Generation of soliton molecules in a 2-μm mode-locked fiber laser

Abstract

We report the experimental results of various soliton molecules in a passively mode-locked thulium-doped fiber laser based on nonlinear polarization rotation (NPR) technology. Not only stable single solitons but also soliton molecules can be observed in the same cavity. With the increase of the pump power, soliton triplets composed of three solitons can also be observed. It is found that the ratio of the pulse separation to the pulse width is less than 5, which indicates that the direct soliton interaction leads to the formation of bound states. On the other hand, the effect of the dispersive wave is to suppress the random relative phase change between the solitons and leads to phase-locking. Meanwhile, we analyzed the complex nonlinear interactions that form soliton molecules and enriched the nonlinear dynamics of soliton molecules at 2-μm.