Paper presentation- Blue-ray

The name Blu-ray is a combination of “Blue” for the color of laser that is used, and “ray” for “Optical ray”.

The thrust for an advanced format of data storage on optical disc led to revolutionary introduction of BLU-RAY DISC. This advances in the race against its competitors DVD (Digital Video Disc) & AOD (Advanced Optical Disc) in that it has high storage capacity, advanced security and privacy features and the A/V high quality O/P (generally video) of the media files stored on it make’s it quite unique & gives an edge over the others, letting BD to be widely adaptable in every application possible.
Surprisingly, the necessity for a next generation disc had begun in 1994 even before the advent of the DVD in the market in 1996. The then scientists predicted the limitations of the DVD format & begun working on BD even before DVD's release.
This paper essentially is confined with the structure, construction, reading issues & advantages of the Blu-Ray Disc. To be effective, at every stage the disc is compared with DVD.

Contents of the paper
1) Introduction
2) Structure
3) Storage
4) Construction
5) Data Access
6) Reading Issues
7) File System
8) Utilities and Technological support
9) Technological Aid
10) Pros & Cons
11) Conclusion
INTRODUCTION:

BD --> Blu-Ray Disc

The founding stones for the Blu Ray Disc technology were laid in 2002 by the Blu Ray Disc Association (BDA) in an attempt to overcome the drawbacks in DVD's. This attempt has almost reached the zenith & the world now is shortly about to use a disc of an incredible storage capacity & with almost all the apex features incorporated, that ensures user security and privacy and enables one to operate the disc in the most efficient and convenient way ever imagined.

WHY BD?
Early in 1997, a new technology emerged that brought digital sound and video into homes all over the world almost thrashing out the then conventional CD's. It was called DVD, and it revolutionized the movie industry. This format ruled the market for over a span of 5 years, but now is facing some very tight challenges. Here are some reasons why there’s been a rush to change from the current format of DVD:
SIZE : A single-sided, standard DVD can hold 4.7 GB (gigabytes) of information. That's about the size of an average two-hour, standard-definition movie with a few extra features. But a high-definition movie, which has a much clearer image, takes up about five times more bandwidth and therefore requires a disc with about five times more storage. As TV sets and movie studios make the move to high definition, consumers are going to need playback systems with a lot more storage capacity, which a DVD cannot support. Also, more space on a single disc invariably results in higher disc size. This bulky size of the disc is neither convincing nor convenient.

SECURITY : CSS is toast, thanks to some smart programmers in Europe and some foolish programmers at the now-defunct Xing Technologies. The group that created the DeCSS software figured out how to break the encryption by reverse engineering Xing's DVD decryption key, which wasn't properly protected. The end result is that DVDs can be copied as easily as music CDs. The market hates the fact that the DVD format is now vulnerable and there's nothing they can do about it, and are eager for a new format that is much more secure.

QUALITY : The final reason for the change is video quality. DVD video is presented in 480p, or 480 lines per screen, progressive scanned video. High Definition TV (HDTV) is presented in 720p or 1080i. You won't notice any difference without a high definition television, but if you do have an HDTV set, the improvement in quality is very noticeable. The quality of the video o/p of the media files on a DVD or a CD is not up to the mark.

SOLUTION :
The industry is set for yet another revolution with the introduction of Blu-ray Discs (BD). With their high storage capacity, Blu-ray discs can hold and playback large quantities of high-definition video and audio, as well as photos, data and other digital content. Also incorporated are some advanced security and privacy options and convenient accessibility features. A single sided blu ray disc has the capacity to store information of about 27 gigabytes, that’s about the size of 13 hr standard definition movie or more than 2.5 hrs of a high definition movie. While the double layered one can store to about 54 gigabytes. This enormous storage capability is considered to be the major plus point of the blu ray disc to that of the conventional DVD’s in the market right now.

BLU-RAY DISC:
Blu ray disc is the next generation digital video disc. It has an edge over the traditional dvd's & lesser used cd's that it has more storage capacity with the size of the disc being constant. Also we'll discuss now the other features of this disc which makes it quite unique & gives it a chance to be well adapted in all sorts of applications everywhere.

STRUCTURE:
The structure of the Blu-Ray disc is shown as below. It differs from the traditional DVD that, in a DVD the data is sandwiched between two 0.6mm polycarbonate layers. While in the case of a BD the data layer is placed on a 1.1mm polycarbonate layer. To prevent the data on the top of the disc from getting erased, the data layer is covered by a 0.1 mm protection layer. This makes the size of all the CD's DVD's & the BD's constant. This packing of the data has many advantages which will be discussed in the later sections.


