| 摘要 |
PURPOSE:To decrease the crosstalk noises of adjacent tracks on a disk information surface by changing the width of a diffraction grating with respect to the pitch thereof from the central part toward the peripheral pat along the grating in the direction where said approximates to the prescribed width. CONSTITUTION:The grating part 13b of the diffraction grating 13 which diffracts the light emitted from a semiconductor laser and splits the light to a main beam and sub-beam is changed in the direction where the width of the grating with respect to the thereof approximates 1/2 from the central part toward the peripheral part along the grating. The quantity of the light of the main beam is thereby decreased from the central part toward the peripheral part and the crosstalk noises of the adjacent tracks on the information surface of the disk are decreased. |
