| 摘要 |
PURPOSE:To miniaturize the entire device by allowing one composite prism element to separate a light beam into a light beam made incident on a recording medium from a light beam generating source and a reflected light beam returning from the recording medium and to obtain two optical beams formed by the orthogonal polarized light component separated with each other based on the reflected light beam. CONSTITUTION:In obtaining a servo error signal for servo control, a light beam incident in the recording medium through an objective lens 5 from the light beam generating source 2 and the reflected light beam returned from the recording medium via the objective lens 5 are separated by one composite prism element 21. Then two light beams whose orthogonal polarized component is separated based on the reflected light beam from the recording medium are obtained. Thus, it is not required to provide the beam splitter and an analyzer having been used conventionally as independent optical components and plural photodetectors detecting individually two light beams obtained from the composite prism element are aggregated in the form of a photodetector unit 26. Thus, the constitution is simplified and miniaturization is attained.
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