Quantum key distribution in optical fibers: a comprehensive design view of the overall quantum layer beyond transmission

This paper reports the network operator point of view about the introduction of quantum key distribution (QKD) in optical networks to secure the data plane and/or specific applications, focusing on the design aspects that go beyond pure transmission. The functional architecture of a quantum key distribution network is depicted focusing on the integration in the existing telecommunications infrastructure. Some use cases of the utilization of the QKD layer, presenting results from in-field demonstrations, are reported together with a technology agnostic numerical model about resource sharing in a metropolitan area network environment.