STORAGE:
It should be noticed that whatever form of the disc may be under consideration the data on the disc is stored on a SPIRAL TRACK running from the centre of the disc to the end of the diameter of the disc. This spiral starting from the centre of the disc gives the flexibility for the disc to be smaller in size than that of the conventional 120 mm. On this spiral tracks exists the BUMPS which actually hold the data. These bumps lie all along the spiral track. These bumps are often called pits. Viewed from the top of the disc these bumps look like PITS.


CONSTRUCTION:
The construction of the bumps (spiral track) is explained here from a closer view of the disc. The view is so close that the bumps can be seen clearly. Here each white hole represents a bump (pit). For clear understanding it is effectively compared with a DVD.












The key terms used here are:
1) Pit Length: It is the length of the pit on the spiral track which holds the data.
2) Track Pitch: It is the distance between any two successive tracks.
From the figure above :
The minimum pit length of a BD is 0.15 microns which is more than twice as small as the pits on the DVD which is at minimum 0.4 microns. Also the track pitch of the BD is 0.32 microns which is more than twice as small as that of the DVD which is 0.74 microns. This small pit & reduced track pitch enables the accommodation of a data of about 25 gb on a single sided Blu-Ray disc which is almost 5 times that of a single sided traditional DVD.

DATA ACCESS:
Now a laser beam has to be chosen such that it reads the data in the small sized pits.
Unlike current DVDs, which use a red laser to read and write data, Blu-ray discs uses a blue laser (technically blue-violet). 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 (µm) long.

There would immediately be a question as why not laser beams of even smaller wavelength be used to read the disc which encourages the reduction of pit size and the track pitch. But this practically isn’t possible. This is because the building material of disc’s i.e. the plastic loose durability when lasers of wavelength shorter than 600 nm are focused on them & some plastics the effect was as if they are sun burnt. A wavelength of 405 was found the least for plastic surfaces.

Numerical aperture=0.45 780-nm infrared laser CD
Numerical aperture=0.6 650-nm red laser DVD
Numerical aperture=0.8 405-nm blue laser BD

From the figure above we can conclude that with the reduction in the laser beam wavelength accompanied with an effective (proportional) increase in the lens aperture, it is possible to read & write data into the pits of very small size. This way more disc space can be provided on a BD.

READING ISSUES ::
The till now regularly used DVD's & VCD's face two basic problems regarding their physical structure. They are:
1) Birefringence.
2) Disk tilt.
Birefringence: 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.
Disk Tilt: If the DVD surface is not exactly flat, and is therefore not exactly perpendicular to the beam (laser), it can lead to a problem known as disc tilt, in which the laser beam is distorted. This sometimes may lead to reading or writing into other undesired memory locations.

SOLUTION:
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.

FILE SYSTEM : The file system here has two important aspects of consideration:

1) Data arrangement.
2) Data retrieval.

1) DATA ARRANGEMENT: The general file system used in Blu -Ray disc is quite unique. It divides entire disk space into two parts.
a) Metadata & Database area.
b) Real time Recordable area.
The real time recordable area is the major part in respect to size on the disc & it contains the real time files used by the user. They vary from a/v streams to s/w programs to documents. While the Metadata & Database area holds the information that manages the data in the real time recordable area. . This MD files actually serves as a means of quick access to the folders & enable the users to open (operate) multiple directories at the same time & help during the system scan & others. In addition to the MD area on the disc, in order to provide robustness, a backup of the MD area files is provided. The files recorded in the area for metadata and database files can be read with a fewer number of seeks, reducing the response time during Play List editing and menu display, resulting in greatly improved system response.
There exists different file systems (derivative of the general one)for different versions of the BD that are BD-ROM , BD-Rewritable , BD-Recordable.
Blu-ray Rewritable discs are non-sequential recording media, where read-modify-write and defect management operations are performed by drive unit, eliminating the need for the Virtual Allocation Table and Sparing Table in the file system.
Blu-ray Recordable discs also include defect management, eliminating the need for the Sparing Table inthe file system. The defect management system allows for the replacement of defective clusters as well as enabling the logical overwriting of previously recorded user data. For Blu-ray Read-Only discs, the requirements are simplified since there is no need for read-modify-write, overwriting or incremental recording of user data.

