Quasi-Bound State in the Continuum of the Intracoupled All-Dielectric Coherent Metasurface.

Metasurfaces have transformed the landscape of nanophotonics by enabling the precise control of light-matter interactions across a wide spectral range. Recently, dielectric metasurfaces have garnered significant attention due to their potential for low nonradiative loss. In this study, we introduce a novel metasurface design that employs biradial circular resonators to induce quasi-bound states in the continuum (q-BIC) through minimal symmetry breaking, demonstrating resonance with a Q factor of 650. It is predominantly driven by the interference of the electric dipole and the magnetic quadrupole. This approach addresses key limitations by simplifying fabrication and enhancing robustness while delivering high tunability, strong photonic confinement, and a 4-fold photoluminescence enhancement experimentally. The proposed strategy not only provides a new pathway for emission enhancement but also underscores the broader utility of q-BIC metasurfaces in light-matter interaction. Through a detailed analysis of the symmetry, resonance tuning, and field distribution, we elucidate the fundamental physics underlying our design.