Dual-symmetry-perturbed all-dielectric resonant metasurfaces for high-Q perfect light absorption

We demonstrate a high-Q perfect light absorber based on all-dielectric doubly-resonant metasurface. Leveraging bound states in the continuum (BICs) protected by different symmetries, we manage to independently manipulate the Q factors of the two degenerate quasi-BICs through dual-symmetry perturbations, achieving precise matching of the radiative and nonradiative Q factors for degenerate critical coupling. We achieve a narrowband light absorption with a >600 Q factor and a > 99% absorptance at λ0 = 1550 nm on an asymmetric germanium metasurface with a 0.2λ0 thickness. Our work provides a new strategy for engineering multiresonant metasurfaces for narrowband light absorption and nonlinear applications.