Low-threshold frequency comb generation using second-order nonlinearities in lithium niobate whispering gallery resonators

Optical frequency combs have become a key technology for optical precision measurements and, moreover, bear potentials to boost the bandwidth of telecommunication networks, to be applied for molecular spectroscopy, and to be used in modern quantum information systems. Owing to their feasibility for such a vast application range, frequency comb technology has seen major advances in terms of complexity, power requirements and size, leading to micro- to millimeter-sized frequency comb generators emitting continuous-wavepumped Kerr combs and, more lately, soliton frequency combs based on third-order ( CH (3) ) nonlinearities.