Nonlinear Gain Dynamics of Quantum Dot Semiconductor Optical Amplifiers

Abstract

In this work the nonlinear gain dynamics of electrically injected quantum dot semiconductor optical amplifiers is investigated. At first the semiclassical modeling ansatz on the basis of Maxwell-Bloch equations is presented. An important aspect are here the carrier scattering processes between the confined quantum dot states and the surrounding quasi-2D carrier reservoir states. Based on a detailed microscopic description of the Coulomb scattering processes density and temperature dependent scattering rates for the quantum dot-quantum well Auger scattering processes are calculated. In the next part of this work the dynamic properties of quantum dot semiconductor optical amplifiers are investigated. The impact of the different scattering channels on the gain recovery of the device is investigated. As a main result it is shown that a cascading relaxation scattering channel drives the ultrafast gain recovery dynamics associated with quantum dot amplifiers. Furthermore, comparisons with gain recovery measurements suggest that carrier heating significantly enhances the gain recovery dynamics. The stability properties of lasers are closely related to the linewidth enhancement factor, or α-factor. In the next part of this work the impact of the coherent interaction of the quantum dot states and the 2D reservoir states on the static α-factor is investigated. As a main result it is shown, that the α-factor of quantum dot based devices is largely determined by the coherent interaction of the reservoir. Furthermore, it is shown that the coherent interaction of the reservoir states also has a huge impact on the phase dynamics and the chirp of ultrashort input pulses. The last part of this work deals with nonlinear wavelength conversion using nondegenerate four-wave mixing. Based on the results on Coulomb scattering, it can be shown that the high bandwidth of nonlinear wavelength conversion in quantum dot semiconductor optical amplifiers is linked to the efficient scattering mechanisms between the reservoir and the quantum dot states.