Design of electro-optic modulators based on graphene-on-silicon slot waveguides.

We present a graphene-on-silicon (GoS) suspended vertical slot waveguide. By changing the Fermi level of graphene, the variation in the effective refractive index (RI) of the waveguide is a factor of two larger than that in the traditional GoS rib waveguide. The improvement is due to the light-intensity enhancement and the poor confinement of the optical mode in the slot nanostructure. We design Mach-Zehnder interferometer (MZI) and microring modulators based on the GoS suspended vertical slot waveguide. Our calculations show that the modulators can be energy-efficient and footprint-compact due to the large phase shift of the propagating mode in the waveguide after applying a gate voltage on the graphene. Fabrication of our design is easy and CMOS-compatible. It paves the way for chip-integrated electronic-RI modulators.