Abstract
The optical disk tilt caused by the high-speed spin and vibration introduces the aberrations of the laser spot on the information layer. The aberrations will change the intensity distribution of the focused spot, and deteriorate the signal quality of the reflected light detected by the photo sensor, and then induce the mistake. Hence, with the increasing storage density of the disk, the phenomenon of the deteriorated signal caused by disk tilt should be discussed and studied thoroughly.This thesis is based on the DVD specification. In this thesis, we simulate and analyze the focus error signal affected by disk vibration in 3-dimensional space, and then try to compensate for this phenomenon. First, we propose the optical theory related to the mathematical model, and discuss the transfer function between the optical components in the system. Then, we propose the aberration theory resulted from the disk tilt. The 3-dimensional tilt angle composed of tangential tilt and radial tilt will be introduced into the mathematical model. Since the tangential and radial axes are perpendicular to each other, the effects of the 3-dimensional tilt angle resulted from these two tilt angles are independent, even are linear under small angle condition. Therefore the 3-dimensional tilt angle exits in the vector space constructed by the tangential and radial orthogonal bases. In other words, the magnitude of the 3-dimensional tilt angle is equal to the length of the vector in the space while the direction is relative to both the tangential and radial tilt angles. The detailed condition in geometric will be proposed in the content. The focus error influenced by different 3-dimensional tilt angles will be simulated and analyzed, and the relations will be established. The compensated method of looking up table will be used once we know the tilt angle from the tilt sensor. Finally, the performances of two focus servo control methods, one using the looking up table directly and the other using the tilt condition prediction beforehand, are compared while a 3-dimensional vibration model is built. It shows that the tilt condition prediction one works better.The mathematical model simulated in this thesis is based on the diffractive wave optics theory, and is built in the mathematical software, MATLAB.