Experimental studies on the start time of a passively mode-locked fiber laser based on nonlinear polarization rotation

In this work, we report our experimental studies on the start time of a passively mode-locked soliton fiber laser based on nonlinear polarization rotation (NPR), with a focus on the impact of different operation states. We found that given the same cavity configuration, the statistical distributions of the start time are strongly correlated with the operation states determined by the pump power and the NPR-induced loss of the laser. While the start time for the single-pulse state exhibits a long-tail distribution, for the multi-pulse state a much faster start time is observed at the same pump level. We also find that the start-time distribution of the multi-pulse state is dramatically sensitive to both the laser pump power and the NPR-induced loss. Numerical simulations have been performed to reproduce these statistical features, revealing their delicate dependence upon the intra-cavity balance between gain and loss. Our work sheds some light on the statistical self-starting dynamics of the mode-locked fiber laser and may provide valuable guidance to practical laser design.