Optical metasurfaces and methods for fabricating optical metasurfaces

Abstract

The present invention relates to an optical metasurface that interacts with incident light and a method for fabricating the optical metasurface. The optical metasurface can be used as a metalens, a blazed diffraction grating, a phase plate, or another optical device. The optical metasurface includes a transparent substrate containing a plurality of nanoholes or nanopillars. The plurality of nanoholes or nanopillars in the transparent substrate are covered by a plurality of shaped layers comprising a transparent dielectric material.

Description

[Technical Field]

[0001] The present invention relates to optical metasurfaces that interact with incident light and methods for fabricating optical metasurfaces, which can be used as metalenses, blazed diffraction gratings, phase plates, holograms, or other optical devices. [Background technology]

[0002] Metasurfaces have the ability to manipulate optical fields. They contain nanoscale / subwavelength-sized structures that can be used to control the amplitude, phase, and polarization of light through subwavelength units, compared to conventional lenses that rely on modulated light beams. Metasurfaces can be used for lenses, blazed diffraction gratings, phase plates, holograms, or other optical devices.

[0003] For example, classical optical devices, such as ophthalmic lenses that can be used in eyeglasses, control the path of light through optical refraction by engineering the shape and thickness of transparent materials. These devices rely on light propagating within the lens material over distances much greater than its wavelength to accumulate the phase change necessary for the desired optical functionality. This dictates how thin the optical device or lens can be made. The same problem exists for blazed diffraction gratings and other optical devices. The thickness and weight of high-power lenses and other optical devices remain unsolved challenges.

[0004] Because metasurfaces are thin and lightweight, metalenses and other optical devices can be made significantly lighter and thinner than classical optical devices. However, using metasurfaces to create effective optical components, such as lenses, that can achieve the required optical properties and quality has not been as successful as desired in the past. Fabrication of metasurfaces has not been possible in a cost-effective, upscalable manner.

[0005] Therefore, improved optical metasurfaces that are amenable to design and production by cost-effective means would be advantageous, and in particular optical metasurface devices that are amenable to mass customization.

[0006] Object of the invention The objective of the present invention is to provide an optical metasurface with high optical performance.

[0007] It is an object of the present invention to provide optical metasurfaces for eyeglasses and other optical devices that apply nanophotonic metasurface flat optics for metalenses.

[0008] A further object of the present invention is to provide an alternative to the prior art.

[0009] Specifically, it can be seen as an object of the present invention to provide an optical metasurface that solves the above-mentioned problems of the prior art. Summary of the Invention

[0010] It is therefore intended that the above objects, as well as certain other objects, be obtained in a first aspect of the present invention by providing an optical metasurface for interacting with incident light, the metasurface comprising: a transparent substrate comprising a plurality of nanoholes or nanopillars, the nanoholes or nanopillars having vertical or substantially vertical sidewalls extending perpendicular to a base plane of the substrate; a plurality of shaped layers including a transparent dielectric material, each shaped layer covering a plurality of nanoholes or nanopillars in the transparent substrate;

[0011] The optical metasurface comprises a transparent substrate on which a transparent dielectric material is deposited, the transparent substrate containing topographical features in the form of a plurality of nanoholes or nanopillars, forming a high-index dielectric structure that is a plurality of shaped layers on the substrate.

[0012] The present invention applies nanophotonics, metasurface flat optics, and microfabrication to fabricate optical metasurfaces.

[0013] The transparency of the substrate and dielectric materials allows light to pass through the optical metasurface, making the present optical metasurfaces particularly suitable for metalenses, which can be used by people in eyeglasses to improve their vision. The present optical metasurfaces can also be used in other optical devices that require light to pass through a lens.

[0014] Nanophotonics and metasurface flat optics relate directly to the fundamental understanding of optics established by Isaac Newton in the late 17th century: that light carries information—frequency-dependent amplitude (color), phase, and polarization—that is encoded into the electromagnetic field of light as it interacts with materials. Modern microfabrication techniques are used to create artificially engineered materials with engineered optical properties, providing a new means of encoding information into light without being constrained by the electromagnetic responses of natural materials and their compounds.

[0015] The base plane is the plane corresponding to the plane of the substrate surface between the nanopillars or nanoholes of the substrate.

[0016] A "shaped layer" should be understood as a uniform layer covering a plurality of nanoholes or nanopillars.

[0017] According to one embodiment, the distance between two adjacent nanoholes or nanopillars is less than half the wavelength of the incident light, which can be ultraviolet, visible, near-infrared and / or infrared.

[0018] The distance between two adjacent nanoholes in a nanopillar is less than the wavelength of the incident light, which has the effect of minimizing or even avoiding unintended light scattering.

[0019] Ultraviolet light has a wavelength between 10 and 400 nm, visible light has a wavelength between 400 and 700 nm, near-infrared light has a wavelength between 700 and 1400 nm, while infrared light has a wavelength between 700 nm and up to 1 mm. Therefore, the choice of the distance between two nanoholes or nanopillars depends heavily on what kind of light the optical metasurface is intended to receive.

[0020] The nanoholes or nanopillars may be evenly spaced on the substrate, meaning that the nanoholes or nanopillars are arranged in a uniform pattern, with the distance between two adjacent nanoholes or nanopillars being equal across the substrate.

[0021] However, alternatively, the nanoholes or nanopillars may not be equally spaced, but may instead be arranged in other patterns, or even randomly arranged, but with the distance between two adjacent nanoholes or nanopillars being less than the wavelength of the incident light.

[0022] The nanoholes or nanopillars may be identical, which should be understood to mean that the nanoholes or nanopillars comprise the same height and diameter.

[0023] The distance between two adjacent nanoholes or nanopillars is measured from the center of one nanohole or nanopillar to the center of the adjacent nanohole or nanopillar.

[0024] According to one embodiment, the optical metasurface is a truncated waveguide metasurface comprising a two-dimensional array of meta-atoms, each meta-atom comprising one nanohole or nanopillar.

[0025] Optical metasurfaces are two-dimensional arrays of nanoscale elements called meta-atoms. The meta-atoms function as individual nanoscale optical antennas, providing, through their size and shape, complete nanoscale control over light (frequency-dependent amplitude, phase, and polarization) as it interacts with the metasurface, e.g., as it transmits through the surface. In contrast to the traditional lensing techniques described above, optical metasurfaces can suddenly provide the required changes (amplitude, phase, and polarization) in an optical field as it propagates less than 1 μm over distances on the order of the wavelength of light. This is used to create ultrathin, so-called metasurface flat optics, including broadband achromatic metalenses. In flat optics metalenses, the size, shape, and morphology of the meta-atoms are varied across the surface area to obtain the required phase change variation for the desired optical function.

[0026] The present invention relates to cost-effective mass customization of so-called truncated waveguide metasurfaces. Truncated waveguides rely on field confinement within nanostructures, whose dimensions can be used to tune the propagation constant. The change in the propagation constant compared to neighboring meta-atoms translates directly into a phase shift.

[0027] Metamaterials are artificial structures with unusual and remarkable properties that stem from carefully designed building blocks, also known as meta-atoms. Metamaterials permeate a wide range of sciences, including electromagnetism and mechanics.

