The focal point in the new screen is at the center of the thin end. An optical trick means that light enters through the edge, bounces around inside the lens (much as if it were in a fiber-optic cable), and, when the light has bounced enough times to reach a specific angle (known as the “critical angle”), it exits through the front of the lens. Bathiche says that the specialized lens design, which includes a rounded, thicker end, dictates how the light bounces around and when and where it can escape.

The direction the light comes out depends on the position of light as it enters the bottom edge of the lens. This is controlled using an array of light-emitting diodes at the bottom of the screen. Viewer-tracking cameras could also be positioned at the bottom edge of the lens; these would collect light traveling the other way through the lens. Bathiche says that system’s viewing angle is about 20 degrees, but hopes that with tweaks to the lens design, this can be increased to 40 degrees.

Bathiche says the 3-D lens can replace the traditional backlight in a liquid crystal display (LCD) to create a glasses-free 3-D display. Light from the lens will shine through the liquid crystals, projecting images at the viewers. The quality of the resulting picture is limited by the screen’s refresh rate. A normal 240 Hertz LCD can accommodate two 3-D views, meaning that each viewer’s eye receives a video that refreshes at a rate of 60 Hertz. Any slower, and the frames the video would be jerky. Alternatively, four viewers could watch their own 2-D video using the same display at a refresh rate of 60 Hertz. If the video were split again, then the frames would become jerkier.

The technology is to some degree “at the mercy of what the LCD panel in front of the backlight can do,” says Michael Bove, director of the consumer electronics laboratory at MIT. To address this, Bathiche says Microsoft is pushing display manufacturers to make faster LCDs. Bathiche’s group is also exploring other ways to use the 3-D lens. If integrated into a backlight of a laptop, he says, it could provide a way to instantly toggle between a private view, in which the backlight steers the images from the screen toward a single person’s eyes, and a shared view, in which the backlight shines the images out in all directions.