Towards private optical communications with mid-infrared chaotic light

Free-space optics constitutes a growing technology offering higher bandwidth with fast and cost-effective deployment compared to fiber technology. Multiple applications are envisioned like private communications. In such a case, the secret message is encoded into a chaotic waveform from which the information is extremely hard for an eavesdropper to extract. For free-space optics applications, the operating wavelength is an important parameter that has to be chosen wisely to reduce the impact of the environmental parameters. In this context, quantum cascade lasers are highly relevant semiconductor lasers because the lasing wavelength can be properly adjusted in the mid-infrared domain, typically at wavelengths for which the atmosphere is highly transparent. The simplest way to generate a chaotic optical carrier from a quantum cascade laser is to feed back part of its emitted light into the device after a certain time delay, beyond which chaos synchronization between the drive and the response lasers occurs. In this paper, we discuss about how quantum cascade laser's chaos can be used to develop private communication lines. We also give realistic perspectives for further developing mid-infrared private communications using chaotic waves.