Optimized Polarization Encoder with High Extinction Ratio for Quantum Key Distribution System

Polarization encoding is a promising approach for practical quantum key distribution (QKD) systems due to its simple and decoding methodology. In this study, we propose self-compensating polarization encoder (SCPE) based on phase modulator, which can be composed of commercial off-the-shelf (COT) devices. We conducted proof-of-concept experiment test the SCPE, demonstrated an in-system bit error rate (QBER) 0.53% long-term running stability without any active adjustments. Additionally, experiments with transmission over fiber spools lengths up 100 km obtained secure finite 3 kbps. Our solution various protocols, including BB84, MDI, RFI.