Development of the next-generation memory is almost at the point where the group, which holds patents on the technology, can start working on its commercial development, according to Professor Kazuyuki Hirao of the department of material chemistry, Graduate School of Engineering, Kyoto University. Hirao said such work would begin before the end of the year.
About two years ago, the group discovered that when a very short pulse of laser light produced by a femtosecond laser is applied to a piece of glass containing the rare earth element samarium, the glass is transformed, a dot around 400 nanometres in diameter where the light hits becoming luminous while the rest remains transparent. This difference allows the glass to be used as an optical memory.
Luminous dots can be spaced 100 nanometres apart on a glass surface that includes samarium -- and now the group has confirmed that these dotted surfaces can be layered. In their experiment they had the equivalent of 2000 layers of dots in a cubic centimetre of glass and managed to store the equivalent of eight terabits of data (eight terabits is one terabyte or 1000 gigabytes), according to Shigeki Sakaguchi at the fine chemical business planning division of Central Glass, a glass manufacturer.
"Until then, each layer could not be read as individual data. But by irradiating with a femtosecond laser and changing the number of elements, we discovered that it is possible," said Kyoto University's Hirao, who specialises in the field of femtosecond lasers.
A femtosecond laser is a laser that irradiates for an extremely short period of time -- one 1000-trillionth of a second. The group discovered, five to six years after it started the project in 1994, that such lasers are required because longer pulses of light causes excessive heat.
"If a nanosecond or picosecond laser is applied on glass, the radiated heat that occurs causes glass to crack. Only a femtosecond laser can irradiate without heat," Hirao said.
Hirao said femtosecond lasers are the only laser which can cut a molecule. Using a femtosecond laser, broadband communication technology that enables transmission of terabits of data per second is possible, he said, talking of another project he is working on.
Another three-dimensional medium, holographic memory, has been around for more than 20 years; however the structure of holographic memory is so complicated that it is not yet possible for it to be developed as a practical memory device, according to Central Glass' Sakaguchi.