INTRODUCTION
Blu-ray, also known as Blu-ray Disc (BD) is the name of a
next-generation optical disc format jointly developed by the Blu-ray Disc
Association (BDA), a group of leading consumer electronics and PC companies.
Namely,
(1) Dell
(2) HP
(3) Hitachi
(4) LG Electronics
(5) Matsushita
Electrical Industrial Co Ltd (Panasonic)
(6) Mitsubishi
Electric Corporation
(7) Pioneer
Corporation
(8) Royal
Philips Electronics
(9) Samsung
Electronics Co Ltd
(10)
Sharp Corporation
(11)Sony Corporation
(12)TDK Corporation
(13)Thomson.
The format was developed to enable recording, rewriting and
playback of high-definition video (HD), as well as storing large amounts of
data. A single-layer Blu-ray Disc can hold 25GB, which can be used to record
over 2 hours of HDTV or more than 13 hours of standard-definition TV. There are
also dual-layer versions of the discs that can hold 50GB.
The name Blu-ray is derived from the underlying technology, which
utilizes a blue-violet laser to read and write data. The name is a combination
of "Blue" and optical ray "Ray". According to the Blu-ray
Disc Association, the spelling of "Blu-ray" is not a mistake. The
character "e" is intentionally left out because a daily-used term
can't be registered as a trademark.
SCOPE
OF SYSTEM
A novel method of optical data storage
could soon be used to hold a terabyte of data on a disk the size of a normal
DVD, according to an international team of researchers.
The researchers realized that the polarity of light might also be
used to encode information. They developed a type of disk that incorporates
angled ridges within the pits in order to subtly alter the polarity of the
light that gets reflected. This can be used to store 10 times’ more data than
is currently possible, they say.
In the new system, light polarized in a single direction is beamed
onto the surface of the disk. Some bounces back with a polarity at 90 degrees
to that of the original beam. By measuring how much light comes back in each of
the two directions, it is possible to work out the precise angle of the slope.
Using the technique, the researchers think it should be possible
to create disks capable of holding 250 gigabytes in a single layer. This is
enough to store 118 hours of video, which could allow every episode of
long-running television shows to be put on one disk. Using a four-layer disk
would mean a terabyte could be stored.
The researchers say information could be encoded using 10
different angles of slope, corresponding to 10 bits of information in each
indent. Provided funding can be found, the team believes it should take about
five years to perfect the technology and a commercial version could be
available by 2010.
Typically, optical storage technology based on the
polarity of light are more difficult to implement and so more expensive this
could be seen as a bonus. "Creating pirate disks would be very difficult
unless you bought the mastering equipment," he says.
The Blu-ray Disc Association (BDA)
and TDK have successfully developed a new hard-coating technology dubbed
“Derbies” that makes the discs even more resistant to scratches and
fingerprints than existing DVDs, without requiring a cartridge to protect the
discs. This development will enable manufacturers to downsize PC drives and
lower their overall media production costs.
HD-DVD
Vs Blu-Ray Disk
Ø Blu-Ray
has slightly more companies with bigger aggregate size. There is not enough
information to say if anyone is in the lead, but with major electronics and
entertainment companies in each camp, there is sure to be a pitched battle.
Ø Technically speaking, both HD-DVD and Blu-Ray
would have enough capacity to hold the same ultra-high quality movies. (With
stunning 1920x1080 resolution, a lot of people will have to upgrade their TV
sets too see it, even recently purchased ones.)
Ø The manufacturing process of HD-DVD requires
little new investment, making the format cheaper to the consumer. Though it is
more expensive, the Blu-Ray disk holds sixty-seven percent more data.
Ø
The basic
disadvantage of the Blu-Ray format is that it requires a new manufacturing
infrastructure resulting in increased expense while implementation could prove
a long-term process. In addition, the Blu-ray Disk format lacks backward
compatibility with current DVDs.
IMPLEMENTATION
A prime supporters of Blu-ray Disc has already developed
Professional Disc. The format is available in two variants and is targeted at
the specific markets of high-definition broadcast quality video and data
archiving and storage. The BDZ-S77 is currently available in the Japanese
market, but there are not any plans for launching the recorder overseas.
Several Japanese companies, including Sony, Hitachi Maxell and TDK, already
offer blank Blu-Ray disc media.
