Ultrahigh-Q Quasi-BICs via Precision-Controlled Asymmetry in Dielectric Metasurfaces

Achieving ultrahigh quality factor optical resonances is crucial for advancing low-threshold lasers, high-sensitivity sensors, and nonlinear photonics. While dielectric metasurfaces supporting quasi-bound states in the continuum (qBICs) show great potential, their experimental realization has been challenging due to the difficulty of precisely controlling symmetry-breaking at the nanoscale. Here, we introduce a precision-controlled symmetry-protected qBIC method using angular perturbations to precisely tune asymmetry, ensuring both high precision and reproducibility of Q-factors. In contrast to traditional SP-qBIC excitation, which relies on uncontrolled asymmetry, our method offers more accurate and…