| 摘要 |
PROBLEM TO BE SOLVED: To accurately reproduce a CD and a DVD without losing a light quantity by adding a ring zonal phase shifter for reducing the aberration of convergent light spots having respective wavelengths together to an objective lens to be integrated as one body at the time of converging these laser beams having two wavelengths on the optical disks having their different substrates in the thickness. SOLUTION: This objective lens 1 for a DVD adds a doughnut-like ring zonal phase shifter area 101 to a normal DVD objective lens. This ring zonal phase shifter area 101 can mount a thin film or the lens can be directly worked in such a form from the first. Since the normal DVD lens is designed so as to be stigmatic when a substrate is 0.6 mm in the thickness, when the DVD is reproduced by a laser beam of a wavelength 650 nm, aberration to be added by this phase shifter is diminished as much as possible. On the other hand, when a CD having the substrate having 1.2 mm thickness is reproduced by a laser beam of a wavelength 780 nm, spherical aberration generated by the substrate thickness having 0.6 mm error is reduced. |
