Monolithically 3D-Printed Spectral-Spatial Meta-Authenticators

Metasurface holography can encode multiple independent images in a single flat element, yet simultaneous operation at several visible wavelengths has typically relied on geometric-phase elements, which require a prescribed circular polarization and bulky polarization optics, and on high-index dielectrics that can suffer from visible-band absorption. Here, we demonstrate a monolithically 3D-printed, low-index, height-coded metasurface that performs polarization-insensitive, broadband holography across spectral (wavelength) and spatial (near- and far-field) channels. The propagation phase accumulated by each resin pillar is set by its height, so a single height map fixes the phase response at every wavelength at once and acts as a multi-wavelength phase library. The symmetric pillar cross-section removes the dependence on input polarization, and the transparent resin keeps the response low-loss across the visible band. A fabrication-aware optimization folds the discrete height levels imposed by two-photon-lithography slicing directly into the loss, so the design is printed as optimized in a single continuous step, without post-optimization rounding. Experimentally, the device reconstructs a far-field image that is read directly as a public key together with wavelength- and distance-selective near-field images that act as locked passwords, realizing a compact, dual-credential optical authentication scheme under unpolarized illumination without polarization optics.