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Laser & Photonics Review

Integrated Photonics and Electronics for High‐Speed Quantum Key Distribution

Z. Chen, Xin‐Zhe Wang, Yang Li, Yu‐Ang Wang, Chao‐Ze Wang, Li‐Kang Zhang, Yanfei Liu, Wen‐Qi Cai, Juan Yin, Ji-Gang Ren, Feihu Xu, Sheng‐Kai Liao, Chengzhi Peng

Published Sep 21, 2025• 1 citation
Publisher

Abstract

Abstract Quantum key distribution (QKD) has made significant advancements over the past few decades and is gradually transitioning from laboratory to industrial domain. This transformation process poses urgent demands for integrated, cost‐effective, and mass‐producible QKD devices. Here, by interfacing a laser diode, a QKD encoding photonics chip, and their associated electronics driver chips, the QKD transmitter has been condensed from several bulky discrete components to integrated modules with dimensions of a few centimeters, while the modulation rate of the transmitter has been enhanced to 3.33 GHz. Based on this transmitter, QKD is demonstrated over a 100 km standard fiber channel, capable of generating secure keys at a record high key rate of 2.82 Mbps over this distance. This work demonstrates the feasibility of high‐speed integrated QKD transmitters, thereby further propelling the research on QKD in practical applications.

DOI
10.1002/lpor.202501080

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Abstract Quantum key distribution (QKD) has made significant advancements over the past few decades and is gradually transitioning from laboratory to industrial domain. This transformation process poses urgent demands for integrated, cost‐effective, and mass‐producible QKD devices. Here, by interfacing a laser diode, a QKD encoding photonics chip, and their associated electronics driver chips, the QKD transmitter has been condensed from several bulky discrete components to integrated modules with dimensions of a few centimeters, while the modulation rate of the transmitter has been enhanced to 3.33 GHz. Based on this transmitter, QKD is demonstrated over a 100 km standard fiber channel, capable of generating secure keys at a record high key rate of 2.82 Mbps over this distance. This work demonstrates the feasibility of high‐speed integrated QKD transmitters, thereby further propelling the research on QKD in practical applications.
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Quantum key distribution (QKD) is nowadays a well-established method for generating secret keys at a distance in an information-theoretically secure way, as the secrecy of QKD relies on the laws of quantum physics and not on computational complexity. In order to industrialize QKD, low-cost, mass-manufactured, and practical QKD setups are required. Hence, photonic and electronic integration of the sender’s and receiver’s respective components is currently in the spotlight. Here we present a high-speed (2.5 GHz) integrated QKD setup featuring a transmitter chip in silicon photonics allowing for high-speed modulation and accurate state preparation, as well as a polarization-independent low-loss receiver chip in aluminum borosilicate glass fabricated by the femtosecond laser micromachining technique. Our system achieves raw bit error rates, quantum bit error rates, and secret key rates equivalent to a much more complex state-of-the-art setup based on discrete components [ Boaron A. et al. , Phys. Rev. Lett. 121 , 190502 ( 2018 ) ].
Quantum key distribution (QKD) provides information-theoretic security independent of computational assumptions, yet the bulk and cost of current systems hinder large-scale deployment. Although integrated photonic technologies have enabled highly integrated QKD chips, practical QKD transmitters are still predominantly implemented as rack-mounted systems. Here, we demonstrate a highly integrated standalone QKD transmitter that integrates all essential functionalities required for practical QKD operation within a compact platform built around a silicon photonic encoding chip. The transmitter occupies only 167×56×21 mm3167 \times 56 \times 21~\mathrm{mm}^3167×56×21 mm3 (∼0.2 dm3\sim 0.2~\mathrm{dm}^3∼0.2 dm3), comparable in size to a half-height, half-width PCIe card and more than 30 times smaller in volume than a conventional 1U rack-mounted system. Paired with a conventional discrete-component receiver, it achieves a secure key rate of 219.1 kbps over 51.3 km of standard single-mode fiber, with performance comparable to that of conventional discrete-component implementations. This work bridges the gap between photonic chip integration and deployable QKD hardware, marking an important step toward transitioning QKD transmitters from conventional rack-mounted equipment to compact board-level platforms.
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Advances in quantum computing pose significant threats to the security of conventional encryption standards. Although quantum key distribution systems offer inherent security, they face challenges in achieving practical secret-key rates over long transmission distances. Photonic Integrated Circuit technologies provide scalability and system efficiency for high key rates using multiplexed time-bin protocols. We present the architecture of a 16-channel multiplexed QKD system at a GHz clock rate realized on integrated photonic chips, promising further scalability. The sender module revolves around an indium-phosphide chip featuring tunable lasers, modulators, and combiners. On the receiver side, low fiber-to-chip coupling loss and waveguide-integrated superconducting nanowire single-photon detectors on silicon nitride provide the necessary detection efficiency.
Silicon (Si) photonics is reaching maturity and has the potential of offering low-cost, reliable, chip-scale systems for quantum key distribution (QKD). On the other hand, QKD is also maturing with the bridging of theory and practice. This work presents a Si integrated photonic transmitter for polarization-encoded QKD. The chip was fabricated in a standard Si photonic foundry process and integrates a pulse generator, intensity modulator, variable optical attenuator, and polarization modulator in a 1.3 mm x 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. A quantum bit error rate of 5.4% and an asymptotic secure key rate of 0.95 kbps is obtained. This work shows the feasibility of foundry based Si photonics for quantum information applications.