  Dielectric optical nanoantennas play an important role in color displays,
metasurface holograms, and wavefront shaping applications. They usually exploit
Mie resonances as supported on nanostructures with high refractive index, such
as Si and TiO2. However, these resonances normally cannot be tuned. Although
phase change materials, such as the germanium-antimony-tellurium alloys and
post transition metal oxides, such as ITO, have been used to tune optical
antennas in the near infrared spectrum, tunable dielectric antennae in the
visible spectrum remain to be demonstrated. In this paper, we designed and
experimentally demonstrated tunable dielectric nanoantenna arrays with Mie
resonances in the visible spectrum, exploiting phase transitions in
wide-bandgap Sb2S3 nano-resonators. In the amorphous state, Mie resonances in
these Sb2S3 nanostructures give rise to a strong structural color in reflection
mode. Thermal annealing induced crystallization and laser induced amorphization
of the Sb2S3 resonators allow the color to be tuned reversibly. We believe
these tunable Sb2S3 nanoantennae arrays will enable a wide variety of tunable
nanophotonic applications, such as high-resolution color displays, holographic
displays, and miniature LiDAR systems.
