Reconfigurable nanophotonics with low-loss phase-change materials

Phase change materials (PCMs) are revolutionizing nanophotonics by providing ways to locally tune and reconfigure optical devices. The last decade has witnessed many exciting reports of novel devices exploiting PCMs such as for example beam-steering, tunable light emission, reflection and absorption, programmable metasurfaces and reconfigurable neural networks. A large majority of the first studies were using standard PCMs such as GeSbTe as simple binary on-off switches, in which the ON state is the amorphous phase and the OFF state the fully crystalline phase. However, PCMs present another degree of freedom for tunability: the possibility to encode multilevel non-volatile states via partial change of phase. Furthermore, recently a new class of low-loss PCMs emerged (e.g. Sb2S3 and Sb2Se3), with negligible optical absorption in the near-infrared. In this talk, we will present recent results on original methods to program PCMs into various multilevel states of crystallization. We will then present nanophotonic devices leveraging this multilevel programming and conclude on the perspectives of this technology