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: An object pickup device includes a light source, an object lens for concentrating light generated from the light source onto an optical disk, a photodetector for detecting a signal from the light reflected from the optical disk, a disk detecting portion for detecting the light quantity in a light spot concentrated on the optical disk by the object lens and for detecting the optical disk type, a focus offset calculating portion for calculating a focus offset corresponding to the detected disk type, a focus servo portion for performing a focus servo mechanism according to the signal calculated from the focus offset and the signals detected in the photodetector, and a light output optimizing means for optimizing the light output of the light source according to the calculated focus offset signal.

Abstract: In a method and an apparatus for correcting aberration due to optical disk tilt, the apparatus includes a correction plate through which a first light beam passes by an object lens in an optical disk, a light source and a photo detector for generating and receiving a second light beam to detect the magnitude of the optical disk tilt, respectively, and an actuator for inclining the correction plate based on the detected signal. The correction plate has the same optical properties as those of the substrate of the optical disk, irrespective of the optical pick surroundings and offset the aberration due to the optical disk tilt. Therefore, while the best performance of the optical pickup is ensured, adverse effects caused by the aberration due to the optical disk tilt can be eliminated through simple circuitry.

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: 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.