400-Gbps Coherent Transmission of 100-Gbps QKD-secured data stream over 184-km of Standard Single Mode Fiber through three QKD Links and two Trusted Nodes

Security of data transported in telecommunication networks is of primary importance for internet service providers (ISP) as data safety is at the basis of the mutual trust with customers. People were looking for theoretically secure transmission techniques since a long-time to ensure long-term confidentiality of data flows exchanged on these networks. Besides advanced encryption algorithms and the recently proposed post-quantum cryptography (PQC), a physics-based technology using quantum key distribution (QKD) was proposed a long time ago to approach this objective. QKD recently gained a renewed interest with many research programs worldwide supported by public authorities, and some pre-industrial QKD systems delivered to the market. However, some constraints of optical transport networks make sometimes complicated the deployment of such QKD systems in the field, such as the need of a dedicated fiber infrastructure for QKD, or the impossibility for a quantum key to pass through an optical amplifier. In this paper, we report the transmission of a coherent 400-Gbps dual-polarization 16QAM channel that transports QKD-secured 100-GbEthernet data stream with other fifty-four WDM channels at 100-Gbps over 184-km of standard single mode fiber (SSMF) through three QKD links (of 66-km, 50-km and 66-km, respectively) and two trusted nodes. On the two longest sections of the link, the quantum key and WDM signals are propagated on two different fibers, while on the shortest section of 50-km the QKD signal and WDM comb co-propagate on a same fiber. Secret key rates (SKR) and quantum bit error rate (QBER) are measured and reported on each of the three fiber sections. Various analyses are carried out on the co-propagation section of 50-km: the SKR / QBER sensitivity to the optical power of the WDM comb, or to the optical signal-to-noise ratio (OSNR) of the WDM channels co-propagating with the quantum signal is studied. The unique arrangement of the most advanced QKD and WDM technologies reported here constitutes, in our opinion, a world first, and demonstrates that QKD and WDM solutions can coexist in already deployed optical transport networks.