| 摘要 |
PURPOSE:To reduce bad influence due to the generation of an offset in push-pull method. CONSTITUTION:Respective detection faces 2, 3 of a photodetector 4 are irradiated with one of reflection beams divided by a beam spliter 11B through a shaping prism 11 without converging its beam diameter by a condenser lens. When the reflection beam is bent in adirection along a division line 1 dividing the faces 2, 3 along the track direction of a disk with the oblique line 11b of the prism 11 at the time of shaping the beam with the prism 11, the width of the beam in a tangential direction is contracted from D1 to D2 to form an elliptic beam. Since the bad influence of offset in the push-pull method generally appears as movement in the approximately rectangular direction to the division line 1 dividing the faces 2, 3, relation that the major axis of the elliptic beam intersects with the division line 1 at approximately right angles can be obtained and the whole change in the movement of the beam on the faces 2, 3 due to the oscillation of the beam can be extremely reduced, reducing the bad influence of offset. |
