Generation of Vortex Beams via All-Dielectric Spin-Multiplexed Coding Metamaterials

The vector vortex beams are generated by the single-phase modulation of metasurfaces, which severely limits the freedom of design. We use the combination of the propagation phase and the geometric phase to construct a transmissive all-dielectric encoded metasurface. Under two orthogonal circularly polarized incidence conditions, vortex beams with different topological charge can be generated. We utilize the hybrid-order Poincaré sphere to characterize various polarization states of Poincaré vortex beams. Based on the near-field and far-field intensity distribution and phase distribution properties of the vortex beam, the design accuracy of the Poincaré vortex beam is confirmed. In order to improve the degree of freedom of control of vortex beams, we introduce the Fourier convolution principle in digital signal processing. The convolution operation of the encoding array and the phase gradient sequence is performed to construct a new encoding metasurface sequence, and the scattering angle of the vortex beam can be adjusted. Using the principle of coded convolution, functions with arbitrary deflection and beam splitting of vortex beams can be realized.