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Radiation losses in dielectric optical waveguides

The effect of irregularities and deviations from the perfect structure of the ideal waveguide is to scatter some of the guided power carried by the modes of the ideal waveguide incident on the irregularity. This scattered power is redistributed over the (non-attenuating) bound modes of the structure and into the radiation modes of the waveguide. The study of this redistribution of the power over the discrete (bound) mode spectrum can be adequately analysed by conventional electromagnetic Coupled Mode Theory. However, the application of this technique for the analysis of the radiative losses, that is, the coupling into the radiation modes of the waveguide proves to be extremely tedious due to the difficulty of normalisation and orthogonalisation of these "improper" modes. The aim of this thesis is to present alternative techniques to the Coupled Mode Theory analysis, which provide simple treatments of these radiation loss processes in weakly guiding dielectric optical fibres. The philosophy of the presentation is to present the technique and choose the least number of practical examples that elucidate the strengths and deficiencies of each approach, rather than list ad nauseum a wide range of practical examples.