Cylindrical Composite Hybrid Plasmonic Waveguides with Ultra-Strong Field Confinements: A FEM Study

Surface plasmons have the unique advantages of local field enhancement and subwavelength field confinement, thus have been widely used in subwavelength photonic as well as nanoscale imaging, nano-lasers, and nonlinear optics. In this work, we report a cylindrical composite hybrid plasmonic waveguide, which supports a plasmon mode with ultra-strong field confinement that is formed due to the coupling of the surface plasmon mode in the Na nanowire waveguide and hybrid surface plasmon mode in the Na-based cylindrical hybrid waveguide. The modal properties of the proposed waveguide are thoroughly investigated by using the finite element method. The proposed structure allows the mode coupling to be enhanced, which in turn gives it superior performance. Further, the optimized parameters are determined, under which the waveguide exhibits an ultra-small normalized mode area of 1.52 × 10⁻⁵ and a high figure of merit over 3.2 × 10³. The proposed waveguide may make a contribution to the development of nanoscale devices in photonic integrated circuits, such as nanowaveguides, resonators, and nano-lasers.