High resolution multicolor holograms encoded into color print images with hybrid dielectric/plasmonic metasurfaces

Abstract

Multicolor holograms encoded into color print images are structures that generate holographic images when illuminated with lasers, while showing completely different images when viewed with the eye or with microscopes under white light incoherent illumination. Despite their promising applications in optical document security, they have been the subject of only a handful of research efforts, underscoring the need for further exploration in this area. Here, we propose a hybrid metasurface that achieves this functionality and thoroughly characterize its performance using simulations. In our device, nanohole arrays in an aluminum film function as plasmonic color filters for blue, green, and red channels with low crosstalk. Amorphous titanium dioxide (aTiO2) nanopillars comprise the hologram metasurface, which modulates the outgoing light's phase to produce a holographic image. Due to the subwavelength dimensions of the unit cell of the color filter (e.g., 415 nm for red, 315 nm for green, and 255 nm for blue wavelengths) and metasurface hologram (e.g., 430 nm for red, 360 nm for green, and 305 nm for blue wavelengths), the color print and holographic images can have very high resolution. Simulations reveal that the metasurface can be perceived as a tricolor image under incoherent white light, whereas under illumination from red, green, and blue lasers, three distinct holographic images can be observed.