Reflective colored image based on metal-dielectric-metal-coated gratings

Subwavelength gratings coated with metal-dielectric-metal layers and embedded in a dielectric exhibit distinctive color properties in reflectance. The reflected color of incident unpolarized white light can be tuned by the modulation depth of the grating. It is shown that reflective colored images may be reproduced by this type of gratings having a laterally adapted modulation depth. Its lightness, as well as the angle tolerance of the image coloring, is even suitable for human observers in ambient light. The gratings with variable depth are manufactured by electron-beam lithography and by a subsequent direct laser writing process. These types of reflective images may be replicated by a simple nano-imprint process on plastic foil. This method is predestined for industrial mass production.