| 摘要 |
PURPOSE:To secure the gain of a tracking servo system which is enough to follow stably a track by changing the tracking error gain in accordance with the detection position of a main spot on a recording medium and correcting the detecting sensitivity. CONSTITUTION:The laser light 11a delivered from a semiconductor laser is divided into three luminous fluxes by a diffraction grating 12 and forms a microspot on a disk 17 via a polarized beam splitter PBS13, a lambda/4 plate 15 and an objective lens 16. While the reflected light travels back and is reflected by the PBS13 and made incident on a photodetector 19 via a condenser lens 18. The output signals of photodetectors 19'a and 19'c are supplied to a differential amplifier 20, and the difference signal between both photodetectors eliminates the deterioration of the tracking error detecting sensitivity by an amplifier 21 and with the control voltage which is supplied from a control voltage generating circuit 22 via a gain control volume 23. Then the differencial signal is supplied to a tracking coil 26 via a phase compensation circuit 24 and a drive circuit 25. |
