Polarization-Independent BIC-Based Electromagnetically Induced Transparency

Recently, electromagnetically induced transparency (EIT) has emerged in nanophotonics for filtering, thermal camouflaging, sensing, and others. However, most of the proposed concepts operate for a specific polarization of excitation, which limits their performance in applications. Here we propose a design providing a polarization-independent EIT resonance. Our approach is based on a silicon metasurface supporting symmetry-protected quasi-bound states in the continuum (quasi-BICs) in the near-infrared range. The metasurface consists of a periodic array of cut silicon disks on a SiO₂ substrate. We achieve polarization independence by combining two different quasi-BIC EIT modes for two orthogonal polarizations of exciting light. By tuning the interference of broad and narrow Mie-resonant multipoles, we have developed a metasurface with the desired properties. The effect is robust for various geometrical parameters. Furthermore, we have fabricated the optimized structure and experimentally confirmed our approach.