  We study the decoherence of polarization-entangled photon pairs subject to
the effects of polarization mode dispersion, the chief polarization decoherence
mechanism in optical fibers. We show that fiber propagation reveals an
intriguing interplay between the concepts of entanglement sudden death,
decoherence-free sub-spaces and non-locality. We define the boundaries in which
entanglement-based quantum communications protocols relying on fiber
propagation can be applied.
