arun’s blog

I have always had a particular jones towards technology, which has aggrandized since my dad bought my first computer with 166 MHz Intel processor and 32 MB RAM configuration. In fact, it has even influenced to a great extent in pursuing my under graduation studies too. I could not help but get fascinated by these next generation optical drives and whet my appetite to contribute significantly. Here is a piece of information to the likewise ardent admirers of technology!!

Physics and Technology: Blue ray acquires its name from the blue-violet laser technology, although HD DVDs also use the low wavelength blue lasers. How does this really make a difference increasing the storage size by about 4 to 6 fold? A Blue-ray disc has around 25GB of storage capacity where as HD DVDs have about 15 GB, on comparison to a 4.7 GB DVD disc. Understanding HOW requires, if not comprehensive, a glancing purview of how optical drives typically work. In optical drives, the digital information is usually encoded in the pattern of pits of varying lengths. The laser beam in the drive is excited on to these information layers and a photo diode collects the reflected light (the pits reflect less light than the adjacent layers). However, it is imperative to agnize that the lens (focusing the laser beam) produces a finite diameter owing to diffraction. So, the pits must be separated by the distance demanded by the diffraction of the light wavelength in order for the data reading to be efficient. This ultimately decides the size of the optical storage disc. By using shorter wavelengths, the spot size for reading pits can be reduced which results in many pits at relatively small distances separating each other, hence the tremendous increase in the size!! To quantify, the pit length has decreased in CD, DVD, HD DVD and blue-ray as 0.8, 0.4, 0.2 and 0.15 micrometers. To physics fanatics, refer 1 and 2.

Does this really make a difference? There is of course increase in the resolution obtained, however, not as high as the resolution obtained as in the case of say, a video-tape to DVD era. Before clambering up the bandwagon, it is essential to know, the technology of the drives demand equal display resolutions from TV or computer displays to bring the best out of it. The maximum resolution of the best displays is about 1080p (progressive scan) > 1080i (interlaced). Blue-ray players typically demand a 1080p resolution whereas HDTV (TV shows) are broadcast at 1080i or 720p. So, watching them on a 1080p TV makes no difference!

It is surprising as to how much increase in the storage capacity can be obtained from basic physics learnt at the level of high-school, Huygens’ wave theory (to those who were taught properly!! I owe it to Mahalakshmi teacher ).