Greek researchers demonstrate an O-band QKD link over carrier-grade fiber network

Experimental Integration of QKD into a GPON Access Network

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

In this publication, researchers from the National and Kapodistrian University of Athens (NKUA) and the National Technical University of Athens (NTUA), notably members of the Quantum Strategic National Plan (QSNP), present a novel approach for integrating an O-band quantum communication link into a standard GPON network. Their experimental setup involves incorporating up to nine Optical Network Terminals (ONTs) to simulate a partially loaded Fiber To The Home (FTTH) network, mirroring the real-world deployments of the COSMOTE operator. The researchers, firstly, transmit the quantum signal downstream alongside the existing 2.5 Gbps 1490nm GPON channel. However, at the same time, it travels upstream in the opposite direction of the O-band GPON channels. Ultimately, the primary goal of this experiment is to assess the performance and feasibility of this coexistence scheme, thereby paving the way for the potential real-world implementation of quantum communication within existing fiber optic infrastructure.

Moreover, the quantum channel’s inherent sensitivity to transmission losses poses a significant challenge, directly impacting achievable distances and Secure Key Rates (SKR). Notably, the experiment revealed an approximate 3 dB SKR degradation with a single ONT, potentially attributed to back-reflected photons escaping from the bandpass filter (BPF) of the QKD receiver. Interestingly, adding more ONTs to the network unexpectedly improved the QKD link’s performance in terms of SKR. This enhancement is attributed to the Power Levelling Sequence (PLS) upstream function of GPON, which actively adjusts power levels to minimize the optical dynamic range, ultimately leading to improved quantum communication performance.

Additionally, the testbed successfully operated during a continuous period of 60 hours, simultaneously serving a total of 9 users. 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.

Reference:

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

 

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