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Title: High-speed laser sources for data communications using multi-level signalling
Author: Coulson, E. E.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2004
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In order to facilitate the increasing traffic demands of optical communications networks high-speed transmitters will be required in future systems. This thesis focuses on routes to achieving 40Gb/s data rates using advanced modulation formats and direct modulation of Distributed Feedback (DFB) semiconductor laser diodes. In particular four-level signalling is employed as a way of achieving 40Gb/s data rates from existing state-of-the-art DFB lasers which are typically limited to speeds of around 20GHz. The potential of using four-level signalling to extend the reach of future systems is demonstrated for the first time by 40Gb/s uncooled signal generation. Transmission tests confirm the feasibility of the technique used and spectral efficiency measurements further show the benefit that can be gained by using advanced modulation formats. A novel technique is presented and demonstrated experimentally for the first time. The new technique, which exploits multi-level signalling of multi-section lasers to achieve high-data rates, can also alleviate some of the complicated electronics usually required by multi-level signalling systems. In this work a twin-contact DFB laser is employed to demonstrate the principle of four-level signal generation by differential amplitude modulation. Results are presented which show the feasibility of the technique and observations are made on the limitations of the device used in experimental demonstration. This leads to the use of a time-resolved travelling wave laser model. The model is adapted to support simulation of multi-section devices with spatially varying injection currents. Extensive simulation is used to suggest an optimised device structure for the generation of four-level signals. A three-contact device geometry is suggested and further work is presented on fabricating such a structure. Focussed-ion-beam-etching of a ridge-waveguide index coupled DFB is carried out to fabricate, for the first time, the optimised device structure. Results are presented which confirm the benefits that can be gained by employing the novel technique of differential amplitude modulation of multi-contact devices for high-speed multi-level signal generation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available