Patent ID: 6545807
Filing Date: 2003-04-08
Classification: G11B

Abstract:
A refractive-diffractive hybrid lens, comprising:a refractive lens; and a diffractive lens structure having a plurality of concentric ring-shaped steps that are formed on at least one lens surface of said refractive lens, wherein said refractive lens comprises a single lens whose at least one surface is an aspherical surface, and said refractive lens is designed such that a change of spherical aberration due to the variation of the refractive index is reduced; wherein said diffractive lens structure generates a negative spherical aberration and is designed to correct residual spherical aberration; and wherein the following condition (1) is satisfied: âˆ’0.20<P4Ã—mÃ—&lgr;Ã—(hMAX/NA)3where NA is a numerical aperture, hMAX is a height from the optical axis of a point where the light ray defining said NA intersects said diffractive lens structure, m is diffraction order, &lgr; is wavelength, and P4 is a fourth order coefficient when an additional optical path length added by said diffractive lens structure is expressed by the following optical path difference function &PHgr;(h): &PHgr;(h)=(P2h2+P4h4+P6h6+ . . . )Ã—mÃ—&lgr;where P2 and P6 are coefficients of second and sixth orders, h is a height from the optical axis.