Numerical analysis of beam self-cleaning in multimode fiber amplifiers

TL;DR

This paper presents a numerical study demonstrating that beam self-cleaning can occur in multimode fiber amplifiers, influenced by local intensity maxima affecting gain saturation, expanding understanding of nonlinear beam reshaping in active fibers.

Contribution

It provides the first detailed numerical analysis of beam self-cleaning in active multimode fibers, highlighting the role of self-imaging and gain saturation effects.

Findings

Beam self-cleaning occurs in amplifying fibers without energy conservation.

Local intensity maxima influence population inversion and gain saturation.

Numerical simulations confirm beam reshaping in diode-pumped graded-index fibers.

Abstract

Recent experimental results have reported the observation of beam self-cleaning or, more generally, nonlinear beam reshaping in active multimode fibers. In this work we present a numerical analysis of these processes, by considering the ideal case of a diode-pumped signal amplifier made of a graded-index multimode fiber with uniform Yb doping. Simulations confirm that beam cleaning of the signal may take place even in amplifying fibers, that is the absence of beam energy conservation. Moreover, we show how the local signal intensity maxima, which are periodically generated by the self-imaging process, may influence the population inversion of the doping atoms, and locally saturate the amplifier gain.