Information Storage in Three Dimensions

Mar 18, 2008 by Laura Mgrdichian feature

For the first time, researchers have successfully turned a glass material into three-dimensional information storage using a light-based technique. This achievement may be a big step forward for the real-life implementation of such materials, which have the potential to store terabits of data (1,000 gigabits, or about 125 gigabytes) in just a single cubic centimeter.

The research was performed by scientists from the University of Bordeaux 1, one of the four universities in Bordeaux, France. The work is described in a paper published in the February 13, 2008, online edition of Optics Letters.

“The necessity for increasing data storage capacity of memory devices, along with the growth of high-density technologies, requires the use of three-dimensional optically based systems,” said physicist Lionel Canioni, one of the paper's authors, to PhysOrg.com.

There are a few methods being explored for optical-based three-dimensional information storage. One method is based on the phenomenon of “photochromism,” which, simply put, is when a material can reversibly change color -- i.e. undergo a chemical change -- when exposed to electromagnetic radiation (light). An everyday example are “transition”-type sunglass lenses.

Photochromism is an example of “single-photon” excitation, meaning that each photon in the light source (such as a laser beam) excites a single electron in the material. When those electrons quickly become de-excited, they each emit a single photon with almost the same energy as the absorbed photon.

Another promising method, explored by Canioni and his colleagues, involves multi-photon excitation—the excited electrons each absorb multiple photons—and is therefore a bit more sophisticated. Because each electron that is excited absorbs more than one photon, the laser interacts with a smaller volume of material. This allows the storage material to be activated with a higher spatial resolution in three dimensions, which allows for a larger information storage density.

The material the group used is a specific type of zinc phosphate glass that contains silver ions. The samples are one millimeter thick, colorless, and highly polished. The researchers irradiated the samples with very short, intense pulses of a laser beam, which were focused 200 micrometers (µm, or millionths of a meter) into the sample. The group varied the laser power and the number of pulses the sample received, and measured how the irradiated area of the material absorbed and re-emitted the light.

They noticed that the irradiation caused the silver atoms to form closely packed clusters with a nanoscale size comparable to that of molecules. At certain values of laser power and number of pulses, the silver clusters re-emitted the laser light at a key frequency—specifically, a frequency three times as high as the laser light, known as the third-harmonic. The researchers used the beam from an intense laser to “write” information into the material. The same beam, but with a lower intensity, induces the third-harmonic from the clusters, which is used to read the information out.

At about the 200 µm depth, the group wrote three layers of information, each layer containing a 12-by-12 grid of bits with a bit spacing of 3 µm and a layer spacing of 10µm (which corresponds to a gigabit per square centimeter). In the first, second, and third layers, respectively, Canioni and his colleagues wrote the letter “U,” the letter “B,” and the number “1” (for University of Bordeaux 1), using the bits to form the characters.

They tested the permanence of the images by subjecting the samples to heat treatments. Only when subjected to a temperature of 400 °C for 20 minutes did the written information vanish as the glass reorganized itself. After re-polishing the samples, the information could be rewritten.

Said Canioni, “We can state that the recording is very stable in standard conditions (up to 85 °C). The third-harmonic signal is not modified, even after several hours of unstopped exposure.”

Citation: Optics Letters / Vol. 33, No. 4 / February 15, 2008

Copyright 2008 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

Explore further: Infrared imaging technique operates at high temperatures

add to favorites email to friend print save as pdf

Related Stories

Research leads to better asphalt roads

11 hours ago

In cooperation with eleven road construction companies, the University of Twente is working on improving asphalt roads in the Netherlands. By using new technology during the asphalt paving process, the resulting ...

Solving an organic semiconductor mystery

Jan 16, 2015

Organic semiconductors are prized for light emitting diodes (LEDs), field effect transistors (FETs) and photovoltaic cells. As they can be printed from solution, they provide a highly scalable, cost-effective ...

Recommended for you

Infrared imaging technique operates at high temperatures

Jan 23, 2015

From aerial surveillance to cancer detection, mid-wavelength infrared (MWIR) radiation has a wide range of applications. And as the uses for high-sensitivity, high-resolution imaging continue to expand, MWIR sources are becoming ...

Football physics and the science of Deflategate

Jan 23, 2015

News reports say that 11 of the 12 game balls used by the New England Patriots in their AFC championship game against the Indianapolis Colts were deflated, showing about 2 pounds per square inch (psi) less ...

Physicists find a new way to slow the speed of light

Jan 23, 2015

(Phys.org)—A team of physicists working at the University of Glasgow has found a way to slow the speed of light that does not involve running it through a medium such as glass or water. Instead, as they ...

User comments : 5

Adjust slider to filter visible comments by rank

Display comments: newest first

superhuman
1 / 5 (2) Mar 18, 2008
>12-by-12 grid of bits with a bit spacing of 3 µm and a layer spacing of 10µm (which corresponds to a gigabit per square centimeter)

Its 11 megabit per square centimeter and 11 gigabit per cube centimeter.
guiding_light
3 / 5 (2) Mar 19, 2008
If an electron absorbs more than one photon, it absorbs the energy total, which could be enough to kick it out of the sample.
ShadowRam
2.3 / 5 (3) Mar 19, 2008
For the first time? I was pretty sure they already accomplished this years ago?
holoman
1 / 5 (2) Mar 19, 2008
ShadowRam,

Polight from Cambridge/Oxford.~ 2000
Ragaar
1 / 5 (1) Mar 26, 2008
@"Polight from Cambridge/Oxford.~ 2000"

"However the likely duration to reach full commercialisation combined with the resulting funding needed was determined to be un-economic in the current difficult financing environment. "

Full story:
http://www.cdrinf...sId=8335

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.