Frequency comb generation in continuously-pumped quadratic nonlinear media

We experimentally demonstrated frequency comb generation in a continuously pumped, cavity-enhanced second-harmonic generation system. Our system shows a striking similarity with generation and dynamics of frequency combs in Kerr microresonators, as confirmed by a simple three-wave theoretical model we developed. This analogy unveils the possibility to predict and observe new effects, paving the way for a novel class of highly efficient and versatile frequency comb synthesizers based on second-order nonlinear materials.