  We investigate mode converters for Si wire to plasmonic slot waveguides at
1550 nm telecom wavelength. The structures are based on a taper geometry. We
provide optimal dimensions with more than 90% power transmission for a range of
metal (Au) thicknesses between 30-250 nm. We provide details on how to
differentiate between the total power and the power in the main mode of the
plasmonic slot waveguide. Our analysis is based on the orthogonality of modes
of the slot waveguide subject to a suitable inner product definition. Our
results are relevant for lowering the insertion loss and the bit error rate of
plasmonic modulators.
