Unlocking quantum communication potential with optical IQ modulator

Exail leverages more than 5 years of expertise in designing and manufacturing reliable optical components for leading Quantum Key Distribution (QKD) players. But few know that Exail offers a modulation solution integrating simultaneously the phase and amplitude modulation functions into one unique component. This component is called the Optical IQ Modulator or “MXIQER”.


Modulators with their matching components and demodulators for QKD

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 (CV-QKD) plays on the wave nature of light with information encoded in the quadrature of its electromagnetic fields. Coherent homodyne or heterodyne detection is used to continuously retrieve the quadrature value of the signal to read the key into it. Exail has been delivering its reliable optical components to the main industrial leaders for both DV-QKD and CV-QKD.

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. For example, Exail has collaborated since 2019 with Quside, a European designer and manufacturer of innovative quantum randomness solution suitable for cryptographic key generation. Quside has been developing innovative solutions for quantum secured space-based communication (space-QKD) and relied on Exail solutions such as the space grade TRL9 Lithium niobate modulators to build a highly integrated high-speed quantum secure communication system.


Implementing telecom standard CV-QKD with the optical IQ modulator MXIQER

In a CV-QKD system, information is encoded in both the amplitude and the phase of laser pulses using modulation solutions such as the one offered by Exail. Using an Arbitrary Waveform Guide (AWG), a first modulation block can be used to generate short optical pulses. Using Exail’s NIR-MX800, MXER1300 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 can be 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 can be obtained for frequency repetition rates up to several GHz.

Two separate modulators are often used for the phase modulation (Exail’s MPX-MPZ Series) and the amplitude modulation (Exail’s MXER Series). But few know that Exail is offering a modulation solution integrating simultaneously the phase and amplitude modulation functions into one unique component. This component, called the Optical IQ Modulator or “MXIQER”, modulates via two RF inputs the in-phase (I, or real part) and the quadrature (Q – or imaginary part) components of the transmitted light.



Simultaneous integration of the phase and amplitude modulation functions into one unique component, the MXIQER, optical IQ modulator

The MXIQER-LN-30 optical IQ modulator is a wide bandwidth, low insertion loss and high extinction ratio Dual Parallel Mach-Zehnder Modulator. Using Exail’s MXIQER offers many advantages compared to a phase modulator and an amplitude modulator used separately. It offers compacity as the two functions are integrated into a modulator as large as any Exail’s modulators (only it has more connectors – see picture/scheme above). If the theoretical performances of both setups are similar, using a unique component especially offers greater efficiency. Indeed, less voltage (low Vπ / low arbitrary tension) is required to apply important phase modulation shifts with the MXIQER than with a separate phase modulator. It is thus the most recommended solution for the implementation of a CV-QKD system with telecom standards, exploiting Exail’s extensive know-how in manufacturing modulation solutions based on Lithium Niobate (LiNbO3).

The MXIQER is an optical IQ modulator enabling coherent modulation of light on the transmitter side of the communication (Alix) in CV-QKD, when Exail’s COH 90° offers an ideal solution for coherent demodulation on the receiver side (Bob).


Exail and Thales partner on the development of new QKD hardware

Exail is partnering with Thales since 2023 for the development of European ready-to-deploy QKD systems within 2025. The QKISS (Quantum Key Industrial SystemS) project, funded by the European Commission within the EuroQCI initiative (European Quantum Communication Infrastructure), also involves two leading academic: team of Prof. Philippe Grangier at Institut d’Optique Graduate School (Univ. Paris-Saclay/CNRS) and team of Dr. Eleni Diamanti at LIP6 laboratory (SorbonneUniv./CNRS).

Logo of the QKISS project