Broadband Spin-Decoupled Meta-Devices Enabled by a Polarization Conversion Metasurface

Achieving arbitrary dual functionalities under two orthogonal helicities has attracted increasing attention in spin photonics. Although spin-decoupled metasurfaces have been proposed to empower two distinct functionalities on the two spins based on linearly birefringent elements, they still suffer from narrow operation bandwidth and undetermined spin-decoupled efficiency. Here, we develop a strategy to facilitate high-efficiency spin-decoupled metasurfaces operating in wide bandwidth. We theoretically show that the spin-decoupled metasurface can be alternatively actualized by directly using cross-polarization conversion meta-atoms, with the working efficiency equivalent to that of polarization conversion. As proof of the concept, two broadband spin-dependent meta-devices are implemented at the microwave region, both showing two completely spin-decoupled functionalities with high efficiency in a wide bandwidth. The proposed method can be readily extended to a high-frequency range for high-efficiency and versatile functionalities, which may facilitate advanced devices in compact and integrated photonics.