Auto-adjustment of the Objective Lens Neutral Position in Optical Disc Drives

Optical axis misalignment, which represents deviated neutral position of the objective lens from the optical axis, is an inevitable assembly error in an optical pick-up. Since the laser power intensity varies with respect to the distance from the optical axis, the misalignment leads to variation of the laser spot power intensity, which is one of the critical factors increasing data bit-error-rate in optical disc drives. In this paper, an auto-adjustment scheme of the objective lens neutral position is proposed to eliminate the undesirable variation of the laser spot power intensity in optical disc drives. An envelope of the data signal is extracted and utilized to detect the optical axis misalignment. Then an adjustment input is added to the driving input of the fine actuator to align the objective lens to the optical axis. Finally, the feasibility is verified by a series of experiments.