Enhancement of Absorption in Graphene Strips With Cascaded Grating Structures

The enhanced absorption effects of graphene strips with cascaded grating structures are investigated. A graphene absorber, which consists of a graphene grating and a dielectric grating backed with a Bragg grating, is designed and studied. The combined effects of guided-mode resonances with dielectric gratings and the photonic bandgap with a Bragg grating lead to the realization of critical coupling, which makes the absorber exhibit near-unity absorption/emission at resonance but with ultra-narrow spectral and antennalike responses. Both the coupled-mode theory and the electric-field distributions are presented to provide a physical understanding of such an absorption behavior. We believe that the conclusions may be useful for the design of graphene-based optoelectronic devices.