Lattice‐Enhanced Fano Resonances from Bound States in the Continuum Metasurfaces

Fano resonances in metamaterials are known for their high quality (Q) factor and high sensitivity to external perturbations, which makes them attractive for sensors, lasers, and nonlinear and slow light devices. However, Fano resonances with higher Q factors obtained through structural optimization of individual resonators are accompanied by lower resonance intensity, thereby limiting the overall figure of merit (FoM) of the resonance. Here, a strategy for simultaneously enhancing the Q factor and FoM of Fano resonances in terahertz metamaterials is reported. Coupling of the Fano resonance, which arises from a symmetry‐protected bound state in continuum, to the first‐order lattice mode of the metamaterial array leads to stronger field confinement and substantial enhancement of both Q factor and FoM. As such enhancement occurs in planar metamaterials independently of the resonator geometry, the proposed approach can be utilized for a wide range of high‐Q and high‐sensitivity terahertz metadevices. Coupling of lattice modes and structural resonances of metamaterials can be used to reduce radiation losses. Herein, structural Fano resonances are coupled to lattice modes, enhancing the quality factor with little reduction of resonance intensity. The Fano resonances arise from the symmetry‐protected bound state in continuum, which possesses an infinite quality factor under ideal conditions.