Generation of high-purity entangled photon pair in a short highly nonlinear fiber

We generate photon pairs at telecom wavelength through a spontaneous four-wave mixing process in a short 10 m of highly nonlinear fiber. We use a counterpropagating scheme to generate a correlated and entangled photon pair. We observe coincidence to accidental-coincidence ratio of 29±3 at room temperature (300 K) and as high as 130±5 when the fiber is cooled to liquid-nitrogen temperature (77 K). Two-photon interference with visibility >98% (>92%) and the violation of Bell's inequality by >12 (≈5) standard deviation are observed at 77 K (300 K), respectively, without subtracting accidental-coincidence count. We obtain a photon-pair production rate about factor 3(2) higher than a 300 m dispersion-shifted fiber at 300 K (77 K).