Space-time holograms based on programmable metasurfaces

Programmable metasurfaces can be used to generate holograms for imaging and sensing applications. However, creating high-capacity dynamic holograms that are programmable and have high refresh rates remains challenging. Here we report on space-time holograms based on programmable metasurfaces. The approach provides thousands of independent holographic channels working simultaneously at different harmonics. We use spatial-time coding to split a monotone injected wave into multi-harmonic reflected beams, and we develop a fast convergence phase-retrieval algorithm to manipulate the wavefront intensities at each harmonic. Using a programmable metasurface with 6,144 elements, we experimentally show that the approach can generate 62 holographic images (digits and Latin letters) simultaneously. We also show that the platform can create 1,024-channel holograms with spot distribution patterns and that it can be used for multi-target tracking.