The sol-gel method was used to grow Cd-doped ZnO (Zn1-xCdxO) (x = 0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) thin films to analyze the optical properties. A Double Facet Coated Substrate (DFCS) theoretical transmittance model was used to analyze the optical transmittance data and to determine the thickness, absorption loss, extinction coefficient, and refractive index of the thin films. The thicknesses and the refractive indices of the films varied in the range of 240-260 nm and 1.54 to 1.63, respectively. The extinction coefficient follows the dispersion relation of Sell-meier and increases with the Cd concentration while the optical band gap declines as Cd increases from 0.0 to 0.05. On the other hand, 5% of doped Cd films have the highest Urbach energy 85 +/- 15 meV. For the structural analysis and determination of surface morphology, we used X-ray diffraction and a scanning electron microscope. For the elemental compositions of the thin films, electron dispersive spectroscopy was used. The study demonstrates the successful application of the DFCS model for accurate determination of refractive index and extinction coefficient which are two essential parameters in the modeling of photolithographic processes in the semiconductor industry.