Will lasers provide a cheaper alternative to large projection and plasma displays?
Over the past couple of years, a variety of flat-screen technologies such as plasma have been replacing the bulky home-theater screens that have dominated the market for large televisions. Now, the newest entrant into the field is called laser TV, a flat-panel display based on projection-television technology that uses high-powered lasers to light up the screen. Mitsubishi and Samsung are expected to have laser TVs on shelves by Christmas 2007.
Using lasers to illuminate screens is not a new idea, but until now, there hasn’t been a light source powerful and cheap enough to be tapped for consumer displays. Sunnyvale, CA-based Novalux has developed laser technology that exploits a new type of laser architecture that combines a few relatively simple components to pump up the power. The patented laser, called Necsel, was invented by Aram Mooradian, CTO of the company and former head of the quantum-electronics group at MIT’s Lincoln Laboratory. Mooradian claims the technology will allow laser TVs to outdo existing displays larger than 50 inches–mostly traditional projection systems and plasma displays–in terms of both price and quality.
At the heart of a laser TV is the same technology found in projection-television systems. Indeed, many of the laser TVs sold by Mitsubishi and Samsung next year will include a popular projection system called digital light processing, or DLP, developed by Texas Instruments. The main difference between traditional projection and laser TV is the light source: most projection systems use a white-light lamp, whereas laser TV uses an array of lasers.
Lasers, emitting beams of red, green, or blue light, shine on an array of thousands of micro mirrors. Each mirror represents a single pixel. The mirrors are controlled by an electrical signal that causes it to tilt either toward or away from the light source. If the mirror tilts away from the laser, the corresponding pixel is black; if it tilts toward the laser, the corresponding pixel is the color of the laser light. These mirrors switch “on” and “off” thousands of times a second, and the lasers shine on the mirrors in varying intensity, mixing the fundamental red, green, and blue. The result is a huge gamut of colors.
In contrast, lamp projection systems produce color by using a color wheel–a spinning disk usually containing red, green, and blue–that is placed between the lamp and the micro mirrors. This spinning wheel also produces an array of hues. However, the main advantage that lasers offer over traditional projection is an increased richness in colors, says Mooradian. The color of light produced by a laser is, by definition, spectrally narrow, varying less than one nanometer on either side of the peak wavelength. The filters used for lamp-based projection systems aren’t as spectrally pure, varying as much as 20 nanometers, he says. Our eyes can detect this difference, and when the colors are more spectrally pure, they appear more vivid.
The new types of lasers used to illuminate a screen are actually made out of the same material–gallium indium arsenide–as the lasers in DVD players. The major difference between a DVD laser and a Necsel laser, Mooradian explains, is the architecture of the laser.
Mooradian decided to look at surface-emitting lasers–mostly used for low-power applications such as short-range optical communication–as an alternative to ones used in DVDs, called edge-emitting lasers. He found that he could get much more high-quality light out of surface-emitting lasers than out of edge emitters. No one had thought seriously about using surface-emitting lasers for high-powered applications before, he says, “and I just got there first.”
The light that comes from gallium indium arsenide laser is naturally at infrared wavelengths invisible to the human eye. Mooradian added a crystal composed of lithium niobate–an inexpensive material found in mobile phones–to knock down the wavelengths to ones visible as red, green, and blue. Then he added the final component of the system: a simple piece of glass that encloses the laser cavity where laser light is amplified.
Using lasers instead of bulbs in a projection system can not only increase the quality of light, Mooradian says, but the laser array also lasts longer and can allow for lighter, thinner, less expensive projection displays.
And compared with plasma televisions, the color produced from lasers is better, says John Reder, worldwide strategy and business-development manager for DLP TV at Texas Instruments. “I think the color gamut is the first thing you’ll notice” when comparing the two types of displays, he says. A pixel’s color in a plasma display is created when an electrically charged gas–the plasma–excites a chemical compound called a phosphor. The phosphor glows when struck by the electrons from the plasma. But, unlike a laser, a phosphor emits light that isn’t spectrally pure.
A laser-based projection system can employ as few as three lasers, Mooradian explains, for smaller applications such as mobile-phone projectors used to share pictures and video or pocket projectors used for presentations. Displays for home theaters will use 72 lasers, with a total laser system taking up less than a cubic centimeter of volume, he says. And, he adds, his company is looking to break into Hollywood with theater-quality laser projection systems containing hundreds of lasers.
There’s little doubt that lasers will allow more colors to be shown on a screen, says Steve Jurichich, director of display technology at DisplaySearch, a consultancy in Austin, TX. But, he adds, the company might be a little ahead of its time because the same color gamut isn’t available over the airwaves or from video cameras. “Ultimately,” he says, “you can show more vivid colors, but it won’t be what’s naturally recorded.” New color standards are imminent, however, and Jurichich suspects that within a few years, broadcast standards and Hollywood will catch up.
Jurichich adds that he expects that laser TV will be competitive with traditional projection television initially, but he is hesitant to say that it will overtake plasma, as prices for that technology continue to drop.
But even if laser TVs don’t dominate the market, they could find a comfortable niche in front of some living room couches. As the home-theater market continues to diversify and expand, consumers are going to be able to get more screen size for the dollar, and image quality will continue to improve, says Texas Instruments’ Reder. And lasers, he believes, “will have an ability to impact the market.”
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