Infinite versus finite 1D-dielectric gratings supporting SP-BIC modes for sensing applications

Abstract

In this paper, we investigate the existence of a special so-called Symmetry-Protected Bound state In the Continuum (SP-BIC) mode in a typical infinite and finite 1D-periodic TiO2-based dielectric structure. Using Finite-Difference Time-Domain (FDTD), Fourier-Modal Method (FMM) and N-order FDTD simulations, a complete optical characterization of the structure is performed. In comparison with the classical Guided Mode Resonance (GMR), the existence and the excitation efficiency of this particular mode are studied with respect to the illumination conditions of the structure and the number of periods when the structure is finite. Our results are an additional contribution to designing efficient resonators for sensing applications. It is shown that for a finite and then more realistic structure, the quality factor is directly related to the number of periods N. It reaches the same value as for the infinite case when the number of periods is N = 200. A high sensitivity, comparable to the infinite case, is also obtained from N = 50.