Dual band and tunable perfect absorber based on dual gratings-coupled graphene-dielectric multilayer structures

In this paper, a mid-infrared perfect absorber based on the dual gratings-coupled graphene-dielectric multilayer structures (DGC-GDM) is proposed, in which GDM is sandwiched between two Au gratings. The DGC-GDM absorber shows advantages of dual-band and tunable absorption, insensitive to polarization, ultrathin thickness and wide angle range absorption. Two kinds of SPPs in the GDM layer can be excited by the upper and lower Au gratings, respectively, which confine the incident light into the GDM and thus contribute to the dual-band absorption. The wavelength of the absorption peak can be effectively changed by varying the Fermi level of graphene. Most importantly, an analytic formulas describing the relationships between the parameters of the absorber and the absorption spectra is derived. And the accuracy of the theoretical formulas is verified by comparing the simulation results with the theoretically calculated ones. Therefore, the exact values of parameters of the structure for an absorption peak as required can be obtained. The proposed structure can be applied to absorbers that are working at other frequencies.