Numerical investigation on dielectric-metal based dual narrowband visible absorber

We propose a dual narrowband perfect visible absorber using periodic dielectric nanoring arrays on aluminum film. This nanostructure can reduce the oxidation problem that noble metal nanostructure is facing. In the designed structure, the resonance peak I corresponds to the first order grating mode, and the resonance peak II is due to the combination of SPP mode, SLR mode and the guide mode. For the application as refractive index sensor, the sensitivity of the two resonance modes is almost the same, and the figure of merit (FOM) of the resonance I and II are 21.8/RIU and 3.5/RIU, respectively. The narrowband perfect absorber has potential applications in sensing application.