  We derive an approach to define the causal direction of the wavevector of
modes in optical metamaterials, which in turn, determines signs of refractive
index and impedance as a function of {\it real and imaginary} parts of
dielectric permittivity and magnetic permeability. We use the developed
technique to demonstrate that the interplay between resonant response of
constituents of metamaterials can be used to achieve efficient dispersion
management. Finally we demonstrate broadband dispersion-less index and
impedance matching in active nanowire-based negative index materials. Our work
opens new practical applications of negative index composites for broadband
lensing, imaging, and pulse-routing.
