High NA objective lens for optical pick-up
AssigneeAsahi Kogaku Kogyo Kabushiki Kaisha
InventorKoichi Maruyama
Life of this patent
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Abstract
A single-element objective lens for an optical pick-up directs an incident light beam to a data recording surface of an optical disc through a cover layer to form a beam spot thereon. A numerical aperture of the objective lens is 0.7 or more. The objective lens is configured to compensate for coma such that a characteristic of a change of spherical aberration due to a degree of divergence/convergence of the incident beam is comparable with respect to a characteristic of a change of spherical aberration due to variation of the cover layer so that the change of spherical aberration due to variation of the cover layer can be cancelled by the change of spherical aberration due to a degree of divergence/convergence of the incident beam.
Claims16
A single-element objective lens for an optical pick-up, said objective lens directing an incident light beam to a data recording surface of an optical disc through a cover layer to form a beam spot, a numerical aperture of said objective lens being 0.7 or more, said objective lens being configured to compensate for coma such that a characteristic of a change of spherical aberration due to a degree of divergence/convergence of the incident beam is substantially comparable with respect to a characteristic of a change of spherical aberration due to variation of the cover layer, thereby the change of spherical aberration due to variation of the cover layer can be cancelled by the change of spherical aberration due to a degree of divergence/convergence of the incident beam.
A single-element objective lens for an optical pick-up, said objective lens directing an incident light beam to a data recording surface of an optical disc through a cover layer to form a beam spot, a numerical aperture of said objective lens being 0.7 or more, said objective lens being configured to compensate for coma such that spherical aberration caused by a change of a degree of divergence/convergence of the incident light beam is substantially proportional to a value OP expressed by equation:
- OP=(1−{square root}{square root over ((1−NA2))}/n−(n−{square root}{square root over ((n2−NA2))}),
- wherein, NA represents a numerical aperture, and n represents a refractive index of the cover layer.
A optical pick-up, comprising:
- a laser source that emits a laser beam;
- a single-element objective lens, said objective lens directing the laser beam emitted by said laser source to a data recording surface of an optical disc through a cover layer to form a beam spot, a numerical aperture of said objective lens being 0.7 or more, said objective lens being configured to compensate for coma such that a characteristic of a change of spherical aberration due to a degree of divergence/convergence of the laser beam incident on said objective lens is substantially comparable with resepct to a characteristic of a change of spherical aberration due to variation of the cover layer, thereby the change of spherical aberration due to variation of the cover layer can be cancelled by the change of spherical aberration due to a degree of divergence/convergence of the incident beam;
- and
- an optical device capable of changing the degree of divergence/convergence of the laser beam incident on said objective lens.
An optical pick-up, comprising:
- a laser source that emits a laser beam;
- a single-element objective lens, said objective lens directing the laser beam emitted by said laser source to a data recording surface of an optical disc through a cover layer to form a beam spot, a numerical aperture of said objective lens being 0.7 or more, said objective lens being configured to compensate for coma such that spherical aberration caused by a change of a degree of divergence/convergence of the laser beam incident on said objective lens is substantially proportional to a value OP expressed by equation:
- OP=(1−{square root}{square root over ((1−NA2))})/n−(n−{square root}{square root over ((n2−NA2))}),
- wherein, NA represents a numerical aperture, and n represents a refractive index of the cover layer;
- and
- an optical device capable of changing the degree of divergence/convergence of the laser beam incident on said objective lens.
Dependencies are inferred from the claim text.