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.