Active Terahertz Tuning With Graphene-Loaded Metasurface Enhanced by Quasi-Bound State in Continuum

We propose and experimentally demonstrate a graphene-integrated terahertz (THz) metasurface supporting a quasi-bound state in the continuum (QBIC) mode for active THz modulation. The metasurface, composed of asymmetric split-ring resonators fabricated on a high-resistivity silicon substrate and covered with monolayer graphene, exhibits a sharp resonance enabled by the QBIC effect. By applying a gate voltage via an ionic liquid electrolyte, the Fermi level of graphene is tuned, allowing modulation of the THz transmission. Numerical simulations and temporal coupled-mode theory confirm the resonance characteristics, and experimental measurements reveal a modulation depth exceeding 50% at a gate voltage of 5 V. These results indicate that introducing QBIC effectively enhances the interaction between THz waves and the graphene-loaded metasurface, enabling a high-efficiency, low-cost, and compact approach for dynamic THz wave modulation.