Blu-ray's big trick was simply a shorter-wavelength laser
A Blu-ray disc is exactly the size of a DVD, yet one layer holds 25 GB. The difference is the light that reads it: a blue-violet laser at 405 nanometres, whose shorter wavelength lets data be packed far more tightly than the red laser in a DVD player allows.
DVD capacity was capped by the wavelength of its red laser diodes. Once blue diodes could be mass-produced, Sony teamed up with Panasonic, Philips and TDK on new formats, one of which, a rewritable project called DVR Blue, grew into Blu-ray. Sony showed prototypes at the CEATEC show in October 2000, and on February 19, 2002, nine founding companies formally launched the Blu-ray Disc name. The group became the Blu-ray Disc Association in October 2004, with 20th Century Fox joining its board.
Physically, the disc stays 12 centimetres across and 1.2 millimetres thick, but its data layer sits just 0.1 mm beneath the surface instead of the 0.6 mm used on DVDs. That thin cover made scratches a real worry, and early discs came in cartridges. In January 2005 TDK announced Durabis, a very hard, very thin polymer coating that made the cartridges unnecessary. Dual-layer 50 GB discs became the standard for films, while the later BDXL format stretched to three and four layers.
Hollywood refused to release films until players carried stronger copy protection than the DVD system, which had been cracked. The first recorder, Sony's BDZ-S77, went on sale in Japan on April 10, 2003, for US$3,800, with no films to play. Movies finally arrived on June 20, 2006, the format's worldwide launch, with early titles such as The Fifth Element and MGM's The Terminator. By then rival HD DVD players had reached shops a few months ahead.
The resulting format war ended in February 2008, when Toshiba, HD DVD's chief backer, dropped its format; it went on to sell its own Blu-ray player in late 2009. Picture quality kept climbing: the original specification topped out at 1080p, while Ultra HD Blu-ray reaches 4K at up to 60 frames per second, and Japan even has an exclusive 8K version. The discs also carry games for recent PlayStation and Xbox consoles.
Source: Blu-ray
