| 摘要 |
PURPOSE:To always and stably provide a tracking error signal by giving astigmatism to diffracted light beams and detecting the tracking error signal based on the distribution of brightness and darkness in the far field of the diffracted light beams. CONSTITUTION:A return beam from an optical recording medium is made incident on a hologram 28 to be diffracted, and first-order diffracted light beams are made incident on photodetectors 31, 34, and spots 35, 36 are formed. Further, zero-order diffracted light beams are diffracted by the hologram 28b, and the first-order diffracted light beams are incident on the photodetectors 32, 33, and the spots 37, 38 are formed. At this time, by the hologram 28b, the astigmatism provided with a focal point in the direction inclined for the direction of the diffracted light beams x, y is imparted. Then, when the track deviation occurs, though the light quantity distribution deviation occurs in the x direction on the pupil of the hologram 28b, the light quantity distribution deviation occurs in the y direction on the surfaces of the photodetectors 32, 33. Thus, the TES is obtained from respective outputs of light receiving areas 32a-32b divided in the y direction of the photodetectors 32, 33 based on the distribution of brightness and darkness in the far field of the diffracted light beams from the prescribed relation. |
