Information recording and reproducing apparatus using light beam modulation on a spiral guide groove disk
 An information recording and reproducing apparatus comprises an optical device for causing a light beam to impinge upon a disc having a spiral guide groove along which a control signal is substantially recorded for scanning the spiral guide groove; a light beam modulating portion operative to intensity-modulate the light beam incident upon the disc in response to an information signal so that the information signal is intermittently recorded on the disc and operative further to cause the light beam to keep a relatively small intensity during a period in which the recording of the information signal is temporarily interrupted; a photo-detecting portion for detecting the light beam coming from the disc; a read signal processing portion operative to obtain, based on a detection output from the photo-detecting portion, a read output signal containing a read output of the control signal and a total amount signal corresponding to momentary total light amount of the light beam received by the photo-detecting portion; a variable gain control portion operative to perform a gain-control to the read output signal in response to the total amount signal when the light beam coming from the disc is detected by the photo-detecting portion; and a signal reproducing portion for obtaining a reproduced output of the control signal on the strength of the read output signal having been subjected to the gain-control performed by the variable gain control portion. 
Sony Corporation
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Yuji Kyoko
Kumai Suzuki