
320 GB Write Once Optical Disc by TDK
TDK Corp. developed a write-once optical disc with an impressive capacity of 320 Gbytes. This goes well above the capacity of a Blu-ray disc that has a total of 25 Gbytes per layer. The means of writing and reading data from this optical disc that requires a blue-violet semiconductor laser with an oscillation wavelength of 405nm and an objective lens with a numerical aperture (NA) of 0.85, that are currently used for the Blu-ray discs. TDK recording format in 2006 that had six layers, each of 33.3 Gbytes in capacity, adding up to the 200 Gbytes total capacity. As the number of recordable layers increase, the signals of each layer get weaker, requiring improvement in the transmittance of the layers. The transmittance of the outermost layer, that needs to be the highest, now reaches more than 90%, while the 2006 prototype barely had 80% to 90%. The layer architecture of the new disc comes as – a cover layer and a hard coat layer are formed on recording layer (the innermost L0 layer to the outermost L9 layer), while the L0 layer features a Si-Cu alloy, which is inorganic.
