Multiple bound states in the continuum based on the dielectric metasurface

Abstract

Optical metasurfaces with high quality factors (Q-factors) of bound states in the continuum (BICs) can substantially boost light–matter interaction for various applications in ultrathin and active metadevices. In this paper, we propose a metasurface supporting both at Γ BICs and off Γ BICs, and they can be modulated regularly. The sensitivities of the monolayer and bi-layer structures can reach 157.918 nm/RIU and 165.76 nm/RIU, respectively, at incident angles of 0.01 deg. For the bi-layer metasurface, four BICs at Γ point are achieved, and they are influenced by the structural parameters dramatically. Additionally, the four at Γ BICs coincide into two and then behave similarly to the monolayer case with the distance being large enough, which is associated with the BICs becoming uncoupled when the layers get far from each other. Furthermore, similar behaviors (four at Γ BICs coincide into two) are observed by varying the nanopore size in one layer of the bi-layer metasurface. For an oblique incidence, two off Γ BICs show up, and their center wavelengths have a dependent relationship with the size of the nanopores and the distance between layers. The results for monolayer and bi-layer metasurfaces are useful for potential applications based on BICs, such as sensors and filters.