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A new fast and distributed optical time-domain sensing technique, employing the slope of Brillouin dynamic gratings in polarization-maintaining fibers, is proposed and demonstrated. The strain sensitivity of the reflectivity of a pulsed probe, orthogonally polarized to the pumps, which generated the Brillouin dynamic grating, is found to be practically independent of the pulse width, suggesting the potential to achieve much higher spatial resolutions than those offered by single-pulse, slope-assisted Brillouin sensing techniques using standard single-mode fibers. The dependence of the strain sensitivity on both pump and probe detuning is described by an experimentally validated theoretical model, which predicts an optimum detuning point, providing maximum strain sensitivity. We report the measurement of 400-Hz strain vibrations (at a sampling rate of 16 kHz) with a spatial resolution of 4.2 cm.
Bergman et al. (Tue,) studied this question.