Light-sensitive memory doesn't fade

By Eric Smalley, 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 medium.

"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 to light.

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," said Tsujioka.

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 a pinhead.

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
Funding:   Corporate
TRN Categories:   Materials Science and Engineering; Data Storage Technology
Story Type:   News
Related Elements:  Technical paper, "Nondestructive readout of photochromic optical memory using photocurrent detection," Applied Physics Letters, April 16, 2001


July 4/11, 2001

Page One

Split pulses speed signals

Gender gap shows cyberspace bias

Software lets appliances speak softly

Molecular shuttle gains light throttle

Light-sensitive memory does not fade


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