Temporal reflection without the need for ultrafast index changes in ENZ-like modes

Time reflection, where an electromagnetic wave reverses direction due to a temporal change in refractive index, typically requires rapid and substantial modulations that are challenging to achieve in the optical domain. In this theoretical study, we demonstrate that time reflection can be achieved using moderate, adiabatic refractive index changes in ENZ-like modes of a plasmonic slab waveguide. Through numerical modeling of ZnO waveguides with optically tunable carrier concentrations, we show that slow modulation of the plasma frequency can reverse the group velocity of light, leading to time reflection without the need for ultrafast pumping. These results provide a foundation for further exploration of temporally modulated materials.