SiN waveguides integrated with graphene oxide 2D films for enhanced nonlinear optics

Self-phase modulation (SPM) is an important third-order nonlinear optical process that has been widely used in many applications, such as broadband optical sources, optical diodes, optical spectroscopy, pulse compression, and many others. The ability to realize SPM based on-chip integrated photonic devices will reap attractive benefits of compact footprint, high stability, high scalability, and low-cost mass production. Here, we experimentally investigate enhanced SPM in silicon nitride (Si3N4) waveguides by integrating with 2D graphene oxide (GO) films. The on-chip integration of GO films is achieved on Si3N4 waveguides through a solution-based, transfer-free, layer-by-layer coating method with precise control of the film thickness. We use both picosecond and femtosecond optical pulses to perform detailed SPM measurements. Owing to the high Kerr nonlinearity of GO, the GO-coated waveguides show significantly improved spectral broadening for both the picosecond and femtosecond optical pulses compared to the uncoated waveguide, achieving a broadening factor of up to ~3.4 for a device with 2 layers of GO. Based on the experimental results which show good agreement with theory, we obtain an improvement in the waveguide nonlinear parameter by a factor of up to 18.4 and a Kerr coefficient (n2) of GO that is about 5 orders of magnitude higher than Si3N4. These results reveal the effectiveness of 2D GO films to improve the nonlinear performance of Si3N4 waveguides.