| 摘要 |
PURPOSE:To obtain a tracking and a focusing signal at the same time by causing reflected light from an optical disk, which has a pit with some depth other than an integer multiple of a quarter of the wavelength of light, to strike four photodetecting elements through a detection prism. CONSTITUTION:Reflected light from a disk is condensed by an objective 56 into nearly parallel luminous flux, which strikes a detection prism 58, having a reflecting surface 59 set nearly at a critical angle to the optical axis of the reflected luminous flux, through a quarter-wavelength plate 55 and a polarizing prism 54. The detection prism 58 is arranged with the incidence surface of its reflecting surface 59 at right angles to the direction of an information track to direct emitted luminous flux to a photodetector 60 arranged in the far field of the information track. Thus, a tracking error signal and a focusing error signal are obtained at the same time from outputs of the photodetection areas 60A-60D of the photodetector 60. |
