Plasmonic rainbow trapping by a graphene monolayer on a dielectric layer with a silicon grating substrate.

Considering the propagation of surface plasmon polaritons (SPPs) supported by a graphene monolayer can be effectively controlled via electrostatic gating, we propose a graphene monolayer on a graded silicon-grating substrate with dielectric spacer as an interlayer for plasmonic rainbow trapping in the infrared domain. Since the dispersive relation of SPPs is dependent on the width of dielectric spacer filling the silicon grating, the guided SPPs at different frequencies can be localized at different positions along the graphene surface, associated with the period of silicon grating. The group velocity of slow SPPs can be made to be several hundred times smaller than light velocity in vacuum. We also predict the capability of completely releasing the trapped SPPs by dynamically tuning the chemical potential of graphene by means of gate voltage. The advantages of such a structure include compact size, wide frequency tunability, and compatibility with current micro/nanofabrication, which holds great promise for applications in graphene-based optoelectronic devices.