Generation of spatiotemporal dark pulse or polarization domain wall solitons in a partial multimode mode-locked fiber laser.

• Spatiotemporal mode locking has been achieved in a partial multimode Er-doped fiber laser. • Through this laser, STML dark pulse, bright pulse, and dark bright pulse pairs can be obtained. • By varying the physical parameter settings, the laser cavity can alternately operates on different STML pulse regimes. In this paper, we have experimentally investigated different operational states of a partial multimode Er-doped spatiotemporal mode-locked (STML) fiber laser. The STML is enabled by nonlinear multimode interference (NL-MMI) effect from the partial multimode cavity structure. It is found that by adjusting the multimode polarization controller (PC) and the pump power, the STML dark pulses, bright pulses, as well as the polarization domain wall solitons can all be obtained, alternatively. The fused-tapered multimode coupler is responsible for the dark pulses generation via the enhanced modal cross-phase coupling. It is believed that the present findings can offer an important insight into the spatiotemporal dynamics of the STML solitons. [ABSTRACT FROM AUTHOR]