| 摘要 |
PROBLEM TO BE SOLVED: To make recording density high by enabling high-precision tracking servo in recording. SOLUTION: A main photodetector 8a has four longitudinal and lateral photodetection parts (A, B, C, and D) and side photodetectors 8b and 8b each have two left and right photodetection parts (E and F or G and H); and the respective photodetectors generate different push-pull signals (SPP1 signal, SPP2 signal, and MPP signal), generate tracking error signals (DPP signal) from the arithmetic outputs of those push-pull signals, and cancel DC offset quantities generated in the push-pull signals of the photodetectors for each push-pull signal. |
