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US 5,754,512 AGranted
Correction elements to lower light intensity around an optical axis of an optical head with a plurality of focal points
AssigneeMatsushita Electric Industrial Co., Ltd.
InventorsYoshiaki Komma, Sadao Mizuno, Hideki Hayashi, Kenichiro Urairi
Life of this patent
Estimating the term…
Abstract
An optical head apparatus which records or reproduces signals stably on optical disks having different thicknesses. A correction hologram element or a correction filter is provided between a light source and a 2-focus lens in order to decrease optical intensity at a portion distant from the optical axis or to change the optical path length. The light which passes the correction hologram element or a correction filter is converged by the 2-focus lens as a micro-spot on an optical disk. The 2-focus lens comprises a hologram lens which diffracts a part of the light beam and an object lens.
Claims19
An optical head apparatus comprising:
- a light source which emits a light beam;
- a lens which converges the light beam emitted by said light source into a micro-spot on an information medium, said lens having a plurality of focal points having different numerical apertures at the same side with respect to said lens, said lens comprising a combination of an object lens which refracts light and a hologram lens;
- a correction element for correcting optical intensity of the light beam emitted by said light source, said correction element being provided in an optical path from said light source to said lens, said correction element having a first portion distant from an optical axis where an optical intensity is lowered more than in a second portion thereof around the optical axis;
- and
- a photosensor which detects a light reflected by the information medium to output an electrical signal in correspondence to an optical intensity of the light.
2 more elements
An optical head apparatus comprising:
- a light source which emits a light beam, said light source emitting the light beam having different rates of change in optical intensity along first and second directions perpendicular to each other and perpendicular to an optical axis of the light beam, the second direction being defined as a direction along which the rate of change in optical intensity is the smallest;
- a correction element for correcting optical path length, said correction element being provided in an optical path from said light source to said lens, said correction element comprising a first portion distant from the optical axis in the second direction and a second portion around the optical axis, the second portion having an optical path length along said optical path shorter than the first portion;
- a lens which converges the light beam emitted by said light source into a micro-spot on an information medium, said lens having a plurality of focal points having different numerical apertures at the same side with respect to said lens, said lens comprising a combination of an object lens which refracts light and a hologram lens;
- and
- a photosensor which detects a light reflected by the information medium to output an electrical signal in correspondence to an optical intensity of the light.
2 more elements
An optical head apparatus comprising:
- a light source which emits a light beam;
- a lens which converges the light beam emitted by said light source into a micro-spot on an information medium, said lens having a plurality of focal points having different numerical apertures at the same side with respect to said lens, said lens comprising a combination of an object lens which refracts light and a hologram lens, said hologram lens being integrated with a plane having a larger curvature of two planes of said object lens;
- and
- a photosensor which detects a light reflected by the information medium to output an electrical signal in correspondence to an optical intensity of the light.
1 more element
An optical head apparatus comprising:
- a light source which emits a light beam;
- a lens which converges the light beam emitted by said light source into a micro-spot on an information medium, said lens having a plurality of focal points having different numerical apertures at the same side with respect to said lens, said lens comprising a combination of an object lens which refracts light and a hologram lens;
- and
- a photosensor which detects a light reflected by the information medium to output an electrical signal in correspondence to an optical intensity of the light;
- wherein said hologram lens of said lens is integrated with a part of a plane of the object lens, an average height of an uneven portion of a grating of said hologram lens is continuous to a height of a portion of said hologram lens having no grating, and an average surface of the uneven portion of the grating pattern and a surface of the portion having no grating pattern are designed to converge a light beam to diffraction limit .
2 more elements
Dependencies are inferred from the claim text.