Focusing and defocusing switching of an indium selenide-silicon photonic metalens.

With a fixed geometric design, homogeneous change of Indium Selenide () switches the focusing length of a silicon photonic metalens between positive and negative values. This unique functionality of the hybrid metasurface is attributed to the fact that the silicon's refractive index is in the middle of the two convertible states in the optical phase change material. The infrared transparency of in both states enables near phase-only metasurface structures. The design is foundry compatible and feasible for implementing nonvolatile adaptive transformation optic systems on-chip.