Well-known transmission line analysis techniques can be used to estimate plasmonic parameters is shown in [Opt.Express(18), pp.6191-6204(2010)] and [IEEE PJ(3), pp.220-233(2011)].
An analytical approximations toolset for analyzing nonlinear silicon-amplifiers is given in [J.Sel.Top.Quan.Electro.(16), pp.200-215(2010)]. The work teaches the art of approximations for similar systems, thus with high educational value.