Development of optical fibre devices for distributed monitoring and point-sensing applications

Abstract

This thesis describes the development of novel optical fibre devices and coatings
for sensing and catalysis. The production of a sensor cable able to detect leaks in petrochemical pipelines is described. The cable consisted of a glass-reinforced central rod that was coated in a thin polymer layer designed to expand in the presence of the target fluids. Swelling of the polymer film induced light loss in an adjacent optical fibre by the production of micro bends. These micro bending losses were detected by optical time domain reflectometry over kilometre lengths of cable, with response times of less than a minute. The development of point sensors using optical fibre is also described. The possibility of coating optical fibres in photoactive semiconductor thin films for sensing or photocatalysis is discussed and a microemulsion technique for the production of nanoscale, mesoporous thin films
of titania is detailed. The sol-gel system consisted of water-containing, inverse
micelles of Triton X-100, (a well characterised non-ionic surfactant) in a dry
cyclohexane environment. Titanium (IV) isopropoxide was used as a precursor and was hydrolysed within the aqueous micelle cores. After thermal treatment of the resultant gels, titania materials were obtained as powders and thin films on
conducting glass slides and optical fibres. Powders and thin films on slides were
well crystallised, mesoporous anatase. BET surface areas were, in some cases,
shown to be in excess of 600 m 2 g1. Calcining of thin films on optical fibre
substrates was shown to be detrimental to fibre integrity and thus, alternative
methods for the crystallisation of films and the removal of organic residues were
explored. Ultraviolet irradiation, hydrothermal treatment and supercritical fluid
extraction were investigated. Supercritical fluid extraction and hydrothermal
methods were shown to be effective in removing organic residues and steam
treatment was successful in the development of an anatase structure at temperatures more than 200 ° cooler than in conventional thermal treatments.

Date of Award	Aug 2003
Original language	English
Awarding Institution	University of Wales, Bangor
Supervisor	Maher Kalaji (Supervisor)