Abstract

As the chemical potential of graphene is larger than half the energy of exciting photons, graphene could support strongly confined surface plasmon polaritons (SPPs), that is, graphene plasmons (GPs), which are surface waves manifesting an antisymmetric electric field distribution on graphene. Graphene has only one-atom thickness and the properties of GPs are significantly different from that of SPPs observed in metallic thin films. GPs have many significant advantages such as shorter wavelength, lower loss, and more flexible tunability. In this chapter, we focus on the optical coupling of GPs in-between graphene sheets. The double-layer graphene system is considered first, and such a system by means of GP coupling may find important applications in optical splitters, switches, and interferometers. We further investigate the coupling of GPs in monolayer graphene sheet arrays (MGSAs) composed of periodically stacked graphene sheets. As the period of the array decreases to below a critical value, strong coupling of GPs occurs. Otherwise, weak coupling should be observed. The critical period is quantitatively determined by the plasmonic thickness of graphene, referring to the effective mode width of GPs in an individual graphene sheet. Several interesting phenomena such as beam self-splitting and collimating of GPs in MGSAs have been numerically demonstrated and theoretically analyzed. The study provides a new platform to manipulate light propagation on the scale of a deep sub-diffraction limit and could find many promising applications in optoelectronic devices and circuits.