High-brightness fiber-based Sagnac source of entangled photon pairs for multiplexed quantum networks

TL;DR

This paper presents a compact, fiber-based Sagnac interferometer that generates high-brightness, entangled photon pairs at telecom wavelengths, suitable for scalable quantum networks with versatile encoding and multiplexing capabilities.

Contribution

It introduces a fully fibered, robust, and versatile entangled photon source based on a Sagnac interferometer using standard fiber components and PPLN waveguides, enabling practical quantum networking.

Findings

Achieved high normalized brightness of 10.3 kpairs/s/nm/mW$^2$

Fidelities, purities, and visibilities exceed 96% across multiple channels

Demonstrated stability and reproducibility in network environments

Abstract

A fully fibered source of entangled photon pairs based on a nonlinear Sagnac interferometer is reported. Operating at telecom wavelengths, the source relies exclusively on standard fiber-optic components and periodically poled lithium niobate (PPLN) waveguides, resulting in a compact, robust, and field-deployable architecture. The generation stage supports both polarization and energy-time entanglement without modification, enabling versatile operation depending on the targeted application. Broadband spontaneous parametric down-conversion allows dense wavelength-division multiplexing over the telecom C and L bands. High normalized brightness (10.3 kpairs/s/nm/mW$^2$) is achieved on a standard 100 GHz ITU channel pair, together with high entanglement quality. Polarization and energy-time encodings are characterized through state tomography and two-photon interference measurements, yielding fidelities, purities, and visibilities exceeding 96 % over multiple wavelength channels. The stability and reproducibility of the source are further evaluated through long-duration operation in a network environment. These results demonstrate that the proposed Sagnac source constitutes a practical and scalable building block for future plug-and-play quantum communication and quantum networking platforms.