Brillouin scattering based fiber optic strain sensor
In this study, stress-induced Brillouin scattering was experimentally analyzed by the weight applied to a specific point of the classical single mode fiber cable. A Brillouin optical time domain analysis (BOTDA) test system was developed for frequency shifts according to different weights applied. For different weights, the frequency values of the scattered light are obtained from the specific point of the fiber cable.
The Effects of Signal Level of the Microwave Generator on the Brillouin Gain Spectrum in BOTDA and BOTDR
In this study, Brillouin Gain Spectrum (BGS) is experimentally analyzed in the Brillouin Optical Time Domain Reflectometry (BOTDR) and Brillouin Optical Time Domain Analyzer (BOTDA). For this purpose, the signal level of the microwave generator is varied and the effects of BGS are investigated. In the setups, 20 km conventional single mode fiber is used to both setups and laser wavelengths are selected around 1550 nm. To achieve best results, it can be used between 5 dBm to 15 dBm signal level of microwave generator for BOTDA and BOTDR setups. Keywords—Microwave signal level, Brillouin gain spectrum, BOTDA, BOTDR.
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 µ.epsilon 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.