A multifunctional meta-hologram design, developed by researchers at Pohang University of Science and Technology (POSTECH), can be used to create different hologram images depending on the direction of the incident light that falls on the device. Conventional meta-holograms can display images when the incident light falls in one direction only. The POSTECH meta-hologram was created from a monolayer meta-holographic optical device. To design directional sensitivity into their meta-hologram, the researchers included direction-controlled, spin-dependent holographic recordings in the monolayer structure. The metasurface hologram they designed consists of nano half-waveplates of low-loss, hydrogenated amorphous silicon. The half-waveplates are designed and optimized for circularly polarized illumination, and can excite electric and magnetic resonances simultaneously, as well as antiferromagnetic modes, to ensure high transmission for the cross-circularly polarized light. The dual magnetic and antiferromagnetic resonances make the device more efficient than a conventional meta-hologram. The new meta-hologram demonstrated a diffraction efficiency higher than 60% with clear, high-quality images. Because silicon is used to make the meta-hologram, it can be easily produced through a conventional semiconductor manufacturing process. Meta-hologram optical device that operates in forward and backward directions. Courtesy of Junsuk Rho (POSTECH). The researchers believe that their meta-hologram, which operates in forward and backward directions, could be the basis for a new hologram platform that could transmit information to multiple users from different locations, overcoming the limits of conventional meta-holograms, which can only transmit one image to a limited number of locations. “A microscopic, ultrathin, ultralightweight, flat optical device based on a metasurface is an impressive technique with great potential, as it can not only perform the functions of the conventional optical devices, but also demonstrate multiple functions depending on how its metasurface is designed,” professor Junsuk Rho said. “We developed a meta-hologram optical device that operates in forward and backward directions and that can transmit various visual information to multiple users from different locations simultaneously. We anticipate that this new development can be employed in multiple applications such as holograms for performances, entertainment, exhibitions, automobiles, and more.” The research was published in Nanoscale Horizons (www.doi.org/10.1039/C9NH00460B). A correction to the paper was also published (www.doi.org/10.1039/D0NH90006K).