Ultrabroad Band Rainbow Capture and Releasing in Graded Chemical Potential Distributed Graphene Monolayer

We propose and numerically analyze a scheme to trap a broadband surface plasmon polariton (SPP) wave on a sheet of monolayer graphene with gradient chemical potential distribution. Different frequency components of the incident wave are trapped at different locations according to the chemical potential, resulting in “rainbow trapping” effect. By appropriately tuning the chemical potential distribution over the graphene sheet, graphene conductivity distribution is modified so that the trapped SPP wave is released. In the proposed structure, the group velocity of the trapped SPP waves is as low as the 10−8 times of the light speed in free space, and the lifetime of the trapped SPP wave is 3.14 ps when the relaxation of the graphene is 0.5 ps. This slow light system offers advantages simultaneously including broadband operation, ultracompact footprint, and dynamic control of group velocity without any complicated and expensive device geometry engineering.