  We demonstrate enhanced four-wave mixing (FWM) in doped silica waveguides
integrated with graphene oxide (GO) layers. Owing to strong mode overlap
between the integrated waveguides and GO films that have a high Kerr
nonlinearity and low loss, the FWM efficiency of the hybrid integrated
waveguides is significantly improved. We perform FWM measurements for different
pump powers, wavelength detuning, GO coating lengths, and number of GO layers.
Our experimental results show good agreement with theory, achieving up to
~9.5-dB enhancement in the FWM conversion efficiency for a 1.5-cm-long
waveguide integrated with 2 layers of GO. We show theoretically that for
different waveguide geometries an enhancement in FWM efficiency of ~ 20 dB can
be obtained in the doped silica waveguides, and more than 30 dB in silicon
nanowires and slot waveguides. This demonstrates the effectiveness of
introducing GO films into integrated photonic devices in order to enhance the
performance of nonlinear optical processes.
