memory doesn't fade
Technology Research News
Optical data storage devices have the potential
to surpass magnetic disk drives in capacity, but the necessary technology
is in its infancy and faces several hurdles. One problem is figuring out
how to use light to read data stored in light-sensitive material without
altering the data.
A team of researchers in Japan has addressed the problem with a recording
medium that can be read more than a million times without damaging data.
The researchers designed the material for near-field recording systems,
which use extremely narrow beams of light to record bits.
The narrow beams are produced by shining light through a tiny hole and
a lens, both positioned extremely close to the surface of the recording
"Information recording is achieved as the reversible -- that is, rewritable
-- photoreaction of the photochromic molecules" in the medium, said Tsuyoshi
Tsujioka, a principal researcher at Sanyo Electric Company's New Materials
Research Center. Photochromic materials change color when they are exposed
Ordinarily, data is read by shining low intensity light on the material
and measuring the change in how it absorbs the light. But each exposure
to low-intensity light produces the same reaction as the recording operation,
only to a lesser degree.
"Repeated irradiation... for information readout destroys the information,"
The researchers got around the problem by using a different color, or
wavelength, of light to read data. Data is written with red light and
read with infrared light. The infrared light does not trigger the photochromic
reaction but does induce a electric current in the medium.
Instead of measuring a change in light absorption, the researcher's system
senses the difference in current through areas of the material that have
been altered by the recording lightwaves.
"The recording density of probe memory systems such as near-field memory
is... related to the size of the probe apex,” said Tsujioka. “Our goal
[is] one bit stored by one molecule.”
If that proves possible, the storage system could hold 100 terabits of
data per square inch, said Tsujioka. That density would be enough to store
about half a million high-resolution photographs in an area the size of
The nondestructive readout method could be ready for use in practical
applications in five to ten years, said Tsujioka.
Tsujioka's research colleagues were Yuji Hamada and Kenichi Shibata Sanyo
Electric Company, and Akira Taniguchi and Takashi Fuyuki of the Nara Institute
of Science and Technology in Japan. They published the research in the
April 16, 2001 issue of the journal Applied Physics Letters. The research
was funded by Sanyo.
Timeline: 5-10 years
TRN Categories: Materials Science and Engineering; Data
Story Type: News
Related Elements: Technical paper, "Nondestructive readout
of photochromic optical memory using photocurrent detection," Applied
Physics Letters, April 16, 2001
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