Storing data with light – at chip level

Storing data with light – at chip level

By eeNews Europe

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A team of researchers of the Karlsruher Institut of Technology (KIT) and the universities of Exeter, Münster and Oxford have succeeded in what they call a substantial step towards the optical computer. Phase change materials that can change their optical properties according to the relative position of the atoms make it possible to store multiple bits in a single storage cell.


Light is already an indispensible ingredient in the information and communications technology, enabling computers to do their work faster and more energy efficient. In data communications, fiber optics offer the fastest and most powerful means of data transport. In the computer however, the data are processed and stored electronically. Using electronic methods to exchange data between the processor and the memory and storage units limits the speed of modern computers; experts call this the von-Neumann bottleneck. To overcome this limitation it is not enough to establish optical data paths because the signals would have to be re-converted into electrical ones. Therefore, scientists have long been looking for ways to perform computations as well as storage exclusively by optical means.


The British-German research collaboration now spoke up in the magazine Nature Photonics to announce their achievement: They succeeded in creating the first non-volatile, entirely optical on-chip storage device. “Optical bits can be written to the device at frequencies up to 1 GHz, making our storage extremely fast compared to existing approaches”, said professor Wolfgang Pernice who led a research team at the Institute of Nanotechnology (INT) of the KIT and now continues his research at the University of Münster. “Our storage device is compatible with known optical data transport systems via glass fibre as well as with the most modern processors,” added professor Harish Bhaskaran from the Oxford university.


The optical storage device can retain data over decades without power supply. Particularly interesting is its capability of storing multiple bits in a single multi-level-memory cell in nanometre dimensions. Instead of the usual binary values 0 and 1, multiple states can be stored in such an element; it is even possible to perform stand-alone computational operations in these cells.


The function of the optical storage device is based on the properties of phase-change materials – novel materials that can change their optical properties as a function of the of the position of the atoms: They can change back and forth between the crystalline and amorphous state. For their storage unit the scientists used a phase-change material that bears the rather exotic name Ge2Sb2Te5, or GST. With ultra-short light pulses it is possible to trigger the change of the states. To read the data, the scientists used weak light pulses.


Non-volatile optical storage at chip level have the potential to significantly increase the performance of computers in the future. At the same time they can help reducing the power consumption. Together with fully optical data links they could reduce latencies and make the energy-consuming process of transforming optical to electronic signals and vice versa a thing of yesterday.


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