Abstract: Apparatus for reading information stored in a track pattern on a radiation reflecting record comprises a source of radiation such as a laser, a diffraction grating for providing at least a zero order beam component and a pair of first order beam components, an objective lens assembly, a photodetector array, the photodetector array comprising a unitary data photodetector disposed for impingement of the zero order beam component for sensing stored information and at least first and second paired photodetector arrays adjacent to the data photodetector including separated sectors disposed along an axis including the data photodetector for providing at least focus error correction signals to the objective lens assembly, and means provided in the optical path between the objective lens assembly and the photodetector array for providing a first portion of the reading beam components which remains relatively fixed in size and a second portion of the reading beam components which varies substantially linearly in size

Abstract: Apparatus for reading information stored in a track pattern on a radiation reflecting record comprises a source of radiation such as a laser for supplying at least a reading beam, an objective lens assembly for passing the reading beam to the record and for controllably focusing the reading beam at a plane of focus, a photodetector array disposed in an optical path with the lens assembly for sensing at least the recorded information and focusing errors, and an astigmatic element disposed in the optical path for producing an astigmatic image of the reading beam in which the photodetector array comprises a unitary data photodetector disposed for impingement thereon of a zero order reading beam component for sensing the recorded information, and a quadrant photodetector array adjacent to the unitary data photodetector and including separated sectors disposed along orthogonal axes for sensing relative differences of the astigmatic image along the orthogonal axes to provide at least focus error correction signals

Abstract: Apparatus for reading information stored in a track pattern on a radiation reflecting record comprises a source of radiation for supplying a reading beam a tracking mirror assembly controllable for directing the reading beam in a radial direction on the record, an objective lens for controlling focus, a data photodetector and at least a first paired photodetector array including separated sectors for providing tracking error correction signals, optical detenting means comprising at least a second source of radiation fixed in place relative to an undeflected position of the tracking mirror and a second paired photodetector array associated with the second source for detecting movement of the tracking mirror from its undeflected position and means coupled from the output of the second photodetector array to the tracking mirror assembly for providing error correction signals to maintain the detent conditions during slewing.