Multiple-band perfect absorbers based on the combination of Fabry-Perot resonance and the gap plasmon resonance

To realize multiple-band perfect absorption, a novel nanostructure consisting of subwavelength periodic metallic grating and a thick metallic substrate, separated by a thin dielectric spacer(MGDM), is proposed in this paper. Compared with the structures without the dielectric spacer, the designed MGDM nanostructure not only possesses the absorption peaks caused by the Fabry-Perot resonance in the grating slits, but also possesses additional absorption peaks. Numerical simulation results show that the additional absorption peaks are caused by the gap plasmon resonance in the dielectric spacer. Besides, the influence of structural parameters on the absorption properties of MGDM are also thoroughly investigated. The combination of Fabry-Perot resonance and the gap plasmon resonance in the proposed MGDM provide another route for designing multiple-band perfect absorber nanostructures, which have an extensive applications in photo-detecting, photo-conversion or photo-harvesting.