Optical-parametric-oscillation-based χ(2) frequency comb in a lithium niobate microresonator

Microresonator frequency combs based on the chi((3)) nonlinearity are nowadays well understood and making their way into different applications. Recently, microresonator frequency combs based on the chi((2)) nonlinearity are receiving increasing attention, as they promise certain benefits, but still require further study. Here, we present the first indication of chi((2)) frequency comb generation, initiated via optical parametric oscillation (OPO) in a lithium niobate mm-sized microresonator. By pumping at 532 nm with 300 mu W of power, we observe 1-THz-wide comb spectra around 1064 nm with degenerate and non-degenerate states. We also show that comb generation requires signal and idler waves to be degenerate in mode numbers and how the fulfillment of this condition can be identified from the temperature tuning curves. The results demonstrate the potential to directly generate frequency combs via OPO beyond 3 mu m wavelengths in the mid-IR by puming in the near-IR region. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.