Strong amplification of graphene surface plasmon polaritons in a time-varying plasmonic waveguide using temporal anisotropy

This paper presents a temporal plasmonic waveguide for significantly amplifying graphene surface plasmon polaritons (GSPPs) using a time-varying anisotropic interlayer medium. GSPPs supported by a double-layer graphene structure are excited in the mid-infrared regime using the Otto prism configuration. Finite-element simulations demonstrate that temporal modulation of the relative permittivity of the medium between the graphene layers, from air to an anisotropic state and subsequently back to air, can substantially enhance the plasmonic field compared with that of a conventional time-invariant plasmonic waveguide. The corresponding dispersion analysis indicates that the amplification originates from the temporal variation of the effective refractive index experienced by the GSPPs at the temporal boundaries. The effects of six key parameters on the amplification are systematically investigated, including the Fermi energy, incident frequency, modulation strength, interlayer separation, number of temporal slabs, and Fermi-energy mismatch between the two graphene layers. The results show that an amplification level on the order of 10 6 can be achieved using four temporal slabs, relative to the conventional time-invariant configuration. In addition, the effects of graphene nonlinear conductivity, material dispersion and loss, and temporal modulation of the graphene Fermi energy on the maximum electric-field amplitude and amplification level are examined. These results provide insight into the amplification of graphene plasmons in temporally modulated plasmonic structures and may be useful for applications in nonlinear optics and plasmonic sensing.