Multi-vortex beams generator based on terahertz reflective metasurfaces

We present a reflective metasurface based on the Pancharatnam–Berry phase theory, designed to generate multi-modal vortex beams with orbital angular momentum (OAM) in the terahertz (THz) range. The proposed metasurface employs a deformed Minkowski fractal structure, enabling the production of multi-mode multi-vortex beams. Through rigorous design and simulation, the metasurface unit demonstrated high reflection coefficients and continuous phase modulation over a broad frequency range from 0.8 to 1.75 THz. By adjusting the rotation angles of individual units, the metasurface array successfully generates multiple OAM modes with high-purity characteristics. Further analysis confirms that the generated vortex beams exhibit high modal purity, which is essential for advanced OAM-based applications. These results highlight the potential of the proposed THz metasurface in enabling practical applications such as OAM multiplexing and multi-vortex beam generation.