Feasibility of C‐Band Converged Satellite‐Fibre QKD Links Through Telescope‐to‐SMF Coupling

This study presents a comprehensive feasibility analysis of low Earth orbit (LEO) satellite‐to‐ground downlink communication for quantum key distribution (QKD), focusing on 1550 nm wavelength. This wavelength is selected for its compatibility with terrestrial fibre‐optic networks, allowing the distribution of quantum keys over extended distances. The analysis models a discrete variable decoy state BB84 protocol, emphasising the system's design requirements for the optical ground station (OGS) receiver, including critical parameters that affect single‐mode fibre (SMF) coupling efficiency. Through extended simulations, we assess atmospheric conditions, turbulence effects and adaptive optics (AO) correction to evaluate their impact on light coupling efficiency and achievable key rates. Results highlight the advantage of AO in sustaining secure key rates, particularly under high‐elevation satellite passes, and quantify the key volumes attainable across varying levels of turbulence and additional fibre transmission losses. Our findings demonstrate that LEO satellite‐based QKD downlinks can be feasibly integrated with terrestrial fibre systems, supporting secure key distribution over potentially large geographic areas without requiring OGSs to be trusted nodes. The results of this work provide practical insights into the technical requirements and configurations needed to realise robust satellite‐to‐ground QKD links, laying a foundation for future advancements in global quantum‐secure communication infrastructure.