This thesis describes the development and performance of short-cavity polarisation-maintaining (birefringent) infibre
Fabry-Perot interferometric sensors for the measurement of temperature or strain. By using a highly birefringent optical fibre in their cavity, these sensors form two interferometers - one for each polarisation axis. As
in the case of other fibre interferometers, each axial interferometer is extremely sensitive to temperature and strain. But this high sensitivity together with the periodic nature of each interferometer output yields a limited unambiguous measurand range (UMR). However, the differential phase between the axial interferometric phase
responses of the birefringent sensors developed in this work can be exploited to provide an extended UMR.