▎ 摘　　要

In this paper, we have shown that tunable nonlinear group delay of reflected light beam at terahertz frequencies can be achieved by a modified Otto configuration with the insertion of monolayer graphene and nonlinear substrate. This large nonlinear reflected group delay originates from the excitation of surface plasmon resonance at the interface of two dielectrics with graphene. Graphene sheet with unique optical properties can enhance the surface plasmon resonance and modulate bistable behavior of the reflected group delay by suitably adjusting the Fermi energy of the graphene and the relaxation time. Moreover, the large negative and positive of reflected group delay is sensitive to the thicknesses of the air layer. We believe these intriguing phenomena are promising for some potential applications in graphene-based optical delay devices.