Blu-ray, also known as Blu-ray Disc (BD) is the name of a next-generation 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. A single-layer Blu-ray Disc can hold 25GB, which can be used to record over 2 hours of HDTV or more than 13 hours of standard-definition TV. There are also dual-layer versions of the discs that can hold 50GB.
While current optical disc technologies such as DVD
, DVD±R, DVD±RW, and DVD-RAM use 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 through the use of a BD/DVD/CD compatible optical pickup and allow playback of CDs and DVDs. 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.
With the rapid growth of HDTV, the consumer demand for recording HD programming is quickly rising. Blu-ray was designed with this application in mind and supports direct recording of the MPEG-2
TS (Transport Stream) used by digital broadcasts, which makes it highly compatible with global standards for digital TV. This means that HDTV broadcasts can be recorded directly to the disc without any quality loss or extra processing. To handle the increased amount of data required for HD, Blu-ray employs a 36Mbps data transfer rate, which is more than enough to record and playback HDTV while maintaining the original picture quality. In addition, by fully utilizing an optical disc's random accessing features, it's possible to playback video on a disc while simultaneously recording HD video.
See also HD-DVD