Versatile multi-soliton patterns of noise-like pulses in a passively mode-locked fiber laser

We experimentally report the dynamics of multi-soliton patterns noise-like pulses (NLPs) in a passively mode-locked fiber laser, which the pulse duration can be linearly tuned from 8.21 ns to 128.23 ns by 2.936 ns / 10 mW. Benefiting from the drastically strengthened nonlinear effects in the cavity and the high gain amplification in the unidirectional ring (UR), the transformation from rectangular-shaped NLP to Gaussian-shaped NLP is experimentally achieved. Versatile multi-soliton patterns are observed in NLP regime for the first time, namely, single-scale soliton clusters, high-order harmonic mode-locking, and localized chaotic multiple pulses. In particular, the spectrum evolution with pump power and spectrum stability in 2 hours are also monitored. The obtained results demonstrate the rectangular-shaped NLP can fully transform into Gaussian-shaped NLP, and the multi-soliton patterns can exist in the NLP regime, which contributes to further understanding the nature and mechanism of the NLP in a passively mode-locked fiber laser.