Meta-optics integrated display

Abstract

The present technology is related to optics and optical systems for display applications and their fabrication and integration with display modules. An inventive fabrication process involves forming meta-optical structures with engineered light emission or scattering characteristics, and their implementation in displays to empower new functions such as 3-D displays, optical combiners for augmented reality, and beyond. In addition to metasurfaces, inventive techniques can be used in other thin optics structures, including but not limited to sub -wavelength optics, metasurfaces, metamaterials, diffractive optical elements (DOEs), holographic optical elements (HOEs), gradient-index (GRIN) optics, micro-optics, hybrid optical systems, etc.

Description

Attorney Docket No. MIT-26227WO01Meta-Optics Integrated DisplayCROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims the priority benefit, under 35 U.S.C. 119(e), of U.S. Application No. 63 / 713,637, filed October 30, 2024, which is incorporated herein by reference in its entirety for all purposes.BACKGROUND

[0002] A conventional display dynamically modulates the light emission intensity at each pixel so that the pixels form a series of images. However, a conventional display offers little control over the light emission direction from each pixel. This angular emission control capability is useful for several reasons. It reduces light trapping by total internal reflection inside the emitter to enhance the display’s efficiency and helps confine optical power within the target field-of- view (FOV). Both lead to higher energy efficiency and lower power consumption. Moreover, the ability to control the light emission angle and hence the light field constitute the foundation for glasses-free 3-D displays (autostereoscopy). One example of a 3-D display groups of pixels (in a 2-D array) according to their emission directions. Each group or subset of pixels projects a unique perspective view of the displayed scene along one viewing angle (and hence the name “multiview display”), thereby creating 3-D stereoscopic perception for the user. Early prototypes of multiview displays have been implemented using parallax barriers, lenticular lenses, or micro-lens arrays on top of flat display panels. These prototypes have severe limitations in efficiency, FOV, and depth of field.

[0003] The challenges encountered by conventional optics have fueled a growing interest in 3- D displays based on flat optics. One solution involves integration of passive diffraction grating arrays on a liquid crystal display (LCD) panel. However, the spatial and angular resolutions of such a multiview display are bounded by the large pixel pitch of the LCD panel. Subpar resolution compromises the user experience in early commercial multiview display prototypes. The poor spatial resolution results in apparent image blur compared with 2-D displays. The small number of angular views causes vergence-accommodation conflict (VAC, the leading cause of eye fatigue and viewer discomfort) and discontinuous motion parallax (which precludes a close-to-reality experience). Moreover, the hybrid integration scheme, which entails attachment of gratings engraved on a glass plate to the LCD panel, limits registrationAttorney Docket No. MIT-26227WO01 accuracy and display resolution. Degraded brightness and contrast due to the limited efficiency of the added grating elements constitute additional concerns.

[0004] An alternative approach involves using diffractive gratings or metasurfaces patterned on micro-light-emitting diodes (micro-LEDs) to engineer the emission pattern. Compared to an LCD, a micro-LED display offers much higher (finer) spatial resolution. However, prior demonstrations of this micro-LED approach rely on structuring of semiconductor or dielectric layers inside micro-LEDs, which presents a dilemma: if the metasurface structures are separated from the active light emission region, they provide only limited control over the emission characteristics due to weak light-metasurface overlap; whereas if the metasurfaces are directly engraved into the active emission layers, defects and exacerbated interface recombination severely degrade the micro-LED performance. A solution capable of simultaneously achieving high emission efficiency and strong light-metastructure interactions is therefore desired.SUMMARY

[0005] An inventive metasurface can provide high emission efficiency and strong light- metastructure interactions simultaneously. Such a metasurface includes a substrate, metaatoms arrayed on the substrate, and index-matching material at least partially encapsulating the meta-atoms. Each meta-atom comprises nanoparticles that are configured to emit or scatter light in a predetermined wavelength band. These nanoparticles are embedded in a host material, such as a transparent polymer, whose refractive index is within 0.1 of the refractive index of the index-matching encapsulation. In some cases, the host material and the encapsulating material are the same, e.g., the same type of resin. In some other embodiments, the refractive index of the host material may differ by more than 0.1 from that of the encapsulation layer. The host and / or encapsulation materials may be configured or patterned to reduce or minimize scattering and / or enhance the overall optical performance. The meta-atoms can have freeform shapes, different sizes, different shapes, and / or different types of nanoparticles. Such a metasurface can be part of a three-dimensional micro-display.

[0006] An inventive metasurface can be made by etching an array of cavities in a substrate, filling the array of cavities with nanoparticles suspended in a solution to form meta-atoms, and at least partially encapsulating the meta-atoms with index-matching material. Alternatively, an inventive metasurface can be made by disposing a layer of nanoparticles suspended in host material on a substrate, patterning the layer of nanoparticles suspended in the host material toAttorney Docket No. MIT-26227WO01 form meta-atoms, and at least partially encapsulating the meta-atoms with index-matching material. In further embodiments, the metasurface layer may be thermoformed, embossed, or transferred onto curved or flexible substrates. This enables conformal integration of the metasurface with refractive optics, image sensors, or micro-LED backplanes. Wafer-level alignment methods such as interferometric registration or optical fiducial tracking may ensure micron-level overlay accuracy. Additional process variants may include inkjet or aerosol -jet printing of nanoparticle inks followed by localized curing or ultraviolet (UV) crosslinking for large-area manufacturing.

[0007] An inventive metasurface has a wide range of applications, including use as an optical combiner for heads-up displays and augmented reality (AR) displays. An optical combiner serves both as a see-through window for the real-world scene and as an optical coupler to redirect light from a micro-display (or a waveguide) to the user’ s eyes. These functions inevitably introduce a trade-off: a see-through window should maximize optical transparency and minimize reflection / scattering / diffraction losses, whereas a coupler should be capable of efficiently re-directing light propagation direction via diffraction or partial reflection. Diffraction or reflection from the coupler can result in rainbow effect and eye glow, which compromises the experience of AR device users. Thanks to the index-matched host and encapsulating materials and the scattering nanoparticles’ extremely narrow scattering cross section, an inventive metasurface with scattering nanoparticles is effectively transparent at wavelengths other than the nanoparticles’ scattering wavelengths, mitigating or eliminating this unwanted diffraction or reflection.

[0008] In other embodiments, the metasurface may be combined with other optical components (e.g., refractive, reflective, diffractive optics), such as a plano-convex or freeform polymer lenses, to form a hybrid optical system. In one example, the metasurface may supply chromatic dispersion correction, while the refractive layer provides focusing power. The hybridization allows advanced functions and performance, such as broadband achromatic imaging / sensing, augmented-reality combiners, miniature projection optics, or light-field modulators, etc. Multiple metasurfaces may also be cascaded with refractive layers to realize multi-functional optical stacks with enhanced polarization, spectral, and / or phase control.

[0009] All combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are part of the inventive subject matter disclosed herein.Attorney Docket No. MIT-26227WO01The terminology used herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.BRIEF DESCRIPTIONS OF THE DRAWINGS

[0010] The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally and / or structurally similar elements).

