Ultrafast Supercontinuum Generation in Silicon Nitride Waveguides With Noise Mitigation

ABSTRACT As a source of ultrabroadband spectrum with a highly correlated phase, the coherent supercontinuum represents a pivotal technology in spectroscopy, microscopy, and frequency metrology. While the synergy between femtosecond lasers and photonic integrated waveguides paves the way for deterministic nonlinear dynamics and multi‐octave‐spanning emission, soliton fission and higher‐order perturbations often compromise spectral continuity. By far, the simultaneous realization of self‐compressed, few‐cycle pulses with a low‐noise figure remains an elusive goal in integrated photonics. Here, we circumvent these limitations of supercontinuum generation by leveraging soliton dynamics in silicon nitride photonic integrated circuits driven by a carbon nanotube‐based ultrafast oscillator. Especially, seeding laser with a low‐pedestal structure, which in lithographically dispersion engineered silicon nitride waveguide chip triggers deterministic self‐compression to the numerically predicted sub‐3 cycles regime and spectral broadening over three‐octaves. This process manifests as a substantial suppression of phase noise and relative intensity noise for the repetition rate, which underscores the coherence of the nonlinear evolution within the waveguide. The narrow‐linewidth optical frequency comb structure driven by the supercontinuum is also validated via online f‐3f self‐referencing. Our results constitute a way to temporo‐spectrally coherent optical frequency combs spanning from visible to mid‐infrared.