Figure 2.

Design principle of a narrowband metasurface. (a) Three-dimensional schematic view of a metasurface based on dolmen structures on a metal backplane. The nanostructures are made of silver, with a 30 nm-thick SiO₂ spacer. (b) Top view of the optimized supercell, with periods of  nm and  nm. The length nm of the central nanorod along the y direction is fixed, whereas the length of the pair of parallel nanorods along the x direction is or 125 nm; the width and thickness are  nm for all structures. (c, d) Calculated (c) amplitude and (d) phase spectra of the fields reflected from two periodic arrays with parallel nanorod pairs of different lengths: and 115 nm. (e, f) The amplitude and relative phase maps as a function of both wavelength and length L₂. The phase is expressed as the relative phase shift with respect to that in the case of L₂=105 nm.