The characteristics of vortex electromagnetic wave generated by coding metasurface were studied, and the transmission-type metasurface of vortex wave was designed based on coding unit. It was found that the coding metasurface could replace the quasi-continuous phase to reduce the difficulty of the unit design. But when the orbital angular momentum increased gradually the spacing of two main lobes increased, the side lobes increased, and the vortex waves of other orbital angular momentum reduced. Based on this limitation, this paper optimizes the arrangement of units by genetic algorithm in order to maximize the performance of vortex electromagnetic wave in the limited metasurface size, so that the vortex electromagnetic wave energy is concentrated in the main lobes, thereby enhancing the purity of the orbital angular momentum mode and reducing the electromagnetic wave carrying the orbital angular momentum with other modes, and reduce the main lobes spacing is conducive to propagation. Finally, the feasibility of the method is verified by simulation measurement.
Trapping neutral particles endowed with a magnetic moment by an electromagnetic wave carrying orbital angular momentum: Semiclassical theory
