  Nanophotonics has garnered intensive attention due to its unique capabilities
in molding the flow of light in the subwavelength regime. Metasurfaces (MSs)
and photonic integrated circuits (PICs) enable the realization of
mass-producible, cost-effective, and highly efficient flat optical components
for imaging, sensing, and communications. In order to enable nanophotonics with
multi-purpose functionalities, chalcogenide phase-change materials (PCMs) have
been introduced as a promising platform for tunable and reconfigurable
nanophotonic frameworks. Integration of non-volatile chalcogenide PCMs with
unique properties such as drastic optical contrasts, fast switching speeds, and
long-term stability grants substantial reconfiguration to the more conventional
static nanophotonic platforms. In this review, we discuss state-of-the-art
developments as well as emerging trends in tunable MSs and PICs using
chalcogenide PCMs. We outline the unique material properties, structural
transformation, electro-optic, and thermo-optic effects of well-established
classes of chalcogenide PCMs. The emerging deep learning-based approaches for
the optimization of reconfigurable MSs and the analysis of light-matter
interactions are also discussed. The review is concluded by discussing existing
challenges in the realization of adjustable nanophotonics and a perspective on
the possible developments in this promising area.
