Gate-Tunable mid-Infrared Plasmonic Planar Band-Stop Filters Based on a Monolayer Graphene

In this paper, the graphene ribbon bus waveguide side-coupled a coplanar short graphene strip, constructed on a monolayer graphene with substrates by spatially varying external gates, is proposed and investigated numerically by using the finite-difference time-domain (FDTD) method. Simulated results exhibit that the outstanding mid-infrared band-stop filtering effect is realized based on the edge mode resonance in the short strip acting as a perfect Fabry-Perot resonator. By changing the locations of gate voltages to vary the size of the short graphene strip, not only the Fabry-Perot resonance mode is tuned effectively but also the original rectangular-loop resonance mode appears. The changes in the coupling distance and substrates are also used for modulating the transmission spectrum. FDTD results are in excellent agreement with the coupled-mode theory (CMT). The simple structure without doubt is a real electrically controlled plasmonic device. Our studies will support the fabrication of planar nano-integrated plasmonic circuits for mid-infrared optical processing.