bluray technnology

7/27/2019 Bluray Technnology

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INTRODUCTION

Blu-ray (not Blue-ray) also known as Blu-ray Disc (BD), is the name of a new opticaldisc format jointly developed by the Blu-ray Disc Association (BDA), a group of the world's

leading consumer electronics, personal computer and media manufacturers (including Apple,

Dell, Hitachi, HP, JVC, LG, Mitsubishi, Panasonic, Pioneer, Philips, Samsung, Sharp, Sony,

TDK and Thomson). The format was developed to enable recording, rewriting and playback of

high-definition video (HD), as well as storing large amounts of data. The format offers more than

five times the storage capacity of traditional DVDs and can hold up to 25GB on a single-layer

disc and 50GB on a dual-layer disc. This extra capacity combined with the use of advanced

video and audio codecs will offer consumers an unprecedented HD experience.

While current optical disc technologies such as DVD, DVDR, DVDRW, and DVD-

RAM rely on a red laser to read and write data, the new format uses a blue-violet laser instead,

hence the name Blu-ray. Despite the different type of lasers used, Blu-ray products can easily be

made backwards compatible with CDs and DVDs through the use of a BD/DVD/CD compatible

optical pickup unit. The benefit of using a blue-violet laser (405nm) is that it has a shorter

wavelength than a red laser (650nm), which makes it possible to focus the laser spot with even

greater precision. This allows data to be packed more tightly and stored in less space, so it's

possible to fit more data on the disc even though it's the same size as a CD/DVD. This together

with the change of numerical aperture to 0.85 is what enables Blu-ray Discs to hold 25GB/50GB.


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HISTORY

Compact Disc

The CD was planned to be the successor of the gramophone record for playing music,

rather than primarily as a data storage medium. From its origins as a musical format, CDs have

grown to encompass other applications. In June 1985, the computer readable CD-ROM (read-

only memory) and, in 1990, CD-Recordable were introduced, also developed by both Sony and

Philips. The CD's compact format has largely replaced the audio cassette player in new

automobile applications, and recordable CDs are an alternative to tape for recording music and

copying music albums without defects introduced in compression used in other digital recording

methods

The Compact Disc (also known as a CD) is an optical disc used to store digital data. It

was originally developed to store and playback sound recordings exclusively, but later expanded

to encompass storage of data (CD-ROM), write-once audio and data storage (CD-R), rewritable

media (CD-RW).

A CD is made from 1.2 millimeters (0.047 in) thick, polycarbonate plastic. A thin layer

of aluminium or, more rarely, gold is applied to the surface making it reflective. The metal is

protected by a film of lacquer normally spin coated directly on the reflective layer. The label isprinted on the lacquer layer, usually by screen printing or offset printing.

A CD is read by focusing a 780 nm wavelength (near infrared) semiconductor laser

through the bottom of the polycarbonate layer. The change in height between pits and lands

results in a difference in the way the light is reflected. By measuring the intensity change with a

photodiode, the data can be read from the disc.

DVD (DIGITAL VIDEO DISCS)DVD is an optical disc storage media format, invented and developed by Philips, Sony,

Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while

having the same dimensions.


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Before the advent of DVD and Blu-ray, Video CD (VCD) became the first format for

distributing digitally encoded films on standard 120 mm optical discs. (Its predecessor, CD

Video, used analog video encoding.) VCD was on the market in 1993. In the same year, two new

optical disc storage formats were being developed. One was the Multimedia Compact Disc

(MMCD), backed by Philips and Sony, and the other was the Super Density (SD) disc, supported

by Toshiba, Hitachi, and Mitsubishi Electric.

DVD was adopted by movie and home entertainment distributors to replace the

ubiquitous VHS tape as the primary means of distributing films to consumers in the home

entertainment marketplace. DVD was chosen for its superior ability to reproduce moving

pictures and sound, for its superior durability, and for its interactivity. Interactivity had proven to

be a feature which consumers, especially collectors, favored when the movie studios hadreleased their films on Laserdiscs.

Security Content Scramble System (CSS) is a Digital Rights Management (DRM) and

encryption system employed on almost all commercially produced DVD-video discs.

Blu-ray Disc

Blu-ray (not Blue-ray) also known as Blu-ray Disc (BD), is the name of a new optical

disc format jointly developed by the Blu-ray Disc Association (BDA), a group of the world's

leading consumer electronics, personal computer and media manufacturers (including Apple,

Dell, Hitachi, HP, JVC, LG, Mitsubishi, Panasonic, Pioneer, Philips, Samsung, Sharp, Sony,

TDK and Thomson). The format was developed to enable recording, rewriting and playback of

high-definition video (HD), as well as storing large amounts of data.

The format offers more than five times the storage capacity of traditional DVDs and can

hold up to 25GB on a single-layer disc and 50GB on a dual-layer disc. This extra capacity

combined with the use of advanced video and audio codecs will offer consumers an

unprecedented HD experience.

