▎ 摘　　要

We have numerically investigated the tunable surface plasmon in graphene square-nanoring structure. Due to an enhancement of the local field, graphene surface plasmons (GSPs) can be strongly confined in the graphene grating region. The expressions of the lifetime for resonant modes have been investigated with the the finite difference time domain (FDTD) simulations and the coupled mode theory (CMT). Altering the Fermi energy and varying the carrier mobility have an important influence in optimizing the light absorption and the lifetime of GSPs. The CMT theoretical results agree well with FDTD simulations. Besides, by utilizing the different inner length and the different refractive index of substrate material, we find that the absorption peak of the GSPs structure can be tuned in a wide wavelength range. Our proposed graphene gratings structure shows good prospects in the mid-infrared region, such as ultracompact tunable integrated modulators and absorbers.