Abstract
This paper introduces a new embedded nonintrusive fiber-monitoring technique for time-division-multiplexing
optical networks. It allows an optical transmitter to characterize the fiber plant from reflections caused by data
bursts transmitted across the network instead of dedicated test signals. The probing is performed with minimal
burden on data traffic so that many measurements can be averaged to improve accuracy. The method is very suitable
for embedded optical time-domain reflectometers (OTDR), which reuse a network node's optical data transmitter for
OTDR excitations and embed a reflectometer inside the fiber endpoint. This paper models the OTDR with Laplace
transforms, an approach previously unpursued, after which it is explained how reflections from multiple data bursts
with arbitrary width can be converted into one normalized format. This new class of OTDR excites the fiber with a
negative step of light instead of the conventional short pulse. The signal-to-noise ratio (SNR) for backscatter and
Fresnel reflections caused by the negative step and pulse are compared theoretically. It is shown that negative-step
OTDR breaks the tradeoff between excitation pulsewidth and distance resolution, has a natural separation between
fiber backscatter and Fresnel reflectors, and improves the SNR of nonreflective events.
© 2007 IEEE
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