Parkhurst & Oliff
Method and apparatus for controlling the focusing and tracking of a light beam using a main and secondary light beam in association with multiple detectors
 An apparatus and method for recording optically an information signal on a disk-like record medium as a spiral track or concentrical tracks by modulating a main beam by the information signal to be recorded and projecting the modulated main beam onto the record medium. In order to obtain a tracking error signal, a sub beam is also projected on the record medium at an edge of an adjacent track which has been previously recorded and the sub beam reflected by the record medium is detected by a light detector to produce the tracking error signal which is then supplied to a high pass filter to remove a low frequency component from the tracking error signal. 
Olympus Optical Company, Ltd.
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G11B G11B G11B
inventional additional inventional
Kenichi Kiichi Tohru
Ito Kato Musha