Nature Photon. http://doi.org/hrp (2012)

Temporary data storage, known as random access memory (RAM), is a crucial concept in computing and information processing. Optical approaches promise faster operating speeds and lower power consumption than the prevalent electronic equivalent. Kengo Nozaki and colleagues have now demonstrated writing, storing and erasing of data in a photonic-crystal-nanocavity memory that uses 300 times less power than previous devices.

A key characteristic of a RAM element is the ability to stably exist in one of two states: '0' and '1'. Such optical switches have been demonstrated before using bistable lasers, but the devices were bulky and didn't take full advantage of the potential power savings offered by optics.

Nozaki et al. use a photonic-crystal cavity in which, above a threshold input power, the light transmittance can take one of two stable values. Decreasing the volume and increasing the quality factor of the cavity reduces this threshold, enabling more efficient operation.

Their structure, etched into a semiconductor membrane, had a memory time of over one microsecond with a power consumption of just 30 nanowatts.