| 摘要 |
PURPOSE:To always secure the stable tracking despite uneven track pitches by obtaining the tracking control voltage of the same level for an equal shift amount regardless of the tracking shift direction. CONSTITUTION:In case a main light beam (0-order diffracted light) 30 irradiates the 1st track 41, the photodetection outputs corresponding to the +2-order diffracted light 31a and the -2-order diffracted light 32b, i.e., the output of the 1st differential amplifier 25 which serves as the difference signal between the outputs of photodetecting parts 22b and 22e is selected by a changeover switch 27 and used as the tracking control voltage 28. When the beam 30 irradiates the 2nd track 42, the photodetection outputs corresponding to the -1-order diffracted light 31b and the +2-order diffracted light 32a, i.e., the output of the 2nd differential amplifier 26 which serves as the differential signal between outputs of photodetectors 22d and 22a is selected by the switch 27 and used as the voltage 28. In such a way, the stable tracking is secured. |
