| 摘要 |
PURPOSE:To reduce the deviation signal due to beam deflection to trace tracks accurately, by providing two photodetecting parts, at least, which detect only light components other than 0-order light components in the photodetector which receives the diffracted light from information tracks. CONSTITUTION:A photodetector 7 consists of photodetecting parts D1 and D2 and a dark part B and has symmetrical axis O arranged in parallel with tracks approximately. The O-order diffracted light of the diffracted light of tracks is irradiated to the dark part B. The primary diffracted light is detected but the 0-order diffracted light is not detected by photodetecting parts D1 and D2. The difference between output signals of parts D1 and D2 becomes a track control signal. Consequently, the deviation signal due to beam deflection is reduced to make an accurate track tracking possible. |
