High-dimensional information encoding with low-divergence rotating gear vortex beams

In free-space optical (FSO) communication systems, vortex beams carrying orbital angular momentum (OAM) have attracted significant attention owing to their unique helical phase structures. To further expand the degrees of freedom of light fields, we propose a novel structured light field termed the rotating gear vortex beam (RGVB), constructed through the mode superposition of two-dimensional Laguerre-Gaussian (LG) beams. The RGVB exhibits a distinctive rotating gear intensity distribution during propagation while maintaining low divergence. Notably, the beam possesses four independent tunable parameters, significantly enhancing the capacity for high-dimensional information encoding. Numerical simulations demonstrate that within a beam quality factor range of 1 to 15, the RGVB provides 204 available encoding modes, which is approximately 3.19 times that of conventional LG beams. Furthermore, the robust encoding performance of the RGVB is validated by transmitting 64-level grayscale images through simulated atmospheric turbulence. Under varying turbulence strengths (D/r₀ ranging from 1 to 4), the RGVB consistently outperforms LG beams, with recognition accuracy improvements reaching up to 25.14% in strong turbulence (D/r₀ = 4). The obtained results indicate that RGVBs offer superior encoding capacity and turbulence resilience, suggesting great potential for applications in high-capacity FSO communication.