To effectively protect and improve the transmittance of ZnS optical elements in the far infrared band, combined amorphous diamond (a-D) and amorphous hydrogenated germanium carbide (a-Ge1-xCx:H) films have been developed. The optical interference coatings were designed according to the layer optics theory. The a-D films, of which refractive index and film thickness were controlled by changing substrate bias and deposition time respectively, were deposited by filtered cathodic vacuum arc technology. The a-Ge1-xCx:H films were prepared by radio frequency sputtering technology. During this process their refractive index was modulated by changing the gas flow rate ratio and their film thickness was controlled by the flow rate ratio and deposition time. It has been shown that the combined films are superexcellent antireflective and protective coatings for ZnS optical elements. (c) 2007 Elsevier B.V. All rights reserved.