Tunable terahertz bound state in the continuum in graphene metagrating

Abstract

Recently, high quality (Q) factor resonances governed by quasi-bound state in the continuum (BIC) have attracted increasing attention due to the fascinating electromagnetic resonance properties that provide a new guideline for the design of metasurfaces. In this paper, we propose a graphene metagrating that can support quasi-BIC by introducing periodic perturbations. We discuss the transmission spectrum at normal and oblique incidence. Resonances are analyzed by the multipolar decomposition of radiative power and the electric field distribution to clarify the mechanism of quasi-BIC. The amplitude of quasi-BIC Fano resonance can be tuned by adjusting the chemical potential of graphene, and the modulation amplitude can reach 74%. Furthermore, the relationship between the Q factor of quasi-BIC and the graphene chemical potential is thoroughly investigated. The Q factor of quasi-BIC resonance can achieve linear tunability within a specific range of chemical potential. The further evolution and comparison of the proposed unit cell show that our method of introducing perturbation is universal to some extent. Altogether, the proposed metagrating can be used as an excellent active THz modulator and has potential applications in biochemical sensing, laser and nonlinear optics.