Quantum Key Distribution

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Modern society relies heavily on private telecommunications. Among the many activities that depend on it are e-banking, e-health, or secure government communications. However, modern encryption techniques used to establish privacy have limitations as they rely most often on the supposition that an eavesdropper has access to a limited computational power. This supposition depends on whether the eavesdropper is an individual or a state agency. Also, his computational power may be much larger in a decade (20-years-old communications are much easier to decrypt nowadays). Now, Quantum Key Distribution (QKD) offers a forever privacy guaranteed by the laws of physics.

Thanks to QKD, a spy trying to intercept some information is detected before a message is even sent. And this is achieved simply by adapting the emitter and receiver hardware of an optical link (no need to send guards all along your optical fiber). In practice, QKD is achieved with optical telecommunication links, either via optical fibers or via the propagation of light in vacuum (or in the atmosphere) for satellite links, where Exail’s solutions are used.

QKD using Exail’s components

There are two different approaches to implement QKD: one focuses on discrete variable (DV-QKD) and relies on single photons with encoded random data. The other one plays on the wave nature of light with information encoded in the quadrature of its electromagnetic fields, it is continuous variable (CV-QKD. Coherent homodyne or heterodyne detection is used to continuously retrieve the quadrature value of the signal to read the key into it.

Exail provides modulation solutions with matching components for the transmitter side of the communication (Alix). For the receiver side (Bob), Exail’s COH 90° optical hybrid demodulator is an integrated solution, based on the company expertise in micro-optic assemblies, dedicated to demodulation of the information as soon as coherent detection is used. The company also has the capacity to integrate its modulation and demodulation solutions within complete systems, including its narrow linewidth single frequency laser as seeder laser.

An example of CV-QKD setup using Exail’s components is given here:


Exail provides reliable components (modulators, VOA, COH) and sub-systems (LAZ-LAB-NL) to implement CV-QKD, both for the transmitter side and the receiver side. The information is encoded in both the amplitude and the phase of laser pulses using our solutions: two amplitude modulation blocks AM1 and AM2 are cascaded with a phase modulation PM1.

Modulators and matching RF amplifiers for QKD

Using an Arbitrary Waveform Generator (AWG), a first modulation block AM1 is used to generate short optical pulses. Using Exail’s NIR-MX800MXER1300 and MXER high contrast and wide bandwidth amplitude modulators, very short optical pulses width from 70 ps can be achieved at 850 nm, 1310 nm and 1550 nm respectively. The modulator is combined with the driver DR-VE-10-MO which can be set either as a limiting or linear amplifier for either square or gaussian pulse waveforms. Using Exail’s bias controller MBC-DG-LAB, a high pulse contrast stability is obtained for frequency repetition rates up to several GHz.


An additional modulation block AM2 generates the random amplitude required for each pulse in CVQKD.
This is achieved using the MXAN-LN (C-Band) or the MXAN1300 (O-Band) or NIR-MX800 (for 850 nm) and the highly linear DR-VE-10-MO.


Multi-level output driver DR-VE-10-MO versus electrical input level

A phase modulator PM1 sets the phase of each pulse. The MPZ-LN-01 (coming with more than 3 GHz electro-optical bandwidth) or the MPZ-LN-10 (typical 16 GHz of bandwidth) is used in combination with the driver DR-AN-10-HO to continuously modulate the phave over the range 0 to 2π. For the O-Band operation, the MPZ-LN-10 is selected to operate at both wavelengths 1310 nm or 1550 nm. For 850 nm, NIR-MPX800-LN-05 (8 GHz bandwidth operation) or the NIR-MPX800-LN-10 (more than 16 GHz bandwidth) are used.

COH 90°, the most advanced demodulation solution for CV-QKD coherent detection stage

CV-QKD uses a coherent detection stage in order to generate the quantum keys, therefore COH (Coherent Hybrid) range of products are widely used for this process.

Exail’s COH 90° optical hybrid is the most advanced solution dedicated to demodulation on the receiver side (Bob) for CV-QKD generation. It is a solution based on a free-space design of a micro-optics assembly, enabling to extract phase, amplitude and polarization by performing interferences between a Signal and a Local Oscillator.

COH 90° optical hybrid is a flexible solution. It relies on iXblue core competencies in the design and the assembly of a free-space optical solution adapted to any kind of modulation (QAM-QPSK-DQPSK) and based on telecom technologies. It can feature a phase tunability option in order to perfectly adjust the 90° of the hybrid depending on the wavelength used.

