▎ 摘　　要

We investigate the absorption enhancement of an unstructured graphene sheet in a broad frequency range from terahertz (THz) to mid-infrared regime. Ultra-multiband graphene absorption enhancement is observed by integrating graphene in a metal-dielectric-graphene (MDG) sandwich structure for polarized waves. Multiple order Fabry-Perot (FP) resonances are demonstrated to be responsible for the multiband absorption. Furthermore, perfect absorption is realized by introducing the MDG structure on a metal reflector to suppress the transmission channel. In addition, the absorption peaks can be easily tuned by changing the doping level of graphene. This work may have potential for improving the performance of graphene based optoelectrical devices and can be regarded as a demonstration of a tunable broadband near-perfect metamaterial absorber. (C) 2017 Optical Society of America