Research on multimodal orbital angular momentum regulation based on cascaded metasurfaces

Perfect vortex beams (PVBs) possess a ring-shaped intensity profile that is independent of their topological charge while carrying orbital angular momentum (OAM), making them attractive for optical manipulation and communication applications. Conventional OAM generation methods rely on bulky optical components, limiting integration and flexibility. In this work, we propose a bilayer metallic metasurface operating at 0.1 THz to realize compact OAM modulation and PVB generation. The cascaded structure consists of a rectangular-pillar quarter-wave plate that converts linearly polarized waves into circular polarization and a square-ring metasurface that introduces the required geometric phase distribution. By optimizing the unit-cell parameters, vortex beams with different topological charges are successfully generated. The proposed design provides an efficient platform for multimode electromagnetic-wave manipulation and offers promising prospects for integrated terahertz communication systems and advanced wavefront-engineering applications.