| 摘要 |
PURPOSE:To make the diameter of a beam spot in the direction of a track small and to prevent the deterioration of quality of a reproducing signal by arranging a main lobe and a side lobe along an optical disk. CONSTITUTION:In a disk in the figure (a), since the diameter of a main lobe LBm in the direction of a track is shorter than the diameter in the same direction when it is not shielded by a liquid crystal shutter 50, the degree of decrease of the amplitude of a reproducing signal complied with the pit is some extent capable of being corrected by an equalizer and the reproducing signal of sufficiently high quality is obtained even when the longest pit length is shortened. In a disk in the figure (b), since the diameter of the main lobe LBm in the direction orthogonal to the track is shorter than the diameter in the same direction when it is not shielded by the liquid crystal shutter 50, the level of cross talk caused by reading a pit on the adjacent track is small enough even when the track pitch is narrowed and a tracking signal of sufficiently high quality is obtained. |
