Non-Volatile Reconfigurable Silicon Photonics Based on Phase-Change Materials

The traditional ways of tuning a silicon photonic network are mainly based on the thermo-optic effect or the free carrier dispersion. The drawbacks of these methods are the volatile nature and the extremely small change in the complex refractive index (Delta n<0.001). In order to achieve low energy consumption and smaller footprint for applications such as photonic memories, optical computing, programmable gate array, and optical neural network, it is essential that the two optical states of the system exhibit high optical contrast and remain non-volatile. Phase change materials (PCMs) such as Ge2Sb2Te5 provide an excellent solution, thanks to the drastic contrast in refractive index between two states which can be switched reversibly and in a non-volatile fashion. Here, we review the recent progress in the field of non-volatile reconfigurable silicon photonics based on PCMs. We start with a general introduction to the material properties of PCMs that have been exploited in integrated photonics and discuss their operating wavelengths. The various photonic switches that are built upon these PCMs are reviewed. Lastly, we review the recent applications of PCM-based photonic integrated circuits and discuss the potential future directions of this field.