  On the basis of a full-vectorial three-dimensional Maxwell-Bloch approach we
investigate the possibility of using gain to overcome losses in a negative
refractive index fishnet metamaterial. We show that appropriate placing of
optically pumped laser dyes (gain) into the metamaterial structure results in a
frequency band where the nonbianisotropic metamaterial becomes amplifying. In
that region both the real and the imaginary part of the effective refractive
index become simultaneously negative and the figure of merit diverges at two
distinct frequency points.
