Researchers have developed a photonic memory which, unlike previous devices that rely on light as a mechanism for storage, is non-volatile and can be simultaneously read and rewritten. This would make it the first optical memory that is analogous to silicon memory, making it a potential building block for all-optical processor.
While promising, the technology has to be proven to scale from its densest implementation thus far, a cell that stores all of 8 bits. But if it can be made to scale, the ramifications for computing and communications systems are profound. An all-optical processor would run incalculably faster than today's fastest silicon processors.
The memory makes use of GST, the same material used in rewritable CDs and DVDs. GST has both crystalline and amorphous states, each of which reflects light differently; having binary states makes it appropriate for storing binary data.
But the researchers, associated with universities at Oxford, Karlsruhe, Exeter and Munster, discovered properties of GST that had been either previously unknown or simply unexploited. The material can toggle between crystalline and amorphous states; the crystalline state affects how much light is absorbed; and the crystalline ratio is controllable (90% crystalline to 10% amorphous, 80/20, and so on).
The researchers created silicon nitride waveguides, upon which they deposited GST. One pulse of light in the waveguide would turn the GST amorphous; a second pulse would return it to a crystalline state. By measuring the light transmitted through each waveguide, they could determine which state the GST was in -- amorphous or crystalline -- a 1 or a 0.
Furthermore, using multiple wavelengths to control the crystalline ratio renders a device that can story data in eight states, going way beyond binary.
The researchers reported that their memory cells feature switching energies as low as 13.4 pJ at speeds approaching 1GHz, with "virtually unlimited" bandwidth.
The advance was originally published in Nature Photonics (subscription required for full article).
— Brian Santo, Senior Editor, Components, T&M, Light Reading