https://phys.org/news/2021-06-quantum-cascade-lasers-private-free-space.html
"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 (EMI), a disturbance generated by external sources that affects electrical circuits and can disrupt radio signals.le 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 (member of Institut Polytechnique de Paris), mirSense, Technische Universität Darmstadt and University of California Los Angeles (UCLA) have recently introduced a unique system for more secure free-space optical communication based on a technology known as quantum cascade laser, a specific type of semiconductor laser that typically emits mid-infrared light."
