| 摘要 |
PURPOSE:To obtain an S-shaped characteristic curve which does not depend upon the width of the division line of a two-division photodetector for focus error detection and to facilitate positioning and adjusting operations by using a cylindrical lens for an optical head and arranging the photodetector at a distance which is about twice as large as the focal length of the lens. CONSTITUTION:An optical beam from the optical head which is reflected by an optical disk 11 and passed through an objective 13 is given a nearly circular cross section and the half of the beam is reflected by a total reflecting mirror knife 14 and made incident on the 1st two-division photodetector 15. The remaining half of the beam is made incident on the 2nd two-split photodetector 17 through an cylindrical lens 15. The 1st detector 15 is light-received and detects the 1st servo signal. Further, the cylindrical lens 16 is set at 45 deg. to the radial direction of the disk 11 and the photodetector 17 is arranged at a distance nearly twice as large as the focal length of the cylindrical lens 16 to detect the 2nd servo signal. Then, the S-shaped characteristic curve which does not depend upon the width of the division lines of the detectors 15 and 17 is obtained to facilitate the positioning and adjusting operations. |
