The lasers...............................
techweb.cmp.com
Red lasers due in time for DVD-RAM drive debut
By Yoshiko Hara
MAKUHARI, Japan -- Laser manufacturers showed off high-power red lasers at the recent InterOpt '97 here, promising that the parts--key components for the coming wave of DVD-RAM drives--will be available in volume in time for the drives' year-end market introduction.
Mitsubishi Electric Corp. plans to begin what would be the industry's first volume production of high-power red lasers. Competing vendors at the show acknowledged that Mitsubishi is ahead of the pack; most are sampling product now, with plans for volume production later this year.
The bulk of the parts feature a wavelength of around 658 nm, rather than 650 nm as specified in the DVD-RAM document. Engineers at the show said that the tolerance is a necessary margin to ensure stable emissions, and they claimed to be negotiating with drive engineers to convince them to implement the higher wavelength in their drive designs.
All of the lasers exhibited were also said to achieve less than 130 dB of relative-intensity noise (RIN). That level would meet requirements for practical use.
Mitsubishi has been sampling its lasers at $44 apiece since May. Output power of the 658-nm-wavelength devices is 35 mW continuous and 50 mW pulsed.The parts operate off 2.7 V and 85 mA.
The company is betting that its head start will help it grab a 50 percent share of the total market for high-power red lasers by 2000, said Masao Aiga, project manager for Mitsubishi's opto-device project. The Electronic Industries Association of Japan projected in May that the DVD market will grow to 30 million units worldwide by the turn of the century, with computer peripherals, including DVD-RAM drives, expected to account for nearly 70 percent of those units.
Mitsubishi plans to ramp production from next month's startup levels to 20,000 units per month by this September, and then to 200,000 units per month by September 1998. "Less than 1,000 yen [around $8.80] is our target price when the production volume reaches 200,000 units,"said Aiga.
Mitsubishi attributes its ability to ramp production quickly to its adoption of 3-inch GaAs wafers--the largest available substrates now being used for the parts. Conventionally, high-power lasers have been manufactured on 25-x-30-mm2 substrates. "About 15,000 lasers can be cut out from the 3-inch wafer, while the square wafer can produce about 2,000 devices at most," said Aiga.
Mitsubishi's laser features a facet-with-window structure, which is claimed to prevent facet breakage. Doping zinc onto the active layer near the facet causes the crystalline structure of the end of the active layer to become transparent to laser light. The window structure is claimed to guard the facets against breakage at more than 150 mW of output power, whereas 90 mW of output will typically break a facet without the window feature.
Industry experts at the show said the technology will be essential for the volume production of lasers.
"The idea itself has existed for a long time, but implementation on a volume production line is another matter," said Aiga. Mitsubishi previously had used the technology for a 685-nm laser with a 30-mW to 60-mW output. "We have much experience with solid-phase diffusion technology, which is used to diffuse zinc in the active layer," Aiga said.
Increasing the facets' durability is claimed to give the lasers a life span of 10,000 MTTF (mean time to failure) at 60C.
Hitachi Ltd. is believed to be running second in the race to bring high-power red lasers to market. October production is planned for Hitachi's entry, which is sampling now.
The company is focusing the efforts of its various subsidiaries on DVD-product development, with plans to grow the total business to about $9 billion (1 trillion yen) annually.
"Major components for DVD-RAM drives were developed within Hitachi groups," Osamu Numata, general manager of Hitachi's Optical Data Storage Systems Operation, said in April when the first DVD-RAM drives were announced.
High-power lasers are certainly one of those essential components. With an eye toward extending device life by minimizing operating temperatures, Hitachi engineers are focusing on lowering the operating current of the laser. So far, they've managed to bring it down to 90 mW.
Hitachi's laser is evaporated on a slanted substrate to widen the bandgap and thereby shorten the wavelength.
The tentative specifications are for a 660-nm wavelength laser in a 5.6-mm-diameter package emitting 35 mW continuously and 50 mW pulsed, over an operating temperature range of -10C to +60C.
Hitachi guarantees less than 1 percent failure in 1,000 hours at 60C. "[Other] vendors would say a 10,000-hour life, but it is a simulated MTTF life, and the failure rate over time is uncontrollable," an Hitachi spokesman said.
Toshiba Corp., which has spearheaded the DVD format in tandem with Matsushita Electric Industrial Co. Ltd., also plans production volumes this year for a red laser it is sampling now.
Toshiba intends to offer its laser with high-speed front automatic power control (APC). The bipolar APC detects and feeds back the wavelength changes to stabilize the wavelength and thereby minimize noise. APC is already used in some magneto-optical drives and eliminates the bulky circuitry otherwise required for high-frequency modulation.
A Toshiba spokesman said the company's high-power red lasers will be manufactured on the same line as its 5-mW lasers to speed the production ramp once development is complete.
Matsushita, meanwhile, has developed a red-laser pickup for DVD-RAM drives. That laser is a 650-nm device with 30-mW power. Sakon Nagasaki, director of Matsushita DVD Business Planning Office, said when the device was developed in May that the company would aggressively sell the pickup on the merchant market. But no marketing plan has yet been disclosed. Consumption of the laser and pickup has so far been limited to internal customers.
Sharp Electronics Corp. came to the exhibit with a 30-mW 635-nm laser for write-once heads that's being codeveloped with Pioneer. "We are focusing on increasing the power of continuous emission. So far, no sample is available yet," said a Sharp spokesman.
The early leader in the market for shorter wavelength lasers has been Sanyo Electric Co. Ltd., which announced a 635-nm, 5-mW device in 1994. Last March, Sanyo announced another 635-nm laser, which operates up to 80C for DVD-ROM players in automobile-navigation systems.
Sanyo entered volume production on 635-nm lasers in December and, according to a spokeswoman, is producing 200,000 units a month, largely for pointer and non-pickup applications. A 30-mW type is also included in the Sanyo portfolio, but the company is watching the market's development before making plans for the part, the spokeswoman said. |
