Free-space optical stealth communication based on wide-band spontaneous emission

We proposed and experimentally demonstrated a free-space optical stealth communication system that hides the stealth signal in wide-band spontaneous emission noise. Spontaneous emission light sources have been widely used for illuminations and has been recently deployed for short distance and indoor free-space optical communications, such as LiFi. Since free-space optical communication is a broadcasting network, the users’ privacy is exposed to eavesdropping attacks. In this paper, stealth communication is achieved by taking advantage of the existing properties of spontaneous emission light sources, random phase fluctuations, and protects users’ privacy in free-space communication networks. The keys to hide and recover the stealth signal are the optical delays at the transmitter and receiver. Only by matching the delay length with the pre-shared keys can the authorized receiver recover the stealth signal. Without the right key, the eavesdropper receives a constant power that is the same as illumination light sources and cannot detect the existence of the stealth signal.