U-020

A positioning method for hard disk servowriter using an auto focus laser encoder

Authors: Weidong Zhou and Lilong Cai
Affiliation: Dept. of Mechanical Eng., Hong Kong University of Science and Technology. W. Zhou is also with Department of Measurement and Control, Sichuan University

Abstract
A novel method for optical storage readout is proposed based on phase jump in a modified differential interferometer. Two polarization-mixing laser beams are produced and focused on an optical disk and scanning along pits and land respectively. When the probe beam scans across a pit, two phase jumps will take place in the interference resultant of the two beams if the phase difference between two beams is pre-fixed at p, resulting in a rectangular phase pulse with an amplitude of 180°. The slopes of rising and falling edges of the phase pulse are infinite and they are not affected by the intensity variation of the light source, stray light and the vibration of the disk. Therefore, this phase pulse can be used to readout the information on an optical disk. The use of phase jump can improve the signal-noise ratio of the readout signal and enhance the density of optical storage. An optical readout using phase jump has been constructed. Both the theoretical design and experimental verification are conducted. Experimental results show that the proposed optical readout is feasible.

Weidong Zhou
Dept. of Mechanical Engineering
Hong Kong University of Science and Technology
Hong Kong, China
mezhou@ust.hk