Different types of noise-like pulse in a nonlinear multimodal interference based mode-locked fiber laser

In this paper, we employ a symmetrical graded index multimode fiber-step index multimode fiber-graded index multimode fiber (GIMF-SIMF-GIMF) structure as artificial saturable absorber to achieve mode-locked operation in an Erbium-doped fiber laser. After optimizing the cavity length, pump power and orientation of polarization controller, noise-like pulse (NLP) is built in anomalous dispersion region experimentally. It is worth noting that except for the traditional NLP, a special NLP with unique features is obtained whose temporal and spectral properties are different from the known case on NLP reported before. According to the experimental results, we also acquire and compare properties of subpulse within NLP envelope with the change of pump power. Last but not least, harmonic of the peculiar NLP is found under appropriate cavity conditions.