A new thin-film technology developed by 3M could enable mobile devices such as cell phones to show 3-D images without the need for special glasses.

Dubbed Vikuiti 3-D, the technology works by guiding slightly different images to the viewer's left and right eyes. Provided that the device is held relatively still, the viewer experiences an "auto-stereoscopic" effect--a sense of depth to the image, says Erik Jostes, business director of 3M's Optical Systems Division in St. Paul, MN.

This optical trick has been around for some time and is essentially the same as the one behind Philips's WOWvx 3-D television displays. However, getting it to work in mobile devices presents new challenges.

In Vikuiti 3-D, prism-shaped reflective structures are embedded on the back of a polymer film, and tiny microlenses are patterned on the front. Together these components steer lights through a liquid-crystal display in front of the film. Light passes through the film from two light-emitting diodes, one positioned to the left and one to the right. The light from each LED bounces off a waveguide and strikes the film at a different angle, causing the embedded optics of the film to steer the light in two different directions.

Because each beam of light passes through a liquid-crystal display showing a slightly different image, providing the display is held at the correct distance, each eye receives a slightly different perspective. To trick the viewer's brain into believing it is seeing the two images at the same time, both the LEDs and the LCD panels have to be switched extremely fast--about 120 times a second, says Jostes.

Mobile devices tend to have both smaller displays and smaller pixels, says David Pepy, general manager of Alioscopy, a company based in Paris, France, that is also developing auto-stereoscopic displays. This means the lens-like structures on the film need to be particularly small, he says.

Not only do the lenses have to be very precisely engineered, Jostes says, but each lens has to be very precisely aligned with the corresponding prism on the back of the film. To achieve this, 3M uses a process called microreplication, a proprietary printing technique that can produce structures tens of micrometers thick in a film just 75 micrometers thick, Jostes says.