This thesis describes an investigation of polarisation conversion effects in gallium arsenide optical waveguides. The research was carried out with the aims of predicting, preventing and harnessing such effects. Experimental results are presented to demonstrate changes in the polarisation state of light propagating in passive deep-etched waveguides. The results are described by established modelling techniques. The effect due to process-dependent features of waveguide cross-section geometry, in particular asymmetry resulting form non-vertical etching, is investigated. The polarisation angles of hybrid waveguide modes are measured, and a novel technique is presented for the measurement of the differences been the effective indices of orthogonally polarised modes. The measurements obtained are used to analyse the evolution of elliptical polarisation states during propagation, and to provide an account of the physical origin of the polarisation conversion. Details of the nature of the optical modes predicted by rigorous numerical method simulations are demonstrated by the experimental results, while quantitative agreement between the simulated and measured data is shown. A simplified account of the behaviour is provided using a coupled-mode formulation. The influence of the linear electrooptic effect in modifying the polarisation conversion behaviour is explored experimentally, and is described using established theory. Waveguide designs are obtained which prevent unintended polarisation conversion in the presence of identified causes, while maintaining the main waveguide parameters of material composition, optical mode size and shape, electrooptic performance, and fabrication process. The polarisation behaviour in waveguides fabricated to these designs is evaluated, and the expected performance benefits are confirmed. A novel waveguide device which provides electrooptic control and switching of the optical polarisation state is presented. The device is capable of converting any input polarisation state into an arbitrary output state using the linear electrooptic effect. A working design is obtained and the fabrication of devices is described. Experimental results are presented which demonstrate the concept. Further developments of the polarisation controller device are proposed, including the realisation of the potential for switching speeds at frequencies of tens of GHz.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:618827 |
| Date | January 2007 |
| Creators | Finlayson, Ewan David |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/5856/ |
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