Conference Paper

Quantum key distribution (QKD) has emerged as a promising approach for secure communication in the context of emerging threats to classical cryptography posed by quantum computing. In polarization-encoded implementations, information is carried in the state of polarization of single photons, requiring accurate and repeatable state generation. However, practical systems must also cope with polarization drift and other possible misalignments in the transmission channel while maintaining high modulation rates [], imposing constraints on the choice of encoding hardware. State-of-the-art implementations typically rely on high-speed interferometric phase-modulation schemes for basis generation, combined with polarization control techniques for channel compensation, which are typically limited to modulation rates in the range of hundreds of kHz to approximately 1 MHz, such as piezoelectric fiber squeezers [].

In this work, we present a lithium niobate-based electro-optic polarization controller (EPC) enabling high-speed polarization state preparation. The device consists of multiple electro-optic stages (6–8), each acting as a fully customizable, voltage-controlled waveplate, allowing arbitrary state of polarization generation without requiring a predefined input state []. Compared to conventional polarization controllers, the proposed approach offers sub-100 ns response times, enabling operation in the tens of MHz range. This flexibility further enables its use for channel compensation, where part of the available waveplate stages are used for polarization drift compensation in the quantum channel, reducing the need for external polarization control equipment typically required in interferometric phase-modulation-based setups.

We demonstrate stable orthogonal polarization state modulation at 21.5 Msps, achieving consistent state preparation across all bases with polarization leakage below 0.5%. Additionally, we present a calibration methodology for this device, addressing the non-uniqueness of voltage configurations in multi-stage systems with fully customizable waveplates.

These results demonstrate a high-speed and flexible alternative to conventional polarization encoding approaches, enabling both state preparation and channel compensation within a single device.