LAZ-LAB-NL, a narrow linewidth laser seeder for integrated QKD solution

Exail’s single frequency fiber lasers (LAZ-LAB-NL-1560) are based on UV Bragg grating technology applied to active rare-earth photosensitive fibers. Integrated into a carefully designed module using in-house ultra-stable pump drivers, this solution delivers a stable single frequency laser line with ultra-low intrinsic noise and linewidth smaller than 0.1 kHz.

Such high-grade and high-performance lasers are ideal laser seeders for QKD integrated setups using Exail’s components.

Variable Optical Attenuator (VOA)

The Polarization Division Multiplexing Emulator (PDME) is a device that enables to control the delay between both polarizations. The PDME can be used to emulate Polarization Division Multiplexing (PDM) signal by launching a polarized signal with a given modulation format. At the output of the device, the modulation format will be emulated on both polarizations.

To have the best emulation, a key point is to have the same power in both arms before they are recombined. Even if the difference is always low it may slightly vary depending on the wavelength used. With the Variable Optical Attenuator (VOA) option, one can easily adjust the power difference between both arms with 0.1dB accuracy and then get a perfect emulation.

Space grade components

Exail is a designer and a manufacturer of space grade optical components. The company has a track-record of successful missions embarking its “flight proven” components, such as: optical LiNbO3 modulators, radiation hardened (rad-hard) fibers and their matching Fiber Bragg Gratings (FBGs), fiber sources, low noise optical amplifiers, Multiplexer/Demultiplexer and other micro-optics assembly.

Our expertise in the telecommunication domain, experience in assembling complex systems, including laser systems, as well as our space background allow us to provide fully integrated optical transceivers for the space markets. The company has all the competencies to provide solutions for quantum communication in space in the near future.

Partnering with the best academic and industry players

Exail’s provides modulation solutions to QKD manufacturers and to research institutions. In addition to the solutions listed above, Exail also offers polarization switches and pulse pickers.

Started in 2019, the OPENQKD project funded by the European Union’s Horizon 2020 program aimed at reinforcing Europe’s global position at the forefront of quantum communication capabilities. The goal was to raise awareness of the maturity of QKD and its seamless integration into existing security and networks for a wide range of use-cases. IN a collaboration with CNRS, Exail (formerly iXblue) has integrated next generation CVQKD systems pushing for higher baud rate with a design compatible with field deployment.

In January 2023 is starting another EU-funded project, Quantum Key Industrial SystemS (QKISS). It brings together two high-tech industrial groups, Exail (formerly iXblue) and Thales, and two leading academic experts Prof. Philippe Grangier (IOGS, Paris-Saclay Univ.) and Dr. Eleni Diamanti (CNRS, Sorbonne Univ.), with the goal to produce a complete, high-performing, secure and certifiable European Quantum Key Distribution (QKD) system. QKISS includes the manufacturing of opto-electronic components, the development of specialized signal processing and coding algorithms, the full system integration and the field demonstrations. QKISS will also produce field evidence of compatibility with telecom network systems, with the QKD systems functioning together with Mistral encryptors from Thales, adapted to the specific QKD framework. After an industrialization phase, QKISS systems will be available for deployment in the EuroQCI and applications relying on private communications: e-banking, e-health, government communication or the management of critical infrastructure.

QKISS: developing ready-to-deploy European Quantum Key Distribution (QKD) systems

Exail’s solutions for QKD presented at the DAMOP21 Workshop

On June 2nd 2021, iXblue presented our solutions for quantum physics at a DAMOP Workshop: from components to fiber system and laser solutions for cold atom and quantum application. In the first part of this live presentation, we introduce iXblue components solutions for Quantum Key Distribution, and more precisely for Continuous Variable QKD. iXblue offers state-of-the-art components that improve Alice’s transmitter efficiency. They are Phase and Amplitude Modulators, RF amplifiers and come with outstanding performance such as low insertion loss modulators, high extinction ratio amplitude modulators, highly linear RF amplifier, …

