  We present a new strategy, based on a Fresnel coefficient pole analysis, for
designing an asymmetric multilayer structure that supports long range surface
plasmons (LRSP). We find that the electric field intensity in the metal layer
of a multilayer LRSP structure can be even slightly smaller than in the metal
layer of the corresponding symmetric LRSP structure, minimizing absorption
losses and resulting in LRSP propagation lengths up to 2mm. With a view towards
biosensing applications, we also present semi-analytic expressions for a
standard surface sensing parameter in arbitrary planar resonant structures, and
in particular show that for an asymmetric structure consisting of a gold film
deposited on a multilayer of SiO2 and TiO2 a surface sensing parameter G =
1.28(1/nm) can be achieved.
