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Blu-ray Discs

Blu-ray Discs

What are Blu-ray discs? How did they get their name? For these answers and more, you must read on.
Manali Oak
Blu-ray is an upcoming and a promising optical storage format used for storing high-definition video and data. Wondering where its name came from? Well, it originated from blue laser, which is used to read from or write in these types of discs. Let us find more about this brilliant storage device, the Blu-ray disc (abbreviated as BD).
With the advent of high-definition television, a digital television broadcasting system, a need was felt to have a technology to record and play high-definition content. This was around 1998. During this time, the use of shorter-wavelength lasers was known to facilitate optical storage of higher densities. Soon Shuji Nakamura, a professor at the Material Department of the College of Engineering, University of California, invented blue laser diodes, which entered the market much later. The development of Blu-ray disc is attributed to the Blu-ray Disc Association (BDA) that also licenses and establishes format standards for these discs.
In the initial days of their development, the data-recording layer was placed close to the surface of the disc, thus making them vulnerable to scratches and contamination. For this reason, Blu-ray discs of those times had to be protected by means of plastic cartridges. The physical specifications of the disc were completed in 2004. In the beginning of 2005, TDK declared of having developed a hard-coating polymer for the discs, thus eliminating the need of cartridges. Sony and Panasonic followed suit by developing hard-coat technologies.
Blu-ray discs use a blue-colored or rather a violet-colored laser that operates at a wavelength of 405 nanometers to read and write data. Owing to the laser's shorter wavelengths, it is possible to store more data on these discs. A laser beam is focused on the disc through the numerical aperture of a lens. If the wavelength is reduced and the numerical aperture is increased, the laser beam can be focused onto a smaller spot, thus enabling more information to be stored on a smaller area. Hence, despite having similar physical dimensions as those of CDs and DVDs, Blu-ray discs facilitate greater data storage. A single-layer blue-ray disc can store 25 GB while a dual-layer disk stores as much as 50 GB data. Isn't that amazing?
How are Blu-ray discs different from existing storage media? Current optical storage devices such as DVDs, DVD-R, DVD-RW, and DVD-RAM make use of a red-colored laser to read and write data whereas Blu-ray discs use a violet-colored laser beam. They offer higher storage capacities as compared to CDs and DVDs, and offer backward compatibility with them.
Even today, the Blu-ray technology is being updated as per the latest advancements. Engineers have come up with quad-layer discs which can store as much as 100 GB data. In 2006, TDK announced to have designed a Blu-ray disc that can store 200 GB data. Ritek Corporation, a Taiwanese consumer electronics group declared that they had devised an optical disc storage process that increases the disc capacity to 10 layers, thus raising the disc capacity to 250 GB. In 2007, Hitachi brought out a 100-GB Blu-ray disc consisting of four layers of 25 GB each. Later that year, Pioneer Corporation came up with a 400 GB Blu-ray disc consisting of 16 data layers of 25 GB each.
Mini Blu-ray discs, BD9/BD5, and AVREC are some variants. Mini Blu-ray discs can store around 7.5 GB data, on the lines similar to MiniDVDs. BD9 and BD5 contain video and audio streams that are compatible with the Blu-ray format. They are suitable for home users and can be used on conventional DVD players. AVREC is used to store content compatible with Blu-ray discs, onto standard DVDs. Similar to recordable and writable CDs and DVDs, BD-R and BD-RE discs are also available. BD-R discs can be written just once while BD-RE discs can be erased and recorded many times.
As of December 2008, over 1200 Blu-ray titles have been released in the United States and more than 640 have been released in Japan. Many more are expected to be released by 2009. Blu-ray discs have revolutionized the field of data storage, and are here to stay.