Propagation Properties of Nanoscale Three-Dimensional Plasmonic Waveguide Based on Hybrid of Two Fundamental Planar Optical Metal Waveguides

In this paper, a nanoscale three-dimensional plasmonic waveguide (TDPW), created by depositing an Ag stripe on a SiO2 layer with an Ag substrate, is introduced and theoretically investigated at visible and telecom wavelengths. By applying the effective index method and finite-difference time-domain numerical simulations, the authors find that the propagation properties of surface plasmon polaritons (SPPs) in the TDPW, including the propagation length and beam width, are mainly decided by the core (the SiO2 layer just under the Ag stripe) itself, due to the much stronger localization of SPPs in the core than in the two side claddings (the SiO2 layer without the covered Ag stripe). And propagating SPPs in the TDPW are strongly confined in the core region, even with a very small waveguide cross section. Furthermore, based on the stronger localization of propagation SPPs in the TDPW, two kinds of bending waveguides, oblique bending and 90 degrees circular bending waveguides, are also investigated. For wavelength of 1550nm, the 90 degrees circular bending guide with a minimum radius as small as 2.6m show nearly zero radiation loss, even with a small waveguide cross section of 70x80nm(2). The proposed TDPW is suitable for planar integration and provides a possible way for constructing various nanoscale counterparts of conventional integrated devices such as splitter, resonator, sensor, and optical switch.