interpolation of complex functions

I am using Comsol 4.4 RF mode and would like some help, I need to use the Parametric Sweep to study the behavior of the wavelength, but in guia'optico contains metal and then the refractive index is imaginary, I wonder whether it has the I interpolating functions of the type n (lambda) = i * + nreal nimag? and how do I? do I have a table of wavelength versus nreal + i * nimag for various metals.
Thank you for listening and I look forward contact