Mechanisms of dual-wavelength dissipative soliton mode-locking in net-normal dispersion fiber lasers

Dual-wavelength mode-locked fiber lasers have attracted great attention due to their enormous potential in facilitating dual-comb spectroscopy. However, mechanism for dual-wavelength dissipative soliton mode-locking and the intracavity dynamics are still elusive. In this paper, we construct a simple and universal model to numerically investigate the intracavity buildup dynamics of dual-wavelength mode-locking in an all-normal dispersion fiber laser. By resolving the pulses evolution and their interactions, we find that the chromatic dispersion induced pulse collision plays an important role in dual-wavelength pulses formation and propagation. At the chaotic stage, the collision-induced energy upheaval results in drastic nonlinear coupling effects, which contribute to the dual-wavelength mode-locking and formation of dual-wavelength soliton molecules. While at the stable dual-wavelength mode-locking stage, the two asynchronous pulses periodically collide, accompanying extremely intense wave generation and spectral explosion. Moreover, cavity energy and gain competition are modeled and optimized to realize the self-started pulse-splitting-free dual-wavelength mode-locking.