Strongly enhanced self-phase modulation of femtosecond optical pulses in
silicon nanowires with graphene oxide films
Abstract
We experimentally demonstrate enhanced spectral broadening of
femtosecond optical pulses after propagation through
silicon-on-insulator (SOI) nanowire waveguides integrated with
two-dimensional (2D) graphene oxide (GO) films. Owing to the strong mode
overlap between the SOI nanowires and the GO films with a high Kerr
nonlinearity, the self-phase modulation (SPM) process in the hybrid
waveguides is significantly enhanced, resulting in greatly improved
spectral broadening of the femtosecond optical pulses. A solution-based,
transfer-free coating method is used to integrate GO films onto the SOI
nanowires with precise control of the film thickness. Detailed SPM
measurements using femtosecond optical pulses are carried out, achieving
a broadening factor of up to ~4.3 for a device with
0.4-mm-long, 2 layers of GO. By fitting the experimental results with
theory, we obtain an improvement in the waveguide nonlinear parameter by
a factor of ~3.5 and the effective nonlinear figure of
merit (FOM) by a factor of ~3.8, relative to the
uncoated waveguide. Finally, we discuss the influence of GO film length
on the spectral broadening and compare the nonlinear optical performance
of different integrated waveguides coated with GO films. These results
confirm the improved nonlinear optical performance for silicon devices
integrated with 2D GO films.