Objective lens and optical information read/write device

An objective lens to be employed for an optical information read/write device that is configured to perform read/write operations for reading and/or writing information on each of a plurality of kinds of optical discs using a corresponding one of a plurality of kinds of laser beams having different wavelengths, the plurality of kinds of laser beams including three kinds of laser beams that have a first wavelength λ1 (nm), a second wavelength λ2 (nm), and a third wavelength λ3 (nm) according to a relationship λ1<λ2<λ3, respectively, the objective lens comprising a phase shift structure on at least one surface of the objective lens that has a plurality of ring-shaped refractive surface zones into which the at least one surface is concentrically divided,

• wherein the objective lens is made of material with an Abbe number νd satisfying a condition:
• 40≦νd≦80, and
• wherein the phase shift structure has a step between each couple of the adjacent refractive surface zones that gives an optical path difference to an incident laser beam, and
• wherein the phase shift structure is configured to satisfy a condition:
• 5.07<|ΔOPD/λ1|<5.25,
• where ΔOPD represents the optical path difference (nm) that the step gives to the laser beam with the first wavelength λ1.

An optical information read/write device configured to perform read/write operations for reading and/or writing information on each of a plurality of kinds of optical discs using a corresponding one of a plurality of kinds of laser beams having different wavelengths, the optical information read/write device comprising an objective lens that has a phase shift structure on at least one surface of the objective lens that has a plurality of ring-shaped refractive surface zones into which the at least one surface is concentrically divided,

• wherein the plurality of kinds of laser beams includes three kinds of laser beams that have a first wavelength λ1 (nm), a second wavelength λ2 (nm), and a third wavelength λ3 (nm) according to a relationship λ1<λ2<λ3, respectively, and
• wherein the plurality of kinds of optical discs includes:
• a first optical disc with a protective layer whose thickness t1 is approximately 0.6 mm, on which the read/write operations are performed using the laser beam with the first wavelength λ1;
• a second optical disc with a protective layer whose thickness t2 is approximately 0.6 mm, on which the read/write operations are performed using the laser beam with the second wavelength λ2;
• and
• a third optical disc with a protective layer whose thickness is approximately 1.2 mm, on which the read/write operations are performed using the laser beam with the third wavelength λ3, and
• wherein the optical information read/write device is configured to satisfy relationships NA1>NA3 and NA2>NA3, where NA1, NA2, and NA3 represent numerical apertures necessary for the read/write operations on the first optical disc, the second optical disc, and the third optical disc, respectively, and
• wherein the optical information read/write device is configured such that the laser beams with the first and second wavelengths λ1 and λ2 are incident on the objective lens substantially as collimated light, and the laser beam with the third wavelength λ3 is incident on the objective lens as diverging light, and
• wherein the objective lens is made of material with an Abbe number νd satisfying a condition:
• 40≦νd≦80, and
• wherein the phase shift structure has a step between each couple of the adjacent refractive surface zones that gives an optical path difference to an incident laser beam, and
• wherein the phase shift structure is configured to satisfy a condition:
• 3.04<|ΔOPD/λ1|<3.29,
• in a first area configured to converge the laser beam with the third wavelength λ3 on a recording surface of the third optical disc, where ΔOPD (nm) represents the optical path difference that the step gives to the laser beam with the first wavelength λ1, and
• wherein the optical information read/write device is configured to satisfy conditions:
• −0.02<f1×M1<0.02;
• −0.02<f2×M2<0.02;
• and
• −0.12<f3×M3<−0.04,
• where M1 and f1 represent an imaging magnification and a focal length in the read/write operations on the first optical disc, respectively, and M2 and f2 represent an imaging magnification and a focal length in the read/write operations on the second optical disc, respectively, and M3 and f3 represent an imaging magnification and a focal length in the read/write operations on the third optical disc, respectively.

An optical information read/write device configured to perform read/write operations for reading and/or writing information on each of a plurality of kinds of optical discs using a corresponding one of a plurality of kinds of substantially collimated laser beams having different wavelengths, the optical information read/write device comprising an objective lens that has a phase shift structure on at least one surface of the objective lens that has a plurality of ring-shaped refractive surface zones into which the at least one surface is concentrically divided,