[0028] The present invention is a cost-effective method for the mass fabrication of personalized optical metasurfaces that can be applied to ultrathin so-called flat optical components (e.g., lenses, diffraction gratings, and phase plates), potentially revolutionizing the €100 billion ophthalmic lens market by introducing the world's thinnest prescription lenses. Furthermore, the present invention can also be utilized for optical sensors and ink-free color decoration (structural color).

[0029] A metalens is a type of flat lens made from a thin metal film, typically a few hundred nanometers thick, deposited on a substrate. Unlike traditional lenses, which are made from glass or plastic and have a curved surface to refract light, a metalens uses nanoscale patterns on its surface to manipulate light in a similar way. This makes them much smaller, lighter, and more versatile than traditional lenses. Metalenses have potential applications in a variety of fields, including optics, microscopy, and consumer electronics. Metalenses is a flat lens technology created by optical components that use metasurfaces to focus light. They can be used in optical applications that take advantage of the flat surface and reduced thickness compared to the classical curved refractive lenses predominantly used in optical devices today.

[0030] The present invention is particularly, but not exclusively, advantageous for obtaining light-weight optical devices and optical devices with high optical performance.

[0031] "Coating the plurality of nanoholes or nanopillars" should be understood as meaning that the transparent dielectric material covers the substrate, such that the plurality of nanoholes or nanopillars are covered by covering the bottoms of the nanoholes and the tops of the nanopillars, as well as the walls of the nanoholes or nanopillars.

[0032] It should be noted that the optical properties of high-index dielectric structures formed by transparent dielectric materials can be related to transmission and / or reflection. For example, a reflected color may be visible at one surface, while a different transmitted color may be visible at the other surface.

[0033] In an embodiment, the high refractive index dielectric structure formed by the transparent dielectric material has a relative dielectric constant at 532 nm of 5 or more, such as 6 or more, for example 7 or more, for example 8 or more, for example 9 or more, such as 10 or more.

[0034] In this context, "optical" may be understood as relating to within the visible electromagnetic spectrum.

[0035] The plurality of geometric layers are high refractive index dielectric structures comprising transparent dielectric materials.

[0036] A "high refractive index dielectric structure" may be understood as a structure (e.g., a high refractive index dielectric nanoparticle, a nanohole of a high refractive index dielectric material, etc.) that may be capable of coupling with electromagnetic radiation of a larger, e.g., much larger, wavelength than the structure due to resonance. It may be understood that a high refractive index dielectric structure may correspond to a plurality of similar high refractive index dielectric structures, such as a periodically arranged structure, and optionally each may correspond to a plurality of structures (e.g., a disk and a nanohole) in which the high refractive index dielectric structure may be divided into unit cells.

[0037] It can be appreciated that high index dielectric structures can exhibit resonances in the visible regime, which can be any one or more of cavity resonances, electric dipole resonances, magnetic dipole resonances, and / or whispering gallery mode resonances.

[0038] The transparent substrate is a support structure, which may be understood as a material that supports the high-index dielectric structures, and may be understood as a solid material on which the high-index dielectric structures are disposed and / or in which the high-index dielectric structures are embedded, such as each of the high-index dielectric structures in the first plurality of high-index dielectric structures.

[0039] It should be noted that a polymer (although a polymer may be considered advantageous, for example, to enable the topographical features provided by nanoimprint lithography) is not required as a material choice for the transparent substrate; in alternative embodiments, it may be another material, such as glass. Examples of possible polymer materials include TOPAS (cyclic olefin copolymer), poly(methyl methacrylate) (PMMA), polyethylene (PE), polystyrene (PS), and composite or hybrid materials such as Ormocer.

[0040] A transparent dielectric material on a transparent substrate can form a metasurface.

[0041] "Topographical features" may be understood as features on the surface of a material that deviate from the plane of the surface, for example protrusions and depressions, such as nanopillars and nanoholes.

[0042] Topographical features in the transparent substrate can be beneficial to enable or facilitate providing high refractive index dielectric structures. For example, if the transparent substrate includes a plurality of nanopillars protruding from the surface, the transparent dielectric material may be provided directly by depositing a high refractive index dielectric film on the transparent substrate.

[0043] A "pillar" may be understood as a protrusion, such as a substantially cylindrical protrusion, protruding from a surface.

[0044] A "hole" may be understood as a depression, such as a substantially cylindrical depression, in a surface.

[0045] The metasurfaces of the present invention can be used in the visible regime, which can be understood as electromagnetic radiation (which can be referred to as "light" in this regime) having wavelengths between 380 nm and 760 nm. The metasurfaces of the present invention can alternatively be for ultraviolet, near-infrared, infrared, and / or far-infrared radiation.

[0046] The present invention adds optical functionality to nanostructured dielectric substrates by one or more overlaid patterned depositions of materials.

[0047] This differs from other metasurface fabrication methods, where nanoscale / subwavelength meta-atoms are individualized by: -Electron beam or deep ultraviolet lithography of each metasurface component, - electron beam or deep ultraviolet lithography of replication masters, e.g. nanoimprint stamps, -Laser machining of metasurfaces using heat from a laser beam. Laser machining uses thermal energy to remove material from a metallic or non-metallic surface. High-intensity monochromatic light falls on the surface, thus heating, melting, and evaporating the material due to photon impacts; and -Focused ion beam deposition.

[0048] The high intensity monochromatic light used for laser processing depends on the material the meta-atoms are made of. For optical components, the material is chosen to be transparent within the window in which the component will operate. For example, TiO2 is used for components in the visible range, in which case the laser is chosen at a wavelength absorbed by TiO2, i.e., below 400 nm. In the experiments, 355 nm was used. Maximum 4.5 J / cm 2 A preferred intensity of up to 10 J / cm may be used. 2 It is possible to use an intensity of 100 Hz. Pulsed lasers may also be used. In experiments, writing was performed using pulsed lasers with pulse lengths of approximately 1 ns and repetition rates of 100 Hz. Pulsed lasers can have repetition rates up to several MHz (10 MHz or more), and it is the repetition rate that determines the writing time for a given area.

[0049] In the invention described herein, local modifications of optical properties such as transmission, reflection, and phase change are controlled through optical properties such as dielectric constant, refractive index, and thickness of the deposited layer of material. The subwavelength / nanoscale features of the meta-atoms that govern their interaction with light (scattering, phase propagation, polarization) are defined in part by the nanohole geometry and in part by the material parameters and thickness of the deposited material.

[0050] The present invention enables mass fabrication of individualized optical metasurface components, where cost-effective UV lithography first creates the required deformations in identical meta-atoms / nanostructures. The UV lithography can be maskless UV lithography, although other types of UV lithography would work as well.

[0051] According to one embodiment, two adjacent shape layers are of different thickness, which results in different phase shifts of the incident light.

[0052] The thickness of the shape layer determines the phase shift of the incident light passing through the shape layer, so different shape layers with different thicknesses have different phase shifts and therefore different phase levels.

[0053] A phase level should be understood as a region where the phase shift is substantially the same. Different isolated regions may have the same phase level. Thus, a metasurface may have multiple shape layers, but only a few phase levels, since two or more of the shape layers may have the same phase level.

[0054] Optical metasurfaces contain two or more phase levels. The phase levels are related to the thickness of the layer of transparent dielectric material. The number of phase levels depends on the deposition technique used to deposit the transparent dielectric material on the substrate. The phase shift of the incident light depends on the thickness of the transparent dielectric material, and therefore, each phase level of the transparent dielectric material results in a different phase shift. The more phase levels a metasurface contains, the more efficient the optical device formed by it will be.

