This document contains additional details on the design, fabrication and experimental characterization, as well as supplementary results. Newly introduced equations are labeled with the prefix “S”, whereas newly introduced figures and tables are referred to as “Supplementary” and are labeled with the prefix “S”; all others pertain to the main text. All references are intended as local, and those already utilized in the main text are repeated.
Our metasurface design relies on a preliminary numerical study of the transmission coefficient pertaining toa 2-D periodic array of identical rectangular nanoholes. These numerical simulations are carried out by means of the RF module available in the finite-element-based commercial software COMSOL Multiphysics (www.comsol.com).
The periodic array is placed at the interface between two homogeneous halfspaces made of silica and air. We consider a square unit-cell with sidelengthwhich, at the operational wavelength of interest , ensures that only the fundamental (zeroth) diffraction order propagates in the two regions.The unit cell is terminated by periodic Bloch-type boundary conditions along the - and - directions. Port-type terminations are instead assumed along the incidence direction , at a distance (i.e., ambient wavelength) from the array, and matched with the zeroth-order modes for both - and -polarized illuminations. An adaptive meshing is utilized, with maximum element size of in the uniform dielectric regions, and of 15 nm in the air regions of the array; for the gold layer, a minimum number of two elements per skin depth ( at ) is employed.