Experimental Demonstration of a 10 Gbps Secure FSO Communication Link Using Chaos-Based Phase Encryption

With the exponential growth in demand for transmission based on optical communication technology, providing secure transmission is crucial for the orderly development of individuals and groups in contemporary society. In the context of free-space optical (FSO) communication, we propose and experimentally demonstrate a novel physical layer security transmission scheme based on phase encryption controlled by chaotic sequences. Utilizing the chaotic Chen's equation to generate pseudo-random sequences as keys, we control the modulation of PAM4 signals on phase modulator to achieve phase encryption and decryption of user data. We successfully achieved 10 Gbps NRZ signal transmission over a free-space distance of approximately 3 meters, with a tested bit error rate (BER) lower than the hard-decision forward error correction (HD-FEC) limit. Additionally, we analyzed the influences of various encryption depths, FSO conditions, and delay matching on the system's transmission performance. To the best of our knowledge, this is the first application of chaotic phase encryption in FSO communication scenarios, which will inspire future developments in secure optical communication.