[0055] According to one embodiment, the nanohole or nanopillar comprises a sidewall and a bottom or top, and a transparent dielectric material is deposited on the sidewall and the bottom or top to form a dielectric cylinder.

[0056] A transparent dielectric material is deposited on the sidewalls of the nanoholes or nanopillars and on the bottom of the nanoholes or top of the nanopillars.

[0057] Transparent dielectric material deposited within the nanoholes or around the nanopillars forms a dielectric cylinder containing the nanotube within the dielectric cylinder, where the phase change of the incident light is controlled by the height, diameter, and thickness of the sidewalls of the dielectric cylinder.

[0058] Nanotubes are the sidewalls of a dielectric cylinder with a hollow core between them.

[0059] Furthermore, a transparent dielectric material is deposited on the flat surface of the metasurface between the nanopillars or nanoholes.

[0060] According to one embodiment, the plurality of shape layers are ring-shaped, and each shape layer is continuous along the ring shape.

[0061] By "multiple shaped layers in a ring shape," it should be understood that each layer forms a closed loop around a center, which may be a circle, an ellipse, or any other shape that creates a closed loop similar to a circle or an ellipse, but not necessarily an exact circle or ellipse. Furthermore, the innermost layer may form a disk that covers the center.

[0062] The ring-shaped shaped layer may be wider near the center and then become smaller further away from the center.

[0063] According to one embodiment, an optical metasurface includes multiple Fresnel rings forming a Fresnel metasurface metalens, each Fresnel ring including two or more shaped layers having different thicknesses.

[0064] For example, each Fresnel ring may include two or more geometric layers with different thicknesses, which result in the geometric layers belonging to different phase levels.

[0065] According to one embodiment, the plurality of shape layers form a closed concentric loop, preferably a circle or an ellipse.

[0066] The shaped layer may be annular, meaning that the layer is shaped like a ring or like a series of concentric rings arranged around a center.

[0067] Each Fresnel ring includes two or more shaped layers, each concentrically arranged around the center. Each shaped layer preferably has a uniform thickness to achieve the same phase shift throughout the shaped layer. Each ring-shaped shaped layer can be elliptical or circular.

[0068] For example, there may be four geometric layers within a Fresnel ring, and the layers may have thicknesses of, for example, 0 nm, 33 nm, 66 nm, and 99 nm, respectively.

[0069] The center may be covered by a disk of dielectric material. The innermost shape layer may form a disk that covers the center. All other shape layers are disposed around the innermost shape layer. Note that the shape layer may have a thickness of 0 nm. Thus, the center may simply be a bare substrate.

[0070] The Fresnel rings form a Fresnel metasurface metalens, which is a counterpart to a Fresnel lens, which consists of a series of concentric rings that are much thinner than conventional lenses, reducing the amount of material required.

[0071] For example, classical ophthalmic lenses, such as those used in eyeglasses, control the path of light through optical refraction by engineering the shape and thickness of a transparent material. They rely on light propagating within the lens material over distances much larger than its wavelength to accumulate the phase change necessary for the desired optical functionality. This dictates how thin the lens can be.

[0072] The thickness and weight of high-power lenses are unresolved problems related to the fact that today's lenses are made by engineering the shape and thickness of the transparent lens material to control refraction, as discussed above.

[0073] Because metasurfaces are thin and lightweight, metalenses and other optical devices can be made significantly lighter than classical ophthalmic lenses. However, using metasurfaces to create effective optical components, such as lenses, that can achieve the required optical properties and quality has not been as successful as desired in the past.

[0074] Using metasurface metalens as Fresnel lenses results in lenses that are much lighter than those used by conventional optical systems.

[0075] According to one embodiment, the transparent dielectric material is selected from the group consisting of TiO2, Al2O3, Si, SiO2, Ge, GaAs, InP, HfO2, BaTiO3, Pb[Zr x Ti 1-x ]O3, SrTiO3, Ba (1-x) Sr x High refractive index dielectric materials selected from the list of TiO3, PbTiO3, CaTiO3, MgO, and ZrO2.

[0076] In the present application, titanium dioxide (TiO2) is the preferred material for the transparent dielectric material, and TiO2 is used in the mentioned examples, but any high refractive index dielectric material instead of TiO2 can be considered for the present invention. These materials include, for example, aluminum oxide (Al2O3), silicon (Si), silicon dioxide (SiO2), germanium (Ge), gallium arsenide (GaAs), indium phosphide (InP), hafnium dioxide (HfO2), barium titanate (BaTiO3), lead zirconate titanate (Pb[Zr]), and the like. x Ti 1-x ]O3(0≦x≦1)), strontium titanate (SrTiO3), strontium barium titanate (Ba (1-x) Sr x TiO3 (0≦x≦1), lead titanate (PbTiO3), calcium titanate (CaTiO3), magnesium oxide (MgO), zirconium dioxide (ZrO2).

[0077] It should be understood that a transparent dielectric material is a high refractive index dielectric material, meaning that it is a type of material with a high refractive index that bends light more than a material with a low refractive index. The bending of light requires a phase shift gradient corresponding to the change in thickness of a conventional wedge or prime. The higher the refractive index, the less material (thickness) is required. These materials are often used in optical devices such as lenses because they can reduce the size and weight of the device while still maintaining its optical performance.

[0078] A second aspect of the present invention relates to an optical device comprising a metasurface, the optical device being selected from the list of a metalens, a blazed diffraction grating, a phase plate, a hologram, a vortex beam generator, a spatial light modulator, an optical switch.

[0079] Metasurfaces can be used in several different optical devices. A blazed grating is a type of diffraction grating consisting of a surface with many closely spaced parallel lines. It diffracts light in a specific direction, known as the "blaze direction," designed to maximize diffraction efficiency for a specific wavelength or range of wavelengths. Blazed gratings work by exploiting the principle of diffraction: light is bent as it passes through the closely spaced lines of the grating. This bending of light causes constructive interference in the blaze direction, resulting in high diffraction efficiency. Blazed gratings are used in a variety of applications, including spectroscopy, laser beam shaping, and optical communication systems.

[0080] A phase plate is a device used to manipulate the phase of light waves. Phase plates are used to change the phase of light by modifying its path length through a transparent material.

[0081] A hologram is a type of optical illusion that creates a three-dimensional image of an object by projecting laser light onto a photographic plate or another medium that records the object's optical interference pattern. Our optical metasurfaces can be used as such a medium.

[0082] A vortex beam generator is a device that produces a type of laser beam known as a vortex beam. A vortex beam is a beam of light that has a phase singularity, or a point where the phase of the light suddenly changes. Vortex beam generators typically use a phase plate or other optical element to impose a phase vortex onto a conventional laser beam, creating a vortex beam. The optical metasurfaces of the present invention can be used as such optical elements.

[0083] Spatial light modulators are used to manipulate the phase and amplitude of light beams. They can be used in applications such as beam shaping, holographic displays, and adaptive optics. The optical metasurfaces of the present invention can be used as such spatial light modulators.

[0084] A third aspect of the invention relates to a pair of eyeglasses comprising at least one metasurface according to claim 1, wherein the shape layer is ring-shaped.

