Nonlinear broadening of electro-optic frequency combs in all-normal dispersion Si3N4 waveguides

Dispersion-engineered silicon nitride waveguides are often used for broadening of frequency combs. Previous experiments have focused on anomalous dispersion waveguides pumped by femtosecond laser pulses, whereby coherent supercontinuum generation relies on soliton compression and dispersive wave emission (see e.g. [1] ). This regime of operation does not work well with high-repetition rate sources, such as microcombs or electro-optic (EO) combs, because the pulse duration is not sufficiently short to drive coherent broadening in anomalous dispersion media. Indeed, octave-spanning coherent broadening of high-repetition rate sources has been attained in anomalous dispersion silicon nitride waveguides, but this required using a pre-broadening stage in a normal-dispersion highly nonlinear fiber (HNLF) [2] . Implementing this stage in a silicon nitride waveguide is the topic we address in this contribution.