Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2001-03-06
2004-08-24
Patel, Gautam R. (Department: 2655)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112070, C369S112130, C369S112190
Reexamination Certificate
active
06781943
ABSTRACT:
TECHNICAL FIELD
This invention relates to an objective lens for use in an optical pickup device which is capable of carrying out the reproducing and/or recording of optical disks having different thicknesses of the transparent substrate respectively and uses light sources having different wavelengths respectively and an optical pickup device employing said lens.
BACKGROUND OF THE INVENTION
In recent years, accompanied by the practical use of the red semiconductor laser having a short wavelength, it has been advanced the development of a high-density optical disk DVD (digital video disk) which has about the same size as a conventional optical disk CD (compact disk) and has been made to have a large capacity. In an optical pickup device for carrying out recording and/or reproducing of information for this DVD, in the case where a semiconductor laser having a short wavelength of 635 nm is used for the light source, the numerical aperture NA of the objective lens at the side of the optical disk for converging the above-mentioned laser beam is made approximately 0.6. Further, in addition to the CD and DVD, optical disks of various standards, for example, a CD-R (a direct read after write, writing once compact disk), an MD (a mini-disk), etc. are commercialized and have come into general use. In Table 1, the thickness of the transparent substrate and the required numerical aperture of various optical disks are shown.
TABLE 1
Required numerical
Thickness of
aperture
transparent
(light source
Optical disk
substrate (mm)
wavelength &lgr; nm)
CD, CD-R
1.2
0.45 (&lgr; = 780)
(reproducing only)
CD-R (recording,
1.2
0.50 (&lgr; = 780)
reproducing)
LD
1.25
0.50 (&lgr; = 780)
MD
1.2
0.45 (&lgr; = 780)
MO (3.5 inch, 230 MB)
1.2
0.55 (&lgr; = 780)
MO (3.5 inch, 6400 MB)
1.2
0.55 (&lgr; = 680)
DVD
0.6
0.60 (&lgr; = 635)
Further, in an optical pickup device for carrying out the recording and/or reproducing for a CD-R, it is necessary that the wavelength of the light source &lgr; is equal to 780 nm; however, for other optical disks, it is possible to use a light source having a wavelength other than the wavelengths noted in Table 1, and in such cases, the required numerical aperture NA is made to be varied in accordance with the light source wavelength &lgr; used. For example, the required numerical aperture NA is approximately expressed by NA=&lgr;(&mgr;m)/1.73 for a CD, and by NA=&lgr;(&mgr;m)/1.06 for a DVD. The numerical aperture (required numerical aperture) referred to in this specification means the numerical aperture of a converging optical system as seen from the side of the optical disk, and the required numerical aperture means the numerical aperture calculated from the spot size d which is required on the recording surface of the optical disk and the used wavelength &lgr;, to be expressed generally by NA=0.83×&lgr;÷d.
As described in the above, there are various optical disks which are different in the thickness of the transparent substrate, the recording density, and the used wavelength on the market; however, it is a large burden for a user to purchase an apparatus for recording and/or reproducing information capable of recording and/or reproducing information to be exclusively used for each of the optical disks. Therefore, it has been proposed an apparatus for recording and/or reproducing information equipped with an interchangeable optical pickup device capable of coping with various optical disks.
For such an optical pickup device, one that is provided with converging optical systems corresponding to different optical disks respectively, and is designed to switch over the optical systems in accordance with the optical disk to reproduce has been proposed. However, in this optical pickup device, a plurality of converging optical systems are required which makes the structure complicated, resulting in making the cost high, which is not desirable.
Therefore, it has been proposed an optical pickup device which reproduces a plurality of optical disks using a single converging optical system. For example, in the publication of the unexamined patent application H7-302437, it is disclosed an optical pickup device which carries out reproducing by dividing the refracting surface into a plurality of ring-shaped bands and making each of the divisional surfaces converge the beam on one of the optical disks having different thicknesses respectively.
However, the optical pickup device disclosed in the publication of the unexamined patent application H7-302437 has the problem that it requires a large laser output because the single objective lens has more than two focal points simultaneously which reduces the spot light quantity per each focal point.
On the other hand, the applicant has proposed the following optical pickup device in the publication of the unexamined patent application H11-96585. That is, the optical pickup device comprises an objective lens provided with a plurality of ring-shaped bands obtained through dividing the lens surface by concentric circles, wherein, for a plurality of light sources having different wavelengths respectively and plural transparent substrates having different thicknesses respectively, each of the ring-shaped bands has its aberration corrected to the refraction limit or under for each of the optical disks by positively utilizing the spherical aberration produced by them. This objective lens has a function that the required numerical aperture can be automatically obtained in accordance with the used wavelength and/or the thickness of the transparent substrate.
However, in the case where the correction is made to the refraction limit or under, it is more desirable to take it into consideration the intensity distribution in the point image, that is, the central intensity of the spot light, in addition to the spot size (spreading of the point image). In order to make this central intensity higher, it is necessary to remark-the phase of the light flux (deviation of the wave front aberration), but there is no description concerning this deviation of the wave front aberration with respect to the optical pickup device disclosed in the publication of unexamined patent application H11-96585.
It is an object of this invention to provide an optical pickup device comprising an objective lens which has four or more divisional surfaces formed and is capable of correcting the deviation of the wave front aberration in the divisional surfaces inside the required numerical aperture for each of the optical disks and the objective lens. Further, it is another object of this invention to provide an optical pickup device and an objective lens having a small amount of loss of light quantity and an excellent S-letter characteristic.
DISCLOSURE OF THE INVENTION
The above-mentioned objects are accomplished by any one of the following structures.
(1-1) An optical pickup device for conducting reproducing and/or recording of information in at least two kinds of optical information recording media, comprises
a first light source to emit light flux having a first wavelength (&lgr;1) in order to conduct reproducing and/or recording of the information in a first optical information recording medium having a first transparent substrate;
a second light source to emit light flux having a second wavelength (&lgr;2) longer than the first wavelength in order to conduct reproducing and/or recording of the information of a second optical information recording medium having a second transparent substrate;
a converging optical system for converging the light flux having the first wavelength or the light flux having the second wavelength on the first information recording surface of the first optical information recording medium or on the second information recording surface of the second optical information recording medium; and
an optical detector for receiving and detecting the light flux reflected by the first information recording surface or by the second information recording surface,
wherein a required numeric
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Konica Corporation
Patel Gautam R.
LandOfFree
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