Active all-dielectric bifocal metalens assisted by germanium antimony telluride

Active metasurfaces provide a new way for applications requiring dynamic tunability and reconfiguration, such as beam steering, holographic displays and so on. In this paper, we proposed an all-dielectric metasurface, composed of phase-change material germanium antimony telluride (GST)/silicon hybrid nanopillars to realize dynamically tunable bifocal metalens operating at near-infrared (NIR) region. By changing the crystallization ratios of GST, simultaneous and continuous intensity modulations of the two focuses in the proposed metalens are achieved. It is ascribed to the large refractive index contrast of GST at different crystallization levels. This study proposes a way to realize dynamic optical modulation.