| 摘要 |
PURPOSE:To detect the position of an objective lens without reducing the light quantity of a light flux which is made incident on the objective lens by arranging on a turn table holding the objective lens a photo detector that light-receives the peripheral part of the light flux which are made incident on the objective lens. CONSTITUTION:Outgoing beams from a light source 12 is made into parallel light beams by a collimator lens 13, and outgoing beams 14 are conducted to the objective lens 17 by a beam splitter 19 and a mirror 30. The turn table 31 holding the lens 17 holds on the incident side of the light flux which are made incident on the lens 17, and furthermore in a lace where the light flux 16 generates vignetting a two-division photo detector for detecting objective lens position 32 having two light-receiving surfaces 32a and 32b, for example. Thus, the displacement with respect to the neutral point of the lens 17 can be detected with the output of a differential amplifier 27, and tracking signals with a large moving range can be outputted from a differential amplifier 28.
|
