Fig. 1. Conceptual illustration of the metasurface-assisted grating-modulation (MAGM) system. (i) Diffraction order of the conventional amplitude-modulated binary grating and phase-modulated sinusoidal grating. (ii) The reconstructed image when the static metasurface is illuminated without grating amplitude modulation. It shows that the static metasurface alone cannot transmit multi-fold information. (iii) The MAGM system with the capability to independently present alternative holographic images. The lower part shows the conceptual schematics for the MAGM system. Time-dependent image information is encoded in incident beams with different grating amplitude distributions. Dynamic holographic images can be shown with these different grating frames.

Fig. 2. Flow chart of the forward pass for complex amplitude hologram optimization. (a) Flow chart of the gradient descent algorithm for generating meta-holograms. (b) Calculated phase profile φ of the meta-hologram. It is partially shown with 100×100  pixels. (c) Loss value as a function of the iteration number in the gradient descent optimization algorithm. (d) Scanning electron microscopic (SEM) images of the fabricated unit cells (top view). The scale bars are 800 nm and 400 nm, respectively.

Fig. 3. Optical characterization and designed scheme for the MAGM system. (a) Schematic view of the experiment setup, switching the holographic images can be realized by moving and rotating the grating in the x–y plane. (b) Illustration of the modulation scheme with the grating displacement to realize a two-channel switch. The bidirectional arrow indicates the motion direction of the grating. (c) Measured two-channel holographic images of each combination. The reconstructed image dynamically switches between “Heart” and “Briefcase,” framed by a light yellow box and compared with the target image at the center.

Fig. 4. Schematic illustration and experimentally measured holographic images of the four-channel scheme. (a) Illustration of the working schematic for the four-channel scheme. The expansion of channels is achieved by continuously switching different grating amplitude distributions. (b) Measured four-channel holographic images of each combination. The reconstructed image dynamically switches among “Gear,” “Star,” “Heart,” and “Briefcase,” framed by a light yellow box and compared with the target image at the center.