The talk presents concepts for integrating essential active optical functions into thin film coatings, which allows a high degree of miniaturization compared to classical alternatives. Due to the amorphous structure of thin film coating materials, only uneven orders of nonlinear effects will be considered. The chosen applications comprise a concept for frequency tripling mirrors, where the third harmonic generation is performed in the thin film stack, and an all-optical switch, the so-called Kerr-band-switch based on the optical Kerr-effect. The chosen materials, design considerations, and measurements validating the function of the concepts will be presented.