Patent ID: 7031233

Claim:
An optical recording/playback apparatus that records and plays back information by projecting a laser beam onto a recording medium having a single information-recording layer or multiple information-recording layers, comprising: objective-lens means having a predetermined numerical aperture, the objective lens means being provided as an output end for the laser beam; compensation optical means for compensating for spherical aberrations caused by the thickness of a transmissive protection layer provided for the information-recording layer of the recording medium; moving means for moving the objective lens along the optical axis; reflected-beam detecting means for detecting the laser beam reflected by the recording medium and for outputting reflected-beam information; determination means for determining the polarity of a focusing error signal generated as the reflected-beam information and the level of a reflected-beam intensity signal generated as the reflected-beam information; and focus control means for performing a focusing operation based on the determination information from the determination means by using the moving means to move the objective-lens means along the optical axis in a state where the compensation optical means is optimized with respect to the thickness of a certain transmissive protection layer, wherein the focus control means performs the focusing operation on the target information-recording layer based on the direction in which the objective-lens means is moved by the moving means and based on the order of occurrences of the polarity information of the focusing error signal obtained by the determination means.