Sa0 mode converter for nano plasmonic integrated circuits.

We propose an Sa0 mode converter (Sa0MC) that transforms Ss0 mode to Sa0 mode in an insulator-metal-insulator-metal-insulator waveguide (IMIMI-W) at a wavelength of 1.55 microm. The proposed Sa0MC is composed of 3.0 microm-wide input and 2.0 microm-wide output IMIMI-Ws connected by a laterally tapered IMIMI-W with vertical silver ridges (VSRs) and lateral silver mirrors (LSMs). The input, tapered, and output IMIMI-Ws were designed to use 20 nm thick Au strips. The VSRs and LSMs were selected to use silver ink. Low-loss polymer was used for the 30 microm-thick upper and lower cladding layers and the 500 nm-thick central insulator layer sandwiched by two Au strips. The approximately 5.1 microm x 4.9 microm input Ss0 mode was converted to a approximately 1.0 microm x 0.5 microm Sa0 mode. The mode converting efficiency was approximately 5.0 dB in simulation. The proposed Sa0MC opens a new route for nano-plasmonic integrated circuits with mode sizes less than the diffraction limit of light.