OBJECTIVE FOR OPTICAL PICKUP AND OPTICAL PICKUP USING THE OBJECTIVE

摘要

An objective for an optical pickup comprises a single lens having a meniscus structure composed of, in order from the light source, a first surface (S1) having a positive refractive power and being aspherical and a second surface (S2) having a negative refractive power and being aspherical. The objective has a numerical aperture (NA) of above 0.8. The aspherical shapes Zi of the first and second surfaces are expressed by the following formula where h is the height from the optical axis (1) (where i is the surface number of the aspherical surface numbered from the light source part, r is the radius of curvature of the aspherical surface, k is the coefficient of cone and k < 0, and A to J are the coefficients of aspherical surface). Another mode of objective satisfying the below condition is also disclosed. (r1/r2) ≤ (2N2−N−4) / {N(2N+1)} (Symbol r1 is the radius of curvature of the first surface, r2 is the radius of curvature of the second surface, and N is the index of refraction of the glass material.)