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Both
Philips and MKM regard the introduction of Double Layer
DVD+R technology as the next important milestone in the
drive
to continually improve and expand the optical data storage
options available to consumers. Users will benefit from the
additional storage capacity of the DVD+R disc as it will
enable them to record 4 hours of DVD-quality video or 16
hours of VHS-quality video, without the need to turn over
the disc. PC users will be able to archive up to 8.5 Gbytes
of computer files on a single disc, which almost doubles
the storage capacity compared with the 4.7Gbytes for the
single-layer DVD+R discs currently available.
The Double Layer DVD+R system uses two thin embedded organic
dye films for data storage separated by a spacer layer
(see figure). Heating with a focused laser beam irreversibly
modifies the physical and chemical structure of each layer
such that the modified areas have different optical properties
to those of their unmodified surroundings. This causes
a variation in reflectivity as the disc rotates to provide
a read-out signal as with commercially pressed read-only
discs.
Initial investigations were started by Philips Research
around 2 years ago at a time when there was general scepticism
throughout the optical storage industry that compatible
Double Layer DVD recordable would ever be possible. Developments
since then, initially by Philips and later in cooperation
with media manufacturer MKM, have dispelled this scepticism
and the new Double Layer DVD+R technology is now fully
endorsed by the DVD+RW Alliance.
“Very soon after the initial developments by Philips,
MKM recognized the potential of this new technology and
contributed its media expertise to help drive the technology
forward,” says Dr Yoshimitsu Kobayashi, CEO of Mitsubishi
Kagaku Media. “The technology is in line with the
strategy of the DVD+RW Alliance which is currently active
in finalizing the new format to bring backward-compatible
Double Layer DVD recording to the consumer.”
A major challenge during development was to maintain compatibility
with the DVD-ROM standard to ensure that the new Double Layer
discs would be playable on commercially available DVD players. “Compatibility
with the installed base of DVD Video players was the key
factor in our research for a Double Layer DVD+R disc,” explains
Dr Frans Greidanus, Senior Vice President of Philips Research. “Although
Double Layer concepts have been proposed before, our team
here at Philips Research was the first to be able to record
on both layers of the dual layer DVD+R disc and play it
back in a standard DVD video player.”
Compatibility has been achieved through the use of a thin
silver-alloy as reflector material in the upper layer giving
a reflectivity from the layer of at least 18% in compliance
with the Double Layer DVD-ROM standard. In addition, the
transmission of the upper recording layer is greater than
50% to allow for read-out and recording of the lower recording
layer. This layer has high power sensitivity since the
upper layer absorbs and reflects part of the incoming light.
It also has a much higher reflectivity (> 50%) which
after double transmission through the upper layer also
results in an apparent layer reflectivity (at the disc
surface) of at least 18%. These high transmission and reflectivity
values have been achieved through careful optimization
of the dye material and deposition, groove shapes and silver
deposition. In addition to optimizing reflectivity, other
parameters such as signal amplitude and tracking signals
were also optimized to ensure full compatibility with current
DVD standards.
The DVD+RW Alliance is setting an aggressive feature and
performance roadmap, and the Double Layer DVD+R format book
is expected to be ready within this year. Recorders for
both the PC and consumer electronics markets are expected
to become available during the course of 2004.
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