Nonlinear beam self-maintaining effect in graded-index multimode fiber

TL;DR

This paper discovers a new nonlinear self-maintaining beam regime in graded-index multimode fibers, where a dominant input mode preserves its structure due to Kerr effects, supported by experiments and simulations.

Contribution

It introduces a novel nonlinear self-organized regime for multimode beam propagation, highlighting the role of Kerr effects in beam cleanup and structure preservation.

Findings

Existence of a self-maintaining beam regime verified experimentally and numerically.

Nonlinear Kerr effects are identified as the driving mechanism.

The regime maintains input mode structure in nonlinear conditions.

Abstract

Multimode fiber systems are desirable for industrial and scientific applications. As an interesting effect for the laser beam propagation in a multimode fiber, nonlinear Kerr beam cleanup has attracted considerable research interest due to the spatial beam compressing. However, its physical mechanisms, especially the influences of input conditions on its performances, remain unclear. Here, we report a new self-organized regime for the multimode beam propagation in a graded-index multimode fiber: when the input laser has a dominant mode in which most of the laser energy is concentrated, the beam profile can be maintaining in a well-defined structure similar to the input dominant mode in nonlinear regime, while it will evolve to an irregular pattern in linear regime. The existence and universality of this nonlinear beam self-maintaining effect have been verified by the experimental and numerical data. Our results also provide evidence that nonlinear Kerr effects can be the driving mechanism and nonlinear Kerr beam cleanup is a specific case of this effect. Further research into this spatial beam shaping effect may provide a new perspective to understand other multimode fiber nonlinearities.