| 摘要 |
A light beam from a light source is introduced to a grating element of a pickup device to create zero order diffracted light, ±first order diffracted light, and ±second order diffracted light. An irradiation system focuses the zero order, ±first order and ±second order diffracted light onto tracks extending on a recording surface of an optical recording medium to form spots. A spot of the zero order diffracted light is formed on a target track, spots of the ±second order diffracted light are formed on tracks adjacent to the target track, and spots of the ±first order diffracted light are formed midway between the spots of the ±zero order and ±second order diffracted light. An optical system guides returning light reflected from the spots to an optical detector. The optical detector has independent light-receiving elements for receiving the returning light. A servo signal calculator creates an error signal based on the output signals from the optical detector. The pickup device can be used for various types of optical discs having different disc structures. The pickup device can obtain a tracking error signal by a differential push-pull (DPP) method whatever optical disc is recorded and played back. The optical pickup device can use a crosstalk cancel (CTC) method whatever optical disc is played back.
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