Intrinsically Stable 2-GHz Polarization Modulation for Satellite-Based Quantum Key Distribution

Satellite-based quantum key distribution (QKD) has made significant strides in the past few years, and an international space race toward practical quantum networks has begun. Being one major encoding method, highly robust, high-performance and miniaturized polarization modulation is critical to meet the needs of future satellite applications. Here, we employ the Sagnac-based method to realize inherent-stable polarization modulation and propose a novel optical design to achieve a state-of-the-art repetition rate of 2 GHz. This value approaches the theoretical repetition frequency limit with commercially-available phase modulators. Furthermore, the polarization encoder is miniaturized into a robust 6.0 cm × 6.5 cm module and two commercially mature phase modulators. A 90-min consecutive test was successfully performed, verifying the robustness of this scheme with an average quantum bit error rate as low as 0.42%. The presented intrinsically stable high-speed polarization modulation provides an effective solution for future satellite applications.