Science Fair Project Encyclopedia
Blu-ray Disc is a next-generation optical disc format meant for high definition video (HD) and high density data storage, and is one of two competing standards for HD optical media. Its competitor is HD-DVD. Blu-ray gets its name from the shorter wavelength (405nm) blue laser that, in addition to other techniques, allows it to store substantially more data on the same sized disc than DVD, which uses a longer wavelength (650nm) red laser. Blu-ray was jointly developed by a group of leading consumer electronics and PC companies called the Blu-ray Disc Association (BDA), which succeeded the Blu-ray Disc Founders (BDF).
Storage capacity and speeds
One single-layer Blu-ray Disc (BD) can hold about 25 GB or almost two hours of HD video plus audio, and the dual-layer disc can hold approximately 50 GB. The data transfer rate is 36 Mbit/s (54 Mbit/s for BD-ROM), but 2x speed prototypes with a 72 Mbit/s 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. Blu-ray Discs with capacities of 100 GB and 200 GB are currently being researched, with these capacities achieved by using four and eight layers respectively.
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.
BD-RE (and by extension BD-R ) does not currently support any codecs except MPEG-2. Because MPEG-2 is currently used to broadcast HDTV, recorders write this 19.3 Mbit/s HD stream directly to the disc. Since there are no consumer grade recorders with the processing power necessary for real-time transcoding from MPEG-2 to any other codec that might be used for BD-RE, MPEG-2 is the only format supported by BD-RE.
An 8 cm BD specification has been finalized and approved. A one-sided, double-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.
Laser and optics
Blu-ray systems use 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.
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 (NA) of the lens used to focus it. By decreasing the wavelength, using a higher NA (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.)
TDK has introduced hard-coating technology that enables bare disk (caddyless) handling. TDK's hard-coating technique gives BDs scratch resistance that allows them to be cleaned of fingerprints with only a tissue, a procedure that leaves scratches on current CDs and DVDs.
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.
Stand-alone recorders and games consoles
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 . 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.
PC data storage
Hewlett Packard announced in November 2004 that they would begin selling desktop PCs equipped with Blu-ray in late 2005, with laptops to follow in early 2006. Then Philips announced in January 2005 a Blu-ray version PC drive, model OPU81, which is scheduled to debut in the second half 2005. 
- PC information updates: Blu-ray.com forums "PC Data Storage"
The primary rival to Blu-ray is HD-DVD, championed by Toshiba and NEC Corporation. It has a lower data density and thus more limited disc capacity, but could in principle benefit from lower manufacturing costs for both the drive units and the pre-recorded/recordable media.
- EVD – a Chinese optical disc system developed as a response to high DVD licensing costs
- Digital Multilayer Disk – the successor technology to Fluorescent Multilayer Disc
- Forward Versatile Disc – Taiwanese backed red laser format
- Holographic Versatile Disc
- Versatile Multilayer Disc
- Blu-ray Disc Association
- Blu-ray.com - News, photos, reports, and forums
- Blu-ray.jp - Japanese guide to Blu-ray technology
- History of violet laser diodes
- Comparison of CD, DVD, BD Specifications
- How Stuff Works on Blu-ray
- Blu-ray for PlayStation 3
- "All-in-one" combo drive petition
- HD-DVD Central
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