Blu-Ray media makes use of a completely new technology that
requires new advanced compression algorithms, and is totally different from
either DVD or HD-DVD (AOD). It will therefore require new facilities for the
manufacture of the discs. Blu-Ray also makes use of a highly specialized high
numerical aperture (0.85) lens and what is called near-field recording
technology, using a single platter 1.1mm thick, with a special 0.1 focusing
over layer on the active side of the disc. Both HD-DVD and Blu-Ray use 405nm
blue-violet lasers for writing and reading.
Blu-Ray was initially targeted at recording of high-definition
video. However, the latest addition of Hewlett-Packard and Dell to the format
steering committee is expected to result in a widening of its target market to
include the computing space.
By reducing the
wavelength of laser light, from red to violet, it is possible to make a
narrower “beam spot”, thus enabling higher recording densities. BD employs a
blue laser with a wavelength of just 405nm, enabling a data density some 2.6
times that of the red laser technology used for conventional optical media.
Moreover, the powerful objective lens (used for focusing the laser beam) has a
numerical aperture of 0.85 - greater than that used for DVDs (NA: 0.6) and MO
discs (NA: 0.575). The resulting narrow beam further doubles recording density.
As a result, track pitch is just 0.32µm, making it possible to record as much
as 23GB on one side of a disc.
LITERATURE REVIEW
By adopting a 405nm blue-violet semiconductor laser, with a 0.85NA
field lens and a 0.1mm optical transmittance protection disc layer structure,
it can record up to 27GB video data on a single sided 12cm phase change disc.
This means that 2 hours of digital high definition video and more than 13 hours
of standard TV broadcasting (VHS/standard definition picture quality, 3.8Mbps)
can be recorded on a disc.
Blu-ray
Disc (BRD) – the next generation of optical discs for storing high-definition
movies, photos and other digital content – will have by far the highest
capacity of any optical disc storage format ever developed for consumers.
Blu-ray Disc holds up to 25 gigabytes of data or high definition video on a
single-layer disc and up to 50 gigabytes on a dual-layer disc. The format will
also offer a robust, comprehensive content protection system that includes
secure AES 128-bit encryption. The key applications of Blu-ray Disc, with its huge
storage capacity, are recording and playback of high definition video. Blu-ray
Disc is also suitable for a variety of applications including PC data storage
and is the perfect storage medium to enable digital convergence bridging
between PC applications and the living room. The Blu-ray Disc specification v1.0 provides four formats:
# BD-ROM: a read-only format
developed for prerecorded content
# BD-R: a write-once format
developed for PC data storage
# BD-RW: a rewritable format
developed for PC data storage
# BD-RE: a rewritable format
developed for HDTV recording
Main Specifications
·
Recording capacity: 23.3GB/25GB/27GB
·
Laser wavelength: 405nm (blue-violet laser)
·
Lens numerical aperture (NA): 0.85
·
Data transfer rate: 36Mbps
·
Disc diameter: 120mm
·
Disc thickness: 1.2mm (optical transmittance
protection layer: 0.1mm)
·
Recording format: Phase change recording
·
Tracking format: Groove recording
·
Tracking pitch: 0.32um
·
Shortest pit length: 0.160/0.149/0.138um
·
Recording phase density: 16.8/18.0/19.5Gbit/inch2
·
Video recording format: MPEG2 video
·
Audio recording format: AC3, MPEG1, Layer2, etc.
·
Video and audio multiplexing format: MPEG2
transport stream
·
Cartridge
dimension: Approximately 129 x 131 x 7mm
·
Modulation:
1.7 PP (Parity preserve/prohibit RMTR)
First attempts have already
been made towards violet emitting semiconductor materials like gallium-nitride
or zincselenide. At least 1999 the Japanese chemics manufacturer Nichia was
able to offer the first 5mW laser diodes at 405nm based on GaN, developed under
the scientific leadership of S. Nakamura. CDs typically use 1.6-micrometer track pitch, which is the radial distance between turns of the spiral tracks. Data marks are nearly one-half as wide as the track pitch. Lengths of data marks and spacing between marks are determined by the encoding scheme used to translate user data into mark patterns along each track. Information is encoded on a normal CD in the form of microscopic indents on the surface of the disk. The presence or absence of an indent corresponds to a binary piece of information - a ‘1’ or a ‘0’. . Indents are detected by beaming light onto a disk with a laser and measuring the amount of light that bounces back. Width of the CD laser spot is slightly smaller than the track pitch. Blu Ray media are similar to CD media in the context of above, except track pitch is smaller (0.32 micrometers), data marks are shorter and narrower, and the laser spot diameter s is smaller and blue laser is used. Since there are more data marks per unit area on a BD compared to a CD, the BD can hold more data.
