Surface plasmon-polaritons in thin metal strips and slabs: Waveguiding and mode cutoff

Abstract

Using a fully vectorial formulation, the normal mode analysis method is used to model for what is believed to be the first time, 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 lambda = 1.55mum for embedded infinite-width slabs and finite-width strip metal waveguides where the metal was Au and the surrounding dielectrics were SiO 2 and LiNbO3. Mode cutoff is induced by an asymmetry between the index of refraction of the top clad and the bottom clad. Comparisons between predictions and experimental results for cutoff finite-width waveguides show very good agreement. The analysis was performed for a range of waveguide dimensions and results show that a dynamic range of better than 20dB is possible for an appropriate waveguide and dielectric asymmetry. Practical applications are outlined to make use of this cutoff effect.