Dual-Helicity Decoupled Coding Metasurface for Independent Spin-to-Orbital Angular Momentum Conversion

Controlling spin-to-orbital angular momentum (OAM) conversion plays an important role in many optical and wireless communication applications. While independent control of different circular-polarized (CP) wavefronts could offer an ultimate degree of freedom in designing advanced multifunctional spin devices, most metasurfaces only provide dependent wavefront control. We propose a reflective dualhelicity decoupled coding metasurface to completely realize independent control of OAM vortices for two orthogonal helicities. The element combines both the propagation phase and geometric phase, thus overcoming the inherent limitation encountered by conventional geometric phase elements whose phase responses are constrained to be opposite values for different CP wavefronts. Several design examples for independently generating OAM vortices in the microwave region are presented where a free combination of different OAM modes, helicity, as well as complex spatial beam editing can be fully achieved. Experiments show good agreements with the full-wave simulations, successfully verifying the design theory. The proposed method could offer an alternative platform for designing high-performance devices with independent CP wavefront manipulations, which may enhance the information capacity of metasurfaces and trigger versatile electromagnetic (em) wave function integrations for advanced compact systems.