Computer simulations of the effects of disk tilt and lens tilt on the push-pull tracking error signal in an optical disk drive

Using computer simulations that utilize a mix of diffraction calculations and geometric-optical ray-tracing, the effects on the tracking error signal (TES) of the various tilts in an optical disk drive can be quantified. In this paper, we report the results of computer simulations pertaining to the offset of the point of peak irradiance from track center and the accompanying change of the TES amplitude. In an optical disk drive both disk tilt and objective lens tilt induce tracking difficulties. The effects of disk tilt on tracking servo are more severe than those of the objective lens tilt for two reasons. First, the displacement of the focused spot caused by disk tilt is over twice that caused by lens tilt. Second, the focused spot is more asymmetric in the presence of disk tilt compared with the case of lens tilt.