Optical pickup for optical disk apparatus

Abstract

Disclosed is an optical pickup and an optical disc device using the same, each including a laser diode, a photo-detector having a region divided into at least six photo-detection areas, and a diffraction grating disposed between the laser diode and the photo-detector and having a region divided into four areas by cross-shaped division lines. The diffraction grating divides a light beam reflected from an optical disc into four diffracted light beams. A focus error signal in accordance with a knife edge method and two kinds of tracking error signals in accordance with a push-pull method and a differential phase detection method are detected by irradiating the light beams diffracted at the areas of the diffraction grating on the detection areas of the photo-detector and/or at boundary lines therebetween, and arithmetically operating light intensity signals obtained from the detection areas of the photo-detector. As a result, there can be realized an optical pickup and an optical disc device, each of which can be matched with various optical discs different in structure by detecting a tracking error signal in accordance with the push-pull method and a tracking error signal suitable for a read only disc using only one photo-detector. Further, in the present invention, a holographic element can be used as the diffraction grating.