Abstract: In detecting a focus error for an optical pickup, an inverse image generator for generating inverse images onto a light beam reflected from an optical disk is used in a focus error detecting method and apparatus thereof. The inverse image generator is composed of a semi-transmissive plane for splitting a light beam into first and second light beams, first and second prisms for inverting the phase of the second light beam, and third and fourth prisms for synthesizing the phase-inverted second light beam with the first light beam. Also, the inverse image generator has two quadrant wave plates, a polarization plane and light synthesizing plane for preventing a light loss. Since the errors due to an optical axis variation is eliminated from the focus error signal detected from the synthetic light beam radiated by the inverse generator, the optical pickup can be driven with stability.

Abstract: A lens device which can be used as an objective lens in an optical pickup apparatus includes an objective lens provided along a light path facing a disc and having a predetermined effective diameter, and light controlling means provided along the light path for controlling the light in an intermediate region between near and far axes of an incident light beam, thus providing a simplified and inexpensive device for using discs of differing thickness in a single disc drive, by reducing the spherical aberration effect.

Abstract: A focus error detector for detecting a signal representing a degree of a focus error of an objective lens with respect to an optical disk in an optical pickup, in order to eliminate errors due to an optical axis shift or tilt of the reflected light reflected from the optical disk, includes a diffraction device for diffracting and splitting the reflected light reflected. The focus error detector a critical angle reflector having critical angle reflecting planes for reflecting the two diffracted light rays at two critical angles, two bi-segmented photo-detectors for receiving the two diffracted light rays reflected from the critical angle reflector, respectively, and detecting signals depending on the received light amount, and a circuit for differentiating and summing each signal of the two bi-segmented photo-detectors so as to offset the light amount difference due to the tilt or shift of the reflected light and outputting a desired signal.

Abstract: An optical pickup for an optical magnetic disc includes a light source, a grating for diffracting the light into a main light beam and auxiliary light beams, a plurality of magnetic dipole tips arranged above the optical magnetic disc so as to interact with the magnetic signal stored in the optical magnetic disc. Also, a plurality of mirror members each attached to the rear of each magnetic dipole tips are for reflecting the light incident on the mirror member, and a photodetector for detecting track errors and the stored information by receiving the light reflected from the mirror members are provided, thereby detecting the error signal and reproducing information by the interaction with the magnetic dipoles of the disc so that the recording density can be increased without increasing the conventional land and groove areas in the disc.

Abstract: A focus error detector for detecting a signal representing a degree of a focus error of an objective lens with respect to an optical disk includes two focusing lenses each for focusing the reflected light of the optical disk by splitting the reflected light into two beams with respect to the optical axis and two photo-detectors for receiving the respectively focused beams, which simplifies necessary components for a beam size method. The two focusing lenses whose focal lengths are different from each other does not necessitate use of a beam splitter, thereby contributing to reduction of necessary components and optimizing the arrangement of the components. Also, the operational stability is secured by removing the sensitivity to the tilt and shift of an optical axis.