  We show that up to 90% reflectivity can be achieved by using guided plasmonic
resonances in a one-dimensional periodic array of plasmonic nanoribbon. In
general, to achieve strong reflection from a guided resonance system requires
one to operate in the strongly over-coupled regime where the radiative decay
rate dominates over the intrinsic loss rate of the resonances. Using an
argument similar to what has been previous used to derive the Chu-Harrington
limit for antennas, we show theoretically that there is no intrinsic limit for
the radiative decay rate even when the system has an atomic scale thickness, in
contrast to the existence of such limits on antennas. We also show that the
current distribution due to plasmonic resonance can be designed to achieve very
high external radiative rate. Our results show that high reflectivity can be
achieved in an atomically-thin graphene layer, pointing to a new opportunity
for creating atomically-thin optical devices.
