| 摘要 |
PURPOSE:To detect an inclination of a recording medium to a light beam with high accuracy by providing a parallel plate in an optical path between a light source and an objective lens, forming two light beams shifted from each other in axis, recording or reproducing information with one of the light beams and detecting the inclination of the recording medium based on reflected light of the other light beam from the recording medium. CONSTITUTION:A light beam from the light source 21 of a semiconductor laser, etc., is incident upon the parallel plate 22, and is reflected by its front surface 22a, while a light beam whose axis is shifted from the above axis by reflecting with the back surface 22b after refracting and transmitting through the front surface 22a is detected together with the above beam, i.e. the two light beams. Then, the light beam reflected by the back surface 22b and transmitted through the front surface 22a is assigned to an auxiliary beam for detecting the inclination. Under such constitution, when the recording medium 24 is inclined to an optical axis of the objective lens 23, an optical axis of reflected light of the auxiliary beam by the recording medium 24 is shifted accordingly, so that intensity distribution of an incident light beam 27 upon a photodetector 26 is changed, and this light beam 27 is not a round due to an eclipse by the objective lens 23. By this method,k the inclining direction of the recording medium 24 can be detected with high accuracy. |
