We describe a high throughput approach to all-inorganic metalens manufacturing using a single step nanoimprint lithography process and titania nanoparticle-based inks. The process yields a refractive index of 1.9, lenses with critical dimensions below 60 nm, feature aspect ratios greater than 8, and efficiencies greater than 55% and consistent device performance across 15 lenses printed within 30 minutes. We further describe pathways to fabricating all-inorganic lenses with RI of 2.1.
With high feature density and subwavelength dimensions, visible
spectrum metalenses are challenging to scalably
manufacture. Electron beam lithography and short-wavelength
photolithography capable of patterning metalenses for the visible
do so at high cost per wafer. Here, we present a low-cost and
scalable fabrication process based on nanoimprint lithography, and
use it to demonstrate metalenses designed for 550 nm light with 4
mm diameter and NA=0.2. Our metalenses are formed of silicon
nitride nanoposts with critical dimensions smaller than 100 nm. In
this presentation we report focusing efficiencies above 50%,
share holographic characterization data, and demonstrate
imaging.
We present system-level models for ideal and realistic metasurfaces that can be used in designing metasurface optical systems. We show that ideal gradient metasurfaces have spatially varying field transmission amplitudes that can exceed one and discuss its effect on the modulation transfer function of metalenses. We introduce a general model for non-ideal metasurfaces based on the discrete-space impulse response concept. The new model takes into account reflections and undesired diffractions from metasurfaces and enables accurate black-box models that can be incorporated into design tools. We also present examples of its applications in analyzing optical systems composed of cascaded metasurface components.
The recent development of efficient dielectric metasurfaces has enabled practical optical components and systems composed of multiple cascaded metasurfaces. In this talk, I present an overview of our work on modeling, design, and implementation of cascaded metasurface components and systems. In particular, I present accurate system-level models for metasurfaces, techniques for designing efficient metasurfaces, multifunctional cascaded metasurfaces, and bilayer birefringent metasurfaces that provide the ultimate control over the wavefront and polarization of light. Furthermore, I will introduce a novel technique for engineering chromatic dispersion by cascading and briefly discuss a single-snapshot hyperspectral imager enabled by cascading multiple metasurfaces.
Optical metasurfaces are subwavelength-thick arrays of meta-atoms that have attracted significant attention due to their superior capabilities compared with conventional optical devices. Designing metasurfaces for practical applications requires system-level models that accurately predict their responses. The conventional approach for modeling metasurfaces is to ignore the coupling among the meta-atoms and to model metasurfaces as phase, amplitude, or polarization masks that are independent of the incident light’s wavefront, which is an inaccurate assumption for large incident angles. In this talk, we will introduce a novel technique for the modeling and design of metasurfaces based on the discrete-space impulse response (DSIR) concept. Because the waves propagating in free space are spatially band-limited, the incident, the transmitted, and the reflected waves can be represented using discrete-space signals that are obtained by sampling these waves at the Nyquist rate (at half a wavelength intervals). As a result, we can define discrete-space impulse responses for metasurfaces that relate the transmitted/reflected waves to the incident waves. We show that such impulse responses are local, accurately model the interactions among neighboring meta-atoms, and completely characterize the metasurfaces’ response to any incident waves. We also introduce a new approach for designing metasurfaces using the DSIR concept. As a proof-of-concept, we present the characterization results of a high numerical aperture meta-lens that is designed using the DSIR technique and show that its focusing efficiency is higher than that of a similar meta-lens designed using the conventional technique.
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