Hybrid Surface Plasmonic Waveguides

Manipulating light on subwavelength scale with less propagation loss is of critical importance in nanophotonics. Although dielectric waveguides are capable of supporting a long propagation distance, the guided mode tends to spread away when its dimension is smaller than the incident wavelength. There-fore, the dielectric waveguides could not obtain a tight confinement, while the surface plasmon polaritons (SPPs) waveguides can achieve the subwavelength confinement by use of a unique mechanism, whereby the light field is coupled to the coherent electron oscillations at the metal-dielectric interface. Due to the ability of breaking diffraction limit, SPPs have prominent advantages in many aspects, such as high sensitivity biosensors, super-resolution lithog-raphy, super-resolution imaging and nanoscale wave guiding. However, the SPP-based waveguides suffer high propagation loss induced by the intrinsic ohmic loss in the metal.Thus there is a sharp conflict between the light confinement and propagation loss in optical waveguides. In order to meet this challenge, a hybrid plasmonic waveguide, consisting of two dielectric nanowires symmetrically put at the opposite corner angles of a rhombic metal, is proposed and numerically analyzed by the finite-element method. Simulations show that the present waveguide can achieve the millimeter propagation distance (1244μm) and deep subwavelength mode area (5.5×10-3μm2), simultaneously. Compared with the previous hybrid waveguides based on cylinder nanowires or flat films, the rhombic corner angles enable our waveguide to achieve both longer propagation distance and smaller mode area. This is due to the enhanced coupling between the dielectric guided mode in nanowires and the surface plasmon polaritons mode at rhombic surface. Furthermore, the extreme confinement near the rhombic corner angles can strengthen the light-matter interaction greatly and make the present waveguide useful in many applications, such as nonlinear photonics, high-quality nanolasers and nanophotonic waveguides.