Writing Data on a BD
The process for exposing data marks on a recordable optical disk is shown for CD, which similar to that is used for BD except NA of the lens used is 0.85, and laser is blue with wavelength 0.405 nm. Here an input stream of digital information is converted with an encoder and modulator into a drive signal for a laser source. The laser source emits an intense light beam that is directed and focused onto the surface by the objective lens. As the surface moves under the scanning spot, energy from the intense scan spot is absorbed, and a small, localized region heats up. The surface, under the influence of heat beyond a critical writing threshold, changes its reflective properties. Modulation of the intense light beam is synchronous with the drive signal, so a circular track of data marks is formed as the surface rotates. The scan spot is moved slightly as the surface rotates to allow another track to be written on new media during the next revolution. As shown in the figure to get NA 0.85 in BD two lenses are kept.
Data marks on prerecorded BDs are
fabricated by first making a master disk with the appropriate data-mark pattern.
Masters for prerecorded BDs are often exposed in a similar manner to exposing
data marks on recordable optical disks, except that the light-sensitive layer
is designed
to produce pits in the master that serve as data marks
in the replicas. Inexpensive replicas of the master are
made with
injection-molding equipment.
Reading data from a BD
Laser irradiance for BD
Ideally, maximum irradiance is located at the
recording material, along with the smallest spot size s. As the distance
increases away from the ideal focus, the spot size increases and the peak
irradiance decreases. A defocus distance z of only a few micrometers
dramatically reduces peak irradiance and increases spot size. A formula used to
estimate the ideal spot size at best focus is S = (0.6)/ (sin ),
where is the marginal ray angle of the illumination optics, as shown in Figure
shown for writing data on a BD. Spot size S is the full width of the
irradiance distribution at the 1/e2 (13.5%) irradiance level relative to the peak. The value of
sin is often called the numerical aperture or NA of the optical
system. For example, BD systems exhibit = 0.405 micrometers and NA =
0.85, which produce a spot size of 0.28 micrometers.
Bit Error Rate
Instead of focusing directly on the recording surface,
optical disks focus through a protective layer, for a simple CD-ROM. The
protective layer prevents dust and other contamination from directly
obstructing the laser spot at the data marks. Instead, the out-of-focus
contamination only partially obscures the laser focus cone, and data can
usually be recovered reliably. Figure below displays the raw bit error rate
(BER) from a contaminated surface as a function of effective layer thickness
for a NA = 0.5 optical system. As
the protective layer gets thinner, the error rate increases to an unacceptable
threshold due to obscuration of the laser beam. This sensitivity decreases as NA
increases; due to the smaller defocus range associated with these systems.
And this technique is used in BD to decrease the
BER; lens with
higher NA = 0.85 is used. The protective layer had to be made thinner, because
the sensitivity to thickness variations and disk tilt is high due to higher NA
of BD systems.
Disk Tilt and Thickness Variation in BD
BD systems are
sensitive to changes in substrate thickness and disk tilt due to high NA. Manufacturing
variations create thickness nonuniformities, which are usually a small
percentage of the total disk thickness. Motor instabilities induce tilt as the
disk spins. If
the disc is not perfectly flat and perpendicular to the laser axis, the beam
can become distorted, a condition known as disc tilt. A BD optical spot degraded by a disk thickness variation
is shown in Figure ‘B’, as compared to an ideal focused spot in Figure ‘A’.
Energy from the central portion of the spot is redistributed to concentric
rings, which degrade the quality of the read out signal. This effect is called spherical
aberration. Figure ‘C’ shows an optical spot degraded from disk tilt.
Energy redistributes asymmetrically, which also degrades the read out signal.
Tilt causes coma, which is another form of aberration.
Sensitivity of the spot to degradation from thickness
variations and disk tilt is plotted in Figure below as a function of total
protective layer thickness for two values of NA. In order to limit these
effects, the substrate is made as thin as possible without sacrificing
contamination protection.
