| 摘要 |
PURPOSE:To easily respond to dispersion in a beam spot gap divided by a prism manufacturing error and to always accurately detect a focal state by forming two parting lines of an optical detector in parallel with each other, and arranging the parting lines by inclining against the ridge of a Foucault prism. CONSTITUTION:Light from a laser beam source 21 is projected on a recording medium 26 via a polarizing beam splitter 22, a collimator lens 23, a 1/4-wave plate 24, and an objective lens 25, and its reflected light is made incident on the Foucault prism 27 via the objective lens 25 and the polarizing beam splitter 22, and is divided into two beams of light, and respective beam of light is received by an optical detector 28. The optical detector 28 is comprised by providing four light receiving areas 28a-28d divided by two parting lines 29a and 29b on the same substrate, and the parting lines 29a and 29b are inclined against the ridge 27a of the prism 27 within a plane intersecting orthogonally to the incident optical axis of the optical detector 28 to the Foucault prism 27. Thus, spot images 30a and 30b can be made incident uniformly on the medium 26 when the lens 25 is set at a focused state. |
