Spatial beam self-cleaning in bi-tapered multimode fibers

TL;DR

This paper demonstrates that bi-tapered multimode fibers can effectively self-clean laser beams, improving beam quality and spectral broadening, which is promising for high-power laser applications and fiber laser device manufacturing.

Contribution

Introduction of bi-tapered structures in multimode fibers to achieve efficient spatial beam self-cleaning and spectral broadening, enhancing high-power laser beam quality.

Findings

Longer tapered lengths improve self-cleaning effect.

Bi-tapered fibers produce centered, bell-shaped beams.

Method is low-cost and suitable for fiber laser devices.

Abstract

We report the spatial beam self-cleaning in bi-tapered conventional multimode fibers (MMFs) with different tapered lengths. Through the introduction of the bi-tapered structure in MMFs, the input beam with poor beam quality from a high-power fiber laser can be converted to a centered, bell-shaped beam in a short length, due to the strengthened nonlinear modes coupling. It is found that the bi-tapered MMF with longer tapered length at the same waist diameter shows better beam self-cleaning effect and larger spectral broadening. The obtained results offer a new method to improve the beam quality of high-power laser at low cost. Besides, it may be interesting for manufacturing bi-tapered MMF-based devices to obtain the quasi-fundamental mode beam in spatiotemporal mode-locked fiber lasers.