An optical device comprising the barrier layer, optical system and projector

An optical device comprising a light-transmissive optical substrate (10), which is provided with a multilayer layer (14) and a barrier layer (12) on its the multilayer film (14) facing side, wherein the barrier layer (12) suppresses the transport of molecules between the substrate (10) and the multilayer film (14), wherein the light-transmitting optical substrate (10) has a refractive index N 1.7 ≤ characterized, in that that the barrier layer (12) of La Al with 0.5 ≤ x and y ≤ 1.5, and having a refractive index N -0.1 ≤