Patent ID: 6795254
Filing Date: 2004-09-21
Classification: G11B

Abstract:
An objective lens for an optical pickup, made up by a single lens of a meniscus structure including, looking sequentially from a light source side, a first surface formed by an aspherical surface, having a positive refractive power, and a second surface, formed by an aspherical surface, having a negative refractive power, with the numerical aperture (NA) of the lens being not less than 0.8, whereinthe aspherical shape Zi of said aspherical surfaces of said first and second surfaces is given by the equation: Zi=ri-1&it;â€ƒ&it;h21+1-(1+ki)&it;â€ƒ&it;ri-2&it;â€ƒ&it;h2+Ai&it;â€ƒ&it;h4+Bi&it;â€ƒ&it;h6+Ci&it;â€ƒ&it;h8+Di&it;â€ƒ&it;h10+Ei&it;â€ƒ&it;h12+Fi&it;â€ƒ&it;h14+Gi&it;â€ƒ&it;h16+Hi&it;â€ƒ&it;h18+Ji&it;â€ƒ&it;h20â€ƒwith the height from the optical axis being h, where i is the surface number, as counted from the light source side, r is the radius of curvature of the aspherical surface, k is the cone constant, with k<0, and A to J denote aspherical coefficients; and wherein the following condition: (r1/r2)&lE;(2N2âˆ’Nâˆ’4)/{N(2N+1)}â€ƒis also met, where r1 is the radius of curvature of the first surface, r2 is the radius of curvature of the second surface and N is a refractive index of the vitreous material.