Experimental observation of internally pumped parametric oscillation and quadratic comb generation in a χ(2) whispering-gallery-mode microresonator

We report on the experimental observation of internally pumped parametric oscillation in a high-Q lithium niobate microresonator under conditions of natural phase matching. Specifically, launching near-infrared pump light around 1060 nm into a z-cut congruent lithium niobate microresonator, we observe the generation of optical sidebands around the input pump under conditions where secondharmonic generation is dose to natural phase matching. We find that a wide range of different sideband frequency shifts can be generated by varying the experimental parameters. Under particular conditions, we observe the cascaded generation of several sidebands around the pump-the first steps of optical frequency comb generation via cavity-enhanced second-harmonic generation. (C) 2020 Optical Society of America