This thesis presents and validates a model for designing multimode SOA-like waveguide devices. This model was used to design an active vertical coupler wavelength converter device making use of both crossgain and cross-phase modulation. The simulated output extinction ratio was over 30dB for a maximum input pump level of under 6 dBm. A multi-quantum well wafer structure was designed and ordered. Two rounds of devices were designed and multiple fabrication processes developed. These included three levels of etch depth, for which one depth was required to be correct within a small tolerance. Also, the dry plasma etch was required to create totally internally reflecting mirrors in a two step etch so much development was required for this step to keep the surface optically smooth. After the fabrication process development devices were successfully fabricated with good quality waveguides and totally internally reflecting mirrors. Characterisation of completed devices exhibit couphng and gain variation due to carrier modulation. The extinction ratio of the devices has been measured as over 30dB with varying current injection. The transmission extinction ratio has been measured as over 20dB with varying injection current. It was discovered that the fabricated devices have a low quantum efficiency (?e). This prevented high carrier concentration which made optical saturation too small to observe. Although all-optical wavelength conversion was not demonstrated, the successful modulation of the coupling due to carrier population changes by injection current has dnonstrated the operation principles. Optical saturation of the carrier density and modulation of the coupling should be achievable with a wafer design that has improved carrier confinement in the active layer. Probable solutions to all these problems have been described which should result in high quality devices.
|Date of Award||2007|