We know that the filter can reach the parameters required by the design, mainly by using the optical interference principle. The realization of the optical interference principle also depends on the design of the film on the filter. But we know that some filters have poor chemical stability of the film, and the mechanical properties of the surface are not good. If a protective film is not coated, the performance of the filter in the atmosphere will gradually decline, and it is prone to scratches. Therefore, it is generally necessary to evaporate a layer of film with good chemical and mechanical properties on the surface of the interference filter to prevent the performance of the internal film from deteriorating, which is called a protective film layer.
The physical properties of DLC protective film (also called diamond film by some engineers) are similar to the physical properties of diamond. It has high hardness, small friction coefficient, wear resistance, and good chemical stability, thermal conductivity, electrical insulation, light transmittance, and biocompatibility. Therefore, it can be used to protect the soft optical filter film of the filter