[0011] FIG. 1A shows a freeform encapsulated meta-atom comprising scattering and / or emitting nanoparticles embedded in the host material, such as a polymer or other suitable material.

[0012] FIG. IB is a top view of the freeform meta-atom, which can be described as a polygon with N vertices.

[0013] FIG. 1C is a side view of the freeform meta-atom illustrating its constituent parts.

[0014] FIG. ID shows meta-atoms with different arrangements and types of nanoparticles and metasurfaces with different arrangements of different types of meta-atoms.

[0015] FIG. IE shows a metasurface with layers that direct incident pump light at different angles to different layers of nanoparticle-impregnated meta-atoms.

[0016] FIG. IF shows a metasurface with layers that emits light at different wavelengths from different layers of nanoparticle-impregnated meta-atoms at different angles.

[0017] FIG. 2A is a plot of the scattering cross section (solid line) and the absorption cross section (dashed line) versus wavelength for a silver-coated silica nanoparticle (inset) that strongly scatters blue light and is suitable for use in a scattering meta-atom.

[0018] FIG. 2B is a plot of the scattering cross section (solid line) and the absorption cross section (dashed line) versus wavelength for a silver-coated silica nanoparticle (inset) that strongly scatters green light and is suitable for use in a scattering meta-atom.Attorney Docket No. MIT-26227WO01

[0019] FIG. 2C is a plot of the scattering cross section (solid line) and the absorption cross section (dashed line) versus wavelength for a silver-coated silica nanoparticle (inset) that strongly scatters red light and is suitable for use in a scattering meta-atom.

[0020] FIG. 2D is a plot of the scattering cross section (solid line) and the absorption cross section (dashed line) versus wavelength for a titanium dioxide nanoshell (inset) that strongly scatters blue light and is suitable for use in a scattering meta-atom.

[0021] FIG. 2E is a plot of the scattering cross section (solid line) and the absorption cross section (dashed line) versus wavelength for a silicon nanoshell (inset) that strongly scatters green light and is suitable for use in a scattering meta-atom.

[0022] FIG. 3 A illustrates a meta-optical structure fabrication process.

[0023] FIG. 3B illustrates an alternative meta-optical structure fabrication process.

[0024] FIG. 4 illustrates a 3-D light field display integrating metausurfaces with angular- dependent responses.

[0025] FIG. 5A illustrates a metasurface optical combiner that integrates real-world and virtual -world scenes. It deflects the image in a narrow bandwidth spectrum from the projector and transmits the broadband light from the real world with minimal wavefront distortion.

[0026] FIG. 5B is a cross-sectional view of a nano trench in the metasurface optical combiner of FIG. 5A (indicated by the dashed line in FIG. 5A). The nano trench is filled with indexmatching polymer where nanoparticles are well-dispersed.

[0027] FIG. 5C is a plot of the scattering cross section versus wavelength of the nanoparticles suitable for use in a meta-optics integrated display. This plot shows that the nanoparticles exhibit narrow band scattering cross sections.

[0028] FIG. 5D illustrates views from different angles of a 3-D projection display like the one shown in FIG. 5A.

[0029] FIG. 6 illustrates a 3-D micro-display including an inventive metasurface.

[0030] FIG. 7 illustrates a process for fabricating the 3-D micro-display of FIG. 6.

[0031] FIG. 8A illustrates a grating with a width of 28 nm.

[0032] FIG. 8B illustrates the grating of FIG. 7 A after fabrication.

[0033] FIG. 8C illustrates a grating with a width of 30 nm.Attorney Docket No. MIT-26227WO01

[0034] FIG. 8D shows that for gratings with a width of 30 nm, there is a higher likelihood of cross-linking to adjacent gratings.

[0035] FIG. 8E shows a grating with a width of 60 nm.

[0036] FIG. 8F shows the grating of FIG. 8E after fabrication.

[0037] FIG. 9A is dark-field optical microscopy image of a grating (scale bar: 10 pm).

[0038] FIG. 9B is an scanning electron microscope (SEM) image of a grating (scale bar: 20 pm).

[0039] FIG. 10A shows a top-view SEM image of a grating (scale bar: 25 pm).

[0040] FIG. 10B shows zoomed-in SEM images of gratings, which fitted well to the example design: 244 nm, 302 nm, 396 nm, and 573 nm.

[0041] FIG. 10C shows an SEM image of the grating taken at an angle of 30° (scale bar: 0.5 pm).

[0042] FIG. 11 A shows a photograph of grating supercells (scale bar: 0.5 cm).

[0043] FIG. 1 IB shows an optical microscopy image of a grating supercell (scale bar: 0.5 mm).

[0044] FIG. 11C shows an SEM image of a grating supercells (scale bar: 5.5 pm).DETAILED DESCRIPTION

[0045] Optical metasurfaces, also termed sub -wavelength diffractive optics, are artificial media comprising 2-D arrays of sub-wavelength optical structures (commonly called metaatoms). Conventional processes for making metasurfaces generally involve lithographic patterning and etching or lift-off of a high-refractive-index medium to form the meta-atoms. Here we present inventive meta-optical structures based on nanoparticle ensembles and inventive fabrication processes for these inventive meta-optical structures. Unlike processes for forming meta-structures based on nanoparticle-impregnated polymers where the nanoparticles serve to boost the refractive index of the polymer without active optical functions, the meta-optical structures described herein rely on the spectrally selective light emission or scattering properties of the nanoparticles to perform different optical functions.Meta-Atoms with Embedded Scattering and / or Emitting Nanoparticles

[0046] FIGS. 1 A-1C depict an inventive meta-atom 120 for an inventive metasurface 100 (also called a meta-optical structure or meta-structure). The inventive meta-atom 120 includesAttorney Docket No. MIT-26227WO01 functional nanoparticles 122 (e.g., quantum dots (QDs) or plasmonic nanoparticles, such as gold, silver, or copper nanoparticles) embedded inside a host material 124 (e.g., a low-index polymer or solution-processed glass material, such as an oxide or chalcogenide). These functional nanoparticles do more than simply increase the meta-atom’s refractive index boost — they impart new optical functions so that the host-particle hybrid acts as more than just an effective medium. For example, the functional nanoparticles can (1) support strong optical resonance features (such as plasmonic or Mie resonances) to impart spectrally selective scattering cross-sections; (2) leverage quantum confinement to enhance light emission, absorption, or scattering (e.g., like QDs or other types of nanoparticles (rods, rings, core-shell, etc.)); (3) have chiral or strong anisotropic properties; or (4) provide nonlinear or active optical functionality (e.g., in response to an applied magnetic or electric field).

[0047] In additional embodiments, the meta-atom 120 may incorporate multi-functional nanoparticles combining emissive, refractive, scattering and / or absorptive properties. The nanoparticles 122 may be selectively configured or positioned within layered or graded-index shells or layered dielectric hosts to enable advanced functions, such as hybrid diffractive- refractive control. In yet other examples, the nanoparticles may be arranged to form coupled resonator arrays that control or enhance near-field energy exchange between adjacent metaatoms, allowing tunable spectral bandwidth and / or polarization control.

