  We present a tunable, hybrid waveguide-fiber optical parametric oscillator
(OPO) synchronously pumped by an ultra-fast fiber laser exploiting four-wave
mixing (FWM) generated in silicon nitride waveguides. Parametric oscillation
results in a 35 dB enhancement of the idler spectral power density in
comparison to spontaneous FWM, with the ability of wide wavelength tuning over
86 nm in the O-band. Measurements of the oscillation threshold and the
efficiency of the feedback loop reveal how an integration of the OPO on a
single silicon nitride chip can be accomplished at standard repetition rates of
pump lasers in the order of 100 MHz.
