The Blu-ray Disc belongs to a new generation of optical discs capable of staging high density data. Blu-Ray technology is based on a blue-violet coloured laser. The blue laser operates at a wave length of 405 nm, while older technology such as DVDs and CDs are based on red and infrared lasers that works at 650 and 780 nm. Since the wave length is shorter with a blue laser, the new Blu-ray technology makes is possible to store much more information

The advantage with the Blu-ray technology is that the laser beam can be focused much more tightly at the surface of the disc. Tight focus means that a smaller spot will be produced on the surface on the disc, and when the spots become smaller there will naturally be room for more information on each disc. The minimum 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, due to 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.

In Blu-ray technology, the diffractions is also affected by the fact that the lens used 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 supreme quality, and the cover layer has been made thinner in order 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 the Blu-ray disc.

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