Optical element, optical head, optical information recording and reproduction apparatus, computer, image recording device, image reproduction device, server and car navigation system

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 2d, depth 3d and depth 4d;
• wherein the depth of the grooves is lined up in the order:
• depth 2d, depth 4d, depth d, depth 3d, or in the order:
• depth 3d, depth d, depth 4d, depth 2d;
• 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.

An objective lens with grooves formed on a surface,

• wherein the expression:
• 380 nm≦(n−1)×d≦420 nm is satisfied, where n is a refractive index of the objective lens 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 2d, depth 3d and depth 4d;
• wherein the depth of the grooves is lined up in the order:
• depth 2d, depth 4d, depth d, depth 3d, or in the order depth 3d, depth d, depth 4d, depth 2d;
• 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 object 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 objective 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 objective lens is focused onto an information surface of a third information recording medium.