Electromagnetically induced transparency in square slotted dielectric metasurfaces supporting bound states in the continuum

In this work, a novel dielectric metasurface consisting of square slotted arrays etched in a silicon layer is proposed and theoretically demonstrated. The structure is designed to support electromagnetically induced transparency (EIT) based on quasi-bound states in the continuum (qBIC). Specifically, the metasurface consists of square slots with a silicon gap that breaks the symmetry of the structure. Thanks to the interaction of the sharp quasi-BIC resonances with a broadband background mode, an extremely high $\mathbf{Q}$ factor EIT response of $\boldsymbol{6\cdot 10^{6}}$ is demonstrated (considering the length scales feasible during fabrication and optical losses). Moreover, the resonator possesses a simple bulk geometry and subwavelength dimensions. The proposed metasurface, its high $\mathbf{Q}$ factors, and strong energy confinement may open new avenues of research on light-matter interactions in emerging applications in non-linear devices, lasing, biological sensors, optical communications, etc.