Coherence analysis of noise-like pulses generated by an erbium-doped fiber mode-locked laser

The noise-like pulses (NLPs) with tunable fraction of the pedestal height in the whole intensity autocorrelation (AC) trace are numerically demonstrated in the designed erbium-doped fiber (EDF) mode-locked laser, which contains the saturable absorber (SA) with nonlinear polarization rotation (NPR), sinusoidal-shaped or Gaussian-shaped filter, two segments of EDFs, and two pieces of single-mode fibers (SMFs) with normal dispersion and anomalous dispersion, respectively. The pedestal ratio of the intensity AC trace can be tuned by changing the gain saturation energies of EDFs. The results show that when the net cavity dispersion is 1.06 ps2, the tuning range of the pedestal ratio for the NLPs can reach its maximum values, which are 0.51-0.89 and 0.58-0.88 for the sinusoidal-shaped and Gaussian-shaped filters, respectively. In addition, an appropriate choice of filter bandwidth is also conducive to obtain a wide range of the tuning pedestal ratio for the intensity AC trace.