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Encyclopedia > Bluray
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Blu-ray discs

Blu-ray Disc is a next-generation optical disc format jointly developed by a group of leading consumer electronics and PC companies called the Blu_ray Disc Association (BDA), which succeeds the Blu_ray Disc Founders (BDF). Because it uses blue lasers, which have shorter wavelengths than traditional red lasers, it can store substantially more data in the same amount of physical space as previous technologies such as DVD and CD.

Contents

Storage and speed

One single-layer Blu-ray Disc can hold about 25GB or almost four hours of HDTV audio and video, and the dual-layer disc can hold approximately 50GB. The data transfer rate is 36Mbps, but 2x speed prototypes with a 72Mbps transfer rate are now in development. The BD-RE (rewritable) standard is now available, to be followed by the BD-R (recordable) and BD-ROM formats in mid-2004, as part of version 2.0 of the Blu-ray specifications. BD-ROM pre-recorded media are to be available by late 2005. Looking further ahead in time, Blu-ray Discs with capacities of 100GB and 200GB are currently being researched, with these capacities achieved by using four and eight layers respectively.


Codecs

The BD-ROM format will include at least 3 codecs: MPEG-2 (the standard used for DVDs), MPEG-4's H.264/AVC codec, and VC-1 based on Microsoft's Windows Media 9 codec. The first codec only allows for about two hours of high-definition content on a single layer Blu-ray Disc, but with the addition of the latter two more advanced codecs, a single-layer disc can hold almost four hours. High-definition MPEG-2 has a data rate of about 25Mbps, while the latter two have data rates of about 15Mbps for video and 3Mbps for audio.


BD-RE (and by extension BD-R) does not currently support any advanced codecs beyond MPEG-2. Because MPEG-2 is currently used to broadcast HDTV, recorders write this HD stream directly to a disc. Since there are no consumer level recorders capable of real-time transcoding from the MPEG-2 used for broadcasting and any other codec that might be used for BD-RE, MPEG-2 is the only format supported by BD-RE.


Encoding methods for the audio stream include Linear PCM, Dolby Digital, DTS and dts++ (lossless compression). The Blu-ray Disc Association is known to be looking into other codecs superior to those supported by the DVD specification.


Variations

An 8 cm BD specification has been finalized and approved. A one-sided, single-layer 8 cm BD can hold 15 GB, giving it the capacity of one and a half regular sized (12 cm) single sided double layer DVDs. This would be an ideal format for small, portable devices, such as portable movie players and digital video cameras.


A new hybrid Blu-ray / DVD combo disc has been developed by JVC and is awaiting acceptance by the Blu-ray Disc Association. This would allow both normal DVD players and Blu-ray players to utilise the disc. Users would be able to purchase a single disc that can be played at either high definition or standard DVD quality, depending on the hardware utilised. Users that do not have a Blu-ray Disc player can view the video content at standard definition using their current DVD player, and enjoy the same content at high definition resolution when upgrading to a Blu-ray disc player in the future.


Technology

Laser wavelength

The technology utilizes a "blue" (actually blue-violet) laser diode 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.


As a color comparison, the visible color of a powered fluorescent black light tube is dominated by mercury's bluish violet emissions at 435.8 nm. The blue_violet laser diodes used in Blu_ray Disc drives operate at 405 nm, which is noticeably more violet (closer to the violet end of the spectrum) than the visible light from a blacklight. A side effect of the very short wavelength is that it causes many materials to fluoresce, and the raw beam does appear as whitish_blue if shone on a white fluorescent surface (such as a piece of paper). While future disc technologies may use fluorescent media, Blu_ray Disc systems operate in the same manner as CD and DVD systems and do not make use of fluorescence effects to read out their data.


The blue_violet laser has a shorter wavelength than CD or DVD systems, and this shrinking makes it possible to store more information on a 12 cm (CD/DVD size) disc. The minimum "spot size" that a laser can be focused is limited by diffraction, and depends on the wavelength of the light and the numerical aperture (NA) of the lens used to focus it. By decreasing the wavelength (moving toward the violet end of the spectrum), using a higher NA (higher quality) dual_lens system, and making the disk 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 therefore 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 and closer track and pit spacing, allowing for even more data to be packed in. (See Compact disc for information on optical discs' physical structure.)


Hard-coating technology

The entry of TDK to the BDF (as it was then), announced on 19 March 2004, was accompanied by a number of indications that could significantly improve the outlook for Blu-ray. TDK is to introduce hard-coating technologies that would enable bare disk (caddyless) handling, along with higher-speed recording heads and multi-layer recording technology (to increase storage densities). TDK's hard-coating technique would give BDs scratch resistance and allow them to be cleaned of fingerprints with only a tissue, a procedure that would leave scratches on current CDs and DVDs.


