  Plasmons in graphene nanostructures show great promise for mid-infrared
applications ranging from a few to tens of microns. However, mid-infrared
plasmonic resonances in graphene nanostructures are usually weak and
narrow-banded, limiting their potential in light manipulation and detection.
Here we investigate the coupling among graphene plasmonic nanostructures and
further show that by engineering the coupling, enhancement of light-graphene
interaction strength and broadening of spectral width can be achieved
simultaneously. Leveraging the concept of coupling, we demonstrate a hybrid
2-layer graphene nanoribbon array which shows 5 to 7% extinction within the
entire 8 to 14 {\mu}m (~700 to 1250 cm-1) wavelength range, covering one of the
important atmosphere "infrared transmission windows". Such coupled hybrid
graphene plasmonic nanostructures may find applications in infrared sensing and
free-space communications.
