Go and return propagation of biphotons in fiber and polarization   entanglement
  Propagation of entangled photons in optical fiber is one of the fundamental issues for realizing quantum communication protocols. When entanglement in polarization is considered, arises the problem of compensating for the fiber effect on photons polarization. In this paper we demonstrate an effective solution where a Faraday mirror allows to cancel undesired effects of polarization drift in fiber. This technique is applied to a protocol for generating Bell states by a narrow temporal selection of the second-order intensity correlation function. 
G. Brida, M.V. Chekhova, M. Genovese, L.A. Krivitsky, E. Predazzi