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Blue-violet laser achieves high
recording density
Data on an optical disc is recorded and read by
passing a beam from the laser through the lens
and onto a spot on the disc called the beam
spot. Since blue-violet light has a shorter wave-
length than red, it can produce a smaller beam
spot. The result is higher recording density.
Blue-violet lasers with a wavelength of 405
nanometer enable Blu-ray Disc to increase
recording density about 2.6 times, and com-
bined with high-powered lenses, the recording
capacity of Blu-ray Disc is six times that of the
standard DVD.
0.1mm optical cover layer improves
reliability
On a Blu-ray Disc, data is stored at more than
2.5 times the density of a DVD, while the width
of the recording tracks is less than half that of a
DVD. Furthermore, the tracks where the data is
stored are only 0.1mm below the disc surface.
Placing the recording tracks closer to the sur-
face means that Blu-ray Discs are less prone to
problems caused by disc warping and other
factors compared to CDs and DVDs.
High-speed data rate of 36Mbps to accom-
modate digital content
Blu-ray Disc has a data rate of 36Mbps, much
greater than the maximum speed of 24Mbps
in digital HDTV from a broadcasting satellite
(BS). This speed enables Blu-ray Disc to easily
record digital HDTV programs from the BS and
play them with remarkably high-quality picture.
Blu-ray Disc recorder
In April 2003, Sony unveiled the world’s first
Blu-ray Disc recorder. By using the same MPEG-
2TS video recording method used in BS digital
TV broadcasts, this unit can record more than
two hours of BS digital TV programming with
no degradation in picture quality.
The development of three-wavelength
recording/playback optical pickups
that are compatible with Blu-ray Disc,
DVDs and CDs
Sony has developed a three-wavelength record-
ing/playback optical pickup that is compatible
with the Blu-ray Disc, DVD and CD. In addition
to reducing the number of components re-
quired and decreasing its size, Sony is striving to
increase the optical pickup’s reliability and
productivity, in order to rapidly commercialize
this product. As the key component for the
Blu-ray Disc system, this new optical pickup is
positioned to contribute to the expansion of
this market.
Prototype of the newly developed three-wavelength
optical pickup for recording and playback
Optical pickup for conventional DVDs/CDs
(top) and Blu-ray Disc (bottom)
Blu-ray Disc recorder
Success in developing a 25GB optical
disc made of paper
Sony and Toppan Printing Co., Ltd., have suc-
ceeded in developing a 25GB paper optical disc
with a paper content of more than 51%. Part of
the disc uses paper because Blu-ray Discs can be
played and recorded on the 0.1mm surface
layer. The use of paper reduces the need for
plastic, making the discs more environment-
friendly and decreasing manufacturing costs. Cross-licensing agreement for optical
disc-related blue-violet laser diode
patents
Sony and Nichia Corporation from Japan have
agreed to cross-license patents involving the
Blu-ray Disc format’s blue-violet laser diode. This
agreement is expected to open the door to
Sony’s mass-production of blue-violet laser
diodes, a big step that will position it to respond
to expansion in the market for Blu-ray Disc-
format products.
A paper disc
NA 0.85
Optical cover layer
For 0.6mm thickness
(same as in a DVD)
Optical cover layer
For 0.1mm thickness
0.6mm 0.1mm
Track pitch of
0.32m
Substrate
Optical
cover layer
Shortest
recording mark
(0.16m for 23GB;
0.149m for 25GB;
0.138m for 27GB)
Recording
layer
Blu-ray Disc
Substrate
Shortest
recording mark of
0.4 m
Track pitch of
0.74 m
Optical cover layer
Recording layer
Scanning electron
microscope view
DVD-RW
Scanning electron
microscope view
(simplified diagram)
1.2
mm 1.2
mm
DVD Blu-ray Disc
0.85
Lens numerical aperture
(approx. doubles density)
650nm 405nm
Laser wavelength
(raises density approx. 2.6 times)
Comparison of beam spot size
19%100%
0.6
(simplified diagram)