City Research Online

Abstract

This thesis focuses on the development of optical fibre Bragg grating based fibre- lasers for potential temperature sensor applications. The fabrication of both type I and type IIA Bragg gratings in B-Ge co-doped and Ge-doped photosensitive fibres was studied and their long-term temperature sustainability was evaluated. The optimisation of several wavelength-matched normal Bragg grating based fibre lasers was studied for sensor applications. The new sensor approach was developed using a full-in-fibre Bragg grating based laser for temperature measurement applications. A chirped fibre grating was used as the second reflector in the laser cavity to achieve temperature tuneable laser action with erbium-doped fibre as the gain medium of the laser. Normal type I or type IIA Bragg gratings were used as the sensing probes of the system, also forming the end reflector in the laser cavity. A special feature was that these gratings were fabricated in various high temperature sustainable photosensitive fibres to enhance the measurement range. The laser-based sensor was also characterised in terms of different values of applied strain to the chirped grating and the performance was compared under both active and passive operating conditions. The laser-based sensor approach was extended for the strain measurement applications when the normal grating was strained. The fabrication of type II chirped gratings was also studied, in order to create better sensor systems.

A detailed investigation into the output characteristics of a uniform wavelength- matched Bragg grating-based fibre laser was evaluated, with each individual Bragg grating acting as the reflector of the laser system, responding to temperature. An analytical model has been created, reflecting the relationship between the grating bandwidth and the temperature, under each of the operational conditions considered. The output characteristics of a very short cavity length fibre laser were analysed when it was tested in an oven. The single point laser-probe approach has been extended for multiplexed sensor applications and simultaneously multi-channel temperature information has been obtained over a wider measurement range. Finally, general conclusions on the work and recommendations for the future research have been made.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QA Mathematics T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Science & Technology > Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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