Thus as shown in the graph effect of
disk tilt is reduced considerably in BD systems and we easily readout the data
even if there is slight nonuniformity in the thickness of the protective layer
and this is other advantage of having higher NA. The overall thickness of the
120mm disc is 1.2mm, the same as that of a DVD disc. However, the recording
layer has a cover layer of just 0.1mm thickness in BD. This effectively
decreases the margin of error when the disc tilts or bends. Tilt tolerance is
thus significantly higher than that for conventional optical discs, enhancing
reliability for read/write operations. Comparison of the effect of disk tilt is
shown in the figure below. Both the systems have NA = 0.85, but thickness of
the protective layers are different. System having 0.1 mm cover layer is BD
while other one is DVD (which is HD-DVD). It is clearly seen that BD system is
more sensitive to disk tilt than DVD.
Disk structure of BD
Disk structure parameters are user data capacity, minimum
channel bit length and track-to-track spacing. A potential implementation of
the Blu-Ray disk is shown in Figure above, where the protective layers on each
side are very thin at 0.1 mm. User data capacity is around 23 to 27 GB. Channel
bit length is 0.047 – 0.053 m.
Track to track spacing i.e. track pitch is 0.32 m. In this case, data are recorded on the substrate, which
does not serve as the protective layer. Instead, a protective layer resin is
spun on and hardened or a thin protective sheet is bonded on each side of the
substrate. Because of the thin protective layer, the Blu-Ray disk should be
used with a cartridge. Violet emitting
semiconductor materials like gallium-nitride or zincselenide are used for the
laser.
Data Management for BD
The logical organization of data on the disk and how those data are used are considerations for data management. Data management considerations have important implications in the application of optical disk technology to storage for HDTV. For example, simply using a more advanced error correction scheme on DVDs allows a 30% higher disk capacity compared to CDs. Data rate, video format, bit-rate scheme and HDTV play time are all data management issues.
There is a basic difference in data management between CDs
and BDs. Since CDs were designed for audio, data are managed in a manner
similar to data management for magnetic tape. Long, contiguous files are used
that are not easily subdivided and written in a random access pattern.
Efficient data retrieval is accomplished when these long files are read out in
a contiguous fashion. To be sure, CDs are much more efficient that magnetic
tape for pseudorandom access, but the management philosophy is the same. On the
other hand, BDs are more like magnetic hard disks, where the file structure is
designed to be used in random-access architecture. That is, efficient recovery
of variable length files is achieved. In addition, the original error
correction strategy for CDs was designed for error concealment when listening
to audio, where BDs utilize true error correction.
Fixed-rate schemes, like magnetic tape, supply data at a
constant rate, no matter what the requirements of the scene. During fast-moving
scenes, the data stream from the tape supplies an adequate data rate. The tape
speed and data rate for these devices are set by the upper limit of the scene
requirements. Since the tape does not slow down during slower scenes, the data
stream is ‘padded’ at these times with useless information that takes up
valuable storage area on the tape. Overall, the random-access architecture of
optical disks is a much more efficient way to use the available storage area.
That is, optical disks do not require as many gigabytes of user data capacity
for an equivalent length and quality HDTV presentation.
The Advanced Optical Disk exhibits acceptable data rate and
reasonable user data capacity for up to two hours of HDTV per side compressed
with variable bit-rate MPEG-2. Blu-ray has slightly higher capacity and data
rate. The two-hour playtime for HDTV with Blu-Ray is really a specification for
real-time recording, which is not easily compressed into an efficient
variable-rate scheme. Blu-Ray easily provides two hours or longer of
prerecorded HDTV per side compressed with MPEG-2. MPEG-2 is a technique for compressing
video data and replaying the data associated with certain rules that are
defined in the MPEG-2 specifications.
The action of the optical disk system is not to compress
data or interpret the video information rules. Instead, the optical disk system
only stores and retrieves data on command from the video operating system.
Therefore, as video operating systems and associated compression technology
become more advanced, no fundamental changes are required to the optical disk
system. MPEG-4 technology is an advanced video compression scheme that utilizes
advanced pre-filtering and post-filtering, in addition to a rule-based
algorithm. Estimated improvement in compression is a around a factor of three
beyond MPEG-2.
Quality control in production of BD
As an important step in establishing new formats the
company groups define detailed standards (coloured books), which contain the
physical properties of the disks, the specifications of the disk drives as well
as the exact data structure. Only such strict definitions guarantee that every
disk can be read back on every drive – if both are according to the standard.
