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At last week’s 70th Autumn Meeting of the Japan Society of Applied Physics (8-11 September), Sharp Corp reported the development of a blue-violet laser (emitting at a wavelength of 405nm for use in Blu-ray Disc recorders) with optical output as high as 500mW under pulsed operation.
Just in June, Sharp started volume production of a Blu-ray laser with 320mW pulsed output that can burn single- and dual-layer discs at 8x speed. Previously, in April 2008, Sharp started production of Blu-ray lasers with pulsed output power of 250mW for recording on dual-layer discs at 4-6x. At that time, Sharp had projected only shipping 350mW lasers by the end of 2009, and 400mW lasers (for multi-layer recording at 8-12x speeds) in 2010.
Picture: Cross section of laser incorporating aluminum oxynitride film.
Sharp enhanced the output power to 500mW by using a new method of processing the edge face of the laser resonator. Normally, the edge face of the laser crystal is protected by a dielectric film. In this case, an aluminum oxynitride (AlON) film was sputtered between the edge face of the laser and the dielectric film, followed by epitaxial growth where the growth axis of the laser epilayers corresponds to that of the AlON crystal. In the past, the crystalline material of the laser was covered just by a non-crystalline dielectric film, so the edge face had a surface state that absorbed laser light, and consequently the crystal was degraded by the heat that was generated. In contrast, the new laser allows more output than was previously possible with just the dielectric alone.
For the new laser structure, Sharp has already verified reliable operation for more than 1000 hours at 80°C with a pulse width of 30ns and an output of 500mW.
The new 500mW laser has the capability of writing at 8x speed on triple- and even quadruple-layer Blu-ray discs. Using current technology (25GB per layer), this would allow 75GB or 100GB recordable discs.
However, Sharp has not decided when to mass produce the new laser because the specifications of triple or more layer Blu-ray disc have not yet been determined. Nevertheless, the firm says that it is ready to commercialize the laser.
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