| 摘要 |
An optical pickup device enables prevention of an increase of spherical aberration during tracking without needing any finite optical system. The diameters of parallel light beams (A, B, C) for the next-generation DVDs, DVDs, and CDs are limited to diameters of a, b, c (a>b>c) in accordance with the NA for each type by a light beam limiting element, the diameter of light beam B is limited to the diameter ranges of b to c and d (=0.85xc) to e (d>e>0), the diameter of the light beam C is limited to the diameter ranges of c to d and less than e. They are passed through a phase correcting element (13B) and focused on the corresponding optical recording medium signal planes by means of a common objective lens. The objective lens is so optimized that the wave front aberration to the light beam A is minimum on the signal plane of the next generation DVD. The phase correcting element (13B) has a phase correcting zones (Z1 to Z4) of diffraction optical structure exhibiting a pseudo-kinoform shape of a step constitution. The spherical aberration to the light beam B is corrected in the zones (Z1, Z3). The spherical aberration to the light beam C is corrected in the zones (Z2, Z4). The light beam A is passed through all the zones of the light beam diameter a without changing the parallel light beam state by optimizing the step heights of the zones (Z1 to Z4).
|
