CVQKD using iXblue Modulators and matching RF amplifiers

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).

Quantum Key Distribution (QKD) offers a forever privacy guaranteed by the laws of physics. 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 the propagation of light in vacuum (or the atmosphere) for satellite links where iXblue modulators are used. 
An example of Continuous Variable QKD (CVQKD) is given. The information is encoded in both the amplitude and the phase of laser pulses using iXblue solutions: two amplitude modulation blocks AM1 and AM2 are cascaded with a phase modulation PM1. 

CV-QKD emitter and receiver

Fig. 1: CV-QKD emitter and receiver
BS: Beam Splitter, AM: Amplitude Modulation, PM Phase modulation, AMP: RF Amplification stage,

AWG: Arbitrary Waveform Generator, SMF28: Single Mode Fiber, BHD: balanced homodyne detectors

Using an AWG, a first modulation block AM1 is used to generate short optical pulses. Using iXblue 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 iXblue bias controller MBC-DG-LAB, a high pulse contrast stability is obtained for frequency repetition rates up to several GHz. 

out 70ps G_25_XP1_40_XP2_85_Vin_180mVpp

Fig. 2 : 70 ps optical pulse generate with the MXER-LN-10 combined with the DR-VE-10-MO


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.

Vout vs Vgg2

Vout vs Vin

Fig. 3: 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 The 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. 

iXblue provides modulation solutions to QKD manufacturers and to research institutions. In addition to the solutions listed above, iXblue also offers polarization switches and pulse pickers. iXblue is also participating to the OpenQKD consortium. By offering dedicated modulators, bias controllers and RF drivers, pulse-pickers for receiver temporal pulse selection, iXblue is proud to contribute efficiently to the deployment QKD.

Dedicated products

Operating Wavelength 1550 nm
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1550 nm band and 10 GHz Very High Extinction Ratio Lithium Niobate Intensity Modulators

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1550 nm band and 10 GHz Very High Extinction Ratio Lithium Niobate Intensity Modulators

Wavelength: 1530 nm to 1625 nm
EO-Bandwidth: up to 10 GHz
Extinction ratio: up to 30 dB
Operating Wavelength 1310 nm
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Operating Wavelength 850 nm
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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...


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)

Vol. 5, No. 8 / August 2018 / Optica