Abstract
In this work, a theoretical model for the description of carrier and light dynamics in a quantum dot laser/amplifier is presented. The model is based on Maxwell-Bloch equations and takes into account the scattering of charge carriers between 2-D wetting layer states and bound quantum dot states, intra-dot scattering between bound dot states, the influence of p-doping on the 2-D wetting layer states, the amplification, diffraction, and wave-guiding of the light fields in the optical cavity. The inhomogeneous broadening of the quantum dots (QDs) is included via a spatially resolved statistical method, where QDs with varying physical properties at different locations form the statistical ensemble. In this way, the inhomogeneously broadened gain spectrum is incorporated into the model. The inhomogeneous broadening of the QDs is also reflected by transition energy dependent carrier-LO-phonon and carrier-carrier scattering rates (calculated separately for each QD in the ensemble). Simulations of quantum dot amplifiers allow the analysis of the occupation probability of the quantum dot levels at steady state and during optical excitation by a femtosecond pulse. The influence of homogeneously and inhomogeneously broadened quantum dot media on spatial and spectral hole burning is revealed. It is shown that spatially varying dot properties lead to a reshaping of the optical pulse in the active medium. Direct modulation of quantum dot lasers at frequencies in the range of 1.0-60 GHz is investigated numerically. The influence of laser geometry and inhomogeneous broadening of the QD material on modulation properties and gain/emission spectra is visualised and discussed. It is shown that an increase of the inhomogeneous broadening leads to a decrease of the differential gain and an increase of the signal to noise ratio. Analysis of laser emission spectra show a spectral broadening due to high frequency modulation.