Beam shaping of photon spin Hall effect based on single-layer dielectric metasurface

The Hall-effect metasurface described in this paper uses a combination of Pancharatnam-Berry ( PB ) phase and geometric phase to achieve independent phase control of different spin states. According to the established vector diffraction rigorous coupled wave model, the genetic algorithm is used to optimize the phase distribution of two different shaping effects. Then, different shaping functions are integrated into one device through the arrangement of metasurface microstructure units. By manipulating the polarization chirality of the incident light, the focusing and wavefront shaping of different spin-state photons can be realized at the same time, and two coaxially distributed composite spots can be obtained to achieve the purpose of multi-dimensional shaping of far-field spin-state photons. By this method, the central beam with better flat-top effect and the annular spot with larger radius can be obtained. The designed diffraction efficiency is greater than 90% and the spot uniformity is less than 15%. The welded products have both the smooth surface of semiconductor laser welding and the high aspect ratio of fiber laser welding.