A Perfect Graphene Absorber with Waveguide Coupled High-Contrast Gratings**Supported by the National Natural Science Foundation of China under Grant No 41675154, the Six Major Talent Peak Expert of Jiangsu Province under Grant No 2015-XXRJ-014, and the Jiangsu 333 High-Level Talent Cultivation Program under Grant No BRA2016425.

Abstract

To achieve the enhancement and manipulation of light absorption in graphene within the visible and near infrared regions, a design consists of high-contrast gratings and two evanescently coupled slabs with graphene monolayer is demonstrated. The operation principle and design process of the proposed structure are analyzed using the coupled mode theory, which is confirmed by the rigorous coupled wave analysis. It is proved that the absorptance of graphene monolayer can be greatly enhanced to unity. The thickness of grating and slab layers can significantly change the line width and resonant mode position in the absorption spectra. Furthermore, high tunability in amplitude and bandwidth of the absorption spectra can be achieved by controlling the structural parameters of the hybrid structure. The proposed devices could be efficiently exploited as tunable and selective absorbers, and could be allowed to realize other two-dimensional materials-based selective photo-detectors.