Dissipative quadratic soliton in the cascaded nonlinearity limit.

Abstract

Dissipative quadratic solitons (DQSs), enabled by nonlinearity engineering through cascaded quadratic processes, have remained a central theoretical prediction in nonlinear optics since their proposal in 1997. Despite their predicted ultralow operational thresholds, remarkable tunability, and potential for spectral extension into unconventional wavelengths, their experimental realization has remained elusive. Here, we demonstrate bright, dual-color DQS generation in the normal dispersion regime, in strong agreement with the proposed theoretical framework. Furthermore, by simply adjusting the nonlinear crystal temperature - without any structural modification - we reverse the sign of the effective nonlinearity and switch from bright DQS to platicon generation in situ. This work not only advances the fundamental understanding of dissipative solitons but also establishes a practical pathway for ultralow-threshold frequency comb generation at unconventional wavelengths, with broad implications for applications such as atomic clocks, optical coherence tomography, and astrocombs.