Spectral characterization of a frequency comb based on cascaded quadratic nonlinearities inside an optical parametric oscillator

TL;DR

This paper experimentally investigates optical frequency combs generated via cascaded quadratic nonlinearities in an optical parametric oscillator, demonstrating high power, mode spacing uniformity, and spectral quality improvements.

Contribution

It provides new insights into comb generation using quadratic nonlinearities, including mode spacing control and high-power output in the near-infrared.

Findings

Narrow-linewidth intermode beat notes achieved

Mode spacing uniformity verified at Hz level

Over 4 W output power at ~2 μm

Abstract

We present an experimental study of optical frequency comb generation based on cascaded quadratic nonlinearities inside a continuous-wave-pumped optical parametric oscillator. We demonstrate comb states which produce narrow-linewidth intermode beat note signals, and we verify the mode spacing uniformity of the comb at the Hz level. We also show that spectral quality of the comb can be improved by modulating the parametric gain at a frequency that corresponds to the comb mode spacing. We have reached a high average output power of over 4 W in the near-infrared region, at ~2 {\mu}m.