2) DATA RETRIEVAL (CONTINUOUS):
When recording, deleting or editing operations are performed repeatedly, small areas of empty space will occur across the disc. These small areas can be used to record a new Real-Time file, which results in a single Real-Time file composed of many small extents scattered across the disc. A group of these extents, each of which is recorded on contiguous logical sectors, is called an Expanse. The Expanse is conceptually a contiguous area to be read, and may include small areas in which Real-Time data is not recorded.
When a single Real-Time file is made up of several expanses, the file is read by jumping from one expanse to the next and reading the expanses in order. However, when jumping from one expanse to another, the disc rotation speed needs to be changed and the optical pickup needs to be moved to a different radius on the disc. Although data cannot be retrieved from the disc during this interval, the decoding/playback of video/audio data must continue without interruption.
To prevent interruption in video/audio playback while reading data from the disc, the buffer memory must not be emptied of data before readout from the next expanse becomes possible. This requirement for continuous supply of data is necessary to insure seamless playback. Therefore the minimum expanse size is defined such that the buffer memory does not become empty when jumping from one expanse to another on the disc.

Utilities :
The file system for a general Blu-Ray disc is mentioned just above. The information about the locations of different expanses of a single file is maintained in the Meta database region of the BD. The utilities of this unique format (file system) are found maximum in the BD-R amongst the BD-R, BD-ROM, and BD-RW formats. Those utilities are mentioned below:

1) Digital Broadcasting Direct Recording Function :
This recording function enables the recording of not only digital broadcast image data without destroying the image quality, but also of data broadcast data and multi-channel sound data altogether. To this end, this format employs the MPEG-2TS (Transport Stream), used by digital broadcasts, as a stream type for recording. Received MPEG-2TS data is recorded on a disc as a Clip AV stream file.
This is mainly enabled by the capability of the Blu-Ray disc of outputting at the rate of 36 Mbps which is more than 3.5 times that of the DVD which is 10 Mbps. This high rate enables both the recording & the data broadcast.

2) Random Access High-speed Playback Function :
To achieve a function that enables random access to a desired scene in MPEG-2TS and high-speed playback, tables to obtain the record position of data corresponding to a playback time requested by the user are provided for each Clip AV stream file. The tables are stored in the Clip Information File.
3) Editing and Marking Function:
The Play List file is provided for removing unnecessary scenes without copying or transferring recorded data like tape media, and editing material recorded on the disc without processing the original image. The Play List file holds the playback order information necessary to designate what part of what Clip AV stream is played back.

4) Contents Search Function:
In each thumbnail related file, thumbnails of the Play List file and bookmarked scenes are stored. This enables the search for recorded contents and bookmarks by viewing thumbnail images.
The last 3 utilities mainly depend on the Meta database information of the real time data stored on the centre of the disc & the backup of which is stored at the end of the disc diameter. The table representing the position of the data corresponding to the playback time is shown in the figure below. This same list is used for the searching & playing the selected part of the media (play list).

TECHNOLOGICAL AID :

1) Laser and optics
Blu-ray systems use a "blue" (technically blue-violet) laser operating at a wavelength of 405 nm to read and write data. Conventional DVDs and CDs use red and infrared lasers at 650 nm and 780 nm respectively.
The blue-violet laser's shorter wavelength makes it possible to store more information on a 12 cm CD/DVD sized disc. 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, using a higher numerical aperture (0.85, compared with 0.6 for DVD), higher quality, dual-lens system, and making the cover layer thinner to avoid unwanted optical effects, the laser beam can be focused much more tightly at the disk surface. This produces a smaller spot on the disc and allows more information to be physically contained in the same area. In addition to the optical improvements, Blu-ray Discs feature improvements in data encoding, allowing for even more data to be packed in. (See compact disc for information on optical discs' physical structure.)

2) Hard-coating technology
Because the Blu-ray standard places data so close to the surface of the disc, early discs were susceptible to dust and scratches & fingerprints and had to be enclosed in plastic caddies for protection. Such an aggravation, the consortium worried, would hobble Blu-ray's adoption in the face of the rival HD DVD standard; HD DVDs can be handled bare (caddy less) like CDs and DVDs, making them familiar to consumers as well as attractive to manufacturers and distributors who might be deterred by additional costs.
The solution to this problem arrived in January 2004 with the introduction of a clear polymer that gives Blu-ray discs unprecedented scratch resistance. The coating, developed by TDK Corporation under the name "Durabis," allows BD’s to be cleaned safely with only a tissue—a procedure that can damage CDs, DVDs, and (presumably) HD DVDs, which are manufactured by the same process as these older optical media. Bare BD’s with the coating are reportedly able to withstand attack by a screwdriver.
Durabis is a brand name for a clear polymer coating developed by the TDK Corporation. One of its principal applications at first will be for scratch-resistance in Blu-ray and other optical disks. It is claimed to be tough enough to resist screwdriver damage and make scratched optical disks (CD and DVDs) a thing of the past.
In order to meet Blu-ray's specifications, TDK's coating had to be less than 0.1 mm thick, be hard enough to resist considerable damage and yet be transparent enough to be easily read. This process essentially spin-coats two layers onto discs. One is for protection against scratches and the other protects against stains and oils.

