Frequency comb generation in non-centrosymmetric optical microresonators

Optical frequency combs are a key technology for precision measurements. In the past years, microresonatorbased frequency combs based on third-order CH (3) (Kerr) nonlinearities have attracted significant attention thanks to their small footprint and their wide-ranging applications in fields such as telecommunications, molecular spectroscopy or ultrafast distance measurements. In this contribution, we present a frequency comb generated in a microresonator made of 5% MgO-doped congruent lithium niobate, a non-centrosymmetric crystalline material, employing the generally much stronger second-order CH (2)-nonlinearities of such a material via a scheme of cascaded nonlinear processes. This approach paves the way towards reduced pump thresholds for comb generation and comes with intrinsic suitability for self-referencing.