Patent ID: 8139463
Filing Date: 2012-03-20
Classification: G02B,G11B

Abstract:
1. An objective lens for selectively focusing each of a plurality of light beams having one of three wavelengths λ 1 , λ 2 , and λ 3 on a signal recording surface of a corresponding optical disc, the wavelengths λ 1 , λ 2 , and λ 3 satisfying at least a relationship λ 1 <λ 2 <λ 3 , the objective lens comprising: a diffraction section disposed on an entry-side surface of the objective lens, the diffraction section including: wherein the first, second and third regions are formed so that an aperture of a light beam having the wavelength λ wherein the objective lens satisfies |φ where, assuming that a positive diffraction order means that an incident light beam is diffracted toward an optical axis, k where φ where φ