Abstract To develop new infrared antireflective and protective coatings on the infrared band, amorphous diamond (a-D) films deposited by filtered cathodic vacuum arc (FCVA) technology have been investigated. The mechanical properties were characterized with the nano-indenter and the stress was calculated using Stoney's equation. The optical properties were analysed with spectroscopic ellipsometry and the microstructure was investigated with EELS. The maximal hardness and Young's modulus consorting with the highest stress are represented at the negative bias of 80 V. When the bias is increased or decreased, hardness, Young's modulus and stress will descend gradually. However, the high impinging energy benefits the better adhesion and the lower stress. In the wide infrared band, the films are transparent. The optical gap and the refractive index exhibit the same changing regularities like hardness and stress, whereas the extinction coefficient demonstrates the reverse trace. The changing rules can be perfectly explained in light of the ratio of the different hybridization and the growth mechanism of the films. In short, a-D films deposited by the FCVA technology are superexcellent infrared protective coatings.