| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an optical head device compatible with two optical disks which use laser beams with the same wavelength but have different substrate thicknesses, and to reproducing a multilayer optical disk. <P>SOLUTION: A refractive lens part 31 and liquid crystal elements 32 and 33 are provided so that laser beams are converged to an optical disk 36 with a thin substrate using a first numeric aperture, and laser beams are converged to an optical disk 35 with a thick substrate using a second numeric aperture less than the first numeric aperture. The refractive lens part is designed so that, in a range of the second numeric aperture, RMS wavefront aberration becomes minimum with respect to an intermediate substrate thickness between the two optical disks, and, in a region outside the second numeric aperture, the RMS wavefront aberration becomes less than 0.05 λ with respect to a substrate thickness of the optical disk 36. The liquid crystal element 32 for compatibility corrects spherical aberration due to a difference of the substrate thickness between the two optical disks 35 and 36, and the liquid crystal element 33 for multilayer corrects spherical aberration based on the selected layer of the multilayer optical disk 37. <P>COPYRIGHT: (C)2009,JPO&INPIT |
