Manifesting Simultaneous Optical Spin Conservation and Spin Isolation in Diatomic Metasurfaces

Abstract

A novel design strategy that uses a di‐meta‐atomic platform to realize the unique chiroptical effect of simultaneous spin conservation and spin isolation at optical frequencies is demonstrated. The proposed strategy provides extra degrees of design freedom and encompasses the ability to encode a desired phase mask. The unit cell of the proposed single‐layered metaplatform includes a pair of achiral nanofins with distinct structural parameters. The mutual coupling of the nanofins yields constructive and destructive interferences in the absence of in‐plane and radial symmetries, and induces a giant linear chiroptical effect in the form of circular dichroism (CD) along with spin conservation. The optimized di‐meta‐atomic structure achieves 72% reflectance for the co‐polarized parameters of left‐handed circularly polarized (LCP) and 98% absorption of right‐handed circularly polarized (RCP) light with an extinction ratio of 70%. Hydrogenated amorphous silicon (a‐Si:H) is used to design and implement a di‐meta‐atomic‐based platform. The underlying mechanism and working principle for the proposed di‐meta‐atomic geometry are explained by multipole scattering. To validate this method, an encrypted metahologram is implemented; it verifies the concept of a spin‐conserved giant chiroptical effect and spin isolation.