Blu-ray Disc(BD) is the name of a next-generation optical disc format jointly developed by members of the Blu-ray Disc Association (BDA). The format was developed to enable recording, rewriting and playback of high-definition (HD) video, as well as storing large amounts of data. It became the sole blue laser optical disc technology in 2008, when the rival format HD-DVD was finally dropped by Toshiba.

Optical drives needed to move from using red to blue lasers, critical because the wavelength of an optical drive’s laser light limits the size of the pit that can be read from the disc. In other words, the blue laser’s smaller wavelength, narrower beam can be more finely focused on a smaller area than that of a red laser. Using blue laser light, several times more data can be stored on a single disk of the same physical size, and also transferred at considerably faster speed.

By employing a short wavelength (405nm) blue violet laser, the Blu-ray Disc (BD) successfully minimises its beam spot size, reducing the lens’ NA to 0.85 and so making it possible to focus the laser spot with much greater precision.

A single-layer disc can hold 25GB, which can be used to record over 2 hours of HDTV or more than 13 hours of SDTV. There are also dual-layer versions of the discs that can hold 50GB. All this is achieved on media that is the same physical size as a CD/DVD.

Read page 52 of the textbook “Exploring Computer Hardware”.