Fast Acquirable Brillouin Optical Time-domain Reflectometry Based on Bipolar-chirped Pulse Pair

In this paper, fast measurement of Brillouin optical time-domain reflectometry (BOTDR) based on a linearly frequency modulated (LFM) pulse and a digital matched filter is studied theoretically and demonstrated experimentally. The Brillouin frequency shift (BFS) change is detected by measuring the time shift of the Brillouin gain spectrum (BGS) along the time axis instead of the frequency shift, as in traditional BOTDR. In the experiment, we propose to use a positive- and negative-swept pulse, named bipolar-chirped pulse pair (BPP), to determine the BFS change with high accuracy. A BGS acquisition of up to 320 Hz is obtained for a fiber length of 2 km with a strain measurement accuracy of ±8 μe. Strain measurements in a range of up to 10000 μe are conducted, and the resulting strain coefficient is equal to 0.048 MHz/μe, which matches that of standard single-mode fibers. The BPP-BOTDR technique is an intrinsic one-end-injection truly distributed system that exhibits high measurement speed and high accuracy, which may pave the way for various BOTDR applications.