| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical head device in which the sensitivity of a focus error signal is not dropped, even when plural kinds of optical disks having different substrate thicknesses are operated by using plural kinds of lens having different effective diameters, or even when they are operated by controlling a numerical aperture in one lens. SOLUTION: When two kinds of lenses having different effective diameters are used with reference to the operation of two kinds of optical disks having different substrate thicknesses, a focus error signal is detected by a light receiving part group having a light receiving part width matched to a beam spot size, in every light receiving face inside a light receiving part which constitutes a first photodetector 58 and a second photodetector 59. As a result, the focus error signal can be detected without lowering the sensitivity of the focus error signal with reference to the two kinds of optical disks having the different substrate thicknesses. |
