▎ 摘　　要

A graphene sheet gated with a ridged ground plane, creating a soft-boundary graphene nanoribbon, is considered. By adjusting the ridge parameters and bias voltage a channel can be created on the graphene which can guide transverse magnetic surface plasmon polaritons. Two types of modes are found; fundamental and higher-order modes with no apparent cutoff frequency and with energy distributed over the created channel, and edge modes with energy concentrated at the soft-boundary edge. Dispersion curves, electric near-field patterns, and current distributions of these modes are determined. Since the location where energy is concentrated in the edge modes can be easily controlled electronically by the bias voltage and frequency, the edge-mode phenomena is used to propose a voltage controlled plasmonic switch and a plasmonic frequency demultiplexer. (C) 2013 AIP Publishing LLC.