On-axis three-dimensional meta-holography enabled with continuous-amplitude modulation of light

Conventional three-dimensional (3D) holography based on recording interference fringes on a photosensitive material usually has unavoidable zero-order light, which merges with the holographic image and blurs it. Off-axis design is an effective approach to avoid this problem; however, it in turn leads to the waste of at least half of the imaging space for holographic reconstruction. Herein, we propose an on-axis 3D holography based on Malus-assisted metasurfaces, which can eliminate the zero-order light and project the holographic image in the full transmission space. Specifically, each nanostructure in the metasurface acts as a nano-polarizer, which can modulate the polarization-assisted amplitude of incident light continuously, governed by Malus law. By carefully choosing the orientation angles of nano-polarizers, the amplitude can be both positive and negative, which can be employed to extinct zero-order light without affecting the intensity modulation for holographic recording. We experimentally demonstrate this concept by projecting an on-axis 3-layer holographic images in the imaging space and all experimental results agree well with our prediction. Our proposed metasurface carries unique characteristics such as ultracompactness, on-axis reconstruction, extinction of zero-order light and broadband response, which can find its market in ultracompact and high-density holographic recording for 3D objects.