Quantum Key Distribution (QKD) has emerged as the main solution against the quantum threat. However, for QKD to be economically viable, it must be integrated into our classical infrastructure, particularly, it should work with the current standardized fiber access networks like Gigabit Passive Optical Network (GPON). The integration of QKD into access networks has been explored in previous studies, aiming to reduce costs and complexity while ensuring quantum-level security in end-to-end network implementations.

In this publication, QSNP members from National and Kapodistrian University of Athens (NKUA) and National Technical University of Athens (NTUA), present a unique coexistence scheme of an O-band link integrated into a single feeder GPON network. The experimental set up includes up to 9 Optical Network Terminals (ONTs) to simulate a partial full load of a Fiber to The Home (FTTH) carrier-grade access network. This design mirrors the real-world deployments of the COSMOTE operator. The quantum signal co-propagates downstream with the 2.5 Gbps 1490nm GPON channel while counterpropagating in the fiber with the O-band GPON upstream channels. The experiment aims to evaluate the performance of such a coexistence scheme.

The sensitivity of the quantum channel to transmission losses poses a challenge, impacting achievable distances and Secure Key Rates (SKR). The implementation demonstrates a ~3 dB SKR degradation with a single ONT, this can be due to back-reflected photons leaking from the bandpass filter (BPF) of the QKD receiver. Surprisingly, when adding more users to the ONT it shows improvement in the performance of the QKD link in terms of SKR. This improvement is attributed to the Power Levelling Sequence upstream function of GPON, which adjusts power levels to reduce the optical dynamic range.

The testbed successfully operated during a continuous period of 60 hours serving a total of 9 users simultaneously. The average SKR achieved was 10.07kbps, with a Quantum Bit Error Rate (QBER) of 5.11%. This experiment demonstrates the potential for quantum-secure communications using real-life access network deployments.


O-band QKD link over a multiple ONT loaded carrier-grade GPON for FTTH applications. N. Makris, A. Ntanos, A. Papageorgopoulos, A. Stathis, P. Konteli, I. Tsoni, G. Giannoulis, F. Setaki, T. Stathopoulos, G. Lyberopoulos, H.Avramopoulos, G. T. Kanellos, D. Syvridis. arXiv:2310.17259 [quant-ph]. Published 26 October 2023