OPTICAL DISK, OPTICAL DISK RECORDER AND OPTICAL DISK REPRODUCER

摘要

PROBLEM TO BE SOLVED: To prevent the unauthorized duplication of an optical exclusive for reproduction by making pit lengths of the optical disk minutely variable. SOLUTION: Aftrer an input signal is subjected to EMF modulation in an EMF encoder, it is inputted to a duty correcting circuit 12, applied with duty corrections and transmitted to an E/O modulation controller to control the output of a laser beam and then cuttings are performed. When the signal is to be recorded in a copy guard area being an objective area where pit lengths are made variable regularly and minutely duty is corrected in the duty correcting circuit 12 by inputting the input signal from the EMF encoder and the delayed signal obtained by delaying the signal in a programable delay element 121 to an AND circuit (or an OR circuit) 122 and by ADDing (or ORing) them. An optical dick reproducer judges whether an optical disk is the disk of an unauthorized duplication or not by detecting the amount of change in the duty while reproducing the disk and comparing this amount of change with the prescribed amount of the change of the minute fluctuation of duty which should be recorded on a formal optical disk to perform a necessary action.