Mid-infrared graphene-insulator-graphene plasmonic modulator

Abstract

Optical interconnects have been proposed to be the next generation interconnect solution to overcome the impending interconnect bottleneck. Large optical devices have hindered integration of electrical and optical components. Plasmonics have enabled nanophotonic components with sub-micron scale optical devices with similar size range as electronics and they promise to bridge the size gap between optical and electrical components. Surmounting research is suggesting that the electronics industry is starting to accept more variety materials in the fabrication process, the most important of which is graphene. The modulator is composed of a thin layer of silicon nitride – a few nm thick – sandwiched between two graphene sheets that are both electrically connected to the signal. Thin Al2O3 layers separate the graphene sheets from the ground electrodes on top and bottom. The electric field generated by applying a maximum of 5V on the graphene sheets changes the fermi level of graphene to switch between a highly lossy metal-like material and a dielectric material. Operating in the mid infrared regime, around 5 μm wavelength, when the Fermi level is located in the band gap, optical absorption is high. When the Fermi level is located away from the bandgap, absorption is minimized. Simulations show that the modulator exhibits over 7 dB / μm extinction ratio and less than 0.1 dB / μm propagation loss. By designing for 3 dB extinction ratio and less than 0.1 dB propagation loss, the footprint of the modulator is only 80 nm x 400 nm for feasible integration in future electronic chips without competing for space.