Abstract

When light is launched into a fibre optic cable, the majority of the light travels through the cable, but a small fraction is backscattered and the property of Brillouin backscattered light is related to cable’s strain and temperature condition. Based on that principle, a Brillouin Optical Time Domain Reflectometry (BOTDR) analyser was constructed and has been recently applied to many infrastructures for strain and temperature monitoring. However, unexpected strain fluctuations were observed from a majority of site’s BOTDR measurement results and it is hardly to distinguish whether the fluctuation is error or real strain. Therefore a temperature and strain calibration bench was established in lab to characterize BOTDR analyser measurements and a fundamental optics model was built to simulate the results. It is found out that BOTDR strain measurement fluctuations are mainly coming from analyser spatial limitation, and the faster strain changes, the more fluctuation there will be. Based on that theory, an enhanced data interpretation methodology is being investigated to minimise BOTDR measurement error and achieve better strain monitoring.