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arXiv:2509.05134 · Optica Quantum

Hybrid-integrated InGaAs/InP SPAD arrays for quantum communications

Joseph A. Dolphin, Rosemary O. E. Scowen, Louise Wells, David G. Ellis, Abbie Lowe, Benjamin Ramsay, Iwan Davies, Andrew J. Shields, Taofiq K. Paraïso, Mark Stevenson

Published Nov 20, 2025• 1 citation

Abstract

Photonic integration is a promising route to miniaturise the hardware of quantum key distribution (QKD), yet the monolithic integration of single-photon detectors remains a significant challenge. QKD receiver chips integrating superconducting detectors have been demonstrated, but their requirement for cryogenic cooling restricts their practical applications. High-frequency gated single-photon avalanche diodes (SPADs) provide a mature non-cryogenic alternative, and their fabrication into compact arrays would enable scalable hybrid integration. However, this faces several challenges related to efficient GHz array gating, inter-pixel crosstalk, and scalable waveguide coupling, which to date remain unaddressed. Here, we overcome the key challenges and develop GHz-gated InGaAs/InP SPAD arrays with performance viable for QKD and negligible inter-pixel crosstalk. We combine the arrays with low-loss silica waveguide chips to produce compact hybrid QKD receivers and perform BB84 protocol experiments, achieving secure key rates over 2 Mbps at short distances and 15 kbps over 100 km of fibre. Our work provides a method for flexible and scalable integration of waveguide-coupled SPADs for quantum information processing applications.

DOI: 10.1364/opticaq.577781

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