  The optical response of graphene micro-structures, such as micro-ribbons and
disks, is dominated by the localized plasmon resonance in the far infrared (IR)
spectral range. An ensemble of such structures is usually involved and the
effect of the coupling between the individual structures is expected to play an
important role. In this paper, the plasmonic coupling of graphene
microstructures in different configurations is investigated. While a relatively
weak coupling between graphene disks on the same plane is observed, the
coupling between vertically stacked graphene disks is strong and a drastic
increase of the resonance frequency is demonstrated. The plasmons in a more
complex structure can be treated as the hybridization of plasmons from more
elementary structures. As an example, the plasmon resonances of graphene
micro-rings are presented, in conjunction with their response in a magnetic
field. Finally, the coupling of the plasmon and the surface polar phonons of
SiO2 substrate is demonstrated by the observation of a new hybrid resonance
peak around 500cm-1.
