▎ 摘　　要

Here we propose a planar graphene/dielectric multilayer configuration to realize low threshold optical bistability at terahertz frequencies. This low-threshold optical bistability is achieved by field enhancement owing to the couple of the surface plasmon polaritons and the planar waveguide mode. We discussed the influence of graphene sheets and planar waveguide mode on the hysteretic response of the TM-polarization reflected light. It is found that the switch-up and switch-down threshold electric fields required to observe the optical bistable behavior are affected markedly by the excitation of surface plasmon polaritons or planar waveguide mode. Besides, the switching threshold value can be further reduced by coupling the surface plasmon polaritons and planar waveguide mode, hence providing a way of realizing low threshold and tunable optical bistable devices.