Optical Chip Memory

Illustration of all-optical data memory: ultra-short light pulses (left) make a bit in the Ge2Sb2Te5 (GST) material change from crystalline to amorphous (or the reverse), and weak light pulses (right) read out the data. Credit: C. Rios/Oxford University

Researchers at the University of Exeter collaborated with colleagues at the Münster University to develop the first full optical chip memory.

Light has been used to transmit data since thousands of years and more recently scientists have been able to funnel laser beams into optical fibres reaching amazing transport capacity, now in the thousand of billion bits per second. 

Light, laser light, has also been used to write and read bits on optical disk, hence storing data on a medium. It hasn't been possible, so far, to use light for storing bits in chips. Computers can receive, and they do, optical signals but need to convert them into electrical signals to store the data (even in the case the storage is made onto an optical disc, the data flowing through an optical fibre have to be converted into electrical signals to drive the laser that writes on the DVD disc). The conversion process requires time and energy.

The prototype of optical chip memory developed by the researchers solves these issues for the first time. It is described in an article on Nature Photonics.

The chip uses a phase changing material (Ge2Sb2Te5). The phase of cluster of its atoms can be changed by a laser pulse, transforming the cluster from amorphous to crystalline. This phase change can be detected by a weak laser beam. Hence the stronger laser pulse is used to write the bit, the weak one to read it. 

In practice one can plug in an optical fibre in the chip and store the bits as they come in (it is actually a tad more complicated that this...). No optical to electrical conversion required.

A further step in the path leading to a full optical computer...

Author - Roberto Saracco

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