Distributed optical fibre sensors based on the coherent detection of spontaneous Brillouin scattering

This thesis reports on the progress that has been made improving the sensing performance of a distributed temperature and strain optical fibre sensor based on the coherent detection of spontaneous Brillouin scattering. To further improve the sensing range and the sensor's performance, the use of Raman amplification was investigated utilising different Raman pump configurations. Using frequency measurements only, a temperature resolution of 5 °C over a 150km sensing range with 50m spatial resolution was achieved using a counter-propagating Raman pump. Using co-propagating Raman pump the temperature resolution was 1.7 °C with 20m spatial resolution at 100km. Measuring both the power and frequency of the Brillouin signal, a simultaneous temperature and strain measurement was performed over 50km; temperature and strain resolutions of 3.5 °C and 85 µe with 5m spatial resolution were achieved, respectively, using co-propagating Raman pump which has the advantage of requiring access to just one end of the sensing fibre.