Simultaneous strain and temperature measurement using a Brillouin scattering based distributed sensor

Recent improvements to Brillouin scattering based distributed sensors have reduced both the spatial and strain resolutions to the point where they are acceptable for many smart structures applications. This type of optical fiber sensor can measure both strain and temperature as both parameters produce a change in the optical fiber's Brillouin frequency. Since both measurands have the same observed effect it is impossible to determine which measurand is responsible for the shift in frequency. This problem must be overcome for these sensors to be suitable for many smart structures applications. Techniques have recently been developed for Brillouin scattering based distributed sensor systems to separate strain and temperature information. However, these methods are limited theoretically to spatial resolutions approaching 5-10 meters. This paper reports on a new technique that was used at a shorter spatial resolution. The Brillouin loss spectrum peak power was determined as a function of strain and temperature at a spatial resolution of 3.5 meters. By combining this information with the conventional Brillouin frequency measurement, strain and temperature were successfully differentiated.