  Reconfigurable optical systems are the object of continuing, intensive
research activities, as they hold great promise for realizing a new generation
of compact, miniaturized, and flexible optical devices. However, current
reconfigurable systems often tune only a single state variable triggered by an
external stimulus, thus, leaving out many potential applications. Here we
demonstrate a reconfigurable multistate optical system enabled by phase
transitions in vanadium dioxide (VO2). By controlling the phase-transition
characteristics of VO2 with simultaneous stimuli, the responses of the optical
system can be reconfigured among multiple states. In particular, we show a
quadruple-state dynamic plasmonic display that responds to both temperature
tuning and hydrogen-doping. Furthermore, we introduce an electron-doping scheme
to locally control the phase-transition behavior of VO2, enabling an optical
encryption device encoded by multiple keys. Our work points the way toward
advanced multistate reconfigurable optical systems, which substantially
outperform current optical devices in both breadth of capabilities and
functionalities.
