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 μm (∼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.