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Micromirrors Enable Microprojectors

Photonics Spectra
Aug 2000
Daniel C. McCarthy, Senior Editor/Special Projects

E-commerce notwithstanding, much of today's work force is still mobile. Thousands of consultants, salespeople and trainers spend a substantial amount of time traveling from one client to another. The tools of the trade for these "road warriors" include a mobile phone, a laptop computer and, increasingly, a projector with which to deliver presentations. Obviously, the smaller and more lightweight these items, the better -- particularly if performance isn't sacrificed.

The new U3 series of palm-size projectors from Plus Corp. in Tokyo have a 7 × 9 × 1.9-in. footprint and weigh less than 3 lb. The projectors owe their small scale to more diminutive lamp and electronics technology, as well as to a smaller micromirror chip from Texas Instruments Inc. in Dallas.

"Last year, our lightest projector weighed 5.7 lb, which means we've nearly halved its weight in one year," said Brian Waite, Plus Corporation of America's marketing coordinator for North and South America.

A close-up of an LCD-projected image (left) shows lower resolution in comparison with an image projected using micromirror technology (right). This is because the micromirrors are very large relative to the gap between them, while elements in LCD projectors are generally much smaller compared with the distance between them. Besides providing XGA resolution, micromirrors helped one projector manufacturer to produce a portable unit that weighs less than 3 lb. Courtesy of Texas Instruments Inc.

The chip in the current projectors is 0.7 in. in diameter. The smaller chip doesn't sacrifice performance, Waite said, adding that the U3 series carry XGA resolution, a difference that is apparent in the display space. XGA resolution displays about a third more information than SVGA projectors.

Texas Instruments' micromirrors are combined with control and formatting electronics to form the company's Digital Light Processing technology. Light in the projector travels from a source through a rapidly moving color wheel and strikes the device's 500,000 micromirrors. The mirrors modulate the light to create a digital image, which is enlarged and projected by a wide-angle throw lens.

Projectors based on liquid crystal displays (LCDs) split light from the lamp through three-color panels and realign the images with a prism. Micromirror technology, however, delivers images using a single panel. "A single-panel architecture allows optical systems -- a key contributor to weight/size -- to be developed which are much smaller and lighter, because they can be less complex," said Ian McMurray, a spokesman for Texas Instruments.

And, because micromirrors are a reflective technology, they typically extract more lumens of output brightness per watt of lamp input than LCD technology, which requires half of the source light to be polarized.

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