We fabricate all-inorganic, high refractive index optics, including metalenses, waveguides, and diffractive optical elements via nanoimprint lithography with TiO2 nanoparticle dispersion inks and report full-wafer fabrication of visible wavelength metalenses with absolute focusing efficiencies greater than 80% (>95% of design efficiency). 3-D metal oxide log-piles are possible via direct NIL using sequential imprint, planarization, imprint cycles followed by removal of the sacrificial planarization layers. 3-D metal log-piles are possible via metallization of imprinted 3-D sacrificial templates. Several examples will be discussed.
We fabricate all-inorganic, high refractive index optics, including metalenses, waveguides, and diffractive optical elements via nanoimprint lithography with TiO2 nanoparticle dispersion inks and report full-wafer, high-throughput fabrication of waveguides and visible wavelength metalenses lenses with absolute efficiencies greater than 75% (>90% of design efficiency). We employ atomic layer deposition (ALD) as a post-imprint treatment that enables tuning of the refractive index from 1.9 to 2.25 using less than 20 cycles, which improves lens efficiency. Tuning RI of the imprinted optics to match that of the substrates removes concerns about residual layer thickness, resolving a critical issue for some applications. Additional cycles of ALD enable precise tuning of feature dimensions and feature spacings. Finally, we demonstrate the excellent optical and material stabilities of the all-inorganic imprinted optics.
This conference presentation was prepared for the Plasmonics: Design, Materials, Fabrication, Characterization, and Applications XX conference at SPIE Optics + Photonics 2022.
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.
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