Patent ID: 6515955
Filing Date: 2003-02-04
Classification: G11B

Abstract:
An objective optical system for an optical pick-up that converges a light beam whose wavelength is shorter than F-line onto an information layer of an optical disc, said objective optical system comprising:a refractive lens, at least one surface of said refractive lens being formed as an aspherical surface whose radius of curvature increases as a height from the optical axis becomes large; 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 to correct chromatic aberration caused by said refractive lens, wherein the following condition (1) is satisfied; 1/(&ngr;3Ã—&lgr;Ã—10âˆ’6)<0.0045 â€ƒâ€ƒ(1) where &ngr; is an Abbe number and &lgr; is a working wavelength (unit: nm).