Coexistence of Classical and Quantum Signals in Hybrid Fiber and Free-Space Optics Links for QKD Integration

Quantum key distribution (QKD) exploits the unique properties of quantum physics. It has evolved tremendously in recent years, attracting considerable attention as a privileged solution capable of enabling future-proof secure communication systems. This contrasts with classical cryptographic systems, whose security is based on computational security. However, before quantum cryptographic systems, e.g. QKD, could be widely implemented, in a coexistence scenario with classical signals, and made widely available to applications and users, they face several crucial challenges related to their real-world implementation. This paper presents our recent investigations to evaluate the coexistence between classical and quantum signals in hybrid fiber (multi-core fiber) and free-space optical links for an optimized integration of QKD systems in the installed fiber communication networks. We present results in terms of spontaneous Raman scattering, inter-core cross-talk and turbulence-induced optical power fluctuations.