Scientists have created the world's first entirely light-based memory chip that can store data permanently.
This incredible new device could significantly improve the speed of modern computing, the University of Oxford reported. The development is significant because today's computers struggle with a relatively slow transmission of electronic data between the processor and the memory.
"There's no point using faster processors if the limiting factor is the shuttling of information to-and-from the memory -- the so-called von-Neumann bottleneck," said Professor Harish Bhaskaran, who led the research. "But we think using light can significantly speed this up."
The processor-memory gap cannot simply be bridged with photons because they must be converted back to electronic signals, but this new light-based system could offer a solution. The world's first all-photonic nonvolatile memory chip uses the phase-change material Ge2Sb2Te5 (GST) that is often used in rewritable CDs and DVDs to permanently store data. The GST is applied to a silicon nitride ridge, known as a waveguide, that works to carry light.
The researchers demonstrated that intense pulses of light sent through the waveguide can change the state of the GST, causing it to quickly melt or cool to form amorphous and crystalline structures. The state of the GST influences how much light is transmitted and the researchers can measure this difference to identify the state.
"This is the first ever truly non-volatile integrated optical memory device to be created," said Clarendon Scholar and DPhil student Carlos Ríos, one of the 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."
The team sent differ wavelengths of light through the waveguide at the same time (wavelength multiplexing) and found they could use a single pulse to write and read to the memory at the same time. This means they could potentially read and write to thousands of bits at once and create an almost unlimited bandwidth. The researchers also demonstrated that different intensities of strong pulses can create various mixtures of amorphous and crystalline structure within the GST. Low intensity pulses that detected differences in transmitted light allowed the scientists to write and read off eight different levels of state composition. This ability could lead to memory units with more than the usual binary information of 0 and 1, allowing single bits of memory to store several states at once.
'This is a completely new kind of functionality using proven existing materials,'" Bhaskaran said. "These optical bits can be written with frequencies of up to one gigahertz and could provide huge bandwidths. This is the kind of ultra-fast data storage that modern computing needs."
The findings were published in a recent edition of the journal Nature Photonics.
