Monday, August 8, 2011
Incredibly, the disc is written and read using the same red laser that DVD's use! What this means that current media hardware doesn't need a complete re-config in order to play the disc. So, if the magic isn't in the laser, then where is it? The answer comes from the world of material science.
The disc's incredible capacity has to do with what its made of, and not so much how the data is written to it. You see, the data writing and reading concept for this disc is essentially the same as its been since the release of the Laserdisc in 1978 (if you don't know what that is, it basically looks like a ridiculously large DVD. Look it it up). Data writing is accomplished by changing the refractive property of certain parts of the disc material so that the changed and unchanged parts together represent 1's and 0's. So, binary disc writing remains the same as its always been. The critical difference with this disc has to do with how the refractive property of the disc is changed.
At right, is a diagram showing how each of the current media discs are written to. Each disc is 1.2 mm thick, but the laser is focused so that data is written to one specific plane within the thickness of the disc (where the transparent pyramids come to a point). This data is represented as lines of tiny divets that are literally burned out of the plastic in the disc. To read the data, a low power laser is sent through the disc, it reflects off of an aluminum backing, and it comes back up to the reader lens, being refracted by the divets. A light sensor can see the difference between refracted and non refracted light, and this information is interpreted by the computer. Unfortunately, this method of writing data has severe limitations because it only allows for writing to a realistic maximum of about 4 planes within the thickness of the disc. The reason for this is that the divets in each plane will interfere too much with the reading laser. What then is the solution?
Remember (vaguely?) all that stuff about electron energy levels? Well, that comes into play here. So, most atoms of a high enough atomic number (remember, that's it's number on the periodic table) will have multiple layers of electrons spinning around each other (imagine each layer, or "shell" as they are called, as layers of a jawbreaker). Each electron layer contains a specific amount of energy, with layers increasing in energy as you go out from the nucleus. What this means is that if you sufficiently increased the energy of the outside layer, the electrons would get kicked up to a higher energy shell layer. Since this higher energy state is forced, and unnatural, the electrons will spit out the extra energy and immediately "fall" back down to their natural energy state, much like when a roller coaster is forced up a hill and is then let go. The extra energy is then released from the atom as light.
Now, you may know that light is composed of photons. Photons, as it turns out can act as a replacement for electrons when shot directly into an atom. The trick with the TeraDisc is that its re-structured molecules require the insertion of two photons in order to kick up the electrons to a higher energy state, and to release said photons upon returning to its normal state. This means that the laser has to be of sufficient intensity (or, for you more sciency types, of sufficient photon density) in order to activate this energy absorption and release.
If you look at the above picture, you will see that the laser (it looks like an orange hour-glass) is focused on one point. This is the point where the laser is most intense, and therefore the only point which will activate the energy absorption-and-release of the surrounding molecules. The disc reader sees the photons (light) released from these molecules in the changed sections, and is therefore able to successfully interpret the data on the disc for each of the 200 layers.
And so, using the latest and greatest in material science technology, media storage is set to once again make a giant leap forward in capacity. The possibilities that this technology holds are exciting to say the least. We could see things like holographic movies, HD at astronomical resolutions, and the ability to hold your current computer's hard drive on one disc. This is something to keep your eye on in the near future.