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Description:
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The statistics of the phase dependent optical time -domain reflectometer have
been analyzed . The optical fiber is modeled by the use of a discrete set of reflectors
positioned randomly along the fiber . The statistics of the reflected light from
a traveling pulse are derived . The statistics of the signal are used to calculate the
characteristics of shot noise in the photodetector , and the probability that noise of
certain intensity will occur . An estimation of the backscattered power is made by calculating
the fraction of the backscattered power that is captured in a guiding mode .
Upper power limits are calculated by considering nonlinear optical effects . An estimation
of noise from thermally excited sound waves , amplified by Brillouin scattering ,
is derived . This noise considers the parameters of a photodetector , giving a model
for the noise in the measurable photocurrent . Two models are used to describe the
fading probability of the signal . The first model , based on the Fabry -Perot interferometer
with a random phase perturbation in the middle , is used to calculate the
probability that the whole signal vanishes for any value of phase perturbation . The
second model , by calculating the correlation between two signals , one perturbed and
one unperturbed , predicts the fading of the signal of interest . The present work gives
the theoretical basis for the phase dependant Optical Time Domain Reflectometry ,
allowing its optimization and setting the fundamental limitations to the performance of the system . |