THE METHOD AND APPARATUS FOR DETECTING A FOCUSSING ERROR SIGNAL OF OBJECTIVE LENS

摘要

A polarized laser light and a photo-detector are used to detect a focusing fault error signal in an objective lens. A light beam from a laser source passes through a collimator lens, a polarizing prism and a quarter wave length of thin film. The thin film is made of a material having a higher refractive index than that of the prism. The light from the track is reflected through a detection prism onto a detector surface. The photo-detector is divided into two parts to detect different refraction. The output of a differential amplifier is the focusing fault signal.