Blu-ray Disks (BD) – blue laser optical disk technology

Optical disc technologies such as DVD, DVD-R, DVD-RW, and DVD-RAM employ a 650 nm red laser, bond 0.6mm-thick discs and use lenses with a numerical aperture (NA) of 0.6. 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. As a consequence, the Blu-ray Disc’s tracking pitch is reduced to 0.32µm, less than half that of a regular DVD, and the minimum mark length is 0.14-micron, down from DVD’s 0.4-micron. In addition, by using a disc structure with a 0.1mm optical transmittance protection layer, the Blu-ray Disc diminishes aberration caused by disc tilt, allowing for disc better readout and an increased recording density. This allows data to be packed more tightly on a Blu-ray Disc than on a DVD. 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. The track format of Recordable Blu-ray Disc is groove-recording, i.e., recording data only on groove or in groove tracks. For the groove recording method, lands are sandwiched between adjacent grooves to block heat transfer between the grooves during recording, preventing signal quality deterioration in one groove track due to the influence of recording data in an adjacent groove tracks with a narrow track pitch. The track pitch between grooves in...

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