Patent ID: 7301862

Claim:
An optical disc drive comprising an objective lens for focusing light on an optical disc with five or more data storage layers that are stacked one upon the other and a tilt control mechanism for controlling a tilt angle to be defined between the optical axis of the light and a normal to the data storage layers, the optical disc drive reading and/or writing data from/on a selected one of the data storage layers of the optical disc by focusing the light on the selected data storage layer, wherein the numerical aperture NA of the objective lens is defined so as to fall within the range of 1.3009×D 3 −2.9315×D 2 +2.3133×D−0.0502 to 1.3009×D 3 −2.9315×D 2 +2.3133×D+0.2028, where D is a distance (mm) from a light incident side of the optical disc to the deepest one of the data storage layers, which is located most distant from the light incident side.