Verification of effective refraction index approach to the surface plasmon propagation in ultrathin tapered metal–dielectric–metal slot waveguides

We verify the effective refraction index approach (ERIA) developed for surface plasmon propagation in ultrathin tapered metal-dielectric-metal slot waveguides by means of comparison of exact solutions obtained within ERIA for two different profiles and different scales of tapering with finite-difference time-domain numerical simulations. We show that for smooth enough tapering, ERIA gives the plasmon field structure closely matched with numerical results. We also outline the range of the taper scales in which ERIA leads to the results different from simulations.