Abstract
In this study, the authors present an experimental and theoretical description of the use of first
order Raman amplification to improve the performance of a Phase-sensitive optical time domain reflectometer
$(\phi {OTDR})$
when used for vibration measurements over very
long distances. A special emphasis is given to the noise which is carefully characterized and minimized along the
setup. A semiconductor optical amplifier and an optical switch are used to greatly decrease the intra-band coherent
noise of the setup and balanced detection is used to minimize the effects of RIN transferred from the Raman pumps. The
sensor was able to detect vibrations of up to 250 Hz (close to the limits set by the time of flight of light
pulses) with a resolution of 10 m in a range of 125 km. To achieve the above performance, no post-processing
was required in the
$\phi {OTDR}$
signal. The evolution of the
$\phi {OTDR}$
signal along the fiber is also shown to have a
good agreement with the theoretical model.
© 2014 IEEE
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