Effects of an asymmetrically molded plastic objective lens on the push-pull tracking-error signal in an optical disk drive

The effects of a plastic objective lens's astigmatism on the push-pull trac king-error signal (TES) of an optical disk. data storage system were invest igated theoretically and experimentally. Astigmatism of plastic objective l enses arises commonly from the asymmetric deviation from their designed sha pe during the molding process. By carefully studying the aberration charact eristics of the objective lens and including the astigmatism of the laser d iode in the analysis, we can calculate the combined effects of astigmatism of these two components on the push-pull TES. It is found, from both the si mulations and the experiments, that, by rotation of the objective lens abou t the optical axis, the peak-to-peak value of the push-pull TES varies with the lens's rotation angle, and a change as great as 340% in its value was observed in a given optical pickup. (C) 2000 Optical Society of America.