[0048] In one preferred embodiment, the host material 124 is encapsulated in another material 130 of a similar refractive index. More specifically, the host material 124 and encapsulating material 130 should have refractive indices within 0.1 of each other (i.e., the difference in the refractive index of the host material 124 and the refractive index of the encapsulating material 130 should be 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, 0.01, or less). Due to the matching refractive index, the host material 124 is optically identical to the surrounding material 130 and does not provide or perform an optical function (other than to transmit light). The nanoparticles 122, which are present in the host material 124 but not the surrounding material 130, form the actual meta-optical components. This means that the meta-atom 120 — and hence a metasurface made up of multiple meta-atoms 120 — is transparent at wavelengths other than the nanoparticles’ functional wavelength, e.g., the scattering wavelength for scattering nanoparticles or the absorption and emission wavelengths for QDs.

[0049] In some embodiments, the encapsulating or host material may be formed as a multilayer or gradient-index (GRIN) film, in which the refractive index varies to provide advanced functions, such as reducing Fresnel reflections. The host material may alternatively include anAttorney Docket No. MIT-26227WO01 organic-inorganic hybrid polymer, sol-gel glass, or perfluorinated resin whose refractive index can be tailored across 1.3-1.8 to match the encapsulant. In still other embodiments, the encapsulating or host material may be patterned or locally doped to create refractive microzones that cooperate with the metasurface phase profile to form a hybrid optical architecture.

[0050] The meta-atom 120 has lateral dimensions that are less than one wavelength (e.g., less than 1 micron) and can take any of a variety of shapes, including the freeform shape shown in FIGS. 1A-1C, which can be characterized as an irregular polygon with N > 2 vertices P. Nanoparticle-filled meta-atoms can take other shapes, including regular shapes, such as circles or regular polygons. More generally, the meta-atom 120 can assume a freeform geometry via inverse design with a non-intuitive geometry. Meta-atoms 120 can be arranged in regular (periodic) 1-D or 2-D arrays, sparse arrays, aperiodic arrays, or any other suitable arrangement, including arrays of identical meta-atoms or arrays of different meta-atoms. These variations can also carry over to the nanoparticles in the meta-atoms.

[0051] FIG. ID shows some variations of meta-atoms and metasurfaces unique to meta-atoms impregnated with functional nanoparticles. At left, the uppermost meta-atom 120 includes irregularly arranged nanoparticles 122, e.g., nanoparticles 122 that are randomly distributed within the meta-atom 120. The middle meta-atom 120’ at left in FIG. ID has nanoparticles 122’ that are arranged in a regular fashion, e.g., through self-assembly or another way of forming a regular or periodic arrangement. For instance, the nanoparticles 122’ can take on a crystalline-like structure, such as simple cubic, body-centered cubic, of face-centered cubic structure. Other meta-atoms may have other ordered arrangements of nanoparticles 122’, including arrangements with defects. The exact ordered arrangement of nanoparticles 122’ may depend on the nanoparticles 122’ themselves and on any optical effect or function provided by the meta-atom 120’. For example, the ordered nanoparticles 122’ may be arranged to impart properties such as optical chirality, coherent scattering, anisotropy, or strong local field enhancement to the meta-atom 120’.

[0052] The meta-atom 122” at lower left in FIG. ID includes several types of nanoparticles 122a-122c, each of which may perform a different function. The different types of nanoparticles 122a-122c may be made of different materials and / or have different shapes or dimensions and scatter or emit light at different wavelengths. For example, the nanoparticles 122a-122c may be plasmonic nanoparticles that scatter red, green, or blue light. The nanoparticles 122a-122c could also be quantum dots that emit red, green, or blue light. Or the nanoparticles 122a-122c could be a combination of scattering and emitting nanoparticles.Attorney Docket No. MIT-26227WO01

[0053] In any event, a given meta-atom could include two or more types of nanoparticles (e.g., two, three, four, or five different types of nanoparticles). A meta-atom could include the same number or concentration of each type of nanoparticle or different numbers or concentrations of each type of nanoparticle. The nanoparticles can be randomly arranged within the meta-atom or arranged in an ordered fashion, e.g., with the different nanoparticles distributed in a uniform, intermingled fashion or in a segregated fashion (e.g., nanoparticles 122a on the bottom, nanoparticles 122b in the middle, and nanoparticles 122c on the bottom).

[0054] A metasurface may include meta-atoms with different types, numbers / concentrations, or arrangements of nanoparticles. FIG. ID shows metasurfaces lOOa-lOOc with different arrangements of different types of meta-atoms 120a-120c, each of which includes a different type of nanoparticle (e.g., red-, green-, and blue-scattering or emitting nanoparticles). In metasurface 100a, these meta-atoms 120a-120c are arranged in the same layer, either periodically as shown in FIG. ID or in an irregular arrangement. The meta-atoms 120a-120c can also be arranged in different layers, for example, with the different meta-atoms 120a-120c stacked on top of each other as in metasurface 100b or in an offset arrangement as in metasurface 100c.

[0055] FIGS. IE and IF illustrate how a multi-layer metasurface 100b can be tailored to direct light at different wavelengths in different directions. More specifically, each metasurface layer in metasurface 100b may have meta-atoms whose shapes, sizes, arrangements, etc. are selected to direct different wavelengths in different directions. For instance, if the nanoparticles in these layers are QDs that absorb light 141 from the same pump source 140 at the same wavelength, they may be configured to diffract light at that wavelength at slightly different angles to account for their spatial separation as shown in FIG. IE. If the nanoparticles absorb light at different wavelengths, e.g., from an array of spatially offset sources, they may be tailored to diffract only the corresponding wavelength and to transmit light at the other (pump) wavelengths. Similarly, if the nanoparticles emit or scatter light at different wavelengths, the corresponding meta-atoms may have shapes, sizes, and / or arrangements selected to direct that light in different directions 121a-121c as shown in FIG. IF, whether those meta-atoms are in the same layer or different layers. (Recall that scattering meta-atoms are transparent at wavelengths other than the scattering wavelength and so should not affect light at these other wavelengths.)Scattering Nanoparticles for Meta-Atoms

[0056] The nanoparticles in the meta-atoms shown in FIGS. 1 A-1D can have scattering cross sections that are sharply peaked at particular wavelengths and substantially zero throughout theAttorney Docket No. MIT-26227WO01 rest of the visible spectrum. They can also have absorption cross sections that are substantially zero throughout the visible spectrum. There are several ways to achieve wavelength-selective narrowband scattering (resonant scattering) in nanoparticles, including surface plasmonic resonances in metal-coated nanoparticles, resonant features (e.g., cavities), and Fano resonances, which are resonances that exhibit asymmetric profiles due to interference between the resonant and background scattering probabilities. Other particles, such as high-index dielectric nanoparticles, and other types of resonances, such as higher-order resonances, may also exhibit suitable wavelength-selective scattering. Moreover, the size, shape, and composition of the nanoparticles can be selected to achieve particular scattering wavelengths, bandwidths, and bandshapes.

