Terahertz all-dielectric unidirectional guided resonance metasurface based on BIC

Abstract:

A high-Q all-silicon structured metasurface is proposed, consisting of two layers of silicon square pillars. By adjusting the lateral offset distance between the upper and lower layers in the x -direction, the out-of plane σz symmetry is broken, allowing for the free control of perfect Bound states In the Continuum(BIC) states, polarization-sensitive quasi-BIC states, and Unidirectional Guided Resonance(UGR) states at different lattice vectors kx. Notably, since the proposed metasurface operates in momentum space, there are no strict spatial position restrictions for the incident light in real space. Simulation results indicate that after breaking the structural geometric symmetry and the symmetry of the external incident angle, quasi-BIC can achieve a Q value of the order from 10³ to 10⁴. The energy leakage of the generated quasi-BIC can be explained by the incomplete destructive interference of magnetic dipoles. By changing the lateral spacing between the upper and lower layers, unidirectional radiation with a maximum unidirectional radiation efficiency of 97.5% can be achieved at off-Γ point. This work demonstrates significant application potential in the fields of biochemical sensing, high-performance communication, and efficient grating coupling.