Failure of the \alpha-factor in describing QD laser dynamical instabilities and chaos

TL;DR

This paper demonstrates that the traditional actor concept fails to accurately describe the complex dynamical instabilities and chaos in quantum dot lasers, especially under high excitation or optical injection conditions.

Contribution

It reveals the limitations of the actor in QD lasers and compares simplified models with detailed non-equilibrium simulations to identify when the actor approximation breaks down.

Findings

The actor concept is invalid for QD laser dynamics under certain conditions.

Conventional quantum well lasers can be approximated with a constant actor.

Different scattering timescales in QD lasers cause the actor approximation to fail.

Abstract

We show that the long-established concept of a linewidth-enhancement factor \alpha to describe carrier-induced refractive index changes in semiconductor lasers breaks down in quantum dot (QD) lasers when describing complex dynamic scenarios, found for example under high-excitation or optical injection. By comparing laser simulations using a constant \alpha-factor with results from a more complex non-equilibrium model that separately treats gain and refractive index dynamics, we examine the conditions under which an approximation of the amplitude-phase coupling by an \alpha-factor becomes invalid. The investigations show that while a quasi-equilibrium approach for conventional quantum well lasers is valid over a reasonable parameter range, allowing one to introduce an \alpha-factor as a constant parameter, the concept is in general not applicable to predict QD laser dynamics due to the different timescales of the involved scattering processes.