Phase change materials (PCMs) are currently revolutionizing nanophotonics by providing ways to tune and reconfigure optical functionalities without any moving parts. Building on this phenomenon, 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 crystallization. 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 paper, we will present recent results on 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 for this technology.

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Capucine Laprais, Lotfi Berguiga, Guillaume Saint-Girons, Xavier Letartre, and Sebastien Cueff, "Programmable multilevel nanophotonics with chalcogenide phase-change materials," Proc. SPIE PC12890, Smart Photonic and Optoelectronic Integrated Circuits 2024, PC128900V (Presented at SPIE OPTO: February 01, 2024; Published: 9 March 2024); https://doi.org/10.1117/12.3010496.2ec9c3d2-9551-ee11-a99c-00505691c5e1.