Light is ideally suited to data transfer, as it can transmit large quantities of information in a very short time, and is an indispensable part of the IT world of today and tomorrow. However, a stumbling block so far has been the storage of large quantities of data directly in the optical domain. While optical fibre cables – and, with them, data transfer by means of light – have long since become part of our everyday life, data on a computer are still processed and stored electronically. But now a team of scientists from Germany and England have made a key breakthrough by capturing light on a chip, so developing the first non-volatile – i.e. permanent – all-optical on-chip memory.
Traditional optical data storage media such as CDs or DVDs are slow, external mass-storage devices. Such technology is not suited to rapid data processing or for data storage on chips. "The all-optical memory devices we have developed provide opportunities that go far beyond any of the approaches to optical data processing available today," says Prof. Wolfram Pernice from the Institute of Physics at Münster University, who recently moved there from the Karlsruhe Institute of Technology and is one of the leading authors of the study. "Optical bits can be written in our system at frequencies of up to a gigahertz or more," adds Prof. Harish Bhaskaran from Oxford University in England, one of the co-authors, "and our approach can define a new speed limit for future processors, by delivering extremely fast on-chip optical data storage" In addition, he says, the written state is preserved when the power is removed, unlike most current on-chip electronic memories.
"With our laboratory prototype," explains Prof. David Wright, a co-author from the University of Exeter in England, "we now have, for the first time, a nanoscale integrated optical memory that is compatible not only with multi-wavelength optical fibre data transmission, but also with on-chip and chip-chip optical signalling, opening up the route towards ultra-fast data processing and storage". Our technology might also eventually be used, he says, to replicate neural-type processing such as that carried in the brain.
The scientists from Oxford, Exeter, Karlsruhe and Münster used so-called phase change materials at heart of their all-optical memory. The distinguishing feature of these materials is that they radically change their optical properties depending their phase state, i.e. depending on the arrangement of the atoms in the material. This changeability – between crystalline (regular) and amorphous (irregular) states – allowed the team to store many bits in a single integrated nanoscale phase-change cell.
Rios et al. (2015): On-chip integratable all-photonic nonvolatile multi-level memory. Nature Photonics Advance online publication (DOI: 10.1038/nphoton.2015.182)