All of the advances in optical disc technology since the CD have been of 3 varieties. You either change the reading laser so it can be focused into a smaller dot, you change the distance from the laser so you can focus it tighter, or you add another recording layer. DVD added a layer and changed the distance, HD-DVD added a layer and changed the wavelength, Bluray changed the distance and the wavelength. 

The problem for the purveyors of future advances is that they’ve hit the limit on changing the distance and of visible light wavelengths, the Bluray disc is about as close as you can possibly get to the surface of the disc. Blue lasers are about the limit of visible light technology as well. TDK decided to go one route with their experimental 100 and 200gig 3-6 layer bluray discs. Is that all they can do? 

Well, I decided to look at what they could do with non-visible EM radiation, and found this old article from Pioneer.http://www.theinquirer.net/default.aspx?article=19531

UV lasers sound like a real departure in a number of ways. They’re going to have to go back to the drawing board with how to make multilayer discs and the like. They can probably even make discs that you can’t see the recording surface with, but transmit UV…

Are we going to see a UVray in the future with 3-6 layers?