Abstract: A grating surface of a diffraction grating diffracts a laser beam emitted from a semiconductor laser device in ±1st order directions. The grating surface is formed in a rectangular or elliptic shape in such dimensions that a light spot formed on an objective lens by ±1st order diffracted beams is located in an aperture of the objective lens and not displaced from the aperture even if the objective lens is horizontally moved in a tracking operation. A grating surface of another diffraction grating has a width smaller than the width of an overlap region of a light spot on the diffraction grating corresponding to a part of a beam, diffracted in the +1st direction, entering an objective lens and a light spot on the diffraction grating corresponding to a part of a beam, diffracted in the −1st direction, entering the objective lens.

Abstract: An optical pickup includes a photo-detector. The photo-detector is structured by light receiving elements on one of which a blind zone is formed. If a relationship between an output of the light receiving element formed with a blind zone and a lens position is displayed as a graph on a measurement signal output device, a point that a beam converges on the blind zone, i.e., a point that a spot size assumes a minimum, is displayed as an edge. In the photo-detector, a region for receiving a sub-beam on light shield side, i.e., one sub-beam having a grater spot size, has a width broader than a width of a region for receiving a sub-beam on an aperture side, i.e., another sub-beam smaller in spot size.

Abstract: A magneto-optical head using a catadioptric focusing device comprised of an incident surface, a bottom reflective surface, a pedestal, and a body. The incident surface is generally flat and is comprised of a central diffractive, optically transmissive facet and a peripheral facet comprised of a kinoform phase profile. In a data writing or reading mode, an incident optical beam, such as a laser beam impinges upon the central facet, and is diffracted thereby. The incident laser beam can be collimated, convergent or divergent. The laser beam passes through the transparent body, and impinges upon the bottom reflective surface. The laser beam is then reflected by the bottom reflective surface, through the body, unto the kinoform phase profile. The laser beam is reflected and refracted by the peripheral kinoform phase profile as a focused beam, through the body, and is focused as a focal point.