A Modular Pointing and Tracking System for Terrestrial Quantum Key Distribution

Inhalt:
This paper presents a modular pointing, acquisition and tracking (PAT) system tailored for terrestrial free-space quantum key distribution (QKD). The design combines up to two two-axis MEMS mirrors with up to three position-sensitive detectors and wavelength-separated beacon lasers. The system enables us to transmit and receive telecom or other near-infrared signal wavelengths for QKD. Owing to the large mechanical field of view of the MEMS mirror, the basic module operates without additional optics over short links. By adding additional optics, the design allows for long-range links of up to 2 km. The modular concept supports three use cases: short-range links, a hand-held transmitter, long-range links (≤ 2 km). Simulations across all scenarios confirm less than 10 dB of total loss, demonstrating that minor hardware changes allow the PAT platform to scale from desktop distances to 2 km free-space channels. The compact, fiber- or free-space-coupled architecture and its compatibility with hand-held devices make this PAT system a flexible solution for terrestrial QKD deployments.