▎ 摘　　要

The hybridization of hyperbolic polaritonics with THz plasmonics has attracted immense attention due to its fascinating applications in this region. However, to effectively enhance the performance of these coupled modes, one way is the usage of smart materials in the heterostructures. Here, we introduce a symmetric graphene-based structure containing hexagonal boron nitride (hBN) layers, where two nonlinear layers have been utilized as claddings to improve the confinement of hybrid surface phonon-plasmon-polaritons (HSP3). A new analytical model is derived by using Maxwell's equations and applying the boundary conditions. A set of nonlinear equations are solved numerically, and the obtained results are reported. Harnessing a nonlinear medium together with hybrid graphene-hBN layers allows one to tune the propagation properties of the structure by changing the chemical potential, the relaxation time, and the nonlinear factor. The study has been done for two frequency regions: the upper Reststrahlen and the lower Reststrahlen bands. The numerical results show a long propagation length (L-prop = 300 mu m) and a large figure of merit (FOM = 98) for HSP3 propagating in the upper Reststrahlen band at the frequency of 45 THz. The proposed structure and its analytical model can open new insight into the design of tunable devices in mid-infrared plasmonics.