Patent ID: 6388964
Filing Date: 2002-05-14
Classification: G11B

Abstract:
An optical disk apparatus comprising:an optical disk mounting device configured to selectively mount first and second optical disks which have a relatively high recording density and a relatively low recording density, respectively, and in each of which information is recorded in a form of pit streams; a light source configured to emit a light beam; an objective lens configured to focus the light beam emitted from the light source to form a beam spot on the optical disk; a tracking device configured to detect light reflected from the optical disk, generate a tracking error signal from the light by a deferential phase detection method, and move the beam spot in accordance with the tracking error signal, the tracking device including a quadrant photodetector having four light detecting regions arranged in matrix; a spot-shifting device configured to shift a center of the beam spot from a centerline of the pit stream formed in the second optical disk, by a predetermined distance in a radial direction of the second optical disk, by delaying a first sum signal of a diagonal two of the four light detecting regions with respect to a second sum signal of a diagonal remaining two of the four light detecting regions; and an information-readout device configured to read out the information from the optical disk.