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Distributed Brillouin temperature measurements without frequency scanning for dymanic process monitoring

Distrbuted Brillouin intensity vs. temperature measurements along an optical fiber are studied theoretically and experimentally using counter-propagating laser beams interacting at a fixed beat frequency. By monitoring the Brillouin temperature spectrum without scanning the beat frequency, one can acquire distributed temperature measurements within seconds rather than minutes, making this acquisition method suitable for dynamic processes such as hot spots and fire detection. This technique requires knowledge of a threshold temperature condition, which is mathematically derived by considering the temperature dependence on Brillouin peak power and linewidth in the frequency domain. Temperature varying fiber regions are monitored using 0.2 and 2 m spatial resolutions along 2 and 11 km fiber lengths respectively.