(Image: Oxford University)
The first integrated on-chip nonvolatile all-photonic memory has been created by scientists at Oxford University (Oxford, England), the University of Münster (Münster, Germany), Karlsruhe Institute of Technology (KIT; Eggenstein-Leopoldshafen, Germany), and the University of Exeter (Exeter, England).1 The new device uses the phase-change material Ge2Sb2Te5 (germanium-antimony-tellurium, or GST), which is the same material used in rewritable CDs and DVDs and switches from an amorphous to a crystalline state and back when prompted by light.
The wavelength-multiplexed device has single-shot reading and switching energies at a 1 GHz speed are as low as 13.4 pJ. The device is a multilevel memory, meaning that various state rations, from entirely crystalline to completely amorphous and in between, can be written, thus storing more than one bit per site.
Researchers have tried to create on-chip photonic memory before, but the results have always been volatile, requiring power in order to store data.
"This is the first ever truly nonvolatile integrated optical memory device to be created," says Carlos Ríos, one of two lead authors of the paper. "And we've achieved it using established materials that are known for their long-term data retention; GST remains in the state that it's placed in for decades."
1. Carlos Rios et al., Nature Photonics (2015); doi: 10.1038/nphoton.2015.182