| 摘要 |
PROBLEM TO BE SOLVED: To perform possible stable recording/reproducing by setting an angle between the tracking direction and a cylindrical lens axis in a specified condition and arranging one side of axes orthogonally intersecting with each other of a quadripartite photodetector in the tracking track direction. SOLUTION: This device is provided with a diffraction grating consisting of at least two gratings with difference characteristics for dividing the luminous flux outgoing from the light source to plural luminous flux, plural tracking tracks and plural information tracks. Then, the cylindrical lens axis is arranged so that the angle θ between the tracking direction and the cylindrical lens axis becomes 0 deg.<θ<45 deg. or 45 deg.<θ<90 deg., and plural light receiving parts of the photodetector are arranged in the tracking track direction. Thus, the deterioration of a signal and the coexistence in the signals due to the leakage of light and the coexistence of light, etc., from the photodetector in respective spots projected on the photodetector are prevented. Stable AF control by an astigmatic method is performed, and stable recording and simultaneous reproduction of plural information tracks are performed. |
