Optical head apparatus

摘要

An optical head apparatus is provided with a holographic element composed of the first grid region which splits the light beam emitted from the light source into a plurality of light beams and the second grid region which diffracts the light beams reflected from the data-recording medium on the same plane, and prevents unnecessary signals from mixing themselves into the reproduction signal by varying at least the diffraction direction or the diffraction angle of the light beams in these grid regions. The first grid region has an elliptic aperture to make the +/- primarily condensed spot beams onto the data-recording medium being extended elliptically to the data-recording direction. The direction of the border of the four photosensitive elements of the photo detector which detects the light beams reflected from the data-recording medium coincides with the direction of the deviation of the condensed spot beams of the reflected light beam, the deviation being caused by the deviation of tracking, the variation of the wave length of the light source and the like.