While current optical disc technologies such as DVD, DVDR, DVDRW, and DVD-

RAM rely on a red laser to read and write data, the new format uses a blue-violet laser instead,

hence the name Blu-ray. Despite the different type of lasers used, Blu-ray products can easily be


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made backwards compatible with CDs and DVDs through the use of a BD/DVD/CD compatible

optical pickup unit.

The benefit of using a blue-violet laser (405nm) is that it has a shorter wavelength than a

red laser (650nm), which makes it possible to focus the laser spot with even greater precision.

This allows data to be packed more tightly and stored in less space, so it's possible to fit more

data on the disc even though it's the same size as a CD/DVD. This together with the change of

numerical aperture to 0.85 is what enables Blu-ray Discs to hold 25GB/50GB.

Laser and optics

While a DVD uses a 650 nm red laser, Blu-ray Disc uses a 405 nm "blue" laser diode.

Note that even though the laser is called "blue", its color is actually in the violet range. The

smaller beam focuses more precisely, thus enabling it to read information recorded in pits that

are less than half the size of those on a DVD, and can consequently be spaced more closely,

resulting in a shorter track pitch, enabling a Blu-ray Disc to hold about five times the amount of

information that can be stored on a DVD.

The lasers are GaN (gallium nitride) laser diodes that produce 405 nm light directly, that

is, without frequency doubling or other nonlinear optical mechanisms. Conventional DVDs use

650 nm red lasers, and CDs use 780 nm near-infrared lasers.

The minimum "spot size" on which a laser can be focused is limited by diffraction, and

depends on the wavelength of the light and the numerical aperture of the lens used to focus it. By

decreasing the wavelength, increasing the numerical aperture from 0.60 to 0.85, and making the

cover layer thinner to avoid unwanted optical effects, the laser beam can be focused to a smaller

spot, which effectively allows more information to be stored in the same area. For Blu-ray Disc,

the spot size is 580 nm. This allows a reduction of the pit size from 400 nm for DVD to 150 nm

for Blu-ray Disc, and of the track pitch from 740 nm to 320 nm.


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Comparison in building

BD AND DVD

Blu-ray is the next-generation digital video disc. It can record, store and play back high-

definition video and digital audio, as well as computer data. The advantage to Blu-ray is the

sheer amount of information it can hold:

A single-layer Blu-ray disc, which is roughly the same size as a DVD, can hold up to 27

GB of data -- that's more than two hours of high-definition video or about 13 hours of

standard video.


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A double-layer Blu-ray disc can store up to 50 GB, enough to hold about 4.5 hours of

high-definition video or more than 20 hours of standard video. And there are even plans

in the works to develop a disc with twice that amount of storage.

Building a Blu-ray Disc

Blu-ray discs not only have more storage capacity than traditional DVDs, but they also offer

a new level of interactivity. Users will be able to connect to the Internet and instantly download

subtitles and other interactive movie features. With Blu-ray, you can:

record high-definition television (HDTV) without any quality loss

instantly skip to any spot on the disc

record one program while watching another on the disc

create playlists

edit or reorder programs recorded on the disc

automatically search for an empty space on the disc to avoid recording over a program

access the Web to download subtitles and other extra features

Discs store digitally encoded video and audio information in pits -- spiral grooves that run from

the center of the disc to its edges. A laser reads the other side of these pits -- the bumps -- to play

the movie or program that is stored on the DVD. The more data that is contained on a disc, the

smaller and more closely packed the pits must be. The smaller the pits (and therefore the bumps),

the more precise the reading laser must be.

Unlike current DVDs, which use a red laser to read and write data, Blu-ray uses a blue laser

(which is where the format gets its name). A blue laser has a shorter wavelength (405

nanometers) than a red laser (650 nanometers). The smaller beam focuses more precisely,

enabling it to read information recorded in pits that are only 0.15 microns (m) (1 micron = 10 -6

meters) long -- this is more than twice as small as the pits on a DVD. Plus, Blu-ray has reduced

the track pitch from 0.74 microns to 0.32 microns. The smaller pits, smaller beam and shorter


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track pitch together enable a single-layer Blu-ray disc to hold more than 25 GB of information --

about five times the amount of information that can be stored on a DVD.

Each Blu-ray disc is about the same thickness (1.2 millimeters) as a DVD. But the two types of

discs store data differently. In a DVD, the data is sandwiched between two polycarbonate layers,

each 0.6-mm thick. Having a polycarbonate layer on top of the data can cause a problem called

birefringence, in which the substrate layer refracts the laser light into two separate beams. If the

beam is split too widely, the disc cannot be read. Also, if the DVD surface is not exactly flat, and

is therefore not exactly perpendicular to the beam, it can lead to a problem known as disc tilt, in

which the laser beam is distorted. All of these issues lead to a very involved manufacturing

process.

