Long-range surface plasmon-polariton mode cutoff and radiation

Using a fully vectorial formulation, the normal mode analysis method is used to model the radiative spreading of surface plasmon-polariton modes input into regions where the bound surface mode is cutoff, or radiative. The analysis was performed at λ0=1.55μm for embedded finite-width metal waveguides where the metal was Au and the surrounding dielectric was SiO2. Mode cutoff is induced by an asymmetry between the index of refraction of the top clad and the bottom clad. Results show that a change in insertion loss of better than 20dB is possible for an appropriate waveguide and dielectric asymmetry. Comparisons between predictions and experimental results show very good agreement.