Abstract
Multi-functional metasurfaces have gained broad attention recently, as they bring great possibilities for high-dense multifunctional meta-devices, such as projecting holograms and displaying continuous gray-scale images simultaneously. However, currently reported metasurfaces to perform these operations separately. Furthermore, their complex multi-layer and super-cell design strategies complicate both design and fabrication processes. This applies a limit on miniaturized, low-cost, integrated multi-functional meta-optics. Here we report a novel single-unit cell-based design strategy to demonstrate a tri-functional metasurface. By merging the spin-decoupling strategy with Mull's law amplitude manipulation, a three-in-one metasurface is designed to project two independent holographic images in the far field and one continuous gray-scale image in the near-field of the metasurface. Specifically, far-field holographic images are projected on orthogonal helicities of white CP light, whereas a near-field image is decoded by creating an orthogonally linearly polarized light path. Furthermore, we optimized a novel gallium phosphide (GaP) material to verify the proposed design strategy for a tri-channel metasurface. The proposed metasurface has high transmission efficiency in the visible regime and verified our design strategy without adding extra complexities to conventional nano-pillar geometry. Therefore, our metasurface opens new avenues in multi-functional meta-device designing and has promising applications in anti-counterfeiting, optical storage, image displays, etc.