Patent ID: 8391121

Claim:
An optical head device, comprising: a signal reading optical system including a signal reading objective lens; and a servo signal detection optical system including a servo objective lens, the optical head device for irradiating a multi-layered optical recording medium including a plurality of recording layers and a single servo layer with a reading light beam via the signal reading objective lens and with a servo light beam through the servo objective lens, and for receiving the reading light beam reflected from the multi-layered optical recording medium through the signal reading objective lens and the servo light beam reflected from the multi-layered optical recording medium through the servo objective lens, the signal reading objective lens and the servo objective lens are disposed such that optical center axes thereof are aligned with a same track of the multi-layered optical recording medium so as to be arranged in a lengthwise direction of the track, and the single servo layer is at different point on the optical center axis of the servo objective lens from the plurality of recording layers, the optical head device further comprising: a common actuator on which the signal reading objective lens and the servo objective lens are disposed; a focal point moving mechanism for moving minutely a focal point of one of the signal reading objective lens and the servo objective lens in a focusing direction relative to the other of the signal reading objective lens and the servo objective lens while the signal reading objective lens and the servo objective lens are driven by the common actuator, and focusing another on the servo layer or one of the recording layers when the one of the signal reading objective lens and the servo objective lens is focused on the one of the recording layers or the servo layer.