Broad-band polarization-insensitive all-dielectric metalens enabled by intentional off-resonance waveguiding at mid-wave infrared

Abstract

Metasurfaces are promising candidates to take the place of conventional optical components as they enable wavefront engineering at sub- and near-wavelength distances along both lateral and vertical directions. Plasmonic metasurfaces containing sub-wavelength metallic structures constitute initial examples of this concept. However, plasmonic metasurfaces cannot achieve satisfactory efficiencies in the transmission mode due to their intrinsic losses. The low efficiencies of transmissive plasmonic metasurfaces motivated solutions using dielectric ones. Such high-efficiency all dielectric metasurfaces depend on either resonance tuning or Pancharatnam–Berry (geometrical) phase approaches. However, these approaches are limited to either narrow operation bands or suffer polarization dependency. Here, we propose and show high-index dielectric nanopillars operated as cylindrical waveguides deliberately in the off-resonance regime to achieve polarization independent wavefront control over wide spectral bands. As a proof-of-concept structure, we demonstrated a focusing metalens operating at wavelengths from 4.0 to 4.6 μm under both s- and p-polarized illuminations. The designed lens maintains the focusing operation with a maximum of 4% focal distance shift having a relative efficiency of >94% and an absolute efficiency of >67% all over the defined spectral band of 600 nm, which outperforms the previously reported metalenses in terms of wide-band operation with high performance.