SPHERICAL GRADIENT-INDEX LENS DESIGNS FOR VIDEO-DISK PICKUP LENS OR THE LIKE

摘要

ABSTRACT OF THE DISCLOSUREThe present invention is in the field of graded-indexoptics and particularly relates to a singlet graded-index lensuseful as a microscopic objective for video-disk lens pickupsystems or the like. For applications such as video-disk lenses,it is important that the lens exhibit very low monochromaticaberrations, particularly low spherical aberration, while atthe same time being inexpensive. The present specificationprovides a spherical singlet lens exhibiting the required lowaberration. Thus the specification provides a singlet lensincluding opposing first and second refracting surfaces havingspherical curvatures C1 and C2, respectively, and a radialrefractive index gradient wherein the refractive index N of thelens varies with radial distance r from the optical axis of thelens approximately according to the power series expansionformula:N(r) = N00 + N10r2 + N20r4wherein adjustment of the third-order spherical aberration ofthe lens to a value of about zero is effected by selectiveadjustment of the power series coefficient N20, wherein adjust-ment of the third order coma of the lens to a value of aboutzero is effected by selective adjustment of the curvature ofthe first refracting surface C1, wherein the remaining aberra-tions of the lens are sufficiently reduced that the lensexhibits an rms optical path difference not exceeding about .lambda./2throughout the entire image field, and wherein the power seriescoefficient N10 and the curvature of the second refractingsurface C2 are selected such that the lens exhibits an rmsoptical path difference not exceeding about .lambda./13 at field heightsbelow 0.7.