3) Codec’s
The BD-ROM format specifies at least three video codec’s: MPEG-2, the standard used for DVDs; MPEG-4's H.264/AVC codec; and VC-1, a codec based on Microsoft's Windows Media 9. The first of these only allows for about two hours of high-definition content on a single-layer BD-ROM, but the addition of the two more advanced codec’s allows up to four hours per layer.
For audio, BD-ROM supports linear (uncompressed) PCM, Dolby Digital, Dolby Digital Plus, DTS, DTS-HD, and Dolby Lossless (a lossless compression format also known as MLP).
In order to remain backwards compatible, BD-RE (and by extension BD-R) will by and large support the MPEG2 codec. For users recording digital television broadcasts, the Blu-ray's baseline data rate of 36Mbit will be more than adequate to record high definition broadcasts. Support for new codec’s will evolve as new codec’s are encapsulated by broadcasters into their MPEG2 transport streams and consumer set top boxes capable of decoding them are rolled out.

4) Java Software Support
At the 2005 Java One trade show, it was announced that Sun Microsystems' Java cross-platform software environment would be included in all Blu-ray players as a mandatory part of the standard. Java will be used to implement interactive menus on Blu-ray discs, as opposed to the method used on DVD video discs, which uses pre-rendered MPEG segments and selectable subtitle pictures and is considerably more primitive. Java creator James Gosling, at the conference, suggested that the inclusion of a Java virtual machine as well as network connectivity in BD devices will allow updates to Blu-ray discs via the Internet, adding content such as additional subtitle languages and promotional features that are not included on the disc at pressing time. This Java Version will be called BD-J and will be a subset of the GEM (Globally Executable MHP) standard. GEM is the world-wide version of the Multimedia Home Platform standard.

5) Compatibility
While it is not compulsory for manufacturers, the Blu-ray Disc Association recommends that Blu-ray drives should be capable of reading DVDs, ensuring backward compatibility.
JVC has developed a three layer technology that allows putting both standard-definition DVD data and HD data on a BD/DVD combo disc. If successfully commercialized, this would enable the consumer to purchase a disc which could be played on current DVD players, and reveal its HD version when played on a new BD player.

6) Security
Blu-ray has an experimental security feature titled BD+ that allows for dynamically changing encryption schemes. Should the encryption be compromised, manufacturers can update the encryption scheme and put it on all new discs, preventing a single crack from opening up the entire specification for the duration of its lifetime. It also uses the Mandatory Managed Copy system allowing users to securely rip a file into a secure format, a feature originally requested by HP. The lack of a dynamic encryption model is what made DeCSS so disastrous in the industry's eyes: once CSS was cracked, all DVDs from then on were crack able.
The Blu-ray Disc Association also agreed to add digital watermarking technology to the discs. Under the name "ROM-Mark," this technology will be built into all ROM-producing devices, and prevent content from being reproduced in the event that a watermark is detected. Through licensing, the BDA believes that it can eliminate the possibility of mass producing BD-ROMs without authorization.

PROS :
() High disc space at almost same cost price
() Security
() reverse compatibility
() high speed data transfer (36Mbps)
() online modifications


CONS :
() High cost of the disc reader
() less data space than AOD (HD-DVD 30 Giga bytes)

CONCLUSION :
It would definitely take a considerable time for the Blu-Ray disc to hit the market & completely takeovers the DVD share hold. Because of the low level compatibility (BD readers able to read both the DVD’s and the CD’s), the task might become a little simpler. But, the high cost of the reader might hinder its quick development. Anyways soon or later this mass storage optical device is going to replace the DVD & let the user experience a world high quality & disc space (Quality & Quantity ensured) with high level of security and privacy ensured.

BIBLOGRAPHY :
1) blu-raydisc.com (official site for blu-ray disc)
2) bitpipe.org (referred to the white paper by john.paulinghton)
3) wikipedia.com (general information source 1)
4) tgdaily.com (referred to a 4 news reports by WARNER BROS and SONY)
5) howstuffworks.com (general information source 2)

SUPPORT :
The rapid strides and the success level of BD is contributed by major organizations such as SONY , WARNER BROTHRS & many others that have joined the BDA (Blu Ray Disc Association) in bringing it into the market such that it satisfies all the needs of the users.
TRIVIA :
The spelling BLU isn’t any spelling mistake. It indicates that a blue colored laser beam is used in this disc technology. But, under the constraint that no regularly used words should be trademarked this disc is named BLU RAY DISC instead of BLUE RAY DISK.