Spin-decoupled manipulation of guided waves with on-chip direction-multiplexed metasurfaces.

Metasurfaces integrated on optical waveguides provide an effective platform for connecting the in-plane and free-space waves, offering enhanced device functionality and broader application scenarios. However, the confined guided-wave illumination scheme presents challenges in achieving versatile and multiplexing capabilities for on-chip metasurfaces. Here, we propose and demonstrate the spin-decoupled manipulation of guided-wave radiation using on-chip direction-multiplexed metasurfaces. By combining the detour and geometric phase modulation, our method selectively extracts the illuminated guided waves along the +x and -x directions into left-handed and right-handed circular polarization channels, respectively, which enables spin-decoupled focusing and holography. This architecture offers a promising pathway toward multiplexed and multifunctional integrated photonic devices with potential applications in augmented reality displays and optical ranging.