Comparison of Models of Fast Saturable Absorption in Passively Modelocked Lasers

TL;DR

This paper compares three advanced models of fast saturable absorbers in passively modelocked lasers, showing they predict larger stability regions and high-energy solutions not captured by the traditional Haus modelocking equation.

Contribution

It introduces a comparative analysis of three higher-order FSA models, demonstrating their improved stability predictions over the Haus modelocking equation.

Findings

All three models predict larger stable regions.

They identify high-energy solutions absent in HME.

Models show similar qualitative stability diagrams.

Abstract

Fast saturable absorbers (FSAs) play a critical role in stabilizing many passively modelocked lasers. The most commonly used averaged model to study these lasers is the Haus modelocking equation (HME) that includes a third-order nonlinear FSA. However, it predicts a narrow region of stability that is inconsistent with experiments. To better replicate the laser physics, averaged laser models that include FSAs with higher-than-third-order nonlinearities have been introduced. Here, we compare three common FSA models to each other and to the HME using the recently-developed boundary tracking algorithms. The three FSA models are the cubic-quintic model, the sinusoidal model, and the algebraic model. We find that all three models predict the existence of a stable high-energy solution that is not present in the HME and have a much larger stable operating region. We also find that all three models predict qualitatively similar stability diagrams. We conclude that averaged laser models that include FSAs with higher-than-third-order nonlinearity should be used when studying the stability of passively modelocked lasers.