A Highly Efficient Bifunctional Dielectric Metasurface Enabling Polarization-Tuned Focusing and Deflection for Visible Light

Multifunctional metasurfaces have attracted drastically growing interest, serving as a prominent candidate to cope with both device miniaturization and integration. Conventional transmissive bifunctional metasurfaces working for visible light inherently suffer from several demerits owing to the use of geometric phase and spatial multiplexing scheme. Research endeavors are mainly devoted to the implementation of static devices. In this work, a highly efficient bifunctional dielectric metasurface, taking advantage of a unit cell (UC), the building block of which capitalizes on a nanopost in hydrogenated amorphous silicon, is proposed and experimentally demonstrated to successfully enable polarization-mediated anomalous beam deflection and focusing in the visible band. Through the tailoring of the UC periodicity, it is found to be capable of efficiently tuning the beam deflection angle and focusing distance. For the fabricated sample, the normal transverse-electric incidence within a spectral band from 600 to 715 nm is angle-resolved to a single diffraction order via the beam deflection, while a bright line focus is attained at the target focal plane for the normal transverse-magnetic incidence at λ = 650 nm. This work will initiate a positive prospect for the development of high-performance tunable multifunctional metasurfaces.