| 摘要 |
PROBLEM TO BE SOLVED: To eliminate a tilt adjustment mechanism for arranging an objective lens nearly vertically to an optical disk surface, to reduce the number of parts and to reduce a manufacturing cost by shortening a wavelength of a laser irradiating an optical disk surface and reducing the numerical aperture of the objective lens. SOLUTION: A light beam emitted from a light source S is converged at an angle θ for an optical axis K by the objective lens 1. At this time, the relation among the wavelength λ of the light beam, the numerical aperture NA and a converged light spot diameter D becomes D=λ/NA. A jitters value being a representative regenerative signal is fluctuated on a large scale in a change due to the tilt of the objective lens 1 according to the large change of NA. Then, from the relation, a required spot diameter is obtained by reducing the wavelength λ, and reducing the numerical aperture NA also, and since the numerical aperture NA is reduced, the jitters value is fluctuated less. Thus, the regenerative signal of required quality is obtained even without performing the tilt adjustment of the objective lens 1. |
