Low loss QKD optical scheme for fast polarization encoding

TL;DR

This paper introduces a compact, low-loss optical scheme for quantum key distribution using polarization encoding, suitable for fiber and free-space channels, with innovations in polarization mode dispersion compensation and autonomous calibration for practical deployment.

Contribution

The paper presents a novel all-fiber polarization encoding scheme with low losses and a new PMD compensation technique, enabling practical, high-rate QKD over long distances.

Findings

Achieved low losses (~2dB) in the receiver's device.

Demonstrated successful QKD over 50 km fiber in laboratory conditions.

Implemented autonomous calibration algorithms for practical use.

Abstract

We present a new optical scheme for BB84 protocol quantum key distribution (QKD). The proposed setup consists of a compact all-fiber polarization encoding optical scheme based on LiNbO3 phase modulators, single laser source and two single-photon detectors. Optical scheme consists of standard telecommunication components and is suitable for both fiber and free-space quantum communication channels. Low losses (~2dB) in Bob's device increase both the key generation rate and distance limit. A new technique for solving polarization mode dispersion (PMD) issue in LiNbO3 is implemented, allowing two crystals to neutralize the effect of each other. Several proof-of-concept experiments have been conducted at 10 MHz repetition frequency over 50 km of standard optical fiber under laboratory conditions and over 30 km of urban fiber with high losses (13dB), which is a link within a QKD network. To achieve this, calibration algorithms have been developed, allowing the system to work autonomously and making it promising for practical applications.