have a width Wy and a length Lx, where the size of Lx may be the same as or different from the size of Wy.

[0059] In one embodiment, the plurality of cell nanostructures 42 may be configured as a plurality of circular metalenses as shown in FIGS. 12A and 12B . Each circular metalens 46 has a diameter Ra of 30 nm to 650 nm. The metalens array 40, 80 has a width M*Ra and a length N*Ra, and the circular metalenses 46 may be spaced apart at a pitch Px in the X direction and a pitch Py in the Y direction. That is, in another embodiment, a plurality of nanostructures 42, 82 are provided on the plurality of metalenses 46. The plurality of metalenses 46 are spaced apart from one another by a second predetermined pitch Pa (e.g., a combination of the X-direction pitch Px and the Y-direction pitch Py). The dimension of Px may be the distance between the center of a circular metalens 46 and the center of another circular metalens 46 adjacent to that circular metalens 46 in the X direction. The dimension of Py may be the distance between the center of the circular metalens array 46 and the center of another circular metalens 46 adjacent to that circular metalens 46 in the Y direction. The number (N) of rectangular metalenses 46 in the x direction may be the same as or different from the number (M) of rectangular metalenses 46 in the Y direction, and the magnitude of Px may be the same as or different from the magnitude of Py.

[0060] In one embodiment, the plurality of cell nanostructures 42, 82 may be provided as a single circular metalens, as shown in Figures 12C and 12D. The single circular metalens may have a diameter Rs, and the metalens array 40 may have a width Wy and a length Lx, where Lx may be the same as or different from Wy.

[0061] 6A , light emitted from microdisplay 10 is circularly polarized by first polarizer 20 (circular polarizer). Circularly polarized light 30 from first polarizer 20 (circular polarizer) reaches metalens array 40, and output light comprising co-polarized light 50 and cross-polarized light 60 is transmitted through metalens array 40. Cross-polarized light 60, which is a focused ray of light, is seen by a user, while co-polarized light, which is an unfocused ray of light, is extinguished by metalens array 40.

[0062] It should be noted that any steps and any technical features in the above embodiments of the present application can be freely combined in any way, and therefore, those skilled in the art can make various modifications to the embodiments without departing from the scope of the present disclosure as defined by the appended claims.

Claims

1. at least one optically transparent substrate; a plurality of nanostructures disposed on the at least one optically transparent substrate; the plurality of nanostructures define one or more metalenses arranged in a predetermined array; 10. A metalens array, wherein the at least one optically transmissive base layer and the plurality of nanostructures are configured to transmit light.

2. 10. The metalens array of claim 1, wherein the plurality of nanostructures are composed of a dielectric material.

3. 10. The metalens array of claim 1, wherein the plurality of nanostructures are made of a metallic material.

4. the metalens array further comprises a cover layer; 4. The metalens array of claim 3, wherein the cover layer is disposed over the plurality of nanostructures and the at least one optically transmissive base layer.

5. 4. The metalens array of claim 3, further comprising: a reflective layer disposed on at least one of the optically transparent base layers; and a spacer layer disposed between the plurality of nanostructures and the reflective layer.

6. the spacer layer is made of a non-conductive material; 4. The metalens array of claim 3, wherein the reflective layer is made of a reflective metal.

7. the metalens array includes a plurality of metalens unit cells; each unit cell of the plurality of metalenses comprises anisotropically shaped nanostructures; 3. The metalens array of claim 2, wherein each of the unit cells of the plurality of metalens are spaced apart from one another by a first predetermined pitch.

8. 6. The metalens array of claim 5, wherein a unit cell of the plurality of metalenses is configured as a single rectangular metal metalens.

9. 10. The metalens array of claim 1, wherein the plurality of nanostructures are arranged into a plurality of rectangular metalens.

10. 8. The metalens array of claim 7, wherein the plurality of rectangular metalenses are spaced apart from one another by a second predetermined pitch.

11. A display device, a microdisplay that displays real images and emits light; at least one metalens array embedded within a housing of the display device; a space between the at least one metalens array and the microdisplay; the at least one metalens array is configured to transmit light illuminated by 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 define one or more metalenses arranged in a predetermined array; 10. A display device, wherein the at least one optically transparent substrate and the plurality of nanostructures are configured to transmit light.

12. further comprising a polarizer; 12. The display of claim 11, wherein the polarizer is disposed between the microdisplay and at least one metalens array and configured to circularly polarize light emitted by the microdisplay.

13. The display device according to claim 11 , wherein the plurality of nanostructures are made of a dielectric material or a metallic material.

14. the metalens array further comprises a cover layer; 14. The display device of claim 13, wherein the cover layer is disposed over the plurality of nanostructures and the at least one optically transparent base layer.

15. 14. The display device of claim 13, wherein the metalens array further comprises: a reflective layer disposed on the at least one light-transmitting base layer; and a spacer layer disposed between the plurality of nanostructures and the reflective layer.

16. the spacer layer is made of a non-conductive material; 14. The display device according to claim 13, wherein the reflective layer is made of a reflective metal.

17. the metalens array includes a plurality of metalens unit cells; each unit cell of the plurality of metalenses comprises an anisotropically shaped nanostructure; 14. The display device of claim 13, wherein each of the unit cells of the plurality of metalens are spaced apart from one another by a first predetermined pitch.

18. 16. The display device of claim 15, wherein the unit cells of the plurality of metalens are configured as a single rectangular metalens.

19. 12. The display device of claim 11, wherein the plurality of nanostructures are arranged into a plurality of rectangular metalenses.

20. 18. The display device of claim 17, wherein the plurality of rectangular metalenses are spaced apart from one another by a second predetermined pitch.

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