We develop a spatiotemporal mode decomposition technique to study the spatial and temporal mode power distribution of ultrashort pulses in long spans of graded-index multimode fiber, for different input laser conditions. We find that the beam mode power content in the dispersive pulse propagation regime can be described by the Bose–Einstein law, as a result of the process of power diffusion from linear and nonlinear mode coupling among nondegenerate mode groups. In the soliton regime, the output mode power distribution approaches the Rayleigh–Jeans law.

中文翻译：

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线性和非线性渐变折射率多模光纤中超短脉冲的时空模式分解

我们开发了一种时空模式分解技术，用于研究不同输入激光条件下渐变折射率多模光纤长跨度中超短脉冲的空间和时间模式功率分布。我们发现色散脉冲传播状态中的光束模式功率含量可以用玻色-爱因斯坦定律描述，这是非退化模式群之间线性和非线性模式耦合的功率扩散过程的结果。在孤子状态下，输出模式功率分布接近瑞利-金斯定律。