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The advantage of mid-infrared wavelength is that it is less affected by atmospheric conditions than conventional near-infrared wavelength, and this optical domain is thus envisioned to play a key role in the 6G standard under development. The directivity of the beam, as well as the stealth conferred by the background emission, makes communication systems based on long-wave infrared quantum cascade lasers (QCL) highly desirable. However, some applications require a further level of privacy. Protecting the communication link against eavesdroppers is possible with chaos-based enciphering. Using this concept, a chaotic master QCL is used to conceal the private message while deciphering is achieved with a second, identical, remote QCL that is called the slave. The deciphering process relies on chaos anti-synchronization where the slave only reproduces the reversed chaotic pattern of the master, thus allowing the recovery of the private message by adding the slave signal and the master signal. The privacy of our system is also assessed and shows that an illegitimate receiver would end with a detrimental error rate during translation, even in the unlikely case this eavesdropper knows the coding format of the private message. We believe our private communication system brings a cost-effective, reliable and versatile alternative for free-space data links, especially in harsh environments where mid-infrared lasers strongly outperform their near-infrared counterparts. Features such as room-temperature operation and highspeed transmission further advocates for a large deployment, and we anticipate that this finding can have a significant impact on the development of novel applications based on QCLs.
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