Blue lasers....................
e-town.com
ROSES ARE RED, LASERS ARE BLUE
Waiting for HD-DVD? Keep watching the blue lights.
by Murray Slovick
June 28, 1999 -- Anyone looking for high-definition DVDs had better keep their eyes peeled for blue or violet lasers, because without this new technology, HD-DVDs will remain a fanciful dream. Yet there is hope that the Holy Grail of home theater enthusiasts -- and top manufacturers -- will find its way to the corner consumer electronics store relatively soon.
Why you need blue
The commercialization of blue laser technology is absolutely imperative if home video is to make its next great leap forward. Here's why: laser pickups used in optical storage systems (such as CDs and DVDs) are classified by the color that corresponds to the laser's particular wavelength, which in turn depends on the characteristics of the materials used to generate the laser light.
Red lasers, commonly used in CD players and laser printers, have wavelengths of more than 630 nanometers (nm). Blue lasers are similar to red lasers, but they have a much shorter wavelength that's in the range of 400 nm to 430 nm. Using laser light with shorter wavelengths translates into an increase in the amount of information stored on an optical disc. For example, each time the wavelength of laser light is halved, the corresponding storage media can contain four times more data.
High-definition DVD (HD-DVD) will require a storage capacity more than three times that of current DVDs. Researchers around the world are conducting intense studies of short wavelength semiconductor lasers. In theory, you should be able to store 15 gigabytes (GB) per side on an HD-DVD with a blue laser. Today's red semiconductor lasers, operating at 650 nm, allow 4.7 GB per side on a standard DVD.
Watch out for the little guys
As so often happens with a new technology that promises to shake things up, the established companies are not the ones leading the way. Indeed, the consumer electronics industry was caught off-guard in 1993 when Shuji Nakamura, chief researcher at little-known Nichia Chemical Industries Ltd. of Japan, used gallium nitride (GaN) to build the first working blue laser. Although silicon is the most popular material used to make electronic devices today, compounds such as GaN are a category of semiconductors that perform functions beyond silicon's electronic properties.
Given that the cast of characters in the blue laser race now includes such corporate powerhouses as Matsushita, Sony and Toshiba, it's surprising that Nichia has maintained its technology lead. Last December, the company began shipping engineering samples of a laser diode that emits violet light (which has a shorter wavelength than a blue laser, although optics experts lump violet and blue together as a single technology).
At $2000 each, Nichia's 5-mW output, 400-nm model NLHV500E clearly is not ready for mass production, since laser pickup assembly costs need to be around $1. On the plus side, however, the lasers are reported to have a life span of 10,000 hours, which is sufficient for consumer DVD use.
Nichia researchers are also working on 30-mW output lasers for recordable formats, but additional progress is needed to achieve continuous operation at room temperature (the minimum requirement for a commercial laser). Researchers expect to produce a prototype 30-mW to 50-mW violet laser for rewriteable DVD formats within a year.
Another relatively tiny challenger, North Carolina-based Cree Research, is working on electronic devices formed in silicon carbide (SiC), which can operate at extremely high temperatures and, notably, emit and detect short wavelength light, which makes possible the fabrication of blue light-emitting laser diodes.
Last month Cree formed a strategic partnership with Seattle's Microvision, Inc., the developer of Virtual Retinal Display (VRD) technology, to develop a commercially viable SiC blue laser diode, as well as blue and green light-emitting diodes (LEDs) suitable for scanned-beam display systems. The VRD device rapidly scans a low-power pinpoint beam of colored light onto the retina of the viewer's eye, creating a high-resolution, full-motion image without the use of screens or externally projected images.
The powers that be strike back
Of course, the big boys are not sitting still. Matsushita is heavily committed to blue laser research, and earlier this year reported successfully running a violet GaN laser for 24 hours at room temperature. What's more, Matsushita researchers said that they had succeeded in minimizing the size of the optical focusing spot, a technique required for next-generation DVD systems. According to Matsushita, two hours of HD video (or seven hours of NTSC content) could be stored on a standard-sized DVD using the violet laser.
Matsushita now has two kinds of violet laser light sources under development: the semiconductor laser diode and an earlier, second harmonic generation (SHG) laser, which is now approaching volume production. To produce light in the blue range from the SHG laser, Matsushita starts with a 100-mW output power red laser at 850-nm wavelength and passes it through an optical waveguide to generate a second harmonic beam at 425 nm.
In terms of cost, the SHG laser is more expensive than semiconductor lasers produced in volume, but it promises outstanding performance. The prototype 425-nm SHG laser produces 26 mW of power, measures just 13 x 5 x 1.5 mm and can be used as a rewriteable optical pickup head. By using both the "grooves" and "lands" of a phase-change optical disc and etching data marks as short as 0.24 microns (µm), such a device can record 15 GB of data on each side of a 5-inch disc.
Matsushita showed the basic idea two years ago, demonstrating then that the SHG laser head can read both 15 GB high-density phase-change disks as well as signals recorded on DVD-ROM and DVD-RAM discs with the same 0.6mm substrate thickness, making future HD-DVD systems read-compatible with current DVDs.
Most optical storage experts believe that commercial HD-DVD players are still several years away. In the meantime, research continues. At the International Conference on Electro-Optics and Lasers last month, University of Tokyo researchers announced the room temperature operation of Indium Gallium Nitride (InGaN)-based vertical-cavity surface-emitting lasers (VCSELs) at blue wavelengths. Although a mouthful of jargon, it means blue lasers are creeping out of the labs. And they are the consumers' best hope for high-definition DVDs.
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