Fluorescence-based chemical sensing using suspended-core microstructured optical fibres.

Abstract

This thesis contains a study on the fluorescence based chemical sensing properties of microstructured optical fibres. Specifically, suspended core optical micro/nano-wires, including those with the core partially exposed along their length, are studied both theoretically and experimentally. Comparisons are made between these exposed-core and enclosed-core optical fibres in terms of their fluorescence sensing performance, fabrication, and function. The application of corrosion sensing of aluminium alloys was the primary motivator for this project and methods for achieving this are presented. However, the findings presented in this thesis could be extended to many other biological and chemical applications. Chapter 1 outlines the motivation of the work and the structure of the thesis. Chapter 2 reviews the state of the art for optical fibre chemical sensing. In Chapter 3 a theoretical model is derived and used to predict the fluorescence capture of high index contrast small-core fibres using vectorial solutions to Maxwell's equations. This model is subsequently used to compare exposed-core and enclosed-core fibres, where distinct advantages are found for liquid-immersed exposed-core fibres due to their asymmetric refractive index profile. In Chapter 4 the fabrication of both enclosed and exposed suspended-core fibres are demonstrated using the extrusion technique for soft-glass preform development. It is then confirmed experimentally that advantages of using exposed-core fibres include the ability to perform real time and distributed fluorescence based sensing. In Chapter 5 two methods of sensitising these fibres for corrosion sensing of aluminium alloys are investigated. Both methods use a fluorescence based indicator molecule for aluminium ions, which is either embedded into a porous polymer coating or chemically attached via polyelectrolytes.