| 摘要 |
A light detecting device includes an object leans for leading a light beam from a light source to a recording medium. The recording medium has a groove and a header portion formed by interrupting the groove. The light detecting device further includes a photo-detector for detecting the light beam reflected on the recording medium and led by the object lens to output a signal corresponding to intensity of the reflected light beam, the photo-detector including a light beam detecting surface in a specified shape to which a component of the reflected light beam diffracted by the header portion is not incident.
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