Tunable Ultra-Multispectral Metamaterial Perfect Absorbers Based on Out-of-Plane Metal-Insulator-Graphene Heterostructures

The out-of-plane metal-insulator-graphene (MIG) heterostructure separated from metal substrates by a silica spacer has been intensively investigated. Both numerical simulations and theoretical calculations exhibit that due to the dominating effect of adjacent metal layers, multiple strongly confined Fabry-Perot (F-P) resonances are simultaneously excited on the ingenious out-of-plane MIG heterostructure; and thus, are conductive to the realization of a nine-band plasmonic perfect absorber at mid-infrared wavelengths. The spectral positions of absorption peaks are handily tuned by changing the structural parameters of MIG heterostructures and the electrically controlled chemical potential of graphene. More interestingly, the good absorption stability at varying incident angles is observed. Numerical simulations are in excellent agreement with theoretical results. Such tunable angle-independent nine-band perfect absorber undoubtedly finds utility in mid-infrared optical filters and modulators. The proposed out-of-plane MIG heterostructure allows possibilities for multispectral enhancement of light-graphene interactions.