| 摘要 |
PROBLEM TO BE SOLVED: To provide a phase change optical disk having a high erasure rate in the use of blue LD and at a high linear velocity. SOLUTION: In the phase change optical disk obtained by successively stacking a lower dielectric layer, a recording layer, an upper dielectric layer and a reflecting layer on a substrate, the reflectance Rc of the disk to light of 380-430 nm wavelength when the recoding layer is a crystalline state is made lower than the reflectance Ra of the disk to light of 380-430 nm wavelength when the recoding layer is in an amorphous state. When the refractive index of each of the dielectric layers at 380-430 nm wavelength λ is represented by n, the thickness of the lower dielectric layer is λ/(9I1) to λ/(3n) and the thickness of the upper dielectric layer is λ/(5n) to λ/(2.5n). The variation ΔRc of the reflectance Rc of the recording layer in the change of the crystalline state due to conditions of recording/erasure of information satisfies the inequality ΔRc/|Rc-Ra|<0.05. Since the reflectance does not vary even if the crystalline state changes, a high erasure rate can be attained. |
