Partial coherence and multi-channel vortices enhance high-security free-space optical communication

Vortex beams (VBs) shift keying is a digital communication technique that encodes data by rapidly switching or shifting the orbital angular momentum (OAM) state of a light beam, improving the performance of free-space optical communication. However, current VB-based shift keying secure systems still face several issues, such as limited capacity, the need for model retraining during key renewal and in some cases, vulnerability to ciphertext-only or known-plaintext attacks. In this article, we address these critical challenges by integrating VB array, phase encoding, spatial coherence modulation and deep learning techniques. By utilizing 9 spatial channels each with 16-ary phase differences in the proof-of-principle experiments, the information content carried by a single symbol reach 36 bits. Moreover, a double-encryption transmission scheme is proposed, leveraging the coherence structure and spatial reading trajectory of the VB array. This method has been experimentally verified to provide ultra-high security at the physical layer, effectively resisting both ciphertext-only and known-plaintext attacks. The corresponding bit error rates and pixel error rates can highly reach at least 3.7 × 10−1 and 8.6 × 10−1, respectively. Our work offers the potential for next generation VB-array-based high security FSO communication. Vortex-beam-based shift keying secure systems enhance secure digital communications, while it faces challenges such as limited capacity and vulnerability to attacks. This paper presents a double encryption scheme leveraging coherent structures and spatial reading trajectories whichenables key updates without retraining, and maintains high security.