"We will consider the enhancement of laser power and shipment plans in accordance with the trends of standards relating to high-speed recording," said Mototaka Taneya, division deputy general manager of Compound Semiconductor Systems Division at the Electronic Components (Elecom) Group in Sharp.
Assuming recording will be done at high-speed on a four-layer disc, the company will strengthen its lineup of products with a laser power of 300mW or higher. In order to enhance the laser power, the company will improve the formation technology of end surface from which the laser beam is emitted, the crystal growth technology and the ridge formation technology.
Among these, the technology to form an end face that can avoid degradation even at a high power is expected to be the most important.
Along with the power enhancement, Sharp is focused on the size reduction of blue-violet laser diode modules. The company provides a 5.6mm diameter CAN package for use in Blu-ray Disc devices for desktop computers and recorders (so-called half-height drive), and a 3.3mm diameter CAN package for use in notebook computers (so-called slim drive).
The 250mW product, released in February 2008, is also prepared in a 3.3mm package, which the company claims is "the smallest in the industry."
In the market for optical devices for personal computers, it is expected that the shipment of slim drives will surpass that of half-height drives in 2009. Thus, the company expects that the demand for small packages will continue to grow in the future.
Nevertheless, it seems to be quite difficult to reduce the diameter of the package to less than 3.3mm. The company uses a frame package with a thickness of only 1.8mm for red laser diodes. However, it is difficult to apply this package to blue-violet laser diodes due to the lack of airtightness inside the package. Therefore, "the frame package will not be used soon," said Taneya of Sharp.
The blue-violet laser beam decomposes air-borne materials because of its short emission wavelength. Thus, when the outer air comes inside the package, the decomposition of materials intensifies, resulting in contamination such as the adhesion of carbon, etc on the semiconductor laser chip and so on. This causes the degradation of light output, which shortens the diode life. Such contamination will not occur in a CAN package, which can maintain airtightness.
Upper limit for red laser diode 400mW
Sharp will ship mass-produced red laser diodes with a light output of 400mW under pulsed operation in April 2008. This laser diode reportedly enables 20x high-speed recording on double layer discs.
According to the company, "the goal of light output will be 400mW for the time being" (Taneya). Now that standards for up to 16x high-speed recording have been set, drive manufacturers and other players are reportedly making decisions on their own as to whether to make products compatible with recording at speeds higher than 16x.
It is less likely for Sharp to enhance light output to higher than 400mW unless drive manufacturers attempt the production of 20x-enabled products.
The oscillator of the 400mW product is about 2mm long and the chip width is about 0.1mm. The laser emission surface is 2μm horizontally and 1μm vertically.
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