Applying the recently developed formalism of quantum-state transformation at
absorbing dielectric four-port devices [L.~Kn\"oll, S.~Scheel, E.~Schmidt,
D.-G.~Welsch, and A.V.~Chizhov, Phys. Rev. A {\bf 59}, 4716 (1999)], we
calculate the quantum state of the outgoing modes of a two-mode squeezed vacuum
transmitted through optical fibers of given extinction coefficients. Using the
Peres--Horodecki separability criterion for continuous variable systems
[R.~Simon, Phys. Rev. Lett. {\bf 84}, 2726 (2000)], we compute the maximal
length of transmission of a two-mode squeezed vacuum through an absorbing
system for which the transmitted state is still inseparable. Further, we
calculate the maximal gain for which inseparability can be observed in an
amplifying setup. Finally, we estimate an upper bound of the entanglement
preserved after transmission through an absorbing system. The results show that
the characteristic length of entanglement degradation drastically decreases
with increasing strength of squeezing.Comment: Paper presented at the International Conference on Quantum Optics and
VIII Seminar on Quantum Optics, Raubichi, Belarus, May 28-31, 2000, 11 pages,
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