OAM-Based Optical Wireless Security: Leveraging Beam Misalignment and Crosstalk for Eavesdropping Resistance

This letter investigates the security of orbital angular momentum (OAM)-based free-space optical (FSO) communication systems under eavesdropping attacks. We analyze the impact of beam misalignment and inter-modal crosstalk on an eavesdropper’s ability to intercept OAM-modulated signals. Unlike conventional FSO links, where misalignment errors degrade system performance, we show that moderate beam misalignment can enhance security by inducing severe crosstalk at the eavesdropper’s receiver. Through numerical simulations, we evaluate the bit error rate (BER) of the eavesdropper as a function of its spatial offset, transmitter tracking errors, and beam waist. The results demonstrate that even with high-quality detection, the eavesdropper’s performance significantly deteriorates beyond a critical misalignment threshold, making interception infeasible. Our findings highlight the intrinsic physical-layer security advantage of OAM-based FSO links, providing insights for designing robust and secure optical communication systems.