| 摘要 |
PURPOSE:To prevent a decrease in the amplitude of a playback signal by using a long circular beam which is expanded only in the width direction of a pit during recording and also using a beam which is as wide as a formed pit or narrower during reproduction. CONSTITUTION:When a beam spot BW on the surface of a medium 1 is put in a defocusing state during recording by placing an objective 9 closer to the medium surface, the beam becomes long and circular because of astigmatism while having the diameter extended in the width direction of a pit at right angles to the moving direction of the medium shown by an arrow, thereby forming the pit P. The objective 9 is put farther in reproduction than in the recording to focus the beam, and then the diameter of the beam spot on the medium surface which is extended in the width direction of the pit P returns to its original size and the spot becomes round. Therefore, even if the beam Br forms a short spot P, neither of areas at both sides of the pit is irradiated. Consequently, reflected light from the medium contains no reflected light component from both side areas of the pit and the playback signal never decreases in amplitude.
|
