Air-clad fibers: pump absorption assisted by chaotic wave dynamics?

TL;DR

This paper investigates how chaotic wave dynamics in air-clad fiber geometries influence pump absorption efficiency, highlighting that certain geometries promote chaos and enhance absorption, while others support regular modes that reduce efficiency.

Contribution

It analyzes the extent of chaotic wave dynamics in air-clad fiber geometries and identifies how symmetry affects pump absorption efficiency.

Findings

Chaotic geometries promote stronger pump absorption.

Symmetric structures support whispering-gallery modes that reduce efficiency.

Efficiency scales with the ratio of core to cladding area in chaotic geometries.

Abstract

Wave chaos is a concept which has already proved its practical usefulness in design of double-clad fibers for cladding-pumped fiber lasers and fiber amplifiers. In general, classically chaotic geometries will favor strong pump absorption and we address the extent of chaotic wave dynamics in typical air-clad geometries. While air-clad structures supporting sup-wavelength convex air-glass interfaces (viewed from the high-index side) will promote chaotic dynamics we find guidance of regular whispering-gallery modes in air-clad structures resembling an overall cylindrical symmetry. Highly symmetric air-clad structures may thus suppress the pump-absorption efficiency eta below the ergodic scaling law eta proportional to Ac/Acl, where Ac and Acl are the areas of the rare-earth doped core and the cladding, respectively.