[0057] As understood by those of skill in the art, when a particle is much smaller than the wavelength of incident light (e.g., a nanoparticle), the particle experiences a local electromagnetic field that is substantially constant in space. As a result, the optical response of this small particle can be determined from the corresponding electrostatic problem. This is called the quasi-static approximation (also known as the electrostatic approximation or dipole approximation).

[0058] The quasi-static approximation can be used to estimate the sharpness of the scattering cross-section in the localized surface plasmon resonances of small metallic particles. This derivation is general and applies to arbitrary particle shapes, including but not limited to spheres, ellipsoids, oblate spheroids, and prolate spheroids. In the quasi-static approximation, the scattering cross-section <7scaaveraged over angle and polarization of the incoming light can be written as:where the angle brackets denote an average over angle and polarization, k = 2TT ETH / A is the wavenumber in the surrounding medium (whose dielectric constant am is purely real and positive), and a , a2, and <z3are the particle’s static polarizabilities in three orthogonal directions. The particle can be a uniform material (e.g., a solid sphere) or a composite of multiple materials (e.g., a core-shell structure).

[0059] One way to achieve wavelength-selective scattering is to use the localized surface plasmon resonances in metallic nanoparticles. A metallic nanoparticle can support a surface plasmon because its dielectric function will have a negative real part at some wavelength range.Attorney Docket No. MIT-26227WO01In particular, a metallic nanoparticle supports a localized surface plasmon resonance that occurs approximately at the wavelength Aofor which(For a sphere, this condition can be simplified to Re(e(A0)) = — 2em.) Near the resonance, the static polarizability aj provides the dominant contribution to the averaged scattering crosssection, so the ratio between the on-resonance (at Ao) and off-resonance (at Ao+ AA, for a small AA of interest) scattering cross-sections is approximately

[0060] This expression can be simplified by writing the polarizability as a rational function and taking the changes in the real and imaginary components of the permittivity with Al to be small relative to their on-resonance values. Analytical expressions for the polarizability of spheres, coated spheres, ellipsoids, and coated ellipsoids appear in C. F Bohren and D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley, New York, 1998), which is incorporated herein by reference in its entirety. These analytical expressions may take the form of rational functions. For more arbitrary geometries, the polarizability can often be locally approximated as a rational function near the resonance.

[0061] Applying these simplifications to Equation (3) yields the following expression for the ratio between the on-resonance (at Ao) scattering cross-section and the off-resonance (at Ao+ AA, for a small AA of interest) for a small particle (e.g., diameter « wavelength) characterized by a dielectric function s:The derivation leading to Equation (4) applies to arbitrary particle shapes and assumes only that the particle is much smaller than the wavelength Aoand that AA is small enough that the permittivity does not change much. Equation (4) applies to localized surface plasmon resonances, but not necessarily to other types of resonances.

[0062] For strong wavelength-selective scattering, the on -resonance scattering cross section, Osca(A0), should be much larger than the off-resonance scattering cross section, trSCa( o + ^A),Attorney Docket No. MIT-26227WO01 such that the ratio given by Equation (4) should be (much) greater than 1. To achieve a large ratio (e.g., much greater than 1), Equation (4) suggests that the nanoparticle material should be characterized by a dielectric function with a small imaginary component, Im(e), and a fastchanging real component, Re(e) , near the resonance wavelength, Ao. Materials whose dielectric functions have small imaginary components and fast-changing real components near a particular resonance wavelength include Drude metals with negligible loss.

[0063] FIGS. 2A-2E are plots of scattering cross sections (solid lines) and absorption cross sections (dashed lines) versus wavelength for scattering nanoparticles suitable for use in a meta-atom. Each of these scattering nanoparticles has a uniformly low absorption cross-section <7abs across the visible spectrum, and a high scattering cross section <7scaat the resonance wavelength Aowith low scattering cross section <7scaelsewhere in the visible spectrum. These nanoparticles can be synthesized, for example, using the Stober process, and embedded in a transparent medium with a refractive index n = 1.44, which is typical of a polymer matrix.

[0064] FIG. 2A shows a silica nanosphere, with a radius of about 1.3 nm, that is coated with a 30.8 nm thick silver shell and scatters blue light (Ao= 458 nm). FIG. 2B shows a silica nanosphere, with a radius of about 22.2 nm, that is coated with a 15.8 nm thick silver shell and scatters green light (Ao= 532nm). And FIG. 2C shows a silica nanosphere, with a radius of about 34.3 nm, that is coated with a 11.0 nm thick silver shell and scatters red light (Ao= 640 nm). The FWHM of the peaks in FIGS. 2A, 2B, and 2C are about 66 nm, about 62 nm, and about 69 nm, respectively.

[0065] FIG. 2D shows the calculated scattering and absorption cross-sections of a titanium dioxide nanoshell that scatters blue light ato= 458 nm, and FIG. 2E shows the same for a silicon nanoshell that scatters green light at Ao= 532 nm. The titanium dioxide nanoshell in FIG. 2D has an inner radius of 25.5 nm and an outer radius of 70.1 nm. The silicon nanoshell in FIG. 2E has an inner radius of 43.8 nm and an outer radius of 68.2 nm. The nanoshells’ resonances exhibit relatively low absorption loss, but the index contrast should be high enough to provide sufficient confinement for the resonances. In FIGS. 2D and 2E, for example, the nanoshells’ cores and surrounding media are assumed to have refractive index n = 1. In practice, the cores and surrounding media may include low-index materials, such as transparent aerogels with transmission lengths of up to 60 mm.Manufacturing Meta-Structures with Embedded NanoparticlesAttorney Docket No. MIT-26227WO01

[0066] FIGS. 3A and 3B illustrate different processes for making inventive metasurfaces. In the process shown in FIG. 3 A, recess cavities 311 are first patterned and etched (301) in a substrate 310 (e.g., glass or polymer) with a low refractive index (e.g., 1.7 or less). The cavities 311 can assume regular geometries (e.g., circular or rectangular shapes), free-form geometries, or any other geometries tailored to provide the desired optical functions. The cavities 311 have sub -wavelength pitch with feature sizes that can be even smaller (especially for freeform structures), with millions or billions of cavities filling a macroscopic (e.g., millimeter-scale) optical aperture.

[0067] Host material 324 containing the nanoparticles 322 is then dispensed over the substrate 310, filling the cavities 311 (303) with the host material 322 and the nanoparticles 324. For example, the nanoparticles 322 may be suspended in the host material 324, which can be in liquid or viscous form, at percentages of 1%, 2.5%, 5%, 7.5%, 10%, 12.5%, 15%, 20%, 25%, 30%, 40%, or more. The host material 324 can be deposited on the substrate 310 and in the cavities 311 using spin coating, dip coating, spray coating, inkjet printing, or another suitable method. The host material 324 can be cured (solidified) in the cavities 311, e.g., by heating or exposure to ultraviolet light, forming meta-atoms 320 with embedded nanoparticles 322. Any excess host material 324 on top of the substrate 310 is removed, before and / or after curing, followed by bonding a cover on top (305) of the cavities 311 to seal the meta-atoms 320, yielding the finished metasurface 300.

