Numerical investigation of the impact of the saturable absorber recovery time on the mode-locking performance of fiber lasers

We investigated the impact of the recovery time of a saturable absorber (SA) on the mode-locking performance of a fiber laser. This study was conducted for two types of fiber cavities with different net cavity group velocity dispersion (GVD) at a wavelength of 1.55 μm: normal and anomalous. The impact of modulation depth variation was also analyzed. It was found that the recovery time of the SA has little influence on the output pulse characteristics in the case of the anomalous net cavity GVD due to an interplay between saturable absorption-induced pulse shaping and modulation instability-induced soliton evolution, irrespective of the SA operating in the fast or slow saturable absorption regime. However, the recovery time was found to have a significant impact on the output pulse characteristics for the case of a normal net cavity GVD. An SA operating in the fast saturable absorption regime produces mode-locked pulses with symmetric temporal shapes for the normal GVD cavity, whereas asymmetric pulses are generated in the slow saturable absorption regime. From the simulation results, the optimum recovery time range for fiber laser mode-locking is discussed.