>>12244791optical holograms work by recreating an optical light field on a surface. to recreate such a field, you need to have features that are smaller than the shortest wavelength by at least half. moreover, to be a display, you'd need to be able to reconfigure the screen. the shortest wavelength you can see is about 400nm, so you'd need features about 200nm. moreover, you'd need to fit in at least 3 colors, so really you need features that are about 50nm in size. tunable materials that can manipulate things like phase and amplitude at these scales are typically quite lossy. it's not easy to make such a screen.
i've seen multiple plates of glass stacked on top of each other to generate volumetric images, but the effect kinda sucks.
honestly, having personal images projected into individuals' eyes would be a much more practical solution to 3d display tech