[0068] FIG. 3B shows an alternative fabrication process, which starts with coating (30F) an unpatterned substrate 310 with a layer of host material 324 impregnated with nanoparticles 322. This layer of nanoparticle-containing host material is then patterned into target geometries (the meta-atoms 320) (303’). This patterning can be done through direct laser / electron beam writing when the host material is a photo / electron beam resist, or via lithographic patterning using photolithography, electron beam lithography, nanoimprint, or various soft lithography techniques. A cover layer with a refractive index closely matching that of the host material is then coated on top (305’) to fully encapsulate the meta-atoms 320, yield the finished metasurface 300.

[0069] The processes in FIGS. 3A and 3B can be repeated to form stacked metasurfaces, potentially with different types of nanoparticles and / or different optical properties, including directing light at different wavelengths or incidence angles in different directions. The processes in FIG. 3 A and 3B can also be modified such that different meta-atoms in the same layer contain different types of nanoparticles. For example, in either process, it is possible toAttorney Docket No. MIT-26227WO01 fill every third cavity with a different type of nanoparticle or to create a first set of cavities, fill them with a first type of nanoparticle, then create a second set of cavities in the same layer, fill the second set of cavities with a second type of nanoparticle, and so on.Meta-Optical Structures with Embedded Nanoparticles

[0070] The nanoparticles can impart unique optical functions on the meta-optical structures. As one example, quantum dots (QDs) are useful as wavelength converters in micro-LED displays. They work by absorbing photons emitted from a single-color (usually blue or purple) pump LED and emitting photons at longer wavelengths, e.g., red, green, or blue (RGB) photons. In other words, the QDs downconvert the incident blue or purple photons into RGB photons. Shaping the QDs into meta-optical structures can: (1) enhance optical absorption of the pump photons via light trapping, thereby decreasing the thickness or volume of QD structures (QD-impregnated meta-atoms); (2) enhance down-conversion emission efficiency of the RGB photons through engineering the local photon density of states (Purcell enhancement); and / or (3) control the angular distribution of re-emitted light from the wavelength converter to facilitate applications such as 3-D light field display. For example, the angular distribution can be selected or controlled by controlling the metasurface’s local photon density of states to increase emission into certain modes that escape at particular angles (like Purcell effect). The meta-structures may be formed fully or partially from the QDs. Other materials may be combined with QDs to form the meta-structures.

[0071] FIG. 4 shows a 3-D light-field display 400 based on a metasurface structure 420 with QD-impregnated meta-atoms. The metasurface structure 420 is sandwiched between a micro- LED display 310, which emits light towards a viewer’s eye 11, and an aperture array 430, which blocks unabsorbed pump light from the micro-LED display 310. The display 400 can be divided into pixels 402, each of which includes one or more micro-LEDs 412, each of which emits blue or purple light. The light from each micro-LED 412 illuminates a corresponding meta-atom 422 or set of meta-atoms 422 in the metasurface structure 420 at a particular angle. Each meta-atom 422 may include a different type of QD (e.g., one that emits red, green, or blue light) arranged in either an interleaved fashion or in multiple layers or may include multiple types of QDs (e.g., ones that emit red, green, and / or blue light) as shown in FIG. ID. The metasurface structure 420 directs light at this pump wavelength to QDs in the meta-atoms 422. The QDs convert this blue or purple light into visible (e.g., red, green, and / or blue) light, which the metasurface 420 redirects at different angles through the aperture array 430 to form different views of a virtual image 40.Attorney Docket No. MIT-26227WO01

[0072] The 3-D light-field display 400 can be a full-color display that incorporates three different types of meta-optical pixels, each with a different type of QD, for R / G / B wavelength conversion. Notably, the design circumvents the trade-off between efficiency (micro-LED material quality) and optical emission control by keeping the micro-LEDs 412 intact and instead shaping the QD wavelength converters into meta-atoms 422 to realize the desired emission pattern control. In this way, high emission efficiency and strong light-metastructure interactions are achieved simultaneously. Moreover, this approach also sidesteps the need to fabricate or transfer micro-LEDs emitting three different colors on the same substrate and dramatically simplifies the packaging and assembly process.

[0073] Another example of a meta-structure with a unique optical function capitalizes on the wavelength-dependent scattering behavior of plasm onic (e.g., metallic or heavily doped semiconductor) nanoparticles. These nanoparticles support one or multiple localized surface plasmon resonance (LSPR) modes (e.g., dipole and quadrupole resonances). At these LSPR resonances, the scattering cross-section of the nanoparticles is dramatically increased. Therefore, the nanoparticles can act as spectrally selective scatterers which strongly interacts only with light of a particular wavelength. This is illustrated in FIG. 5C, which shows the wavelength-dependent scattering cross-section of nanoparticles peaking at an LSPR resonance wavelength o. The resonance wavelength and line shape (which impacts spectral selectivity) can be engineered by changing nanoparticle size, shape, and composition. The possible examples include using non-spherical nanoparticles (e.g., nanorods), core-shell structures, etc., including those described above with respect to FIGS. 2A-2E.

[0074] FIG. 5A shows a plasmonic-nanoparticle metasurface combiner 500 for use in an augmented reality headset. The metasurface combiner 500 includes meta-atoms 520 permeated with scattering nanoparticles and deflects or reforms light from a projector 502 into a virtual image projected into the human eye 11, creating a virtual reality scene while transmitting real- world light 50 with minimal wavefront distortion. The projector 502 emits light in the narrow spectral bands scattered by the nanoparticles, whereas the real-world light 50 encompasses a broad spectral bandwidth. Because the nanoparticles have very narrow scattering cross sections, they scatter hardly any of the real -world light 50, so the real-world light 50 propagates through the metasurface combiner 500 largely unimpeded thanks to the index-matching of the host material 524 in each meta-atom 520 to the encapsulating material (substrate 510) that surrounds the meta-atoms 520. (The refractive index of the host material 524 may be within 0.1 of the refractive index of the substrate 510.) At the same time, the projector 502 emitsAttorney Docket No. MIT-26227WO01 monochromatic light at wavelengths matched to the nanoparticles’ peak scattering, so the metasurface 500 redirects most if not all of the light from the projector 502 into different angles for highly efficient formation of the virtual image. This allows the human eye 11 to simultaneously perceive real-world and virtual scenes, achieving augmented reality.

[0075] FIG. 5B shows the details of the meta-atom 520 surrounded by the dashed line in FIG. 5A. This meta-atom 520 is formed of a nano trench 511 etched into a transparent substrate 510 and filled with the host polymer material 524 that contains well-dispersed, engineered nanoparticles 522. The flat upper surface of the metasurface 500 / meta-atom 520 can accommodate functional coatings like antireflection layers or optical filters. Since each nanoparticle 522 selectively scatters only one wavelength Ao, the nanoparticles 522 remain almost completely invisible (transparent) to light at other wavelengths. (Other nanoparticles may be engineered to scatter light at multiple discrete wavelengths or over broader bands.) The refractive index of the polymer host 524 is similar to that of the substrate 510 (e.g., within 0.1, 0.05, 0.01, or less), and the nanoparticle’s feature size is in the deep subwavelength range. Consequently, the nanoparticle-in-polymer metasurface 500 imparts minimal distortion to the wavefront of light across a broad bandwidth, except at the nanoparticle’s working (scattering) wavelength of Ao.

