36-Channel Spin and Wavelength Co-Multiplexed Metasurface Holography by Phase-Gradient Inverse Design

Metasurface holography has emerged as a versatile tool for manipulating light at subwavelength scales, offering enhanced capabilities in multiplexing high-resolution holographic images. However, the scalability of channel multiplexing remains a significant challenge. In this paper, a high-capacity single-cell metasurface is presented capable of maximizing channels by multiplexing holographic images across both spin and wavelength using a single-phase map. The achievement of simultaneous multiplexing of left- and right-circular polarization states is detailed across a broad spectral range, from visible to near-infrared wavelengths, by using a single-cell metasurface, optimized through an inverse design to minimize loss between the target and output images by automatic differentiation. The phase profile is optimized to encode multiple holographic images without requiring complex meta-atoms, thereby reducing the fabrication complexity while maintaining high performance. Using this method, two metasurface implementations are demonstrated, an 8-channel hologram covering both the visible and near-infrared regions and a 36-channel hologram operating in the full-visible spectrum across 18 wavelengths separated by 20-nm intervals. Furthermore, noise-related loss functions are incorporated into the optimization process to suppress background noise and minimize inter-channel crosstalk, resulting in significantly improved image quality and fidelity. This approach offers a reliable solution for further photonic applications such as displays, optical data storage, and information encryption.