So far, Blu-ray is the most advanced CD format which can save document files with a volume of about 25GB which is as five times large as the existing(single layered)DVDs. And the recording speed is marvelous with 4.5 to 9 GB recorded each second.
The popular DVD technology applies a wavelength of 650nm red laser and a 0.6 numerical aperture focusing lens, disc thickness of 0.6mm. The Blu-ray technology uses a wavelength of 450nm blue-violet laser, through the wide-angle lens on a ratio of 0.85 numerical apertures, thus successfully minimizing the focused spot size. In addition, the Blu-ray disc structure applying optical 0.1mm thick transparent protective layer can reduce the rotating discs in the process of reading and writing due to disorders caused by tilt, which makes it easier to read the disc data, and to increase storage densities as much as possible.
Blu-ray disc has a track pitch reduced to 0.32μm which is only half of that of the current red DVD disc, and its record unit – grooves (or phase-change chemicals unit) is the minimum diameter of 0.14μm which is also far smaller than that of the red light. Single-sided single-layer Blu-ray disc storage capacity is defined as 23.3GB, 25GB and 27GB, with the highest capacity (27GB) is the current red-sided single-layer DVD disc capacity (4.7GB) nearly six times that of enough to store more than 2 hours playback time, high-definition digital video content, or more than 13 hours playback time, the standard television programs (VHS format image quality, 3.8MB / s).
In fact, to replace the red laser with a blue one was not contrived by the DVD Forum, a principal member of the research and development, instead, it was initiated by Japan’s Nichia (Japan Asia) and Toyoda Gosai. According to IDG’s relevant reports, the two companies had disputes for as long as six years to compete for Blu-ray storage technology, which substantially delays the development and application of this technology. However, in the Mid-August of 2002, the dispute finally reached an agreement; the two companies launched peace talks and began to license its technology to other vendors, thereby clearing the Blu-ray technology in the development process of a major obstacle.
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