Optimisation of semiconductor optical amplifiers for optical networks

This thesis is concerned with the design, fabrication and testing of Multiple Quantum Well Semiconductor Optical Amplifiers (SOAs) in the Indium Phosphide (InP) material system at a wavelength of 1.55μm. Following an introduction to optical communication systems and an overview of SOAs, the realisation of two SOAs is described. First, the design and fabrication of an SOA for linear amplification is presented, which uses integrated mode expanders to match the output mode to that of an optical fibre. In conjunction with angled facets, these mode expanders allow the reduction of the intrinsic facet reflectivity so that anti-reflection (AR) coatings are not required for travelling wave operation. It is shown that despite the effective reflectivity being very low, the mirror loss can be improved by the application of a single layer AR coating. Devices with this AR coating are shown to have state of the art performance in terms of gain and noise. Secondly, the requirements for non-linear switching using SOAs are investigated, through a combination of theory and experiment. From these findings, methods for optimisation are outlined, and an SOA is designed and fabricated which incorporates these changes. Following basic characterisation, the SOA is shown to have improved characteristics through CW measurements. The performance is demonstrated by world leading wavelength conversion experiments at 100Gbit/s and finally the prospects for operation of a 100Gbit/s interferometer using this device are investigated. (author)