  Layered 2D GO films are integrated with silicon on insulator (SOI) nanowire
waveguides to experimentally demonstrate an enhanced Kerr nonlinearity,
observed through selfphase modulation (SPM). The GO films are integrated with
SOI nanowires using a large area, transfer free, layer by layer coating method
that yields precise control of the film thickness. The film placement and
coating length are controlled by opening windows in the silica cladding of the
SOI nanowires. Owing to the strong mode overlap between the SOI nanowires and
the highly nonlinear GO films, the Kerr nonlinearity of the hybrid waveguides
is significantly enhanced. Detailed SPM measurements using picosecond optical
pulses show significant spectral broadening enhancement for SOI nanowires
coated with 2.2 mm long films of 1 to 3 layers of GO, and 0.4 mm long films
with 5 to 20 layers of GO. By fitting the experimental results with theory, the
dependence of the n2 for GO on layer number and pulse energy is obtained,
showing interesting physical insights and trends of the layered GO films from
2D monolayers to quasi bulk like behavior. Finally, we show that by coating SOI
nanowires with GO films the effective nonlinear parameter of SOI nanowires is
increased 16 times, with the effective nonlinear figure of merit (FOM)
increasing by about 20 times to greater than 5. These results reveal the strong
potential of using layered GO films to improve the Kerr nonlinear optical
performance of silicon photonic devices.
