Converged Satellite to Fiber QKD Links: A Feasibility Analysis

This paper presents a comprehensive feasibility analysis designed to model Low Earth Orbit (LEO) satellite-to-ground communications for Quantum Key Distribution (QKD), focusing on the 1550nm wavelength to facilitate the distribution of information through fiber segments. Discrete Variable Decoy State Polarization-based BB84 protocol is assumed whereas various detection setups and environmental conditions are simulated. Our analysis focuses on the receiver's design in terms of aperture and focal length to deliver a general framework by examining the coupling efficiency, a parameter strongly affecting the QKD satellite downlink. Through detailed simulation, we identify optimal configurations and operational parameters for various receiver designs, significantly enhancing the efficiency and reliability of satellite-to-ground QKD systems. The findings offer promising directions for extending the range of QKD systems, potentially revolutionizing secure communications by integrating satellite-transmitted quantum keys with terrestrial fiber networks. This study not only underscores the feasibility of advancing satellite-to-ground QKD technology but also lays the groundwork for future innovations in global quantum communications infrastructure.

I. Introduction

Quantum Key Distribution (QKD) represents a paradigm shift in secure communications, leveraging the principles of quantum mechanics to enable two parties to produce a shared random secret key known only to them, which can then be used to encrypt and decrypt messages. The advent of satellite-to-ground QKD [1] has further broadened the horizons of secure communication, enabling global reach beyond the limitations of terrestrial fiber networks [2], offering a new pathway to achieving global secure communication coverage. Yet, the integration of satellite QKD systems with existing fiber networks and the extension of their capabilities to serve wider, more geographically dispersed areas remain less explored, particularly in the context of rural and remote regions. This work positions itself within this evolving narrative by specifically addressing the gap between the high potential of satellite-based QKD systems for global coverage and the practical challenges of extending their reach through effective integration with ground-based fiber networks. More specifically, this paper presents a feasibility analysis between Low Earth Orbit (LEO) satellites and various Optical Ground Stations (OGSs) located in rural areas. The simulation focuses on the 1550 nm wavelength, chosen for its potential to distribute qubits further through fiber segments post initial ground reception, addressing a critical challenge in extending the range of QKD systems. Technical challenges such as the effect of turbulence in coupling efficiency from the receiving telescope to a Single Mode Fiber (SMF) are discussed. Variables such as atmospheric turbulence, receiver aperture size and focal length are modelled to understand their effects on telescope to fiber coupling efficiency. The choice of the 1550 nm wavelength for communication further reflects a targeted approach to enhance the compatibility between satellite signals and terrestrial fiber segments, aiming to mitigate the loss and extend the effective range of QKD systems beyond their current limitations. By conducting a detailed feasibility analysis and exploring the technical intricacies of coupling efficiency, atmospheric conditions, along with the integration with fiber segments, this study contributes to the practical realization of a global, secure quantum communication network, paving the way for the next generation of secure communications.