  The influence of losses in the interferometric generation and the
transmission of continuous-variable entangled light is studied, with special
emphasis on Gaussian states. Based on the theory of quantum-state
transformation at absorbing dielectric devices, the amount of entanglement is
quantified by means of the relative-entropy measure. Upper bounds of
entanglement and the distance to the set of separable Gaussian states are
calculated. Compared with the distance measure, the bounds can substantially
overestimate the entanglement. In particular, they do not show the drastic
decrease of entanglement with increasing mean photon number, as does the
distance measure.
