  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.
