Owing to the sensitivity of the MM-16 Spectroscopic Ellipsometer and the advanced modeling features included in the DP2 software, this note describes the successful characterisation of complicated anti-reflective structures. Accurate and simultaneous determination of thickness and optical properties have been performed in the visible range. Similar analyses have been applied to other high-k material such as Ta2O5 / glass, Al2O3 / 3*{A2O3/a-Si} / GaAs, SiO2 / 2*{HfO2 / SiO2) / glass.