Spatiotemporal mode locking is a nonlinear process of multimode soliton self-organization. Here the real-time buildup dynamics of the multiple solitons in a spatiotemporal mode-locked multimode fiber laser are investigated, assisted by the time-stretch technique. We find that the buildup processes are transverse mode dependent, especially during the stages of relaxation oscillation and $Q$-switching prior to multiple soliton formation. Furthermore, we observe that the transverse modal composition of these generated pulses among the multiple solitons can be different from each other, indicating the spatiotemporal structure of the multiple soliton. A simplified theoretical model based on pulse energy evolution is put forward to interpret the role of 3D saturable absorber on spatiotemporal structures of spatiotemporal mode-locking multiple solitons. Our work has presented the spatiotemporal nonlinear dynamics in multimode fiber lasers, which are novel to those inside the single transverse mode fiber lasers.

中文翻译：

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时空锁模光纤激光器中多孤子的形成动力学

时空锁模是多模孤子自组织的非线性过程。在这里，在时间拉伸技术的辅助下，研究了时空锁模多模光纤激光器中多个孤子的实时累积动力学。我们发现累积过程依赖于横向模式，尤其是在弛豫振荡和$问$-在多个孤子形成之前切换。此外，我们观察到这些产生的脉冲在多个孤子之间的横向模态组成可能彼此不同，表明多个孤子的时空结构。提出了一种基于脉冲能量演化的简化理论模型来解释3D可饱和吸收体对时空锁模多孤子时空结构的作用。我们的工作展示了多模光纤激光器中的时空非线性动力学，这对于单横模光纤激光器内部的那些是新颖的。