Abstract: A magneto-optic optical disc system which uses the magneto-optic differential data detection channel, with addition only a low pass filter, to also detect focus error. The differential data detection channel includes a pair of photodetectors, the first photodetector being located a predetermined distance within the focal length of the detector lens associated with that photodetector and the second photodetector being located beyond the focal length of the detector lens associated with that photodetector. The output of a differential amplifier receiving the photodetector outputs is the data signal and the output of a low pass filter connected to the output of the differential amplifier is the focus error signal. The dual functionality of the differential data detection channel eliminates a separate optical focus channel, and relative to separate astigmatic focus and data detection channels elmininates a quadrature detector, several optical elements, several electrical elements, and the space they occupy.

Abstract: Plural overlapped Gaussian-shaped solid state semiconductor laser beams are focused onto the recording medium surface of a printer and will not optically interfere and cause any nonuniformity in printing due to optical interference because the respective laser beams are sequenced in ON/OFF operation so that relative to two or more overlapping laser beam spots focused to a recording medium surface, only one laser beam will be ON at any given time.

Abstract: In a focus correction servo loop which maintains optical focus on an optical disk by movement of an objective lens, a focus error signal generating system which utilizes a pair of photodetectors in a differential channel, the first detector being located a predetermined distance within the focal length of the detector lens associated with that detector and the second detector being located beyond the focal length of the detector lens associated with that detector by the same predetermined distance. When the disk is at the focal point of the objective lens, equal light will fall on both detectors. When the disk position deviates from the focal point of the objective lens, more light will fall on one detector than on the other detector. The dc value of the difference between the detector signals is the focus error signal utilized by the servo loop.

Abstract: The output beam of a read laser for an optical memory is diffracted to provide a plurality of read beams of substantially equal intensity for simultaneously scanning all of the data tracks of a selected data channel with a different one of the read beams, whereby each of the read beams is optically modulated in accordance with the data recorded on a respective one of the data tracks. The optically modulated read beams are applied to respective detectors, whereby the data recorded on the different data tracks is simultaneously converted into corresponding video electrical signals. Those signals are, in turn, output selectively or in parallel.

Abstract: A prismatic anamorphic system for use with an optical correlator. The prismatic anamorphic system incorporates four rotatable prisms arranged within the optical correlator thereby permitting correlator operation about unity magnification with no image rotation and no axial translation as the magnification is varied. In this manner proper correlation of a pair of photographs can be performed in an economical and highly reliable fashion.