BiO_x films are prepared by reactive direct current(DC)magnetron sputtering from a metallic bismuth target in Ar + O_2 with different O_2/Ar ratios.It is found that the optical property of BiO_x films is sensitive to O_2/Ar ratios and the films deposited at O_2/Ar ratio of 0.5 have the best reflectivity contrast under the same conditions.The structure and optical characteristics of the films are studied by X-ray diffraction (XRD),X-ray photoelectron spectroscopy(XPS),and spectrophotometer.As revealed by investigations, the phase transition is mainly responsible for the change of optical properties.The static test results indicate that the BiO_x films have good writing sensitivity for blue laser beams.A high reflectivity contrast of about 52% at a writing power of 11 mW and writing pulse width of 800 ns is obtained.In addition,the films demonstrate good stability after being read for 10000 times. BiO_x films are prepared by reactive direct current (DC) magnetron sputtering from a metallic bismuth target in Ar + O_2 with different O_2 / Ar ratios. It is found that the optical property of BiO_x films is sensitive to O_2 / Ar ratios and the films deposited at O 2 / Ar ratio of 0.5 have the best reflectivity contrast under the same conditions. The structure and optical characteristics of the films were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and spectrophotometer. by investigations, the phase transition is mainly responsible for the change of optical properties. The static test results indicate that the BiO_x films have good writing sensitivity for blue laser beams. A high reflectivity contrast of about 52% at a writing power of 11 mW and writing pulse width of 800 ns is obtained. addition, the film demonstrates good stability after being read for 10000 times.