In this experiment, a commercial Quantum-Key-Distribution (QKD) system from Toshiba was integrated into a carrier-grade Fiber to the Home (FTTH) optical access network. The setup replicated real-life FTTH deployments with a 1:16 user GPON configuration. The QKD transmission occurred over a total of 4km consisting of two spitting stages. By optimizing transmission powers, a QKD link with 17 kbps Secure Key Rate (SKR) and 4.63% Quantum Bit Error Rate (QBER) was achieved, while maintaining 9 operational ONTs providing high-speed internet services. This successful demonstration showcases the feasibility of QKD over a GPON, enhancing access network security.
A novel transmitter implementation, which will be capable of operating in both classical and quantum light regimes since it will be able to send single photons across a quantum channel and at the same time to serve as analog RoF transmitter currently deployed in X-haul topologies, is proposed. By spectrally isolating the sidebands of analog RoF signal and by controlling the EML’s modulation index, different mean photon numbers launched in one sideband can be obtained. We report on the architecture of our proposed transmitter station, and we demonstrate its operation through proof-of-concept experiments by performing successful RoF transmission links and by carrying out photon-counting measurements. The transmission of 200 Mbaud QPSK-modulated signal with acceptable EVM measurements of < 17.5%, as well the variation of the mean count rate of the filtered sideband as a function of the peak-to-peak driving voltage of radio signal at 28GHz were successfully performed, confirming that the sidebands of A-RoF transceivers can be used as single-photon carriers for quantum information.
For enabling and realizing long-haul Quantum Key Distribution (QKD), satellite communication infrastructure is exploited to deliver symmetric encryption keys to ground segments. In this direction the European Quantum Communication Infrastructure (Euro-QCI) initiative, supported by the European Space Agency (ESA), aims to build a secure quantum communication network that will span across the EU. In this framework, ESA has selected three observatories in Greece to support European activities in optical communications and QKD systems. In this study, a QKD feasibility analysis between a LEO satellite constellation (100 satellites) and the three selected Optical Ground Stations (OGSs) in Greece, using an entangled based QKD protocol is presented. This contribution focuses on the performance evaluation and the applicability validation of an entanglement-based QKD system in a pragmatic regional segment of Euro-QCI. The time varying atmospheric channel is modeled taking into account the joint cloud coverage of the OGSs, the turbulence, the pointing errors and the solar background radiance. The performance of the regional entangled-based QKD system is validated in terms of annual availability as well as the number of shared distilled key bits between the ground stations per year.
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