Graphene disk as an ultra compact ring resonator based on edge propagating plasmons

We report a plasmonic structure consisting of a graphene ribbon and a graphene disk. The plasmonic structure can work as a promising waveguide-ring resonator in ultra compact devices, in which the ribbon and the disk support different surface plasmons. We prove that disk's resonant modes are edge propagating surface plasmons. Strong optical coupling between the ribbon and the disk occurs when the momentum mismatch between plasmons in the ribbon and plasmons in the disk is weak. We also investigate the dependence of the optical coupling on the distances between the ribbon and the disk in parallel and vertical directions.