Researchers hope optical memory will lead to a faster Internet

Scientists working on methods to create a faster internet have come up with an idea which uses optical holes which can be switched between light-transmitting and light-blocking states to construct digital signals.

According to the journal Nature Photonics, which we get for its Sunday colour supplement, the researchers at NTT have been working on such devices for several years, but they used too much power and could not retain data long enough.

But the new memory cells use just 30 nanowatts of power, 300 times less than previous designs, and can retain data for one microsecond, which is four times longer than the previous record of about 250 nanoseconds.

Masaya Notomi, director of the Photonic Nanostructure Research Group at NTT said that is enough to support processing. Notomi said that the first target is memory in network routers or servers. This is because at high data rates, optical signals are much more efficient than electrical ones, and the need to convert them back and forth wastes energy.

Stage two would be to “replace RAM in high-speed computers,” Notomi said,

To make the optical memory, the researchers took a thin slab of indium phosphide. In the centre, they buried a strip of another optical material, indium gallium arsenide phosphide. This strip is about four micrometers long and 300 nanometres wide and serves as the memory cell. The indium phosphide is etched with nanoscale holes, creating a structure that transmits only certain wavelengths of light. A path through the middle of the cell is left unetched, to guide light.

The next stage needed a laser which means that the researchers had to ask a responsible adult to help them. They tuned the laser so that when a wavelength shined on the cell, the material’s refractive index changes so that it either will or will not transmit a pulse of light, to create either a “1” or “0” bit. The next light pulse reverses it.

The NTT researchers went on to integrate four of the memory cells on the same chip. Theoretically they can mix a million cells to create a device with a power consumption of 30 milliwatts. Flash memory uses on average 150 milliwatts. He and his group are now working on adding the lasers and light detectors needed to read and write optical memory to the same chip.