| 摘要 |
PURPOSE:To shorten the access time of an optical disk device by forming a plane vertical and symmetrical to the optical axis at the light input side of an objective lens and forming the light output side into a wedge prism form respectively. CONSTITUTION:A light source 1 is provided so that the light beam is made incident on an objective lens 2 vertically to the light incident on the lens 2 which reads the information recorded on an optical disk. The lens 2 is formed into a plane 2a at the side of the source 1 to avoid dispersion of the light beam of the source 1. While the part of the lens 2 opposite to the source 1 is formed into wedge prism shapes 2b and 2c so that the light beam of the source 1 made incident on the lens 2 is divided into two parts. The 2-split sensors 3a and 3b are set vertical to the light beam of the source 1 in order to receive those two divided light beams. Thus it is possible to detect the degree of deviation of the lens 2 from the increase or decrease of the outputs of the detection signals of both sensors 3a and 3b as well as the deviated direction of the lens 2 and the differential output of a differential amplifier 5.
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