Abstract
We report a long-range and high-spatial-resolution distributed measurement
of the birefringence of a polarization-maintaining fiber based on Brillouin
dynamic grating (BDG) through optimizing the pump and probe scheme in the
time-domain. The optimal scheme includes a CW pump1, a long pump2 pulse, and
a short probe pulse, where the long pump2 pulse can effectively excite a BDG
with a relatively low power to avoid other nonlinear effects in a long-length
fiber, and the short probe pulse is used to improve the spatial resolution.
The numerical simulations verify that with this scheme the spatial resolution
is determined by the duration of the probe pulse, while the BDG reflection
spectrum width increases with shorting the duration of the probe pulse. In
experiment, a measurement of a 500-m Panda polarization-maintaining fiber
with a 20-cm resolution is realized by using a 20-ns pump2 pulse and a 2-ns
probe pulse. The results clearly show the 49-cm spatial period of the birefringence
variation caused by the uneven stress as winding the fiber around a spool.
Besides, longer spatial periods of the birefringence variation are also observed,
which could be caused by the residual stress during the fiber drawing and
coating processes or the nonuniformity of fiber preform.
© 2013 IEEE
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