| 摘要 |
PURPOSE:To omit a track exclusive for follow-up and to improve the information recording density by forming a diffraction grating on each track surface and discriminating a relevant track to its adjacent tracks based on the difference of diffraction characteristics. CONSTITUTION:A recording tracks include the tracks 4 (4a, 4b) of a first attribute and the tracks 5 (5a, 5b) of a second attribute. Then a diffraction grating is formed with a diffraction constant (d) to each track 4 in the direction of +45 deg. to the track forming direction and also to each track 5 in the direction of -45 deg. to the track forming direction respectively. As a result, the different diffraction characteristics are secured between those tracks 4 and 5. Thus the diffracted beams have different emitting directions. Therefore all tracks can be used as recording tracks and the information pits are formed on all tracks. As a result, the information recording density is improved. |
