Tunable multi-band absorbers based on graphene metasurfaces for infrared sensing and switching

In this paper, a kind of dynamically tunable graphene metasurface which can act as a multi-band refractive index sensor or a four-state optical switch is proposed. Based on the plasmonic hybridization mechanism of a simple graphene ring array, this design exhibits dual-channel resonance modes to realize ultrahigh sensitivity for refractive index sensing, which is 4.25μm/RIU at mid-infrared band and 11.33μm/RIU at far-infrared band, respectively. The proposed design manifests an ultrabroad sensing range through tuning the Fermi level of graphene and a good insensitivity to the incident angle. In addition, we numerically demonstrate a reflective optical switch with the structure of dual-layer graphene disks which indicates that a four-state optical switch is achieved and the cut-off absorptivity is more than 98%. The concise structures are of high feasibility for fabrication and the results illustrate considerable potential in various applications including graphene optics and integrated photonic systems.