Patent ID: 7864650

Claim:
A Complex optical lens comprising an objective lens and an optical element, wherein grooves are formed on the optical element, wherein the expression: 380 nmâ‰¦(nâˆ’1)Ã—dâ‰¦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 2 d, depth 3 d and depth 4 d; wherein the depth of the grooves is lined up in the order: depth 2 d, depth 4 d, depth d, depth 3 d, or in the order: depth 3 d, depth d, depth 4 d, depth 2 d; 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.