Light beams carrying orbital angular momentum arrays in time-varying scattering media

Light carrying orbital angular momentum (OAM) holds great potential in various application areas. In this paper, we report pattern recognition of light carrying OAM arrays in time-varying scattering media. The data is first encoded via a superposition of two Laguerre–Gaussian beams. Then, the beam patterns are spatially located to generate an OAM-array beam pattern, which is further encoded into a computer-generated hologram, and structured modulation is conducted by using a series of random binary patterns followed by wave propagation in a free-space optical channel through complex scattering in dynamic media. At the receiver, a series of light intensities are collected by a single-pixel detector, and untrained neural networks without any training datasets or labels are first designed to recover OAM-array beam patterns. Image registration and fast normalized cross correlation are further developed to automatically recognize each encoded OAM beam pattern and decode the transmitted bit sequences. It is demonstrated in experiments that the proposed method enables high-capacity OAM transmission (e.g., 16-bit data) in harsh environments via accurate recognition of the light carrying the encoded OAM-array beam patterns. The approach could present a pathway toward high-robustness and high-capacity OAM transmission in challenging environments.