[0085] The metasurface can form a metalens. Two metalenses can be used for a pair of eyeglasses worn by a person. Each shaped layer is preferably continuous along the ring shape.

[0086] Optical metasurfaces can form ultralight lenses for eyeglasses, with lenses realized as thin nanostructured films (<1 mm), suitable for lens production, where identical mass-manufactured nanostructured substrates are transformed into personalized optical components by maskless photolithography, making optical metasurfaces a cost-effective way to mass-customize lenses.

[0087] This aspect of the invention is particularly advantageous, but not exclusive, in that metalens are significantly lighter than classic ophthalmic lenses, and therefore a pair of eyeglasses comprising a metalens is significantly lighter than a classic pair of eyeglasses.

[0088] A fourth aspect of the present invention relates to a method for fabricating an optical metasurface for interacting with incident light, the method comprising: - providing a transparent substrate comprising a plurality of nanoholes or nanopillars, the nanoholes or nanopillars having vertical or substantially vertical sidewalls extending perpendicular to a base plane of the transparent substrate; - covering at least a portion of the transparent substrate with shaped layers of transparent dielectric material, such that each shaped layer covers a plurality of nanoholes or nanopillars in the transparent substrate.

[0089] A transparent substrate is provided, which may be made in different ways, and how the transparent substrate is made is not part of the present invention.

[0090] The transparent substrate includes a plurality of nanoholes or nanopillars. A portion of the transparent substrate is covered by a shaped layer of different thickness. A portion of the transparent substrate may not be covered at all.

[0091] This aspect of the invention is particularly, but not exclusively, advantageous in that the method according to the invention may result in light-weight optical devices and optical devices with high optical properties.

[0092] According to one embodiment, covering at least a portion of the transparent substrate with a shaped layer of transparent dielectric material comprises: - a) covering a transparent substrate and / or a previously deposited transparent dielectric material with a layer of photoresist; -b) exposing the photoresist to electromagnetic radiation, wherein the transparent dielectric material is placed in contact with a transparent substrate or a previously deposited transparent dielectric material, or wherein the transparent dielectric material is not placed in contact with a transparent substrate or a previously deposited transparent dielectric material; -c) removing either the photoresist that has been exposed to electromagnetic radiation or the photoresist that has not been exposed to electromagnetic radiation; -d) covering at least a portion of the substrate and / or a previously deposited transparent dielectric material with a deposited layer of transparent dielectric material; - e) removing the remaining photoresist, thereby also removing the transparent dielectric material deposited on top of the photoresist; -f) repeating steps a) to e) a predetermined number of times.

[0093] A shape layer can include zero, one, two, or more deposition layers. The deposition layers can be of different thicknesses. Essentially, the idea is to deposit different deposition layers of transparent dielectric material to form a shape layer.

[0094] The lift-off process may use a positive tone photoresist, in which areas of the photoresist irradiated with electromagnetic radiation, preferably ultraviolet radiation, are removed, or a negative tone photoresist, in which areas not irradiated are removed.

[0095] When the transparent dielectric material is first deposited, since there is no previously deposited transparent dielectric material, a layer of photoresist is placed on the transparent substrate. Then, a portion of the transparent photoresist is irradiated with electromagnetic radiation, and then the irradiated photoresist is removed or the unirradiated photoresist is removed, thereby transferring the desired pattern / shape of the transparent dielectric material to be deposited into the photoresist.

[0096] After removing a portion of the photoresist, a transparent dielectric material is deposited, covering both the photoresist and the substrate, and the photoresist is then removed. The remaining photoresist is then removed, leaving the transparent dielectric material deposited on top of the photoresist to form the first deposition layer.

[0097] If two or more layers of transparent dielectric material are to be deposited, steps a) through e) are repeated. For each additional layer of transparent dielectric material, the transparent substrate and the previously deposited transparent dielectric material are first covered with a layer of photoresist in step a), and then a portion of the photoresist is irradiated with electromagnetic radiation in step b). Then, in step c), the irradiated or unirradiated photoresist is removed where the next layer of transparent dielectric material will be deposited. Then, in step d), a transparent dielectric material is deposited, and in step e), the remaining photoresist and, thereby, the transparent dielectric material deposited on top of the photoresist are removed, leaving an additional layer of transparent dielectric material on top of the previously deposited transparent dielectric material and / or on top of the substrate. The additional layer typically covers a portion of the previously deposited transparent dielectric material and a portion of the substrate, in this case, a portion of the substrate that was not previously covered.

[0098] Steps a) through e) are repeated a preselected number of times to form a feature layer having the required number of phase levels. Each time steps a) through e) are repeated, the number of phase levels increases. If the process is performed only once, the metasurface contains two phase levels. If the process is performed once, and thereby twice, the metasurface contains four phase levels. If the process is performed three times, the metasurface contains eight phase levels; if the process is performed four times, the metasurface contains 16 phase levels, and so on.

[0099] It is also possible to combine different dielectric materials by using different transparent dielectric materials in step d) each time the process is carried out.

[0100] The first deposited layer is typically the thickest. The second layer may be half the thickness of the first, the third layer may be half the size of the second, etc., so that with each iteration of depositing a layer, the layer is half the thickness of the previous layer. Thus, the number of phase levels doubles with each additional layer.

[0101] In an alternative embodiment, covering at least a portion of the transparent substrate with a shaped layer of transparent dielectric material is achieved by depositing a layer of transparent dielectric material on the transparent substrate and then cutting away a portion of the transparent dielectric material to obtain the shaped layer.

[0102] According to one embodiment, covering at least a portion of the transparent substrate with a shaped layer of transparent dielectric material comprises: - covering at least a portion of a transparent substrate with a transparent dielectric material; - geometrically modifying the transparent dielectric material on the transparent substrate by removing portions of the transparent dielectric material to form a shaped layer.

[0103] "Geometrically modifying" may be understood as modifying the geometry, thereby modifying the shape, size, and / or relative position of the transparent dielectric material. It may be understood that geometric modification of high refractive index dielectric structures may affect their optical properties.

[0104] The layer of transparent dielectric material can serve to remove portions of the transparent dielectric material, which increases the possibility of modifying the metasurface.

[0105] According to one embodiment, the method comprises: further comprising removing a portion of the layer of transparent dielectric material by laser ablation.

[0106] Laser ablation or photoablation is the process of removing material from a solid (or sometimes liquid) surface by irradiating it with a laser beam. At low laser fluxes, the material is heated by the absorbed laser energy and vaporizes or sublimes. At high laser fluxes, the material is typically converted to plasma. Laser ablation usually refers to removing material with a pulsed laser, although it is possible to ablate material with a continuous wave laser beam.

[0107] The described "high laser flux" and "low laser flux" regimes depend on the particular material of the meta-atom, the particular geometric shape and size of the meta-atom, the particular laser wavelength relative to the optical spectrum of the meta-atom material, and the optical resonance of the meta-atom.

[0108] Portions of the transparent dielectric material can be removed by laser ablation, whereby a smoother surface can be obtained by removing gradual transitions between different phase levels or by subdividing phase levels into additional phase levels.

