▎ 摘　　要

Guiding terahertz waves below the diffraction limit of light typically excite graphene plasmons (GPs). However, the mode confinements of conventional GPs using graphene-dielectric interfaces are limited. To further squeeze the optical mode sizes, a graphene-dielectric-metal (GDM) configuration supporting an image graphene plasmon (IGP) has been reported recently through the plasmon interactions in a graphene sheet and its mirror image inside a metal with out-of-phase charge oscillations. This study proposes a waveguide structure consisting of a cylindrical dielectric wire over a GDM to achieve an ultraconfined mode area by coupling a dielectric waveguide and an IGP mode. Furthermore, this work examines the dependence of waveguide dimensions and material properties on the mode characteristics of the proposed hybrid IGP (HIGP). This HIGP achieves plasmon wavelengths 20 times shorter and normalized propagation lengths twice longer than GPs, accompanying a mode size of 3 x 10(-8)A(0), where A(0) is the diffraction-limited mode area. Moreover, the simple structure makes the HIGP easy to be verified experimentally. This work demonstrates that the HIGP delivering strong light-matter interactions at extremely compact dimensions can be exploited for building highly integrated, enhanced nonlinear, high-resolution sensing and imaging THz devices.