Decreased costs

Unsurprisingly, members of the BDA have been directing efforts towards lowering manufacturing and other costs, on a number of different fronts. On 15 April 2004 for instance, Sony and Toppan Printing announced the successful development of a Blu-ray Disc that is 51% (by mass) composed of paper, which could reduce production costs and improve its environmental friendliness.


Compatibility

The BDA announced that, while it was not compulsory for manufacturers, Blu-ray lasers and drives are capable of reading the various DVD formats, ensuring backward compatibility. This makes the upgrade more attractive to consumers as it does not require replacing their collections of DVDs.


Recorders

The first Blu-ray recorder was unveiled by Sony on March 3, 2003, and was introduced to the Japanese market in April that year. On September 1, 2003, JVC and Samsung Electronics announced Blu_ray based products at IFA in Berlin, Germany. Both indicated that their products would be on the market in 2005.


In March 2004, both Sony and Matsushita announced plans to ship 50 GB Blu-ray recorders the same year. The Matsushita product is to ship in July 2004 in the Japanese market under the Panasonic brand. Sony is to follow by the end of 2004 and has announced that the Playstation 3 will be shipped with a read-only Blu-ray drive [1] (http://www.gamesindustry.biz/content_page.php?section_name=dev&aid=3919). Meanwhile, LG Electronics is expected to ship a recorder equipped with a 200GB hard disk into the U.S. market by Q3 2004. These products are to support single-sided, dual-layer rewriteable discs of 54GB capacity. Sony's machine will also support BD-ROM pre-recorded media, which are expected to be available by Christmas 2005.


Studio support

Unsurprisingly, Sony Pictures Entertainment and MGM Studios have both announced their support for the Blu-ray Disc format.


On October 3, 2004 20th Century Fox announced that it was joining the BDA, it has not yet decided which format to support, although it seems likely now that it will be Blu-ray.


On 8 December 2004 The Walt Disney Company (and its home video division, Buena Vista Home Entertainment) announced its non-exclusive support for Blu-ray.


On 7 January 2005 Vivendi Universal Games (VU Games) and Electronic Arts (EA Games) announced their support for the Blu-ray Disc format.


Alternatives

The primary rival to Blu-ray is HD-DVD, championed by Toshiba and NEC Corporation. This has a lower data density, but could (in principle) benefit from lower manufacturing costs for both the drive units as well as the pre-recorded/recordable media.


On 29 November 2004 four Hollywood studios announced plans to support HD-DVD in favour of Blu-ray (although the deal is not exclusive): New Line Cinema, Paramount Pictures, Universal Studios and Warner Bros..


Future optical media

In the opinion of many researchers (including those at the BDA themselves), BD possibly represents the last of the plastic-based, visible laser optical disc systems. Shorter violet and ultraviolet wavelengths are absorbed strongly by the plastic used in disc manufacturing, and it is difficult to cheaply manufacture a much higher-quality lens. The light absorbed by the disk would not make it back out to be read by the drive. In addition, most plastics decay when exposed to ultraviolet light, changing color and becoming brittle. An ultraviolet system would destroy plastic media used with it. Future technologies would likely involve glass platters (which do not absorb long-wave ultraviolet nearly as much as plastic), ultraviolet readout lasers, and/or multilayer fluorescent media formats.


See also

  • Competitor: HD-DVD
  • Competitor: EVD (a Chinese optical disc system developed as a response to high DVD licensing costs)
  • Competitor: Versatile Multilayer Disc
  • Competitor: Digital Multilayer Disk (the successor technology to Fluorescent Multilayer Disc)
  • Competitor: Holographic Versatile Disc (http://fr.wikipedia.org/Holographic_versatile_disc) (in French)
  • Competitor: Forward Versatile Disc (Taiwanese backed (http://www.boser.com.tw/news/20041227.htm) red laser format)

External links

  • Blu-ray Disc Association (http://www.bluraydisc.com/)
  • Blu-ray.com (http://www.blu-ray.com/) - News, photos, reports, and forums
  • Blu-ray.jp (http://www.blu-ray.jp/) - Japanese guide to Blu-ray technology
  • History of violet laser diodes (http://www.repairfaq.org/sam/laserdio.htm#dioabg)
  • Comparison of CD, DVD, BD Specifications (http://repairfaq.ece.drexel.edu/sam/cdfaq.htm#cdccddvd)
  • How Stuff Works on Blu-ray (http://electronics.howstuffworks.com/blu-ray.htm)
  • Blu-ray for PlayStation 3 (http://www.ps3portal.com/?view=article&article=39)
  • "All-in-one" combo drive petition (http://www.petitiononline.com/combo/petition.html)





 
 

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