First all-optical permanent on-chip memory developed

Researchers, including one of Indian-origin, have created the first all-optical permanent on-chip memory that can store data for decades, an advance that may lead to the development of optical computers.
With optical elements, computers can work more rapidly and more efficiently. Optical fibres have long since been used for the transmission of data with light. But on a computer, data are still processed and stored electronically.
Electronic exchange of data between processors and the memory limits the speed of modern computers.
To overcome this, it is not sufficient to optically connect memory and processor, as the optical signals have to be converted into electric signals again. Scientists, hence, look for methods to carry out calculations and data storage in a purely optical manner.

Scientists from Karlsruhe Institute of Technology (KIT), the University of Munster, Oxford University, and Exeter University have now developed the first all-optical, non-volatile on-chip memory.
"Optical bits can be written at frequencies of up to a gigahertz. This allows for extremely quick data storage by our all-photonic memory," said Professor Wolfram Pernice, who headed a working group of the KIT Institute of Nanotechnology (INT) and recently moved to the University of Munster.

"The memory is compatible not only with conventional optical fibre data transmission, but also with latest processors," added Professor Harish Bhaskaran of Oxford University.
The new memory can store data for decades even when the power is removed. Its capacity to store many bits in a single cell of a billionth of a metre in size (multi-level memory) also is highly attractive.

Instead of the usual information values of 0 and 1, several states can be stored in an element and even autonomous calculations can be made.
This is due to so-called phase change materials, novel materials that change their optical properties depending on the arrangement of the atoms: Within shortest periods of time, they can change between crystalline (regular) and amorphous (irregular) states.
For the memory, the scientists used the phase change material Ge2Sb2Te5 (GST). The change from crystalline to amorphous (storing data) and from amorphous to crystalline (erasing data) is initiated by ultrashort light pulses. For reading out the data, weak light pulses are used.

Permanent all-optical on-chip memories might considerably increase future performance of computers and reduce their energy consumption.
Energy-intensive conversion of optical signals into electronic signals and vice versa would no longer be required.
The study is published in the journal Nature Photonics.