Optical RAM and integrated optical memories: a survey

The remarkable achievements in the area of integrated optical memories and optical random access memories (RAMs) together with the rapid adoption of optical interconnects in the Datacom and Computercom industries introduce a new perspective for information storage directly in the optical domain, enabling fast access times, increased bandwidth and transparent cooperation with optical interconnect lines. This article reviews state-of-the-art integrated optical memory technologies and optical RAM cell demonstrations describing the physical mechanisms of several key devices along with their performance metrics in terms of their energy, speed and footprint. Novel applications are outlined, concluding with the scaling challenges to be addressed toward allowing light to serve as both a data-carrying and data-storage medium. Integrated optical memory technologies may in the future become an attractive option for storing data in an energy efficient and compact manner. The progress that has been made in the field has now been reviewed by three Greek researchers. Theoni Alexoudi and Nikos Pleros from Aristotle University of Thessaloniki and George Kanellos from University of Bristol describe how the energy consumption, speed and size of optical Random Access Memory (RAM) and flip-flop memory has been transformed over the past 25 years. They report how the footprint of optical memory cells has shrunk from the meter to the sub-micrometer scale, while the energy per bit has now reached 1 fJ/bit and access times have approached a few tens of picoseconds. Schemes based on semiconductor optical amplifiers, micro-ring and micro-disk lasers and photonic crystals are all discussed.