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Is There A Laser In Your Future?

Although laser imaging technology has been around for a few years, we haven't seen it in a projection TV application ?until now.

How do you get rid of speckle? By diffusing the laser's beam as much as possible. Of course, it's no longer coherent as a result, which means the light output drops off considerably. (You can't get something for nothing!)

Back in 1998, I took a trip to Portsmouth, NH, to visit the offices of the Corporation for Optical Laser Research (COLOR), a company that, at the time, had a subsidy from Sony to develop a practical light engine for a cinema-grade projector. The lasers would work in conjunction with a light modulator known as the grating light valve, or GLV. (Remember the GLV?)

I was shown, among other things, a room with a 9- by 12-foot optical bench, loaded with diffusers and mirrors, focusing red, green, and blue laser beams into the combining prism of a Sony XGA-resolution LCD projector. By the time the image got to the screen, it was largely free of speckle, had saturated colors — and wasn't terribly bright.

Not all that impressive, considering the wall of 6-foot-tall rack units powering and controlling the lasers. (Remember, I said laser illumination for projectors was possible back then, not necessarily practical.) Effectively, the COLOR engineers had created the world's largest portable LCD projector.

The Mitsubishi line show demo, if nothing else, generated lots of good PR for the company. As to its claim that the product would be at retail by the fourth quarter of 2007, I'd have to be pretty skeptical. Aside from the speckle issue, lasers are considered hazardous because their coherent light can literally cook your retina if you stare directly at them.

That means the laser imaging assembly would have to be completely sealed and accessible only by the factory. Considering the power supply and lasers for the Mitsubishi demo weren't even inside the ultra-slim 10-inch RPTV cabinet, but located below it in a large black box with numerous cooling fans, there are other packaging issues to be addressed before this product is marketable.

Novalux isn't the only company showing demonstrations of laser engines. Photonics giant Coherent Inc. recently exhibited at the UDSC-Needham Investment Conference in New York City in March, and had hacked together a laser projection engine for a Samsung 52-inch DLP RPTV. The green laser was a straight diode design, while the red and blue lasers were pumped. It, too, took up the insides of a large support chassis with cooling fans positioned under the TV.

The Coherent/Samsung demo did away with the standard multi-segment color wheel, which also removed the single-chip DLP rainbow artifact I find so distracting. I didn't see the rainbow during the Mitsubishi demo either, and am guessing it was also using sequential laser color illumination with a fast refresh rate, as its presentation slides illustrated.

One other issue with laser color: Both of these demonstrations talked about the laser's ability to far exceed the NTSC color gamut. In fact, the green, red, and blue coordinates of lasers at 620, 530, and 460 nanometers create a color space almost equal to the visible color gamut! All fine and dandy, except that the program material being displayed on these TVs is coded into specific color spaces that are much smaller, such as REC 709 and SMPTE-C.

So it doesn't do any good to exceed the level of green by a magnitude of two or three, nor does it make much sense to push reds into candy-apple territory on such a TV. The smart move is to make sure all of the colors within a specific gamut (and that could include the new DCI cinema color space) are reproduced accurately, something that obviously wasn't happening during the Mitsubishi demo.

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