Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
2001-08-27
2003-12-09
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C369S044230, C369S112010
Reexamination Certificate
active
06660985
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical pick-up device and an objective lens, and for example, to an optical pick-up apparatus by which the information recording and/or information reproducing can be conducted on two optical information recording media having different transparent substrate thickness, and to an objective lens for use in it.
Recently, as the a short wavelength red semiconductor laser is put to practical use, the development of a DVD (digital versatile disk) which is the high density optical disk having the larger capacity whose dimension is about the same as the CD (compact disk) which is the conventional optical disk, that is, the optical information recording medium is advanced. In the optical system of the optical information recording and reproducing device whose medium is such the optical disk, in order to intend the increase of the density of the recording signal, it is required that the size of a spot converged onto the recording medium by the objective lens is reduced to a smaller one. Accordingly, there is the actual condition that the reduction of the wavelength of the laser as the light source and the increase of the NA of the objective lens are intended.
For example, in the optical pick-up device to conduct the recording and/or reproducing of the information on the DVD, when the short wavelength semiconductor laser of 655 nm is used as the light source, the numerical aperture NA on the optical disk side of the objective lens to converge such the laser light is about 0.6. In this connection, in the CD and DVD, there are various standards of optical disks, for example, a CD-R (recordable compact disk), and other than the CD and DVD, a MD (mini disk) is put in the market and is widely spread.
On the one hand, the light source having the wavelength &lgr;=785 nm is necessary in the optical pick-up device to conduct the recording and/or reproducing of the information on the CD-R, however, in 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, the necessary numerical aperture NA is changed corresponding to the light source wavelength &lgr; to be used. For example, in the case of the CD, the necessary numerical aperture NA=&lgr;(&mgr;m)/1.73, and in the case of the DVD, the necessary numerical aperture NA=&lgr;(&mgr;m)/1.06, are respectively approximated as each NA. The numerical aperture in the present specification is the numerical aperture of the converging optical system viewed from the optical disk side, and the necessary numerical aperture is the numerical aperture calculated from a spot size d and the wavelength &lgr; to be used which are required on the recording surface of the optical disk, and generally, NA=0.83×&lgr;÷d.
As described above, various optical disks having different transparent substrate thickness, recording density, and wavelength to be used, exist in the market, and to individual optical disk, it is a large burden for the user to purchase an exclusive information recording and reproducing apparatus by which the recording and/or reproducing of the information can be conducted. Accordingly, the information recording and reproducing apparatus provided with a compatible optical pick-up device which can cope with various optical disks, is proposed.
In such the optical pick-up device, when the luminous flux having different wavelengths is incident onto the substrates having different thickness, it is necessary that the spherical aberration is corrected to a value not larger than a predetermined amount, and it is necessary that, in order to make the writing and reading of the information adequate, the spot diameter of each luminous flux also comes into within a predetermined range.
In contrast to it, an optical pick-up device which is provided with individual converging optical systems respectively corresponding to different optical disks, and in which the converging optical systems are switched by the optical disks to be reproduced, is proposed. In such the optical pick-up device, when the luminous fluxes having the different wavelengths are incident onto the substrates having the different thickness, the spherical aberration can be corrected to an amount not larger than a predetermined amount, and the spot diameter of each luminous flux can also be within a predetermined range. However, in this optical pick-up device, because a plurality of converging optical systems are necessary, the structure becomes complicated, and so the cost is increased, which is not preferable.
To such the problem, an objective lens by which the luminous flux having not larger than a predetermined numerical aperture is converged into a spot light, and the luminous flux having not smaller than a predetermined numerical aperture is made a flare light, is now developed. According to such the objective lens, to the different optical information media such as the CD-R or DVD, a spot light which is necessary for recording or reproducing of the information can be obtained.
In this connection, generally, in the optical pick-up device, an optical detector to detect a tracking error by receiving the light reflected from the optical in formation recording medium is provided. In the conventional optical detector, because only a spot light is reflected from the optical information recording medium, so far as the spot light is irradiated onto the correct recording position on the optical information recording medium, there is a low possibility that the optical detector erroneously detect it. However, when the luminous flux is through the above-described objective lens, because the luminous flux more than a predetermined numerical aperture is irradiated onto the optical information recording medium as a flare light, when the reflected light is detected by the detector, there is a possibility of the false detection.
Namely, primarily, when light is irradiated correctly at a recording position on a optical information recording medium, there may be no deviation in light intensity of the light received by the detector. However, if the reflected light of flare light comes to be incident unevenly into the detector, a deviation in light intensity of the light received by the detector is caused by the uneven incidence or the light intensity becomes unstable. As a result, even if no tracking error takes place, there is a possibility to cause an erroneous detection to inform that a tracking error takes place.
SUMMARY OF THE INVENTION
An object of the present invention is, although a small number of optical elements or objective lens is used, to provide an optical pick-up device and an objective lens for use in the device, by which recording and/or reproducing of the information (hereinafter, called simply recording reproducing) can be conducted on the optical information recording media having different thickness, and the false detection for the tracking error can be suppressed.
The above object can be attained by the following structures.
An optical pickup apparatus for reproducing information from or recording information in at least two kinds of optical information recording medium, comprises:
a first light source to emit a first light flux having a first wavelength &lgr;
1
;
a second light source to emit a second light flux having a second wavelength &lgr;
2
(&lgr;
2
>&lgr;
1
);
a converging optical system having an objective lens provided with a diffractive section, to converge the first light flux emitted from the first light source through a transparent base board of a first optical information recording medium onto a recording surface and to converge the second light flux emitted from the second light source through a transparent base board of a second optical information recording medium onto a recording surface;
an optical detector to receive a reflected light flux and/or a transmitted light flux from the first and second optical information recording medium;
wherein the first light flux is irradiated to re
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Konica Corporation
Pyo Kevin
LandOfFree
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