QTTH – Quantum to the Home? : Abstract

In recent years Quantum Key Distribution (QKD) has been rising to prominence as a fundamentally secure encryption technique for point-to-point communication links. QKD enables generation of random secret encryption keys that are symmetrically shared between two legitimate parties. The QKD protocols, through continuous monitoring of the physical channel parameters, interpret channel imperfections as a result of eavesdropping attempts and ensure that an adversary does not have any information about the eventually generated secure key. This technique, while very attractive for point-to-point links of up to several tens of km, has its practical limitations. With the increasing deployment of FTTx, a broader type of architecture needs to be addressed, specifically multi-user access networks based on Passive Optical Networks (PON) [1] . Here we discuss recent efforts to address the emerging need for economically viable key generation in form of DV (discrete variable) and CV (continuous variable) QKD in both upstream and downstream directions. Practical limitations arise from the optical loss, spontaneous Raman scattering (SRS) noise, and prohibitive deployment costs related to single photon detectors or bespoke network architectures. DV-QKD systems can support up to 64 users in a PON architecture [2 , 3] , while achieving Secure Key Rates (SKR) above a few kbps and requiring dual feeder architectures. Furthermore, when considering single-feeder bidirectional PON, the attainable fiber length for 64 network users becomes a few km depending on the PON standard [4] . The CV-QKD has been shown to perform well and generate higher SKR in shorter networks in downstream direction, as it enables concurrent key generation for multiple users (up to 375 kbps per user for 8-users in an 11 km access link) [5] compared to upstream CV-QKD achieving SKR of 0.5 kbps for 19-user, 13.5 km long link [6] . Difficulties related to the deployment of QKD protocols in PON architectures encourage exploration of alternative quantum-safe physical layer security solutions [7] . Among these, Optical Key Distribution (OKD) [8 , 9] can be considered as a cost-effective method for generating secret keys between the Optical Line Terminal and individual Optical Network Units that are secure against passive eavesdropping even if the fraction of the signal available to an eavesdropper exceeds that reaching a legitimate recipient.