Abstract
In this Letter, we demonstrate highly efficient, polarization-insensitive planar lenses (metalenses) at red, green, and blue wavelengths (λ = 660, 532, and 405 nm). Metalenses with numerical apertures (NA) of 0.85 and 0.6 and corresponding efficiencies as high as 60% and 90% are achieved. These metalenses are less than 600 nm-thick and can focus incident light down to diffraction-limited spots as small as ∼0.64λ and provide high-resolution imaging. In addition, the focal spots are very symmetric with high Strehl ratios. The single step lithography and compatibility with large-scale fabrication processes make metalenses highly promising for widespread applications in imaging and spectroscopy.
Highlights
M etasurfaces[1−6] have emerged as one of the leading platforms for the development of miniaturized optical components
Achieving highly efficient metalenses in the visible spectrum poses a plethora of challenges mostly arising from the intrinsic optical loss of the constituent materials, which usually consist of either silicon[21,31−37] or plasmonic noble metals.[38−42] One can alternatively use dielectrics with a transparency window in the visible spectrum; achieving high aspect ratio subwavelength structures with vertical sidewalls is typically very challenging for these materials using current top-down fabrication processes, i.e., lithography followed by dry etching
They demonstrated a TiO2-based lens (NA = 0.25) in the near IR (λ = 860 nm)[44] but experienced similar difficulties with tapered wall profiles and surface roughness, which are commonly associated with this process
Summary
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