Plasmons in graphene nanostructures show great promise for mid-infraredapplications ranging from a few to tens of microns. However, mid-infraredplasmonic resonances in graphene nanostructures are usually weak andnarrow-banded, limiting their potential in light manipulation and detection.Here we investigate the coupling among graphene plasmonic nanostructures andfurther show that by engineering the coupling, enhancement of light-grapheneinteraction strength and broadening of spectral width can be achievedsimultaneously. Leveraging the concept of coupling, we demonstrate a hybrid2-layer graphene nanoribbon array which shows 5 to 7% extinction within theentire 8 to 14 {\mu}m (~700 to 1250 cm-1) wavelength range, covering one of theimportant atmosphere "infrared transmission windows". Such coupled hybridgraphene plasmonic nanostructures may find applications in infrared sensing andfree-space communications.
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