Bragg-Berry flat reflectors for transparent computer-generated holograms and waveguide holography with visible color playback capability.

Various approaches are being pursued to realize compact optical elements with the ability to manipulate light, but it is difficult to simultaneously achieve high reflectivity and the ability to see through the element. Here, we present a reflective computer-generated hologram that is completely transparent in the visible, based on the Berry (geometric) phase in a self-organizing Bragg reflector. The Bragg reflector has a helical dielectric tensor distribution with the phase information imprinted in the distribution of the optic axis on the substrate. The structure possesses only a single Fourier component and high-order reflections are suppressed; thus, the device appears completely transparent by setting the main reflection band outside the visible range for all angles of incidence accessible by ambient light. On the other hand, the encoded phase information can be played back using visible light by increasing the accessible incidence angle, which we demonstrate experimentally by (i) attaching a coupling prism, and (ii) integrating the device in a waveguide. Bragg-Berry reflectors thus enable a new route to realize advanced optical elements with no apparent reflection in the visible region.