APPARATUS FOR READING AND WRITING AN OPTICALLY READABLE INFORMATION STRUCTURE

摘要

A light beam from a laser is focussed into a read spot by an objective lens onto optically recorded information on a drive. A reflector rocks about an axis when driven by a drive system and a polarised beam divides and quarter wave blade enables the reflected beam modulated by the information to be separated from the transmitted laser beam. Photodiodes determine the spot intensity w.r.t. the centre of the recorded track and a substraction circuit provides a tracking signal. This is applied to the reflector drive system via an amplifier in order to null the tracking signal by movement of the reflector.