An optical lever approach to photodetector measurements of the pickup-head flying height in an optical disk drive

In order to increase the storage capacity and the density of near-field optical disk drives, a flying pickup-head has to allow a slider to fly at a stable height above the disk surface with the use of near-field optics. Since both the precision of the track pitch and the flying height are of a nanometre scale, it is necessary to increase the motion accuracy of the pickup-head. In this study, a piezoelectric bender is used as an actuator of the pickup-head, and two quadrant photodetectors are used to sense the pickup-head displacement and the rotating disk deformation. Based on an optical lever method that magnifies a small displacement, the flying height variation of the pickup-head above the disk is measured. Further results show that using the proposed measurement method in the real-time control of flying height is feasible.