blu-ray disc (BD)
A Blu-Ray disc (BD) is an optical storage device, the size of a compact disc( CD) and multi-layered like a digital versatile disc( DVD), but with a much larger storage capacity. Blu-Ray discs have multiple layers in which the laser track can be burned in, theoretically up to eight storage layers can be accessed.
The Blu-Ray disc gets its name because of the blue laser light, which has a very short wavelength. This allows the data tracks to be kept much tighter than on DVD, as well as the pits and lands are much smaller, resulting in the higher storage density.
The focused beam diameter of the Blu-Ray disc is 0.58 µm, compared to 1.32 µm for the DVD and 2.11 µm for the compact disc (CD).
The most important characteristics of the Blu-Ray disc
The Blu-Ray specifications were first developed by members of the Blu-Ray Disc Founders( BDF), and later by the Blu-Ray Disc Association( BDA). In addition to the laser wavelength of 405 nm and the numerical aperture of 0.85, the most important specifications include the thickness of the carrier layer, which is only 0.1 mm. Blu-Ray technology, supported mainly by Sony and Matsushita, is coated on both sides. With single layer( SL) coating, the storage capacity is 23.3 GB, 25 GB or 27 GB/side, which is related to the channel bits, and with dual layer( DL) coating, up to 50 GB/side. The maximum data rate is 36 Mbit/s, which is 3.3 times that of a DVD.
In addition, there is the Ultra HD Blu-Ray with a storage capacity of 100 GB aud dual-layer. With the storage capacity of a normal Blu-Ray disc, you can record about 13 hours of normal video and about two hours of high-definition television( HDTV).
In August 2004, BD Profile 1.0 of BD-ROM was adopted for the physical level of formatting. Furthermore, the Universal Disk Format( UDF 2.5) and the codecs for audio and video were specified: Pulse Code Modulation( PCM), MPEG-2, Dolby Digital and Digital Theatre Sound( DTS), and Video Codec 1( VC-1) and H.264/ AVC. The audio file formats Dolby Digital Plus( DD+) and Digital Theatre Sound High Definition( DTS-HD) must be supported by the BD-ROM, and Dolby TrueHD is also provided as an optional audio codec. As copy protection, the Blu-Ray disc uses High-Bandwidth Digital Content Protection( HDCP) to encrypt data transfer between the Blu-Ray player and display.
The different Blu-Ray formats
Blu-Ray discs are available in the formats BD-ROM (Read Only Memory), BD-R (Recordable), BD-RE (Rewritable), BDAV (Blu-Ray Disc Audio Video), BDMV (Blu-Ray Disc Movie), BD-Video, BDXL and Ultra HD Blu-Ray. Whereby the Ultra HD Blu-Ray has three layers and the BDXL (Blu-Ray Disc XL) stands for a Blu-Ray disc with three or four layers, with which a storage capacity of 100 GB and 128 GB can be achieved. Furthermore, development is underway on Blu-Ray discs with up to eight layers, which are expected to have a storage capacity of 200 gigabytes (GB) per side.
Other storage technologies that used a short-wavelength blue laser included HD-DVD, Ultra Density Optical( UDO), Enhanced Versatile Disc( EVD) and Professional Disc for Data ( PDD). The latter three were pure development projects with no market presence, while the HD-DVD had competed with the Blu-Ray disc for a long time, but was no longer developed further in 2008.