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Optical Fi-Wi QKD Exchange with Monolithic QKD Transmitter

Florian Honz, W. Boxleitner, Mariana F. Ramos, Michael Hentschel, Hannes Hübel, Bernhard Schrenk

Published Sep 22, 2026• 0 citations
Publisher

Abstract

We show a handheld-inspired end-to-end key exchange over optical-wireless channel and up to 32-km fronthaul link, using a silicon QKD transmitter with on-chip light source operable up to 80°C and 29 WDM channels. We further prove co-existence with a 5-Gb/s Fi-Wi data link.
DOI
10.5281/zenodo.22902447

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We present a silicon optical transmitter for polarization-encoded quantum key distribution (QKD). The chip was fabricated in a standard silicon photonic foundry process and integrated a pulse generator, intensity modulator, variable optical attenuator, and polarization modulator in a 1.3 mm ×\times× 3 mm die area. The devices in the photonic circuit meet the requirements for QKD. The transmitter was used in a proof-of-concept demonstration of the BB84 QKD protocol over a 5 km long fiber link.
The realization of large-scale, practical quantum key distribution (QKD) networks relies on the development of scalable architectures and integrated hardware. We demonstrate a metropolitan wavelength-division multiplexing (WDM) QKD network based on hybrid-integrated quantum node transceiver chips that integrate both transmitter and receiver functionalities, including high-speed pulse modulation, decoy-state modulation, tunable attenuation, time-bin encoding, and decoding. The packaged module offers a wavelength tuning range exceeding 85 nm, with its silicon photonic Mach–Zehnder modulator (MZM) achieving a single-photon equivalent dynamic extinction ratio (SP-EDER) of over 20 dB across the entire tuning range at a 1.25 GHz pulse repetition rate. In combination with a simple 1.25 GHz clocked integrated time-bin QKD system, we generate secret keys at a rate of 865.4 kbps over a channel with 9.08 dB of fixed attenuation and at a rate of 168.2 kbps over a distance of 80 km at 1550.12 nm. Our work demonstrates an integrated WDM QKD network capable of supporting scalable and cost-effective metropolitan quantum-secure communications.
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