Distance‐Driven Terahertz Metallic Metasurface Supporting QGM in the Continuum

Abstract The metasurfaces that support high‐ Q resonances can provide ultra‐sharp resonance and achieve strong light‐matter interaction, which promotes their application in various fields such as sensing, lasing, and imaging. Bound modes, unable to radiate into free space, can be transformed into quasi‐bound modes and coupled with external radiation, achieving high‐ Q resonances. For periodic structures, by introducing appropriate periodic perturbations, the guided modes (GMs) below the light line can be exposed above the light line, forming the high‐ Q quasi‐guide modes (QGMs). Herein, a metallic metasurface is designed that supports the QGM in the continuum by introducing the Brillouin zone folding strategy. The simulation and experiment demonstrate that the GM below the light line can be transformed into the QGM in the continuum by tuning the distance parameter, and a typical “electromagnetic‐induced transparency‐like (EIT‐like)” spectrum is observed. The design unlocks additional degrees of freedom for generating high‐ Q metallic metasurface. The advantage of avoiding the production of asymmetric defects contributes to releasing the strict requirement on manufacturing precision. The combination of the metallic metasurface supporting QGM resonance with high‐ Q factors and the flexible substrate can improve the performance of the flexible devices and broaden its application in terahertz optoelectronic devices.