Intermodal Bragg-Scattering Four Wave Mixing in Silicon Waveguides

We demonstrate optical wavelength conversion in a multi-mode silicon waveguide using four wave mixing Bragg scattering enabled by a dual-pump CW scheme. The original signal and the generated idler pair excite one spatial mode (first, TE mode), while the two pumps excite a different spatial mode (second, TE mode) of the same waveguide. Our approach exploits the differences in the group velocities of the various supported spatial modes to ensure phase matching only for the desired nonlinear process. In this proof-of-principle experiment, any unintended idlers are generated with an extinction ratio up to 12 dB relative to the phase-matched idlers for a pumps-to-signal-idler-pair wavelength detuning of about 70 nm. The scalability of the scheme to achieve larger and multiple signal wavelength detunings from the pump frequencies is also discussed.