Blu-ray

Blu-ray, also known as Blu-ray Disc (BD), is the name of a next-generation optical disc format jointly developed by the Blu-ray Disc Association (BDA), a group of the world's leading consumer electronics, personal computer and media manufacturers (including Apple, Dell, Hitachi, HP, JVC, LG, Mitsubishi, Panasonic, Pioneer, Philips, Samsung, Sharp, Sony, TDK and Thomson). The format was developed to enable recording, rewriting and playback of high-definition video (HD), as well as storing large amounts of data. The format offers more than five times the storage capacity of traditional DVDs and can hold up to 25GB on a single-layer disc and 50GB on a dual-layer disc. This extra capacity combined with the use of advanced video and audio codecs will offer consumers an unprecedented HD experience.

While current optical disc technologies such as DVD, DVD±R, DVD±RW, and DVD-RAM rely on a red laser to read and write data, the new format uses a blue-violet laser instead, hence the name Blu-ray. Despite the different type of lasers used, Blu-ray products can easily be made backwards compatible with CDs and DVDs through the use of a BD/DVD/CD compatible optical pickup unit. The benefit of using a blue-violet laser (405nm) is that it has a shorter wavelength than a red laser (650nm), which makes it possible to focus the laser spot with even greater precision. This allows data to be packed more tightly and stored in less space, so it's possible to fit more data on the disc even though it's the same size as a CD/DVD. This together with the change of numerical aperture to 0.85 is what enables Blu-ray Discs to hold 25GB/50GB.

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Blu-Ray is presently supported by its inventor, Sony, and Dell, Hitachi, Hewlett-Packard, Panasonic, Pioneer, Philips, Samsung and other IT equipment producers. But, as the format will have a big word to say in the movie industry, the movie studios supporting it are also important. So far, Metro-Goldwyn-Mayer and Walt Disney declared their support for Blu-Ray. The format had also two of the major game companies announcing their support: Electronic Arts and Vivendi

Overall, the figure behind this association, with Apple the most recent joining member, is around 450 billion USD. But things are not very clear. The movie studios support is not exclusive, so if the rival format manages to get ahead sooner, we may witness important forsakings.


Beyond the financial aspects, Blu-Ray is a more important technological development compared to the DVD. The laser ray used for reading CDs and DVDs belongs to the red spectrum, with wavelengths of 708, respectively 650 nm.

Blu-Ray uses a blue spectrum laser (violet-blue, in fact), which operates on a wavelength of 405 nm, meaning a bigger quantity of information can be written on the same surface as a CD/DVD.

But the minimum "spot size" that a laser can be focused is limited by diffraction, and depends on the wavelength of the light and the numerical aperture of the lens used to focus it. By decreasing the wavelength (moving toward the violet end of the spectrum), using a higher dual-lens system, and making the disk thinner, the laser beam can be focused much more tightly at the disk surface. This is, in a few words (in addition to the optical improvements), the technological advancement proposed by Blu-Ray.

The protecting layer for CDs and DVDs (cover layer) is 0.6 mm. in thickness, while Blu-Ray's cover layer is only 0.1 mm. thick, which, roughly, means a better access to the recording area.

The advantage? On the same 12 cm. surface (standard dimension of a CD/DVD), 25 GB of data can be stored (single layer), which translates to 2 hours of HDTV video and audio content. And this, with MPEG-2 encoded data, the same as for DVDs.

And while using MPEG-4 H.265/AVC or VC-1, a codec derived from Windows Media 9, up to 4 hours of HDTV content can be stored.
The transfer rate for such a disc is 36 MB/s, compared to the 5MB DVD can provide, and Blu-Ray discs 2x (72 MB/s) are already under study.

And Blu-Ray is not going to stop here. 100 and 200 GB discs are under study, evolving from dual-layer to 4 or 8 layer.

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