A semi-empirical model for the optical properties of SiGe alloys is proposed, based on physical considerations and the summation of Tauc-Lorentz and parametric oscillators. The key parameters of the oscillators are intuited from the optical transition and the symmetry points in the band structure. The model is fitted on extensive experimental data, for different temperatures, germanium concentrations and for both unstrained and strained on (100) Silicium wafer cases. This model can be used in optical simulation tools, in order to help the design of optoelectronic devices based on SiGe materials.