In a potentially significant leap toward optical computers, researchers at the Karlsruhe Institute of Technology (KIT) in Germany and the universities of Münster, also in Germany, and Oxford and Exeter, both in the UK, have developed the first nonvolatile all-optical chip memory based on phase-change materials that change their optical properties depending on the arrangement of the atoms, allowing for the storage of several bits in a single cell.
The new all-optical permanent on-chip memory device stores information in the atomic order of a nanoscale phase-change material. The optical absorption of the material changes drastically when switching between the amorphous and crystalline state. “Therefore, by looking at transmission past the memory we can tell in which phase state the material is,” says Professor Wolfram Pernice, who worked in the KIT Institute of Nanotechnology (INT) before recently moving to the University of Münster. “By using a short laser pulse the memory element can be set into either to the crystalline or the amorphous state and thus modifies the absorption value. We then read out the memory by sending a weak light pulse past the element to check whether the transmission is low (0) or high (1).”Read more