OPTICAL DISK AND ITS TRACKING METHOD

摘要

PURPOSE:To reduce the circuit scale by varying the depth of a V groove on an optical disk every second track and in a fixed cycle and therefore increasing the record area on a sloping surface and also detecting only the cycle by a tracking control circuit. CONSTITUTION:A pilot signal is recorded to a V groove every second track of an optical disk 1 at a frequency (f) and with the depth varied periodically. The track depth is changed with the amplitude frequency (f) on sloping surfaces A and B respectively with the fixed depth kept for tracks of sloping surfaces C and D. When the reflected light sent from the disk 1 is received by photodetectors M and N and a laser spot is shifted toward a sloping surface E, the intensity is increased for the pilot signal of a frequency (f) detected by the detector M. While the intensity of the pilot signal detected by the detector N is reduced. Therefore two laser spots can be tracked on both surfaces C and D by having the same intensity between reproduction pilot signals of detectors M and N. This eliminates the need to switch the control polarity, and it is desired for a tracking control circuit to detect just the frequency (f). Thus the scale of the tracking control circuit can be reduced.