A bright idea: storing data using light-based memory chips
The world's first fully light-based storage chip that can store data permanently was developed by scientists at the University of Oxford in collaboration with scientists in Exeter, plus Karlsruhe and Münster, both in Germany. Built with materials used in rewritable CDs and DVDs, these chips could dramatically help improve data transfer speeds in modern computers.
Today's computers are slowed down by the relatively slow data transfer speeds between a processor and the memory itself. "There is no point in installing faster processors when a kind of brake is in transferring information to and from the memory - the so-called Neumann bottle neck", says Professor Harish Bhaskaran, who lead the research. "But we think light can speed up the transfer considerably."
However, it’s not as simple as solving the processor-memory bottleneck by throwing in a few photons; the data must first be converted into optical signals and then back into electronic signals once it has been transferred. To truly increase data transfer speeds, both the memory and the processor would have to work with light.
Researchers have tried repeatedly to develop such a photonic memory, but the data stored is always volatile, meaning that energy is required to maintain its integrity. Therein lies the problem; a computer hard drive must be able to store data indefinitely with or without power supply.
A bright idea
Now an international team of researchers, including scientists from the Department of Materials at Oxford University, has produced the world's first photonic non-volatile memory chip. This new chip uses the Ge2Sb2Te5 (GST) phase change material, which is also used for rewritable CDs and DVDs. This material may adopt an amorphous state (such as glass) or a crystalline state (such as metal), regardless if electrical or optical pulses are used. The researchers used a small area of the GST known as a ‘waveguide’ to successfully transport the light pulses.
The team showed that intense light pulses sent through the waveguide can change the state of the GST. An intense pulse causes the material to melt abruptly and cool down rapidly, thereby adopting an amorphous structure; a slightly less intense pulse can transform it into a crystalline state. The two states result later, when light with much lower intensity is transmitted through the waveguide, which is transmitted more or less depending on the state, in the form of a ‘1’ or ‘0’. "This is the first true non-volatile optical memory", explains Clarendon Scholar and DPhil student Carlos Ríos. "And we have even been able to achieve our goal with common materials known for long-term data retention."
Increasing speed and performance
By simultaneously transmitting light with different wavelengths, the team also showed that they could use a single pulse to read and write data simultaneously. "In theory, this means that we can read and write thousands of bits at the same time, which promises nearly unlimited bandwidth”, explains Professor Wolfram Pernice of the University of Münster, Germany.
The researchers have also found that different intensities of strong pulses produce exactly and repeatedly different mixtures of the amorphous and crystalline structure within the GST. When weak pulses were sent through the waveguide to read out the contents of the memory, they could detect subtle differences in transmitted light. They were able to produce eight different compositions (from completely crystalline to completely amorphous), store them as data and read them out again. This multi-state capability could provide storage units with more than the usual binary information of 1’s and 0’s so that a single bit of the memory can store multiple states or even perform calculations itself, thus relieving the processor of this activity.
In the report, Professor Bhaskaran mentions: "This is a whole new kind of functionality with proven materials. These optical bits can be described at frequencies of up to one gigahertz, delivering gigantic bandwidths, which is the kind of ultra-fast data storage that modern computing needs."
In the meantime, the team is working on a series of test projects that will use the new technology. They are particularly interested in the development of a new electro-optical link that allows the memory chips to connect directly to other components using light rather than electrical signals. Time will tell just how important this breakthrough could be for future data storage technologies and what the implications might be for industries around the world.
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