| 摘要 |
An electro-optical focus detector is an apparatus used to provide signal indications regarding the magnitude and polarity of focus error in a light beam impinging on a surface, such as a recording surface in a recording or playback system. The detector includes a beam splitter, to divide the beam reflected from the recording surface into two reflected beams of equal power, and includes an aperture placed in the path of the two reflected beams. When the original beam moves out of focus with the recording surface, both focus points of the reflected beams move in the same direction to increase the light falling on one of the photodetector elements and decrease the light falling on the other, such that the differential output derived from the photodetector element provides a signal indication of the focus error.
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