[0109] The first, second, third and fourth aspects of the invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0110] Optical metasurfaces and methods for fabricating optical metasurfaces according to the present invention will be described in more detail with reference to the accompanying drawings, which illustrate one way of implementing the invention and should not be construed as limiting other possible embodiments within the scope of the appended claims. [Brief explanation of the drawings]

[0111] [Figure 1] 1 illustrates an optical metasurface according to the present invention. [Figure 2]1 shows a truncated waveguide metasurface architecture used in the present invention. [Figure 3] 1 shows a cross section of a meta-atom with a nanohole. [Figure 4] 1 shows a cross section of a meta-atom with nanopillars. [Figure 5] We outline a process flow for the cost-effective fabrication of personalized optical metasurfaces. [Figure 6] 1 shows the creation of four phase levels by a two-step UV lithography lift-off process. [Figure 7] We present an example of numerical simulation for metasurface design. [Figure 8a] 1 illustrates a metalens, an optical metasurface in accordance with the present invention, comprising multiple ring-shaped shaped layers. [Figure 8b] 4 shows the four ring-shaped layers of Fresnel rings. [Figure 9a] 1 shows another optical metasurface in accordance with the present invention: a blazed grating. [Figure 9b] Figure 9a shows the metasurface with four different thicknesses of shaped layers. [Figure 10a] 10 shows the simulated phase shift as a function of the TiO2 thickness of the dielectric material for different nanohole diameters. [Figure 10b] Figure 1 shows the simulated phase shift as a function of the dielectric material TiO2 thickness t for different nanohole depths h. [Figure 11a] 10 shows the simulated phase shift as a function of the TiO2 thickness of the dielectric material for different periods. [Figure 11b] 10 shows the simulated phase shift as a function of TiO2 thickness for different diameter to period ratios. [Figure 12](Top left) Microscope image of an 8 mm diameter 15 diopter binary phase Fresnel metasurface metalens, (top right) microscope image of an 8 mm diameter 2.5 diopter binary phase Fresnel metasurface metalens, and (bottom) microscope image of the 15 diopter lens focused on the DTU logo. [Figure 13] The following phase lens designs are shown: (a) the desired phase modulation profile for the metalens, (b) the phase discretization, and (c) the theoretical lens efficiency as a function of the phase discretization level N. [Figure 14] 1 shows an SEM image of the first lift-off process on a fused silica substrate. [Figure 15] 1 shows an SEM image of the second lift-off process on a fused silica substrate. [Figure 16] 1 is a flow chart illustrating the main method of the present invention. [Figure 17] 10 is a flowchart illustrating an alternative method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0112] FIG. 1 shows an optical metasurface 10 according to the present invention. The metasurface comprises a transparent substrate 16 with a plurality of regularly spaced nanoholes 17. The nanoholes have sidewalls 24 that extend perpendicular to a base plane 23, which corresponds to the surface of the substrate. A plurality of shaped layers 11 are deposited on the substrate.

[0113] Figure 1 shows four feature layers. Each feature layer shown in Figure 1 has a different phase level, here Δφ = 0, Δφ = π / 2, Δφ = π, and Δφ = 3π / 2, which are obtained by overlaying two deposited layers 25 (see Figure 7) of patterned TiO films with thicknesses t = h1 and t = h2 by conformal deposition (here, atomic layer deposition, ALD) on the surface of an optically transparent substrate pre-patterned with a uniform nanohole array (hole depth h, hole diameter d, hole array period p). This divides the surface 26 into regions with TiO film thicknesses t of 0, h1, h2, or h1 + h2, each with a corresponding different optical phase modulation Δφ.

[0114] The nanohole diameter d and the period p of the nanohole array are subwavelength, here p = 200 nm, while the size of the TiO2 film pattern elements is 500 nm to 10 mm. The patterned TiO2 film is produced by two successive photolithography processes: UV lithography, conformal deposition of TiO2 (thickness h1), lift-off, UV lithography (with overlay alignment to the first TiO2 pattern), conformal deposition of TiO2 (thickness h2), and lift-off.

[0115] This process has been demonstrated to produce four phase-level phase-modulating Fresnel lenses and diffraction gratings.

[0116] This process has broader / general applications for diffractive optical elements, including optical gratings, phase masks, and holograms. The surface is divided into pixels with side lengths up to 1 micrometer (limited by the applied UV lithography), and each pixel is assigned to one of four available phase levels (specific values ​​given by the nanohole geometry and TiO2 film thickness).

[0117] FIG. 2 outlines the truncated waveguide metasurface architecture and meta-atoms used in the present invention.

[0118] Figure 2 (left) shows a metasurface 10 comprising a transparent dielectric material 15 on a transparent substrate 16. The transparent substrate has a nanohole 17, which is covered by a transparent dielectric material 15 that also recesses the nanohole 17 and is deposited at the nanohole bottom 5 and nanohole sidewalls 24, leaving a nanotube 21 in the center of the nanohole.

[0119] FIG. 2 (right) illustrates a meta-atom 20 that is part of a metasurface containing only one nanohole or one nanopillar, which may be covered by a transparent dielectric material 15, leaving behind a nanotube 21.

[0120] 3 shows a cross section of a meta-atom 20 that includes a substrate 16 covered by a dielectric material 15. Nanotubes 21 are formed within nanoholes 17 in the substrate 16 when the dielectric material 15 is deposited on the substrate 16.

[0121] A medium-index transparent dielectric substrate 16, exemplified here by fused silica with a refractive index n of about 1.46, is fitted with an array of identical nanoholes 17, with a nanohole diameter d of about 150 nm, a nanohole depth h of about 500 nm, and an array period p of about 200 nm. The truncated waveguide meta-atom 14 is formed by conformal deposition of a dielectric material 15, preferably TiO2 (with a refractive index n of about 2.7) of thickness t. For a given nanohole array dimension, diameter d and height h, the phase change of the transmitted light is controlled by the thickness t of the deposited material, i.e., the nanotube wall thickness.

[0122] 4 shows a cross section of a meta-atom 20 that includes a substrate 16 covered by a dielectric material 15. Dielectric cylinders 19 are formed on the nanopillars 18 of the substrate 16 when the dielectric material 15 is deposited on the substrate 16.

[0123] The nanopillar depth, h, is preferably approximately 500 nm, the pillar diameter, d, is 300 nm or less, and the period, p, which is the center-to-center distance of the pillars, is 100-400 nm, e.g., 200 nm. Obviously, it is observed that the pillar diameter should be smaller than the center-to-center distance.

[0124] Figure 5 shows an overview of the process flow for the cost-effective fabrication of individualized optical metasurfaces 10 by UV lithography on a nanostructured substrate 16. Each panel shows a cross-section of a metasurface component at a different step in the process flow. Panels (1)-(9) show the fabrication of a transparent dielectric substrate 16 with an array of identical nanoholes 17 using nanoimprint lithography (NIL). Panels (10)-(14) show the deposition of a transparent dielectric material 15 in the form of a patterned film of TiO2 to define a metasurface 10 with two distinctly shaped layers 11.

[0125] A metasurface 10 encoded with multiple shaped layers 11 corresponding to different phase levels is defined by depositing a transparent dielectric material 15, preferably TiO2, in a pattern as outlined in Figure 5. The TiO2 deposition is selectively controlled by masking the metasurface 10 with photoresist 40, known as a lift-off process. In this way, two shaped levels 11 can be achieved, one containing TiO2 and the other not, which results in a phase difference between the two shaped levels.

