| 摘要 |
PROBLEM TO BE SOLVED: To inexpensively and accurately reproduce optical disks having their different substrates in thickness without a loss of a quantity of reproducing light by adding an annular phase shifter for reducing aberrations of both two coverged spots which are different in wavelength to an objective lens to form one body. SOLUTION: At the time of reproducing the CD having its substrate 1.2mm thick with a laser beam of a wavelength 780nm, by adding a doughnut-like annular phase shift area 101 to the objective lens for the DVD, a spherical aberration caused by a substrate thickness difference 0.6mm from the DVD is reduced. Moreover, by adding an opposite annular shifter of a negative phase -ϕopposite to a phase difference ϕ generated at the time of reproducing the CD to an area other that the annular phase shifter area in order that a phase is shifted only by the CD, so as not to increase the aberration at the time of reproducing the DVD, the aberrations of the converged spots on the CD and the DVD are reduced. Furthermore, by combining divided lenses, optimization can be carried out on the substrate thickness. |
