Semiconductor ring lasers for high speed communications
The work described in this thesis is aimed at exploring the possibility of optically integrating an OTDM transmitter operating at 4X10Gb/s on an appropriate substrate. It has been shown that such an OTDM transmitter system could be integrated on III-V semiconductor quantum well (QW) substrates if the design of the substrate, the choice of fabrication techniques and the design of the devices are carefully considered. Suitable device structures for the three main kinds of devices involved in OTDM transmitters, namely light source, optical multiplexers (couplers) and optical modulators, have been discussed. Significant progress regarding these aspects, both theoretical and experimental, has been achieved. In this work, it has been intended to investigate all the devices from the integration point of view. This has been reflected in many aspects in the device design and fabrication process. Integration has always been a very important factor to consider in the determination of substrate material structure, device configuration, waveguide structure and fabrication techniques. As a result, the devices developed in this project are suitable for the proposed purpose of an integrated OTDM transmitter system. Investigation into integration techniques has also been carried out. The most important was to introduce bandgap difference on a semiconductor QW material. IFVD technique is studied and produced some encouraging results such as the extended cavity SRL, which integrates an active section with a passive MMI coupler. Vertically coupled waveguide structures have also been invstigated in an attempt to produce extended cavity lasers. The design considerations of extended cavity lasers employing this waveguide structure have been discussed.