Multicolor and 3D Holography Generated by Inverse-Designed Single-Cell Metasurfaces.

Metasurface-generated holography has emerged as a promising route for fully reproducing vivid scenes by manipulating the optical properties of light using ultra-compact devices. However, achieving multiple holographic images using a single metasurface is still difficult due to the capacity limit of a single meta-atom. In this work, an inverse design method based on gradient-descent optimization is presented to encode multiple pieces of holographic information into a single metasurface. The proposed method allows the inverse design of single-cell metasurfaces without the need for complex meta-atom design strategies, facilitating high-throughput fabrication using broadband low-loss materials. By exploiting the proposed design method, both multiplane red-green-blue (RGB) color and three-dimensional (3D) holograms are designed and experimentally demonstrated. Multiplane RGB color holograms with nine distinct holograms are achieved, which demonstrate the state-of-the-art data capacity of a phase-only metasurface. The first experimental demonstration of metasurface-generated 3D holograms with completely independent and distinct images in each plane is also presented. The current research findings provide a viable route for practical metasurface-generated holography by demonstrating the high-density holography produced by a single metasurface. It is expected to ultimately lead to optical storage, display, and full-color imaging applications.

Scalable and High-Throughput Top-Down Manufacturing of Optical Metasurfaces.

Metasurfaces have shown promising potential to miniaturize existing bulk optical components thanks to their extraordinary optical properties and ultra-thin, small, and lightweight footprints. However, the absence of proper manufacturing methods has been one of the main obstacles preventing the practical application of metasurfaces and commercialization. Although a variety of fabrication techniques have been used to produce optical metasurfaces, there are still no universal scalable and high-throughput manufacturing methods that meet the criteria for large-scale metasurfaces for device/product-level applications. The fundamentals and recent progress of the large area and high-throughput manufacturing methods are discussed with practical device applications. We systematically classify various top-down scalable patterning techniques for optical metasurfaces: firstly, optical and printing methods are categorized and then their conventional and unconventional (emerging/new) techniques are discussed in detail, respectively. In the end of each section, we also introduce the recent developments of metasurfaces realized by the corresponding fabrication methods.