In this paper the optical properties of amorphous DLC films containing SiOx (DLC:SiOx) prepared by plasma enhanced chemical vapour deposition are studied. For this study a combined optical method based on simultaneous interpretation of experimental data obtained within variable angle spectroscopic ellipsometry and near-normal spectroscopic reflectometry is used. The interpretation of these combined experimental data is performed using a new empirical dispersion model of the optical constants characterizing the films under investigation. This dispersion model is based on parameterizing the density of the electronic states belonging to both the valence and conduction bands. It is shown that there are the strong differences between spectral dependences of the optical constants of the DLC films on the one hand and DLC:SiOx films on the other hand. Further, it is shown that the absorption of the DLC:SiOx films is smaller than the absorption of the pure DLC films in the visible. This is explained by the fact that the density of the pi electrons inside the DLC:SiOx films is lower than the density of these electrons in the pure DLC films. It is also found that the existence of small amounts of the silicon and oxygen impurities contained in the DLC films strongly influence their optical properties.