They have 3D (without glasses) displays now. It's quite simple how they work

It's just a flat screen that spins. It's like those fans that have a clock on them as the blades spin. It's the same principle; different pixels light up as the screen spins. It sort of 3D prints the air as it goes round so it's really just a series of flat images that change as the screen spins really fast, so fast that that the series of images appear to be happening at the same time.

LED Clock Fan: