Simplified analytic expressions are obtained for the phase velocity and propagation length of a surface polariton on a layered structure that consists of a dielectric film on a surface-active material.
J. D. McMullen, "Perturbation analysis of the influence of a thin dielectric film on the propagation constants of a surface optical wave," J. Opt. Soc. Am. 65, 1253-1256 (1975)