Graphene based metasurface with near unity broadband absorption in the terahertz gap

摘要

This paper reports a novel graphene metasurface exhibiting near-unity absorptionover a wide bandwidth of 9.74 THz ranging from 2.06 to 11.80 THz with a fractionalbandwidth of 140.86% with respect to the center frequency of 6.93 THzwithin the terahertz gap of the electromagnetic spectrum. The proposed structureconsists of two layers of graphene separated by silicon dioxide (SiO_2). On the top ofSiO_2, a modified fractal-shaped 1 nm thick graphene pattern is deposited while asquare-shaped graphene pattern of identical thickness completely covers the backsideof the SiO_2 substrate. The absorber was found to be polarization independentunder the normal incidence of the approaching electromagnetic wave (EM) towardthe top layer of the structure due to its 4-fold structural symmetry. The designedstructure offers stable absorption up to 60° incident angle under TE polarizationand 40° incident angle under TM polarization. The structure is ～λ/55.9 thin andmaintains periodicity of ～λ/21.7; thereby validating the effective homogeneity conditionin the sub-wavelength domain. This graphene-based absorber can find severalapplications including, sensors, detectors, spatial light modulators, and inspectroscopic detectors, and so forth, in the “Terahertz Gap” for next-generation 5Gcommunication system and beyond.