  We created a novel optical security device that integrates multiple
computer-generated holograms within a single colour image. Under white light,
this "holographic colour print" appears as a colour image, whereas illumination
with a red, green, or blue beam from a handheld laser pointer projects up to
three different holograms onto a distant screen. In our design, all dielectric
layered pixels comprising phase plates (phase control) and structural colour
filters (amplitude control) are tiled to form a monolithic print, wherein
pixel-level control over the phase and amplitude of light allows us to
simultaneously achieve hologram multiplexing and colour image formation. The
entire print is fabricated in a single lithographic process using a femtosecond
3D direct laser writer. As the phase and amplitude information is encoded in
the surface relief of the structures, our prints can be manufactured using
nanoimprint lithography and could find applications in document security.
