14 October 2008—The first laser TV is set to go on sale soon in North America, but engineers from the Academy of Opto-Electronics at the Chinese Academy of Sciences and Phoebus Vision Opto-Electronics, in Beijing, say they’ve already brought the eye-popping color of laser-generated images to the big screen with a digital cinema projector that uses lasers as the light source. The team combined several lasers with the MEMS technology used in digital projectors today. They describe the device in September’s Journal of Display Technology.
The technology ”will be the next generation of cinema display,” says Yong Bi, a professor at the Chinese Academy of Sciences and chief technology officer at Phoebus, which is commercializing the projector. However, others in the industry question whether laser cinema will be ready in time and inexpensive enough to catch much of the market.
Bi’s projector replaces the white light and color filters used in today’s digital projectors with several red, green, and blue lasers. The lasers illuminate a digital micromirror device, a MEMS chip invented by Texas Instruments. The chip has an array of microscopic mirrors that each correspond to a pixel on the screen. The chip turns the pixels on or off by tilting the mirrors to direct light either toward or away from the screen.
Engineers have been interested in replacing the white light source and its accompanying color filters with lasers for years. Russell Wintner, consultant with WinterTek, a business, technology, and digital-media consulting firm based in Los Angeles, says the range of color that can be produced from lasers is the most attractive feature of the technology. ”Lasers get closer to what the human eye can see than any other technology,” he says. ”It makes for a much more lifelike image.”
Another advantage is that lasers are more energy efficient. Xenon lamps, the standard projection light source today, dissipate a lot of their energy as heat instead of light. In addition, xenon bulbs produce infrared radiation, which has to be filtered out so that it doesn’t damage the projector’s optics.
Despite these advantages, lasers have been considered too costly for digital projectors. Michael Karagosian, president of MKPE Consulting, a business, technology, and entertainment consulting firm in Los Angeles, estimates that a laser lamp could cost between US $10000 and $20000, while a xenon lamp costs just a couple of thousand dollars. However, he says, the energy savings could make a laser projector economically viable, particularly if mass production brings the cost down.
Another problem with lasers is ”speckle,” a kind of self-interference that makes images shimmer and sparkle, says Bob Rushby, chief technology officer at Christie Digital. When a laser hits a rough surface, its waves reflect randomly and interfere with each other, either adding or canceling each other out, to produce bright and dark spots when the light reaches the viewer’s eye. Lasers are especially susceptible to speckle because they are ”coherent”—their light is of one wavelength. Noncoherent white light is made up of many different wavelengths, so the interference is not visible. To reduce the speckle of interference, Bi and his colleagues used multiple lasers, each of a slightly different wavelength, to produce each color. This reduces the coherence of the beam so that the speckle is not visible, according to the researchers.
Rushby, who's firm makes digital projectors, says that while this technique does work, it doesn’t completely eliminate speckle, and he wasn’t convinced that an audience would not detect it.
”Speckle is an extremely challenging problem,” he says. ”The method helps, but it is not yet suitable for theatergoing audiences.” Other techniques to reduce speckle include vibrating the movie screen or bouncing the lasers off rotating mirrors in the projector, both of which make the speckle pattern change so quickly that it becomes less perceptible.
Christie Digital is also researching laser projector technology, but Rushby would not give details on any potential products. ”We believe laser has a future, but we have some problems to solve,” he says.
But if laser doesn’t come to the market soon, it may lose out to other technologies, WinterTek’s Wintner thinks. The industry is already starting to invest in white-light digital projectors, he says. And once theaters have made a huge capital investment in the projectors, they won’t be looking for a replacement.
”If you had [a laser digital cinema projector] working today and could demonstrate it, it would be huge. But in another two years, it might be too late,” he says.