they do it with mirrors

Flipping through channels a couple of weeks ago, in a rare (these days) moment of TV-viewing leisure, I caught Texas Instruments' latest commercial for its Digital Light Processing (DLP) technology. You know the one: an adorable little girl is strolling along with an elephant -- willing suspension of disbelief, people! Work with me! -- holding a very small box. She opens it to reveal a beam of pretty light shining upwards, and the little girl says in awestruck sotto voce: "It's amazing. It's the mirrors."

Most people viewing that commercial probably have only the vaguest idea what it's about, other than describing a key enabling feature of high-definition TV. (They're probably distracted by wondering, "What's with the elephant? Why an elephant?") But TI's Larry Hornbeck must feel a special frisson of satisfaction every time he sees it, since he's the guy who invented that enabling technology in the first place. All those HDTVs, digital movie projectors, and the digital displays used by so many schools and businesses? Hornbeck's research gave us that. And last week the American Institute of Physics rewarded him with its 2007 Prize for Industrial Applications of Physics, "for his invention and pioneering innovations in both the design and manufacturing of Digital Micromirror Devices (DMDs) integrated into metal-oxide semiconductor (MOS) technology." He can add that award to the Emmy he snagged in 1998 for the same technology, and his 33 (and counting!) US patents.

Just what are these miraculous mirrors? It just so happens I wrote a feature article back in June 1997 on the DMD technology. (You can read items from Physics News Update about DMDs here and here.) At heart, it is a complex, rectangular array of as many as 2 million microscopic mirrors nestled on an integrated circuit. Each mirror measures less than one-fifth the width of a human hair, if you need a comparison point to get a handle on the tiny scale we're talking about. The DMD acts like a light switch: each mirror is hinge-mounted so it can tilt on its, regardless of what the other mirrors are doing. This enables a digital image to be processed from a digital signal, because each mirror acts as a single pixel and can be switched on and off thousands of time per second, reflecting light onto a screen.

It all started back in 1997, when Hornbeck was working on building an analog light modulator for optical processing. He based the device -- which appeared four years later -- on a deformable mirror mounted on a metallic membrane. Then he got the idea for replacing that with an array of tilting mirrors connected by hinges, and the DMD concept was born. It was admittedly rudimentary, and too limited in how much light it produced to be immediately implemented into display applications, but Hornbeck and his TI colleagues did manage to develop a useful product: a ticket printer for commercial airlines. At the time, the airline industry was looking for a way to move past carbon-copy ticketing (older readers may remember those pre-e-ticket artifacts) with high-speed, high-resolution printing. The DMD proved ideal for that purpose.

The real breakthrough occurred in 1989, when DARPA awarded the company a $10 million grant to develop cutting-edge projection display systems. By then the DMD technology had sufficiently advanced optically that the notion was perfectly feasible. A year later, Hornbeck came up with the current design, and the first 640-by-480 pixel projection display using DMD appeared in 1992. Further improvements came fast and furious: the earliest devices had thousands of the tiny mirrors, but today's version boasts millions.

By 1997, when I wrote my article, TI was integrating the DMD technology with DLP, which proved to be the winning combination for the commercial marketplace. Thanks to the incorporation of DMD technology, the DLP chip is frequently described as "the world's most sophisticated light switch." Feed a digital or graphic signal to the chip, combine it with a light source and projection lens, and voila! All those tiny mirrors reflect a fully digital image onto your surface of choice (screens are nice).

Inside the DLP chip, the hinge-mounted mirrors tilt towards the light source for the "ON" position, and away from it to indicate the "OFF" position. "ON" corresponds to a light pixel on the screen, while "OFF" corresponds to a dark pixel. Various shades of gray (up to 1,024 -- I didn't know there were that many) can be achieved by switching on and off several thousand times per second. If a mirror is "ON" more than "OFF", it reflects a light gray pixel, and if it's "OFF" more than "ON", it reflects a dark gray pixel. The result is a high-resolution gray scale image.

But we don't live in a gray scale world, so the DLP system passes the white light generated by the lamp serving as an illumination source through a color wheel (or a prism) as it travels to the surface of the DLP chip, filtering the light into red, green and blue. The  "ON" and "OFF" positions for each micromirror are coordinated with those basic color building blocks, such that a mirror responsible for projecting purple (one purple pixel) will only reflect red and blue light to the projection surface. Our perception blends the rapidly alternating flashes of color and will "see" the intended color (purple) in the projected image. TVs, home theater systems and business projectors are 1-chip systems capable of producing at least 16.7 million different colors, while the more advanced 3-chip systems can produce a whopping 35 trillion colors. The mind boggles. Truly it does.

Is DLP perfect? Probably not -- nothing is. Its main competitors in the HDTV marketplace are LCDs and plasma flat panel displays, and each probably has its benefits and drawbacks. The closest competitor is Liquid Crystal on Silicon (LCoS), which uses a stationary mirror mounted onto a chip and relies on a liquid crystal matrix -- similar to those used in LCDs -- to control the reflected light. Thus far, DLP is holding its own quite well. More than 13 million DLP subsystems have been sold to date, with more than 50 manufacturers offering various models in late 2004. TI is reaping the economic benefits: DLP chips constitute a good 5% of the company's total sales.

Innovations are still being made, too. Early in September, TI showcased its high-definition 3D DLP technology at a major home theater and entertainment industry expo (CEDIA), which gives 3D stereoscopic capability to existing HDTVs for a truly immersive viewing experience. Now you can truly feel like you're in the midst of the action if you're watching a spectacular chase scene or action sequence -- and it's designed for easy adaption of existing 3D computer games, which should give all hardcore gamers a warm, happy feeling. This latest innovation builds upon DLP Cinema, launched a few years ago and now in use on more than 4500 movie screens globally. This was a boon to films like Meet the Robinsons, Harry Potter and the Order of the Phoenix, and Beowulf, all of which were shot in 3D. Industry buzz has it that Hollywood intends to expand the number of 3D theatrical releases in the future.

And to think, it all started with one small deformable mirror and the fertile imagination of a gifted , creative physicist. The next time you're at a cocktail party and someone wonders aloud how all this high-falutin' digital TV and 3D cinematic technology is possible, you can bask in the warm glow of superior knowledge, lean over, and whisper the industry's secret: they do it with mirrors. Be sure to mention Hornbeck -- a.k.a. The Founding Father -- by name.

Comments

[Andrew Woods]

Nice article!

In case you're interested, Dr Larry Hornbeck will be giving the Keynote Presentation at the 2008 Stereoscopic Displays and Applications conference. His talk will be titled "Stereoscopic and Volumetric 3D Displays Based on DLP Technology". More info here: http://www.stereoscopic.org/2008/program.html#key

And one small clarification... "Harry Potter and the Order of the Phoenix" was not shot in 3D. IMAX converted selected scenes from the movie using a "2D to 3D conversion" process and this was shown only in IMAX 3D theatres.

[A N]

"It all started back in 1997" ... "the real breakthrough occurred in 1989". Typo....

[Ram]

I was told that TI accidentally hit at this product design, while they were doing R&D funded by Hewlett-Packard to develop some processing technology for HP's printers.