# [ExI] 1000 Terabytes on a DVD

Anders Sandberg anders at aleph.se
Sat Jun 22 11:29:37 UTC 2013

```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

```