Silicon Nitride microresonators enable the generation of frequency combs from a single continuous wave laser source. Due to a balance of Kerr nonlinearity and the dispersion of the resonator equally spaced lines are generated through nonlinear processes, when the pump laser operates above a certain threshold. Dispersion engineering of the resonator is made easy due to the ability to shape height and width of the resonator through the fabrication process. The final repetition rate, i.e. the distance between two lines is given by the diameter of the resonator and can be customised from 20 GHz up to 1 THz.
Optical spectrum of a frequency comb generated with a microresonator. The diameter of around 670 μm provides a repetition rate of 50 GHz. (courtesy of LPQM, EPFL)