Patent ID: 7864650
Filing Date: 2011-01-04
Classification: G02B,G11B

Abstract:
1. A Complex optical lens comprising an objective lens and an optical element, wherein grooves are formed on the optical element, wherein the expression: 380 nm≦(n−1)×d≦420 nm is satisfied, where n is a refractive index of the optical element at a wavelength of 400 nm, and d (nm) is a depth per step of the grooves; wherein the grooves are formed in four steps of depth d, depth wherein the depth of the grooves is lined up in the order: depth wherein the depth d of the grooves per step provides a light path difference of about one wavelength with respect to light of a first wavelength in a range of 380 nm to 420 nm and provides a light path difference of about 0.6 wavelengths with respect to light of a second wavelength in a range of 630 nm to 680 nm, and provides a light path difference of about 0.5 wavelengths with respect to light of a third wavelength in a range of 780 nm to 820 nm; the light of the first wavelength having passed through the complex optical lens is focused onto an information surface of a first information recording medium; first order diffraction light of the light of the second wavelength having passed through the complex optical lens is focused onto an information surface of a second information recording medium; and first order diffraction light of the light of the third wavelength having passed through the complex optical lens is focused onto an information surface of a third information recording medium.