Pocket Projectors

Microprojector technology could let handheld gadgets like mobile phones and iPods display big pictures.

Mobile devices can store pictures and videos, but viewing them on such a small screen isn't ideal. Microvision, based in Redmond, WA, hopes to solve this problem with a microprojector the company plans to reveal at next year's Consumer Electronics Show. The system, composed of semiconductor lasers and a tiny mirror, will be small enough to integrate into a phone or an iPod, says Randy Sprague, chief engineer at Microvision.

Illustration of a mobile-phone projector envisioned by Microvision. The company expects to have a prototype by early next year, and products by 2008. Credit: Microvision

Right now there is great interest in putting projectors in phones. Indeed, major phone manufacturer Nokia is "looking at" different technologies to integrate projectors into mobile devices (see "The Future of Cell Phones"). As the fabrication technology used to make the components of these projectors matures, it is becoming more economically feasible to create a projector small enough to fit into a handheld device, says Microvision's Sprague.

The projector developed at Microvision is composed of two main parts: a set of red, blue, and green lasers made of semiconductor material, such as gallium indium arsenide, and a mirror--one millimeter across--that tilts on two axes. The lasers shine on the mirror, and the mirror reflects the pixel of light onto a wall or other surface. The intensities of the lasers change to produce different colors: when all three are pumping out light full blast, the pixel is white; when all three are off, the pixel is black. Other colors are produced from various combinations in between.

As the lasers flash on the mirror, the mirror gimbals on its two axes, flickering to produce 30 million pixels a second, each illuminating a surface for 20 nanoseconds. Using this laser and single-mirror setup, the projector paints a scene onto a surface one pixel at a time, says Sprague. It does this so quickly that our eyes perceive a static image or a continuous movie.

One of the challenges is to design a rapidly gyrating mirror that can coordinate with the lasers that turn on and off 100 million times a second. "This mirror is thrashing all around, and the lasers are buzzing like crazy," says Sprague, "so you have to synchronize."

Integrated into the Microvision mirror, he says, are silicon mechanical structures that measure strain on the mirror, detecting what position it's in. This information is fed back into the laser modulator--the device that determines when a laser is emitting light or not--and the feedback loop allows the system to constantly adjust, depending on the demands of the projected image.