[0076] The metasurface 500 can also be configured to provide angle-dependent functions. For example, each meta-atom 520 can be engineered to deflect light from the projector 502 towards a specific angle, so that the optical system can be used to generate a 3-D display similar to the principle illustrated in FIG. 4. The meta-atoms 520 may be further configured to be sensitive to polarization, wavelength, and / or incidence angle to provide different optical functions depending on the properties of the incident light. In addition, the metasurface 500 can include multiple layers of meta-atoms 520, with meta-atoms 520 in different layers containing nanoparticles 522 that scatter light at different wavelengths, e.g., as in FIG. ID, or a single layer of interleaved meta-atoms 520 with different scattering nanoparticles 522, again as in FIG. ID.

[0077] In other embodiments, one or both sides of the metasurface substrate 510 may be flat or curved. The metasurface 500 and / or the substrate 510 may be rigid, flexible, or stretchable. The pitch or lattice of the meta-atoms 520 may have any suitable shape and period (e.g., square, rectangular, or hexagonal). The metasurface 500 can include different types of meta-atoms 520, including meta-atoms with different shapes, sizes, and / or concentrations / numbers / types of nanoparticles 522. The meta-atom lattice may also be aperiodic, with varying or randomAttorney Docket No. MIT-26227WO01 distances between adjacent meta-atoms 520. In some examples, the gaps between adjacent meta-atoms 520 may be constant.

[0078] FIG. 5D shows images of a box projected by a metasurface grating viewed at angles of -10 degrees (left) and +10 degrees (right) in a projection display like the one shown in FIG. 5A. The metasurface grating was formed by plasmonic metal nanoparticles (embedded in a resin index matched to the surrounding cover). The pixelated grating is illuminated by a monochromatic light near the peak of the localized surface plasmon resonance of the metal particles, and the reflected / diffracted light projects different images along different viewing angles. The grating is almost completely invisible at other wavelengths and so acts as a transparent AR combiner that one can see through while also seeing the projected cube image.3-D Micro-Displays with Inventive Metasurfaces

[0079] Glasses-free 3-D display technology (autostereoscopy) is poised to transform humanmachine interactions. Unlike conventional display panels which reproduce only the intensity of light emanating from an object, an autostereoscopic display restores the light field information including both intensity and propagation direction.

[0080] FIG. 6 depicts a 3-D micro-display 600 that uses an inventive metasurface 620 to produce light field information instead of just intensity. The 3-D micro-display 600 in FIG. 6 combines micro-LEDs 612 in a micro-LED array 612 with integrated meta-structured wavelength converters 622a-622c implemented as meta-atoms in the metasurface 620. The micro-LED array 610 is flip-chip bonded or otherwise attached to complementary metal -oxide- semiconductor (CMOS) electronics 630, which in turn are coupled to a chip carrier 650 via a ball grid array (BGA) 640 or other suitable set of electronic connections. In operation, the CMOS electronics 630 actuate the micro-LEDs 612 in the micro-LED array 610. The micro- LEDs 612 emit blue or purple light that is absorbed by the quantum dots in the wavelength converters / meta-atoms 622a, 622b, and 622c, which emit red, green, and blue light, respectively, in specific directions as shown in FIG. 6 due to the engineering of the metasurface 620. The metasurface 620 is also engineered to direct the blue or purple light from the micro- LEDs 612 in a different direction than the emitted light — in this case, to channel normally incident blue or purple light, instead of angled direction.

[0081] Each wavelength converter / meta-atom 622 includes quantum dots embedded in a polymer that is index -matched to the surrounding medium. Each wavelength converter / meta- atom 622 modulates the wavelength and light output intensity of a corresponding micro-LEDAttorney Docket No. MIT-26227WO01612 and at the same time directs its wavelength-downconverted light emission to a specific direction. The wavelength converters / meta-atoms 622 can be grouped or arranged in subsets according to their emission directions. Each subset projects a unique perspective view of the displayed scene along one viewing angle (and hence the name “multiview display”), thereby creating 3-D stereoscopic perception for the user.

[0082] This 3-D micro-display 600 addresses challenges plaguing existing multiview 3-D displays. Its advantages include:• micro-LED technology offers unparalleled fine pixel pitch, which translates to over 10x improvement in spatial and angular resolution; this is a significant advantage for 3-D displays since it provides continuous, realistic motion parallax and further affords a viewing zone interval smaller than the eye pupil, thereby allowing the eye to focus correctly on virtual 3-D images and avoiding VAC;• while the efficiency of traditional diffraction gratings is limited by power dissipation into high-order diffraction, metasurfaces with a meta-atom pitch of less than one wavelength (less than a half wavelength for certain incidence angles) avoid undesirable diffraction orders to significantly boost efficiency and reduce background noise;• the exceptional light bending capability of metasurfaces accommodates large viewing angles without compromising efficiency, which contributes to enlarging the eye box;• metasurfaces allow densely packed pixels with a large fill factor (e.g., pixels with a pitch of < 20 pm) to improve display resolution without inducing excessive crosstalk; and• dynamic tuning capability of the monolithically integrated active metasurface enables temporal multiplexing, where the emission directions of pixels are rapidly and repeatedly toggled through several angular positions. In this way, each pixel can address multiple angular views, alleviating the trade-off between spatial and angular resolution. Metasurface pixel arrays with switchable light directing properties can be further coupled with an eye tracking sensor such that the number of angular views broadcasted toward the viewer is dynamically optimized in real-time.

[0083] The high-performance 3-D micro-display 600 in FIG. 6 is well-suited for virtual reality (VR) and augmented reality (AR) applications thanks to its high resolution, large eye box, high efficiency, and large contrast. Furthermore, unlike VR / AR devices that are based on binocularAttorney Docket No. MIT-26227WO01 disparity to stimulate vergence but do not provide accommodation cues, the 3-D micro-display 600 can manipulate 3-D light field with nearly continuous angular views to circumvent VAC.

[0084] FIG. 7 depicts a process for making the chip in the 3-D micro-display 600 of FIG. 6. The upper portion of FIG. 7 shows the III-V and CMOS integration process, starting with bonding (791) the III-V micro-LED array 610 to the CMOS electronics 630’. At this point, the III-V wafer containing the micro-LED array 610 is still attached to a silicon handler wafer 614, and the CMOS electronics 630’ still sit on a relatively thick base wafer. Next, the silicon handler wafer 614 is removed (793), exposing the emitting surface of the micro-LED array 610.

