Enhanced light absorption of graphene sheet with large bandwidth tunability in visible and near-infrared range

We present a detailed investigation into the bandwidth-tunable absorption enhancement of a graphene sheet across the visible and near-infrared spectral range. The graphene sheet is engineered in a unique sandwiched configuration, positioned between a periodic array of metal strips and a dielectric spacer layer on a metallic substrate. This configuration facilitates a near-field plasmon interaction between the individual metal strips and the substrate, leading to the formation of a localized magnetic resonance. The interplay between this magnetic resonance and the propagating surface plasmon resonance on the substrate surface results into the emergence of two hybrid modes. These hybrid modes are directly responsible for the appearance of two distinct absorption peaks in the graphene sheet's absorption spectra. By systematically varying the period of the metal strip array, we demonstrate a remarkable tunability in the graphene absorption bandwidth, ranging from 100 nm to 5 nm. This tuning capability is accompanied by a maximum light absorption efficiency of approximately 80 %, highlighting the potential for precise optical control. To further elucidate the underlying mechanism, we employ a double oscillator coupling model, which successfully explains the observed shifts in absorption peak positions as a function of the array period. The observed bandwidth-tunable absorption enhancement in graphene not only advances our fundamental understanding of light-matter interactions in hybrid plasmonic systems but also holds significant promise for practical applications.