[ExI] 1000 Terabytes on a DVD

[Anders Sandberg]

On 21/06/2013 23:40, Kelly Anderson wrote:
> http://theconversation.com/more-data-storage-heres-how-to-fit-1-000-terabytes-on-a-dvd-15306
>
> Can anyone with a physics background comment on this please? How does 
> one make a doughnut of light? Isn't the edge of the doughnut also 
> "fuzzy"? I kind of get it, but it makes me wonder if these guys are 
> smoking their own crack.

For the real details, check out the paper
http://www.nature.com/ncomms/2013/130619/ncomms3061/full/ncomms3061.html

Beams can have near arbitrary cross-sections. The standard beam is 
Gaussian-shaped, but it is entirely possible to make beams with holes in 
them. In this case they use the trick of having a resin that reacts to 
two beams, one of which inhibits the change. Only points where the 
writing beam intensity is high enough will be changed, and the optical 
trickery is all about ensuring this is as tiny as possible. If you 
handle that right you can make patterns smaller than the wavelength of 
light.

Whether this actually is a good way for data storage is another 
question. How do you read them without an electron microscope? They also 
note that making lines had a scanning speed around 160 microns per 
second. If we assume 52 nm resolution between the lines, there will be 
192,307 lines per cm. So writing a square centimeter takes 192,307 * 
(0.01/160e-6) = 12 million seconds, or about 140 days. This can 
presumably be speeded up by parallel writing, but I suspect the 
individual line writing speed is tough to change since it is about 
having enough photons absorbed in a certain volume without heating it 
too much - it is likely thermally limited.



-- 
Anders Sandberg,
Future of Humanity Institute
Oxford Martin School
Faculty of Philosophy
Oxford University