(Nikkei BP Group)
(No.1 High-Tech News Site in Japanese)
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| Matsushita Develops 8.5GB Rewritable Optical Disk
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September 16, 1998 (TOKYO) -- Matsushita Electric Industrial Co., Ltd.
said it developed a rewritable, phase-change optical disk with double
recording layers (dual-layer).
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It is a new technology for a DVD-RAM disk that can store 8.5GB per side,
company officials said. Current DVD-RAM disks have a storage capacity
of 2.6GB on a single side.
DVD disks with dual-layers already have been used for read-only, or playback,
disks. It reportedly was difficult to create dual-layer rewritable optical
disks.
The light absorption factor of the recording layers must be increased
to realize rewritable optical disks, because heat energy from a laser
is used to store data on them. But, this increase makes the outer layer
absorb more light and the inner layer, which is further away from the
laser head, does not get sufficient light.
If the absorption factor is decreased, there will not be enough light
for the outer layer, and thus, so a high-power laser becomes necessary.
It had been assumed that the rewritable dual-layer system needs a semiconductor
laser with an output at least twice as high as that of read-only optical
disks.
Matsushita developed a dual-layer system that needs almost the same level
of laser output to rewrite on each of the recording layers, and reads
out almost the same level of data from each of the two layers.
This technology is called balanced structure random access memory (BS-RAM).
It uses germanium-antimony-tellurium (GeSbTe), a material that has been
used for phase-change recording films.
The company said the laser output needed for the rewriting mode has been
reduced to approximately 13mW, about 1.2 times that of conventional
DVD-RAM disks. The optical system used for the experiments was the same
as that for existing DVD-RAM drives. Its light-source wavelength was
658nm, and the numerical aperture of the objective lens was 0.6.
That means a large storage capacity of 8.5GB for a single side could
be realized by using existing DVD-RAM drives with only a few modifications.
(Nikkei Electronics)
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