Fiber-Optic Sources of Quantum Entanglement
  We present a fiber-based source of polarization-entangled photon pairs that is well suited for quantum communication applications in the 1.5$\mu$m band of standard telecommunication fiber. Quantum-correlated signal and idler photon pairs are produced when a nonlinear-fiber Sagnac interferometer is pumped in the anomalous-dispersion region of the fiber. Recently, we have demonstrated nonclassical properties of such photon pairs by using Geiger-mode InGaAs/InP avalanche photodiodes. Polarization entanglement in the photon pairs can be created by pumping the Sagnac interferometer with two orthogonally polarized pulses. In this case the parametrically scattered signal-idler photons yield biphoton interference with $>$90% visibility in coincidence detection, while no interference is observed in direct detection of either the signal or the idler photons. 
P. Kumar, X. Li, M. Fiorentino, P. L. Voss, J. E. Sharping, and G. A.   Barbosa