Ten layers, plenty of space
TDK Corp seems to be keen on sending the Blu-ray packing, as the company developed a 10-layer optical disc with capacity of 320GB, where each layer is capable of storing up to 32GB of data. Just for comparison, Blu-ray discs can store up to 25GB per layer.
Apparently, the more layers the medium has, the weaker the signal gets, so expanding optical drives by introducing more layers requires improved transmittance, something that TDK effectively tackled by enhancing the composition of used materials.
The first layer (L0) is made of an inorganic Si-Cu alloy, whereas the rest is a material made of bismuth peroxide and germanium dioxide. Apparently, TDK enhanced the transmittance by adjusting the density of germanium dioxide, as well as introduced materials which can lessen the damaging effects of heat.
The new medium will utilize the same laser found on Blu-ray drives - a blue-violet semiconductor laser with an oscillation wavelength of 405nm and an objective lens with a numerical aperture (NA) of 0.85. The symbol error rate is said to be less than 10-4, which the company claims is comercially viable and the laser output is less than 30mw. The prototype will be showcased at CEATEC Japan 2009.
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