FOCUS CONTROL SCHEME WITH JUMPING FOCAL POINT

摘要

The present invention relates to a focus control apparatus and method of controlling focus of a radiation beam onto a first spatial level of a record carrier, wherein a focus control loop is locked onto a reflection signal obtained from a second spatial level located at a predetermined distance from said first spatial level, and is then opened to move an objective means towards the second spatial level by a predetermined amount related to the predetermined distance. This stepwise procedure enlarges the margin for mechanical overshoot and hence reduces the risk of bumping into the disc. Additionally, no ambiguous focus error signals are detected and robustness of initial focusing is improved if a thin transparent cover layer is present. ® KIPO & WIPO 2007