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A Chip-Scale Transmitter Module for Real-Time Continuous-Variable QKD

Igor Servello, Martin Hauer, Moritz Baier, Emmeran Sollner, Peter Gleißner, Sebastian Randel, Ulrich Eismann, Emanuel Eichhammer, Imran Khan

Abstract

Continuous-variable quantum key distribution (CV-QKD) enables secure communication over standard telecom infrastructure, yet its 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 built from commercial telecom components. By integrating a micro-optic external-cavity laser with a monolithic photonic integrated IQ modulator, we provide high performance, enabling secret-key generation over 102 km of optical fiber, while reducing the size of the optics by 95%. Moreover, real-time operation overcomes the offline post-processing bottlenecks of experimental setups. This work bridges laboratory demonstrations and field-deployable technology, with a scalable architecture for cost-effective quantum networks.

A Chip-Scale Transmitter Module for Real-Time Continuous-Variable QKD

Abstract

Continuous-variable quantum key distribution (CV-QKD) enables secure communication over standard telecom infrastructure, yet its 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 built from commercial telecom components. By integrating a micro-optic external-cavity laser with a monolithic photonic integrated IQ modulator, we provide high performance, enabling secret-key generation over 102 km of optical fiber, while reducing the size of the optics by 95%. Moreover, real-time operation overcomes the offline post-processing bottlenecks of experimental setups. This work bridges laboratory demonstrations and field-deployable technology, with a scalable architecture for cost-effective quantum networks.
Paper Structure (14 sections, 3 equations, 8 figures, 2 tables)

This paper contains 14 sections, 3 equations, 8 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Real-time CV-QKD System
  3. Transmitter
  4. Receiver
  5. Real-time CV-QKD Protocol
  6. End-to-end Signal Flow
  7. Results
  8. Real-time CV-QKD Analysis
  9. Performance Evaluation over Optical Fiber
  10. Performance Evaluation over Emulated Optical Fiber with Variable Loss
  11. Conclusions
  12. Funding:
  13. Acknowledgments:
  14. Data availability:

Figures (8)

  • Figure 1: Concept of a real-time chip-scale CV-QKD transmitter module. This work demonstrates the integration of the optical components of the system (highlighted by the red square) and the automation of the CV-QKD pipeline. Parts of this figure were generated using the AI-assisted image generation tool Nano Banana.
  • Figure 2: Schematic of the experimental setup, to scale. The miniaturized CV-QKD transmitter under study (Alice, bottom left) is connected via optical fiber to the receiver (Bob, top right), which is implemented using bulk optical components. On the left hand side are shown photographs (partially obfuscated) of the chip-scale modules used in this work: the IQ modulator and the laser, shown alongside a 1-euro coin for scale.
  • Figure 3: Illustration of the schematic of the chip-scale modules. On the left, the PIC incorporating the IQ modulator. Only one polarization was modulated in this study. The details of the unused PIC section are not reported. On the right, the chip-scale laser, composed by the InP gain chip and the external cavity. Components are abbreviated as follows: WG: waveguide; PD: photodiode; TOPS: thermo-optic phase shifter; EOPM: electro-optic phase modulator; PRBS: polarization rotator beam splitter; SSC: spot-size converter.
  • Figure 4: Diagram illustrating the signal flow in the CV-QKD protocol.
  • Figure 5: Characterization over time of the CV-QKD system featuring the chip-scale transmitter over optical fibers of 26, 52, 77, and 102 km. The plots show the real-time operation of the protocol, displaying: (a)–(d) the total established secret key; (e)–(h) the key length of the successful shots; and (i)–(l) the corresponding excess noise. The red lines in (e)–(l) for shot key length and excess noise represent their average values. The average shot key length also accounts for the unsuccessful shots.
  • ...and 3 more figures