Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2000-11-15
2003-12-30
Hindi, Nabil (Department: 2655)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112080
Reexamination Certificate
active
06671247
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical pick-up apparatus, optical elements, and an objective lens, and specifically to an optical pick-up apparatus which can information-record on two optical information recording media whose transparent substrate thickness are different, or can information-reproduce from two optical information recording media whose transparent substrate (base plate) thickness are different, and to optical elements and an objective lens for use in the apparatus.
Recently, as a short wavelength red semiconductor laser is put to practical use, the development of a DVD (digital video disk) which is a high density optical disk whose size is almost the same as the conventional optical disk, that is, a CD (compact disk) which is an optical information medium, and whose capacity is greatly increased, is advanced. In an optical system of an optical information recording and reproducing apparatus which uses such the optical disk as a medium, in order to attain the high increase of the density of a recording signal, it is required that the diameter of a spot which is converged by an objective lens, is reduced. Therefore, there is a real situation in which the shortening of the wavelength of a laser as a light source and an increase of NA of the objective lens are promoted.
For example, in the optical pick-up apparatus for recording and/or reproducing the information on and from the DVD, when the short wavelength semiconductor laser of 635 nm is used as the light source, the numerical aperture NA of the objective lens to converge the laser light, on the optical disk side, is about 0.6. Incidentally, in the CD, or DVD, there are many kinds of standards of optical disks such as, for example, CD-R (Compact Disk-Recordable), and other than CD, or DVD, MD (Mini Disk)or the like, is put into the market, and comes into wide use.
On the one hand, in the optical pick-up apparatus to record the information and/or to reproduce the information on or from the CD-R, the light source having the wavelength &lgr;=780 nm is necessary, however, for the other optical disks, the light source having the wavelength other than the specific light source wavelength can be used, and in such the case, corresponding to the light source wavelength to be used, the necessary numerical aperture NA is changed. For example, the following values are approximated: in the case of CD, necessary numerical aperture NA=&lgr; (&mgr;m)/1.73, and in the case of DVD, the necessary numerical aperture NA=&lgr; (&mgr;m)/1.06. The numerical aperture in the present specification is the numerical aperture of a converging optical system viewed from the optical disk side, and the necessary numerical aperture is the numerical aperture calculated from a spot size d required on the recording surface of the optical disk and the wavelength to be used &lgr;, and generally, NA=0.83×&lgr;÷d.
As described above, various optical disks whose transparent substrate thickness, recording density, and wavelength to be used, are different from each other, exist in the market, and to purchase the exclusively used information recording and reproducing apparatus by which the information can be recorded and/or reproduced on or from each of optical disks, is a large burden on the user. Accordingly, an information recording and reproducing apparatus provided with the optical pick-up apparatus which can cope with various optical disks and is interchangeable, is proposed.
In such the optical pick-up apparatus, when the light flux having the different wavelength is entered into the substrates with the different thickness, it is necessary that the spherical aberration is corrected to a smaller amount than a predetermined amount, and in order to appropriately write and read the information, the spot diameter of each light flux is made to be within a predetermined range.
Accordingly, the optical pick-up apparatus which reproduces a plurality of optical disks by using one converging optical system is proposed. For example, in Japanese Tokkaihei No. 7-302437, the optical pick-up apparatus in which the refraction surface of the objective lens is divided into ring-like plural areas, and the information is reproduced when the light beam is image-formed on one of the optical disks with the different thickness, by each of the divided surfaces of the objective lens, is disclosed.
However, in the optical pick-up apparatus disclosed in Japanese Tokkaihei No. 7-302437, because one objective lens has more than 2 focal points simultaneously, and the spot light amount of the focal point per one is reduced, there is a problem that it is necessary to increase the laser output.
On the one hand, in Japanese Tokkaihei No. 10-142494, a 2 composition high NA lens for the pick-up, which can cope with 2 kinds of information recording media with different transparent substrate thickness, is shown. However, in the technique disclosed in this application, because, by changing the interval between 2 lenses, the lens copes with the transparent substrates with different thickness, there is a problem that the structure becomes complicated.
Further, in Japanese Tokkaihei No. 9-54973, an optical system using a hologram optical element by using the transmitted light (0-order diffracted ray) of 635 nm, and −1 order diffracted ray of 785 nm, and an optical system using the hologram optical element by using +1 order diffracted ray of 635 nm, and the transmitted light (0-order diffracted ray) of 785 nm, are disclosed. However, according to this hologram optical element, because the difference in level of the hologram is large, the integration with the objective lens is difficult.
Further, in Japanese Tokkaihei No. 11-96585, the optical pick-up apparatus in which 3 divided surfaces are provided on the refraction surface on the light source side of the objective lens, and in the case of the reproduction of the first optical disk, the light flux passing through the first divided surface and the third divided surface is used, and in the case of the reproduction of the second optical disk whose transparent substrate thickness is different from the first optical disk, the light flux passing through the first divided surface and the second divided surface is used, is disclosed. However, according to this objective lens, the residual aberration becomes large on the optical disk (for example, CD) whose transparent substrate is thicker than the other.
Further, the present inventors previously proposed the optical pick-up apparatus in Japanese Tokuganhei No. 11-312701, in which the action of the diffraction surface and the refraction surface is cancelled for a plurality of light sources with different wavelengths and the spherical aberration is corrected by an objective lens on whose refractive surface the diffracting ring-shaped band is provided. In this case, there is a case where the chromatic aberration is generated, when the wavelength is changed in the light source whose wavelength is shorter than the other.
Incidentally, normally, in the optical pick-up apparatus, a detector to detect a tracking error or the like, when it receives the reflected light from the optical information recording medium, is provided. In the. conventional optical pick-up apparatus, because only the spot light is reflected from the optical information medium, as far as the spot light is irradiated on the correct recording position on the optical information recording medium, the possibility that the light is erroneously detected by the detector, is low. However, when the reflected light passes through the above objective lens, because the light flux more than a predetermined numerical aperture is irradiated on the optical information recording medium as a flare light, when the reflected light is detected by the detector, the possibility of the erroneous detection is generated.
In contrast to this, an optical pick-up apparatus in which respective converging optical systems corresponding to each of different optical disks are provided,
Arai Norikazu
Kojima Toshiyuki
Ota Kohei
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Hindi Nabil
Konica Corporation
LandOfFree
Optical pick-up apparatus, optical element, and objective... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical pick-up apparatus, optical element, and objective..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical pick-up apparatus, optical element, and objective... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3180651