[0085] The lower portion of FIG. 7 illustrates fabrication of the metasurface 620 using a process like the one shown in FIG. 3 A. (The metasurface 620 could also be made according to the process shown in FIG. 3B.) Nano-trenches 711 are patterned (701) into a glass substrate 710 coated with a metal mask 712 that defines the locations, sizes, and shapes of the nanotrenches 711. Next, the nano-trenches 711 are filled (703) with polymer loaded with quantum dot (QD) emitters and cured to form the wavelength converters / meta-atoms 622a-622c. In this case, there are three different types of QD emitter meta-atoms 622a, 622b, and 622c that downconvert the 415 nm emission from the micro-LED array 610 underneath to red, green, and blue wavelengths, respectively. The cured wavelength converters / meta-atoms 622a-622c are covered or encapsulated with an index-matched layer or substrate 732 to form the metasurface 620, which is configured to optimize both pump absorption and directional emission in the QDs. The QD meta-structure pixel designs are then assembled (795) with the micro-LED array 610 and CMOS electronics 630 according to the angular view distribution and the CMOS substrate is thinned (797) to form the full reticle design.

[0086] Micro-optical structures such as optical funnels can also be integrated on the same glass wafer to mitigate color crosstalk. Optical funnels are tapered microstructures that collect and guide light emitted from each micro-LED pixel, thereby reducing lateral leakage and optical crosstalk. By redirecting the wide angular emission of the micro-LEDs into a narrow, vertically oriented cone, the optical funnels confine light within each pixel and prevent the light from spreading into neighboring pixels. The pixels’ reflective or high-index-contrast sidewalls act as optical barriers, enhancing pixel isolation while simultaneously improving light extraction efficiency. As a result, optical funnels improve color purity, image contrast, and overall display sharpness, particularly in high-density micro-LED arrays.Attorney Docket No. MIT-26227WO01Meta-Structure Fabrication Example

[0087] FIG. 8-11 illustrate fabrication of meta-structures with a 1 : 1 solution of ma-N photoresist 2405 (from Micro Resist Technology) and nanoComposix 50 nm PVP Coated Silver Nanospheres - 150 mg dispersed in 50 mL of toluene (3 mg / mL stock solution). For each meta-structure, this solution was deposited on a 0.5 mm thick fused silica substrate etched with a grating using electron beam lithography. The substrate was cleaned using an O2 plasma, then spin-coated with adhesive promoter before being rinsed with de-ionized water. The photoresist / nanoparticle mixture was sonicated, then dropped onto the substrate surface with a syringe / filter (10 pm pore size, hydrophobe PVDF). The photoresist / nanoparticle mixture was spin-coated onto the sample before being baked. The sample was then spin-coated with chargedissipating agent for electron beam lithography without baking.

[0088] FIGS. 8A-8F illustrate fabrication limits for the gratings. The narrowest gratings, shown in FIGS. 8A and 8B, have a width of 28 nm and are gone after fabrication, possibly due to their large aspect ratios. Gratings with a width of 30 nm, shown in FIGS. 8C and 8D, are more likely to cross-link to the adjacent gratings. Gratings that are at least 60 nm wide survive fabrication, and the sizes support the meta-surface design as shown in FIGS. 8E and 8F.

[0089] FIGS. 9 A and 9B illustrate challenges associated with fabrication. For example, FIG. 9A is a dark-field optical microscope image showing Ag clusters, possibly formed by Ag nanoparticles that were not totally dispersed during sonication of the photoresist / nanoparticle mixture. Increasing the sonicator power and / or sonication time could reduce this clustering.

[0090] Another example is the stitching error during the electron beam lithography writing of gratings as shown in FIG. 9B. The large gratings are composed of several writing fields, so when the stage moved from one field to another one, the transparent substrate could have produced different apparent thicknesses or positions, causing the stitching error. This can be suppressed by placing an un-polished Si substrate on the backside of transparent substrate. Also, this un-polished Si substrate should be tightly attached to the transparent substrate to avoid interference at the interfaces.

[0091] FIGS. 10A-10C show the qualified morphology of the fabricated gratings. In other words, FIGS. 10A-10C show the meta-gratings prior to being embedded in the index-matched medium (they cannot be imaged once they have been embedded in the index-matched medium due to the index matching). The actual grating dimensions match the design dimensions well. No missing gratings or cross-link to adjacent gratings can be seen in FIGS. 10A-10C.Attorney Docket No. MIT-26227WO01

[0092] FIGS. 11A-11C show grating supercells made of different gratings. These supercells project different patterns to different diffraction angles.Conclusion

[0093] Clause 1. A metasurface comprising: a substrate; meta-atoms arrayed on the substrate, each of the meta-atoms comprising nanoparticles in a host material, the nanoparticles configured to scatter or emit light in a predetermined wavelength band; and index -matching material at least partially encapsulating the meta-atoms, the index-matching material having a refractive index within 0.1 of a refractive index of the host material.

[0094] Clause 2. The metasurface of clause 1, wherein at least one of the meta-atoms has a freeform shape.

[0095] Clause 3. The metasurface of clause 1, wherein at least one of the meta-atoms comprises different types of nanoparticles.

[0096] Clause 4. The metasurface of clause 1, wherein different ones of the meta-atoms comprise different types of nanoparticles.

[0097] Clause 5. The metasurface of clause 4, wherein the different ones of the meta-atoms are arranged in a single layer on the substrate.

[0098] Clause 6. The metasurface of clause 4, wherein the different ones of the meta-atoms are arranged in different layers on the substrate.

[0099] Clause 7. The metasurface of clause 1, wherein the nanoparticles comprise quantum dots configured to emit light.

[0100] Clause 8. The metasurface of clause 1, wherein the host material comprises transparent polymer.

[0101] Clause 9. A three-dimensional micro-display comprising the metasurface of clause 1.

[0102] Clause 10. The three-dimensional micro-display of clause 9, further comprising: an array of light-emitting diodes (LEDs), bonded to the metasurface, to illuminate the nanoparticles with blue or purple light, wherein the nanoparticles are quantum dots configured to absorb the blue or purple light and to emit red, green, or blue light in predetermined directions in response to absorbing the blue or purple light so as to produce a three-dimensional light field.Attorney Docket No. MIT-26227WO01

[0103] Clause 11. The three-dimensional micro-display of clause 10, further comprising: complementary metal-oxide-semiconductor (CMOS) electronics, bonded to the array of LEDs, to actuate LEDs in the array of LEDs.

[0104] Clause 12. A method of making a metasurface for an optical component, the method comprising: forming meta-atoms of nanoparticles suspended in a host material, the nanoparticles being configured to scatter or emit light in a predetermined wavelength band; and encapsulating the meta-atoms in an index-matching material having a refractive index within 0.1 of a refractive index of the host material.

[0105] Clause 13. The method of clause 12, wherein forming the meta-atoms comprises: etching an array of cavities in a substrate; and filling the array of cavities with the nanoparticles suspended in the host material.

[0106] Clause 14. The method of clause 12, wherein forming the meta-atoms comprises: disposing a layer of nanoparticles suspended in the host material on a substrate; and patterning the layer of nanoparticles suspended in the host material to form the meta-atoms.

