The wave turbulence theory predicts that a conservative system of nonlinear waves can exhibit a process of condensation, which originates in the singularity of the Rayleigh-Jeans equilibrium distribution of classical waves. Considering light propagation in a multimode fiber, we show that light condensation is driven by an energy flow toward the higher-order modes, and a bi-directional redistribution of the wave-action (or power) to the fundamental mode and to higher-order modes. The analysis of the near-field intensity distribution provides experimental evidence of this mechanism. The kinetic equation also shows that the wave-action and energy flows can be inverted through a thermalization toward a negative temperature equilibrium state, in which the high-order modes are more populated than low-order modes. In addition, a Bogoliubov stability analysis reveals that the condensate state is stable.

波浪湍流理论预测，非线性波的保守系统会出现凝聚过程，这源于经典波的瑞利-金斯平衡分布的奇点。考虑到光在多模光纤中的传播，我们表明光凝聚是由流向高阶模式的能量流驱动的，以及波作用（或功率）向基模和高阶的双向重新分布模式。近场强度分布的分析提供了这种机制的实验证据。动力学方程还表明，波作用和能量流可以通过向负温度平衡状态的热化进行反转，其中高阶模式比低阶模式更密集。此外，