A valve assembly for controlling the amount of coolant exiting an engine is provided. The layer sequence advantageously acts as a diffusion barrier for the dopant of the p-doped layer. One of the sensors is positioned adjacent the barrel on the rotating group to sense rotational speed and the other senses displacement of the swashplate. Furthermore, the light rays are impinging on the first mirror and the second mirror with incidence angles \u226630\xb0 or \u226760\xb0 relative to a surface normal of the first and second mirror. 5 to 3 atom % of silicon, and at least 6 atom % of aluminum.