Guided-wave-driven eight-channel spin- and direction-multiplexed on-chip metasurface for light manipulation

On-chip metasurfaces provide a compact route for wavefront shaping under guided-wave illumination, but their multiplexing capacity is often limited by conjugate phase degeneracy between counter-propagating guided waves and by insufficient degrees of freedom in single-meta-atom designs. Here, we demonstrate a guided wave driven metasurface that encodes eight channels through the joint use of propagation direction and output spin. The fundamental TE0 mode is launched from four in-plane directions, and the LCP and RCP components of the radiated field are separated to reconstruct two different holographic images for each input direction. Unlike supercell designs composed of multiple nanobricks, each unit cell in our metasurface employs a single anisotropic nanobrick whose length, width, in-plane displacements, and rotation angle jointly regulate the propagation, detour, and geometric phase responses. The optimization links these five structural variables to the optical responses of the eight channels while incorporating diffractive propagation and a collision-avoidance constraint. Numerical reconstructions demonstrate clear eight-channel holographic images with strong channel selectivity under guided-wave excitation. The scheme removes the need for free space illumination or mechanical switching and provides a compact route to high-capacity integrated holography, optical encryption, and multifunctional photonic chips.