Polarization-entangled photon pairs with factorable spectra engineered by using an uneven four-stage nonlinear interferometer

Abstract

We report the generation of polarization-entangled photon pairs in the 1550 nm band by pumping an uneven nonlinear interferometer loop with two orthogonally polarized counterpropagating pump pulses. The uneven nonlinear interferometer, providing a more ideal interference pattern due to the elimination of secondary maxima, consists of four pieces of dispersion-shifted fibers sandwiched with three pieces of standard single-mode fibers, and the lengths of the nonlinear fibers follow the binomial distribution. The mode number of the photon pairs deduced from the measured joint spectrum is ∼1.03. The collection efficiency of the photon pairs is found to be ∼94% (after background noise correction). The directly measured visibility of two-photon interference of the polarization-entangled photon pairs is ∼92%, while no interference is observed in the direct detection of either the signal or idler photons.