Mid-infrared, plasmonic switches and directional couplers induced by graphene sheets coupling system

In this letter, the original switch effect induced by a double-layer graphene sheets coupling system is investigated comprehensively by using the finite-difference time-domain method (FDTD). Simulation results reveal that the transmission varies periodically with the increase of the graphene sheets' overlapping length. The switch effect can be modulated by an ingenious and simple way of displacing one monolayer graphene horizontally in the graphene coupling system. At the same time, tuning the space between the graphene sheets and its chemical potential can also give rise to the perfect switch effect. The FDTD results are consistent with the theoretical calculations. As an application, a three-layer graphene coupling system is constructed. By the same principle, it works not only as an effective optical spatial switch but also as a perfect directional coupler. The proposed structures are operational in the mid-infrared region and will play a significant role in nano-integrated circuits for optical processing and switching.