Study on the characteristics of grating structure sensing based on off-Γ bound states in the continuum

Abstract

Due to the polarization dependence, there are two kinds of off-Γ bound states in the continuum (BIC) modes (TM-like mode and TE-like mode) for C2 symmetric grating structure. Compared to symmetrical protection BIC, off-Γ BIC is more susceptible to environmental changes, resulting in high refractive index sensitivity. In this paper, the influence of grating structure parameters on refractive index sensitivity of off-Γ BICs is studied, and the responses of two BIC modes to environmental refractive index are summarized. The refractive index sensitivities of TM-like mode and TE-like mode have different responses to grating structure parameters. The maximum sensitivity and figure of merit (FOM) of TM-like mode are 476 nm RIU−1 and 15866 RIU−1, while these of TE-like mode are 720 nm RIU−1 and 1440 RIU−1 respectively. These conclusions provide insights for the assembly and research of grating optical sensors based on off-Γ BICs.