Excitation of Tunable Dual Quasi-Bound States in the Continuum in Graphene Metasurface and Terahertz Sensing Application

This study proposes an all-graphene metasurface supporting dual band symmetric bound state in the continuum (BIC) in the terahertz (THz) range for the first time. The structure consists of a unit cell containing a double-gap split ring resonator periodically on a dielectric substrate. By introducing symmetry breaking, two plasmonic quasi-BIC (Q-BIC) transmission dips are observed with finite Q-factors and high modulation depth. Simulation and analysis results simultaneously exhibit that the Q-factors of Q-BICs follow an inverse square dependency with the asymmetry degree. Via changing the graphene’s chemical potential, the Q-BICs’ operating frequency range can be actively expanded. The dual Q-BICs are immune to the variation of incident angle and have a significant slow light effect with time delay up to 23.8 ps. In addition, the sensing performance in THz region is investigated. A maximum sensitivity of 267.5 GHz/RIU is obtained with a FOM of 24.08 RIU−1. Our work shows an alternative way to design the class of tunable Q-BIC metasurface, which will provide a valuable reference for future dynamic sensor and other fields.