On the Beam Profile and Beam Quality of Gain-Guided Index-Antiguided Fibers with Finite Cladding Boundary

TL;DR

This paper derives a closed-form expression for the beam quality factor of gain-guided index-antiguided fibers with finite cladding, highlighting the limitations of traditional infinite cladding approximations for accurate predictions.

Contribution

It provides a rigorous analysis of the beam quality factor considering finite cladding boundaries, improving upon previous models that assumed infinite cladding.

Findings

Finite cladding boundary significantly affects beam quality predictions.

The derived formula aligns well with recent experimental results.

Infinite cladding approximation is inadequate for index-antiguided fibers.

Abstract

The beam quality factor $M^2$ for the fundamental LP01 mode of a step-index fiber with a finite cladding diameter is calculated in the presence of gain, in a closed form, as a function of the complex generalized V-number. It is shown that the conventional infinite cladding diameter approximation cannot be used for index-antiguided gain-guided fibers, and the rigorous analysis presented in this paper is required for accurate prediction of the beam quality factor, as reported in recent experimental measurements.