Figures of merit for 2D surface plasmon waveguides and application to metal stripes.

Three figures of merit, useful as quality measures for 2D surface plasmon waveguides, are discussed and applied to help trade-off mode confinement against attenuation for the symmetric mode propagating along metal stripes. Different stripe geometries are considered, and Au, Ag and Al are compared as the stripe metal over the wavelength range from 200 to 2000 nm. Depending on which figure of merit is used, and on how mode confinement is measured, different preferred designs emerge. For instance, given a mode area, narrow thick stripes are better than wide thin ones, but given a distance from the light line, the opposite is true. Each of the metals analyzed show wavelength regions where their performance is best. The figures of merit are generally applicable and should be useful to help compare, assess and optimize designs in other 2D surface plasmon waveguides or in other absorbing waveguides.