| 摘要 |
PURPOSE:To improve the track density 1.5-2 times, by shaping the crosssection of an optical disc into a waveform having a cycle shorter than the diameter of a light spot, and providing its mountain parts and valley parts as information track parts in concentric circles or spirally. CONSTITUTION:A conventional track guide groove is disused, and mountain parts and valley parts are used as center parts of tracks, and the track pitch is made shorter than the diameter of the light spot. With respect to a tracking signal, a diffracted light in a continuous change part of height or depth of mountain parts and valley parts is used. In Fig., a1, a2- indicate centers of mountain parts, and b1, b2- indicate centers of valley parts. Only mountain parts are tracked when the polarity of a tracking control circuit is set to a certain direction, and only valley parts are tracked when the polarity is made opposite. Consequently, the track pitch is doubles equivalently, and the track density is improved 1.5-2 times. |
