Independent ultrahigh-Q dual-band resonances via coating a resonator on a BIC-driven metasurface

Traditional designs driven by symmetry-protected bound states in the continuum (SP-BICs) hardly support independent dual-band resonances, and they require extremely small perturbations to obtain an ultrahigh-Q. Here, we propose an SP-BIC-driven structure composed of a metasurface and a resonator, which supports independent dual-band resonances and enables ultrahigh-Q at large perturbations. The underlying mechanism enabling this is to form reasonable eigenfield distributions of two BICs by coating a dielectric layer on the metasurface. One eigenfield is confined within the metasurface and the bottom of the resonator, while the other one concentrates at the top of the resonator. Thus, two resonances with different originations can be supported, and the effect of metasurface perturbations on the eigenfields is weakened. This work provides a promising pathway for unlocking the potential of SP-BICs, enhancing light trapping and manipulation across diverse applications.