The electronic structure and optical properties of have been studied by the ab initio full-potential and full-relativistic LMTO methods. Calculations are employed to elucidate the influence of the stacking sequence on the band states and optical spectra. Unusually strong hybridization of the Ca spd states with the Si p states is evident in both of the crystal polymorphs. The Fermi velocities and charge-density distributions indicate significant spatial anisotropy in the TR3 structure. For both of the crystal structures, large in-plane and out-of-plane anisotropy of the optical conductivity has also been found.