Wednesday, June 25, 2008

JJNN 32 June 25th, 2008

Welcome again to JJNN for Wednesday June 24th, 2008. Today I want to talk about a new idea from Japan that should be able to increase the storage capacities of optical media.

The Institute of Multidisciplinary Research for Advanced Materials at Tohoku University in Northern Japan released a paper in which they described a way to increase the storage capacity in optical media like CDs and DVDs by up to 9 times. The original story can be found here. A one sided DVD with only one layer now has a storage capacity of up to 4.7GB. This new type of DVD could possible have a storage capacity of up to 42GB. That is a lot for just one tiny disc.

Before I get into the details of why this new disc can hold so much more data than a traditional disc I want to say a little bit about how a DVD works in the first place. Probably everyone knows that it all has to do with lasers, I mean they do call it an optical drive after all. But, how does that laser read data off the disc? Well that is the fun part. All CDs and DVDs have flat microscopic pits on their surface. A laser light is shone upon the bottom of the disc and either hits a pit or a flat spot. Because of the slight difference of depth between the bottom of the pits and the tops of the pits the laser light is either reflected into a laser pickup assembly. If the laser is reflected onto the assembly the result is a "1." If the reflected laser does not hit the assembly the result is a "0." These ones are zeroes are binary and when a whole string of them together the result is a nice movie watching experience (or any other form of data).

Well that may be simple enough, but how do we end up increasing the amount we can store on a DVD without cramming a lot more of those pits onto it? Well this is where Tohoku University stepped in. They asked themselves why all those pits have to be flat. They found that if all the pits are shaped like Vs the storage capacity is greatly increased.

The reason that the capacity is increased is because when the laser light hits the v-shaped pit the light is reflected back with elliptical polarization which is oriented in a plane that is dependent on the orientation of the v-shaped pit. That was quite a pain in the wrist to write and I assume a headache to read, so I will try to do a better job to explain how this works. The light that is shone into a pit will be reflected no matter what, but the orientation of the pit will change how the laser light is polarized. This difference of polarization leads to a difference in the output for pits that are in different orientations, which means that one pit can actually act like many different pits if the detector or the laser source is turned with respect to the pit. In experimentation the disc was rotated over 180 degrees which was split into 512 segments. They found that one pit can actually hold as much information as 2^9 traditional pits.

This sounds good to me. I don't know if I actually need a DVD that can hold that much data, but it would not be a bad thing to have. This could mean that start of bigger and cheaper storage devices. I can't wait to see where this will good. But, as with all good news, there is some bad news. Normal DVD or CD players could not play these new discs. The disc reader assembly would have to be replaced for one made for the new type of disc. If that doesn't cost too much I am all for it.

Any way, it is now time for the word of the day. Today's word is 記憶容量(きおくようりょう). It is pronounced kioku-youryou and means storage capacity. I remember back in the day when we had to save on those huge black floppy disks. Now that is how a real man saves data!

That's it for today. See you next time at JJNN.

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