Design Consideration of Optical Pregroove Dimensions

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.