| 摘要 |
PURPOSE:To generate a large astigmatism to the reflected light by providing the 2nd parallel plate correcting the astigmatism expanded by the 1st parallel plate and acting like an astigmatism generating means without the provision of an optical component for generating an astigmatism onto a reflected light path by a beam splitter. CONSTITUTION:The astigmatism of laser light from a semiconductor laser 1 is expanded once by the 1st parallel plate 3 and corrected by the 2nd parallel plate 4. Thus, the astigmatism of laser light collected onto an optical disk 2 via a light collecting optical system is eliminated and a light beam of a prescribed shape is always collected onto the optical disk 2. Further, an astigmatism is generated to the reflected light from the optical disk 2 by the 2nd parallel plate 4 and sent to a photodetecting means via a reflecting optical path change means. Thus, the astigmatism being the addition of the astigmatism generated by the 1st parallel plate and the astigmatism by the semiconductor laser is generated and the detection accuracy of a focus error signal obtained by the photodetection means is improved. |
