Focus error detection with two symmetrically splitted reflected beams

摘要

In an optical pickup, a focus error detector for detecting a focus error of an objective lens for an optical disk includes a focusing lens for focusing the reflected light of the optical disk, a diffraction optical device for diffracting the reflected light focused by the focusing lens into two light rays, two bi-segmented photo-detectors for receiving the two split light rays, respectively, and a circuit for outputting a desired focus error signal from the signal detected from the photo-detectors. The circuit outputs a pure focus error signal without errors created by the deviation of the light amount in the photo-detectors due to the tilt or shift of the reflected light, thereby contributing to the stable operation and miniaturization of the optical pickup.