Double split-loop resonators as building blocks of metasurfaces for light manipulation: bending, focusing, and flat-top generation

Abstract

In this paper, we demonstrate the concept of simultaneous controlling of the phase and the polarization handedness of a circularly polarized (CP) incident beam over an array of bilayer double split-loop resonators (DSLRs). The physical parameters are optimized by means of the finite-difference time-domain method in such a way that each unit-cell exhibits the half-wave-plate response. By simply rotating the unit-cell, the phase shift of the transmitted cross polarized beam can be controlled in the range of 0−2π without any restrictions. This plasmonic metasurface provides optimal cross polarization transmission efficiency (>70%) at 1.55 μm wavelength. An array of DSLRs with helicity dependency and spatially varying phase response offers the possibility of designing anomalous bending and bifunctional (convergence/divergence) metasurfaces in which the bending direction and convergence/divergence feature can be directly controlled by the handedness of the impinging CP wave. Furthermore, a metalens with the capability of converting a CP Gaussian beam into a uniform irradiance profile (flat-top beam) is designed, and the performance of structure is evaluated in detail. All the designs are composed of the same DSLR elements with space-variant orientations.