In‐Plane Metasurface Design for Perfect Chiral Dichroism in Inhomogeneous Environment

Bound states in the continuum represent a captivating and significant phenomenon in the realms of photonics, materials science, and quantum mechanics. These exceptional resonant states have emerged as crucial elements in a diverse array of nanotechnology applications including chiral nanophotonics. Applying bound states in the continuum for chiral applications is a challenging problem and usually requires some additional complicated steps such as multi‐layer lithography, adding superstrate with index matching materials and geometry parameters adjusting. Nevertheless, creating a structure placed in inhomogeneous background that is capable to perfectly convert one circular polarization to the opposite one is still a challenging problem. This work presents chiral metasurface based on bound states in the continuum allowing to achieve perfect unitary circular conversion in an inhomogeneous environment. This approach is based on a coupling of two chiral but not perfect resonances which makes it possible to get one mode with chiral dichroism value of 1. A theoretical model is built, perform numerical calculation and conduct an experimental verification to prove this concept. The presented results could find many applications in sensing, optics, telecommunications, biomedical and chemical analysis.