Pocket Projectors

Pocket Projectors

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

By Kate Greene

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.

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.

The mirror, its mount, and the other mechanical components are all made of silicon, putting the projector in a class of device called MEMS (microelectromechanical systems). Sprague says that Microvision developed most of the technology a couple of years ago, but it was waiting for one particular component to become available: a green laser that modulates at the rate required for the projector to work. Only recently have such compact, high-powered lasers become commercially available, he says (see "Ultra-Colorful TV").

Adding a projector to a handheld device, says Ming Wu, professor of electrical engineering at the University of California, Berkeley, could change the way people communicate. Friends might share more movies and pictures, and business professionals who hesitate to pack a bulky projector for a presentation might start using more visuals when they pitch their products, Wu says. "I think it will dramatically change how people will interact with one another," he says. "People won't hesitate to use more image-based communications."

However, some researchers are skeptical that Microvision can pull off a commercially successful microprojector. A prototype is a far cry from a mass-manufactured device that phone makers and consumers will want to buy, says Olav Solgaard, professor of electrical engineering at Stanford. "It's a question of if they can do it reliably and at a reasonable cost," he says. Sprague wouldn't say how much a projector would add to the price of a cell phone.

Microvision expects to release its first products, a stand-alone projector (for media players, cell phones, laptops and other portable devices) and an embedded projector for a smart phone, in 2008. The company has signed a deal with an undisclosed electronics manufacturer in Asia, but the exact timeline for the products depend on the needs of partners and the energy efficiency of the lasers, Sprague says. In an embedded system, he explains, laser-energy efficiency could be a concern: it's expected that projectors made using existing technology would tap a battery fairly quickly. A phone in "projector" mode would use about 50 percent more power than a phone in "call" mode, Sprague says. But over time, he adds, "it will improve to the point where I do believe people will be watching full-length movies from their cell phones."