Guidance Properties of Plasmonic Nanogrooves: Comparison Between the Effective Index Method and the Finite Integration Technique

In this letter, we compare the effective index method (EIM), applied to derive an analytical model of the guidance properties of plasmonic groove waveguides, to full-wave simulations based on finite integration technique (FIT). We apply our results to different plasmonic groove geometries, with particular attention to the triangular (V-groove) waveguide. We first approximate the V-groove geometry with a multiple-sections rectangular-stepped waveguide, for which EIM may be applied in closed form. Explicit formulas for the dispersion properties are given in terms of a set of transcendental equations, which are then solved with standard numerical complex-zeros-searching routines. Our numerical results are then compared and validated with FIT full-wave simulations, showing the range of validity of EIM and providing an efficient analytical description and physical insights into the guided propagation in V-groove plasmonic waveguides.