High-Resolution Analysis of Leaky Modes in Surface Plasmon Stripe Waveguides

An in-house developed full-vector finite-element imaginary-distance beam propagation method (FV-FE-ID-BPM) is employed to calculate the modes of a surface plasmon metal-stripe waveguide. Leaky modes, which possess less propagation losses compared with corresponding bound modes, are particularly studied. The calculated real and imaginary parts of the modal effective indices are shown to be with local-overshoot characteristics versus the stripe width when fine width steps are used. Using fine enough spatial mesh resolution, the field profile within the metal-stripe region is revealed and examined, and the local-overshoot characteristics could be correlated with the integer number of quasi-periods associated with the field variation along the interface between the metal stripe and the substrate.