Optical Head for Digital Audio Disks

Abstract

A novel optical head for digital audio disks has been successfully developed. The head consists of a GaAIAs laser diode, a quadrant PIN photodiode and a single-beam optical system for focusing and radial tracking. All of the data, focusing, and radial tracking signals are derived from a single quadrant PIN photodiode. Focusing and radial tracking servocontrol of the head are characterized by two-dimensional actuation of an objective lens and all the other optical components including the photodiode are kept fixed. However, it maintains superiod characteristics over a wide range of objective lens movement and disk tilt. The detection method of the error signals and their dependence upon both the objective lens movement and the disk tilt are described.