| 摘要 |
PURPOSE:To enable the tracking even for a different wavelength of recoding and reproducing laser beams by forming tracking guide groove and a preformat groove with a specific depth. CONSTITUTION:The tracking guide groove G is formed in parallel or in a concentric circular or spiral form on a transparent substrate 10A and on one portion of the information track L set as an intermediate region between the adjacent guide grooves in the orthogonal guide groove direction, the preformat is formed by severance of the groove PL. A recording film 10B with a light absorption property is provided on a surface at the same side as the side where the groove G and the PL were formed. Here the refractive index of the transparent substrate 10A is N, the wavelengthes of n kind of recording and reproducing laser beams being lambda1-lambdan, the minimum wavelength being lambda1, the maximum wavelength being lambdan, and the effective depths of the guide groove and the preformat groove are respectively Deff and deff, then by setting them in the ranges of 0.075/N<=Deff<=0.2lambda1/N, 0.26lambdan/N<=deff<=0.45lambda1/N, thereby the tracking even for a light source with the different wavelength is enabled. |
