  Layered 2D graphene oxide (GO) films are integrated with microring resonators
(MRRs) to experimentally demonstrate enhanced nonlinear optics in the form of
four wave mixing (FWM). Both uniformly coated and patterned GO films are
integrated on CMOS compatible doped silica MRRs using a large area, transfer
free, layer by layer GO coating method together with photolithography and lift
off processes, yielding precise control of the film thickness, placement, and
coating length. The high Kerr nonlinearity and low loss of the GO films
combined with the strong light matter interaction within the MRRs results in a
significant improvement in the FWM efficiency in the hybrid MRRs. Detailed FWM
measurements are performed at different pump powers and resonant wavelengths
for the uniformly coated MRRs with 1 to 5 layers of GO as well as the patterned
devices with 10 to 50 layers of GO. The experimental results show good
agreement with theory, achieving up to 7.6 dB enhancement in the FWM conversion
efficiency (CE) for an MRR uniformly coated with 1 layer of GO and 10.3 dB for
a patterned device with 50 layers of GO. By fitting the measured CE as a
function of pump power for devices with different numbers of GO layers, we also
extract the dependence of the third-order nonlinearity on layer number and pump
power, revealing interesting physical insights about the evolution of the
layered GO films from 2D monolayers to quasi bulk like behavior. These results
confirm the high nonlinear optical performance of integrated photonic
resonators incorporated with 2D layered GO films.
