Germanium metasurface near-infrared high-q absorber with symmetry-protected bound states in the continuum

Abstract

The all-dielectric germanium nanohole (GNH) metasurface with a sub-wavelength thickness supports simultaneous excitation of quasi bound state in the continuum (BIC) and super radiant mode. By selecting the different hole depths in a germanium slab, we present a trade-off metasurface between high Q-factor and high absorption in the photonic system. The presented device demonstrated absorption of super-radiant mode ∼98.5% and quasi-BIC ∼93% without back-metal reflector at the telecommunication wavelength. The numerical results, obtained by the finite difference time domain (FDTD) method are explained in the framework of temporal coupled mode theory (TCMT).