Patent ID: 7245407

Claim:
A complex objective lens comprising: a hologram; and a refraction type lens, wherein said hologram includes a grating having a sawtooth cross-sectional shape formed in at least an inner circumferential portion, and a depth h 4 of the sawtooth cross-sectional shape provides a difference in an optical path length larger than 1.7 wavelengths and smaller than 2 wavelengths to a first light beam having a wavelength λ 1 in a range of 390 nm to 415 nm to enable the first light beam to generate +2nd-order diffracted light, and enable a second light beam having a wavelength λ 2 in a range of 630 nm to 680 nm to generate +1st-order diffracted light, and wherein, in order to place a focal point position on an optical disk side away from the complex objective lens, the hologram is configured so as to have: a larger function as a convex lens when condensing the second light beam passing through an inner circumferential portion of the hologram through an optical recording medium base with a thickness t 2 , as compared to condensing the first light beam through an optical recording medium base with a thickness t 1 , wherein the thickness t 2 is larger than the thickness t 1 ; or a smaller function as a convex lens when condensing the first light beam through the base with the thickness t 1 , as compared to condensing the second light beam passing through the inner circumferential portion of the hologram through the base with the thickness t 2 .