The HMD arena is due for a dose of practicality, sources said, having failed to move much beyond the heavy, expensive headgear for technicians and maintenance workers who absolutely require a hands-free screen. The crop of miniature-LCD technologies brought to market within the past year is a breath of fresh air for HMDs, however. MicroOptical's design is based on such an LCD, but the company applies the display to the wearable-monitor problem in a novel way.

"The conceptual demand for HMDs is very high but nobody's gotten the ergonomics right," said Tom Holzel, vice president of sales and marketing for MicroOptical (Westwood, Mass.), which will demonstrate the Eyeglass Display at the at the Society for Information Display conference in San Jose, Calif.

Holzel called the integrated version "a featherweight personal display with an appearance nearly indistinguishable from conventional glasses. We can build this monitor into prescription eyeglasses, safety glasses, military goggles, whatever. We just need a couple of millimeters of glass to shoot light into from the side."

Using eyeglasses as "an integral part of the optical train" is the breakthrough that allows the design to shed bulk, said Holzel. The conventional HMD positions a display in front of the eye, but MicroOptical breaks the problem down into two tasks — image creation and image presentation — to create a very unobtrusive HMD.

The company locates the miniature LCD in the temple piece of a pair of glasses or in an L-shaped optics module that clips onto the temple. The "screen" is a tiny lens/mirror combiner that sits in front of the eye, residing on a transparent stalk or integrated into the eyeglass lens itself, and reflecting the image into the eye. The optical path from display to combiner goes through the stalk or lens.

A spin-off of miniature-LCD maker Kopin Corp. (Taunton, Mass.), MicroOptical was founded in 1995 and captured a two-year grant from the Defense Advanced Research Projects Agency (Darpa) in 1996 for a headgear project. The company's part of the project was to develop a compact microelectromechanical system (MEMS) that could fit into the temple of eyegear, initially a scanning-mirror system that directed light to the eye via optical fiber.

Then, said company founder and chief executive officer Mark Spitzer, "microdisplays came on real fast and we didn't have to do a wiggling scanner anymore." Instead, the project adopted miniature active-matrix LCDs and active-matrix electroluminescent displays as its media.

Late last year, the company completed its first round of venture-capital funding and nabbed a second Darpa grant to further develop the current optics for military applications. The technology is "ready now" for commercial use, said Spitzer. "It's easy to build something you're going to look at for a minute, but for something you may look at for an hour, that's a different story."

'See-through' monitor

Besides its small size and light weight, what's unusual about the Eyeglass Display is its "minimal occlusion," Spitzer explained in a private demonstration for EE Times this month.

"This is the first real ergonomic breakthrough to make this [HMD] thing practical," Holzel said.

With this "see-through" monitor technology, the eye easily focuses back and forth between the monitor image and the real world beyond it, and the user views the image without feeling cut off from the world. "Think in terms of adding information to the normal view," said Holzel, "or superimposing information on the normal view."

Such superimpositions, he said, "might be an image of a night-vision camera mounted in a soldier's glasses. A firefighter might use it with a special camera to see through smoke, a diver to see through tepid water, a fighter pilot to aim a missile. Or you can simply watch your personal TV or computer screen on an airline without caring whether the guy in front of you leans his seat back all the way."

Spitzer said that MicroOptical has already sold a variety of optometrists and opticians on the concept of the integrated monitor. "There is a very nice distribution channel of people in place who fit optical devices to the head," he said.

The company has delivered a 1/4-VGA color HMD to Darpa and there's one now in use at the MIT Media Lab, the latter integrated into a set of prescription eyeglasses. Based on a CyberDisplay miniature LCD from Kopin, the monitor weighs 30 grams in the clip-in version, 100 grams in the built-in version, and requires 50 to 80 milliwatts, including its LED light source. Its virtual image can be adjusted, Holzel said, "to float at any comfortable distance, from 2 feet to infinity." Diagonal field of view is 12 to 15 degrees.

Holzel promised that a full-VGA color version would be ready by the SID conference. An SVGA version is also in the works. The Eyeglass Display beta-test program kicks off next month, with clip-ons available to qualified OEMs for $1,500 and an integrated version for $5,000.