Opportunities for Wideband Wavelength Conversion in Foundry-Compatible Silicon Waveguides Covered With Graphene

Abstract

We numerically examine the opportunities for wideband wavelength conversion through four-wave mixing (FWM) in a foundry-compatible $220\text{-}\text{nm}$ -thick silicon-on-insulator (SOI) waveguide covered with the highly nonlinear two-dimensional material of graphene. As a case study, we consider a foundry-compatible SOI waveguide shaped as a double spiral and covered with two separate graphene sheets, which are covered in turn by two solid polymer electrolyte gates. When combining subwatt-level pump powers with a short waveguide length of only a few hundreds of micrometers, “perfectly phase-matched” conversion with significant efficiencies close to $-20\;\text{dB}$ can be obtained over a more than $40\text{-}\text{THz}$ -wide signal band adjacent to the pump frequency. Because of the tunability of the graphene properties using the electrolyte top gates, it is also possible to obtain “quasi-phase matched” FWM conversion through a periodic sign reversal of the graphene third-order nonlinearity along the waveguide. Conversion efficiencies exceeding $-30\;\text{dB}$ can be achieved over a $3.4\text{-}\text{THz}$ -wide signal band that is situated as much as $58\;\text{THz}$ away from the pump frequency. Finally, the tunability of the graphene also allows for switching the converter from the perfectly phase-matched to the quasi-phase-matched operation mode.