While it's not the 3D Star Wars hologram you're hoping for, Mitsubishi is developing a system to project video in mid-air, which it hopes to commercialize in time for the Tokyo 2020 Olympics. To pull it off, the company is using two types of optical tech: a beam splitter, which divides incoming photons into reflected and transmitted light, and a retro-reflective sheet that bounces light back in exactly the same direction it came from. By arranging them just so with a display (below), the light reconverges to form an image that appears to float in the air.
Mitsubishi developed a special optical simulation program to figure out how to arrange the elements in order to create a 56-inch diagonal image that sits a meter (40 inches) from the beam splitter. It said the main problem with the tech is that "people who are not accustomed to focusing their eyes on open space find it difficult to understand where an aerial images is being displayed." As a result, the system also projects guide images on walls place on either side of the "screen" so you know where to look.
Mitsubishi thinks it could be used to project large images in public spaces or display "life-sized images of people for remote communication." It expects to commercialize the tech by 2020, but hopefully they'll have some kind of proof-of-technology prototype coming soon.