Patent ID: 6807019
Filing Date: 2004-10-19
Classification: G02B,G11B

Abstract:
An objective lens for an optical pick-up that converges light beams of at least two different wavelengths onto recording layers of optical discs of different standards, respectively, said objective lens comprising:a refractive lens having a positive power; and a diffractive lens structure having a plurality of concentric ring areas with minute steps at the boundaries therebetween, said diffractive lens structure being formed on at least one surface of said refractive lens, wherein said diffractive lens structure is designed such that the diffraction order where the diffraction efficiency is maximized at the shorter wavelength is higher than the diffraction order where the diffraction efficiency is maximized at the longer wavelength, wherein said diffractive lens structure maximizes the diffraction efficiency of the third order diffracted light at the shorter wavelength and said diffractive lens structure maximizes the diffraction efficiency of the second order diffracted light at the longer wavelength.