It is known that the ultimate spatial resolution for a Brillouin-based sensor is limited by the lifetime of the phonons in the fiber that mediate the Brillouin loss process. At optical pulse widths less than 10 ns (corresponding to one meter spatial resolution) the Brillouin line width is considerably broadened, causing a severe penalty in resolving the Brillouin frequency shift. Around 5 ns the Brillouin line width is too broad to allow an accurate frequency determination. The fiber optics group at the University of New Brunswick, Canada, has recently developed an automated system for strain measurements in a distributed sensing system that uses a novel signal processing technique to measure strain at resolutions finer than the Brillouin line width limit. Strain has been resolved to 20 at 500 mm and to 40 at 250 mm.
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