All‐Dielectric Metasurface for Manipulating the Superpositions of Orbital Angular Momentum via Spin‐Decoupling

Vortex beams, carrying orbital angular momentum (OAM), have plenty of applications ranging from particle manipulation to high‐capacity data transmissions. In particular, the superpositions of OAM patterns are significant in classical physics and quantum science. The flexible control of spin angular momentum (SAM) to OAM can provide more freedom for the design of multifunctional devices. Here, a kind of dielectric metasurface is proposed that generates polarization‐controllable superpositions of OAM patterns in the terahertz (THz) band, which is achieved by the interleaving of anisotropic and isotropic meta‐atoms. The conversions of arbitrary SAM to OAM have been realized by combining Pancharatnam‐Berry (PB) and propagation phase. Not only multiple superposition states of OAM can be generated in the transverse polarization, but also two superposition states of OAM with arbitrary topological charges can be realized in the longitudinal polarization. Several metasurfaces have been designed to demonstrate the multifunctional design, and the feasibility of the theory has been verified in the experiment. Such multifunctional design can find applications in particle manipulation, communication, harmonic generation, and other fields.