Mechanism Behind Angularly Asymmetric Diffraction in Phase-Gradient Metasurfaces

Abstract

Phase-gradient metasurfaces (PGMs) provide remarkable control over the propagation of light. One expects that the number of unit cells $m$ in a supercell should not change the nature of a PGM's diffraction characteristics, yet recent experiments have indicated $m$-dependent asymmetric absorptivity. An analytical description of the relationship between absorptivity and $m$ is needed, but lacking. This study offers a simple, intuitive semianalytical approach to explaining the observed asymmetric absorptivity. Here the phase gradient ensures additional, multiple total internal reflections inside the grating, leading to more dissipation and the asymmetric diffraction response.