The advantage of Blu-ray technology is that the laser beam can focus more closely on the surface of the disk. Tight focus means that a smaller spot will be produced on the surface of the disc, and when the seats are smaller, there will naturally be room for more information on each disk. The smallest spot size of any laser depends on a naturally accruing phenomenon called diffraction. The narrow beam of light sent out from a laser will always diverge into a wider beam eventually, because of the natural diffraction of waves. Diffraction will also occur the waves meet an obstruction. By reducing the wavelength of a laser, we can affect the diffraction.
The Blu-ray technology diffraction is also affected by the fact that the lens to focus the light has a higher numerical aperture than the lenses found in ordinary DVDs - 0.85 instead of 0.6. Blu-ray technology based appliances are also equipped with a dual-lens system of the highest quality, and the cover layer is made thinner to prevent unwanted optical effects. All this makes it possible for a Blu-ray laser to focus on much smaller spots. The optical improvements are accompanied with a new method for encoding data which makes it possible to store even more data on Blu-ray Disc.
The standard for Blu-ray technology has been developed as a joint venture between several major manufacturers of PCs and consumer electronics, including Sony and Philips. The group is called Blu-ray Disc Association (BDA). The first Blu-ray recorder was launched in
The main competitor to Blu-ray technology is the HD DVD format, which is also able to store more information than a standard DVD. Blu-ray technology, however, provides more information per layer than HD-DVD format - 25 GB compared to 15 GB. Blu-ray technology, on the other hand most likely be more expensive to support, at least initially, making HD DVD a tempting alternative. In a Blu-ray disc, the data is stored extremely close to the surface. This made the first Blu-ray discs are extremely vulnerable to scratches, and many users preferred the tougher HD DVD discs. Since 2004, all Blu-ray discs are coated with a clear polymer called "Durabis", which makes them much more durable. According to the developers of Durabis, the TDK Corporation, a coated Blu-ray disc work, even after being attacked with a screwdriver.