Symmetry-engineered dielectric metasurfaces for polarization-dependent quasi-BIC modes with reconfigurable optical responses

Abstract

Bound states in the continuum (BICs) in optical metasurfaces, characterized by their high-quality factors, offer significant opportunities for advanced photonic applications. In this paper, we demonstrate a polarization-dependent quasi-BIC (qBIC) platform via symmetry-engineered silicon metasurfaces. By strategically breaking translational and reflection symmetries, the proposed structure supports multiple high-quality factor resonances, including translational-symmetry-protected, accidental, and reflection-symmetry-protected modes. These resonances can be dynamically modulated by adjusting the polarization state of the incident light. The physical origins of the qBICs are elucidated via the electromagnetic field distributions and multipole decomposition analysis. Notably, strong coupling between qBICs gives rise to electromagnetically induced transparency-like effects with a remarkably high group index of ∼39 000. Furthermore, the metasurface exhibits excellent sensing performance with a sensitivity of 536 nm/RIU and enables high-contrast polarization-dependent optical switching, achieving a maximum modulation depth of 99.66%. These results highlight the versatility and tunability of the proposed metasurface, offering promising opportunities for applications in sensing, slow-light devices, and polarization-controlled photonic systems.