3D displays are displays that project images which appear 3-dimensional. Early models require the use of stereoscopic goggles, and will not be truly 3D, but some scientists expect full-fledged 3D displays to hit the market by around 2015. A primary limitation is that holograms are only designed to be viewed from one angle. Research towards making 3D displays possible focusing on head-tracking optics designed to follow a viewer's gaze from around the room, or holographic projections that can be viewed from more than one angle. Holograms and other 3D display attempts have been around for decades, but it will still be a while before we see the technology on shelves.
A company called IO2 technology has created a display called the M2i which can project full-color 3D display images in thin air, available today for about $20,000 US Dollars a unit. The display uses a rear projection system to create images in what they call "transformed air." The images look somewhat ethereal. However, the technology works in all types of lighting. The M2i display is a definite precursor to a more mature 3D display technology.
A more sophisticated 3D display was recently created by scientists at Japan's National Institute of Advanced Industrial Science and Technology. They bill the technology at the "first true 3D display," which uses overlapping laser beams to create tiny plasma flashpoints in the air, the afterglow of which is picked up by human eyes. The system generates as many as 100 airborne dots, and generates plasma "pops" at a rate of 100 times per second. Because the lasers superheat tiny portions of air to produce the plasma, the display creates a constant crackling noise, and can only produce white dots, definite impediments to commercial deployment, but an interesting approach nonetheless.
One difficulty in creating 3D displays is producing high-quality content to port to the displays. Filming a 3D image takes multiple cameras viewing from different angles, and specialized software to convert the 2D images into a 3D spatial map. The practicalities of this could hold 3D displays back for a while even after the technology becomes feasible in principle. The slow adoption rate of HDTVs is also another factor that companies will consider in choosing where to place their research and development dollars. But sooner or later, it seems that civilization will succumb to 3D display technology. What's the future without a holodeck?