| 摘要 |
PROBLEM TO BE SOLVED: To improve recording density and to make correctly reproducible multi-valued data by forming pits having two different depths on a substrate and making the wavelength of the light beams used and the refractive index of an optical disk substrate satisfy a prescribed relationship. SOLUTION: Pits having two different depths (D1 and D2) are formed on the substrate of an optical disk. Moreover, the depths are determined so as to satisfy 0<D1<λ/4n and λ/4n<D2<λ/2n, where λ is the wavelength of the light beams used and n is the refractive index of the substrate of an optical disk. Moreover, the depths D1 and D2 of the pits are determined so as to satisfy λ/8n<D1<λ/4n and λ/4n<D2<3λ/8n. Then, recorded data are reproduced by combining the signals based on the amount of reflected light beams from the disk and tangential push-pull signals. Since the polarities of the tangential push- pull signals are made different by the differences in the pit depths, an optical disk having high density three value recording is realized by varying pit depths. |
