The thesis at hand investigates the suitability of quantum dot (QD) material for use in long-distance coherent communication. The thesis was written in the frame of the SASER project MONOLOP that is aiming for a compact, monolithically integrated light source with a tunable wavelength covering the C+-band and narrow spectral linewidth below 500 kHz. The thesis reviews the theoretical background of quantum dot material based on the InP material system and distributed feedback (DFB) lasers with lateral gratings as well as semiconductor optical amplifiers (SOA). The design and fabrication of the investigated laser devices is reviewed. The design of an integrated device consisting of a set of four DFB lasers, a cascaded Y-coupler and a semiconductor optical amplifier and its fabrication are described and basic properties, i.e. the wavelength, side mode suppression ratio, output power and amplification of the SOA, are evaluated. A wavelength tunability of more than 10nm for a single monolithic laser could be shown. An array of just four lasers yielded coverage of the C+-band at a tuning range of more than 45 nm. The focus of this work is the spectral linewidth of quantum dot lasers with different epitaxial and device structure. The linewidth was measured by delayed selfheterodyne method. The setup and its evolution will shortly be described. The linewidth of stand-alone DFB lasers was evaluated for the impact of number of quantum dot layers, facet coatings, heat sink temperature and mounting. A minimum linewidth of 110 kHz was found. The influence of the Y-coupler was investigated with and without pumping of the coupler section. Finally, the linewidth of the whole device was measured and the influence of the SOA amplification on the linewidth was determined. A minimum linewidth of 130 kHz from the SOA that was hardly altered with SOA current was found. The results clearly show the potential of quantum dot material for future coherent communication and the suitability of the designed integrated device as laser light source in these transmission systems.
@phdthesis{doi:10.17170/kobra-20191210859,
author ={Becker, Annette},
title ={1.55 μm Quantum Dot Lasers for Telecommunication},
keywords ={500 and 530 and Telekommunikation and Quantenpunkt and Laser},
copyright ={http://creativecommons.org/licenses/by-nc-sa/3.0/de/},
language ={en},
school={Kassel, Universität Kassel, Fachbereich Mathematik und Naturwissenschaften, Institut für Physik},
year ={2019}
}