| 摘要 |
<P>PROBLEM TO BE SOLVED: To avoid the occurrence of an offset caused by the shift of beam spots following the shift of an objective lens. <P>SOLUTION: Light reception regions 5a, 5b, 5c, 5d are divided into divided light reception regions A1 and A2, B1 and B2, C1 and C2, D1 and D2, respectively, by parallel dividing lines L4, L5 (an angle α to a dividing line L3 and mutual distance (b)) prescribed in a region P3 of a photodetector 5 sandwiched by regions P1, P2 having a beam spot SP2 (diameter (a)). A tracking control section calculates a difference ((S1+S2+S7+S8)-(S3+S4+S5+S6)), based on electrical signals S1-S8 indicating the quantity of received light in respective divided light reception regions A1-D2, and obtains a tracking error signal by subtracting a correction value Δte (=a×((S2+S4)-(S6+S8))/(b×sinα)) from the difference. <P>COPYRIGHT: (C)2009,JPO&INPIT |
