| 摘要 |
PURPOSE:To enable track servo independently of presence of information recording, by providing V-shaped or inverse trapezoidal grooves of cross section on a metallic film between tracks or within the track and using a reflected light from the groove side wall. CONSTITUTION:Before information is recorded on a disc 5, a V-shaped groove 7 of a metallic film 6 is formed concentrically or in spiral. If a relative position shift is caused between an optical beam 9 and a track 8, a part of the beam 9 irradiates a side wall 7a of a groove 7 and is reflected on this part. When this reflected light flux 13 is detected at 11, the relative position shift between the beam and the track can be known. If the position shift of track is caused toward reverse direction to the optical beam, it is detected by a photodetector 12 located oppositely to the photodetector 11 with a condenser lens 10, in-between, and the light beam can be followed accurately to the movement of track with a signal corresponding to the position shift. |
