Ever heard about Von Neumann bottle-neck? It is actually a phenomena in which the speed with which electrons can be sent down the interconnects, between memory and processor are slower than the speeds at which faster silicon can eat through the information. So in a nutshell, electrons are quick, but they are not quick enough. Infact they are so slow that they are actually holding back the speed of modern computing.
It has been noticed that the clock speeds of chips haven’t really increased so instead of accommodating more in one place, our computers now come equipped with multi-core processors, marking out tasks to be completed on separate chips. The reason for this is the inability to transmit data between memory and chip and that too keeping up with higher clock speeds. Considering all these things, a team has developed the world’s first ever light-based memory chip that can store data permanently, and it could help change the face of computing.
It is based on the concept that if the electrons could be swapped with photons and the electrical interconnects could be replaced with something optical, information could be sent between memory and processor at the speed of light. Then, there would be no trouble in transmission keeping up with the speed of computation. Scientists have tried to create this kind of photonic memory before, but it’s always required power to store data. When the power was turned off, the data was lost.
Considering all these aspects, the new kind of memory, developed by researchers from the Universities of Oxford and Exeter in the UK and the University of Munster and KIT in Germany, uses what’s known as a phase-change material as the basis of its storage. It uses an alloy of germanium-antimony-tellurium known as GST —the same material that’s used in rewritable CDs and DVDs. This substance is advantageous in the way that it can be forced to assume an amorphous state, like glass, or a crystalline state, like a metal, by using either electrical or optical pulses. And according to Harish Bhaskaran, from the University of Oxford’s Department of Materials, “These two states have very different physical and properties, and that means you can store information in the state of the material.”
Bhaskaran and his team managed to build the device in which a one micron piece of GST sits on top of a silicon nitride ridge, known as a waveguide that acts a miniature fibre optic cable that can carry light. When the team fires high intensity pulses of light down the waveguide, they can change the state of the GST. A very intense pulse can be used to momentarily melt and quickly cool the GST, causing it to assume an amorphous (glass-like) structure. By sending a slightly lower intensity pulse down the waveguide, the team can raise the temperature above the crystallization point but below the melting point, which puts it into a crystalline state. But the twist in the story is: when a light with a much lower intensity is sent through the waveguide, a little of light seeps out into the GST. Depending on what state the GST happens to assume, a little more or a little less light is transmitted from one end of the waveguide to the other. The team can measure the differences with incredible accuracy, which allows them to tell if the GST is crystalline or amorphous. By writing with strong pulses and reading with weak pulses, the researchers can easily replicate the 1s or 0s you’d find in normal memory. And the best part is, unlike the previous optical memory, the new device holds on to what’s written on it, with or without power.
The team was also able to show that it was possible to send different wavelengths of light through the waveguide at a given point of time. Theoretically this means, that the team can read and write to thousands of bits at the same time, providing infinite bandwidth.
There is another surprise element associated with the device. The team has found that different intensities of strong pulses can actually be used to create different mixtures of amorphous and crystalline structure within the GST — making it 10 percent amorphous and 90 percent crystalline say, or 50-50. When the lower intensity pulses are then sent down the waveguide to read the contents of the device, those subtle differences in composition can be seen in the transmitted light, too, allowing the researchers to reliably write and read off eight different levels of state composition — from entirely crystalline to completely amorphous.
This multi-state capability of the device can usher a whole new era of computing because using this device instead of the usual 0 or 1, the researchers in theory would be able to represent a 0, 1, 2, 3, 4, 5, 6 or 7, quadrupling the amount of data that can be stored in a single bit.
Though this whole concept and device is at its nascent stage and there is still work to be done like shrinking the device a little in size and the most important thing: the architecture required to make purely optical computing a reality. So understandably the next thing on the team’s agenda is the opto-electrical interconnects that are required to link the memory to a processor.
Using photons instead of electrons is surely a revolutionary idea in itself and when and how this idea turns into reality is something worth waiting for!
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Author:Technology Blog
