A flexible modular all-fiber based photon pair source for quantum key distribution in a network

TL;DR

This paper presents a versatile, all-fiber photon pair source for quantum key distribution that is tunable, alignment-free, and suitable for field deployment, supporting various QKD protocols and operating modes.

Contribution

The authors introduce a modular, all-fiber photon source based on SPDC that is flexible, tunable, and compatible with different QKD protocols, with integrated SHG and SPDC in a single crystal.

Findings

High heralding efficiencies demonstrated

Supports continuous-wave and pulsed operation

Compatible with various QKD protocols

Abstract

Entanglement-based QKD protocols require robust and stable photon pair sources in terms of high heralding efficiencies or photon pair generation rates even under harsh environmental conditions, e.g. when operated in the field. In this paper, we report on a flexible, tunable, alignment-free, all-fiber coupled photon source based on spontaneous parametric down-conversion in periodically poled crystals. It can be operated in continuous-wave and pulsed modes, respectively. Its rack-compatible and modular setup allows a straight forward plug-and-play integration of coding-modules e.g. interferometers to enable various QKD protocols such as phase or phase-time coding. We demonstrate operation as a type-II and a type-0 SPDC stage proving the high flexibility of our source. Furthermore, we demonstrate simultaneous operation of SHG and SPDC in a double-pass configuration within the same nonlinear crystal further simplifying the hardware requirements of our source. To evaluate the conversion efficiencies of our modules, we employ data post-processing to remove artefacts from detector afterpulsing and deadtimes of the detectors. We investigate the source performance for various repetition rates.