Parity-protected anomalous diffraction in optical phase gradient metasurfaces

Abstract

Optical phase gradient metasurfaces (PGMs) have provided unprecedented opportunities for arbitrarily controlling wave propagation via the generalized Snell's law (GSL). However, the whole picture of wave diffraction therein has not been clearly presented, particularly for the incident angles beyond the critical angle. Although a parity-dependent diffraction effect was found in acoustic metagratings, little is known about whether this effect holds true in typical optical PGMs. Here we demonstrate the universality of the parity-dependent diffraction effect by employing some optical PGMs with popular designs, such as all-dielectric and plasmonic meta-atoms. It is first shown that the parity in optical PGMs plays a significant role in determining the diffraction physics, producing a robust reversal effect of outgoing waves from the reflection to the transmission side. As an alternative degree of freedom in PGMs, the parity-dependent diffraction effect, together with the GSL, provides a complete theory to manipulate wave fields, further advancing various explorations in unique wave phenomena and promising applications.