Realizing Ultrahigh-Q Resonances Through Harnessing Symmetry-Protected Bound States in the Continuum

Harnessing the power of symmetry-protected bound states in the continuum (SP BICs) has become a focal point in scientific exploration, promising many interesting applications in nanophotonics. However, the practical realization of ultrahigh quality (Q) factor quasi-BICs (QBICs) is hindered by the fabrication imperfections. In this work, an easy approach is proposed to achieve ultrahigh-Q resonances by strategically breaking symmetry. By introducing precise perturbations within the zero eigenfield region, QBICs with consistently ultrahigh-Q factors, beyond conventional limitations are achieved. Intriguingly, intentionally disrupting symmetry in the maximum eigenfield region leads to a rapid decline in QBIC's Q-factors as the asymmetry parameter increases. Leveraging this design strategy, ultrahigh-Q modes with a high Q-factor of 36,694 in a silicon photonic crystal slab are experimentally realized. The findings establish a robust and straightforward pathway toward unlocking the full potential of SP BICs, enhancing light-matter interactions across diverse applications.