High-Q transparency band and high optical sensitivity of an all-dielectric THz metasurface based on the bound state in the continuum

Bound state in the continuum (BIC), as a novel eigenmode with infinitely high quality factor (Q-factor), has received great attention in modern optical science. We design a metasurface composed of two rods and a square ring in one lattice in the terahertz band. Three symmetry-protected BICs are observed of the composed metasurface, in which two BICs come from the rods resonator and one is deserved from the square ring resonator. It demonstrates that the number of the BICs in the considered waveband can be regulated by these resonators in one lattice []of the metasurface and electromagnetically induced transparency (EIT) appears when the quasi-BIC (q-BIC) coupling to the leaky mode coincidentally. Furtherly, we can modulate the center frequencies of both these BICs and the leaky mode by adjusting structural parameters. Especially, dual-EITs and an interference BIC are formed of the composed metasurface by adjusting the distance between two resonators in one lattice. Additionally, the sensitivity and group index of the metasurface reach a very high level, these results are helpful in the development of the terahertz optical device.