| 摘要 |
PURPOSE:To detect focusing on an information recording face by arranging the titled head device such that the light from the information recording face is made incident on a part of the photodetection plane of a photodetector only when the light from a light source is not in the focusing state on the information recording face. CONSTITUTION:The luminous flux from a laser light source 13 is made incident on a polarized beam splitter 15 through a collimator lens 14 are the luminous flux reflected on the splitter 15 is collected onto the information recording face 18 provided on the base 17 of an information medium by an objective lens 16 to form a spot. The luminous flux reflected on the recording face 18 is made again incident on the splitter 15 through the lens 16, the linearly polarized light is transmitted and made incident on a diffraction grating 20 through a light spliter base 19. The light diffracted or reflected by the grating 20 is transmitted through the base 19 and detected by the photodetector 21 and the recorded information is reproduced. A part of the light receiving plane of the detector 21 is arranged such that the light from the recording face 18 is made incident only when the light from the light source 13 is not in the focusing state on the recording face 18, and the output of the light receiving plane of the detector 21 is processed to detect the focusing on the recording face 18. |
