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Chinese Optics Letters

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

Liang Cui, Haoran Chen, Jiamin Li, Xiaoying Li

Published Jan 1, 2024• 0 citations
Publisher

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.

DOI
10.3788/col202422.052701

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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.
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We present a fiber-based source of polarization-entangled photons that is well suited for quantum communication applications in the 1550 nm band of standard fiber-optic telecommunications. Polarization entanglement is created by pumping a nonlinear-fiber Sagnac interferometer with two time-delayed orthogonally polarized pump pulses and subsequently removing the time distinguishability by passing the parametrically scattered signal and idler photon pairs through a piece of birefringent fiber. Coincidence detection of the signal and idler photons yields biphoton interference with visibility greater than 90%, while no interference is observed in direct detection of either signal or idler photons. All four Bell states can be prepared with our setup and we demonstrate violations of the Clauser-Horne-Shimony-Holt form of Bell's inequality by up to 10 standard deviations of measurement uncertainty.
We present a fiber-based source of polarization-entangled photon pairs that is well suited for quantum communication applications in the 1.5μμμm 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.
We demonstrate a novel alignment-free all-fiber source for generating telecom-band polarization-entangled photon pairs. Polarization entanglement is created by injecting two relatively delayed, orthogonally polarized pump pulses into a piece of dispersion-shifted fiber, where each one independently engages in four-photon scattering, and then removing any distinguishability between the correlated photon-pairs produced by each pulse at the fiber output. Our scheme uses a Michelson-interferometer configuration with Faraday mirrors to achieve practically desirable features such as ultra-stable performance and turnkey operation. Up to 91.7% two-photon-interference visibility is observed without subtracting the accidental coincidences that arise from background photons while operating the source at room temperature.