Spatial beam self-cleaning in multimode fiber

TL;DR

This paper demonstrates that the Kerr effect in graded-index multimode fibers enables ultrafast, all-optical beam self-cleaning, producing a spatially coherent output beam resistant to fiber bending, without requiring dissipative nonlinear processes.

Contribution

It reveals that nonlinear beam reshaping into the fundamental mode is possible via Kerr effect alone, offering a new method for beam quality improvement in multimode fibers.

Findings

Kerr effect induces beam self-cleaning in multimode fibers.

Self-cleaned beams are robust against fiber bending.

Process occurs without stimulated scattering mechanisms.

Abstract

Multimode optical fibres are enjoying a renewed attention, boosted by the urgent need to overcome the current capacity crunch of single-mode fibre systems and by recent advances in multimode complex nonlinear optics [1-13]. In this work, we demonstrate that standard multimode fibres can be used as ultrafast all-optical tool for transverse beam manipulation of high power laser pulses. Our experimental data show that the Kerr effect in a graded-index multimode fibre is the driving mechanism for overcoming speckle distortions, leading to a somewhat counter-intuitive effect resulting in a spatially clean output beam robust against fibre bending. Our observations demonstrate that nonlinear beam reshaping into the fundamental mode of a multimode fibre can be achieved even in the absence of a dissipative process such as stimulated scattering (Raman or Brillouin) [14,15].