High-Q Silicon-Based Metasurface Perfect Absorber via Geometrical Perturbation Assisted Resonances

A multi-band high-
$Q$
silicon-based metasurface light absorber is demonstrated via introducing geometrical perturbation for excitation of multipolar resonances. The displacement perturbation enables the ultra-sharp and near-unity absorption bands, leading to a 30-fold increase of the spectral
$Q$
factor and 12-fold enhancement of the absorptance in comparison to that of the un-perturbed silicon resonators. Moreover, owing to the overlapping of the electrical and magnetic dipoles, and the co-existence of electrical quadrupole modes, a new sharp absorption peak with the
$Q$
factor up to 539.1 is obtained, paving a new insight on achieving narrowband absorption. These findings suggest new methods for manipulation in spectral lineshape and also hold wide applications in optoelectronic modulators and devices.