Multistability and hysteresis phenomena in passively mode-locked fiber lasers

A passively mode-locked fiber laser is theoretically investigated. The mode locking is achieved using the nonlinear polarization technique. We consider the practical case of the ytterbium-doped fiber laser operating in the normal dispersion regime. The effect of the phase plates is explicitly taken into account. The resulting model reduces to one iterative equation for the optical Kerr nonlinearity, the phase plates and the polarizer, and one partial differential equation for the gain and the dispersion. Numerical simulations allow us to describe several features observed in passively mode-locked fiber lasers such as bistability between the mode lock and the continuous regime, multiple pulse behavior, hysteresis phenomena. The dynamics of the number of pulses as a function of the pumping power is also reported. Pump power hysteresis is demonstrated.