Enabling Coherent Supercontinuum from Picosecond Pulses

Pumping with femtosecond (fs) pulses is widely considered to be a prerequisite to generate coherent supercontinuum (CSC) spectra [1]. Under anomalous group-velocity dispersion (GVD),
$\beta_{2} < 0$
, where pulse spectral broadening is more efficient [2], pulses experience self-phase modulation (SPM) and modulation instability (MI), and depending on which mechanism dominates, their spectral broadening is either coherent or incoherent. In particular, MI tends to govern the evolution of picosecond (ps) or longer pulses resulting in incoherent regimes, hence the limitation to fs pulses to produce CSC [1]. Importantly, this long-standing fundamental issue is currently preventing CSC from integrated mode-locked lasers [3] because they typically deliver ps pulse widths [4].