Abstract

Pregrooved optical disks have the advantage of making the tracking servo easy when writing data and enabling the disk to be exchanged. In pregrooved disks, push-pull tracking servo signals are detected by a change in the intensity distribution of the diffracted beam. Both tracking and focusing servo signal can be obtained by the same photo diode placed in a far field. However, interference between tracking error signals and focusing error signals makes the focusing servo unstable, and the decrease in light intensity due to groove diffraction causes a reduction in signal amplitude. These problems depend not only on the width and the depth but also on the gradient of the edge of a pregroove.

© 1985 Optical Society of America