Blu-Ray Disc~he full Story ~ TYroTecHs
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Blu-Ray Disc~he full Story

| Monday, February 25, 2008 |

Blu-ray is our next form of optical storage, and it will become popular in India soon. Demand has to be created for the product – and this time let's please not dilly-dally, we always lag behind when it comes to tech stuff (whiny tone). We enjoyed some HD content through our PS3, and it looks insane. So it's about time.

Tech2 spoke to leading Blu-ray brands in India, like Samsung, Sharp, Sony, and asked them to send us their latest players and discs, so we can start having some high-def fun. But before that let's consider some basics, pointers, and trivia about our new friend...

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Why Blu
Before explaining why and how Blu-ray functions, one must know that an optical disc stores digital info (1s and 0s) in the form of bumps burnt in on the aluminum layer, in the form of concentric rings. The laser scans outwards, reflects off these bumps and flat part sequentially. The reflected rays obviously are different, and thus an optical sensor records a ‘1’ for bump and ‘0’ for no bump. (Here 1 means a higher signal level and not the number 1!). A bitstream is created and sent to the DAC (digital-analog converter).

So how does this relate to Blu-rays having more info? The answer is in the type of laser used, the numerical aperture of the lens, the distance between bumps (track pitch), its thickness etc. They are all lessened or increased accordingly. E.g. while DVDs use a red laser of 635-650nm wavelength to read information on discs, the amount of data that can be stored and read is only 4.7 GB for single layer discs.

Back in around 2003, when terrestrial digital broadcasting started, the great minds in the heads of great companies (now known as the BDA) figured out that recording about two hours of HD media on to a disc would need 22GB, something that a DVD cannot provide. Thus Blu-ray discs were born (and also HD DVD, then known as AOD).

The abbreviation is BD, and the cause for having such a name is due to the type of laser used: a blue violet laser of lesser wavelength, 405 nm. This facilitates a more accurate focus, and thus more info can be written and read from the same space. Another point is that the numerical aperture is made larger: 0.85 from 0.60 in DVDs. This facilitates a smaller diameter of the laser point (more accurate), allowing more info to be assimilated on the discs. That explains why BD discs are of the same diameter and thickness (120mm and 1.2 mm respectively) as normal discs, though the storage capacity is 25GB for single layer and 50GB for dual layer.

One cool thing of BDs is that they have a harder coating; the data is read off this itself, and thus they claim to be very resistant to dirt and other stuff. But this we will have to look at more closely before we commit ourselves...

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