Secure Communication Channels Using Atmosphere-Limited Line-of-Sight Terahertz Links

Terahertz wireless links offer great promise for realizing physical-layer security due to the high directionality and the high path loss. In this work, we investigate the resilience against eavesdropping attacks in a directional terahertz link which exploits the attenuation due to the water vapor absorption resonances for enhanced security. The magnitude of the atmospheric attenuation can be controlled by tuning the carrier frequency relative to the peak of a water vapor absorption line. This idea can be used to thwart an eavesdropper by restricting the broadcast range of the signal. We develop a channel model for an eavesdropping scenario in which an attacker is located along a line-of-sight link. We explore through both experiments and calculations the performance of the terahertz channel, as well as the tradeoff between performance and security. Our results demonstrate the feasibility of limiting the broadcast range by making use of atmospheric conditions, paving the way for a simple yet powerful physical-layer security protocol for the terahertz range.