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US 6,674,059 B1Granted
Objective lens and optical pickup
AssigneeSony Corporation
InventorSatoshi Nakano
Life of this patent
Estimating the term…
Abstract
By providing an area of a smaller numerical aperture and an area of a greater numerical aperture on an objective lens, forming holograms of different characteristics corresponding to the respective areas, and using diffracted light beams of the same order of light beams having different wavelengths emitted from two light sources so as to carry out recording to and reproduction from an optical disc, it is possible to carry out recording and reproduction of information signals to and from a plurality of optical recording media of different types while efficiently using the light beams, and to eliminate the problem of a stray light due to an unwanted diffracted light.
Claims19
An objective lens comprising:
- a convex lens;
- and
- a diffractive optical element provided on at least one surface or in the vicinity of the convex lens, said convex lens having a first portion which is effectively covered by the diffractive optical element and a second portion which is not effectively covered by the diffractive optical element;
- wherein when the convex lens condenses an incident light beam having a first wavelength onto a condensation surface via a parallel plate with a first predetermined thickness, spherical aberration is corrected in the second portion of the convex lens, and wherein when the convex lens condenses an incident light beam having a second wavelength onto a condensation surface via a parallel plate with a second predetermined thickness, spherical aberration is corrected by the diffractive optical element for the portion of the incident light beam passing through the first portion of the convex lens.
1 more element
An optical pickup device comprising:
- two light sources for emitting light beams with different wavelengths;
- an objective lens for condensing the respective light beams emitted from the respective light sources onto a signal recording surface of a first or second optical recording medium via a respective transparent cover layer provided on the optical recording medium;
- a light beam branch element for branching a light beam reflected by the signal recording surface from optical paths returning to the light sources;
- and
- a photodetector for receiving the light beam branched by the light beam branch element;
- wherein the objective lens has a convex lens and a diffractive optical element provided on at least one surface or in the vicinity of the convex lens, and condenses diffracted lights of the same order generated by the diffractive optical element, of the two light beams with different wavelengths emitted from the respective light sources, onto the signal recording surface, thereby condensing the respective light beams onto the signal recording surface in the state where spherical aberration generated in the transparent cover layer is corrected.
3 more elements
An optical pickup device comprising:
- two light sources for emitting light beams with different wavelengths;
- an objective lens for condensing the respective light beams emitted from the respective light sources onto a signal recording surface of a first or second optical recording medium via a respective transparent cover layer provided on the optical recording medium;
- a light beam branch element for branching a light beam reflected by the signal recording surface from optical paths returning to the light sources;
- and
- a photodetector for receiving the light beam branched by the light beam branch element;
- wherein the objective lens has a convex lens and a diffractive optical element provided on at least one surface or in the vicinity of the convex lens, and condenses diffracted lights of the same order generated by the diffractive optical element, of the two light beams with different wavelengths emitted from the respective light sources, onto the signal recording surface, thereby condensing the respective light beams onto the signal recording surface in the state where spherical aberration generated in the transparent cover layer is corrected;
- wherein the light sources emit a light beam with a first wavelength λ1 and a light beam with a second wavelength λ2 longer than the first wavelength λ1, respectively, the numerical aperture of the objective lens with respect to the light beam with the first wavelength λ1 is a first numerical aperture NA1, the numerical aperture of the objective lens with respect to the light beam with the second wavelength λ2 is a second numerical aperture NA2, the thickness of the transparent cover layer corresponding to the light beam with the first wavelength λ1 is a first thickness t1, and the thickness of the transparent cover layer corresponding to the light beam with the second wavelength λ2 is a second thickness t2 greater than the first thickness t1,
- wherein when the wavelength of the light beam is the first wavelength λ1 and the numerical aperture is the first numerical aperture NA1, the spherical aberration in the case where the thickness of the transparent cover layer is the first thickness t1 is corrected to not more than λ/100 RMS by a first-order diffracted light diffracted by the diffractive optical element, and
- wherein when the wavelength of the light beam is the second wavelength λ2 and the numerical aperture is the second numerical aperture NA2, the spherical aberration in the case where the thickness of the transparent cover layer is the second thickness t2 is corrected to not more than λ/30 RMS by a first-order diffracted light diffracted by the diffractive optical element.
6 more elements
An optical pickup device comprising:
- two light sources for emitting light beams with different wavelengths;
- an objective lens for condensing the respective light beams emitted from the respective light sources onto a signal recording surface of a first or second optical recording medium via a respective transparent cover layer provided on the optical recording medium;
- a light beam branch element for branching a light beam reflected by the signal recording surface from optical paths returning to the light sources;
- and
- a photodetector for receiving the light beam branched by the light beam branch element;
- wherein the objective lens has a convex lens and a diffractive optical element provided on at least one surface or in the vicinity of the convex lens, and condenses diffracted lights of the same order generated by the diffractive optical element, of the two light beams with different wavelengths emitted from the respective light sources, onto the signal recording surface, thereby condensing the respective light beams onto the signal recording surface in the state where spherical aberration generated in the transparent cover layer is corrected;
- wherein in the case where a light beam with a third wavelength λ3 longer than the second wavelength λ2 and a third numerical aperture NA3 smaller than the second numerical aperture NA2 are used, the spherical aberration in the case where the thickness of the transparent cover layer is a third thickness t3 greater than the second thickness t2 is corrected to not more than λ3/50 RMS by a first-order diffracted light diffracted by the diffractive optical element.
4 more elements
An optical pickup device comprising:
- two light sources for emitting light beams with different wavelengths;
- an objective lens for condensing the respective light beams emitted from the respective light sources onto a signal recording surface of a first or second optical recording medium via a respective transparent cover layer provided on the optical recording medium;
- a light beam branch element for branching a light beam reflected by the signal recording surface from optical paths returning to the light sources;
- and
- a photodetector for receiving the light beam branched by the light beam branch element;
- wherein the objective lens has a convex lens and a diffractive optical element provided on at least one surface or in the vicinity of the convex lens, and condenses diffracted lights of the same order generated by the diffractive optical element, of the two light beams with different wavelengths emitted from the respective light sources, onto the signal recording surface, thereby condensing the respective light beams onto the signal recording surface in the state where spherical aberration generated in the transparent cover layer is corrected;
- wherein the diffractive optical element is a blazed-shape hologram
- wherein the direction of inclination of the blazed shape is such that the height is lower on the outer side than on the center side of the objective lens;
- and
- wherein the depth d of the blaze is expressed by
- 0.8·λ1/(n1−1)<d<1.2·λ2/(n2−1)
- in which n1 represents the refractive index of the medium of the objective lens when the wavelength of the light beam is the first wavelength λ1, and n2 represents the refractive index of the medium of the objective lens when the wavelength of the light beam is the second wavelength λ2.
9 more elements
An optical pickup device comprising:
- a light source for emitting a light beam;
- a finite-type objective lens for condensing the light beam emitted from the light source onto a signal recording surface of an optical recording medium;
- a light beam branch element for branching a light beam reflected by the signal recording surface from an optical path returning to the light source;
- and
- a photodetector for receiving the light beam branched by the light beam branch element;
- wherein the objective lens is made up of a convex lens made of a synthetic resin and a blazed-shape hologram provided at least on one surface of the convex lens, and uses a plus-first-order diffracted light or a minus-first-order diffracted light of the hologram to cancel spherical aberration generated by a change in the refractive index of the synthetic resin material forming the convex lens due to a temperature change.
3 more elements
Dependencies are inferred from the claim text.