[0107] Clause 15. A metasurface comprising: transparent material patterned with: a first set of meta-atoms, each meta-atom in the first set of meta-atoms comprising a first type of nanoparticle in a host material having a refractive index within 0.1 of a refractive index of the transparent material, the first type of nanoparticles configured to scatter or emit light in a first predetermined wavelength band; a second set of meta-atoms, each meta-atom in the second set of meta-atoms comprising a second type of nanoparticle in the host material, the second type of nanoparticles configured to scatter or emit light in a second predetermined wavelength band different than the first predetermined wavelength band; and a third set of meta-atoms, each meta-atom in the third set of meta-atoms comprising a third type of nanoparticle in the host material, the third type of nanoparticles configured to scatter or emit light in a third predetermined wavelength band different than the first predetermined wavelength band and the second predetermined wavelength band.

[0108] Clause 16. The metasurface of clause 15, wherein the first set of meta-atoms, the second set of meta-atoms, and the third set of meta-atoms are interleaved in a single layer of the transparent material.

[0109] Clause 17. The metasurface of clause 15, wherein the first set of meta-atoms is in a first layer of the transparent material, the second set of meta-atoms is in a second layer ofAttorney Docket No. MIT-26227WO01 the transparent material disposed on the first layer, and the third set of meta-atoms is in a third layer of the transparent material disposed on the second layer.

[0110] Clause 18. The metasurface of clause 15, wherein the first type of nanoparticles comprises quantum dots configured to emit light in the first predetermined wavelength band.

[0111] Clause 19. The metasurface of clause 15, wherein the first type of nanoparticles comprises scattering nanoparticles configured to scatter light in the first predetermined wavelength band.

[0112] Clause 20. The metasurface of clause 15, wherein the first predetermined wavelength band corresponds to red light, the second predetermined wavelength band corresponds to green light, and the third predetermined wavelength band corresponds to blue light.

[0113] Clause 21. A hybrid optical system comprising a metasurface layer and other optical layers or components (e.g., refractive, reflective, and / or diffractive optics), such as a plano-convex or freeform lens, wherein the metasurface includes nanoparticle-embedded meta- atoms.

[0114] Clause 22. A metasurface wherein the encapsulating or host material comprises a layered or gradient-index material whose index profile is tailored to modulate or redirect light.

[0115] Clause 23. A metasurface with encapsulating or host material that is configured, patterned, or structured to modulate or redirect light.

[0116] Clause 24. A metasurface with nanoparticles have varying concentration.

[0117] Clause 25. A metasurface with meta-atoms comprising anisotropic nanoparticles oriented to produce polarization-dependent diffraction, scattering or emission.

[0118] Clause 26. The metasurface of Clause 25, wherein the anisotropic nanoparticles comprise nanorods or elliptical nanodisks configured for different polarization channels.

[0119] While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the function and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurationsAttorney Docket No. MIT-26227WO01 described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the inventive teachings is / are used. Those skilled in the art will recognize or be able to ascertain, using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

[0120] Also, various inventive concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

[0121] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0122] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0123] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and / or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and / or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B onlyAttorney Docket No. MIT-26227WO01(optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0124] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0125] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0126] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shallAttorney Docket No. MIT-26227WO01 be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

Claims

Attorney Docket No. MIT-26227WO01CLAIMS1. A metasurface compri si ng : a substrate; meta-atoms arrayed on the substrate, each of the meta-atoms comprising nanoparticles in a host material, the nanoparticles configured to scatter or emit light in a predetermined wavelength band; and index-matching material at least partially encapsulating the meta-atoms, the indexmatching material having a refractive index within 0.1 of a refractive index of the host material.

2. The metasurface of claim 1, wherein at least one of the meta-atoms has a freeform shape.

3. The metasurface of claim 1, wherein at least one of the meta-atoms comprises different types of nanoparticles.

4. The metasurface of claim 1, wherein different ones of the meta-atoms comprise different types of nanoparticles.

5. The metasurface of claim 4, wherein the different ones of the meta-atoms are arranged in a single layer on the substrate.

6. The metasurface of claim 4, wherein the different ones of the meta-atoms are arranged in different layers on the substrate.

7. The metasurface of claim 1, wherein the nanoparticles comprise quantum dots configured to emit light.

8. The metasurface of claim 1, wherein the host material comprises transparent polymer.

9. A three-dimensional micro-display comprising the metasurface of claim 1.

10. The three-dimensional micro-display of claim 9, further comprising: an array of light-emitting diodes (LEDs), bonded to the metasurface, to illuminate the nanoparticles with blue or purple light,Attorney Docket No. MIT-26227WO01 wherein the nanoparticles are quantum dots configured to absorb the blue or purple light and to emit red, green, or blue light in predetermined directions in response to absorbing the blue or purple light so as to produce a three-dimensional light field.

11. The three-dimensional micro-display of claim 10, further comprising: complementary metal-oxide-semiconductor (CMOS) electronics, bonded to the array of LEDs, to actuate LEDs in the array of LEDs.

12. A method of making a metasurface for an optical component, the method comprising: forming meta-atoms of nanoparticles suspended in a host material, the nanoparticles being configured to scatter or emit light in a predetermined wavelength band; and encapsulating the meta-atoms in an index-matching material having a refractive index within 0.1 of a refractive index of the host material.

13. The method of claim 12, wherein forming the meta-atoms comprises: etching an array of cavities in a substrate; and filling the array of cavities with the nanoparticles suspended in the host material.

14. The method of claim 12, wherein forming the meta-atoms comprises: disposing a layer of nanoparticles suspended in the host material on a substrate; and patterning the layer of nanoparticles suspended in the host material to form the meta- atoms.

15. A metasurface comprising: transparent material patterned with: a first set of meta-atoms, each meta-atom in the first set of meta-atoms comprising a first type of nanoparticle in a host material having a refractive index within 0.1 of a refractive index of the transparent material, the first type of nanoparticles configured to scatter or emit light in a first predetermined wavelength band; a second set of meta-atoms, each meta-atom in the second set of meta-atoms comprising a second type of nanoparticle in the host material, the second type of nanoparticles configured to scatter or emit light in a second predetermined wavelength band different than the first predetermined wavelength band; and a third set of meta-atoms, each meta-atom in the third set of meta-atoms comprising a third type of nanoparticle in the host material, the third type ofAttorney Docket No. MIT-26227WO01 nanoparticles configured to scatter or emit light in a third predetermined wavelength band different than the first predetermined wavelength band and the second predetermined wavelength band.

16. The metasurface of claim 15, wherein the first set of meta-atoms, the second set of meta-atoms, and the third set of meta-atoms are interleaved in a single layer of the transparent material.

17. The metasurface of claim 15, wherein the first set of meta-atoms is in a first layer of the transparent material, the second set of meta-atoms is in a second layer of the transparent material disposed on the first layer, and the third set of meta-atoms is in a third layer of the transparent material disposed on the second layer.

18. The metasurface of claim 15, wherein the first type of nanoparticles comprises quantum dots configured to emit light in the first predetermined wavelength band.

19. The metasurface of claim 15, wherein the first type of nanoparticles comprises scattering nanoparticles configured to scatter light in the first predetermined wavelength band.

20. The metasurface of claim 15, wherein the first predetermined wavelength band corresponds to red light, the second predetermined wavelength band corresponds to green light, and the third predetermined wavelength band corresponds to blue light.

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