Integrated Phase-Change Photonics for Memory and Computing

Chalcogenide-based phase-change materials, such as the ternary alloy Ge2Sb2Te5 (or GST for short), are well-known for their use in non-volatile memory applications. They have been used for many years (since the 1980s) for re-writable optical disk applications, and more recently for electrical memories (the 3D-xpoint memory announced by Intel and Micron in 2016 is phase-change based). However, with the dawn of the so-called silicon photonics revolution, in which chip-to-chip and even on-chip signals can be routed optically instead of electrically, the question naturally arises as to whether phase-change materials can be used to deliver a new generation of optical storage technologies – not one based around mechanically rotating disks, but one compatible with, and able to take advantage of, the ever-increasing capabilities of integrated photonic systems. Here we show that this is indeed possible, by embedding phase-change cells into standard integrated photonic devices and circuits (waveguides, resonators etc.). In particular we show that both binary and multilevel integrated phase-change photonic memories can be provided, along with a wavelength-division multiplexed capability. Since a multi-level memory facility can also be used to provide arithmetic, logic and neuromorphic (i.e. brain-like) processing capabilities, our approach can also be extended into these areas, as we demonstrate.