Optical head device and optical information device using the same, computer, optical disk player, car navigation system, optical disk recorder, and optical disk server

An optical head device, comprising:

• a blue laser light source for emitting a blue light beam;
• an infrared laser light source for emitting an infrared light beam;
• an objective lens for receiving light beams emitted from the blue laser light source and the infrared laser light source and focusing then into a spot on a recording surface of an optical disk;
• and
• an optical detector in which is formed an optical detector portion for receiving a light beam reflected by the recording surface of the optical disk and outputting an electric signal that corresponds to a light amount of the light beam;
• wherein, due to the objective lens, the blue light beam emitted by the blue laser light source is focused into a spot on the recording surface of an optical disk after passing through a substrate having thickness t1, wherein t1 is approximately 0.1 mm or less;
• wherein a relay lens is disposed between the infrared laser light source and the objective lens;
• wherein the infrared light beam emitted from the infrared laser light source is converted by the relay lens so that the infrared light beam exiting the relay lens converges to have a smaller diameter than the infrared light beam incident on the relay lens and then, as the infrared light beam diverges once again, the infrared light beam is incident on the objective lens, and the objective lens focuses the infrared light beam into a spot on the recording surface of an optical disk, after passing through an approximately 1.2 mm substrate;
• wherein the objective lens is a compound objective lens composed of a hologram and a refractive lens;
• wherein the hologram comprises a grating having a sawtooth cross-sectional shape formed on at least an inner circumferential portion;
• wherein a depth h1 of the sawtooth cross-sectional shape is
• a depth that generates a positive second-order diffraction light by providing a light path difference of approximately two wavelengths with respect to a first light beam having wavelength λ1 in the range of 390 nm to 415 nm, and
• a depth that generates a positive first-order diffraction light with respect to a second light beam having wavelength λ2 in the range of 630 nm to 680 nm;
• wherein the hologram has a convex lens form so that if the first light beam is focused passing through a substrate having thickness t1, the first light beam is subjected to a convex lens effect by the hologram, a change in a focal length is reduced if the wavelength λ1 changes by about several nm;
• wherein the positive second-order diffraction light of the first light beam is focused after passing through a substrate having thickness t1, and the positive first-order diffraction light of the second light beam that passes through the inner circumferential portion of the hologram is focused after passing through a substrate having thickness t2;
• wherein t1<t2;
• and
• wherein if the first light beam is focused passing through a substrate having thickness t1, then
• by having the hologram exert a greater convex lens effect than if the second light beam that passes through the inner circumference portion of the hologram is focused passing through a substrate having thickness t2, or
• by having the hologram exert a smaller convex lens effect when the second light beam that passes through the inner circumference portion of the hologram is focused passing through a substrate having thickness t2 than when the first light beam is focused passing through a substrate having thickness t1,
• a focal position on an optical disk side is moved away from the compound objective lens.