Extending the Dynamic Range of Sweep-Free Brillouin Optical Time-Domain Analyzer

Sweep-free Brillouin optical time-domain analysis (SF-BOTDA) replaces the sequential frequency scanning of classical BOTDA by parallel interrogation of the fiber-under-test using the simultaneous interaction of multiple pump tones with counter-propagating multiple probe tones. While the basic SF-BOTDA technique boosts the measurement speed by a factor equal to the number of probe tones used, its dynamic range is limited to approximately the pump tone spacing, which is of the order of 100 MHz. This paper provides an in-depth analysis of our method to significantly extend the dynamic range to the GHz regime. Based on sequential interrogation with up to three sets of multiple tones, each having a different frequency spacing, this method provides a major speed advantage over the classical BOTDA in spite of the use of three sets of tones. With this development, which does not require any additional hardware, SF-BOTDA offers distributed sensing of optical fibers over practical dynamic ranges of strain/temperature variations, with the potential to become one of the fastest sensing techniques.