| 摘要 |
PURPOSE:To give a number of degrees of freedom to arrangement relations of a detecting system which detects light and to reduce the error of focus detection due to an influence of the deviation of the optical axis or the like by providing a control means to increase the size of the beam spot of light with which a photodetector is irradiated. CONSTITUTION:A condensing means 16 which condenses light on an information recording medium 18, an optical means 14 which is arranged in the optical path of light led from the information recording medium 18 and has plural light reflection areas, condensing means 22 and 24 which condense the light reflected from plural areas of the optical means 14 in one direction, and a detecting means 26 which detects the light condensed by condensing means 22 and 24 are provided. The position of the condensing means 16 to the information recording medium 18 is controlled in response to the detection result from the detecting means 26 to detect the focus error. Thus, a number of degrees of freedom can be given to arrangement relations of optical elements or the like of the photodetector, and optical elements or the like are effectively arranged. |