[0126] The spin-coated photoresist 40 of step 10 of FIG. 5 is exposed to UV light in step 11 of FIG. 5 using a maskless aligner for UV lithography (e.g., Heidelberg Instruments' MLA150 maskless aligner), which has a practical resolution limit of 1 μm. Therefore, this technique can be used to produce metalenses with a diameter of 6 cm and a focusing power of up to 9 diopters. The exposed portions of the photoresist 40 are dissolvable using a chemical developer, such as Microchemical's AZ® 726 MIF. Thus, the nanostructured fused silica surface of the transparent substrate 16 can be selectively covered with the unremoved photoresist 40. A dielectric material 15 is deposited in step 13 of FIG. 5, preferably using atomic layer deposition (ALD).

[0127] This conformal deposition method covers all exposed surfaces with a uniform layer of TiO2. The unexposed photoresist 40 can then be removed in an acetone solution (step 14 in Figure 5) using ultrasound. This process, known as a lift-off process, dissolves the photoresist 40 and removes it, along with the TiO2 on top of it, from the fused silica nanostructures on the transparent substrate 16. Thus, TiO2 remains on the fused silica nanostructures on the transparent substrate 16 that were not covered by the photoresist. In this way, the shaped layer 11 can be created. This enables the rapid fabrication of large-area optical metasurfaces at the expense of only two phase levels. Subsequent lift-off processes can fabricate multiple phase levels. A four-phase-level optical metasurface can be fabricated by two consecutive lift-off processes.

[0128] The steps are illustrated in FIG. Step 1: The transparent substrate of choice is fused silica. Step 2: A layer of poly-Si is deposited onto the substrate using low pressure chemical vapor deposition (LPCVD) techniques. Step 3: Use a spin-coating procedure to deposit a UV nanoimprint resist layer on the poly-Si. Step 4: Using ultraviolet nanoimprint lithography, remove portions of the spin-coated UV nanoimprint resist at locations where nanoholes 17 will be made. Step 5: Remove further UV nanoimprint resist by descum method. Step 6: Using dry etching, remove the poly-Si where nanoholes 17 will be made. Step 7: Nanoholes 17 are further created in the substrate by using a dry etching method. Step 8: Remove remaining UV nanoimprint resist by plasma ashing. Step 9: Remove the remaining poly-Si by a wet etching process. Step 10: Photoresist 40 is deposited on the substrate. Steps 11 and 12: The photoresist is removed where a transparent dielectric material 15 is to be deposited onto the substrate by UV exposure and development. Step 13: TiO2 is deposited onto the photoresist and substrate. Step 14: A lift-off process is used to remove the photoresist and the TiO2 on top of the photoresist, leaving the substrate with the deposited TiO2. Steps 10-14 can be repeated to create TiO deposition layers of different thicknesses and to create more phase levels.

[0129] Figure 6 shows a two-step UV lithography lift-off process, where the first deposition (S1) step provides a 1π phase shift, and the second step (S2) provides a π / 2 phase shift, and when added to S1, a 1.5π phase shift.

[0130] A metasurface with four phase levels 30 can be fabricated by overlaying two UV lithography and lift-off process steps, as illustrated in Figure 6. The first step (S1) consists of depositing a TiO2 layer 25 with a thickness h1, which provides a π phase shift. The second step (S2) consists of depositing a TiO2 layer 25 with a thickness h2, which provides a π / 2 phase shift. In addition, if S2 overlaps with S1, a 1.5π phase shift can be achieved by obtaining a TiO2 thickness of h1 + h2. Through this two-step lift-off process, a total of four phase levels are obtained: 0, 1 / 2, 1, and 1.5π phase shifts. Each phase level corresponds to a shaped layer of the same thickness. Each phase level can be achieved by several shaped layers of the same thickness. A metalens with such a phase profile is estimated to have a diffraction efficiency of approximately 70-80%. Initial tests have verified that the Heidelberg Instruments MLA150 maskless aligner can provide the required overlay accuracy in the DTU nanolab.

[0131] A phase shift of 1π radians corresponds to a rotation of 180 degrees in the complex plane. In a wave or signal, a phase shift of 1π means that the wave or signal is delayed by half a period, or is 180 degrees out of phase. In other words, the peaks of the wave or signal are shifted by half a period.

[0132] Figure 7 shows an illustration of the numerical simulation of the metasurface design. Figure 7(a) shows the overall geometry of the model. Figure 7(b) shows the individual components / materials in the model: the substrate 16, the dielectric material 15, and the air 42.

[0133] To realize a metasurface 10 with a specific phase profile Δφ(x,y), a COMSOL (finite element simulation) model was developed. The model solves for a plane wave propagating through the metasurface for a desired wavelength, allowing for fast calculation of the transmittance, absorptance, and S-parameters (from which the phase change can be determined) of a given metaunit cell. The model can be seen in Figure 7. The model also allows for investigation of the electric field strength and stored energy at specific resonant modes, which can be used when the metasurface is applied for optical detection.

[0134] FIG. 8a illustrates an optical metasurface 10 according to the present invention. The optical metasurface forms a Fresnel metasurface metalens. The metasurface includes multiple ring-shaped layers 11 that form metalenses corresponding to Fresnel lenses, with four ring-shaped layers forming a Fresnel ring 12. Each Fresnel ring may include four ring-shaped layers 11a, 11b, 11c, and 11d. FIG. 8b is an enlarged cross-section of FIG. 8a, illustrating a portion of the four ring-shaped layers 11a, 11b, 11c, and 11d that form a Fresnel ring. The innermost ring-shaped layer covers the center 13, thus forming a disk, while all other ring-shaped layers have open centers.

[0135] FIG. 9a shows another optical metasurface 10 according to the present invention. The metasurface includes four shaped layers of different thicknesses, forming a four-level blazed grating, whereby the blazed grating includes four phase levels. Here, the shaped layers are substantially linear. FIG. 9b is a magnified image of the cross section of FIG. 9a, showing the four shaped layers of different thicknesses.

[0136] Figure 10a shows the simulated phase shift as a function of the TiO thickness t of the dielectric material 15 for different nanohole diameters d for metasurface geometries: h = 500 nm and p = 200 nm. As the diameter increases, the available phase span also increases.

[0137] From the Comsol simulation, the phase shift Δφ of the transmitted light measured relative to the bare nanostructured substrate, i.e., TiO2 thickness t = 0, is extracted. In Fig. 10a, we evaluate the influence of the nanohole diameter d and TiO2 thickness t for a metasurface with period p = 200 nm and nanohole depth h = 500 nm.

[0138] As can be seen from Figure 10a, the phase shift Δφ increases with the TiO2 thickness t of the dielectric material 15. It is also observed that larger nanohole diameters d provide larger phase shifts as the TiO2 thickness is varied. Therefore, it is preferable to increase the nanohole diameter as much as possible. However, it is important to keep the diameter d below a period of p = 200 nm; otherwise, the nanoholes will begin to merge, resulting in shallower nanoholes (smaller h) or, in the worst case, completely destroying the unit cell structure.

[0139] Figure 10b shows the simulated phase shift as a function of the TiO2 thickness t of the dielectric material 15 for different nanohole depths h for geometries: d = 180 nm and p = 200 nm. As the nanoholes penetrate deeper into the substrate, the phase span increases. A depth of 500 nm is required to span the 2π phase space.

