  We present numerical simulations for the propagation of surface plasmon
polaritons in a dielectric-metal-dielectric waveguide using COMSOL multiphysics
software. We show that the use of an active dielectric with gain that
compensates metal absorption losses enhances substantially plasmon propagation.
Furthermore, the introduction of the active material induces, for a specific
gain value, a root in the imaginary part of the propagation constant leading to
infinite propagation of the surface plasmon. The computational approaches
analyzed in this work can be used to define and tune the optimal conditions for
surface plasmon polariton amplification and propagation.
