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Multiple dissipative solitons are numerically studied in the normal-cavity-dispersion Yb-doped fiber laser. Soliton pairs and triplets of different types are found in parameter domain where single soliton mode-locking is unstable. Similar scenario is found for soliton pair and triplet: an additional weak soliton supplements already existing solitons, then with increasing gain the solitons start oscillating and at higher gain the soliton complex becomes stable. Spectral profiles of the solitons dynamically change taking either parabolic-like or Pi-like or M-like shape similar to those described in the literature for individual dissipative soliton at different pump level.

Stable mode-locked operation in a simple normal-cavity-dispersion laser oscillator that consists of only Yb-doped fiber and saturable absorber is studied. The Yb-doped fiber design parameters: group velocity dispersion (GVD), nonlinearity coefficient, bandwidth (Yb-BW), length and gain are considered to be the controlling parameters of the laser cavity. The pulse characteristics such as the temporal width, spectrum and pulse energy as a function of these elements are reported here. A pulse spectrum transition from M-like to Pi-like and then to parabolic-like shape is observed with different values of the controlling parameters which are similar to that has been observed before in a solid-state laser. The stability limits in the domain of the Yb-BW and length are studied. The stability dependence on GVD, nonlinearity coefficient and gain of the Yb-doped fiber are elucidated. Moreover, the pulse instability dyn ics beyond stability limits are found to be similar to that reported before for similariton.

Stability of the similariton mode-locked regime in Yb-doped fiber laser in the vicinity of zero cavity dispersion is studied by means of numerical simulations. It is shown that similariton pulses which initially arise from laser noise collapse into a continuous wave state. The mode-locked pulses are found to be stable after a certain cavity dispersion threshold is exceeded. From analysis of the instability development, we conclude that instability has parametric nature. We compare our results with stability analysis based on the Ginzburg-Landau approach. Analogies with instabilities found in the long-haul fiber communication systems are also discussed.

Novel features in stretched-pulse and similariton mode-locked regimes of Yb-doped fiber laser with photonic bandgap fiber used for dispersion compensation are found by means of numerical simulations. We show that the mode-locked pulse may become shorter with increasing third-order dispersion. Analytical estimations explain observed behavior through resonant interaction of the main pulse with dispersive waves involving both resonant sidebands and zero-group-velocity dispersion waves. Switching between the stretched-pulse and the similariton regimes is also studied.