| 摘要 |
PURPOSE:To arrange a light detecting means in the vicinity of a light source, and to reduce the size and the weight of the titled head by making both light beams, one led from the light source to an information storage medium, and the other led from the information storage medium to the light detecting means, go forward on the approximately same optical path. CONSTITUTION:Because both the laser beams L, one fed from a semiconductor laser 2 to the information storage medium 16, and the other led from the infor mation storage medium 16 to the photodetector 22, go forward in the approxi mately same optical path, the photodetector 22 be arranged in the vicinity of the semiconductor laser 2, and an optical head can be miniaturized and lightened. Besides, the laser beam L, emitted from the semiconductor laser 2, can be converted from an elliptical section to a circular section by a cylindri cal concave lens 4 and a cylindrical convex lens 10, and at the same time, by the cylindrical concave lens 4, the cylindrical convex lens 10 and a light reflective cylindrical plane 20, the spot shape of the laser beam L on the photode tector 22 can changed so that blooming a can be detected by an astigmatism method. |
