| 摘要 |
PROBLEM TO BE SOLVED: To provide the optical system of an optical head capable of utilizing an optical disk the thickness of the protection layer of which is different, made good in off-axis aberration characteristic and securing a sufficient working distance even for the optical disk the protection layer of which is thick. SOLUTION: This optical system has 1st and 2nd laser modules 21 and 22, a collimating lens 24, and the objective 10. The ignition point of the 1st laser module is aligned with the focus of the collimating lens, and a 1st laser beam is made incident on the objective as parallel beams. The ignition point of the 2nd laser module is more proximate to the objective than the focus of the collimating lens, and a 2nd laser beam is made incident on the objective as a divergent light beam. A part of the spherical aberration caused by the difference of the thickness of the protection layer is compensated by using the difference of divergence. Diffraction lens structure is formed on the lens surface 11 of the objective, and the rest of the spherical aberration caused by the difference of the thickness of the protection layer is compensated by utilizing the wavelength dependency of such structure. |
