An Investigation of Low-Loss Sodium Plasmon Waveguides Based on FEM

A sodium-based hybrid plasmonic waveguide consists of the Na film and wedge-shape Si ridge waveguide is designed. The overall performance of the waveguide and its application as a nano-laser are studied by using the finite element method (FEM) with emphasis on effective index, propagation length, normalized mode area, figure of merit, confinement factor, gain threshold, and Purcell factor. The results point out that the designed waveguide exhibits the strong field confinement ability as well as high figure of merit. Particularly, a large Purcell factor of 536 and an ultra-low gain threshold of 0.066 μm⁻¹ could be concurrently obtained, which is far smaller than that of conventional Ag-based plasmonic waveguides. The proposed waveguide could potentially advance the utilization of sodium-based plasmonic waveguides in the field of nano-laser, resonator, modulator, and other nanophotonic devices.