Hypermultiplexed Off‐Chip Hologram by On‐Chip Integrated Metasurface.

The waveguide‐integrated metasurface introduces a novel photonic chip capable of converting guided modes into free‐space light. This enables functions such as off‐chip beam focusing, steering, and imaging. The challenge lies in achieving hyper‐multiplexing across diverse parameters, including guided‐wave mode type, direction, polarization, and notably, multiple wavelengths. Here, a comprehensive end‐to‐end inverse design framework is introduced, rooted in a physical model, for the multifunctional design of on‐chip metasurfaces. This framework allows for metasurface optimization through a target‐field‐driven iteration process. A hypermultiplexed on‐chip metasurface capable of generating red‐green‐blue holograms at multiple target planes is demonstrated, with both independent and cooperative control over guided‐wave direction. Significantly, the proposed method streamlines the design process utilizing only the positions of meta‐atoms as the design variable. Nine independent holographic channels are demonstrated through a combination of wavelength and distance multiplexing. Moreover, by incorporating the excitation direction into the design, the metasurface produces a total of 36 distinct holograms. The robustness of these results against fabrication discrepancies is validated through 3D full‐wave electromagnetic simulations, aligning well with advanced manufacturing techniques. The research presents a universal design framework for the development of multifunctional on‐chip metasurfaces, opening up new avenues for a wide range of applications. [ABSTRACT FROM AUTHOR]