• wherein the plurality of kinds of laser beams includes three kinds of laser beams that have a first wavelength λ1 (nm), a second wavelength λ2 (nm), and a third wavelength λ3 (nm) according to a relationship λ1<λ2<λ3, respectively, and
• wherein the plurality of kinds of optical discs includes:
• a first optical disc with a protective layer whose thickness t1 is approximately 0.6 mm, on which the read/write operations are performed using the laser beam with the first wavelength λ1;
• a second optical disc with a protective layer whose thickness t2 is approximately 0.6 mm, on which the read/write operations are performed using the laser beam with the second wavelength λ2;
• and
• a third optical disc with a protective layer whose thickness is approximately 1.2 mm, on which the read/write operations are performed using the laser beam with the third wavelength λ3, and
• wherein the optical information read/write device is configured to satisfy relationships NA1>NA3 and NA2>NA3, where NA1, NA2, and NA3 represent numerical apertures necessary for the read/write operations on the first optical disc, the second optical disc, and the third optical disc, respectively, and
• wherein the objective lens is made of material with an Abbe number νd satisfying a condition:
• 40≦νd≦80, and
• wherein the phase shift structure has at least two kinds of steps, each of the steps between each couple of the adjacent refractive surface zones giving an optical path difference to an incident laser beam, and
• wherein the phase shift structure is configured to satisfy a condition:
• 3.04<|ΔOPD1/λ1|<3.29,
• in a first area configured to converge the laser beam with the third wavelength λ3 on a recording surface of the third optical disc, where ΔOPD1 (nm) represents the optical path difference that at least one of the at least two kinds of steps give to the laser beam with the first wavelength λ1.

An optical information read/write device configured to perform read/write operations for reading and/or writing information on each of a plurality of kinds of optical discs using a corresponding one of a plurality of kinds of substantially collimated laser beams having different wavelengths, the optical information read/write device comprising an objective lens that has a phase shift structure on at least one surface of the objective lens that has a plurality of ring-shaped refractive surface zones into which the at least one surface is concentrically divided,

• wherein the plurality of kinds of laser beams includes three kinds of laser beams that have a first wavelength λ1 (nm), a second wavelength λ2 (nm), and a third wavelength λ3 (nm) according to a relationship λ1<λ2<λ3, respectively, and
• wherein the plurality of kinds of optical discs includes:
• a first optical disc with a protective layer whose thickness t1 is approximately 0.6 mm, on which the read/write operations are performed using the laser beam with the first wavelength λ1;
• a second optical disc with a protective layer whose thickness t2 is approximately 0.6 mm, on which the read/write operations are performed using the laser beam with the second wavelength λ2;
• and
• a third optical disc with a protective layer whose thickness is approximately 1.2 mm, on which the read/write operations are performed using the laser beam with the third wavelength λ3, and
• wherein the optical information read/write device is configured to satisfy relationships NA1>NA3 and NA2>NA3, where NA1, NA2, and NA3 represent numerical apertures necessary for the read/write operations on the first optical disc, the second optical disc, and the third optical disc, respectively, and
• wherein the objective lens is made of material with an Abbe number νd satisfying a condition:
• 40≦νd≦80, and
• wherein the phase shift structure has at least two kinds of steps, each of the steps between each couple of the adjacent refractive surface zones giving an optical path difference to an incident laser beam, and
• wherein the phase shift structure is configured to satisfy a condition:
• 5.07<|ΔOPD1/λ1|<5.25,
• in a first area configured to converge the laser beam with the third wavelength λ3 on a recording surface of the third optical disc, where ΔOPD1 (nm) represents the optical path difference that at least one of the at least two kinds of steps give to the laser beam with the first wavelength λ1.

An objective lens to be employed for an optical information read/write device that is configured to perform read/write operations for reading and/or writing information on each of a plurality of kinds of optical discs using a corresponding one of a plurality of kinds of laser beams having different wavelengths, the plurality of kinds of laser beams including three kinds of laser beams that have a first wavelength λ1 (nm), a second wavelength λ2 (nm), and a third wavelength λ3 (nm) according to a relationship λ1<λ2<λ3, respectively, the objective lens comprising a phase shift structure on at least one surface of the objective lens that has a plurality of ring-shaped refractive surface zones into which the at least one surface is concentrically divided,

• wherein the objective lens is a single lens made of material with an Abbe number νd satisfying a condition:
• 20≦νd<40, and
• wherein the phase shift structure has a step between each couple of the adjacent refractive surface zones that gives an optical path difference to an incident laser beam, and
• wherein the phase shift structure is configured to satisfy a condition:
• 2N+0.70<|ΔOPD/λ1|<2N+1.25,
• where ΔOPD represents the optical path difference (nm) that the step gives to the laser beam with the first wavelength λ1, and N represents a non-negative integer.