# Pulsed Sagnac source of polarization-entangled photon pairs in telecommunication band

## TL;DR

This paper presents a polarization-entangled photon pair source in the 1550-nm telecommunication band using a Sagnac interferometer and spontaneous parametric down-conversion, demonstrating high entanglement quality and Bell inequality violation.

## Contribution

The work introduces a novel polarization-entangled photon source based on a Sagnac interferometer with a non-collinear PPLN crystal in the telecom band, achieving high entanglement fidelity.

## Key findings

- Polarization entanglement verified with >96% visibility.
- Bell inequality violation with S=2.72 1 0.04.
- Source suitable for quantum communication applications.

## Abstract

We report a source of polarization-entangled photon pairs in the 1550-nm telecommunication band, which is based on non-collinear spontaneous parametric down-conversion in a periodically poled lithium niobate crystal pumped by picosecond pulses. This source is realized utilizing a polarization-based Sagnac interferometer employing a type-0 non-collinear quasi-phase-matching configuration. Polarization entanglement is verified through measurement of the polarization-correlation interference fringes with visibility >96% and by testing the experimental violation of the Clauser-Horne-Shimony-Holt (CHSH) form of Bell inequality. The CHSH-Bell parameter S is found to be 2.72 \pm 0.04, with 18 standard deviations from the statistical uncertainty.

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Source: https://tomesphere.com/paper/1904.00164