  Layered 2D graphene oxide (GO) films are integrated with silicon nitride
(SiN) waveguides to experimentally demonstrate an enhanced Kerr nonlinearity
via four wave mixing (FWM). Owing to the strong light matter interaction
between the SiN waveguides and the highly nonlinear GO films, the FWM
performance of the hybrid waveguides is significantly improved. SiN waveguides
with both uniformly coated and patterned GO films are fabricated based on a
transfer free, layer by layer GO coating method together with standard
photolithography and lift off processes, yielding precise control of the film
thickness, placement and coating length. Detailed FWM measurements are carried
out for the fabricated devices with different numbers of GO layers and at
different pump powers. By optimizing the trade off between the nonlinearity and
loss, we obtain a significant improvement in the FWM conversion efficiency of
7.3 dB for a uniformly coated device with 1 layer of GO and 9.1 dB for a
patterned device with 5 layers of GO. We also obtain a significant increase in
FWM bandwidth for the patterned devices. A detailed analysis of the influence
of pattern length and position on the FWM performance is performed. Based on
the FWM measurements, the dependence of GOs third-order nonlinearity on layer
number and pump power is also extracted, revealing interesting physical
insights about the 2D layered GO films. Finally, we obtain an enhancement in
the effective nonlinear parameter of the hybrid waveguides by over a factor of
100. These results verify the enhanced nonlinear optical performance of SiN
waveguides achievable by incorporating 2D layered GO films.