How Blu-ray Reads Data

The Blu-ray disc overcomes DVD-reading issues by placing the data on top of a 1.1-mm-thick

polycarbonate layer. Having the data on top prevents birefringence and therefore prevents

readability problems. And, with the recording layer sitting closer to the objective lens of the

reading mechanism, the problem of disc tilt is virtually eliminated. Because the data is closer tothe surface, a hard coating is placed on the outside of the disc to protect it from scratches and

fingerprints.

The design of the Blu-ray discs saves on manufacturing costs. Traditional DVDs are built by

injection molding the two 0.6-mm discs between which the recording layer is sandwiched. The

process must be done very carefully to prevent birefringence.

1. The two discs are molded.2. The recording layer is added to one of the discs.

3. The two discs are glued together.


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Blu-ray discs only do the injection-molding process on a single 1.1-mm disc, which reduces cost.

That savings balances out the cost of adding the protective layer, so the end price is no more than

the price of a regular DVD.

Hard-coating technology

Since the Blu-ray Disc data layer is closer to the surface of the disc compared to the DVD

standard, it was at first more vulnerable to scratches. The first discs were housed in cartridges for

protection, resembling Professional Discs introduced by Sony in 2003.

Using a cartridge would increase the price of an already expensive medium, so hard-coating of

the pickup surface was chosen instead. TDK was the first company to develop a working scratch-

protection coating for Blu-ray Discs. It was named Durabis. In addition, both Sony and

Panasonic's replication methods include proprietary hard-coat technologies. Sony's rewritable

media are spin-coated, using a scratch-resistant and antistatic coating. Verbatim's recordable and

rewritable Blu-ray Discs use their own proprietary technology, called Hard Coat. [65]

The Blu-ray Disc specification requires the testing of resistance to scratches by mechanical

abrasion. In contrast, DVD media are not required to be scratch-resistant, but since development

of the technology, some companies, such as Verbatim, implemented hard-coating for more

expensive lineups of recordable DVDs.


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Advanced Access Content System

The Advanced Access Content System (AACS) is a standard for content distribution and digital

rights management, intended to restrict access to and copying of the "next generation" of optical

discs and DVDs.

AACS uses cryptography to control and restrict the use of digital media. It encrypts content

under one or more title keys using the Advanced Encryption Standard (AES). Title keys are

decrypted using a combination of a media key (encoded in a Media Key Block) and the Volume

ID of the media (e.g., a physical serial number embedded on a pre-recorded disc).

The principal difference between AACS and CSS, the DRM system used on DVDs, lies in how

the device decryption keys are organized.

Encryption

AACS uses cryptography to control and restrict the use of digital media. It encrypts content

under one or more title keys using the Advanced Encryption Standard (AES). Title keys are

decrypted using a combination of a media key (encoded in a Media Key Block) and the Volume


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ID of the media (e.g., a physical serial number embedded on a pre-recorded disc).

The principal difference between AACS and CSS, the DRM system used on DVDs, lies in how

the device decryption keys are organized.

Under CSS, all players of a given model are provisioned with the same shared decryption key.

Content is encrypted under the title-specific key, which is itself encrypted under each model's

key. Thus each disc contains a collection of several hundred encrypted keys, one for each

licensed player model.

In principle, this approach allows licensors to "revoke" a given player model (prevent it from

playing back future content) by omitting to encrypt future title keys with the player model's key.

In practice, however, revoking all players of a particular model is costly, as it causes many users

to lose playback capability. Furthermore, the inclusion of a shared key across many players

makes key compromise significantly more likely, as was demonstrated by a number of

compromises in the mid-1990s.

The approach of AACS provisions each individual player with a unique set of decryption keys

which are used in a broadcast encryption scheme. This approach allows licensors to "revoke"

individual players, or more specifically, the decryption keys associated with the player. Thus, if a

given player's keys are compromised and published, the AACS LA can simply revoke those keys

in future content, making the keys/player useless for decrypting new titles.

AACS also has traitor tracing. The standard allows different versions of short sections of a movie

to be encrypted with different keys. A certain player will only be able to decrypt one version of

each section. By embedding a digital watermark in the different versions and analyzing what

sections of the movie the attacker publishes, the compromised keys can eventually be identified

and revoked (this feature is called Sequence keys in the AACS specifications).

Volume IDs

Volume IDs are unique identifiers or serial numbers that are stored on pre-recorded discs with

special hardware. They cannot be duplicated on consumers' recordable media. The point of this is


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to prevent simple bit-by-bit copies, since the Volume ID is required (though not sufficient) for

decoding content. On Blu-ray discs, the Volume ID is stored in the BD-ROM Mark.

To read the Volume ID, a cryptographic certificate (the Private Host Key) signed by the AACS

LA is required. However, hackers claim to have circumvented that particular protection bymodifying the firmware of an HD DVD reader.

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