METHOD AND APPARATUS FOR CONTROLLING TRACK SERVO BY USING REFERENCE BEAM SERVO IN HOLOGRAPHIC ROM

摘要

The present invention is a two-stage step so that there is a slit in the side for passing only a specific track played beam making a shape having a height, and provide the tracking error signal obtained by focusing on the 4 division PDIC light passing through the slit surfaces to the tracking servo controller to change the tracking servo control so as to precisely and, also, the focusing by the two-division PDIC a reference light optical axis error signal for controlling the light source so as to be positioned at the center of the slit is always based on the reference light beam optical axis to provide a servo controller, a first course of action for this is incident on the holographic disk to generate a reference beam from the light source and, a second transforming process and a plurality of circularly polarized light alone as the light in the same polarization direction by reproducing the image with the reference track through the objective lens and the polarization beam splitter and / 4 polarization plate on the disc by the graphical reference light, the light is changed to circularly polarized light is passed through the slit surfaces having a two-stage height and optical lens 4 is focused on the process of partition and the third claim 1 PDIC, is the light reflection surface does not pass the slit optics and / 4 polarization plate while the S-polarized light is passed through the fourth process includes focusing the second split claim 2 PDIC. Thus, because all the time so as to generate an error signal based on the center position of the three holes when the slit light applied to the reference light such errors using a servo signal, tracking the holographic ROM disk of the third hole is the desired track by moving the objective lens when the servo Since it is always able to play the track position can be located always in the reference light center, it is possible to obtain a high level of the RF signal, and therefore the slope of the linear region, the tracking error signal increases, the effect of the tracking servo, the servo precision is also higher there.