Sony 4k projectors used for 3D
Sony explains how it will use 4k projectors for efficient 3D projection. The Sony projector displays two stacked images, one for each eye in the same picture. Then a special lens to the optical trick and sends both images at the same place.
Cheap passive glasses will then filter the correct image for each eye. Explanation and a nice schematic are available here.
(info coming from www.lesnumeriques.com, original text in French)