Patent ID: 6711103
Filing Date: 2004-03-23
Classification: G11B

Abstract:
An optical disk reproducing apparatus which is able to reproduce the recorded signals recorded through an optical head and an optical system on two types of the optical disk having two kinds of thickness, the apparatus comprises:numerical aperture setting means for substantially setting a numerical aperture (NA) of lens for laser beams emitted from the optical head to be set at a first value of the numerical aperture (NA) or a second value of the numerical aperture (NA); focus search means for moving said optical head or said optical system in a focus direction to thereby perform a focus search in the status of setting the first value of the numerical aperture (NA) by said numerical aperture setting means; first measuring means for measuring a first detection signal and a second detection signal, both of which are obtained from said optical head during the focus search by said focus search means; first control means for controlling a focus of said optical head or said optical system, in the case of being fit for the relation between the first value of the numerical aperture (NA) and the thickness of the optical disk in accordance with the first detection signal and the second detection signal, both of which are measured by said first measuring means; second measuring means for measuring a third detection signal and a fourth detection signal, both of which are obtained from said optical head during the focus search by said focus search means in the status of setting the second value of the numerical (NA) by said numerical aperture setting means, in the case of being unfit for the relation between the first value of the numerical aperture (NA) and the thickness of the optical disk in accordance with the first detection signal and the second detection signal, both of which are measured by said first measuring means; second control means for controlling a focus of said optical head or said optical system in accordance with the third detection signal and the fourth detection signal, both of which are measured by said second measuring means.