OPTICAL HEAD DEVICE

摘要

An optical head device having a structure in which a divergent light beam, not a parallel beam, is made incident on an objective lens and the influence of the wave aberration on the recording/reproducing characteristics is suppressed even if the size, thickness, and cost are reduced. A diffraction optical element (6) is given a diffraction function and, for example, even a function of causing astigmatism so as to cancel the astigmatism caused when the light source is moved away from the lens optical axis of the objective lens (9) in a radial direction of an optical disk information-recording medium (8). Specifically, by forming the diffraction surface or the back surface of the diffraction optical element (6) into a toric or cylindrical surface, and by adjusting the curvature, the degree of the astigmatism is controlled.