is Blu Ray Technology?
Background of Blu-ray Disc Technology
Blue laser precision
The Blu-ray Disc recording layer
CD, DVD, BD : A Comparison
HD – DVD
HD – DVD vs BD
Uses and Necessity
What is Blu Ray technology?
Blu-ray, also known as Blu-ray Disc (BD) is the
name of a next-generation optical disc format.
The format was developed to enable recording,
rewriting and playback of high-definition
television (HDTV). Blu-ray makes it possible to
record over 2 hours of HDTV, or more than 13
hours of SDTV on a 27GB disc. There are also
plans for higher capacity discs that are expected
to hold up to 54GB of data.
Background of BD
The format was developed by the Blu-ray Disc Founders
(BDF), a group of eleven leading consumer electronics
LG Electronics Inc.
Matsushita Electric Industrial Co., Ltd.
Mitsubishi Electric Corporation
Royal Philips Electronics
Samsung Electronics Co., Ltd.
In January 2004, the world's two largest PC
manufacturers, HP and Dell, were accepted into the
group to help further develop the format for PC data
Blue laser precision
In order to play back full- length feature movies, DVD-Video discs store
digitally encoded video and audio information in the form of ‘pits’ that are
impressed into a recording track that spirals out from the center of the disc
to its edge. The different reflectivity of the pits enables the laser pick-up to
read information from the disc.
A fundamental law of physics states that the diameter of the laser spot is
directly proportional to the wavelength of the laser light and inversely
proportional to the numerical aperture of the objective lens (a figure that
depends on the diameter of the lens, its radius of curvature and the material
from which it is made). To reduce the size of the laser spot you can
therefore use a shorter wavelength laser or increase the numerical aperture
of the lens. Better still, you can do both, which is the approach adopted in
the Blu-ray Disc specification. It results in the ultimate optical disc format,
with the lowest achievable wavelength and the highest NA that is achievable
under industrial conditions.
Blu-ray Disc drives use a 405 nm blue laser and a lens with a numerical
aperture of 0.85, instead of the 650 nm red laser and 0.60 numerical
aperture lens used in current DVD drives.
Blu-ray Disc recording layer
The recording layer in a Blu-ray Disc sits on the surface
of a 1.1-mm thick plastic substrate, protected by a 0.1mm thick cover layer. With the substrate material no
longer in the optical pathway, birefringence problems are
eliminated. In addition, the closer proximity of the
recording layer to the drive’s objective lens reduces disc
tilt sensitivity. This only leaves the problem of surface
scratching and fingerprints, which can be prevented by
applying a specifically developed, innovative hard-coat
on top of the cover layer. This protective coat is hard
enough to prevent accidental abrasions and also allows
fingerprints to be removed by wiping the disc with a
tissue. Both the cover layer and hard coat can be applied
by low-cost manufacturing techniques such as spincoating.
Despite the fact that Blu-ray Discs require the application of a cover layer
and an optional hard coat, this should have little overall impact on disc
DVD production.currently requires the injection molding of two 0.6-mm discs
(one of which must meet stringent birefringence limits), the application of a
recording layer to one of the discs, and a gluing operation to bond the two
Blu-ray Discs only require the injection molding of a single 1.1- mm
substrate with non-critical optical characteristics, which reduces injection
molding costs. This cost saving offsets the additional cost of applying the
cover layer and hard coat, while the techniques used for applying the
recording layer remain the same.
As a result, the overall cost of manufacturing a Blu-ray Disc will be no more
expensive than producing a DVD, while some equipment such as injection
molding machines can actually be used more efficiently. Because of the
thinness of the cover layer, surface- flatness tolerances become far less
stringent, while relative cover-thickness tolerances remain almost the same
as for current DVD production.
Although no blue- laser disc will be readable using a red-laser, combined
blue/red drives will be perfectly feasible. Servo- mechanisms that are
capable of meeting Blu-ray Disc’s track positioning will be more than
capable of meeting DVD requirements, while it should also be possible for
both the blue and red laser to share a major part of the optical pathway. The
relatively long development time for new drives means that drive
manufacturers must stay well ahead of developments in optical storage so
that they can get products to market quickly once a particular format gains
market acceptance. With respect to Blu-ray Disc, several leading drive
manufacturers have already demonstrated drives for consumer products
such as video recorders that can read and write DVD and Blu-ray Discs.
According to the Blu-ray Disc v1.0 specification, 1x speed will require a
36Mbps data transfer rate, which means it will take about 1 hour and 40
minutes to record 27GB. The Blu-ray Disc Founders are currently working
on the v2.0 specification, which will support 2x speed to cut the time it takes
to copy content from one disc to another in half. In the future, the data
transfer rate is expected to be raised to 8x or more.
HD - DVD
An alternative version has been developed by Toshiba and NEC and a
provisional specification approved by the DVD Forum. The original name
was AOD (Advanced Optical Disc).
There are three versions in development.
HD DVD-ROM discs are pre-recorded and offer a capacity of 15 GB per
layer per side. These can be used for distributing HD movies.
HD DVD-RW discs are re-writable and can be used to record 20 GB per
side for re-writable versions.
HD DVD-R discs are write-once recordable discs with a capacity of 15
GB per side.
Like Blu-ray discs they need a blue laser of 405 nm wavelength, but are
physically similar to DVD discs, as they use a cover layer of 0.6 mm.
Therefore HD DVD discs can be manufactured using existing DVD lines,
and existing UV mastering equipment.
HD DVD vs BD
It is not yet clear which format will win. Blu-ray currently seems to have the
most support, but HD DVD presents fewer manufacturing problems,
particularly for pre-recorded versions. HD DVD can be mastered and
replicated with current equipment, while Blu-ray requires new equipment
and processes for both.
Uses and Necessity
As HDTV becomes more widespread, the consumer demand for
recording HDTV programming will rise. Blu-ray was designed with
this application in mind and enables direct recording of the MPEG-2
TS (Transport Stream) used by digital broadcasts, which makes it
highly compatible with global standards for digital television. This
means that HDTV broadcasts can be recorded directly to the disc
without any extra processing or quality loss. To handle the
increased amount of data required for HDTV, Blu-ray employs a
36Mbps data transfer rate, which is more than enough to record and
playback HDTV while maintaining the original picture quality. In
addition, by fully utilizing an optical disc's random accessing
features, it's possible to playback video on a disc while
simultaneously recording high-definition video.
Blu-ray is expected to replace VCRs and current DVD technology
within a few years. The format is also likely to become a standard
for PC data storage and high-definition movies in the future.