Quasi-coherent noise-like pulses in a mode-locked fiber laser with 3D rotatable polarization beam splitter

For the first-time, we experimentally observed a novel type quasi-coherent noise-like pulses in a simplified nonlinear polarization evolution mode-locking fiber laser when appropriate polarization was maintained for the lasing light through a three-dimensionally rotatable polarization beam splitter inside the cavity. The degree of first-order coherence was evaluated after an interferogramme asurement. Evolution of the measured shot-to-shot spectrum revealed that the noise-like pulses possess quasi-coherence. Self-started ultrafast soliton pulses switching to quasi-coherent noise-like pulses at higher pump power levels were due to the preservation of the soliton features, mainly the Kelly side band sin the spectrum. Quasi-coherentnoise-like pulses with average power of 56.58 mW and 10.4% slope efficiency were achieved with single pulse energyof3.22nJ.