  This report concerns analytical solutions predicting the complex refractive
indices of doped crystals, based on empirical values of the refractive indices
of the dopant and the undoped crystal. An analytical approach in calculating
the refractive index of Erbium doped Gadolinium Gallium Garnet was reported by
another author previously. My first comment is related to the proposed solution
by the other author, where I have shown an alternative approach that leads to a
different solution. Although my comments are made in relation to Erbium as the
dopant and Gadolinium Gallium Garnet as the undoped lattice, the analytical
solution I propose here may be applied to any doped crystals. My second comment
concerns the limitations and mistreatment of McCumber relation in this context.
