Rayleigh–Jeans thermalization vs beam cleaning in multimode optical fibers

Classical nonlinear waves exhibit, as a general rule, an irreversible process of thermalization toward the Rayleigh-Jeans equilibrium distribution. On other hand, several recent experiments revealed remarkable effect spatial organization optical beam that propagates through graded-index multimode fiber (MMF), phenomenon termed self-cleaning. Our aim here is to evidence qualitative impact disorder (weak random mode coupling) on by considering two different experimental configurations. In first experiment, we launch speckle beams in relatively long MMF. results report clear and definite demonstration light propagation MMFs, over broad range kinetic energy (i.e., degree coherence) injected beam. particular, property equipartition among modes clearly observed condensed regime. The also double turbulence cascade process: while power flows fundamental (inverse cascade), higher-order (direct cascade). 2nd coherent laser launched into short MMF length. It reveals cleaning driven incipient thermalization. As discussed numerical simulations, fast 1st experiment can be attributed due phase dynamics modes, which favoured injection increased system.