Switching BIC through polarization of incident light on bilayer malposed photonic crystal slabs

Abstract

Bound states in the continuum (BICs) are initially regarded as special modes of structure and independent of external conditions. The dynamical modulation of BICs or quasi-BICs is based on the tuning of structure parameters, which meets the technological challenge. In this paper, we propose a new formation mechanism of BICs that is induced by the combination of intrinsic and extrinsic factors. Through a sandwiched structure constructed with a photonic crystal (PC) slab–waveguide–PC slab configuration, four eigen modes have been found at the Γ point. The translational displacement between the two PC slabs leads to change in frequencies and decrease in quality factors of the four modes. In the transport spectra of the structure, the combination of the polarization direction of incident light and displacement vector can transform Γ resonance modes into a new type of BICs with an infinite Q factor and a forming mechanism different from any current ones. The unique mechanism makes it possible to dynamically switch the BIC with extreme flexibility. Furthermore, around the BIC, a transformation from line polarization (input) to circular polarization (output) has been achieved.