▎ 摘　　要

In this paper, a highly sensitive and tunable graphene-based quad-band perfect or nearly perfect absorber is theoretically investigated. The proposed design is composed of a stacked nanohole and cross-shaped graphene on top of a gold layer separated by an insulator. Based on the numerical simulations, four absorption peaks are observed in the proposed structure, which can reach to 100% at 9.47 mu m, 93% at 10.03 mu m, 97% at 13.93 mu m, and 96% at 18.81 mu m in the infrared range. It has been shown that the absorption peaks can be independently tuned by varying the Fermi energy level of the graphene layers as well as the geometrical parameters of the structure, which is highly desired for wavelength selective sensing. In addition, the proposed absorber can be used as a plasmonic sensor for refractive index sensing with maximum sensitivity of 12.86 mu m/RIU and figure of merit of 49.90, which is very remarkable compared to the previous reported values. Due to the symmetry of the proposed device, a wide angle-insensitive high absorption is maintained for all of the bands under transverse-electric and transverse-magnetic polarizations. With its excellent performance, our graphene-based tunable multiband absorber can be used in biosensors, chemical sensors, and many other nanophotonics devices. (C) 2021 Optical Society of America