Dense, uniform SiOx (0 <= x <= 2) films were deposited by reactive magnetron sputtering. By controlling the oxygen flow rate and/or sputtering power during deposition, the refractive index of SiOx films can be continuously tuned from 1.44 to 3.69 at lambda = 1550 nm. The authors fabricated an 11-layer bandpass filter of SiOx/SiO2 with high refractive-index contrast (n(H)/n(L)=1.91 at lambda = 1550 nm) and, a 35-layer SiOx optical filter with a graded refractive-index profile. The measured reflectance and transmittance spectra correlate well with the designed spectra. This work demonstrates that SiOx material can be used to make infrared optical filters with graded refractive index and high refractive-index contrast. (C) 2008 American Vacuum Society.