We experimentally investigate the pressure dependence of the Brillouin frequency shift (BFS) in a polymer optical fiber. The BFS dependence on pressure shows a hysteresis, but after several cycles of increasing/decreasing pressure, the hysteresis is mitigated. The pressure dependence coefficient at this state is +4.3 MHz/MPa, the absolute value of which is 5.8 times as large as that of bare silica fibers (the sign is opposite). The reason for this unique behavior is discussed. This result indicates that, by using plastic optical fibers instead of silica fibers, distributed pressure sensing with a higher sensitivity is potentially feasible.
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