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

Abstract

We report on the experimental observation of internally pumped parametric oscillation in a high-$!Q$Q lithium niobate microresonator under conditions of natural phase matching. Specifically, launching near-infrared pump light around 1060 nm into a $ z $z-cut congruent lithium niobate microresonator, we observe the generation of optical sidebands around the input pump under conditions where second-harmonic generation is close 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.