▎ 摘　　要

Abstarct An ultra-narrow-band perfect absorber based on collective resonances in an Ag nanoring period array is theoretically proposed for the absorption enhancement of monolayer graphene, where the absorptivity can reach as high as 99.4% with the full-width-half-maximum as narrow as 3.6 nm in the visible band. This outstanding absorptive characteristic can be attributed to the excitation of surface lattice resonance modes by Ag nanoring periodic array. The as-designed structure possesses high refractive-index sensitivity, reaching 557.9 nm RIU-1 with its figure of merit attaining 155 RIU-1. This work provides promising guidance for developing high-performance graphene-based photonic devices.