Monolithically 3D‐Printed Spectral‐Spatial Meta‐Authenticators

ABSTRACT

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.