Data readout from compact disks by a laser pickup with diffraction optics

A pickup with a diffraction focusing objective was developed for a digital laser compact disk player. The pickup consisted of two functional elements: a semiconductor laser and a glass plate carrying on one side a diffraction objective and a ring-shaped photodetector. It was predicted theoretically and connrmed experimentally that data could be retrieved from compact disks using a pickup with a ring photodetector. A diffraction objective with an efficiency of 30% could be used in the optical system of the pickup. It was possible to obtain a radial tracking signal (by subtracting the voltage from opposite sectors of a ring photodetector) and to suppress the optical feedback noise (by hf modulation of the current supplying the semiconductor laser).