We report on theoretical calculations of the optical conductivity of Ba
[Fe(1-x)Co(x)]2 As2, as obtained from density functional theory within the full
potential LAPW method. A thorough comparison with experiment shows that we are
able to reproduce most of the observed experimental features, in particular a
magnetic peak located at about 0.2 eV which we ascribe to antiferromagnetic
ordered magnetic stripes. We also predict a large in-plane anisotropy of this
feature, which agrees very well with measurements on detwinned crystals. The
effect of Co doping as well as the dependence of plasma frequency on the
magnetic order is also investigated
