Nonlinear Manipulation of Surface Plasmon Polaritons in Graphene-Based Bragg Reflector

Here, we take the advantage of the strong electromagnetic field of surface plasmon polaritons (SPPs) on graphene to design a tunable terahertz plasmonic Bragg reflector by the intensity of propagating SPP wave. A periodic variation in the effective mode index of SPPs in the direction of their propagation on a graphene layer, required for Bragg scattering, is created by a properly designed siliconsilicon dioxide substrate. A small change in the applied voltage between the graphene sheet and the substrate leads to a noticeable tuning of the stopband region of the reflector. Deposition of a Kerr nonlinear medium on the substrate and in the immediate vicinity of the graphene layer is employed to control the propagation characteristics of SPPs by their intensity. Our numerical simulation results via a developed nonlinear finite difference time domain method reveal that by increasing the SPP wave intensity up to 0.9 MW/cm² which is below the damage threshold of graphene, a red shift in the Bragg frequency up to 220 GHz is achievable. Valuable potential applications can be envisioned for this Bragg reflector as filters and switches due to its fast and high level of tunability with applied gate voltage and the intensity of propagating SPP wave.