  All-dielectric metasurfaces provide unique solutions for advanced wavefront
manipulation of light with complete control of amplitude and phase at
sub-wavelength scales. One limitation, however, for most of these devices is
the lack of any post-fabrication tunability of their response. To break this
limit, a promising approach is employing phase-change-materials (PCM), which
provide a fast, low energy and non-volatile means to endow metasurfaces with a
switching mechanism. In this regard, great advancements have been done in the
mid infrared and near infrared spectrum using different chalcogenides. In the
visible spectral range, however, very few devices have demonstrated full phase
manipulation, high efficiencies, and reversible switching. Here, we
experimentally demonstrate a tunable all-dielectric Huygens metasurface made of
antimony sulfide (Sb2S3) PCM, a low loss and high-index material in the visible
spectral range with a large contrast (nearly 0.5) between its amorphous and
crystalline states. We show close to 2pi phase modulation with high associated
transmittance and use it to create switchable beam steering and holographic
display devices. These novel chalcogenide PCM metasurfaces have the potential
to emerge as a platform for next generation spatial light modulators and to
impact application areas such as tunable and adaptive flat optics, LiDAR, and
many more.
