| 摘要 |
An optical pickup system for determining a focussing error by utilizing an improved astigmatic method, the system comprising: a light source; an optical detector, including a square light-reception surface formed by arranging four square photoelectric cells; a beam splitter provided with a reflection surface for reflecting the light beam from the light source and for transmitting the light beam reflected from the recording surface; a first and a second adders for adding outputs from each of two opposite corners of the square light-reception surface; an objective lens, disposed between the beam splitter and the optical disk; a graded index lens, located between the beam splitter and the optical detector, for making the light beam transmitted through the beam splitter astigmatic as it passes therethrough; and a differential amplifier for generating a focussing error signal.
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