[0140] The effect of nanohole depth h on metasurfaces with d = 180 nm and p = 200 nm was investigated using Comsol simulations. Three different nanohole depths were chosen: h = [500, 600, 700] nm. The results of these simulations are shown in Figure 10b. First, note that a minimum nanohole depth of h = approximately 500 nm is required to span the Δφ = 2π phase shift range before the nanoholes are filled with TiO2 (d = p). Second, as the nanohole depth increases, higher phase shifts are expected when the TiO2 thickness t is varied. While the specified nanohole depth of 500 nm spans the 2π phase space, deeper nanohole depths are preferable. Clearly, there is a limit to how deep nanoholes can be fabricated, and a value of 500 nm may already be approaching this limit.

[0141] Figure 11a shows the simulated phase shift as a function of TiO2 thickness for the dielectric material 15 for different periods for the following geometries: h = 500 nm and d = 170 nm. A phase span penalty is observed as the period increases. (Right) Simulated phase shift as a function of TiO2 thickness for different diameter to period ratios for the combination of d = [160, 170, 180, 190], p = [190, 200, 210, 220] nm, and h = 500. It can be observed that d / p is an important design parameter to be maximized.

[0142] The effect of the period p was investigated. Four periods were chosen: p = [190, 200, 210, 220] nm. The results of these simulations are shown in Figure 11a. Note that this suggests that shortening the period would be desirable. This may follow the same trend as increasing the diameter, so the figure of merit to maximize is the ratio of nanohole diameter to period, or d / p. This is shown in Figure 11b. Therefore, if the period is changed from the standard geometry, the nanohole diameter should also follow, and generally, a higher d / p ratio is preferable. Note, however, that increasing the d / p ratio by minimizing the period may limit the maximum possible TiO2 thickness.

[0143] Further Comsol simulations show that the obtained phase shift has little or negligible dependence on the dielectric substrate refractive index for values ​​between 1.4 and 1.5.

[0144] Figure 12 shows: (Top left) Microscope image of an 8 mm diameter 15 diopter binary-phase Fresnel metasurface metalens. (Top right) Microscope image of an 8 mm diameter 2.5 diopter binary-phase Fresnel metasurface metalens. (Bottom) The 15 diopter lens is focused on the DTU logo.

[0145] A prototype lens was demonstrated (see Figure 12). The lens is a binary-phase Fresnel zone lens with a lens diameter of 8 mm and phase modulation Δφ~π. Two lenses were fabricated: one with a diopter of 2.5 (40 cm focal length) and one with a diopter of 15 (6.7 cm focal length). The diffraction efficiency was estimated to be 41% for the 15 diopter lens, close to the theoretical maximum (40.5%) for a binary-phase lens.

[0146] The metalens includes a ring-shaped shaped layer that is generally wider closer to the center and smaller further from the center.

[0147] Lithographic resolution required for a Fresnel zone plate lens with N phase levels:

[0148] The demonstrated metalens is designed as a phase-modulating Fresnel zone plate. The ring-shaped layer has a radius r n Having:

number

[0149] where n=1, 2, ... is the number of layers, λ is the wavelength of the incident light, and f is the focal length.

[0150] The focal length is the distance between the lens and the point where light converges to a single point.

[0151] Diameter D l For a (two phase level) lens, the thinnest, outermost layer has a width of:

number

[0152] Lens diameter D l = 4 cm, the minimum feature size Δr required to write an f = 8.33 cm lens (12 diopters) with two phase levels min is 1.1 μm (using λ=532 nm).

[0153] Correspondingly, lenses with N=3, 4, ... phase levels require lithographic resolution (minimum line width).

number

[0154] Figure 13 illustrates the design of a phase lens. Figure 13(a) shows that the phase modulation profile required for the metalens (solid curve) is wrapped to 2π (dashed curve) to form concentric "Fresnel zones" with a phase progression from 0 to 2π. Figure 13(b) illustrates the phase discretization. To create the metalens, the 0 to 2π phase modulation in each zone (smooth curve) is discretized into N phase levels (dashed step curve). Figure 13(c) shows the theoretical lens efficiency as a function of phase discretization level N.

[0155] Lens efficiency (i.e., the fractional power of the incident light focused on the lens) can be significantly improved by increasing the number of phase levels 30. In a phase-modulated FZP lens, the phase modulation profile required for the lens is wrapped from 0 to 2π. See Figure 13(a). To create a metalens, the 0 to 2π phase modulation is discretized into a number of phase levels, N, as shown in Figure 13(b). A binary phase metalens with N = 2 phase levels (0 and π) has a theoretical maximum efficiency of 40.5%. Metalens efficiency increases with increasing number of phase levels 30, as shown in Figure 13(c).

[0156] Processes on fused silica Sample preparation The process begins with the preparation of a nanostructured fused silica substrate 16 using nanoimprinting. A master stamp with silicon nanoholes was used, processed by electron beam patterning, followed by silicon dry etching on a 4-inch silicon wafer. A daughter stamp with nanopillars was fabricated via imprinting using the photoresist OrmoStamp. The daughter stamp was then transferred via imprinting to a fused silica wafer, which had been pretreated with LPCVD silicon deposition. The photoresist 40 used was mr-NIL200, and a nanohole pattern in the photoresist was constructed on the fused silica wafer. To develop the nanohole structure on the fused silica wafer, O2 plasma etching of the photoresist and reactive ion etching (RIE) of silicon and silicon oxide were performed sequentially. Then, photoresist and silicon strips were removed by dry etching to complete the preparation of the nanostructured fused silica substrate.

[0157] Lift-off process Using the nanostructured fused silica substrate described above, large-area UV lithography and lift-off patterning of TiO was carried out. In the first lithography, photoresist AZ5214E ​​was spin-coated onto a 4-inch fused silica wafer with a thickness of approximately 1.5 μm, followed by 70 mJ / cm 2 A maskless aligner (MLA) was written with a dose of 0.01 μm and developed with a single puddle for 60 seconds. Next, ALD deposition of 66 nm of TiO2 was performed, with the deposition temperature set to 100 °C. After ALD deposition, lift-off was performed in an ultrasonic acetone bath to remove the photoresist pattern and TiO2 above these photoresist patterns. The areas without the photoresist pattern (developed after mask UV writing) allowed TiO2 to deposit directly onto the nanoholes, which allowed the TiO2 to remain after the lift-off process, resulting in a phase difference between adjacent zones. The lift-off acetone bath temperature was approximately 30 °C.

[0158] After the lift-off process, the nanohole structure on the fused silica wafer was examined using a scanning electron microscope (SEM). For the second lithography and lift-off patterning, the process was the same as the first, except that a 33 nm thick TiO2 was coated using ALD. Thus, by combining the first 66 nm of TiO2, there were four levels of TiO2 with thicknesses of 0 nm, 33 nm, 66 nm, and 99 nm, with the 99 nm being the overlap of the two TiO2 depositions.

[0159] SEM image after lift-off Figure 14 shows an SEM image of the first lift-off process on a fused silica substrate. After the first lift-off process, the nanohole structure was confirmed using SEM. See Figure 14. The SEM image shows that the nanoholes were retained after the lift-off process. The left scan of Figure 14 shows a crossover between nanoholes with and without TiO2 deposition. The left side shows nanoholes covered with 66 nm of TiO2, which are smaller in size than the uncovered nanoholes (right side). This TiO2 coating provides phase retardation.

