| 摘要 |
<p>In an optical head apparatus for two or more different types of discs (A, A', B), there are provided a first light source (11) for a first wavelength light beam, a second light source (12) for a second wavelength light beam, and an objective lens (6, 6', 6") for leading the first and second wavelength light beams to one of the discs. A holographic optical element (5', 5") is provided to converge or diverge only one of the first and second wavelength light beams. Or, an aperture limiting element (2801) is provided to adjust an effective numerical aperture of the objective lens for only one of the first and second wavelength light beams. <IMAGE></p> |
