Observation of second-harmonic generation in silicon nitride waveguides   through bulk nonlinearities
  We present experimental results on the observation of a bulk second-order nonlinear susceptibility derived from both free-space and integrated measurements in silicon nitride. Phase-matching is achieved through dispersion engineering of the waveguide cross-section, independently revealing multiple components of the nonlinear susceptibility, namely X(2)yyy and X(2)xxy. Additionally, we show how the generated second-harmonic signal may be actively tuned through the application of bias voltages across silicon nitride. The nonlinear material properties measured here are anticipated to allow for the practical realization of new nanophotonic devices in CMOS-compatible silicon nitride waveguides, adding to their viability for telecommunication, data communication, and optical signal processing applications. 
Matthew W. Puckett, Rajat Sharma, Hung-Hsi Lin, Muhan Yang, Felipe   Vallini and Yeshaiahu Fainman
physics.optics