Generation of high-purity telecom-band entangled photon pairs in dispersion-shifted fiber

We study the purity of correlated photon pairs generated in a dispersion-shifted fiber at various temperatures. The ratio of coincidence to accidental-coincidence counts greater than 100 can be obtained as the fiber is cooled to liquid-nitrogen temperature (77 K). We then generate polarization-entangled photon pairs by using a compact counterpropagating scheme. Two-photon interference with visibility > 98% and Bell's inequality violation by > 8 standard deviations of measurement uncertainty are observed at 77K, without subtracting the accidental-coincidence counts due to background Raman photons. (c) 2006 Optical Society of America