Pulse-train nonuniformity in a fiber soliton ring laser mode-locked by using the nonlinear polarization rotation technique

We report on the experimental observation of periodical intensity fluctuations on the output of a fiber soliton ring laser passively mode-locked by using the nonlinear polarization rotation technique. It is found that the appearance of such intensity fluctuations is independent of the orientation of the polarizer in the cavity, but closely related to the pump intensity. We have also numerically simulated the pulse dynamics of the laser. Our numerical simulations confirmed the experimental observations and showed that the soliton pulse nonuniformity is caused by the interaction between the nonlinear polarization rotation and the polarizer in the cavity.