Tunable Graphene-Based Metasurface for Polarization-Independent Broadband Absorption in Lower Mid-Infrared (MIR) Range

This paper proposes a tunable graphene-based wideband metasurface for high absorption in the lower mid-infrared frequency region. The unit cell of the proposed structure consists of slot generated out of modified fractal-shaped graphene layer deposited on top of amorphous silicon dioxide (SiO2) grown over 0.1-μm-thick gold layer. The structure exhibits distinctive high absorption greater than 90% absorptivity over the range of 3.69-9.77 THz covering a wideband of 6.08 THz. Incorporation of graphene in the metastructure can tune the absorption bandwidth owing to conductivity modulation of graphene by the control of impurity doping and mechanical stretching. Besides, the absorber is polarization independent under normal incidence because of the fourfold symmetry of the deposited graphene pattern. The designed prototype has been studied under oblique incidences for both transverse electric and transverse magnetic polarizations where wideband absorption has been experienced up to 40° incident angles for both cases. The prototype is found to be as thin as ~λ/11 with respect to the lowermost frequency of the absorption. The period of the unit cell is ~λ/13 supporting the effective homogeneity condition in subwavelength region. The structure can have applications toward sensing, spectroscopy, etc.