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

TL;DR

This paper reports the experimental observation of internally-pumped parametric oscillation and quadratic comb generation in a high-Q lithium niobate microresonator, demonstrating natural phase-matching and cascaded sideband generation for optical frequency combs.

Contribution

It presents the first experimental demonstration of internally-pumped parametric oscillation and quadratic combs in a lithium niobate microresonator with natural phase-matching.

Findings

Observation of optical sidebands around 1060 nm pump

Generation of multiple equally-spaced sidebands

Cascaded sideband generation indicating initial steps of frequency combs

Abstract

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 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 equally-spaced sidebands around the pump -- the first steps of optical frequency comb generation via cavity-enhanced second-harmonic generation.