OAM-Enabled Holographic MIMO Communications with Stacked Intelligent Metasurfaces

This study investigates orbital angular momentum (OAM)-based holographic multiple-input multiple-output (HMIMO) links enabled by stacked intelligent metasurfaces (SIM) in the radiative near-field. By using multilayer programmable metasurfaces at both link ends, SIMs enable analog electromagnetic domain wave processing for low-complexity and energy-efficient flexible wavefront synthesis. We analyzed OAM mode generation and reception with SIM-based transceivers and quantified their ability to synthesize near-orthogonal modes in practical discrete HMIMO architectures. We further developed a correlation-driven optimization algorithm that maximizes reconstruction accuracy of OAM beams. Numerical evaluations revealed a fundamental decoupling between the required antenna aperture, which limits the supported mode orders, and the SIM layer depth, which governs crosstalk suppression. The results confirm that properly dimensioned SIM architectures provide robust near-field spatial multiplexing, nearly balanced per-mode capacities, and graceful degradation across link distances without requiring continuous phase re-optimization, thereby supporting scalable and low-overhead HMIMO communications.