Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2001-05-23
2004-02-03
To, Doris H. (Department: 2655)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112250, C369S112260, C359S719000
Reexamination Certificate
active
06687209
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an objective lens used for conducting recording and/or reproducing of an information recording medium in an optical pickup apparatus, and to an optical pickup apparatus.
BACKGROUND OF THE INVENTION
For an optical pickup apparatus capable of conducting recording and/or reproducing of information for a plurality of information recording media (for example, optical disks) each having different recording density and a different thickness of a transparent base board, such as CD and DVD, it has been demanded that downsizing and cost reduction of the apparatus are realized by using at least an objective lens in common, and various objective lenses and various optical pickup apparatuses for that demand have been suggested.
For example, there has been known an objective lens wherein ring-shaped notches are provided on one surface of the objective lens as specific ring-shaped zones to constitute the surface with a plurality of divided surfaces (for example, three divided surfaces), and a part (for example, a first divided surface closer to the optical axis) of the plural divided surfaces is made to be used for recording and/or reproducing of information for two types of information recording media each having different recording density and a different thickness of a transparent base board, a part (for example, a second divided surface that is adjacent to the first divided surface) of the remaining divided surfaces is made to be used for recording and/or reproducing of information for the information recording medium on one side (for example, the information recording medium having a smaller necessary numerical aperture), and the rest (for example, a third divided surface that is adjacent to the second divided surface) is made to be used for recording and/or reproducing of information for the information recording medium on the other side (for example, the information recording medium having a larger necessary numerical aperture). As an example of the foregoing, there may be given one described in TOKKAIHEI No. 11-96585. However, erroneous detection has sometimes been caused for focus signals on the objective lens on which ring-shaped notches are provided as stated above. For example, in the case of recording or reproducing of DVD through the second divided surface that is corrected in terms of spherical aberration for CD among three divided surfaces provided on one surface of the objective lens, a light flux which has passed through the second divided surface has sometimes been converged on a sensor through defocusing, to cause erroneous detection for focus signals.
In TOKKAIHEI No. 10-283668, there is described an optical pickup apparatus wherein a ring lens of a hologram type is used, and with regard to a hologram portion, light having a wavelength of 650 nm for DVD is used as zero-order light, while, with regard to light having a wavelength of 780 nm for CD, one-order diffracted light is used.
However, in the case of one wherein divided surfaces are provided on an objective lens as stated above, and one of the divided surfaces is made to be a hologram or a diffractive surface for which zero-order light is used for a wavelength on one side and primary light is used for a wavelength on the other side, the diffraction efficiency is lowered, and quantity of light coming from a light source cannot be utilized sufficiently, resulting in erroneous detection that is sometimes caused for focus signals.
In TOKKAI No. 2000-81566, there is described an objective lens wherein a diffractive structure is formed on a lens surface in a pattern of ring-shaped zones whose centers are on an optical axis, and the diffractive structure is made to have wavelength-dependency so that diffracted light with the same order number by at least two light fluxes each having a different wavelength may form an excellent wave front respectively for two types of optical disks each having a different thickness of a protective layer.
However, since the diffractive structure is formed on the objective lens equipped with diffractive structure on the entire surface of the lens surface as stated in the official gazette mentioned above so that the diffracted light with the same order number appropriate for light fluxes with at least two wavelengths may be obtained, there has been a problem that efficiency of the objective lens for using quantity of light from a light source is lower than that of an objective lens composed of a refraction surface on which no diffractive structure is provided. Further, since the number of diffractive ring-shaped zones is large, productivity for a metal mold for forming a lens is lowered, and production cost for a metal mold is enhanced, which has also been a problem. When recording information on an optical information recording medium, in particular, the recording requires greater quantity of light, compared with reproducing, and therefore, the problem of the fall of efficiency for using quantity of light is serious.
Further, when using a plastic lens, a change in aberration caused by temperature fluctuation has also been a problem.
SUMMARY OF THE INVENTION
In view of the problems in the prior art stated above, an object of the invention is to provide an optical pickup apparatus wherein quantity of light coming from a light source can be used fully, erroneous detection of light from an information recording medium is not caused, and an increase in production cost can be controlled, and to provide an objective lens to be used for the optical pickup apparatus. A further object is to provide an optical pickup apparatus capable of providing sufficient quantity of light when recording information on an optical information recording medium and to provide an objective lens to be used for the optical pickup apparatus stated above. Still another object is to provide an optical pickup apparatus that can control a change in aberration even when ambient temperature is changed, and to provide an objective lens to be used for the optical pickup apparatus mentioned above.
The objects stated above can be attained by the following structures.
(1) An optical pickup apparatus for conducting reproducing or recording information of at least two kinds of optical information recording media, comprises:
a first light source to emit first light flux having a first wavelength to conduct reproducing or recording information of a first optical information recording medium having a first transparent base board;
a second light source to emit second light flux having a second wavelength to conduct reproducing or recording information of a second optical information recording medium having a second transparent base board;
an optical converging system having at least one optical element; and
a photo detector to receive and detect light transmitting through or reflecting from a first information recording surface of the first optical information recording medium or light transmitting through or reflecting from a second information recording surface of the second optical information recording medium;
wherein the first wavelength is different from the second wavelength and the thickness of the first transparent base board is different from that of the second transparent base board,
wherein the optical element comprises a first region including an optical axis and a second region adjoining the first region and locating at the outside of the first region, the first region is a refractive surface and the second region is a diffractive surface,
wherein when the first light flux passes through the second region of the optical element, the light amount of n-th order diffracted ray of the first light flux is larger than that of any other order diffracted ray of the first light flux, and when the second light flux passes through the second region of the optical element, the light amount of n-th order diffracted ray of the second light flux is larger than that of any other order diffracted ray of the second light flux, where n is an integer except 0,
wherein the optical converging
Arai Norikazu
Ota Kohei
Criado Jorge L Ortiz
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Konica Minolta Holdings Inc.
To Doris H.
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