Coupling-Enhanced Broadband Mid-infrared Light Absorption in Graphene Plasmonic Nanostructures

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 two-layer graphene nanoribbon array which shows 5-7% extinction within the entire 8-14 pm (similar to 700-1250 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.