Guided wave techniques are powerful to study the properties of different optical coatings. The latest results are presented to illustrate the interest of these techniques: the dependence on ion energy of the anisotropy of ion assisted TiO₂ films is given; the measurement of losses during propagation permits to study the origin of losses in multilayer coatings and in particular to demonstrate that absorbing transition layers have to be introduced in the model; properties of ion implanted Ta₂O₅ layers are also investigated. The refractive index profile of Ta₂O₅ layers implanted with Ti is determined by using the m-line technique; coupling a pump beam at 488 nm in different guided modes, the photoluminescent properties around 1.53 mm of Er implanted Ta₂O₅ layers are also shown.