Numerical simulation of high Q based on merging bound states in the continuum for high-sensitivity terahertz refractive index sensing

High quality (Q) factor is pivotal in applications such as fluorescence enhancement, biological detection, and nonlinear optics. Currently, high Q relies on the utilization of bound states in the continuum (BIC). Nevertheless, conventional designs driven by symmetry-protected BICs exhibit an exceptional sensitivity to structural perturbations, impeding a high Q factor and limiting practical applications. Here, we have devised two metal block structures. By adjusting the spacing between the metal blocks to acquire Friedrich-Wintgen BIC (FW-BIC) and modifying the asymmetry of the structure to obtain symmetry-protected BIC (SP-BIC), numerical simulations show that the merger of these two BICs leads to an enhancement of the Q factor in the terahertz band. This enhancement is sustained over a broader region, overcoming the limitations imposed by structural perturbations. Furthermore, this method is extendable to similar asymmetric all-dielectric metasurface. Additionally, the theoretically calculated refractive index sensitivity is determined to be 1315 GHz/RIU based on the designed structure. Our proposed method offers a promising avenue for nanostructures with high Q factor and potential applications in sensor devices.