Sagnac-type entangled photon source using only conventional polarization optics

TL;DR

This paper presents a novel, stable, and versatile Sagnac-Mach-Zehnder interferometer-based source of polarization-entangled photons using only standard optics, achieving high entanglement quality over a wide wavelength range.

Contribution

The authors introduce a new interferometer configuration combining Sagnac and Mach-Zehnder setups that does not need multi-wavelength polarization optics, enabling stable, high-quality entangled photon generation with commercial components.

Findings

Achieved polarization entanglement with 95.5% visibility.

Demonstrated violation of CHSH inequality with S=2.70.

Maintained phase stability with an Allan deviation of 8° over 1 hour.

Abstract

We designed and implemented a novel combination of a Sagnac-interferometer with a Mach-Zehnder interferometer for a source of polarization-entangled photons. The new versatile configuration does not require multi-wavelength polarization optics, yet it performs with a good polarization quality and phase-stability over a wide wavelength range. We demonstrate the interferometer using only standard commercial optics to experimentally realize the pulsed generation of polarization-entangled photon-pairs at wavelengths of 764nm and 1221nm via type-I spontaneous four-wave mixing in a polarization-maintaining fiber. Polarization entanglement was verified by a polarization-correlation measurement with a visibility of 95.5% from raw coincidence counts and the violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality with $S=2.70\pm0.04$. The long-term phase-stability was characterized by an Allan deviation of 8$^\circ$ over an integration time of about 1 hour with no active phase-stabilization.