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System-Level Demonstration of a Fully Integrated CV-QKD transmitter with On-Chip Laser

Julian Konig, Daniel Pereira, Martin Achleitner, Aaron Stadler, Ozan Çirkinoglu, Kevin Williams, Hannes Hübel, Xaveer J. M. Leijtens

Published Apr 1, 2026• 0 citations
Publisher

Abstract

We demonstrate the first fully integrated continuous-variable quantum key distribution (CV-QKD) transmitter, combining a narrow-linewidth laser, high-speed IQ modulator, and variable optical attenuator on a single indium phosphide (InP) chip. The transmitter occupies a compact footprint of 2 mm by 4.6 mm. Component characterization confirms single-mode laser operation with 120 kHz linewidth, >8 GHz modulator bandwidths, and 58 dB attenuation range. Deployed in a complete heterodyne CV-QKD system with probabilistically shaped 64-QAM, the system achieves an average excess noise of 0.1 shot noise units (SNU) and a secret key rate of 8.4 Mbit/s over a 14.3 km fiber link in the asymptotic regime. These results establish a practical and scalable route toward fully integrated quantum-secure communication systems.

DOI
10.1364/opticaopen.31891186

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We demonstrate the first fully integrated continuous-variable quantum key distribution (CV-QKD) transmitter, combining a narrow-linewidth laser, high-speed IQ modulator, and variable optical attenuator on a single indium phosphide (InP) chip. The transmitter occupies a compact footprint of 2 mm by 4.6 mm. Component characterization confirms single-mode laser operation with 120 kHz linewidth, >8 GHz modulator bandwidths, and 58 dB attenuation range. Deployed in a complete heterodyne CV-QKD system with probabilistically shaped 64-QAM, the system achieves an average excess noise of 0.1 shot noise units (SNU) and a secret key rate of 8.4 Mbit/s over a 14.3 km fiber link in the asymptotic regime. These results establish a practical and scalable route toward fully integrated quantum-secure communication systems.
We demonstrate the first fully integrated continuous-variable quantum key distribution (CV-QKD) transmitter, combining a narrow-linewidth laser, high-speed IQ modulator, and variable optical attenuator on a single indium phosphide (InP) chip. The transmitter occupies a compact footprint of 2 mm by 4.6 mm. Component characterization confirms single-mode laser operation with 120 kHz linewidth, >8 GHz modulator bandwidths, and 58 dB attenuation range. Deployed in a complete heterodyne CV-QKD system with probabilistically shaped 64-QAM, the system achieves an average excess noise of 0.1 shot noise units (SNU) and a secret key rate of 8.4 Mbit/s over a 14.3 km fiber link in the asymptotic regime. These results establish a practical and scalable route toward fully integrated quantum-secure communication systems.
Continuous-variable quantum key distribution (CV-QKD) enables secure communication over standard telecom infrastructure, but scaling is stalled by bulky, discrete optical hardware. We address this bottleneck by demonstrating a real-time CV-QKD system driven by a chip-scale hybrid transmitter using commercial telecom components. Combining a micro-optic external-cavity laser with a monolithic photonic integrated IQ modulator we enable secure secret-key generation over 102 km of optical fiber while reducing optical volume by 95% relative to the commercial discrete-component counterpart. Moreover, real-time operation overcomes offline post-processing bottlenecks of experimental setups. This work bridges laboratory demonstrations and field-deployable technology for cost-effective quantum networks.
Continuous-variable quantum key distribution (CV-QKD) enables secure communication over standard telecom infrastructure, but scaling is stalled by bulky, discrete optical hardware. We address this bottleneck by demonstrating a real-time CV-QKD system driven by a chip-scale hybrid transmitter using commercial telecom components. Combining a micro-optic external-cavity laser with a monolithic photonic integrated IQ modulator, we enable secure secret-key generation over 102 km of optical fiber while reducing optical volume by 95% relative to the commercial discrete-component counterpart. Moreover, real-time operation overcomes the offline post-processing bottlenecks of experimental setups. This work bridges laboratory demonstrations and field-deployable technology for cost-effective quantum networks.
Integrated quantum key distribution (QKD) systems based on photonic chips have high scalability and stability, and are promising for further construction of global quantum communications networks. On-chip quantum light sources are a critical component of a fully integrated QKD system; especially a continuous-variable QKD (CV-QKD) system based on coherent detection, which has extremely high requirements for the light sources. Here, for what we believe is the first time, we designed and fabricated two on-chip tunable lasers for CV-QKD, and demonstrated a high-performance system based on these sources. Because of the high output power, fine tunability, and narrow linewidth, the involved on-chip lasers guarantee the accurate shot-noise-limited detection of quantum signals, center wavelength alignment of nonhomologous lasers, and suppression of untrusted excess noise. The system’s secret key rate can reach 0.75 Mb/s at a 50 km fiber distance, and the secure transmission distance can exceed 100 km. Our results mark a breakthrough toward building a fully integrated CV-QKD, and pave the way for a reliable and efficient terrestrial quantum-secure metropolitan area network.
Quantum key distribution (QKD) is the fastest-growing and relatively mature technology in the field of quantum information, enabling information-theoretically secure key distribution between two remote users. Although QKD based on off-the-shelf telecom components has been validated in both laboratory and field tests, its high cost and large volume remain major obstacles to large-scale deployment. Photonic integration, featured by its compact size and low cost, offers an effective approach to addressing the above challenges faced by QKD. Here, we implement a high-performance, integrated local local oscillator continuous-variable (CV) QKD system based on an integrated silicon photonic transmitter and receiver. By employing a high-speed silicon photonic integrated in-phase and quadrature modulator, a low-noise and high-bandwidth silicon photonic integrated heterodyne detector, and digital signal processing, our CV-QKD system achieves a symbol rate of up to 1.5625 GBaud. Furthermore, the system achieves asymptotic secret key rates of 31.05 and 5.05 Mbps over 25.8 and 50.4 km standard single-mode fiber, respectively, using 8-phase-shift keying discrete modulation. Our integrated CV-QKD system with a high symbol rate and long transmission distance paves the way for the quantum secure communication network in metropolitan areas.