Quantum cascade lasers could drive private free-space communications

Free-space optical communication, the communication between two devices at a distance using light to carry information, is a highly promising system for achieving high-speed communication. This system of communication is known to be immune to electromagnetic interference. While some studies have highlighted the possible advantages of free-space optical communication, this system of communication has so far come with certain limitations. Most notably, it is known to offer limited security against eavesdroppers.

Researchers at Télécom Paris (a member of Institut Polytechnique de Paris), mirSense, Technical University of Darmstadt and University of California Los Angeles have recently introduced a novel system for more secure free-space optical communication based on a quantum cascade laser emitting mid-infrared light.

The core idea behind our research is that private free-space communication with quantum key distribution is promising, but it is probably years away, or even further,” commented Olivier Spitz, one of the researchers who carried out the study. “Currently, the main limitations of this technology are its requirements for cryogenic systems, very slow data rates, and costly equipment.”

Spitz and his colleagues propose an alternative to previously proposed systems for achieving private free-space communication, which implement a cryptographic protocol based on the laws of quantum mechanics. The new system they devised is based on the use of two uni-directionally coupled quantum cascade lasers. It is described in Nature Communications.

The researchers’ approach combines chaos synchronization with the mid-infrared wavelength of QCL technology. Chaos synchronization is a specific property that has been examined in the context of semiconductor lasers for decades. Spitz explained, “Chaos synchronization is the key to private communication, while mid-infrared wavelength means that the attenuation of the atmosphere is low in comparison with near-infrared wavelength, where most of the semiconductor lasers emit.”