[0160] Figure 15 shows SEM images of the second lift-off process on a fused silica substrate. The second process appears to be good, with four phase levels corresponding to four TiO thicknesses: 0, 33, 66, and 99 nm, clearly visible in terms of both color and nanohole size.

[0161] Figures 9a and 9b show optical microscope images of a four-level Fresnel lens. Similar to the SEM scan, four different levels are observed, corresponding to four TiO thicknesses: 0, 33, 66, and 99 nm.

[0162] FIG. 16 is a flowchart illustrating the main method of the present invention. First, in step S1, the method provides a transparent substrate 16 having a plurality of nanoholes or nanopillars. Then, in step S2, a layer of photoresist 40 covers the transparent substrate 16 and / or a previously deposited transparent dielectric material 15. In step S3, the photoresist is exposed to electromagnetic radiation, and the transparent dielectric material is either placed in contact with the transparent substrate or a previously deposited transparent dielectric material, or the transparent dielectric material is not placed in contact with the transparent substrate or a previously deposited transparent dielectric material. In step S4, either the photoresist exposed to electromagnetic radiation or the photoresist not exposed to electromagnetic radiation is removed. In step S5, at least a portion of the substrate 15 and / or the previously deposited transparent dielectric material 16 is covered with a deposited layer 25 of transparent dielectric material. In step S6, the remaining photoresist 40 is removed, thereby also removing the transparent dielectric material deposited on top of the photoresist. Steps S2-S6 can be repeated a predetermined number of times. If steps S2-S6 are to be repeated, the method proceeds to step S2; if not, the method is complete.

[0163] 17 is a flowchart showing an alternative method of the present invention. First, in step S1, the method provides a transparent substrate having a plurality of nanoholes or nanopillars. Then, in step S8, the method covers at least a portion of the transparent substrate 16 with a transparent dielectric material 15. Then, in step S9, the method geometrically modifies the transparent dielectric material 15 on the transparent substrate 16 by removing a portion of the transparent dielectric material 15 to form a shaped layer (11).

[0164] While the present invention has been described with reference to specified embodiments, it should not be construed as being limited to the examples presented. The scope of the present invention is defined by the appended claims. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Moreover, references to references such as "a" or "an" should not be construed as excluding plurals. The use of reference signs in the claims for elements shown in the drawings should also not be construed as limiting the scope of the present invention. Furthermore, individual features recited in different claims may be advantageously combined, and reciting these features in different claims does not exclude that combination of features is impossible or advantageous.

Claims

1. An optical metasurface (10) that interacts with incident light, comprising: a transparent substrate (16) comprising a plurality of nanoholes (17) or nanopillars (18), said nanoholes or nanopillars having vertical or substantially vertical sidewalls (24) extending perpendicular to a base plane (23) of said substrate (16); - a plurality of shaped layers (11) comprising a transparent dielectric material (15), each shaped layer covering a plurality of said nanoholes (17) or said nanopillars (18) of said transparent substrate; An optical metasurface comprising:

2. the distance between two adjacent nanoholes (17) or nanopillars (18) is less than half the wavelength of the incident light, which can be ultraviolet, visible, near-infrared and / or infrared; The optical metasurface of claim 1 .

3. the optical metasurface (10) is a truncated waveguide metasurface comprising a two-dimensional array of meta-atoms (20), each meta-atom comprising one nanohole (17) or nanopillar (18); 3. The optical metasurface of claim 1 .

4. two adjacent shape layers (11) are of different thickness (t), which results in different phase shifts of the incident light; The optical metasurface according to any one of claims 1 to 3.

5. The nanohole (17) or nanopillar (18) comprises a sidewall (24) and a bottom (27) or top (28), and the transparent dielectric material (15) is deposited on the sidewall and the bottom or top to form a dielectric cylinder (19). The optical metasurface according to any one of claims 1 to 4.

6. The plurality of shaped layers (11) are ring-shaped, and each shaped layer is continuous along the ring shape. The optical metasurface according to any one of claims 1 to 5.

7. The optical metasurface (10) includes a plurality of Fresnel rings (12) forming a Fresnel metasurface metalens, each Fresnel ring including two or more shaped layers (11) having different thicknesses. The optical metasurface of claim 6.

8. The optical metasurface according to any one of claims 1 to 7, wherein the plurality of shaped layers (11) form concentric closed loops, preferably circles or ellipses.

9. The transparent dielectric material is TiO ２ , A.L. ２ O ３ , Si, SiO ２ , Ge, GaAs, InP, HfO ２ , BaTiO ３ , Pb[Zr ｘ Ti １－ｘ ]O ３ , SrTiO ３ , Ba （１－ｘ） Sr ｘ TiO ３ , PbTiO ３ , CaTiO ３ , MgO, ZrO ２ is a high refractive index dielectric material selected from the list The optical metasurface according to any one of claims 1 to 8.

10. An optical device comprising a metasurface (10) according to any one of claims 1 to 9, the optical device is selected from the list of a metalens, a blazed diffraction grating, a phase plate, a hologram, a vortex beam generator, a spatial light modulator, an optical switch; Optical devices.

11. A pair of eyeglasses comprising at least one metasurface (10) according to claim 1, wherein the shape layer (11) is ring-shaped. A pair of glasses.

12. 1. A method for fabricating an optical metasurface (10) for interacting with incident light, the method comprising: - providing (S1) a transparent substrate (16) comprising a plurality of nanoholes (17) or nanopillars (18), said nanoholes or nanopillars having vertical or substantially vertical sidewalls (24) extending perpendicular to the base plane of said transparent substrate (16); - covering at least a portion of said transparent substrate (16) with shaped layers (11) of a transparent dielectric material (15) such that each shaped layer covers a plurality of said nanoholes (17) or nanopillars (18) of said transparent substrate (16); A method comprising:

13. Covering at least a portion of the transparent substrate (16) with a shaped layer (11) of a transparent dielectric material (15) - a) covering (S2) said transparent substrate (16) and / or previously deposited transparent dielectric material (15) with a layer of photoresist (40); - b) a step (S3) of exposing the photoresist to electromagnetic radiation, wherein the transparent dielectric material is placed in contact with the transparent substrate or the previously deposited transparent dielectric material, or wherein the transparent dielectric material is not placed in contact with the transparent substrate or the previously deposited transparent dielectric material; -c) removing the photoresist that has been exposed to electromagnetic radiation or that has not been exposed to electromagnetic radiation (S4); - d) covering (S5) at least a portion of said substrate (15) and / or said previously deposited transparent dielectric material (16) with a deposited layer (25) of transparent dielectric material; - e) removing (S6) the remaining photoresist (40), thereby also removing the transparent dielectric material deposited on top of the photoresist; -f) repeating steps a) to e) a predetermined number of times (S7); 13. The method of claim 12, comprising:

14. Covering at least a portion of the transparent substrate (16) with a shaped layer (11) of a transparent dielectric material (15) - covering (S8) at least a portion of said transparent substrate (16) with a transparent dielectric material (15); - a step (S9) of geometrically modifying the transparent dielectric material (15) on the transparent substrate (16) by removing portions of the transparent dielectric material (15) to form the shape layer (11); 14. The method of claim 12 or 13, comprising:

15. The method comprises: - further comprising removing a portion of said layer of said transparent dielectric material by laser ablation, The method according to any one of claims 12 to 14.

Images