Model and computational advancements to full vectorial Maxwell model for studying fiber amplifiers

TL;DR

This paper introduces advanced modeling and computational techniques for a full vectorial Maxwell finite element model to simulate fiber amplifiers, capturing complex physical effects with high accuracy and efficiency.

Contribution

It develops a novel high-fidelity 3D Maxwell model with a rescaling approach to reduce computational cost while maintaining accuracy for fiber amplifier simulations.

Findings

Validated the scaled model on ytterbium-doped fiber amplifier

Demonstrated simulation of up to 240 wavelengths

Showed the model's capability to handle nonlinear and thermal effects

Abstract

We present both modeling and computational advancements to a unique three-dimensional discontinuous Petrov-Galerkin finite element model for the simulation of laser amplification in a fiber amplifier. Our model is based on the time-harmonic Maxwell equations, and it incorporates both amplification via an active dopant and thermal effects via coupling with the heat equation. As a full vectorial finite element simulation, this model distinguishes itself from other fiber amplifier models that are typically posed as an initial value problem and make significantly more approximations. Our model supports co-, counter-, and bi-directional pumping configurations, as well as inhomogeneous and anisotropic material properties. The longer-term goal of this modeling effort is to study nonlinear phenomena that prohibit achieving unprecedented power levels in fiber amplifiers, along with validating typical approximations used in lower-fidelity models. The high-fidelity simulation comes at the cost of a high-order finite element discretization with many degrees of freedom per wavelength. This is necessary to counter the effect of numerical pollution due to the high-frequency nature of the wave simulation. To make the computation more feasible, we have developed a novel longitudinal model rescaling, using artificial material parameters with the goal of preserving certain quantities of interest. Our numerical tests demonstrate the applicability and utility of this scaled model in the simulation of an ytterbium-doped, step-index fiber amplifier that experiences laser amplification and heating. We present numerical results for the nonlinear coupled Maxwell/heat model with up to 240 wavelengths.