| 摘要 |
PURPOSE:To obtain a pickup head which is free from parasitic resonance and has good follow-up performance, by selecting properly the focal distance of an objective lens, the distance between the main surface of an astigmatic lens system and the center of a circle of least confusion, and the astigmatic difference, respectively. CONSTITUTION:The luminous flux radiated from a light source 20 transmits through a collimator lens 21 and then through lambda/4 plate 24 after its optical path is bent by a polarizing beam splitter 23. Then a microspot is formed on a disk recording surface 26 by an objective lens 25. The reflected luminous flux goes backward and is focused to an optical signal detector 28 through an astigmatic lens system 27 consisting of a convex lens 27-1 and a cylindrical lens 27-2. A position controlling signal is amplified by a sero-amplifier 31 from a part of a signal 30 which underwent photoelectric conversion through the detector 28. This controlling signal is then applied to a driving circuit 32 to give a mechanical displacement to a mobile lens barrel part 29 for both focusing control and tracking control. |
