Microcomb generation in normal dispersion spiral resonators

Kerr frequency combs (microcombs) arise when a continuous-wave laser couples into an optical microresonator, generating evenly spaced, coherent lines through Kerr nonlinearity, dispersion, and dissipation. While most studies rely on anomalous dispersion, requiring thick waveguides and non-standard fabrication, we explore microcomb generation in the normal-dispersion regime using CMOS-compatible silicon nitride (SiN) resonators. Two approaches are demonstrated: (1) pumping with electro-optic sidebands synchronized to the resonator’s free spectral range (FSR), and (2) employing photonic crystal resonators with engineered dispersion perturbations for spontaneous comb emergence. Both designs use compact 20 GHz-FSR spiral resonators on 350 nm-thick SiN, achieving intrinsic quality factors up to 10 million. This work establishes a scalable, foundry-compatible platform for normal-dispersion microcombs with potential extension into the visible spectrum.