Cascaded metasurface for polarization-dependent varifocal vortex beam manipulation

Abstract

Vortex beams, characterized by orbital angular momentum (OAM), hold significant potential in optical communications, quantum information processing, and optical manipulation. However, existing metasurface designs are largely confined to single-degree-of-freedom control, such as static OAM generation or fixed focal points, which limiting their ability to integrate polarization multiplexing with dynamic focal tuning. To address this challenge, we propose a tunable multifunctional cascaded metasurface that synergizes polarization-sensitive phase engineering with interlayer rotational coupling, overcoming conventional device limitations. The designed metasurface independently generates distinct OAM states in orthogonal circular polarization channels under right-handed circularly polarized (RCP) incidence, that is, a vortex beam with topological charge ℓ = −1 in the left-handed circularly polarized (LCP) channel and a superimposed vortex state (ℓ = +1, −1) in the RCP channel. Continuous focal tuning is achieved via interlayer rotation in the axis-direction, with experimental validation at target frequency. Experimental results demonstrate the focal length modulation range from 25.9λ to 9.5λ as the interlayer rotation angle varies between 90° and 240°. This multi-degree-of-freedom control strategy establishes a new method for high-capacity optical communications, dynamic holography, and quantum state manipulation, while advancing the development of intelligent metasurfaces for 6G networks and integrated photonic systems.