Hybrid Ytterbium/Brillouin Gain Assisted Partial Mode Locking in Yb-Doped Fiber Laser

We have demonstrated experimentally and theoretically that the hybrid ytterbium/Brillouin gain can contribute to partial mode locking in the high-loss ytterbium-doped fiber laser. With only few cavity modes contained within the Brillouin gain curve, the dynamics of self-pulsing was not observed for the stimulated Brillouin scattering signal generated by each pump mode in the experiment. The results from two different experimental schemes show that both the Brillouin and ytterbium gains are required to support enough Brillouin pump and stokes cavity modes for partial mode locking. We also show that it is the coupling between the stimulated Brillouin scattering of the neighboring Brillouin pump modes that plays a direct role in the partial phase synchronization between different stokes modes. Furthermore, we proposed a theoretical model about the partially mode-locked laser dynamics. Based on the model, the numerical results agree quantitatively with the experimental ones. It is also found numerically that the extent of the phase synchronization can be enhanced by the cascaded stimulated Brillouin scattering according to the same physical mechanism.