Patent ID: 6266302
Filing Date: 2001-07-24
Classification: G11B

Abstract:
An optical disk apparatus having a reduced offset in the focal shift amount between the grooves and lands, said apparatus comprising:an optical disk on which recording tracks are formed in both grooves and lands thereof;a laser source for emitting a laser beam;an objective lens for focusing the laser beam emitted by said laser source to form a fine spot on a recording track of the optical disk;an astigmatic element placed in a convergent optical system for focusing the beam reflected by the optical disk and emit an astigmatic beam; anda photodetector for detecting the astigmatic beam emerging from said astigmatic element,said optical disk apparatus serving to perform at least focal adjustment of said objective lens by using a detection signal from said photodetector,wherein a relation0.8<.lambda./(Tp.multidot.NA)<1.1is satisfied, where .lambda. is a wavelength of the laser beam emitted by said laser source, NA is a numerical aperture of said objective lens, and Tp is a pitch size of said grooves, thereby causing a reduced offset in the focal shift amount between the grooves and lands.