For the disk replicators, which replicate disk with highly efficient molding
and coating processes the quality Assurance is an important and central control
task.
In quality testing
online tests and offline tests can be distinguished: In an online process for a
few seconds every disk is checked for its physical properties during the
manufacturing (e.g. substrate defects, substrate thickness, deformation,
reflectivity). Therefore this kind of test is called physical test. In the
complementary in electrical test, it is checked whether all data can be read
back completely and correctly requiring to fully playing a random sample disk
on a drive. The time effort makes this test to be performed offline only.
The measurement parameters of the electrical test are
divided as follows:
1.
RF
parameters, i.e. the structure of the electrical high frequency signal that is
created by the reflected laser beam at
place of the detector.
2.
Digital
errors, i.e. how precisely the data can be extracted from the disk.
3.
Physical
parameters, i.e. the precision of the place of the different storage areas
on the disk surface.
4.
Jitter-analysis,
i.e. fluctuations of the shape of the data structures.
5.
Servo
parameters, i.e. the quality of the signals used to keep the laser in focus
and on track.
A typical parameter is the ratio I8/I8H. It tells how well
the data structures (called pits) provide a negative interference (obstruction)
of the back-reflected light. The superimposed measurement signal (figure below)
shows the sinusoidal waveforms, that are generated by the pits if the scope
trigger is set on the leading edge of each pit (this special picture is called
eyepattern): Short pits generate a smaller amplitude modulation than longer
pits. The longest pits with a duration of 8 internal clock units define the
maximum amplitude modulation I8/I8H, which should be > 0.40 according to the
standard. This value needs to be measured over the whole disk surface and tells
whether the molding process was uniform over the whole disk.
A Reference Drive for Blu-ray
Important question is on which type
of drive or player such electrical tests should be performed. Already in the
early days of CD it became clear that the vast differences between the drives
of different manufacturers – even amongst a drive generation of the same
manufacturer – generate very differing measurement results. But since the CD
community was very dependent on comparable measurements it decided to define a
certain drive as reference. In case of CD the Philips CDM-4 was chosen, in case
of DVD the Pulstec SDP-1000 became reference. Toptica Photonics AG together
with the partner AudioDev in Malmoe/ Sweden have set themselves the target to
develop a reference drive for the next generation optical disks.
The two
companies say such paper-based disks will be cheaper to make and less
environmentally harmful.
The substrate is normally made from a polycarbonate plastic, which
is ultimately derived from crude oil. But Sony and Toppan Printing have
replaced this with a mixture of paper and another polymer.
The
resulting prototype consists of 51 per cent paper but is still capable of
storing up
to 25 gigabytes of data. Regular DVDs have less than half this capacity. “Oil
is a limited resource but paper can be recycled,” said Sony spokesman Taro
Takamine. "One of the initial advantages of the paper disk will be a
decrease in the amount of raw material needed to produce a disk." Another
benefit of the paper-based disks is ease of disposal, according to Hideaki
Kawai, head of Toppan's R&D division "Since a paper disk can be cut by
scissors easily, it's simple to preserve data security when disposing of the
disk," Kawai says.
Since the Blu-ray Disc does not require laser
light to travel through the
substrate,
we were able to develop this paper disc. By increasing the capacity of the disc
we can decrease the amount of raw material used per unit of information."
Technical Parameters
Parameters |
BD
|
BD
|
HD-DVD
|
HD-DVD
|
Storage
capacity
|
25GB
|
50GB
|
15GB
|
30GB
|
Number of
layers
|
Single-layer
|
Dual-layer
|
Single-layer
|
Dual-layer
|
Laser
wavelength
|
405nm
|
405nm
|
405nm
|
405nm
|
Numerical
aperture (NA)
|
0.85
|
0.85
|
0.65
|
0.65
|
Protection
layer
|
0.1mm
|
0.1mm
|
0.6mm
|
0.6mm
|
Data transfer
rate
|
36Mbps
|
36Mbps
|
36Mbps
|
36Mbps
|
Video
compression
|
MPEG-2
MPEG-4 AVC VC-1 |
MPEG-2
MPEG-4 AVC VC-1 |
MPEG-2
MPEG-4
AVC
VC-1 |
MPEG-2
MPEG-4
AVC
VC-1 |
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