Discriminative temperature and strain measurements by Brillouin optical frequency domain analysis in specialty fibers

We demonstrate a method for discriminative measurements of strain and temperature, based on high-spatial resolution Brillouin optical frequency-domain Analysis (BOFDA) measurements in two types of specialty fibers: highly-birefringent spun fibers, and few-mode fibers. In both, fiber birefringence manifests itself as an undulation in the Brillouin gain spatial profile, with a period equal to the associated beat length. Since the latter changes with temperature and strain with opposite sign, the simultaneous measurement of Brillouin frequency shift and birefringence provides a means to unambiguously separate the strain and temperature effects.