[opendtv] 3 Terabyte CDs
- From: "John Shutt" <shuttj@xxxxxxxxx>
- To: "OpenDTV" <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 15 Sep 2006 11:07:45 -0400
3 Terabyte CDs coming to a Player near you (blue lasers need not apply...)
John
http://www.technologyreview.com/read_article.aspx?id=17504&ch=infotech&ch=infotech
How to Burn a Three Terabyte CD
A new nano-optical device can focus laser light tighter than traditional
optics, which could lead to higher-density data storage.
By Kate Greene
A computer simulation of the optical nano antenna that Harvard researchers
have fabricated. Consisting of two gold-coated nano rods separated by a
30-nanometer gap, the antenna can focus light from a commercial laser to a
spot just 40 nanometers wide. It could be used to write terabytes, rather
than gigabytes, of data to a CD or DVD.
As gigabytes of movies, pictures, audio, and text fill up more and more CDs
and DVDs, there's clearly a need for better ways to save more data. A
research team at Harvard University has developed a technique that could
help to significantly boost the capacity of conventional optical discs.
They've fabricated a nano antenna--built directly onto an inexpensive,
off-the-shelf laser--that focuses light to a much smaller spot size than is
possible with even the best traditional lenses, potentially enabling more
bits to be written onto an optical disc.
The storage capacity of a disc increases as the wavelength of light used to
write data to it decreases; CDs are written and read using light with a
wavelength of 780 nanometers, DVDs use 650 nanometers, and HD-DVDs and
Blu-ray discs use 405 nanometers. Wavelengths shorter than 405 nanometers
would require light sources far too expensive for consumer electronics.
The problem is that conventional lenses can only focus light to half their
wavelength, a physical barrier called the diffraction limit. The Harvard
researchers sidestepped this limit, however, by abandoning traditional
optics in favor of nano-optical techniques. "We can get around the
wavelength limitation by using an antenna," says Ken Crozier, assistant
professor of electrical engineering at Harvard.
The team of Crozier, Federico Capasso, professor of applied physics at the
university, and graduate students Eric Kort and Ertugrul Cubukcu designed
the optical antenna to focus light from a commercial laser (with a
wavelength of 830 nanometers) to a spot size of 40 nanometers. With this
resolution, "you'd be able to pack more than three terabytes [3,000
gigabytes] worth of data onto something the size of a CD," Crozier
estimates. That's enough to hold more than 300 feature-length movies. By
comparison, a dual-layer HD-DVD or Blu-ray disc can hold 30 gigabytes or 50
gigabytes, respectively.
The antenna consists of two gold-coated nano rods, separated by a
30-nanometer-wide gap, according to Crozier. When light from the laser hits
the nano rods, it applies a force to the electrons in the gold, nudging them
out of place. The electrons don't stay displaced for long, however, and are
pulled back toward their original position. But they overshoot it, Crozier
says, and bounce back out of place, oscillating "like a mass on a spring."
These oscillating electrons affect the tiny gap between the nano rods. If
you took a snapshot of the antenna, Crozier says, you'd see that positive
charges collect on one side of the gap, and negative charges on the other.
The nano rods and gap act as a tiny capacitor--with opposite charges on
opposite sides of the gap--that effectively concentrates the energy from the
laser light into a spot about the size of the gap. This spot maintains its
size to about 10 nanometers away from the antenna before it starts to spread
out.
Although the 10-nanometer gap is minuscule, researchers could build a new
type of optical reading and writing head using the technology, suggests
Crozier. The magnetic storage industry, he points out, works with a
similarly small gap between the head and medium.
Using nano antennas to focus optical light is not an entirely new idea,
Crozier says, but their work, published in Applied Physics Letters, is the
first time an antenna has been integrated directly onto a laser. This offers
an advantage in production because the light source and antenna are in one
package. "It's extremely compact and easier to use because alignment with
the laser and the antenna is all done in fabrication," he says.
There's a lot of research activity to reduce the spot size of light, but
it's especially attractive to the data storage industry, says Bae-Ian Wu, a
research scientist in the Research Laboratory of Electronics at MIT. Using a
nano antenna is just one way to gain "super resolution smaller than the
wavelength of light." But, he says, the Harvard researchers work "is very
good in the sense that they are doing optical experiments to back up their
theory, while some papers are only in the realm of theory." The Harvard
scientists, he adds, "just did it."
Crozier says his team is exploring fabrication techniques that can further
decrease the spot size to 20 nanometers. They're also exploring alternatives
to the gold metal that currently coats their nano rods. Silver, for
instance, could focus light more efficiently than gold at the wavelengths
used by the consumer electronics industry.
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