Dispersion-engineered compact twisted metasurfaces enabling 3D frequency-reconfigurable holography

We propose a dispersion-engineered inverse design framework based on the bilayer configuration of cascaded metasurfaces to realize the frequency-reconfigurable holography. The compact twisted metasurface system is composed of an integrated feeding RA-M and a rotational P-M. The RA-M is used to provide the modulated excitation for P-M, while the in-plane rotation of P-M achieves the dynamic switching of the holograms. The inverse design framework is applied to optimize the phase profile of both RA-M and P-M to realize high-quality reconstruction of the target dispersion-customized holographic images. A proof-of-concept meta-device prototype is fabricated and measured to confirm the validity of our method. The switching of 3D frequency-space multiplexing holography and achromatic holography is demonstrated in the microwave region. This approach finds promising applications in microwave computational imaging/detection and near-field communications. For the former, frequency-multiplexed holographic metasurfaces enable independent control of near-field modes across frequencies. This significantly reduces RF hardware channels and associated complexity. Crucially, it allows parallel multi-mode measurement via simultaneous multi-frequency illumination and echo acquisition per measurement cycle, accelerating data capture. Integrating spatial multiplexing enables high-dimensional encoded illumination (multi-frequency, multi-plane holography), providing richer and more discriminative data for computational imaging. Reconfigurability further focuses energy on critical information-rich regions/modes on demand, boosting imaging efficiency and precision . For the latter, these metasurfaces enable precise subwavelength focusing and arbitrary beam shaping. By leveraging frequency multiplexing within a single aperture, they simultaneously generate multiple independent beams directed to distinct near-field locations, serving different users or devices. Concentrating energy within specific target zones and utilizing frequency/spatial isolation drastically reduces signal leakage. This directional beamforming significantly enhances resilience against interference and eavesdropping from non-target directions, improving communication security. Furthermore, system reconfigurability allows real-time adjustments to the holographic distribution, enabling instant re-optimization of beam configurations to adapt to changing near-field environments, maintaining optimal performance. Our framework provides fundamental new insights for dispersion engineering in metasurface-based holography and establishes a versatile platform readily expandable across the EM spectrum for dispersion-related applications.