  An active plasmonic switch based on single- and few-layer doped graphene
ribbon array operating in the mid-infrared spectrum is investigated with
theoretical and numerical calculations. It is shown that significant resonance
wavelength shifts and modulation depths can be achieved with a slight variation
of the doping concentration of the graphene ribbon. The few-layer graphene
ribbon array device outperforms the single-layer one in terms of the achievable
modulation depth. Our simulations reveal that, by modulating the Fermi-energy
level between 0.2 eV and 0.25 eV, a four-layer graphene ribbon array device can
achieve a modulation depth and resonance wavelength shift of ~13 dB and 0.94
micron respectively, compared to ~2.8 dB and 1.85 micron for a single-layer
device. Additionally, simple fitting models to predict the modulation depth and
the resonance wavelength shift are proposed. These prospects pave the way
towards ultrafast active graphene-based plasmonic devices for infrared and THz
applications.
