PURPOSE: To decrease the number of tracking deviation signals and to attain the accurate tracing of a track, by cutting off the 0-order light which contains no tracking information and gives an evil effect to the tracking.
CONSTITUTION: The light beam emitted from a laser 1 is focused on a disk surface 5 after passing through a prism 3 and a stop-down lens 4. A light spot 6 is diffracted at the edge of a track 51, and the reflected light of this diffraction is received by photodetectors 7a and 7b which are set to hold the track 51 between them. The outputs of the detectors 7a and 7b control an actuator 10 via a differential amplifier 8 and a tracking control circuit 9 and gives a minute movement to the lens 4 to trace the track 51. These detectors 7a and 7b are set with a distance (w) which is smaller than the diameter 4 of a diffracted luminous flux on the surface of the photodetector and larger than the quadruple of the maximum degree of shift of the lens 4 to the optical axis of the diffracted luminous flux on the surface of the photodetector. As a result, the number of deviation signals contained in the differential signal can be reduced.
KOIKE RIYUUICHI
YONEZAWA SEIJI
SUGIYAMA TOSHIO
| JPS50115546A | 1975-09-10 |