Periodic intensity fluctuations in spatiotemporal mode-locked lasers

We report the periodic intensity fluctuations and period-timing bifurcation in a spatiotemporal mode-locked multimode fiber laser. By adjusting the intracavity waveplate or the pump power, the intensity pattern of the spatiotemporal modelocked output could transit from uniformity to period-2, then to period-4. We further find that, in the state of multipleperiod pulsations, the extent of intensity fluctuation of different transverse modes varies. This indicates that not only the entire energy, but also the shape of the output spatial profile alters with multiple-period. A simple model is proposed to interpret the output pulse dynamics of multimode fiber lasers. This investigation would contribute to the understanding of the complex nonlinear dynamics in spatiotemporal mode-locked multimode fiber lasers.