Parkhurst & Oliff
Optical information recording and/or reproducing apparatus and optical record medium for use in such apparatus
 A disc-shaped record medium has a recording surface which is divided into a number of concentric recording regions and has a number of concentric guide tracks formed at boundaries between successive recording regions. A number of concentric or spiral information tracks are formed in an optically readable form in respective recording regions with a constant pitch in reference to respective guide tracks and the guide tracks are also recorded in an optically readable form. In an instance of effecting the recording or reproducing for a certain recording region, the guide track related to the relevant recording region is always read out by a tracking light beam which is controlled to trace the guide track and a recording or reproducing light beam is controlled with reference to the guide track so as to trace the information track precisely. The tracking light beam and the recording or reproducing light beam are focussed by a common objective lens onto the record medium and an inclination angle of the recording or reproducing light beam with respect to the tracking light beam is changed in a stepwise or continuous manner by rotating a swingable mirror arranged in the path of the recording or reproducing light beam. The recording or reproducing light beam is shifted in a radial direction of the record medium disc to trace the concentric or spiral information tracks. In the guide tracks are formed additional signals, such as address signals and synchronizing signals which are used for effecting random access. 
Olympus Optical Co., Ltd.
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Kiichi
Kato