Patent ID: 6333907
Filing Date: 2001-12-25
Classification: G11B

Abstract:
An optical disk apparatus comprising:a pick-up unit including a light source, an optical system which focuses a light beam emitted from the light source onto an optical disk, and a photo-detector which detects reflection light from the disk, the pick-up unit reproducing information recorded on the disk along a predetermined track; andan opening limiting unit which limits an opening of the objective lens such that numerical apertures NAlr and NAlt in a disk radial direction and a track tangential direction of the objective lens in a case where said optical disk is a first disk optimized with respect to a wavelength .lambda.1 of the light source, and numerical apertures NA2r and NA2t in the disk radial direction and the track tangential direction of the objective lens in a case where said optical disk is a second disk optimized with respect to a wavelength .lambda.2 (.lambda.1<.lambda.2) of the light source, satisfy formulae: ##EQU6## 0.95.multidot.NAlt.ltoreq.NA2t.ltoreq.1.1.multidot.NAlt.