Dedicated products

Wavelength max (nm) : 780 – 1625

Product Specification Datasheet
ANalog Drivers
DR-VE-10-MO 12 GHz VErsatile RF Amplifier PDF More info
DR-AN-10-HO 10 GHz Analog High Output Voltage Driver Module PDF More info
MXER1300-LN-10-PD-P-P-FA-FA-30dB 1310 nm band
10 GHz High Extinction Ratio Intensity Modulator
PDF More info
MX1300-LN-10-PD-P-P-FA-FA 1310 nm band
10 GHz Intensity Modulator
PDF More info
MPZ1300-LN-10-00-P-P-FA-FA 1310 nm band
10 GHz Phase Modulator
DC coupled option phase modulator
PDF More info
C+L Bands
MPZ-LN-10-00-P-P-FA-FA 1550 nm band
10 GHz Phase Modulator
DC coupled option phase modulator
PDF More info
NIR 800 nm Band
NIR-MX800-LN-10-00-P-P-FA-FA 800 nm band
10 GHz Intensity Modulator
PDF More info
NIR 800 nm Band
NIR-MPX800-LN-05-00-P-P-FA-FA 800 nm band
10 GHz Phase Modulator
PDF More info
NIR-MPX800-LN-10-00-P-P-FA-FA 850 nm band
16 GHz Phase Modulator
PDF More info
Photonic Solutions
LAZ-LAB-NL-1560 1560 nm wavelength
Other wavelengths available in C-Band
PDF More info


  • Practical continuous-variable quantum key distribution with composable security

    Nitin Jain, Hou-Man Chin, Hossein Mani, Cosmo Lupo, Dino Solar Nikolic, Arne Kordts, Stefano Pirandola, Thomas Brochmann Pedersen, Matthias Kolb, Bernhard Ömer, Christoph Pacher, Tobias Gehring & Ulrik L. Andersen

    Nature Communications volume 13, Article number: 4740 (2022)

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  • Demonstration of Probabilistic Constellation Shaping for Continuous Variable Quantum Key Distribution

    François Roumestan, Amirhossein Ghazisaeidi, Jérémie Renaudier, Patrick Brindel, Eleni Diamanti, and Philippe Grangier

    OFC Conference 2021, Washington, DC United States

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  • Experimental Demonstration of High Key Rate and Low Complexity CVQKD System with Local Local Oscillator

    Shengiun Ren, Shuai Yang, Adrian Wonfor, Richard Penty, Ian White (University of Cambridge)

    Optical Fiber Communication Conference – January 2020

    We experimentally demonstrate a 250MHz repetition rate Gaussian-modulated coherent-state CVQKD with local local oscillator implementation which is capable of realizing record 14.2 Mbps key generation in the asymptotic regime over 15km of optical fiber…

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  • Orbital Angular Momentum States Enabling Fiber-based High-dimensional Quantum Communication

    Daniele Cozzolino, Davide Bacco, Beatrice Da Lio, Kasper Ingerslev, Yunhong Ding, Kjeld Dalgaard, Michael Galili, Karsten Rottwitt, Leif Katsuo Oxenlowe (TU of Denmark) ; Poul Kristensen (OFS-Fitel) ; Siddharth Ramachandranh (Boston University)

    Quantum networks are the ultimate target in quantum communication, where many connected users can share information carried by quantum systems. The keystones of such structures are the reliable generation, transmission, and manipulation of quantum states. Two-dimensional quantum states, qubits, are steadily adopted as information units. However, high-dimensional quantum states, qudits, constitute a richer resource for future quantum networks, exceeding the limitations imposed by the ubiquitous qubits…

  • Continuous-variable quantum key distribution based on a plug-and-play dual-phase-modulated coherent-states protocol

    Duan Huang, Peng Huang, Tao Wang, Huasheng Li, Yingming Zhou (Shanghai Jiao Tong University) ; Guihua Zeng (Shanghai Jiao Tong University) (Northwest University Xi’an)

    We propose and experimentally demonstrate a continuous-variable quantum key distribution (CV-QKD) protocol using dual-phase-modulated coherent states. We show that the modulation scheme of our protocol works equivalently to that of the Gaussian-modulated coherent-states (GMCS) protocol, but shows better experimental feasibility in the plug-and-play configuration…

  • Polarization-multiplexing-based measurementdevice-independent quantum key distribution without phase reference calibration

    Hongwei Liu, Jipeng Wang (National Univ. of Defense Technology, Hunan) (Beijing Univ. of Posts and Telecom.) ; Haiqiang Ma ((Beijing Univ. of Posts and Telecom.) ; Shihai Sun (National Univ. of Defense Technology, Hunan)

    Optica Vol. 5, No. 8 / August 2018

    Reference-frame-independent measurement-device-independent quantum key distribution (RFI-MDI-QKD) can reduce the complexity of practical systems caused by the alignment of the reference frame. Lengthening the transmission distance and improving the system clock rate are essential in practical applications of QKD. ..

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  • Experimental demonstration of long-distance continuous-variable quantum key distribution

    Paul Jouguet, Sébastien Kunz-Jacques, Anthony Leverrier, Philippe Grangier & Eleni Diamanti

    Nature Photonics volume 7, pages 378–381 (2013)

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Optical, space & quantum communications / Photonics France Business Meeting – March 2023

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