Optical-parametric-oscillation-based $\chi^{(2)}$ frequency comb in a lithium niobate microresonator

TL;DR

This paper demonstrates the generation of a $ ext{chi}^{(2)}$ frequency comb in a lithium niobate microresonator via optical parametric oscillation, highlighting its potential for mid-IR applications beyond 3 μm.

Contribution

It introduces a novel method for $ ext{chi}^{(2)}$ comb generation using OPO in a lithium niobate microresonator, expanding the understanding and capabilities of nonlinear frequency combs.

Findings

Achieved 1-THz-wide comb spectra around 1064 nm.

Demonstrated comb generation with 30 μW pump power at 532 nm.

Identified conditions for degenerate mode operation from temperature tuning curves.

Abstract

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 demonstrate the generation of a $\chi^{(2)}$ frequency comb, initiated via optical parametric oscillation (OPO) in a lithium niobate mm-sized microresonator. By pumping at 532 nm with 30 $\mu$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.