Information recording and reproducing apparatus using light beam modulation on a spiral guide groove disk

Claim 1

An information recording and reproducing apparatus comprising: optical means for causing a light beam to impinge upon a disc-shaped record medium, on which a spiral guide groove surrounding a central portion of the disc-shaped record medium is formed to have side-wall portions opposite to each other and meandering in response to a predetermined control signal so that the predetermined control signal is substantially recorded along the spiral guide groove, for scanning the spiral guide groove continuously; light beam modulating means operative to intensity-modulate the light beam incident upon the disc-shaped record medium for scanning the spiral guide groove in response to an information signal so that the information signal is intermittently recorded on the disc-shaped record medium 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; photo-detecting means for detecting the light beam coming from the disc-shaped record medium on which the spiral guide groove is scanned by the light beam; read signal processing means operative to obtain a read output signal containing a read output of the predetermined control signal recorded along the spiral guide groove and a total amount signal corresponding to momentary total light amount of the light beam coming from the disc-shaped record medium to be received by said photo-detecting means on the strength of a detection output signal obtained from said photo-detecting means; variable gain control means operative to perform a gain-control to the read output signal obtained from said read signal processing means in response to the total amount signal obtained from said read signal processing means when the light beam coming from the disc-shaped record medium is detected by said photo-detecting means, in which the gain control performed by said variable gain control means provides a gain control characteristic to said read output signal such that an amplitude of said read output signal is reduced in proportion to an increase in a level of said total amount signal so that when the level of the total amount signal increases in response to variations in a level of the information signal the amplitude of said read output signal is reduced; and signal reproducing means for obtaining a reproduced output of the predetermined control signal recorded along the spiral guide groove on the strength of the read output signal having been subjected to the gain-control performed by said variable gain control means.